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Old 12-14-2017, 09:48 PM
AbnMike AbnMike is offline
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Hey all, I'm curious about the misfire code cycle. Logic (at least mine) dictates if something misfires once, it should constantly misfire until whatever caused it is fixed. I threw a Cyl 5 misfire. Cleared it. Ran about 100 miles. It popped again. Changed the plug. It popped again. Plug is fine, Fuel Trims are still at 0%.

Ran it another 200 miles, never popped. It was pretty random.

Can these codes be stored a long time and then just re-appear? My only guess is that the coil for that cyl is going bad, but it didn't pop on the opposite cylinder.

Plugs were all pretty new, wires are 8mm and new. I had done a lot of work resealing the valve covers and intake and whatnot prior to this.

To my simplistic understanding if there's something causing a misfire, the misfire should be constant. But this wasn't. Very random. Similar driving type and temperature and all that other stuff.
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Last edited by AbnMike; 12-14-2017 at 10:05 PM.
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Old 12-15-2017, 08:08 AM
discostew discostew is online now
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Put a plug wire on it. Your talking the difference between a hard misfire and an intermittent misfire. A misfire can happen during warm up, heavy load, or idling in park hot.

I don't know what it is about that #5 plug wire. Maybe Nigel fucked them all up, might be more heat in that area, but #5 has a really high failure rate. More than the others.
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Old 12-16-2017, 05:23 PM
AbnMike AbnMike is offline
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Quote:
Originally Posted by discostew View Post
Put a plug wire on it. Your talking the difference between a hard misfire and an intermittent misfire. A misfire can happen during warm up, heavy load, or idling in park hot.

I don't know what it is about that #5 plug wire. Maybe Nigel fucked them all up, might be more heat in that area, but #5 has a really high failure rate. More than the others.
Thanks. Seems to happen when it is sitting for awhile idling in the morning. Threw one this morning, cleared it, drove 100 miles, didn't pop again. I'll switch out the plug wire and see what happens, though they're fairly new (less than 5k miles).
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Old 12-16-2017, 05:54 PM
discostew discostew is online now
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Hate to say it but that sounds like coolant getting into #5. If it only misses on start up then clears up like that its a sign. To verify you could put some dye in the coolant and look at the plug with a black light. If you decide to try that test just let it start and shut it off, the less it runs the better so you don't burn the dye out of the cylinder.
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Old 12-16-2017, 06:17 PM
AbnMike AbnMike is offline
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Quote:
Originally Posted by discostew View Post
Hate to say it but that sounds like coolant getting into #5. If it only misses on start up then clears up like that its a sign. To verify you could put some dye in the coolant and look at the plug with a black light. If you decide to try that test just let it start and shut it off, the less it runs the better so you don't burn the dye out of the cylinder.
Not really right on start up, only after sitting for awhile idling. Never pops when I first start it up. Today it idled about 15 minutes (waiting on the wife of course) and then half a mile down the road it threw the check light.
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Old 12-16-2017, 06:51 PM
discostew discostew is online now
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Misfire on light load like idle in park could be a cracked spark plug. I know you said you just replaced them, does your spark plug socket have a rubber insert to protect the plug? Or hopefully some vac leaks will hurt one cylinder more than others.

Is it something you can feel happening? Or is it just the phantom misfire you only know about because the light?
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Old 12-16-2017, 06:57 PM
discostew discostew is online now
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Are we talking about a Disco1 ? Cause if it is I would tell you to check something else. GEMS trucks really don't have all those issues I was talking about.
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Old 12-16-2017, 10:05 PM
AbnMike AbnMike is offline
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Quote:
Originally Posted by discostew View Post
Are we talking about a Disco1 ? Cause if it is I would tell you to check something else. GEMS trucks really don't have all those issues I was talking about.
Yep. 96 Disco 1
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Old 12-17-2017, 08:48 AM
discostew discostew is online now
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I still think you should look for a vacuum leak along the runners of your intake manifold. But on the GEMS engine the crank sensor uses little tabs on the flywheel that pass the crank sensor to make your crank signal. Those little tabs are really easy to bend. If one gets bent it will effect just one cylinder. If the crank signal is just a little tweeked on #5 then it could misfire just when conditions are harder to fire the cylinder. Like warm up.

Another thing you have to think about on these GEMS engines and the real early Bosch engines is the exhaust valves stick in the guides. Usually in those center 4 cylinders. (3,4,5,6). The way you check that is kind of a bitch so I would go thru that after you run down just about everything else.

Sometimes on these really hard to find and duplicate misfires your going to have to start moving a couple components around to different cylinders and hope that your misfire moves with one of those parts. Like take the #5 plug and switch it with another cylinder that's easy to get at. Clear the codes and hope the next time it happens its on the other cylinder. Same deal with the injectors. And don't overlook the lower injector o ring for a vacuum leak that would make one cylinder too lean.

Another thing that is really good for checking vac. leaks is a smoke machine. But I know not many of us have access to a smoke machine.
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Old 12-17-2017, 02:28 PM
AbnMike AbnMike is offline
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Thanks for the assist.

My long term fuel trims have been between 0.8 and 0.0 for a few hundred miles now. Shouldn’t that indicate no lean (vacuum leak) condition?
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Old 12-18-2017, 08:03 AM
discostew discostew is online now
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Yes I would think that would. I guess the order I would go in is first switch a plug since it's easiest. Next check the reluctor wheel and last switch the injector.

Or if your luck is like mine and it's the worst case scenario you probably have. Start checking for sticking exhaust valves. You seem like you have a handle on this whole drivability thing. Since it's not a hard misfire your more than likely not going to see a vacuum gauge bounce. But I would put one on it and try to duplicate the misfire. If it's a valve hanging open you might see the needle on the gauge bounce around. If not and you still think it's a valve there is a way to know for sure. But it will take a few hours even if your pretty fast.
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Old 12-19-2017, 10:08 AM
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WaltNYC WaltNYC is offline
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When you replaced the injectors you might have not seated #5 properly or the o-ring is just a bit off as discostew suggested.


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