Not sure if it applies to your situation but I had power loss under boost that was intermittent. My mechanic smoke tested the intake side and found an intake leak that way - I'm only mentioning this because it has the potential to help identify otherwise hard to find intake leaks.

 

I took the car back from the mechanic. He wasn't able to find the problem. The intake was smoke tested and passed. No leaks. I hesitate to put chips in to "fix" the problem. I don't want to override the overboost protection with aftermarket chips as there may be something wrong that needs to be sorted out. Just not sure where to go from here. What are your suggestions?

 

I thought this was a good time to restate what has been checked to this point:

Swapped main computer with 2 known good ones running stock chips.
Swapped turbo computer with a known good one with no change.
Smoke checked intake system and found no leaks.
Replaced Speed and Reference Sensors with no change.
Checked all sensors.
New Fuel Pressure Regulator.
New dme temp sensor.
Checked cross over valve.
Checked bypass waste gate.
Plugs are new.
Swapped DME Relay.

I have not checked/changed the coil or plug wires.
I have not tried to get a blink code yet.

I don't have the ability to data log, and I don't have a wideband.

The car is also running rich when cold.

Thanks for putting some brain power to this.

 

Dont swap chips to "fix" the problem, just to test for it. If it goes away w/ an aftermarket DME chip installed, then you know for certain it is the DME overboost protection kicking in (although your symptoms sure seem to indicate that is what is happening).

Without looking back and reading all previous posts/threads - What boost level is the car running (checked w/ an additional gage)? Are you absolutely sure its not actually overboosting?

For actual overboost, you want to check the CV and the Wastegate function. If you are sure its incorrectly detecting overboost, I would start by swapping an AFM.

 

OK... just some ideas.... When you smoke checked the intake, was the smoke under pressure similar to the cutout situation? I ask because your boost system seems to be working up to a point. And, up to that pressure point I would expect the smoke test to be a go. If in doubt, you could make simple boost test adapter like I did here when I had this problem.

Also, interesting about running rich at idle. A disconnected or open circuit for the DME temp II sensor will do that. So, did you test it together with the wiring (to/from the DME)? Bruce

 

I finally have a few minutes to work on this problem again. I got a used AFM and swapped them last night. The car ran very different (worse). With the different AFM, it would backfire (make a popping noise from the engine area). I assume this means it is running lean. I haven't had an opportunity to test the AFM, just take a short test drive. The barn door spring seems to have more resistance than the one I removed. I had a problem years ago with something similar to this.

I had the problem fixed last time by an independent mechanic. They said they needed to adjust things in the MAF to get it working. Here is the thread from that fix. https://rennlist.com/forums/924-931-...o-project.html Do you think it is possible/likely they could have adjusted something in the AFM that was a bandaid and now I have a couple of different issues that have been masked by their bandaid?

 

Popping through the intake is usually a sign of being lean.

The AFM adjustment is a concern... Two good AFMs, you should not be able to feel any difference in the springs / door resistance.

 

Thanks Joshua,

I thought they just retracked the contacts on the wiper arm. But now I am not so sure. I just swapped out the coil and now I seem to have added a popping from the exhaust at idle. Maybe was already there before putting in the coil. Not sure at this point. Next step is to inspect the plugs and check the gaps.

 

Just checked 1st cylinder and it is really black. Gap seems to be about .28. Tried to test it after putting the plug back in. Started up and sounded better for a few seconds then the popping out of the exhaust came back. Tried to pull plug wire for the first cylinder. Didn't seem to make any difference on the engine. Cylinder 2 and 3 made a big difference. 4 wasn't much of a difference again. What does this tell me?

 

That cylinder 1 and 4 isnt firing properly...
It could be a few things:
Ignition based - spark plug, cap & rotor, plug wires.
Fuel based - fuel pressure, bad injector, AFM.
Mechanically based - bad cylinder compression, bad oil ring.

 

Okay.... Back to the basics.... Not sure I can trust that my independent mechanic did anything he said. So... Now I am checking everything that might cause trouble for this myself. First thing I did since I felt like it was a vacuum leak all along is I finally got a device to test seal off the intake system and pump in some air. I quickly found two significant leaks. First one was the Idle Adjustment screw. I think it backed out significantly and was leaking air there. Second one was the banjo bolt on the intake between the third and fourth cylinders. There was a nasty bad washer there. Trying to figure out how it should be put together correctly to seal the leak. Once I have the intake system sealed, I will attack the next problem. I have already replaced all of the lines so hopefully this will not require removing the intake manifold again.

 

I have the big leaks plugged. Put in new spark plugs and took a little drive. Much better this time, I was able to get boost without the overboost issue. However, now I am getting popping from the exhaust under boost. I think there might still be a small leak in the intake. I also need to make sure I have all of the cylinders firing correctly. I am finally making some progress though.

 

When I pressurize the system, I hear a leak that sounds like it is coming from under the J boot. Is there a connector there or is it most likely a tear in the J boot itself?

 

Theres a vacuum hose that connects to the bottom of the Throttle Body. Bruce

 

LOL there is also a plastic bolt under the gas pedal that you could have unscrewed a bit. but i love this method also