secondary boost problem
01-09-05, 02:32 AM
#1
Birds can DRIFT YO...!!!!
Thread Starter
secondary boost problem
well my primary boost is fine and transition is fine and i also get boost from the second turbo but its weird, it feels and sounds like its studdering, something like that and it starts dropping. i've checked my couplers in case i had a boost leak but i'm gonna double check it again, wat else can i look for? i have an m2 ecu, arc intake, dp, and catback. thanks for the help
01-09-05, 11:19 AM
#3
From scuderiaciriani.com:
-----------------------------
Date: Sat, 5 Sep 1998 11:41:28 -0500
From: "Steve Wynveen"
Yeehaa, my car is finally 100%, probably for the first time since I bought in April '97. I also fixed my problem with always having low boost on the second turbo in 1st gear only. The problem was with the solenoid valve that controls the vacuum signal to the turbo control actuator (TCA). It turns out the bad solenoid was going open circuit when it got hot (from engine heat). This somewhat intermittent nature made it a true pain to diagnose. Luckily, the problem was getting worse this year & the low boost was cropping up more consistently. I now see 10 psi on the second turbo in 1st gear all the time...what a difference in acceleration!
I must also thank Peter Farrell for giving me some advice over the phone on the order to carry out my troubleshooting. Here is what I did, and the equipment used:
My already had a boost gauge in my car (installed late last summer). In addition, I purchased a vacuum/ pressure test gauge from Sears for $20, and already owned a vacuum hand pump with gauge (Mity Vac), a pressure hand pump with gauge (sold in personal watercraft catalogs - used for testing pop-off pressure on diaphragm carburetors), and a good multi meter. The low boost on the second turbo made the TCA suspect, in that it wasn't getting either the pressure or vacuum signal, both of which it needs to work correctly. Here is the test procedure:
1. Tee into the side fitting on the TCA, right next to the TCA. This is the pressure port. Go out and warm up the car thoroughly. Accelerate from 2k rpm at WOT in 2nd gear to well past the turbo transition point at 4500 rpm. Before the transition, the test gauge should read atmospheric (0 psi, actually 0 psig, but I won't get into the nomenclature). At the transition, the gauge should IMMEDIATELY jump to pressure (>7 psi ?) and hold as long as you have the gas mashed (don't hit the rev limiter, please). If you don't see the jump to pressure, this tells you that something in the pressure side of the control system is awry. I had pressure, so I didn't go down this road.
2. Tee into the fitting in the center of the actuator, the one that points toward the front of the car. I pulled off my plastic under tray for better access to the actuator (you don't want to drive you car for very long or had without the tray. I have heard of people overheating their cars without it). Again, tee into the line and go for a drive. With the car fully warmed, do the WOT test in 2nd gear from 2k rpm again. This time, you should see the gauge jump to vacuum at the transition, and hold. I saw no vacuum. In fact I saw a very quick jump to ~1/2 psi pressure, which immediately fell back to 0 psi. This is just because, on my car, the pressure side of the system was still enough to drive the TCA, only slower than intended. When the pressure pushes the diaphragm down inside the TCA, the vacuum side of the TCA reduces in volume, causing the quick, slight pressure spike.
3. So, we know I am getting no vacuum to the TCA. This means either that the turbo control solenoid valve has failed, the vacuum check valve has failed, a vacuum hose has popped off, or one of the other two solenoid valves in this vacuum system is stuck open, venting to atmosphere. The easiest to check was the check valve. I pulled out the appropriate check valve and applied 12 psi to it from the manifold side, to simulate running under boost conditions. The valve didn't leak, and shaking it around didn't make it leak either. Next, I drew vacuum through it, and it let vacuum flow in the proper direction. So, the check valve is eliminated. Next, plug my Mity Vac into the line coming off the check valve and pump the system up to ~ 15 inHg vacuum (a fair amount of pumping). The system held vacuum, indicating no major leaks when all solenoid valves are de-energized and no cracks in the vacuum reservoir.
