STR FTR 1

1986 Irocz 305 TPI, when driving at freeway speed for about 3 miles service engine light comes on. When stop and turn off engine and restart service engine light stays off until freeway driving again for again about 3 miles. Only does it at freeway speed. Sometimes not always when this occurs when the engine is restarted the engine will idle real ruff for about 5-7 seconds then smooth out then runs fine. The engine runs great around town and never a service engine light until freeway speeds.

Injuneer

If the SES light comes on, whatever caused it sets a code in the ECM. Scan the code by shorting the ALDL pins, and counting the SES light flashes, as shown in this procedure.... will work for pre-1993 models:

Courtesy of Shoebox

http://shbox.com/1/dlc2.jpg

After you get the code, post it, and we can help you out.

STR FTR 1

OK, so I got a friends OBD1 reader and the results are:
Code # 53: System voltage to high over 17.7 volts to ECM or EGR system fault or alternator voltage not normal or vehicle theft system. Checked voltage from alternator got 14.24 volts. No vehicle theft system. Question: Is it possible that the vacuum hose from the EGR to wherever it goes being old have cracks due to age ( never been changed) cause the problem.

Code #51: Computer problem faulty wrong or incorrectly installed prom circut or ecm/pcm failure. Nothing new installed

Code # 45: Rich exhaust indicated- left side on dual oxygen models. Have not verified yet but not sure if it has dual oxygen sensors.

Any idea which of these work cause my service engine light to come on as described.

Thanks

Injuneer

Some of the codes you pulled may have been older, "stored" codes. Clear them, and see which one (or more) comes back when the SES light turns on. Again, you don't need a code reader.

Chiltons shows the 86 5.0L TPI has a single O2 sensor.

From the Chiltons code list specific to the F-Body application of that engine:

DTC 45 = Indicates the engine is running to rich. Could be caused by too high fuel pressure, exhaust leaks before the O2 sensor, misfires, or faulty O2 sensor or wiring, If the EGR hose you mentioned attaches to the exhaust manifold, and it's leaking, could cause the O2 sensor to read "lean", and force the ECM to add extra fuel the engine doesn't need. If the broken hose is the vacuum line from the intake manifold to the EGR solenoid, its a vacuum leak, but probably not enough to upset the A/F system.

DTC 51 = EPROM error. Could be the chip coming loose, corroded pins, etc. No necessarily related to any work on the ECM.

DTC 53 Most likely over voltage. EGR failure code is DTC 32.

EGR is used primarily when cruising at part throttle loads and low RPM, when the engine may be subjected to "lugging". That raises combustion chamber temps, and EGR is used to reduce combustion chamber temps and limit NOx emissions. But I'd expect to see DTC 32.

STR FTR 1

This is great information. Questions are, How do I clear the codes. And I don't know where the chip is to check if it's loose or to pull out and check for corrosion. I kind of remember hearing at sometime to reset computer to pull the fuse located under the hood on the passenger side fender . Is this correct. I sure appreciate your assistance. Thanks

Injuneer

If there is an "ECM BAT" fuse, pull that for 30 seconds. Alternatively disconnect the battery cable for 30 seconds.

The "chip" plugs into a socket in the ECM. It holds the programmable data.