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On my 1990 F150 the check engine never comes on. I know that there are codes stored in the computer (33 and 44, one of the previous owners decided to rip out the emissions equipment). It doesn't even come on when the key is on and the engine is off. Ive checked the bulb in the dash, its good. I even tried swapping bulbs with one of the turn signals, no joy.
Also when i try to pull the codes, it wont let me run the Koeo test. When i put the scanner (actron) from hold to test the light on the scanner stays on, and the relays click but doesn't run the test. When itry to run the koer test, it will sometimes work, sometimes wont.
thats probably what it is considering that ive cleaned the iac valve valve and it still wants to die upon start up unless i give it throttle. Im fairly sure the truck has 340k miles on it so a failing computer wouldn't suprise me. Ill check it soon
The eye isn't blocked off, but I'm not sure if its operational. I just rehooked up the vacuum lines for the egr and can't pull codes to see if it eliminated the code for the egr
Last edited by Housley11; Jul 14, 2017 at 02:55 PM.
Reason: spelling error
Until the Check Engine Light is turned on when turning the key the Run position you have no reason to look at the EGR system.
In the off chance the CEL circuit is open try cleaning the pins on the data link with contact cleaner or if they are really corroded use a small fingernail file to clean them up. Then attach your code reader. If the KOEO tests do not run, then you have a bad computer.
Well i just tried to pull the codes the old fashioned way with a jumper and a test light. For the koeo test, the test light did not go off but was varying in bright ness in accordance with a 33 code. My intuition says the the circuit is grounding out some where and the computer controlled ground is just changing the resistance of the circuit instead of opening and closing it. Are where would the most likely place be for the circuit to short and ground out at?
So i tried to run a koeo test with a jumper and test light. While the test light would not go off, it did slightly dim, just barely noticeable. Paying close attention i got a code 33, which was expected.
So i tried to run a koeo test with a jumper and test light. While the test light would not go off, it did slightly dim, just barely noticeable. Paying close attention i got a code 33, which was expected.
Yes, you have (2) capacitors that are leaking and that a near complete failure.
Get them changed before the electrolyte fluid destroys the traces on the board.
Ok. Ill probably get to them sometime around November or December. Im going to be out of state for a couple months for work.
Also i tested the cel circuit and even with 12v applied thru the vehicle side of the ecu connector, the cel doesn't iluminate. The filament just kinda glows when you're looking right at the bulb. I know the bulb is good because i swapped it with the turn signal, and it lights up fine with the turn signal. I jumped the circuit at the cluster connector with a test light and it lights up just fine. I just cant figure out why the bulb isnt lighting up in the cluster.
2nd from the left is cel. This is with 12v applied thru ecu connector
Welp after 7 years, over which the truck sat unused for most of the time, i finally figured out the issue with the CEL, and wanted to provide closure incase someone stumbles across this with a similar issue. Using the ford service manuals, i traced the circuit from the fuse and found the issue: there was a break in the the circuit within the cluster "wiring", if you could call thin copper strips sandwiched between acetate sheets as wiring. Swapped out the cluster with a tach one that a nabbed from the parts yard a year or two ago, and no the CEL works great and i can reliably pull codes (for anyone not aware, the code circuit runs through the CEL. Non-op CEL = no ability to pull codes). And yeah, the 33 and 44 codes are still present, but thats a different topic.
Good find on the cluster circuit. Did you also do what was suggested seven years ago and replace the PCM?
Eventually, yes. I first tried replacing the leaking capictors on the original computer, which if i recall correctly didn't change a thing. I ended up rebuilding the engine in late 2017. It turns out that i cant time a distro to save my life while installing one, so the truck sat for a while before eventually going to the shop to figure out what i messed up in the rebuild. One of things i had done post rebuild while trying to get it to start was to replace the PCM.
