miss under load

joe_mnMay 21, 2010

my car has a slight miss at idle. comes and goes. when i turn on the a/c the miss is more pronounced. does that usually point you in one direction as to what the issue is? car has new plugs, intake manifold gaskets, pcv system seems fine. no loose fittings or hoses. i get a occasional egr code but that might be due to my egr valve sticking open on occasion. i have taken it off and checked the pintle and seems ok. would hate to think this is due to a sticky egr valve. don't really want to replace that. but i could.

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If you have ignition 'wires', were these replaced?

An ERG valve stuck partly open would affect all cylinders and the engine will stumble.

Poor quality fuel can cause intermittent misfire on random cylinders at idle. I had this problem with my vehicle after it had been stored over the winter. Refilling with new fuel fixed it.

Let us know what you find.

    Bookmark   May 21, 2010 at 4:07PM
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96 seville. it has plug wires. 5 yrs old. delco brand. don't feel like spending 100 for wires. but it could fix car.

    Bookmark   May 21, 2010 at 10:48PM
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It should not cost you $100 for ignition leads if you replace those yourself. Price out a set at your favorite auto parts store.

But first, some simple checks are in order. Measure the resistance of the leads. Those should be no more than 5000 to 8000 ohms per foot of length. If you one that is greater than this, replace the whole set. But if they are equal or less than the range given above, more tests are needed. Ignition leads can test good when cold and go high when hot.

Important: When removing ignition leads, do not grab the wire part and pull. The fragile connection inside the end covers can be pulled loose and/or the leads can be damaged if stretched. Static suppresion leads do not have a metal conductor, but instead may be a carbon loaded string or packed resistance material. Remove by rotating and pulling on the end covers. In some cases, a plug wire extractor may be helpful provided there is room enough for it, and it must get a good grip over the end of the wire cover.

If simple quick tests are not helpful, then its time for more help with a good diagnostician who is well equipped. There are a varitey of problems that can cause the engine to misfire at idle when its load is increased, such as the air conditioner kicking in.

You have a '96 Cadillac. Perchance, do you have the 4,6,8 firing system? The engine may seem to run rough at low RPM when operating on 6 cylinders. Also, this system is designed to periodically change the active cylinders when running in the 4 or 6 cy mode. This change of cylinders was designed to be as smooth as possible, but it may be detected by a person who is peering under the hood.

I don't know the Cadilac line very well, but I am under the impression that the 4,6,8 system was offered for only one year.

    Bookmark   May 23, 2010 at 1:49AM
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4-6-8 was in 1982? no northstar ever had that technology. plug wires for a northstar are 100 for delco or 50 for generic at AZ. OHC motor so plug boots seal against valve cover. long extended boots.

    Bookmark   May 25, 2010 at 10:56PM
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