4. Road test. Tee into the vacuum system either just PAST the check valve, or by the entrance to the vacuum reservoir. Go for a drive and do the WOT test from 2k rpm in 2nd gear again. You should see vacuum all the time, and a drop in vacuum as it gets used at the turbo transition point. When driving gently, the system should hold a high, steady vacuum. In not, something else in the system is wrong, possibly a solenoid valve. If, at the transition, the system drops to zero, or something very low, a vacuum line popped off somewhere is indicated. In my case, everything looked like it should, high stead vacuum (~20 inHg) with a slight drop at the transition (to ~15 inHg).
5. All indications at this point were to the turbo solenoid valve that runs vacuum. This is the one bolted to the secondary air control valve assembly. It is the valve NOT in the big rack of valves by the spider. On my under hood diagram (1994 car) it is item #12. At this point it must either be a bad solenoid valve, a blockage or pinched off line before or after the valve, or electrical. There's only one way to check this, pull off the extension manifold (yipee!). So, about 1.5 hours later I'm down to the solenoid valve. (By the way, I'd highly recommend gently stuffing some paper towels or rags in the 4 passages exposed on the lower manifold. It is just WAAAY to easy to drop something down there accidentally - like puke, sorry Isaac I couldn't resist -, and then you really have big problems.
First, I checked the valve by applying battery voltage across it by using jumper wires. The top terminal is +, and the bottom is ground. Peter Farrell told me that clicking is not enough to indicate a good valve. Sometimes they click, but the plunger is broken internally. So, I first used my Mity Vac to put the vacuum system into ~ 15 inHg vacuum (same place as used before). When I applied voltage it clicked, and I could hear the actuator move. This also eliminates a blocked or kinked off line to the TCA. Damn, I thought, an electrical problem in the harness. Just what I need.
6. Check out the electrical harness. I reconnected the battery & turned on the ignition (DON'T turn over the engine - you'll suck up the towels in the manifold I recommended in step 5). This sends power to all the solenoids. The ECU runs them by grounding the other side of them. The solenoid valve had battery voltage. OK, it has to be the ground. So, I should pull out the ECU and measure continuity between the solenoid's plug (yellow/blue wire) the appropriate ECU harness terminal (#4R). However, there is an easier way. The electrical diagram shows that both turbo control solenoid valves (pressure and vacuum) are grounded by the same 1 wire at the ECU. Somewhere along the way they join together. We know the pressure solenoid valve works (saw pressure at the TCA in step #1) so its connection to the ECU must be fine. Therefore, we can just check for continuity between the ground terminals of both solenoid valves (valves #12 and #26 on the underhood diagram, ground is yellow/blue on both). I used a long skinny screwdriver as the conductor to get to the #26 valve without having to dig the valve out. I saw .2 Ohm. Damn, everything checks out, what the hell is wrong!!
7. Back to step 5. I played around with the jumper wires to the solenoid valve some more. At this point, things were still a bit warm, as I pulled the manifold off without letting the car cool for very long. All of a sudden, the valve stopped clicking. I pulled out the valve and did some more testing on a bench. It clicked again. I though to myself, maybe it is heat related. Next, I measured the resistance of the solenoid - 34 Ohm. Then, I pre-heated my oven to 175 deg F and baked the solenoid for 3 min. When I pulled it out and check continuity - open circuit. As the solenoid cooled, it began to show very high resistance and slowly came back to a realistic valve. Yipee, I though, here's the problem, a temperature sensitive valve.
8. I ordered up a new valve and manifold gaskets to get overnighted from Mazda Comp. Put the car back together, and it now works as Mazda intended.
