wierd boost problem... please HELP (kinda long)
08-01-01, 08:45 PM
#1
Accepting Donations.
Thread Starter
Join Date: Mar 2001
Location: San Francisco, Ca.
Posts: 323
Likes: 0
Received 0 Likes
on
0 Posts
wierd boost problem... please HELP (kinda long)
hey guys. i have a really strange boost problem, i ran a pretty thorough search, but it seems different than the more common problems other fds seem to have. i was wondering if anyone else has ever had the same problem or has any suggestions to help.
here goes...
first, i noticed that my car doesnt boost like any of my friends' fds so i hooked up a boost gauge, and performed the third gear boost test described in the service manual, and i noticed that i only boost around 4 pounds all through the powerband after 3500 rpm. i checked around and asked some friends but nobody had any idea of how to remedy it except maybe i have a boost leak somewhere in my piping or maybe cracked turbo housing. checked that out, but no obvious cracked piping, and my turbos checked out okay.
however, i dont think that's the problem, because once in a while if i let off the gas a little around 4k rpms there is a strange very loud surging police siren type of sound and my car gives me full 10-11 pound boost all the way to redline. usually when it gives me only 4 lbs of boost it makes this same sound along with the blow off valve after i let off the throttle. (its different than the air pump noise, much louder and uglier.)
i am guessing that my problem has something to do with one of the many actuators, sensors, or turbo solenoids, but im not how to test each and every one of them, and if any of you sequential twin turbo geniuses has any idea of what might be causing the problem, i would really appreciate your input.
if it makes any difference, i have intake and full exhaust (no cats), and hks blowoff valve. please help me out, it feels pretty ricey with such a loud flashy car without the speed to back it up.
here goes...
first, i noticed that my car doesnt boost like any of my friends' fds so i hooked up a boost gauge, and performed the third gear boost test described in the service manual, and i noticed that i only boost around 4 pounds all through the powerband after 3500 rpm. i checked around and asked some friends but nobody had any idea of how to remedy it except maybe i have a boost leak somewhere in my piping or maybe cracked turbo housing. checked that out, but no obvious cracked piping, and my turbos checked out okay.
however, i dont think that's the problem, because once in a while if i let off the gas a little around 4k rpms there is a strange very loud surging police siren type of sound and my car gives me full 10-11 pound boost all the way to redline. usually when it gives me only 4 lbs of boost it makes this same sound along with the blow off valve after i let off the throttle. (its different than the air pump noise, much louder and uglier.)
i am guessing that my problem has something to do with one of the many actuators, sensors, or turbo solenoids, but im not how to test each and every one of them, and if any of you sequential twin turbo geniuses has any idea of what might be causing the problem, i would really appreciate your input.
if it makes any difference, i have intake and full exhaust (no cats), and hks blowoff valve. please help me out, it feels pretty ricey with such a loud flashy car without the speed to back it up.
Last edited by rx7speed811; 08-01-01 at 08:52 PM.
08-01-01, 10:29 PM
#2
There and back again
Join Date: Feb 2001
Location: Camarillo, Ca
Posts: 967
Likes: 0
Received 0 Likes
on
0 Posts
What you have just described is actually closer to what most people have issues with than you may think, and it’s called sequential hell.
What I think that you have described is a leaking vacuum system that controls the turbo control actuator (TCA). This may be the single most problematic area of the sequential system I have seen in my own boost troubleshooting research.
First, as most of us have at one time or another discovered during our own personal journeys into “Sequential Hell”, it takes both boost and pressure to make the turbo control actuator move quick enough (or at all) to deflect exhaust gasses to the second turbo. The lack of a significant source of boost means that the pressure side of the actuator will not be able to help much in moving that actuator’s arm without a good source of vacuum to help with the load of the exhaust and mechanical resistances. Since the pressure that’s applied to the TCA is directly contributed from what the primary turbo boosts, pre-4500 RPM, there would need to be at least 7.5-8 PSI stored in the pressure chamber (The black box on top of the motor) to push the TCA open. There would also need to be at least 15” of vacuum supporting the pressure to quickly open the TCA door to the secondary turbo for quick boost up. If there is a leak in either the pressure or the vacuum system leading to the TCA, you would need at least one of the two performing as per normal to slowly open the TCA. If you have a leaking vacuum system between the vacuum chamber and the TCA and you only produced less than 7.5 PSI before reaching the crossover point, 4500 RPM then the TCA will not have enough energy from either the pressure of vacuum system to open the TCA. So, by letting off the gas and getting back on it again you have ultimately charged the system just enough to open that door using the vacuum system, and then were able sustain it by the increased boost produced by the combination of the two turbos. Make sense?
So, easiest thing to do is to test the system. Check to see that the Vacuum chamber is not leaking, then the check-valve, then the hoses connecting to the switching solenoids as well as to the actuator its self, and last but not least the actuator alone.
This testing goes pretty quick with the exception to testing the switching solenoid, but you can easily do it yourself.
Don't forget to inspect the pressure system as well.
Good luck
What I think that you have described is a leaking vacuum system that controls the turbo control actuator (TCA). This may be the single most problematic area of the sequential system I have seen in my own boost troubleshooting research.
