Stalls sometimes after boost

[GeneralChaos]

Noticed this problem, its not a huge deal nor does it happen 100% of the time but it leaves me wondering.

Basically if I get on the car, sometimes when I let off it will stall coming down. the harder I get on it the more chance of this happening but its still never 100%. While the rpm are coming down I look at my vacuum and see it down near 20-25, which seems unusually high to me. Sometimes it will catch it self before the rpm get to low and it wont stall, otherwise I see all the lights on the dash come on so I have to turn the car back on while rolling.

besides being an inconvienience when the cars off the power steering doesnt work, and that can be dangerous as it almost has been once it shut off before going around a turn and caught me off guard.

any ideas what it is?

 

[oldman]

The to4b v-trim is a pretty large turbo, ON PAPER it's suppose to flow 50 lb/min. What supporting mods do you have? If your profile is updated, what psi are you running?

 

[JessesTalon]

Do you also have uncontrolable idle? or idles really high?

Could be TPS sensor? mine does that randomy, not very often but i also get weird idle 1500-2000

 

[Necromancer69]

Are you venting to the atmosphere..?? if so thats your problem.

 

[GeneralChaos]

ok ill start answering these.

yes I have the v-trim, no I dont have any supporting mods but thats because my turbo blew so I just bought a better one.

psi runs about 18 or so but its probably a horribly ineficient 18psi, and I probably have boost leaks everywhere, not to mention I need to resurface my manifold because it leaks there a little bit

im not venting to the atmosphere.


Im actually thinking it may be a bad TPS because on VERY rare occasions sometimes the cars idle will bounce from like 1000-1500 up to 2000 then fall back down, repeat. This hardly happens but it does, after I drive it for a second and stop again its gone.

Yesterday on the way home from work the car stalled out on me on the highway and I was just cruising around 70, I was going around a bend and had to brake because the car infront of me and next thing I know I could hardly steer the car, got the adrenaline going thats for sure.

Hope this helps narrow it some.

 

[cfisher]

I'm having the same problem. I'll go out of gear and put it in neutral and the car bogs down to 400RPM for about 5 seconds and then pops up to 750RPM and everything is back to normal. It seems like I'm almost getting a slow reaction time from something because it always takes a couple seconds to cure itself. I also have died a couple times when I have to brake hard.

 

[oldman]

1. Turn that boost down and run the actuator minimum setting until you upgrade your fuel system. Running 18psi on stock pump and injectors on a 16g is already questionable, definitely a problem with anything bigger.

2. Boost leak test, a vacuum leak will cause your car to stall.

3. Service manual shows how to test the TPS.

 

[GeneralChaos]

for all I know the fuel system could be upgraded. I dont know if you can tell by just looking at the injectors.

but the guy before me did have a t3/t4 turbo on there for a while just for break it (I know this by looking up all his old posts on here before I bought it, and probly installed it because the t25 was bad)

and the car is all kinds of rigged together but I planned on putting a 6 bolt in it anyway. So there is a possibility he put some 650's and a tune chip in there or something, since I dont hit fuel cut for some reason.

and every time I try a leak test it doesnt really work, I think I have some problems with the tester, or some serious blow-by. should probly do a compression test when I get the chance.

 

[oldman]

and the car is all kinds of rigged together but I planned on putting a 6 bolt in it anyway. So there is a possibility he put some 650's and a tune chip in there or something, since I dont hit fuel cut for some reason.

Very possible. You can check the ecu easily and sometimes you can tell by looking at the injector depending on the brand. tell us what color and what they look like and we might be able to help you figure it out.

and every time I try a leak test it doesnt really work, I think I have some problems with the tester, or some serious blow-by. should probly do a compression test when I get the chance.

Let's focus on the leak test, describe what's going on in detail.

 

[GeneralChaos]

me and my buddy might be working on cars tonight so if I get a chance ill take a look at the injectors, but were mostly working on his so cant garauntee it.


Anyway with the leak test, it just doesnt pressurize. the highest weve got it to was 3 psi. we had the entire IC systems out of the car basically and put it all back together nice and tight.

So after fixing a few leaks (TB needed new gaskets and BIS screw, some bov leaks also, and a j-coupler was leaking) it still didnt help anything.

we went over the car very thoroughly with soapy water but couldnt find anything new. Im using a tester from http://www.boostpro.net/ and it seems to leak a small amount around the gauge and the nozzle, so I need to take them out and put some sealant in there, but I dont think that would make that much of a problem.

we messed around with the crank bolt or whatever its called thinking maybe we werent TDC but it hardly changed anything, it went up .5 psi (to reach the max of 3 psi).

for all I know the head could be fubar'ed or even the rings. I think I need to do more tests but after 18 hours of straight work you need a break.


So basically im at a loss for the boost leak test, unless im doing it wrong but I really doubt that.

and the engine is so rigged it could be something in there although I didnt hear any air coming from a hose, but theres certain hoses just sitting in there not plugged into anything, but didnt go to indepth as to where they lead (since they didnt seem to be doing anything anyway) since I was tired. maybe one of those is causing vac problems somehow.

 

[oldman]

First fix the leak on the tester then repeat the test with the oil cap open and listen for leaks into the crank case. Post back the result.

 

[boostnmt]

this sounds like the same problem that I am now dealing with after installing a 14b in my 1g with a lot less miles on it. When i step on it it gets to about 3k and the rpms drop and the car will shut off and I also have to start it while it's rolling. curious about how you fixed this problem?

 

[Tommy31]

It might be a bad ISC. If it's faulty and it sticks closed then not enough air will make it through and it will stall the car. You may want to test that too. My $.02 for what it's worth.

But fixing your intake leaks is also important.

If you're worried about leaks past your rings, etc then take the intake pipe off the throttle body and block it with something and clamp it down tight (a spray paint can or something maybe??). Be sure it's well clamped otherwise you risk it popping out and hitting somthing/you. That way you'll test the intake path without your engine leaks misleading you.

Good luck.