In closing, I must thank Mr. Farrell for his guidance in getting me started. I must also say for shame to those mechanics that told me it was normal to not get full boost on the second turbo in 1st gear because it is so transient and the engine is loaded down enough. Also, as I discussed with Mr. Farrell, do you think any Mazda mechanic would have taken the time and effort to do the diagnosis like I did? It is much easier to guess a part is bad and replace it (making money on the part and labor to install) than it is to do a proper diagnosis. Not to mention, many mechanics don't have the proper training or understanding to be able to diagnose such a complex system.
_______________
Date: Fri, 23 Apr 1999 22:13:58 -0400
From: Max Cooper
A new check valve fixed my second turbo boost problem, too. It was the valve that connects to the pressure tank, and I replaced it with a $4 generic check valve. Problem fixed; no problem with the cheap check valve yet.
_______________
Date: Sun, 12 Dec 1999 03:51:40 -0500
From: Wael El-Dasher (wael.el-dasher@efini.net)
> I have been trying to diagnose the cause for my lack of boost above 4500rpm.
> I have gone through as many hoses as I can manage to find and everything
> looks good. The hose from the charge relief valve was very loose. I
> thought I had found my problem. The hose looked good and I put new clamps
> on it to keep it in place and figured everything would be fine. Upon
> testing, good primary boost (10 or 11), but once over 4500, boost drops to 2
> or 3 and there is a massive hissing sound. I know there is a leak
> somewhere, but I just can't seem to figure out which hose it is. This leak
> is in front of the passenger side and sounds like it is something big. I had
> almost everyone of those hoses from the intake and turbo off, but they all
> looked okay. HELP!!!!
>
> Another question, since this leak sounds so large. is it possible the large
> 2 peice hose on the intake can do that? The stock springclamps on it seem
> ok, but do these ever leak, or are they not under too much pressure?? I am
> asking because it just sound like sooooo much air is rushing through.
> Thanks for any advice.
I am really sorry to hear that you are still having trouble with your secondary boost. I would like to point out that Rob Robinette is correct, don't expect to find a large hole. It would more likely be a hose that popped off or one with a small slit.
Since your secondary is producing a small amount of boost (2-3psi) with the primary after switchover then it is more likely a slit. But there are a few key solenoids you should look at first. Below I described what I would do to trouble shoot this problem. This e-mail assumes you already checked the Charge Control Solenoid and it's associated hoses that allow the Charge Control Actuator to open the valve for the secondary turbo to come online. I will not go through them as I already explained them to you in an earlier post. I am assuming you already checked them and followed my instructions and found no trouble.
Before I begin, if you do not have a Workshop manual or a Service Highlights Manual then get either of them first. If you do have one then follow my descriptions with the diagrams and drawings to understand the routes I described. Here goes.
First, a simple rule that I always followed is to check the hoses that are exposed, so check the 4 hoses going into both, the Wastegate Control & Turbo Precontrol Solenoids, they are the 2 attached to the front of the upper intake manifold and are paired together (sort of army green colored). If the hoses are fine then I assume it is something related to the secondary coming online.
During high speed/high load conditions (secondary online) there are 2 solenoids that control the secondary turbo coming online:
1. Charge Relief Solenoid
2. Turbo Control Solenoid (actually there are 2 turbo control solenoids)
The Charge Relief Solenoid's function is to control the Charge Relief Valve (CRV). While the secondary is spooling vacuum travels through the hose that is attached to the top half of the CRV, after 4500rpm, at switchover, boost travels through that hose, so the CRV is closed and the secondary turbo does not bleed air while it is online.
Therefore, the Charge Relief Solenoid is what controls when vacuum or boost travel through the hose attached to the top half of the CRV. To track down any leaks you will need to look at the source of the boost that is supplied to the Charge Relief Solenoid, allow me be to explain.
Let me step back and explain a very simple way to understand how the solenoids direct air, I think it is important to know this as it will help you trouble shoot solenoid problems in the long run.
Solenoids recieve boost from the back (if they have a line coming in the back, if they have a filter then they recieve boost from the front), it is the metal nipple in the back near the connector. The solenoids themselves are not linear, ie they are simple on/off (I/O).
