mhuppertz Posted March 24, 2019 Share Posted March 24, 2019 The engine runs perfectly, even under hard acceleration, until the car is about to upshift, then it falls flat until I let off the pedal. I can floor it again and it is fine, so it isn't a fuel pressure issue. I could swear that there is some sort of torque management that is failing. This issue is driving me crazy. I replaced the TPS and dialed it in to the right idle voltage. Replaced the coil pack when they failed, and the electronic controller under the coils previously, not 100% sure the issue was present before that. The car will run 90 all day long, just stumbles on upshift. Makes no sense. Ideas? Link to comment Share on other sites More sharing options...
DAVES89 Posted March 24, 2019 Share Posted March 24, 2019 Mass Air Flow sensor? Link to comment Share on other sites More sharing options...
padgett Posted March 25, 2019 Share Posted March 25, 2019 Quote '88s with 440T4 had issues with shifting, if you hit 6,000 rpm the limiter will shut off fuel. Link to comment Share on other sites More sharing options...
mhuppertz Posted March 25, 2019 Author Share Posted March 25, 2019 No errors from the MAF, and it isn't acting like what I would expect a bad MAF to. On the fuel cutoff at 6k, it happens at various RPM, usually anything above say half throttle. Like I said, if I stay in it it runs flawlessly, but if I let out to upshift, falls flat (like fuel or electrical cutout). Imagine a newer car that has torque management, and there is something wrong with the ECU so that when an upshift is triggered the computer pulls nearly all the fuel out, that's what it feels like. Link to comment Share on other sites More sharing options...
2seater Posted March 25, 2019 Share Posted March 25, 2019 I don't have a reasoned conjecture at this point but simply a caution to not assume a sensor is operating correctly just because there are no error codes. It is possible for a sensor, such as the MAF, to give incorrect information and remain within parameters so it doesn't trigger a code. Todays control systems are much more powerful and cross check multiple inputs, but our older systems are much more coarse. That said, something like a snapshot of sensor readings where it is acting up may reveal something, or simply pick a sensor to watch to see if it performs as expected, such as a steady increase in MAF reading as acceleration ramps up. From previous experience I would expect a maximum of 125ish on the MAF at the full throttle shift point. Now if the engine stumbles, the MAF will drop, so careful observation as to timing of events is necessary. I only use the MAF as an example. Take a look at O2's, Integrator and Block Learn to get an idea if it is running out of fueling, or perhaps something is triggering the knock sensor which will pull timing. 1 Link to comment Share on other sites More sharing options...
Ronnie Posted March 26, 2019 Share Posted March 26, 2019 On 3/23/2019 at 8:57 PM, mhuppertz said: The engine runs perfectly, even under hard acceleration, until the car is about to upshift, then it falls flat until I let off the pedal. If you think the transmission upshifting is causing the engine problem you can unplug the electrical connector going to the transmission and see if the problem goes away. That would eliminate the transmission having any effect on how the engine runs. The connector is located near the modulator on the transmission. The transmission will shift just fine with the electrical connector unplugged. The ECM doesn't control the transmission on your '89 but the transmission does have switches inside it that tell the ECM what gear the transmission is in when it shifts. Link to comment Share on other sites More sharing options...
Dashmaster Posted March 26, 2019 Share Posted March 26, 2019 Does it do this on all Up shifts or just 3rd to 4th ? Also what is the load when it does it. Pulling Hill ? or accelerating on an on ramp? Link to comment Share on other sites More sharing options...
mhuppertz Posted March 28, 2019 Author Share Posted March 28, 2019 It happens on any upshift. If I lean on it more than, say half load or more it will do it. If I stay in it when it stumbles it keeps stumbling and decelerates, until I let out of it more, then it upshifts and everything is fine. Like I said if I stay hard in it it will pull hard all the way to upshift. Weird. I have a new knock sensor and O2 sensor that I am going to throw in it while I am under the car looking for A/C freon leaks. I need to be driving this car, but it is getting pretty warm without A/C. Just got my collection of o rings and seals to try to seal it up, but that is a subject for another thread. Funny thing is, I can hop in it and drive 200 miles north at 85 or 90 no problem and get 24 mpg doing it. Just can't accelerate too hard without blipping the gas to let it upshift. Link to comment Share on other sites More sharing options...
2seater Posted March 28, 2019 Share Posted March 28, 2019 Well, full throttle goes to open loop. I don't remember exactly where in the TPS scale, but at a certain point, like 3/4 or so, it goes into fuel enrichment. I am not certain what that all means, but things do change above a certain throttle position, and it is easier to fire a slightly rich mixture vs a lean one. Link to comment Share on other sites More sharing options...
avgwarhawk Posted March 28, 2019 Share Posted March 28, 2019 (edited) Check the TPS voltage through its throw. In short, what is the voltage when at idle and at WOT? That TPS although new may have a flat spot. TPS controls a lot. As a side note, MAP sensor appears ok? Wires to VSS ok? Edited March 28, 2019 by avgwarhawk (see edit history) Link to comment Share on other sites More sharing options...
mhuppertz Posted April 6, 2019 Author Share Posted April 6, 2019 It was the ignition module. Changed to a later style Delco ignition controller and coils, problem gone. If there is no feedback from the transmission this shouldn't have fixed it. Very irritating not to know why, but glad it is resolved. Link to comment Share on other sites More sharing options...
2seater Posted April 7, 2019 Share Posted April 7, 2019 Good to know it is happy now. As these cars and systems age, the normal and expected failure modes seem to morph into new ways to test our resolve. 1 Link to comment Share on other sites More sharing options...
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