Engine cut out during heavy throttle, idle ok

[FroMigizims]

93 laser rs turbo
The engine cuts out really bad when throttled, but idles ok (boost/vac wavers around-7).
When free revving it is almost impossible to rev above 4g, on the road very little throttle can be used or engine will cut out (not die).
Multiple tests conducted:
ECM codes, MAF, TPS, spark plugs, wires, Ign module, Injector waveform, all checked OK
Also no visible carbon build up in intake manifold
HELP!! I am a auto mechanic w/10 years under me, and this problem is making me INSANE!

 

[theSicKness]

it could be a boost leak...vacume should be -18 not -7.. id start w/ a boost leak test

hope it helps
Jesse

 

[DSM BEEYACH]

Sounds like a major boost leak. Do a yank and, pull test on every hose connection starting from your turbo all the way up to your throttle body. Check every connection with you hands not just your eyes. Make sure that all your hose connections are nice and, tight.

 

[spidy3]

getting enough fuel?


Dom

 

[eclipsh]

If the engine won't rev past 4k without any load then I doubt it is boost related. You won't be making any significant pressure without any load on the engine.

I'd test the fuel pressure and the coil pack.

 

[darkness_fallz]

Sounds like a major boost leak. Do a yank and, pull test on every hose connection starting from your turbo all the way up to your throttle body. Check every connection with you hands not just your eyes. Make sure that all your hose connections are nice and, tight.

Or ya know- you could go through and do a Leak down test on your system with the tool and process they have detailed at www.vfaq.com . just a tad bit more reliable than pulling on stuff and all of that.. *nods*

Now when it starts cutting out, does it stutter? buck? try to turn around and punch you in the face?

 

[DSM BEEYACH]

Or ya know- you could go through and do a Leak down test on your system with the tool and process they have detailed at www.vfaq.com . just a tad bit more reliable than pulling on stuff and all of that.. *nods*

Now when it starts cutting out, does it stutter? buck? try to turn around and punch you in the face?

wrong!!!!! care to tell me what a leak down test have to do with a boost leak. A leak down test diagnoses where you're losing compression before you open up your engine. A boost leak test is different. A simple yank and, pull test will show you if you have a major boost leak somewhere like if maybe your hose popped of somewhere. A boost leak test with the use of compressed air will help you pinpoint smaller leaks.

 

[CrippleFight]

93 laser rs turbo
The engine cuts out really bad when throttled, but idles ok (boost/vac wavers around-7).
When free revving it is almost impossible to rev above 4g, on the road very little throttle can be used or engine will cut out (not die).
Multiple tests conducted:
ECM codes, MAF, TPS, spark plugs, wires, Ign module, Injector waveform, all checked OK
Also no visible carbon build up in intake manifold
HELP!! I am a auto mechanic w/10 years under me, and this problem is making me INSANE!

what size turbo do you have on there? If its upgraded make sure you have a supplimental fuel system(injectors, fuel pump, Fuel Pressure Regulator(if necessary)

 

[Mist3r Spool]

93 laser rs turbo
The engine cuts out really bad when throttled, but idles ok (boost/vac wavers around-7).
When free revving it is almost impossible to rev above 4g, on the road very little throttle can be used or engine will cut out (not die).
Multiple tests conducted:
ECM codes, MAF, TPS, spark plugs, wires, Ign module, Injector waveform, all checked OK
Also no visible carbon build up in intake manifold
HELP!! I am a auto mechanic w/10 years under me, and this problem is making me INSANE!

You need to do a boost leak test. You should be getting around 18"-20" of vacuum at idle.

 

[95AWD_TSI_TALON]

A simple yank and, pull test will show you if you have a major boost leak somewhere like if maybe your hose popped of somewhere. A boost leak test with the use of compressed air will help you pinpoint smaller leaks.

Ok. Yank and pull???????? First off "this test" would only find MAJOR boost leaks. This would be completly a waste of time leading to a true boost leak test. I have had customers cars with boost leaks in the Rubber IC piping from it rubbing a wearing a hole in it's under side. Tugging would have never shown a hole the size of a quarter in it......a boost leak test POINTED IT OUT FOR ME. Yank and pull- pointless.
Matthew

 

[AmpleEclipse]

It doesn's sound like a "boost leak" as much as a vacuum leak. I just had a vac hose pop off of my turbo (under the intake) and it caused my car to do that. My vac was around 10 and it wouldn't rev past 4k with full boost. To sum it up, go through your small vac lines and make sure everything is ok! Hope this helps -Matt

 

[ivanr4g63]

Did it all of a sudden started acting up like this... or was it right after some installation you did under the hood?

Like stated above start looking for obvious vacuum leaks, sounds like something is loose somewhere in there, also you could try the boost leak pinpoint and fix them if any.

let us know.

 

[greytalon26]

My guess would be you're not getting enough fuel, and there could be a boost leak.

