Flashing check engine light
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Senior User
Joined: Jan 2021
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Flashing check engine light
1995 Ford F-150 5.0L with 233k mi. Just installed my new radiator and electric fans combo over the weekend. Drove fine yesterday. Drove earlier today and no sooner than 1 minute of driving I got a check engine light. The light would come on for about 30 sec. to a minute, then shut off. Then randomly come on about a minute later and do the same thing. No codes came up. Dove again later today. The light still comes on and off for seemingly no good reason. The truck runs a little rough. It does backfire every so often now as well. I heard it coming from the driver's side exhaust manifold. Looking for some advice. I have done wires, plugs, cap and rotor in the last two months. I routed the wires the correct way as well. I made sure of that. Also, I know on obd2 systems a flashing check engine light means a misfire, but I didn't think obd1 had that.
Fleet Mechanic
Joined: Aug 2015
Posts: 1,838
Likes: 367
From: Candy Mountain
The light coming on means the computer is seeing a fault, and should be at least storing a code... I don't know of any other reason it would come on while driving. I also don't know what to think about it not having at least a stored code.
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
There is a lot of info available about the CEL flashing with KOEO and KOER. KOER means a misfire or misfires, which is what is happening in this situation and should be addressed before further driving. The only thing I know about this from the info I looked up on another truck that had flashing CEL with KOEO, so if you Google it you will see info and some from this forum also. See what you think. I only know what I read about it.
Cross-Country
Joined: May 2016
Posts: 91
Likes: 0
From: Kalamazoo, Mi
I just ran into a similar thing with an OBD-1 5.0L . Here is what mine does: On cold start up, I get a flashing check engine light. I honestly think it is running codes on it's own. It will cycle them about 3 times then suddenly dies. It will sometimes turn the light on and run fine all day but has extreme high idle. Other times the CEL will go out all together and then start the code read all over again. Dies and then the 3rd time is usually a charm CEL will come on and run fine but w/High idle. The idle is so high I have to unhook the ISC and set idle with the screw to compensate. Originally it had KOER 122-0 code for TPS too low. 357- 0 Separator 10 and then 512- C and Done This thing has sat and so it turned 30 years old. I put new CTS, TPS,EGR valve, MAF, ISC sensors on it just to renew them all. All codes cleared but 121-0 and 512-C exist. I know the throttle screw is causing 121-0 expected idle not met-high/low. In any case with idle screw fully retracted if I plug that ISC back in and it just races at about 3500+ rpm. I checked for vacuum leaks and found the usual upper intake with slight leak. Any ideas???
Cross-Country
Joined: May 2016
Posts: 91
Likes: 0
From: Kalamazoo, Mi
I just ran into a similar thing with an OBD-1 5.0L . Here is what mine does: On cold start up, I get a flashing check engine light. I honestly think it is running codes on it's own. It will cycle them about 3 times then suddenly dies. It will sometimes turn the light on and run fine all day but has extreme high idle. Other times the CEL will go out all together and then start the code read all over again. Dies and then the 3rd time is usually a charm CEL will come on and run fine but w/High idle. The idle is so high I have to unhook the ISC and set idle with the screw to compensate. Originally it had KOER 122-0 code for TPS too low. 357- 0 Separator 10 and then 512- C and Done This thing has sat and so it turned 30 years old. I put new CTS, TPS,EGR valve, MAF, ISC sensors on it just to renew them all. All codes cleared but 121-0 and 512-C exist. I know the throttle screw is causing 121-0 expected idle not met-high/low. In any case with idle screw fully retracted if I plug that ISC back in and it just races at about 3500+ rpm. I checked for vacuum leaks and found the usual upper intake with slight leak. Any ideas???
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