QuestionQUESTION: Hello again Roland, Thanks for your reply it was very informative, I have soldered very wire that looked broken or melted, I have replaced the fusible links that were slightly melted but still continuous, I have cleaned the pins of the SEMC and I have sealed up every vacuum leak and the cold air feed ducting (in case the air flow meter was giving a false signal by the intake manifold pulling in air from around the ducting instead of through the air flow meter) even sealed the hole in the bottom of the air filter housing (about the size of a nickel, perfectly round looked like a factory made hole maybe for a mounting grommet ?). There are no codes stored in the SEMC other than the 12 number of key-ons, 33 (AC relay) and the always good to see 55. I have cured the ‘bump-shifting’ by adding a thick ground wire straight from the battery terminal to one of the TCM mounting bolts. The car is shifting perfectly even the kick down is working perfectly, the car is driving great with plenty of power and acceleration … until the gauge rises and when it rises it still loses power and I can hear popping from the air filter housing and the exhaust when I mash the gas pedal, if I turn it off for any length of time (5-10 seconds) and start it up it drives great again for a couple of miles so I am led to believe that the temperature is immaterial and more about the time driving like maybe a component cannot go the distance? Or does my car have a charge temperature sensor and if so that is the only thing left what colour are the wires to this? (I found a yellow and black/blue wire going to nowhere but assumed this was for the EGR as it looked like it had never been plugged in because my car has no EGR system) . Oh and it is a little harder to start from cold now too but that is not a problem just thought it might help you to diagnose the problem running out of ideas, the O2 sensor, the CTS and the thermostat are new and the TPS and MAP sensor are functioning correctly all the voltages to these are correct and I have not got a clue where to go next. Your help has been invaluable thus far and if you cannot help me any further you have at least gotten me this far. – Thanks -Paul
ANSWER: Hi Paul,
I might mention to you that there is no air flow meter in this system. The tps, MAP and rpm give the equivalent information. If there is an air leak it us sensed by the other sensors and results in a mixture adjustment that usually causes a higher idle speed. So I wouldn't modify anything due to that concern.
There was a charge temp sensor on the throttle body of the '88 model but not the '89 model. It's wire color is black/red and black/light blue and the former goes to pin 21 of the SMEC (again, 88 model only). The only solid yellow wire I can find runs between the two plugs of the SMEC and is for "dwell control". Is it a solid yellow or a trace yellow? Maybe the color has changed due to heat? The reset of the problem by turning off the engine and then the repeat of the problem might be tied to recycling the "loop" control system (engine runs in open loop until a defined time period then goes into closed loop). Former is based on preset parameters, latter uses all sensor data.
How about the exhaust system, perhaps the lack or catalytic converter if one was originally provided, or the air leaks, either one of which might be throwing off the oxygen sensor, which would impact the mixture when you enter closed loop operation?
So that is the best I can offer. Let me know if any of this helps or you come up with other observations.
Roland
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QUESTION: Hello Roland thanks for the speedy reply.Is there any way I can ground or power a wire that will force the computer to stay in closed loop as it drives fantastically? The wire is grey with a yellow trace or maybe started out white with a yellow trace and blue (the white/grey with yellow comes from a 4 wire plug at the back of the battery. I know that the TCM learns and must re-learn is it too much too hope that the SEMC does the same? as I have no ideas left about what it could be, I have covered all the input sensors (TPS,MAP,CTS & O2) I get no codes now but the 33 12 & 55 are there any other sensors you are aware of on this vehicle? The exhaust is 2.5" tubing but I kept the original muffler it does leak a little though you think that could be the problem? I thank you for your continued help on this most perplexing matter
AnswerHi Paul,
OK, the gray-yellow*/dark blue is indeed for the EGR solenoid in California-only vehicle. Thus you can see the importance of describing exactly the wire color(s).
There are no other sensors I can find. You might want to consider replacing the MAP sensor as it can be inaccurate without being so bad that the SMEC senses it and sets a fault code. That happened to me on my '89 2.5L 4 cyl.
I can't comment on the likelihood of the exhaust system being the problem. It would seem to be less likely than a faulty MAP in my mind. You can monitor the MAP sensor voltage to see if it is tracking when you modulate the throttle valve, but even so without a set of expected voltages I am not sure how to validate it. It costs around $75.
I don't believe there is a way to outsmart the SMEC in its choice of closed vs. open loop and besides you will probably find that although it runs great your fuel economy may be down due to an not optimum mixture/advace/etc. that comes from being in closed loop. And you are welcome, thank you for the kind remarks. I see you may have been reassigned to an appropriate expert category. Good luck.
Roland
