'90 TurboII only boosts to 5.5 psi (and 1 psi on stock gauge :) )
 

I hooked up a testing gauge to my '90 TurboII, and it's only showing 5.5 psi at full boost on a testing gauge.

I've been talking around about this lately, but haven't found a real answer, first the gauge wasn't showing right, kinda fixed that, determined that it was messed up, because I'd start the car, it'd go to WELL below -20, then pull the line, it SHOULD read 0 atmospheric, but doesn't.. it's at about -20 now.. then blow into it REAL hard and it almost reaches 0.

So anyhow, any idea on why a mechanical gauge is only showing 5.5 psi (I'm guessing this is accurate) and if this is going to be a problem that's caused by the pressure sensor, or caused by the boost gauge? And how I can get full boost out of this sucker?

I know you's guyses have SOME suggestions, if it's a shot in the dark let me know that, if it's something that you really really think is the problem, let me know..

I've heard so far that the precats might be clogged, the wastegate stuck open (but it boosts to 5.5 psi?), the boost controller was open or something? and I'm also thinking maybe one of the LITTLE vacuum lines is open somewhere, causing it to under-read?

As it stands right now, the only thing I don't think is hooked up right is this thing that is on the upper intake manifold, on one side (towards the front of the engine) is a 2 wire connector, and on the other side sticking up is this vacuum connection or something, I've got a little piece of hose connected to that with a bolt in it, I'm not sure what that thing is.

Ok, here's a picture of that vacuum line thing that I don't know where it goes. It LOOKS like it's going to the power brake booster or something (on the firewall) on this car (it's a picture of a car from New Zealand I think).

But you see, on the right side of that thing there's a blue label, where something plugs into it. On the left side of that piece, there's that hose sticking up. I don't have a clue where it's supposed to go on mine, and it's just disconnected right now.

By the way, I'm 99.9% sure it's an A-Spec manifold that I'm using, as it came off the engine that came with the car, and that was an A-spec I believe (it's different from any J-spec I've ever seen)

make sure your map sensor has a good vacuum signal from the manifold or your stock boost guage won't work. i need a picture so what you are talking about. i swapped in a JSPEC complete into my car and it runs ok. still have some bugs to work out but its a bat out of hell at WOT :D

5.5 PSI is normal for a full stock exhaust with precat, main cat, and stock POS catback ;)

5.5 is normal? 8 psi was stock wasn't it? I've got mostly stock on it, with I guess a OBX catback (aka rice looking exhaust, it's fugly, I need the full racing beat exhaust)

I tested with the mechanical pressure gauge off the same line that the stock pressure sensor and BOV was on (used tees)

your stock boost controller isn't working. the S5's run 5.5 psi on the wastegate spring, and have an electric boost controler that makes it 8. either its not working or has been bypassed.

the fact that the stock gauge isn't moving over 1 means the ecu propably isn't trying to make the controller work yet.

heheh i unpluged my wastegate and i still only got 8psi.... and mods are in my sig i dont know why... my car has some problems :(

anyone have a picture of the wastegate actuator vacuum lines (or wherever it is?)

oh yeah, here's a picture of that thing that I think might not be connected correctly:

https://www.rx7club.com/forum/attach...&postid=482533

See, on the right side of that thing there's a blue label, where something plugs into it. On the left side of that piece, there's that hose sticking up. I don't have a clue where it's supposed to go on mine, and it's just "disconnected" right now with a hose coming off of it, and a bolt stuck in that hose.

That's the BAC, it bumps up the idle to compensate for accessories when turned on, A/C, lights, etc. The two horizontal lines are coolant lines. US-Spec models have a screw to adjust the idle in the BAC and J-Spec models do not.

Thats strange.... is that your brake and clutch resevoir?? Is yours a right hand drive car?? Hmm.

Check the small restrictor thats inside the vac line. It should be only a few inches away from the boost sensor. Maybe it got plugged with something??

no, it's not my car.. I think it's a car from New Zealand

If your car looks like that pic, get a couple of hose clamps for that stupid hose under the BAC valve.&nbsp It has a tendency to leak - I dunno why Mazda was stupid NOT to clamp that hose from the factory.



-Ted

mine looks just like that, and trust me, that sucker ain't coming off.. I had to put a LOT of force on that thing to get it on there, twisted and contorted in all sorts of directions, and if I DO clamp it, it'll crack becuase it can't move ever so slightly like it seems to want to (my stock one did, I bought some new hose that should hopefully take care of it)

That’s my engine. I’ve been meaning to do that for ages, using a piece of heater hose or something. It’s not leaking at the moment, so it keeps slipping from my mind... :D

If my memory serves me right on my90 tII that hose goes to the underside of your intercooler. You are talking about the large hose on the top left rear of your BAC, right? There should be a medal fitting(nipple) on the back bottom portion of your intercoolerfor it to connect to. As for your actuator boost lines, the only one that I know that is easy to get to is located right in front of your compressor. If you remove your turbo inlet duct hose and look at your compreesoryou will see a circular piece of medal(waste gate actuator) to the left with a single boost line coming out of it. It will go to the right and connect to another piece of medal tubing which leads back to your turbo itself. As for your low boost, I'm not sure what to tell you. You probably should get a boost line diagram from fc3s.org. This might help you solve your problem. I hope this helps.

how many miles are on the clutch? Is it a stock clutch? I had a similar problem with low boost and it was actually a clutch that was starting to slip, causing less resistance which creates less boost. I know this for a fact, I also have a friend who bought an stock fd and kept saying the thing was a slug. He put a boost gauge in and was only seeing 4 to 5 psi, he put a new clutch in and the low boost pressure was fixed. Good luck.

there is no line comming up from the BAC. but there is one comming up from the AWS. right above it. should be going to the intercooler. here is the best pic I have handy.


that hose being blocked off isn't too bad. just gets rid of the 3000 startup which sucks. but you have to make sure the hole in the IC is blocked too. or that would cause the low boost.


http://www.1300cc.com/howto/how2/ic/ic2.jpg

Im having the same problem with my 90. I think I talked to you earlier. I boost quickly to 3psi, but I cant get it beyond it. I have no cats. If i plug the line to the Wastegate valve actuator I can get a ton of boost right away. Its helping me diagnose whats really going on. Maybe this can help you.

i have NOTHING on my TII but it boosts 10-11 psi perfectly. all emissions solenoids are removed. only thing left is the boost solenoid and one filter. i think i have a vacuum leak on my LIM though. @ wot the car is amazing. just doesn't want to idle ;)

Check and see if the actuator arm/lever is connected to the wastegate. If the c-clip comes off, or rusted off in my case, it will only produce about 4 or 5 psi, maybe less.

My whole wastegate assembly was bent causing the arm to bind and stay open and leak out the boost leaving me with only 2-3 PSI at times.

ok I'll have to dig through to find out exactly WHERE this lever is at, I've got ABS on mine so it's tough to get in there

Right below the turbo, can't miss it. Cylindrical in shape about three inches in diameter with a rod coming out the back going towards the rear of the car.

**EDIT**

This is on a J-Spec, BTW.

Hey Jimmy, what color is your TII?