98 Expedition Misses on Acceleeration or Load

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May 26, 2013 | 03:12 PM

zacajawea1

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98 Expedition Misses on Acceleeration or Load

My 98 expedition misses under load. I have changed the fuel and air filters since it was due and to rule out the cheap stuff. I am an able home mechanic, but this isn't throwing a code. Occurs mostly when the engine is at operating temperature. I am not afraid to tear the top components off, I once replaced a transaxle in a chevy beretta in the garage. I am patient, I just don't want to keep replacing things that don't need it. If anyone has symptom questions to ask, please do. Again, no code.

May 26, 2013 | 04:35 PM

alloro

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Is the engine a 5.4L with COPs or a 4.6L with coil packs?

May 26, 2013 | 05:16 PM

zacajawea1

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Its the COPs, I know that seems like it is the culprit. Just wondering if there are other likely sources as well.

May 26, 2013 | 08:51 PM

pdqford

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Beg, buy, or borrow a scan tool that can display Mode 6 data. Display test ID $53 and it will show the rate of misfire per 200 revolutions for each cylinder, even though the rate of misfire has not exceeded the threshold to trip the CEL.

How many miles on the plugs/coils/boots?

If you can pin point a misfiring cylinder, you could swap its coil/plug/boot&injector with non-misfiring cylinders to pin point if any of those items is/are the culprit before throwing new parts at it.

May 26, 2013 | 09:21 PM

zacajawea1

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Thanks for the reply. The coils plugs boots haven't been changed since I've owned it @ 55,000 miles. I took it to Pep Boys and it didn't have any stored codes. I also have a code reader and got nothing, that's why I took it in for a diagnostic. They told me they would change the plugs for $400. I said no thanks I would do it.

May 26, 2013 | 11:38 PM

alloro

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Quote:

Originally Posted by zacajawea1

The coils plugs boots haven't been changed since I've owned it @ 55,000 miles.

You can buy just the boots for about $3 each. Often it's just the rubber boot that has dried out and cracked and the COP is still good.

May 27, 2013 | 12:15 AM

zacajawea1

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Quote:

Originally Posted by alloro

You can buy just the boots for about $3 each. Often it's just the rubber boot that has dried out and cracked and the COP is still good.

Can you explain to me how the worn out boot could cause this problem? Is it the spark jumping to ground?(shorting out?)
I forgot to mention a week ago we had some real bad rain. When I drove through some deep standing water the missing was much worse. Does this make sense with your diagnosis?

Thanks for your replies, I really appreciate them.

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May 27, 2013 | 03:11 PM

zacajawea1

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OK, so to test the theory, with the engine cold, I sprayed off the engine and started it and drove it around the block. It ran worse than ever. Usually when I drive it from a cold start it runs fine for just a bit, then when it warms to operating temps it get worse. In your opinion, do you think this confirms the diagnosis? Again, I really appreciate your help Alloro. Jason

May 27, 2013 | 07:52 PM

#10

SilverSS

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From: Ocala FL

Easy enough to pull the cop's out and inspect the boots. If the spark plugs could use changing you could do that as well. The 4 rear plugs aren't fun though.

May 27, 2013 | 09:42 PM

#11

BAD RONALD

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From: Proctorsville VT

Quote:

Originally Posted by zacajawea1

... I sprayed off the engine and started it and drove it around the block. It ran worse than ever.

A really good way to create misfires in these COP ignition systems is to spray off the engine. A real bummer if you appreciate things clean under the hood.

I'm due for a sparkplug change and ordered new COP's which will be installed with appropriately greased boots. Even then I will still cover the COP's and wires with a shop towel before an engine wash.

May 28, 2013 | 04:06 PM

#12

alloro

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Quote:

Originally Posted by zacajawea1

I sprayed off the engine and started it and drove it around the block. It ran worse than ever.

In your opinion, do you think this confirms the diagnosis?

Yes, I'd say that pretty much confirms the COP boots as being the problem.