KOER Code 538
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Junior User
Joined: Feb 2005
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KOER Code 538
"Insufficient RPM change during Dynamic Response Test/invalid cylinder balance test due to throttle movement during test."
Symptoms= rough idle. Runs fine at speed. Passes the KOEO test.
Trying to trouble shoot I've changed the plugs (double platinum) and wires. Also changed the IAC and cleaned the MAF.
When starting the test, the RPMs increase for about 30 seconds and then fall back to normal. I guess that's what's triggering the code but it does it every time and I don't know if that's normal when doing this test.
Any ideas??
Symptoms= rough idle. Runs fine at speed. Passes the KOEO test.
Trying to trouble shoot I've changed the plugs (double platinum) and wires. Also changed the IAC and cleaned the MAF.
When starting the test, the RPMs increase for about 30 seconds and then fall back to normal. I guess that's what's triggering the code but it does it every time and I don't know if that's normal when doing this test.
Any ideas??
Postmaster
Joined: Dec 2001
Posts: 3,742
Likes: 2
From: UT
KOER 538 almost always means that you neglected to perform the dynamic response (aka "goose") test at the appropriate time during the KOER test. Review your instructions. If they don't mention a goose test, dynamic response test, or otherwise mentions performing a brief wide open throttle during the KOER test, then get a new set of instructions. Ken00 has posted instructions in his tech info thread at the top of the BII and Ranger forums.
Posting Guru
Joined: Jul 2003
Posts: 1,978
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From: Alvin, Texas.
Yeah, you have to MASH the hell out of the gas pedal for a good second....as if you are ready to run over an ex with the truck.
That got me when I first tried that test....got bent out of shape to get motivation for the goose job and passed the test.
Good luck.
That got me when I first tried that test....got bent out of shape to get motivation for the goose job and passed the test.
Good luck.
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Junior User
Joined: Feb 2005
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OK, I'll try that. But any idea where to look next for the cause of the rough idle? It's not that bad but I'd like to get it right. It's the least I can do for the old girl. She's been good to us!!
Postmaster
Joined: Dec 2001
Posts: 3,742
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From: UT
If everything else is pass (111) and you now get it to pass the KOER test, then the problem is something the EEC-IV computer doesn't see. EEC-IV isn't always smart enough to see every sensor fault, so we have to start checking things.
1) Any kind of vacuum leak will be bad for idle quality. Make certain there are no vacuum leaks.
2) Check fuel pressure, and check for fuel in the vacuum line to the fuel pressure regulator (FPR)
3) Clean MAF and IAC valve.
See where that gets you.
1) Any kind of vacuum leak will be bad for idle quality. Make certain there are no vacuum leaks.
2) Check fuel pressure, and check for fuel in the vacuum line to the fuel pressure regulator (FPR)
3) Clean MAF and IAC valve.
See where that gets you.
Trailering
Joined: Apr 2021
Posts: 23
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