Williamlindsey

1991 base, just replaced one injector, cool, engine idles and runs fine. good throttle response. But when temp gets up in the upper range throttle response goes out the door and Idles rough.

ctmccloskey

Sometimes the Ignition control unit mounted on the passengers side of the under hood area will do just what you describe. When it gets hot it can shut off completely or just make the engine run poorly, cooled off it will work again until it hits a specific temperature and happen all over again. I have also seen the device mounted inside the distributor fail and do what you are describing, on one I saw the previous installer did not use the thermal paste that came with the part and it cooked the little 5 or 7 pin device which made running issues.
I get the impression that what you are dealing with here is probably ignition related but I would still verify that your fuel pressure system is working okay. It is so easy to hook up a fuel pressure gauge to the schraeder valve on the fuel rails and check that your car's FPR is working like it should. You might want to check that the vacuum line from the fuel pressure regulator is not smelling of raw gas indicating a bad FPR diaphragm. Otherwise just check the fuel pressure and be sure that it is above 40 and working according to your cars specs. I am still betting on the ignition control system.

Please keep us posted on what you find! I hope that you can get that car running smoothly all the time! Good Luck!

Williamlindsey

fuel pressure not running with ignition on is 40, running at idle drops to 36.

ctmccloskey

Hello again Williamlindsey,
Your fuel pressure sounds like it should at least run okay as my numbers are very close to yours. When the car starts running poorly check your spark, I still think that what you described could be ignition related. The optimum situation would be to have it at a shop where they could monitor your ignition after it gets hot. How old are the wires, distributor cap and spark plugs? The fact that it happens when hot makes me think electrical related.
Have you checked the EGR for proper operation? EGR's can make idle issues a nightmare. Warm idle issues can be traced to the EGR occasionally. While checking it be sure to verify that it has a source of Vacuum and that the EGR Solenoid is working properly.
How long does it take for the car to start running poorly? Is your car idling in "Closed Loop" roughly and not in the startup "Open Loop" mode? If it happens right after the transition then I would check your O2 sensor as well. The car uses the O2 sensors in the "Closed Loop". O2 sensors are supposed to be replaced every 50-70,000 miles anyway but few do until they fail. You can verify the O2's are working by measuring the output.
One way or another this problem is only "temporary".... Somebody on this forum will have the right answer!
I hope that you have success in finding this issue and resolving it!

billschroeder5842

Check your coolant sensor. If this gets wonky, your computer will think it is hot when your engine is cold, or cold when your engine is hot. It will send the wrong signals for your rick/lean and air and your engine runs poorly.

Williamlindsey

thanks guys lots of info on the forums, some great some not so great.

aklim

Why did you replace 1 injector? If that was bad after all these years, I'd replace the set. Also, if they are different, the flow rates might be different and could cause issues. The newer ones are not fuel cooled and won't be affected by ethanol.

MatthewMiller

It could also be an O2 sensor. Basically it sounds like once the engine goes into closed-loop mode (after warm-up) some sensor is giving the ECM bad info. When in open-loop it is ignoring that sensor. Can you data-log the sensors to see if one of them is flat-lined? Also, do the same for coolant temp sensor and others.

QCVette

To me it sounds like a couple things already mentioned.

--There have been problems with the ICM when it gets hot.
--The O2 sensors could be giving a bad reading to the ECM in closed loop. Bad O2.

The wild guess, but free and easy to try is simply disconnect the battery for a few minutes. If there are some bad values stored, disconnecting the battery will clear the learned values. If there is a different flow rate on the new injector, it may need to learn a new value. Like I said, it is a wild guess, but I had a problem with my '95 after some bad gas, and disconnecting the battery allowed it to relearn and run fine again. Maybe you will get lucky with an easy one.

Good luck.

84 4+3

once its warm get an ohm meter on the injectors and check them. When the ones in my cousins gta went out the same thing happened. It was okay cold and just got worse as it warmed up. South main auto has a very detailed video on YouTube about this too. If you have hard starting at any time I would explore this...

aklim

If he had Multecs dump all and get Bosch so he could fuel up anywhere. Also the single one could be flowing differently from the rest and hence the problem