Losing Power at WOT - No Codes


Mar 28, 2021
Hi all,

Got an issue that creeped up just recently on my GN that's making me scratch my head a bit. 3rd gear WOT it will feel either like the trans is slipping or the engine is trying to cut out. RPM's bounce so I'm assuming it's the trans that's slipping, plus there's no codes. It happened one time this summer when I had the emissions/pump gas chip in, but I also had to pull out of the pedal as I noticed the timing was being pulled back (crap Colorado gas). So at that time I assumed it was a fluke. The slipping/cutting out (whatever it is) is much worse on E85 with the extra power and I can duplicate it every time now (bonus is zero timing is pulled with E85 and it runs smooth as silk otherwise).

I have the Scanmaster, full set of gauges including fuel pressure. Never drops pressure, nothing unusual that I can see anywhere other than the bouncing RPM's. I'm no expert with the Scanmaster so feel free to school me there.

When I bought the car several years ago I was told it was a built trans with a PTC 2800 converter, no idea who actually built the trans. It's always shifted great. I've also had a previous issue with the engine cutting out when I ran at Bandimere a few years ago, but it did trigger a code immediately and it was a simple throttle body adjustment that fixed the problem. Car has been a restoration project over the last several years so I haven't put a lot of miles on it in the 3+ years I've owned it.

Looking for any insight or ideas of what to start checking. Still trying to learn this car and the quirks, but without a trouble code to point me in a direction I'm a bit lost.

Thanks in advance!

On edit: crap not sure how my signature got deleted. Here's the car info:
87 GN, 60# Deka injectors, Precision 5931 turbo, PTC 2800 converter, E85
Valve springs gone soft?
No idea. I'm the 4th owner so some of the history may be a gray area. It was supposed to already have the valve springs upgraded. At least that's what the previous owner told me. Ran fine up until now.

I did take it out again yesterday and it happened again at a little over half throttle in 3rd gear. Just feels like it's hitting hard and then suddenly like it's just coming out of gear for a split second. It doesn't sound like an engine cutting out. When I had the fuel issue at Bandimere that was definitely a different feel and sound altogether when it was cutting off the fueling.
you should have a better scan tool like a power logger
Maybe see if anyone in the Denver/Springs area has one that they would be willing to take a ride and see if anything shows up. I'm only good with diesel tuning, never messed with gas tuning before so I'm not all savy on what to look for.

If it was tripping a code then I could find the problem. But this one has me more or less blindfolded in a knife shop trying to feel my way around.
Idont see how a throttle body could of fixed the problem temporarily the only problem you can have with a throttle body is the shaft cam leak and cause a drop in fuel pressure
Idont see how a throttle body could of fixed the problem temporarily the only problem you can have with a throttle body is the shaft cam leak and cause a drop in fuel pressure
The issue with the throttle body a few years ago when it was at the track was code 21 for TPS voltage too high. At 5 seconds of WOT the code would trigger, check engine light come on, and the fueling would be cut back. As a comparison this current problem feels way different than fuel being cut back.