-Drew

 

[selmerguy]

all of you talking about a boost leak test and saying that a boost leak would effect idle vac need to stop smoking the crack. to prove this go start your car, look at the boost/vac gauge and see what it says. now pull your cold pipe from your tb. then go look at your gauge again. guess what it is the same!!! now that is the biggest boost leak i can think of. now to the subject at hand

check your compression. look for vacuum leaks. also check for fuel and spark. it sounds like when you romp on the gas you loose either fuel or spark. your a wrench and if the problem is not motor related(compression, vac leak) then you have to play with that electric stuff till you find it.

i would bet your compression is low. and that you have some leaky valves.

good luck

 

[95AWD_TSI_TALON]

all of you talking about a boost leak test and saying that a boost leak would effect idle vac need to stop smoking the crack. to prove this go start your car, look at the boost/vac gauge and see what it says. now pull your cold pipe from your tb. then go look at your gauge again. guess what it is the same!!! now that is the biggest boost leak i can think of. now to the subject at hand

A boost leak= leak before TB
Vacume leak= after TB

performing a "boost leak test" finds BOTH , not just boost leaks. without being able to free rev, almost sounds like the MASS is not completly connected. Other wise, what SELMERGUY stated is same opinion here.
Matthew

 

[selmerguy]

A boost leak= leak before TB
Vacume leak= after TB

performing a "boost leak test" finds BOTH , not just boost leaks. without being able to free rev, almost sounds like the MASS is not completly connected. Other wise, what SELMERGUY stated is same opinion here.
Matthew

agreed. i was just trying to say that a boost leak does not cause idle problems. and after thinking about it i have never seen a vac leak stall out a motor. please post your compression numbers to satisfy my curiosity

 

[FroMigizims]

I'm back
OK... free revving it WILL make plenty of boost 14+ pegging the needle
have checked vac and other related hoses with no sucking sounds or change in idle
motor does not stall out or die, it revs a little until the vac/boost is around 0 then looses all power and makes a popping sound out the tailpipe.
sorry no compression numbers, gauge broken, will get one tomorrow

 

[oldman]

I hate doing this but a lot of clean up needs to be done in this thread.

Sounds like a major boost leak. Do a yank and, pull test on every hose connection starting from your turbo all the way up to your throttle body. Check every connection with you hands not just your eyes. Make sure that all your hose connections are nice and, tight.

Never ever rely on anything but a REAL BOOST LEAK TEST unless you heard a pop on the highway and have no access to a tester. A false sense of security can sometimes cause greater damage.

If the engine won't rev past 4k without any load then I doubt it is boost related. You won't be making any significant pressure without any load on the engine.

Considering -7hg of vacuum, anything is possible.

It doesn's sound like a "boost leak" as much as a vacuum leak. I just had a vac hose pop off of my turbo (under the intake) and it caused my car to do that. My vac was around 10 and it wouldn't rev past 4k with full boost.

In most cases, vacuum leaks become boost leaks once the car is in boost so eventially they are the same.

all of you talking about a boost leak test and saying that a boost leak would effect idle vac need to stop smoking the crack. now to the subject at hand

Please try and be respectful of others even when you're right, not to mention you're not. like I have mentioned above, most vacuum leaks = boost leaks. When people say boost leak, it's usually understood that vacuum leaks are included as well.

to prove this go start your car, look at the boost/vac gauge and see what it says. now pull your cold pipe from your tb. then go look at your gauge again. guess what it is the same!!! now that is the biggest boost leak i can think of.

If I'm not mistaken, 420a does not use a mas, excuse me if I'm wrong. Unless you're running a blow through setup, pulling any IC pipes after the mas will cause wrong air flow signal to be sent to the ecu and cause the car to stall.

A boost leak= leak before TB
Vacume leak= after TB

Boost leak = before and after the TB.
Vacume leak= after TB


As for the thread starter, the following posts were the best advice IMO that was given in this thread.

it could be a boost leak...vacume should be -18 not -7.. id start w/ a boost leak test

You need to do a boost leak test. You should be getting around 18"-20" of vacuum at idle.

check your compression

 

[selmerguy]

i'm sorry for being a butthole. also i forgot the 4g63 mass air flow insdead of map. so don't pull that pipe now i do realize that vac leaks turn into boost leaks. but at idle you have no boost. i still would like to see compression numbers.

 

[eclipsh]

I'm back
OK... free revving it WILL make plenty of boost 14+ pegging the needle
have checked vac and other related hoses with no sucking sounds or change in idle
motor does not stall out or die, it revs a little until the vac/boost is around 0 then looses all power and makes a popping sound out the tailpipe.
sorry no compression numbers, gauge broken, will get one tomorrow

Is that with a real boost gauge or the factory one? The factory one is not at all accurate, it just guesses.

 

[oldman]

Is that with a real boost gauge or the factory one? The factory one is not at all accurate, it just guesses.

Good point, I wonder if -7 (psi or hg) was read from the stock gauge.

 

[FroMigizims]

I did not much time last night (I have 2 kids) to work in the shop
but i did manage to yank the exhaust, and it sounded BITCHIN!!
however when throttled hard it cut out, popped, and sputtered.
there was a lot of black(fuel) smoke when it did screw up.
but when idling no smoke
still no codes
i also checked ALL vac, boost and pressure pipes & hoses

I forgot to mention that this all happened after the original turbo sized(bearing failure)
the car was run (NOT by me, and with much protest) for 1-2 months 5-10mi every day
the problem with cut out gradually got worse until the car became undrivable.
then I replaced the sized turbo with a known good one, with little effect on drivability.
now here I am 2 weeks later still trying to sort it out.

P.S.
I live in the country w/o net access
and must use internet in town.
hence I can only post once or twice per day.

 

[FroMigizims]

by the way the car is bone stock

 

[munguiaoh]

i would check your spark plugs ( make sure there are gapped correctly) , spark plug wires.

 

[4rsfed]

Hey, my car had the same type of problem, so I checked all the vacuum lines and solenoids the lines hooked up to. I found that the purge control solenoid was not working. I replaced the solenoid and it solved the problem. I could not find the original solenoid to replace it but any solenoid with the same function (closed when activated or open when activated) will work. Who knows but it could be the same problem as I did. Good luck.