2G Severe power loss. Please help! Searching 6 months

[bibdrums]

1996 Gst spyder A/t, Hallman MBC, MHI big 16g, 3” turbo back exhaust, IPT retorqued converter, IPT shift kit, Autometer boost gauge, 20K on stock rebuild


About 6 months ago I was cruising on the highway doing about 70 when the car had a bad miss-fire and started feeling like it was running on 2 cylinders and sort of chugging. I pulled over and the car idled fine. So I gave it some gas and it sounded normal but was lacking a lot of power. It moved so slowly from a stop that it was hard to pull out into traffic. When I got home I checked for codes and had a p0300.


I have been chasing this problem for 6 months. Yesterday, out of nowhere, the car ran amazing for about an hour. Then, just as suddenly, it started running like crap again. Feels like it’s pulling timing or not getting enough/too much fuel. Also, the exhaust manifold is getting MUCH hotter than ever before. It melted the condenser fan. Builds boost very well though and holds it.


This is what I have checked or replaced:

Fixed ALL boost leaks
Checked timing (like 5 times)
Checked compression (all good)
New knock sensor (was leaking black goo)
Swapped in known good coils
New coolant temp sensor
Swapped in known good ECU
Turbo had play so had it rebuilt
Checked fuel pressure
New FPR
New egr
Salvaged power transistor
New alternator
Ran open exhaust to rule out catalytic converter
New O2 sensor
New exhaust manifold (was cracked and leaking)
New plugs ngk bpr6es gapped properly
New wires
New tps
New crank position sensor
New MAF


When I checked the fuel pressure it was a little high - 43 with the vacuum line connected and 50 disconnected, that’s why I changed the FPR but the new one is showing almost the same so it may be the gauge? Or a clogged return line maybe?


Does anyone have any other ideas on what to check next. I don’t have link, a wideband or anything to log with yet but I am getting link and a wideband in the next month or two. Does anyone have any ideas of stuff I may have missed in the meantime?


Thanks!

 

[xGxTxRx]

Check you Power transistor unit connector located behind the fuel injectors. My connecter was worn and would not hold together properly since the connector clip was missing/broken. Try and wiggle that connection and see if anything changes while running. Good luck

 

[bibdrums]

I finally figured it out!!!

It turns out that it was a timing issue all along. I thought that I was getting knock which was causing the timing to be pulled but once I got ecmlink I was able to rule that out. Unfortunately link wasn't much more help than that. Everything else on my logs seemed ordinary - AFR was good and nothing looked out of place except for how slowly the rpm's were climbing at wide open throttle and the airflow was really low. All the symptoms were pointing to the timing being retarded though. Low power across rpm range, extra hot exhaust gas and popping from unburned fuel in the exhaust and incredibly bad fuel mileage all while afr looked almost perfect.

I started advancing the timing across the entire table in ecmlink to see what would happen and what do you know, the more I advanced the timing the more the power came back.

Turned out that when one of the mounting ears on the cam sensor broke it moved and hit the timing plate that bolts on the inside of the intake cam gear. It must have bent it enough to throw off the timing signal that the ecu was getting and retarded the timing significantly. However, as soon as I advanced the timing in ecmlink the power can back and it feels like it has even more power now because of all the other stuff I fixed while I was trying to diagnose this problem.

And now the search is on for a 1g cas.

Thanks so much to everyone that helped out! I'm not sure how much this will help anyone in the future because this seems like it wouldn't be something that happens very often but you never know.

 

[1990TSIAWDTALON]

Plenty of 1g CAS's around. Keep your eyes on the classifieds, they pop up quite a bit.
Glad you posted up the solution. So many threads have questions but never the final answer.