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Discussion Starter #1
Hello all,
I have a 99 9-5, SQR tuned stage 4. TD-04, 3" downpipe, FMIC, and all the goodies. Now my question, this only happens on the 3rd to 4th gear shift, but if i run 3rd gear up to almost redline, and shift quickly to 4th, i see a monster sized boost spike. This is 25-30psi and then it backs way off and drops to base boost, and slowly builds pressure back up. Normally I see about 15-17 psi hold strong in all gears, and maybe an 18-19psi spike in the higher gear shifts. It seems like it hits a "safety net" and brings it back to reasonable levels, and then a couple good adaptation pulls and all is well and back to normal, after running really slow for a while until adapted.

When it does hit that "cut" or whatever point it is that it pulls boost way back, the car shoots unburned gas out the exhaust. A friend of mine was following one day, and had to use his windsheild wipers when it happened:lol:
If only the exhaust was hot enough to ignite it:lol:.

I have tried a new BPC, countless ECU resets, cleaned the air intake temp sensor, cleaned both MAP sensors, swapped the two map sensors, checked and replaced all vacuum lines (a preventative thing also), cleaned and lubed the forge bypass valve, cleaned the MAF, tightened the downpipe to turbo nuts (which were slightly loose), ran some fuel injector cleaner and still cant figure it out. No CEL's either. I have been tuned for a long while now, at least a year and a half, so it is not the tune. this has been a fairly recent thing, like the last month or so.

If anyone has any insight on this, please let me know.
 

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If only the exhaust was hot enough to ignite it:lol:.
Then you would have lit your friends car on fire...

My first guess would be the bypass valve. Does the forge bpv have an adjustable spring?

I say this because the pressure on the output of the induction portion of the turbo will spike when you release the throttle for your shift. The throttle body closes and the turbo is still going with a great deal of inertia. The BPV is designed to allow the release of that pressure without stalling the turbo. It shoulds like the turbo is stalling. This drops the pressure on the trottle body even further (likely down to vacuum) when the throttle body opens up as you hit the throttle again. You now have no boost and as it builds back up you may have extra fuel that is run out the exhaust.

This could be the wastegate actuator, but I think you would have other symptoms.

If you can adjust the spring on that forge, adjust it so that it blows off at a lower pressure. You should still keep your boost but it may prevent the turbo stalling that sounds like is going on.

This is just a guess and may not be the problem, but it is fairly simple to check if you have a stock bpv and the problem goes away when it is fitted, you have your culprit.
 

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Discussion Starter #3
same issue with the stock valve and i have played with the springs in the forge valve to double check, and no change

other than this issue on the 3rd to 4th shift at the top of 3rd gear, the car runs and drives flawlessly.
 

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Strange,

I would not know what else to look for. I wonder if there is something in the ECU that acts as an upper limit to boost and retards timing when hit. Does the tuner who did this ECU have any clue?
 

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Guaranteed is that little black valve that the vacuum line to the dump valve runs to. You'll notice that the dump valve is completely controlled by the ECU, and if you hook a boost gauge up to the dump valve line, when you floor it, vacuum goes to zero and no higher, and when it reaches the max boost, you'll notice it opens up the valve a little by putting vacuum in the line. That little black 3 way electrical valve is what controls the dump valve, it could be sticking because of all the pressure from the boost from a tuned engine and then takes a second to dislodge it's self. Try getting another one of those and do a swap test, they are called a "bypass control valve." I'm having a hard time finding a part number, but I'll keep looking.
 

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Discussion Starter #7
to test that, i might just run a vacuum line right to the intake manifold, where that spot with the two nipples are. That should create that valve working when it should iirc. We will see if it works. If not, i will try another one of those control units if i can find one to test with!

Thanks guys and keep the suggestions coming,
Nick
 

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StX221 said:
to test that, i might just run a vacuum line right to the intake manifold, where that spot with the two nipples are. That should create that valve working when it should iirc. We will see if it works. If not, i will try another one of those control units if i can find one to test with!

Thanks guys and keep the suggestions coming,
Nick
Make sure you plug the hole your going to be leaving open on that valve, and put in a little 3 way T off of the 2 nipple thing on the manifold so you don't starve any vacuum lines of their food!
 

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StX221 said:
I planned on doing all of the above.
:::High Five!::: :cool:

No...? Too 3rd grade...? ;oops:
 

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Discussion Starter #11
well i plugged the line to the bypass valve actuator box (if thats what its called), and connected the bypass valve straight to the intake manifold spot. drove fine, bpv sounded great, and was fine. then came the 3-4 shift and bam, the peak hold on the boost gauge records 28.5psi...

i picked up some new t-bolt clamps for the IC piping. tomorrow or sometime in the next week, i will pull all the piping off and clean the fittings, just to make sure that there isnt a slight leak or something like that...
 