Now when air comes in the back it is allowed to exit from the front through the upward pointing nipple (plastic nipple). This is what the manual calls the OFF position. The nipple pointing forward in the front (not upwards) is always closed until the solenoid opens it, when it does open the forward pointing nipple, this is called the ON position, however in the ON position both the forward and upward nipples are open (if someone know s otherwise please advise). This is simply how the solenoids work, think of them as air management.
Back to your problem. During boost (secondary) the Charge Relief Solenoid recieves it's boost from the Charge Control Solenoid. The hose that carries the boost from the Charge Control Solenoid comes from the forward pointing nipple of the Charge Control Solenoid, which is activated after 4500rpm, ie ON after 4500rpm, but it is not used before 4500 rpm(Charge Control Solenoid OFF). So check that hose.
Next, if that hose is fine then move downstream, once the Charge Relief Solenoid is ON, boost is allowed to exit from the 2 hoses in the front, both are U shaped hoses. Check them.
If these 2 hoses are fine, then follow each downstream. I will take the upwards pointing nipple off the Charge Relief Solenoid first. We know this on has vacuum before 4500rpm, but you can't assume it has vacuum and that all is well before 4500rpm, even if it had a leak, your CRV will vent because the pressure from the secondary turbo spooling could be great enough to open the CRV without the aid of vacuum in the top half of the CRV. So check the hose going from the top half of the CRV. It goes from the CRV to a nipple on the lower intake manifold and eventually routed to the Charge Relief Solenoid. Check also the 4 vacuum lines that come out together on the other side of the lower intake manifold.
If all these are well then it is time to track the forward pointing nipple from the Charge Relief Solenoid. Check the horizontal U shaped hose, if it is OK, then it's time to follow it to the end. It goes into the metal lines, but these line take it to 2 places; the first is to the vacuum chamber behind the powersteering and A/C pulley plate (under and to the right of the alternator), and the second to the Turbo Control Solenoid (not the one next to the Charge Control Solenoid in the rack, but the other one next to the Air Control Valve on the lower intake manifold).
So check the hose going into that Vacuum Chamber, it tends to break easily if it was never replaced, expecially when you change the belts. The Vacuum Chamber is connected (not directly but through a T earlier in the metal rack lines) to the hose which carries the small Check Valve going into the front of the upper intake manifold (there is only one hose inthe front that has a small Check Valve). Check that hose, and make sure the one way valve works only in the direction pointing into the manifold. This one way valve is there to allow the boost coming out of the Charge Relief Valve (after 4500rpm) to only go into the upper intake manifold, and under 4500rpm it prevents the boost from the primary from forcing the Charge Relief Solenoid to open it's forward pointing nipple. I hope this is all making sense.
With that behind you, it's time to turn attention to the Turbo Control Solenoid (on the lower intake manifold), the lower hose going into the solenoid is the one carrying boost from the Charge Relief Solenoid, and the one on top (or closer to the manifold if you prefer) is the one going to the Turbo Control Actuator (it controls the exhaust valve port that allows the secondary turbo to come online at 4500 rpm at full song, ie after it pre-spooled). So check that hose too.
Now finally also check the 2 hoses going out of the Turbo Control Solenoid 2 (the one in the rack next to the Charge Control Valve). The one coming out of the upwards pointing nipple carries boost after 4500rpm and is meant to balance the boost from the other Turbo Control Solenoid so the Actuator will open the exhaust gate for the secondary turbo. The forward pointing nipple goes to the rack's metal lines but it is the same line that goes into the Pressure Chamber (the black box behind the alternator, it sits right on top) and the line coming from the Y-pipe with the large one way valve is meant to carry boost into the chamber (hence the name Pressure Chamber) then into the Turbo Control Solenoid 2 's front nipple (when it is ON, front nipple is open). So check that hose. BTW, that is why this solenoid has a mini-air filter on the back nipple, ie it recieves boost from the front when it is ON and it vents it from then filter.
