Shakes and dies while boosting

[greddy_1700]

Hey, So again my DSM has yet another problem. This time after I just spent the time and effort of replacing/breaking in my clutch I go to have a bit of fun tonight only to find out my car has other plans. Basically as I was going on the highway I shifted to 3rd gear, hit the throttle to about 60% and listened to my turbo spool up. Now when my engine hit 4000RPM and my turbo hit about 3/4 Boost the car shook and wouldnt go any higher... I know it has something to do with my air fuel mix one way or another because if I take it very easy on the throttle I can rev past 4000RPM if I dont boost. So what could be causing this behaviour on my 91 TSI AWD? Could this be the infamous fuel cut I hear so much about? I am thinking my fuel pump could have bit the big one, but I really have no evidence to back that up... Let me know.

Thanks in advance,

Garret

 

[kenamond]

First, update your profile. Is the clutch the only mod? If so, you'd only hit fuel cut if your WGA had failed, wasn't getting a boost signal (broken vaccuum line, etc.) or if you have bad boost leaks. Fuel cut is when the ECU detects too much airflow. It protects against WGA failure whereby the boost is not being limited. If the WGA failed, it's just doing its job. If you have big boost leaks, the turbo is pumping much more air than is making it to the engine. I've never experienced fuel cut, but the stories all sound similar to, "felt like I blew the motor" with "almost crapped myself" thrown in. In other words, it's not subtle.

I'd suggest routine maintenance/tests at this point. Do a boost leak test. When were your plugs last changed, what plugs are in there, and what are they gapped to? What's the condition of your motor? Stuff like that.

Do you have a logger?

Hard to tell what's wrong until you eliminate some of the potential problems or give more info.

I'd put boost leak test and plugs/wires near the top of the to-do list.

Good luck and keep us posted.

 

[Mr Peepers]

Try checking for boost leaks. It's a good idea even if turns out to be something else; at least it rules a possibility out.

 

[kenamond]

^^^ Yeah.

Also, if you have REALLY bad boost leaks, you'll be running really rich. If you're stuttering from being that rich, you may see black smoke.

Bad (weak) spark/ignition can also lead to stutter under boost. When you start cramming more air into the combustion chamber (due to boost), the air is denser, and the spark has a harder time jumping through that denser air. If your plugs, wires, or coilpacks are fading, they won't spark as well under boost as they will at less boost. If this happens, you often hear backfiring, because the air/fuel that isn't burned in a cylinder with inadequate spark will ignite in the exhaust manifold when it's combined with the super hot gas from other cylinders that did fire.

 

[95burgundyesi]

putting bigger injectors and a fuel pump without some way to control the new amount of fuel you are getting will make the car run like crap once it starts to build boost. but I didn't see much in your profile so... do a leak test if you have not touched anything.

 

[greddy_1700]

Hmm ok, well The plugs I just replaced about a month ago with the recommended NGK plugs on the site here. The car just had a complete tune up but I had just done some extensive work to it. I had replaced the Turbo, and almost the entire front suspension, And yes, the performance clutch is my only mod at the moment. I will do a boost leak test again today, i had just done one after the turbo went in and it was fine but something could have blown.

On a side note because I know this will come up, Yes the turbo worked great after I replaced it, never did this once. My clutch blew two weeks after driving with the new turbo.

So basically I am looking at a boost leak test, and maybe a new coil pack?

 

[kenamond]

Hmm ok, well The plugs I just replaced about a month ago with the recommended NGK plugs on the site here. The car just had a complete tune up but I had just done some extensive work to it. I had replaced the Turbo, and almost the entire front suspension, And yes, the performance clutch is my only mod at the moment. I will do a boost leak test again today, i had just done one after the turbo went in and it was fine but something could have blown.

On a side note because I know this will come up, Yes the turbo worked great after I replaced it, never did this once. My clutch blew two weeks after driving with the new turbo.

So basically I am looking at a boost leak test, and maybe a new coil pack?

Are the plugs NGK BPR6ES? Are they gapped to 0.028"? If not, that could be part of the problem.

When you do the boost leak test, how do you know how boost is holding without an aftermarket boost gauge? Is there a gauge on your tester? If not, you need that. You might want to consider getting an aftermarket boost gauge anyway. You don't have to fully install it yet, but you could use it in the interim as a gauge for the leak test.

You should pressurize to 20psi, stop adding air, then hold 20psi. Mine leaks down about 1psi every few seconds.

Also, did you change the plug wires recently?

So I'd say do a *proper* boost leak test, fix all leaks, check your plugs (type and gap), and go from there.

Do you plan on modding your car? If so, give us a brief target. I might start recommending some other things if you plan on doing more to your DSM.

Good luck!