First, as most of us have at one time or another discovered during our own personal journeys into “Sequential Hell”, it takes both boost and pressure to make the turbo control actuator move quick enough (or at all) to deflect exhaust gasses to the second turbo. The lack of a significant source of boost means that the pressure side of the actuator will not be able to help much in moving that actuator’s arm without a good source of vacuum to help with the load of the exhaust and mechanical resistances. Since the pressure that’s applied to the TCA is directly contributed from what the primary turbo boosts, pre-4500 RPM, there would need to be at least 7.5-8 PSI stored in the pressure chamber (The black box on top of the motor) to push the TCA open. There would also need to be at least 15” of vacuum supporting the pressure to quickly open the TCA door to the secondary turbo for quick boost up. If there is a leak in either the pressure or the vacuum system leading to the TCA, you would need at least one of the two performing as per normal to slowly open the TCA. If you have a leaking vacuum system between the vacuum chamber and the TCA and you only produced less than 7.5 PSI before reaching the crossover point, 4500 RPM then the TCA will not have enough energy from either the pressure of vacuum system to open the TCA. So, by letting off the gas and getting back on it again you have ultimately charged the system just enough to open that door using the vacuum system, and then were able sustain it by the increased boost produced by the combination of the two turbos. Make sense?
So, easiest thing to do is to test the system. Check to see that the Vacuum chamber is not leaking, then the check-valve, then the hoses connecting to the switching solenoids as well as to the actuator its self, and last but not least the actuator alone.
This testing goes pretty quick with the exception to testing the switching solenoid, but you can easily do it yourself.
Don't forget to inspect the pressure system as well.
Good luck
Last edited by spooledUP7; 08-01-01 at 10:36 PM.
08-03-01, 05:51 AM
#4
Accepting Donations.
Thread Starter
Join Date: Mar 2001
Location: San Francisco, Ca.
Posts: 323
Likes: 0
Received 0 Likes
on
0 Posts
thanks for the advice
spooledup7, i really appreciate the tips. i am planning to do a diagnosis of the problem on monday, when i have the whole day off of work. do you know of anywhere i can find detailed pictures or diagrams of what i am going to be inspecting?
you did an excellent write up of what to look for, but id feel even better knowing more about what the vacuum/pressure control actuator system is supposed to be set up correctly. also, is there anything in particular i should expect to see with the symptoms i am getting right now (i.e. loose/cracked hoses, etc.)? and are there any special tools i should have handy before starting my inspection?
thanks again, your help is much appreciated.
you did an excellent write up of what to look for, but id feel even better knowing more about what the vacuum/pressure control actuator system is supposed to be set up correctly. also, is there anything in particular i should expect to see with the symptoms i am getting right now (i.e. loose/cracked hoses, etc.)? and are there any special tools i should have handy before starting my inspection?
thanks again, your help is much appreciated.
08-03-01, 06:01 AM
#5
Accepting Donations.
Thread Starter
Join Date: Mar 2001
Location: San Francisco, Ca.
Posts: 323
Likes: 0
Received 0 Likes
on
0 Posts
by the way, what is the noise i am getting that seems like it is related to the actuator being shut? do you think somebody more experienced than me at enduring "sequential hell" might be able to tell if it is a vacuum or pressure problem by hearing what the noise sounds like and when it occurs?
im so excited now... after fixing this seemingly simple problem, my car might actually run (consistently) right for once.
im so excited now... after fixing this seemingly simple problem, my car might actually run (consistently) right for once.
08-03-01, 06:16 AM
#6
Resident Retard
Join Date: Apr 2001
Location: Cockaigne
Posts: 1,918
Likes: 0
Received 0 Likes
on
0 Posts
spooledup7,
I agree, that is by far the best explanation I've seen of how things work...thanks. Can you see the actuator move from above. I think one of the sites said you can only see it from below. Good luck with that without a rack or jack. RX7speed check out http://home.istar.ca/~dvandit/turbocharger.htm
I agree, that is by far the best explanation I've seen of how things work...thanks. Can you see the actuator move from above. I think one of the sites said you can only see it from below. Good luck with that without a rack or jack. RX7speed check out http://home.istar.ca/~dvandit/turbocharger.htm
08-03-01, 06:51 AM
#7
Accepting Donations.
Thread Starter
Join Date: Mar 2001
Location: San Francisco, Ca.
Posts: 323
Likes: 0
Received 0 Likes
on
0 Posts
HOLY ****
that looks like its going to be a pain in the ***...
is there anything else anyone thinks i should check before embarking on this mission? looks scarier than i thought it would. thanks for the link, weaklink (no pun intended).
is there anything else anyone thinks i should check before embarking on this mission? looks scarier than i thought it would. thanks for the link, weaklink (no pun intended).
Trending Topics
08-03-01, 07:06 AM
#8
Accepting Donations.
Thread Starter
Join Date: Mar 2001
Location: San Francisco, Ca.
Posts: 323
Likes: 0
Received 0 Likes
on
0 Posts
thats an excellent site. just started combing through it for more info on the turbo control.
could one of you guys please give me a short briefing on how you would recommend going about the testing of the turbo control actuator apparatus, like how you performed it and what instruments you used for testing?
could one of you guys please give me a short briefing on how you would recommend going about the testing of the turbo control actuator apparatus, like how you performed it and what instruments you used for testing?
Thread
Thread Starter
Forum
Replies
Last Post