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Jerry Newton
Jerry Newton, Cadillac Technician
Category: Cadillac
Satisfied Customers: 4410
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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2003 Cts cylinder misfires in 1 &2? Runs rough at idle and

Customer Question

2003 Cts cylinder misfires in 1 &2?
JA: Thanks. Can you give me any more details about your issue?
Customer: Runs rough at idle and no low end power. I replaced fuel filter, plugs, and coil boots with no change compression tests on cylinders went from 150-167. Before I did coil boots it was cylinders 1&6 now it is 1&2.
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Submitted: 7 months ago.
Category: Cadillac
Expert:  Jerry Newton replied 7 months ago.

Can you determine for a fact that the misfire is occurring on cylinders 1 and 2? Or is this just what the scan tool is telling you?

Customer: replied 7 months ago.
This is what scan tool is telling me.
Expert:  Jerry Newton replied 7 months ago.

This is a hard thing to determine, since you can't unplug the coils individually, and you can't access the injectors easily to unplug them.

A higher end scan tool has the capability to disable cylinders for purposes of balance testing, do you have a scan tool that will do this?

Customer: replied 7 months ago.
No I have generic code reader. The end of the coil packs on cylinder one and two seemed more coroded than the others.
Expert:  Jerry Newton replied 7 months ago.

Coil packs themselves go bad, again, it comes down to finding a way to isolate and pinpoint which cylinder is actually misfiring.

My recollection is that the coils are interchangeable, it would be reasonable to swap them from side to side and see if the misfire follows the coil, but again, you have to be sure you can actually identify the misfiring cylinder.

Customer: replied 7 months ago.
What about the oil in cylinders 1,2,3? It was on Top of the plugs so I did the valve cover. The plugs were covered in it today..
Expert:  Jerry Newton replied 7 months ago.

The O ring seals do leak, but usually the oil doesn't cause an issue. You did the right thing by fixing the leak and putting boots in. I probably would have removed the plugs and had a look at them, too, inspecting for cracked insulators or anything like that.

So, the oil leak issue is rectified now?

Customer: replied 7 months ago.
There wasn't any on top of the plugs as before. Possible to be residual from the old issue inside? I did inspect the plugs and gaps as well while doing compression test. 1,3,5 were covered in oil 2 was dry rusty looking 4 and 6 seemed normal.
Expert:  Jerry Newton replied 7 months ago.

It's possible that it's residual. At any rate, if it's just a small amount of oil, it's nothing to be overly concerned about. Oil can weep into these plug wells and just sit there indefinitely, with no ill effect.

That alone isn't an issue to worry about.

Customer: replied 7 months ago.
I have two ideas remaining. I replace coil packs/ switch around for different codes. After that it would be an computer issue correct? Or am I missing something?
Customer: replied 7 months ago.
Is it possible to test my injectors on this motor?
Expert:  Jerry Newton replied 7 months ago.

It is possible to test injectors. You run an ohmmeter across them, they should all have the same resistance within 1-2 ohms. Test them both hot and cold.

It's not likely to be a bad injector, though. I don't recall ever replacing a bad injector in one of these engines, and I've looked at a lot of them. This is almost certainly going to be a faulty plug or coil pack, based on my history with them.

Customer: replied 7 months ago.
I was going to get the coil packs next. Since it is on both sides of the motor I was thinking fuel or exhaust issues..
Expert:  Jerry Newton replied 7 months ago.

This goes back to my earlier point: we don't know for certain which cylinders are misfiring, so we can't make that assumption.

If it is cylinders 1 and 2 (the front two cylinders) I'd be looking for a vacuum leak or something that is common to those two cylinders. You cannot rely on trouble codes to get you here, though, the computer will often mistake which cylinder is misfiring, or report two cylinders misfiring when only one is actually missing.

Again, a good scan tool will pin this particular detail down and make it easier. Lacking that, you'll have to find a way to identify the misfiring cylinders manually. Frankly, the $75 or so that would be spent having it professionally diagnosed would probably be a money saver for you.

Expert:  Jerry Newton replied 7 months ago.

Did you get this worked out? Wanted to follow up and make sure you got what you needed from me.

Please remember to rate my answers, that's how I get compensated.

Customer: replied 7 months ago.
Still waiting on the diagnostic I will keep you posted
Expert:  Jerry Newton replied 7 months ago.

OK, thank you.

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