I know this sounds complicated, but it isn't. Go over all the routes I described carefully in the manual and they will be clear, toggle between the manual, my notes and your engine bay and it will all make perfect sense.
-------------
Dave
-----------------------------
Date: Sat, 5 Sep 1998 11:41:28 -0500
From: "Steve Wynveen"
Yeehaa, my car is finally 100%, probably for the first time since I bought in April '97. I also fixed my problem with always having low boost on the second turbo in 1st gear only. The problem was with the solenoid valve that controls the vacuum signal to the turbo control actuator (TCA). It turns out the bad solenoid was going open circuit when it got hot (from engine heat). This somewhat intermittent nature made it a true pain to diagnose. Luckily, the problem was getting worse this year & the low boost was cropping up more consistently. I now see 10 psi on the second turbo in 1st gear all the time...what a difference in acceleration!
I must also thank Peter Farrell for giving me some advice over the phone on the order to carry out my troubleshooting. Here is what I did, and the equipment used:
My already had a boost gauge in my car (installed late last summer). In addition, I purchased a vacuum/ pressure test gauge from Sears for $20, and already owned a vacuum hand pump with gauge (Mity Vac), a pressure hand pump with gauge (sold in personal watercraft catalogs - used for testing pop-off pressure on diaphragm carburetors), and a good multi meter. The low boost on the second turbo made the TCA suspect, in that it wasn't getting either the pressure or vacuum signal, both of which it needs to work correctly. Here is the test procedure:
1. Tee into the side fitting on the TCA, right next to the TCA. This is the pressure port. Go out and warm up the car thoroughly. Accelerate from 2k rpm at WOT in 2nd gear to well past the turbo transition point at 4500 rpm. Before the transition, the test gauge should read atmospheric (0 psi, actually 0 psig, but I won't get into the nomenclature). At the transition, the gauge should IMMEDIATELY jump to pressure (>7 psi ?) and hold as long as you have the gas mashed (don't hit the rev limiter, please). If you don't see the jump to pressure, this tells you that something in the pressure side of the control system is awry. I had pressure, so I didn't go down this road.
2. Tee into the fitting in the center of the actuator, the one that points toward the front of the car. I pulled off my plastic under tray for better access to the actuator (you don't want to drive you car for very long or had without the tray. I have heard of people overheating their cars without it). Again, tee into the line and go for a drive. With the car fully warmed, do the WOT test in 2nd gear from 2k rpm again. This time, you should see the gauge jump to vacuum at the transition, and hold. I saw no vacuum. In fact I saw a very quick jump to ~1/2 psi pressure, which immediately fell back to 0 psi. This is just because, on my car, the pressure side of the system was still enough to drive the TCA, only slower than intended. When the pressure pushes the diaphragm down inside the TCA, the vacuum side of the TCA reduces in volume, causing the quick, slight pressure spike.
3. So, we know I am getting no vacuum to the TCA. This means either that the turbo control solenoid valve has failed, the vacuum check valve has failed, a vacuum hose has popped off, or one of the other two solenoid valves in this vacuum system is stuck open, venting to atmosphere. The easiest to check was the check valve. I pulled out the appropriate check valve and applied 12 psi to it from the manifold side, to simulate running under boost conditions. The valve didn't leak, and shaking it around didn't make it leak either. Next, I drew vacuum through it, and it let vacuum flow in the proper direction. So, the check valve is eliminated. Next, plug my Mity Vac into the line coming off the check valve and pump the system up to ~ 15 inHg vacuum (a fair amount of pumping). The system held vacuum, indicating no major leaks when all solenoid valves are de-energized and no cracks in the vacuum reservoir.
