The "Issues with my Wagon" thread (was "Runs horribly especially with A/C on. '91 TBI 305.")

Hello everyone, I've been having a weird issue as of late. Basically after the car warms up it runs like absolute dog turd. Think 50% throttle and 2,000+ RPM to go 20MPH. The transmission shifts so late probably because I have to have the pedal so far down to accelerate. The A/C makes the issue so much worse. Think drop from 1,500 to near 500 RPM during the 1-2 shift. Here I have two TunerPro RT logs that show the issue.

The only difference between 5:44 and 5:45 in log 1 is the fact that I turned off the A/C.

Log 2 has the car running better............with the MAP sensor disconnected. It still jerks but it isn't as bad. In this you can see how the O2 sensor voltage goes to or damn near 0. Ignore the jumble between 5:29 and 5:31. Damn tablet.

I'll try to get another log for tonight's drive.





edit: title change

Could the Cat be clogged, causing a back pressure issue?

I would check the ground at the thermostat housing. The ground is for the computer and the O2 sensor.

I think the cat is OK, because it would run at idle, and just no have any power as you try to go faster.

Thanks guys for your suggestions.

Now for a little update: Pulled the electrical connector from the EGR solenoid and the car runs perfectly. Plug it back in and the problem comes back.

A better description of the problem (now that my brain is clear): When accelerating at light to medium throttle, the RPMs

hold -> increase a little -> hold -> increase a little

and then when it shifts from 1 to 2 you really have to push the pedal down a bit further to get it to start accelerating again.

Cars are weird

That sort of gives you a hint about the issue. It is probably the solenoid.

I just can not win with this car. Now the fuel pump relay coil will not stay energized when cranking the car. It's energized when the key is on and the engine is off until it starts cranking, then the voltage goes away. I had to get it home by rigging the fuel pump prime to connector B on the ESC module. (<- don't ask.)

Tested it with a multimeter just now. 12v to relay when the key is first turned to run, then when turned to start to crank, .6 volts.

Just to update everyone, turns out the oil pressure sender is (partially) faulty. Yeah sure the gauge works, but according to the FSM the oil pressure switch serves as a backup to the fuel pump relay and it didn't work. I jumped the two contacts on the oil pressure sender connector (C&D I believe) and the damn thing started right up. It makes me wonder if the FSM is wrong and the fuel pump relay only serves to prime and that's why I only see 0.6v when cranking and it running after I jumped the relay to test. Anyway, time for a new sender so I don't have to buy an ECU (cheap me). So now its either A1 Cardone, Standard Motor Products or DuraLast.

Okay, I've decided to throw parts at it and see what sticks. ECU, oil pressure sender, etc., etc.


I absolutely hate electrical issues.

Change the parts one at a time, so that you know what fixes it, and what does not. The parts that do not fix it, are still good, and you should save them for spares.

Fred Kiehl wrote:

Change the parts one at a time, so that you know what fixes it, and what does not. The parts that do not fix it, are still good, and you should save them for spares.

Yep, that's the plan. I'm going to test the ECU first with it hanging and not bolted in because if that isn't the problem, that $89 sucker is going right back

I know the oil pressure sender is partially faulty. The gauge works but it does NOT power the fuel pump with oil pressure as it should. (confirmed by jumping terminals C and D on the sender's connector. If only it were ignition hot and not battery hot. I would have jumped it at the connector and left it at that.)

Confirmed the ECU was the issue. Replaced it first and the car started right up.