Engine cuts out just before upshift

[mhuppertz]

I have a 1989 Reatta that generally runs great. The issue I am having is when I am accelerating to get on the freeway (for instance) it pulls strong all the way to the shift point, then the engine cuts out like it is running out of gas. I can keep accelerating for a long time and it doesn't so it, just at upshift time. If I let completely out it is fine after the upshift.

It isn't the fuel pump because I can accelerate in high gear on the freeway no problem.

I replaced the coils and electronic ignition module, plugs and wires are fairly new. 

I bought a TPS thinking that might be it but haven't tried it yet.

 

No error codes

 

Really scratching my head on this one.

[2seater]

Is this a new issue that has been okay up until the present? What are the rpm's where it cuts out?

[mhuppertz]

It is a fairly new issue, and is not really RPM dependent because if I keep it floored it will keep revving until it is time to upshif. Does the same thing at part throttle. At low throttle position it doesn't do it.

Really weird. It actually feels like it is hitting the rev limiter when it isn't.

[2seater]

16 hours ago, mhuppertz said:

It is a fairly new issue, and is not really RPM dependent because if I keep it floored it will keep revving until it is time to upshif. Does the same thing at part throttle. At low throttle position it doesn't do it.

Really weird. It actually feels like it is hitting the rev limiter when it isn't.

So the engine doesn't actually quit, but the power level reduces suddenly, and the effect is similar at a full power shift of say 5000rpm as well as a part throttle shift at 3500rpm or so? There was, and perhaps still is, a torque reduction protocol in the ECM to reduce power at shift points, but that shouldn't happen at part throttle. You can monitor various sensors in diagnostics to see if something looks off, or take a snapshot when this happens. Was anything done recently, like a tune-up or other work under the hood?

[mhuppertz]

It actually leans out, because it pops a little.

Today I held it in 1st and it reved all the way up but when I let off it stumbled, kind of a raspy, poppy sound like a antilag on a turbo car.

Chances of finding a good 1989 ECU is probably nill I would think.

This car sits all winter, and that probably isn't good for it. 

 

[Ronnie]

2seater may know better than me on this but I think it's possible that the Mass Air Flow sensor is bad. Try unplugging it and see if the problem is the same.  The engine may not run as good with the sensor unplugged but if the problem changes it might indicate the MAF is bad. It should set a code if it's bad but who knows?

[2seater]

2 hours ago, Ronnie said:

2seater may know better than me on this but I think it's possible that the Mass Air Flow sensor is bad. Try unplugging it and see if the problem is the same.  The engine may not run as good with the sensor unplugged but if the problem changes it might indicate the MAF is bad. It should set a code if it's bad but who knows?

I was thinking along the same lines but the occurrence under different load conditions is a little confusing, pretty much why I suggested a snapshot of what the ecm thinks is happening. Full throttle is pretty much open loop, but MAF is still online for sure. If the MAF gives no data, the ecm knows for sure there is a problem, but bad data may go undetected. I don't know how my car would react to full throttle in low gear and then back-off, I would expect it might make unusual noises. Fuel pressure should be checked under load if giving symptoms of leaning out but the O2 activity, BLM and Integrator readings will give a clue if it is trying to add or subtract fuel. The diagnostics are a very useful tool built in and may be helpful and give us data to work with.

[mhuppertz]

I pulled the MAF connector and it did the same thing. Could it be a marginal O2 sensor?