4. Road test. Tee into the vacuum system either just PAST the check valve, or by the entrance to the vacuum reservoir. Go for a drive and do the WOT test from 2k rpm in 2nd gear again. You should see vacuum all the time, and a drop in vacuum as it gets used at the turbo transition point. When driving gently, the system should hold a high, steady vacuum. In not, something else in the system is wrong, possibly a solenoid valve. If, at the transition, the system drops to zero, or something very low, a vacuum line popped off somewhere is indicated. In my case, everything looked like it should, high stead vacuum (~20 inHg) with a slight drop at the transition (to ~15 inHg).
5. All indications at this point were to the turbo solenoid valve that runs vacuum. This is the one bolted to the secondary air control valve assembly. It is the valve NOT in the big rack of valves by the spider. On my under hood diagram (1994 car) it is item #12. At this point it must either be a bad solenoid valve, a blockage or pinched off line before or after the valve, or electrical. There's only one way to check this, pull off the extension manifold (yipee!). So, about 1.5 hours later I'm down to the solenoid valve. (By the way, I'd highly recommend gently stuffing some paper towels or rags in the 4 passages exposed on the lower manifold. It is just WAAAY to easy to drop something down there accidentally - like puke, sorry Isaac I couldn't resist -, and then you really have big problems.
First, I checked the valve by applying battery voltage across it by using jumper wires. The top terminal is +, and the bottom is ground. Peter Farrell told me that clicking is not enough to indicate a good valve. Sometimes they click, but the plunger is broken internally. So, I first used my Mity Vac to put the vacuum system into ~ 15 inHg vacuum (same place as used before). When I applied voltage it clicked, and I could hear the actuator move. This also eliminates a blocked or kinked off line to the TCA. Damn, I thought, an electrical problem in the harness. Just what I need.
6. Check out the electrical harness. I reconnected the battery & turned on the ignition (DON'T turn over the engine - you'll suck up the towels in the manifold I recommended in step 5). This sends power to all the solenoids. The ECU runs them by grounding the other side of them. The solenoid valve had battery voltage. OK, it has to be the ground. So, I should pull out the ECU and measure continuity between the solenoid's plug (yellow/blue wire) the appropriate ECU harness terminal (#4R). However, there is an easier way. The electrical diagram shows that both turbo control solenoid valves (pressure and vacuum) are grounded by the same 1 wire at the ECU. Somewhere along the way they join together. We know the pressure solenoid valve works (saw pressure at the TCA in step #1) so its connection to the ECU must be fine. Therefore, we can just check for continuity between the ground terminals of both solenoid valves (valves #12 and #26 on the underhood diagram, ground is yellow/blue on both). I used a long skinny screwdriver as the conductor to get to the #26 valve without having to dig the valve out. I saw .2 Ohm. Damn, everything checks out, what the hell is wrong!!
7. Back to step 5. I played around with the jumper wires to the solenoid valve some more. At this point, things were still a bit warm, as I pulled the manifold off without letting the car cool for very long. All of a sudden, the valve stopped clicking. I pulled out the valve and did some more testing on a bench. It clicked again. I though to myself, maybe it is heat related. Next, I measured the resistance of the solenoid - 34 Ohm. Then, I pre-heated my oven to 175 deg F and baked the solenoid for 3 min. When I pulled it out and check continuity - open circuit. As the solenoid cooled, it began to show very high resistance and slowly came back to a realistic valve. Yipee, I though, here's the problem, a temperature sensitive valve.
8. I ordered up a new valve and manifold gaskets to get overnighted from Mazda Comp. Put the car back together, and it now works as Mazda intended.
In closing, I must thank Mr. Farrell for his guidance in getting me started. I must also say for shame to those mechanics that told me it was normal to not get full boost on the second turbo in 1st gear because it is so transient and the engine is loaded down enough. Also, as I discussed with Mr. Farrell, do you think any Mazda mechanic would have taken the time and effort to do the diagnosis like I did? It is much easier to guess a part is bad and replace it (making money on the part and labor to install) than it is to do a proper diagnosis. Not to mention, many mechanics don't have the proper training or understanding to be able to diagnose such a complex system.