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HMM.. nick still having issues? I never looked that closely at my boost guage ( and don't have a recorder) to see what happend. I had crazy boost issues before replacing the boost pressure sensor. Crazy enough to see it.

Now if I would get the PSI limit it would maybe it would be to quick to notice...

I may try hooking up a boost guage with a peak recorder and see what I get...

The only thing I have not yet tried to change yet is the overboost pressure sensor... I think by its name that if it detects overboost it does something to the boost...

And oh yeah what kind of intake are you running?? Stock box or open element? I am in the stock box, I was thinking maybe restricted intake flow might cause it???
 

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Something is causing the system to not release the excess pressure fast enough, and it's puzzling. I don't think it's an issue of overboost, but it seems like his dump valve is sticking. It can't be a vacuum leak, a leak that big would cause a CEL. Your problem in it's self should throw also a CEL according to the WIS, which puzzled me more.

Oh I meant to ask earlier but forgot: how long does it hit the 25-30 psi range for?
 

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Discussion Starter #14
Yeah J, still having problems. I figured i would hit this board for a little bit more technical info. And i am running an open element 3" k&n. so there definitely isnt a lack of air if you know what i mean.

And sector, no CEL is ever present. it holds that 25-30psi for a second or two. enough to see it clearly on the gauge. Then its like someone put a brick wall in front of the car to try and stop it. And then the "stuff" (sooty, black dark unburned gas stuff) comes shooting out the exhaust.

I am not sure if it is an overboost thing. it seems like it just gets away from itself and then sees what is going on and cuts all the fun.:roll:

I cant seem to figure it out, because it isnt like it happens in every gear or gear change, only the WOT 3rd gear to WOT 4th gear change. and if i roll onto 4th relatively smoothly into WOT, it doesnt do it.
So there is definitely something amiss, and i want to know what it is. I bought some new constant tension hose clamps for the Intercooler piping just in case any break when I try to take it apart to see if something is wrong there, so I might take a stab at that sometime soon here.

After re-reading this, I remembered that sometimes the boost comes on funky. Go WOT and the needle climbs, pauses breifly at 5psi or so, then continues to build. Maybe a wastegate actuator could cause this? And then it also wouldnt react fast enough to the rapid change in boost that comes with a super quick shift at WOT?? But, most of the time boost comes on nicely. But i can always count on that crazy spike!
 

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Could be a boost control valve now that you say that. (Or is that what you meant by BPC?)

(Not the bypass control valve! Lol there is a difference.)

It's attached to the intake cobra, and has 3 hoses attached to it. I'm sure you know what I'm taking about though.

I don't think wastegates go out that frequently, though it may be worth a try.
 

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Discussion Starter #16
I have tried a new BPC (the one on the intake cobra pipe) and no change.

I might see if anyone has a wastegate actuator for a t7 td-04 kicking around and maybe test that out. If anyone has one that they arent using or something like that, PM me please! thanks.
 

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StX221 said:
Yeah J, still having problems. I figured i would hit this board for a little bit more technical info. And i am running an open element 3" k&n. so there definitely isnt a lack of air if you know what i mean.
I cant seem to figure it out, because it isnt like it happens in every gear or gear change, only the WOT 3rd gear to WOT 4th gear change. and if i roll onto 4th relatively smoothly into WOT, it doesnt do it.
After seeing your issues and not having a problem for a while I had it happen Saturday Night when I was playing with a Mustang GT. I had to shut the car off at 60 MPH and restart to reset....

I'm gonna try this on the way home tonite, I dont remember what brought my boost lock on, If I can remember it was when I went WOT on a quick shift ( any gear) without letting it rev very high...

StX221 said:
After re-reading this, I remembered that sometimes the boost comes on funky. Go WOT and the needle climbs, pauses breifly at 5psi or so, then continues to build. Maybe a wastegate actuator could cause this? And then it also wouldnt react fast enough to the rapid change in boost that comes with a super quick shift at WOT?? But, most of the time boost comes on nicely. But i can always count on that crazy spike!

My car used to have the same pause ( at 10psi if I remember) when it was doing this regularly. I think I even have it caught on a dyno run where I was capturing boost. I'm going to look at this tonite as well...
 

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Discussion Starter #18
does anybody know if the wastegate actuator on a gt17 is the same as the actuator on the mistu td-04 unit?

or if i could swap them just to test?
 

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something is drastically wrong with your car. all 9-5's should boost a minimum 25-30 psi. if you are not boosting 30+ regularly, you should get it straightened out asap. time to go bigger my friend. nice running with you this weekend.

dave
 
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