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Intermittent performace issue

Discussion in 'Technical, Maintenance and Modification' started by Andyb89gt, Aug 7, 2017.

  1. Andyb89gt

    Andyb89gt New Member

    Hello all,
    I am new to this group and was not quite sure which forum to post this under, but here goes and we can move this to the appropriate area if necessary.

    I have a completely stock 89 GT. I have some sort of a problem either in the fuel delivery system or the ignition system. After the car has been running f0r a while, when I get to about 1800 rpm, there is a hesitation in power and then once it gets past that speed, it seems to resume normal function. As the run time continues, the problem keeps getting worse until it is almost undriveable. Somebody watching me would think I did not know how to drive a manual transmission.

    A friend of mine was following me the other day and observed black exhaust indicating it is running rich, but I already knew that because I use almost a 1/4 tank of gas going to Walmart, which is outrageous.

    I have also noticed the temp gage is completely bottomed out. I do not know if it is related, but I know the gage and the sensor must be working because I have noticed it in the normal operating range on occasion.

    My mechanic was unable to offer a solution, but he was able to observe the problem. We discussed things like catalytics getting clogged, fuel system needing a cleaning. He did change out the thermostat, but the temp gage problem remains.

    Anybody have suggestions on where to go with this?

  2. broncojunkie

    broncojunkie Active Member

    I believe there are two temperature sensors. One that sends data to the ecm and another for the gauge. If the temperature never reaches operating temp, it will run rich (closed loop). Some people will run lower temp thermostats thinking they are helping cool the engine, but it will eventually start running rough due to the rich condition. Also, some parts stores will automatically give you the lowest temp t-stat thinking you are probably replacing it due to an overheating issue.

    You should also test the throttle position sensor , which is a common problem and will cause the issues you describe. There are videos on YouTube. Another problem area is the mass airflow sensor. They need cleaned periodically to work properly. It's a small wire in the intake tube. It's very easy to damage it, so it's not recommended to touch it. You can buy mass airflow cleaner in an aerosol can.

    These are a few ideas to get you started, but you can pull codes using a test light or multimeter. There are videos online and instructions on the web. OBD1 systems won't give you as much info as the newer cars with obd2, but it should at least help point you in the right direction.

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