_______________
Date: Fri, 23 Apr 1999 22:13:58 -0400
From: Max Cooper
A new check valve fixed my second turbo boost problem, too. It was the valve that connects to the pressure tank, and I replaced it with a $4 generic check valve. Problem fixed; no problem with the cheap check valve yet.
_______________
Date: Sun, 12 Dec 1999 03:51:40 -0500
From: Wael El-Dasher (wael.el-dasher@efini.net)
> I have been trying to diagnose the cause for my lack of boost above 4500rpm.
> I have gone through as many hoses as I can manage to find and everything
> looks good. The hose from the charge relief valve was very loose. I
> thought I had found my problem. The hose looked good and I put new clamps
> on it to keep it in place and figured everything would be fine. Upon
> testing, good primary boost (10 or 11), but once over 4500, boost drops to 2
> or 3 and there is a massive hissing sound. I know there is a leak
> somewhere, but I just can't seem to figure out which hose it is. This leak
> is in front of the passenger side and sounds like it is something big. I had
> almost everyone of those hoses from the intake and turbo off, but they all
> looked okay. HELP!!!!
>
> Another question, since this leak sounds so large. is it possible the large
> 2 peice hose on the intake can do that? The stock springclamps on it seem
> ok, but do these ever leak, or are they not under too much pressure?? I am
> asking because it just sound like sooooo much air is rushing through.
> Thanks for any advice.
I am really sorry to hear that you are still having trouble with your secondary boost. I would like to point out that Rob Robinette is correct, don't expect to find a large hole. It would more likely be a hose that popped off or one with a small slit.
Since your secondary is producing a small amount of boost (2-3psi) with the primary after switchover then it is more likely a slit. But there are a few key solenoids you should look at first. Below I described what I would do to trouble shoot this problem. This e-mail assumes you already checked the Charge Control Solenoid and it's associated hoses that allow the Charge Control Actuator to open the valve for the secondary turbo to come online. I will not go through them as I already explained them to you in an earlier post. I am assuming you already checked them and followed my instructions and found no trouble.
Before I begin, if you do not have a Workshop manual or a Service Highlights Manual then get either of them first. If you do have one then follow my descriptions with the diagrams and drawings to understand the routes I described. Here goes.
First, a simple rule that I always followed is to check the hoses that are exposed, so check the 4 hoses going into both, the Wastegate Control & Turbo Precontrol Solenoids, they are the 2 attached to the front of the upper intake manifold and are paired together (sort of army green colored). If the hoses are fine then I assume it is something related to the secondary coming online.
During high speed/high load conditions (secondary online) there are 2 solenoids that control the secondary turbo coming online:
1. Charge Relief Solenoid
2. Turbo Control Solenoid (actually there are 2 turbo control solenoids)
The Charge Relief Solenoid's function is to control the Charge Relief Valve (CRV). While the secondary is spooling vacuum travels through the hose that is attached to the top half of the CRV, after 4500rpm, at switchover, boost travels through that hose, so the CRV is closed and the secondary turbo does not bleed air while it is online.
Therefore, the Charge Relief Solenoid is what controls when vacuum or boost travel through the hose attached to the top half of the CRV. To track down any leaks you will need to look at the source of the boost that is supplied to the Charge Relief Solenoid, allow me be to explain.
Let me step back and explain a very simple way to understand how the solenoids direct air, I think it is important to know this as it will help you trouble shoot solenoid problems in the long run.
Solenoids recieve boost from the back (if they have a line coming in the back, if they have a filter then they recieve boost from the front), it is the metal nipple in the back near the connector. The solenoids themselves are not linear, ie they are simple on/off (I/O).
Now when air comes in the back it is allowed to exit from the front through the upward pointing nipple (plastic nipple). This is what the manual calls the OFF position. The nipple pointing forward in the front (not upwards) is always closed until the solenoid opens it, when it does open the forward pointing nipple, this is called the ON position, however in the ON position both the forward and upward nipples are open (if someone know s otherwise please advise). This is simply how the solenoids work, think of them as air management.
