Missing Under Load @ Low Rpm's

Dave0803 · Jul 11, 2012

Just got back from vacation for a week and the car gave me no problems. It sat for 2 days after that and when I drove it it seems to have a miss under load and sometimes at idle @ low RPM's. The plugs, COP's, and fuel filter have all been changed recently. You don't really feel it just crushing unless you try to accelerate while the RPM's are below 2K. If you barley give it gas it is still pretty smooth. No codes are shown. Please help

40oz · Jul 11, 2012

Why were the COPs changed? Did you replace them with the factory COPs or with aftermarket pieces? The reason I ask is in my experience a bad COP is the reason for misses. I cannot imagine a scenario where every COP is bad and they all need replacing.

If you replaced the COPs with aftermarket units, I'd start by putting the factory COPs back on. And I don't know when you last changed your plugs, but it might be worth doing at the same time.

Dave0803 · Jul 11, 2012

I replace my COP's with Granateli motor sport coils from American Muscle. It's had a vibration that I feel between 1000 & 1500 RPM's in neutral. It's had it since I got the car so I've just slowly been replacing things. They have been on there for about a mouth and this problem just started on Monday. I took the car on vacation for a week and got home last Friday and parked it for the weekend. On Monday it started missing while driving in low RPM's. The plugs were changed several months before the COP's.

Dave0803 · Jul 11, 2012

I did notice today that my IAT sensor was not seated in the hole in the intake. Would the unmetered air from that be enough to cause a miss fire? I'll see later if that did the trick.

40oz · Jul 11, 2012

If you do a search on GMS COPs you'll find numerous stories of people happy at first, then having to replace them ridiculously often. I've got ~75K on my factory COPs with no issues. I had a '99 GT that had a miss after a rapid oil change shop spilled oil on the motor, causing one COP to short against the block under load. Replaced it and had no issues when I sold the car.

I don't know that I would ever notice a vibration between 1000-1500 rpms in neutral, but a problem in gear I would try to address by diagnosing the problem before buying any aftermarket parts.

I'd still put your factory COPs back on and do the routine maintenance I mentioned above. If the miss still exists, you can get a diag at most Ford dealers for ~$100 and work from there. But that's just me.

Dave0803 · Jul 11, 2012

I'll try it with the stock COP's and see what happens, Thanks for the help.

Dave0803 · Jul 12, 2012

They never came with any instructions for the install. I just assumed that they were a direct replacement for the stock coils. So you are saying I need to swap the wires on the plugs that connects to the coils?

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Dave0803 · Jul 13, 2012

I checked on the site for the coils and they are supposed to be plug-n-play. It was definitely worth checking into though...thanks. I have had them in for about a week before this miss/stumble developed with no issues. The problem only seems to occur under 2K and only if I am trying to give it a lot of gas in a higher gear that would keep me in that low RPM band. I can cruise down the road fine, and can take of fine if I keep my revs above 2K.

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1eo · Jul 14, 2012

Dave0803 said:
Just got back from vacation for a week and the car gave me no problems. It sat for 2 days after that and when I drove it it seems to have a miss under load and sometimes at idle @ low RPM's. The plugs, COP's, and fuel filter have all been changed recently. You don't really feel it just crushing unless you try to accelerate while the RPM's are below 2K. If you barley give it gas it is still pretty smooth. No codes are shown. Please help

I have the same exact problem.... I stop driving the car often and one day it developed the same issue. The only difference is that I haven't changed a thing... I don't even know what COP's stand for.

what should I do/try first?

Dave0803 · Jul 14, 2012

COP stands for coil-on-plug. A lot of time it is just water in the spark plug hole. I wish mine were that simple. Hopefully that's all yours is.

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1eo · Jul 14, 2012

Dave0803 said:
COP stands for coil-on-plug. A lot of time it is just water in the spark plug hole. I wish mine were that simple. Hopefully that's all yours is.

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How can take the water off?

I kind off recall seeing someone taking a coil off and spraying air from a compressor on my brother's crown vic and fixed his misfire... but he had a code and new which coil was having trouble. Like you I have no codes

Dave0803 · Jul 14, 2012

That would be how I would remove the water, Leave the plug in when blowing the water out though?

40oz · Jul 15, 2012

Yes. If there is water in the plug well and you remove the plug, the water drains into the cylinder. It's good practice to blow air into the plug well with the COP removed prior to changing the plug to keep any debris from entering the cylinder.

I've never had an issue with water. Water will evaporate quickly when the engine reaches operating temp. I cannot imagine a scenario where water was causing a consistent misfire unless you didn't have a hood and it rained every day. Oil, on the other hand, will cause the coil to short to the block under load. Motor oil does not play well with the coil's rubber insulation. I didn't have a CEL, but the misfire was obvious under load. And the dealer was able to identify the failing COP and replace it in short order.

Any decent Ford dealer can put your car on a rolling road and find the misfire under load. Non-decent Ford dealers exist that are incapable of diagnosing a misfire to a specific cylinder, but in my experience they are the minority, thankfully. The first Ford dealer I took my car to wanted to replace all the COPs because they couldn't find the issue. I paid them $90 for their asinine opinion and drove down the road to the next dealer who identified the issue and fixed it. Pissed about the first shop, happy to pay the second. Private shops and "non-decent" dealer shops won't have that level of equipment, forcing them to throw parts at the problem, costing you money and not solving the problem.

mudsadesbenz · Jul 15, 2012

40oz said:
Yes. If there is water in the plug well and you remove the plug, the water drains into the cylinder. It's good practice to blow air into the plug well with the COP removed prior to changing the plug to keep any debris from entering the cylinder.

I've never had an issue with water. Water will evaporate quickly when the engine reaches operating temp. I cannot imagine a scenario where water was causing a consistent misfire unless you didn't have a hood and it rained every day. Oil, on the other hand, will cause the coil to short to the block under load. Motor oil does not play well with the coil's rubber insulation. I didn't have a CEL, but the misfire was obvious under load. And the dealer was able to identify the failing COP and replace it in short order.

Any decent Ford dealer can put your car on a rolling road and find the misfire under load. Non-decent Ford dealers exist that are incapable of diagnosing a misfire to a specific cylinder, but in my experience they are the minority, thankfully. The first Ford dealer I took my car to wanted to replace all the COPs because they couldn't find the issue. I paid them $90 for their asinine opinion and drove down the road to the next dealer who identified the issue and fixed it. ****ed about the first shop, happy to pay the second. Private shops and "non-decent" dealer shops won't have that level of equipment, forcing them to throw parts at the problem, costing you money and not solving the problem.

Dave0803 · Jul 23, 2012

I wouldn't think so either man, but I had that problem with my 07 F150. It never had a problem and them one day it had a consistent miss. It ended up being water ( not coolant, oil, or anything else) in my #6 spark plug hole. Got the water out and it cleared right up and haven't had a problem since.

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GOKBGO · Aug 12, 2012

A while back I replaced all 8 COPs with Granatellis, and have already had to replace 4 of those. I'll never buy GMS COPs again.

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