Check engine light flashing

LoganTheSnowman

LoganTheSnowman

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Dec 24, 2015
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Hey all a while back my check engine light would come on in my 1999 4.0l tj, and it read a random misfire and a misfire in cylinders 3 and 4. Took it to my dad's mechanic and they cleaned the injectors, spark plugs and distributor as well as crankshaft sensor had been replaced recently. Afterwards my check engine light would start flashing and then stay on for a while. It's been a few months now. The check engine light will start flashing while I'm driving, and then go off. I haven't felt anything weird when this happens and I'm just wondering if anyone else has had this issue and have a solution as that blinking check engine light bothers me as I know it usually means it's doing damage to something but like I said it runs like normal, nothing weird. Thanks all.
 
A flashing CEL is serious, find out what the problem is asap. It often means a serious misfire is causing raw fuel to make it into the exhaust system where it can raise the temperature of the catalytic converters enough to seriously damage them which would be very expensive to repair.

When the CEL is flashing, that means a serious problem... don't wait to get it taken care of.
 
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Agree with everything said above. That's usually a sign of something very serious. Did you find out what codes it's throwing?
 
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Chris said:
Agree with everything said above. That's usually a sign of something very serious. Did you find out what codes it's throwing?
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When it would stay on after blinking it was still the misfire codes. Now however the light doesn't stay on, it just blinks every few days for a few seconds. My father believes the injector needs to be replaced possibly. But he told me not to worry about it because I've never felt it struggle or a loss of power or anything when it the check engine light would come on for the misfires. It would do it anywhere from while sitting at a light idling, to go 60 mph down the highway. It's been flashing for a few months without the light staying on after. So while it does concern me, it hasn't actually done anything to make me think there's a problem other than the check engine light flashing. I haven't rechecked it after the last time a few months ago because it doesn't stay on and was the same misfire codes when it would stay on.
 
And thanks all for the information, I've researched the check engine light flashing but usually when it's causing damage it's noticeable but in my case it just chugs on like normal.
 
The mechanics did what they could think of and suggested unplugging the check engine light and I know it's flashing for a reason but I'm not entirely sure it's actually for a misfire as like I said even though it says that's what happens it doesn't run rough, or lose power.
 
Jerry Bransford said:
A flashing CEL is serious, find out what the problem is asap. It often means a serious misfire is causing raw fuel to make it into the exhaust system where it can raise the temperature of the catalytic converters enough to seriously damage them which would be very expensive to repair.

When the CEL is flashing, that means a serious problem... don't wait to get it taken care of.
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So can I assume that's if it's a steady light or not flashing that it is less serious? I'm getting a P0304 code indicating a #4 cylinder misfire but it's running fine.
 
Willhe said:
So can I assume that's if it's a steady light or not flashing that it is less serious? I'm getting a P0304 code indicating a #4 cylinder misfire but it's running fine.
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A steady light generally indicates a less serious problem that is usually related to the smog system or that the problem may be producing more emissions. A steady CEL is more serious, like a problem that is likely to damage the catalytic converter.
 
Jerry Bransford said:
A steady light generally indicates a less serious problem that is usually related to the smog system or that the problem may be producing more emissions. A steady CEL is more serious, like a problem that is likely to damage the catalytic converter.
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Thanks for the quick reply. I'm not so concerned now. Maybe it will go out on it's own. It was just inspected last week.
 
A flashing CEL means its currently misfiring. If the miss goes away the light goes off but stores a history code. Unplugging or disabling the light is never a good answer. That doesn't fix anything and in some states is illegal. Serious engine damage can occur from driving with a misfire. This is something you need to address immediately.
 
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Came across a jeep post regarding misfire on cyl 3 and 4 months ago so I don't have a link,
This misfire was due to the increased heat generated in this central area of the motor.

This misfire was fixed by replacing the material recommended in a jeep TSB for this problem on the 4.0.
Sorry to be somewhat vague but recalling from memory here
Has this problem started since the brutal summer heat began?
 
KCsTJ said:
Came across a jeep post regarding misfire on cyl 3 and 4 months ago so I don't have a link,
This misfire was due to the increased heat generated in this central area of the motor.

This misfire was fixed by replacing the material recommended in a jeep TSB for this problem on the 4.0.
Sorry to be somewhat vague but recalling from memory here
Has this problem started since the brutal summer heat began?
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I think you're referring to the TSB that came out for 2003-2004 4.0L engines where the #3 fuel injector gets so hot from the exhaust manifold that its fuel vaporizes and causes a #3 cylinder misfire. The fix is to wrap the #3 fuel injector with insulation and zip-tie it into place. I kinda doubt that's what is happening to his older '99 4.0L.
 
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LoganTheSnowman said:
suggested unplugging the check engine light
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Bad suggestion, it's telling you there is a problem, plus you will have no warning for other issues requiring the light.

Jerry Bransford said:
Not necessarily. Other problems beside a misfire can cause the CEL to flash.
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Curious as to what else, for future reference. I was led to believe it was a catalyst damaging misfire.
 
I had a cyl#3 misfire, code 43, pop up on my 2.5L last week.
I thought it was the CKP sensor possibly installed wrong, since it had just been in the *%#*!@ tranny shop.
Turns out it was bare insulation on cylinder 3 fuel injector wire, arcing to ground under load. Repaired wire and no more misfire.
 
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