1987 Ford F-250 self testing

  • 1987 FORD F-250
  • 5.8L
  • V8
  • 4WD
  • 180,000 MILES
1st I ran KOEON test and codes, result MAF/TPS+3 others. I cleaned my MAF w/TBcleaner hoping it would clear TPS code and others. My question why wont pcm read codes in KOEOFF? Other codes were o2, coolant temp, engine temp & fail koeoff. Test conn. Used are tan lt/grn & w/lt bl
Do you
have the same problem?
Friday, October 30th, 2015 AT 6:54 PM

1 Reply

Diagnostic fault codes were in their infancy in '87 and didn't provide much information. Even in newer cars today that can have over 2,000 potential fault codes, there is no code related to a dirty throttle body. There is no way to monitor that so the Engine Computer would have no way to know when to set such a code. The best you can hope for is to find a fault code related to the results of a dirty throttle body, but even that is mostly wishful thinking. You could have a hesitation on acceleration, but there is no actual defect with a sensor, and no problem with the exhaust gases being monitored, so no fault code would be set. Oxygen sensors were rather primitive too in '87. What they report to the computer has to be pretty bad before a code will be set.

As far as reading codes with the engine running or off, you're typically going to find the same codes either way. The bigger issue is what will read those codes. Some scanners do more functions on one car model and less on other models compared to a different brand of scanner. You can use a test light or voltmeter on your car too to read codes. We have come so far beyond that, even in the mid '90s, as to make codes on an '87 model of limited value. In '87 Ford was way behind every other manufacturer both in ease of reading codes, and in what they had the capability to tell you. With Chryslers, you just cycle the ignition switch a few times, then read the codes. With GMs, you short two wires together, then read the codes the same way. With Fords, you monkey around playing with jumper wires under the hood, snapping the throttle to initiate some magical sequence, then try to figure out what the flashing light is showing. Then, starting with some '91 models, Ford was the first to use three-digit codes because they advanced well ahead of other manufacturers.

When you have so many codes at the same time, look for what they have in common and expect to find the cause there. You aren't going to have three or four sensors all fail at the same time, but you can have three or four sensor CIRCUITS all set codes at the same time if they're related to the same wiring problem. Many sensors share a common 5.0 volt feed circuit and a common ground circuit. Only their signal circuits are separate.
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Friday, October 30th, 2015 AT 8:10 PM

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