Back to your problem. During boost (secondary) the Charge Relief Solenoid recieves it's boost from the Charge Control Solenoid. The hose that carries the boost from the Charge Control Solenoid comes from the forward pointing nipple of the Charge Control Solenoid, which is activated after 4500rpm, ie ON after 4500rpm, but it is not used before 4500 rpm(Charge Control Solenoid OFF). So check that hose.
Next, if that hose is fine then move downstream, once the Charge Relief Solenoid is ON, boost is allowed to exit from the 2 hoses in the front, both are U shaped hoses. Check them.
If these 2 hoses are fine, then follow each downstream. I will take the upwards pointing nipple off the Charge Relief Solenoid first. We know this on has vacuum before 4500rpm, but you can't assume it has vacuum and that all is well before 4500rpm, even if it had a leak, your CRV will vent because the pressure from the secondary turbo spooling could be great enough to open the CRV without the aid of vacuum in the top half of the CRV. So check the hose going from the top half of the CRV. It goes from the CRV to a nipple on the lower intake manifold and eventually routed to the Charge Relief Solenoid. Check also the 4 vacuum lines that come out together on the other side of the lower intake manifold.
If all these are well then it is time to track the forward pointing nipple from the Charge Relief Solenoid. Check the horizontal U shaped hose, if it is OK, then it's time to follow it to the end. It goes into the metal lines, but these line take it to 2 places; the first is to the vacuum chamber behind the powersteering and A/C pulley plate (under and to the right of the alternator), and the second to the Turbo Control Solenoid (not the one next to the Charge Control Solenoid in the rack, but the other one next to the Air Control Valve on the lower intake manifold).
So check the hose going into that Vacuum Chamber, it tends to break easily if it was never replaced, expecially when you change the belts. The Vacuum Chamber is connected (not directly but through a T earlier in the metal rack lines) to the hose which carries the small Check Valve going into the front of the upper intake manifold (there is only one hose inthe front that has a small Check Valve). Check that hose, and make sure the one way valve works only in the direction pointing into the manifold. This one way valve is there to allow the boost coming out of the Charge Relief Valve (after 4500rpm) to only go into the upper intake manifold, and under 4500rpm it prevents the boost from the primary from forcing the Charge Relief Solenoid to open it's forward pointing nipple. I hope this is all making sense.
With that behind you, it's time to turn attention to the Turbo Control Solenoid (on the lower intake manifold), the lower hose going into the solenoid is the one carrying boost from the Charge Relief Solenoid, and the one on top (or closer to the manifold if you prefer) is the one going to the Turbo Control Actuator (it controls the exhaust valve port that allows the secondary turbo to come online at 4500 rpm at full song, ie after it pre-spooled). So check that hose too.
Now finally also check the 2 hoses going out of the Turbo Control Solenoid 2 (the one in the rack next to the Charge Control Valve). The one coming out of the upwards pointing nipple carries boost after 4500rpm and is meant to balance the boost from the other Turbo Control Solenoid so the Actuator will open the exhaust gate for the secondary turbo. The forward pointing nipple goes to the rack's metal lines but it is the same line that goes into the Pressure Chamber (the black box behind the alternator, it sits right on top) and the line coming from the Y-pipe with the large one way valve is meant to carry boost into the chamber (hence the name Pressure Chamber) then into the Turbo Control Solenoid 2 's front nipple (when it is ON, front nipple is open). So check that hose. BTW, that is why this solenoid has a mini-air filter on the back nipple, ie it recieves boost from the front when it is ON and it vents it from then filter.
I know this sounds complicated, but it isn't. Go over all the routes I described carefully in the manual and they will be clear, toggle between the manual, my notes and your engine bay and it will all make perfect sense.
-------------
Dave
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trickster
2nd Generation Specific (1986-1992)
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07-01-23 04:40 PM