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Old 11-18-2007, 01:44 AM   #1
defl8ed
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Engine misses, but not at idle

Hello,

2001 ZX3 stock everything, manual transmission. Recently car started shuddering every once in a while under acceleration, only when engine was cold. Thought the problem was EGR sensor (have already had that damn thing replaced 3 times), as the symptoms were similar. Waited for CEL to come on and confirm my idea, but when it did, the code was p0302 - missing on cylinder #2. Performance gradually worsened, but basic symptoms the same - engine starts and idles fine, but shudders (sometimes violently) when attempting to accelerate. Pulled out spark plug for #2 cylinder to see if it was blackened/damp, but it was not - this makes sense, since it appears that the cylinder is firing when the engine is idling which would burn off any uncombusted fuel in the cylinder. Drove car around the block to see if there was any difference, and got CEL code p0352 - which apparently indicates a bad ignition coil. "Ah Ha" I thought - ran down to the store, purchased a new coil, installed, and engine ran fine - for approximately 20 hours, at which point the problem reappeared - worse than ever. Got code p0302 again the next day. The plugs and cables were both replaced less than 30K miles ago, and the plug for number 2 cylinder is fine visually. If I look at the engine while idling, I can detect no arcing, so I don't believe it's the cable. Replaced DPFE sensor and disabled the EGR valve to make sure that wasn't actually the problem - (didn't think that was it, since that wouldn't cause a single cylinder to misfire, but wanted to cover all bases) - no change at all. So my question at the end of all this is "What can cause a cylinder to misfire when under load, but not when at idle?"

Vital stats -

2001 ZX3 with 97K Miles
2.0 Zetec
Alternator is new (replaced 2 months ago) and tested good
Battery is < 1 year old, also tests good
DPFE sensor replaced
EGR disabled
Spark Plugs and Wires Good as far as I can tell and have been replaced recently
Ignition Coil replaced after getting p0352, but no change.

Any Ideas?


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Old 11-19-2007, 10:51 AM   #2
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Followup

As a follow-up to clarify, the engine will not miss as long as there is no load - not just at idle. As long as the car isn't moving, you could sit there and rev the engine and hold it at high rpms forever, and it will not miss once, but once the gear is engaged, it will start to miss and jerk.
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Old 11-19-2007, 12:49 PM   #3
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Try the pigtail connector to the coil, when driving the engine moves more around...
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Old 11-19-2007, 11:01 PM   #4
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Pigtail

Nope, all wiring is visually okay. No wires pulled taut across a corner, no frayed or cut wire jackets.
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Old 11-19-2007, 11:13 PM   #5
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I"ll bet its a spark plug wire going south already, swap two of them around and see if the miss follows the wire. ( If you have enough length ). I"ve seen some cheaper wires go south in under 30K.
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Old 03-09-2008, 08:37 AM   #6
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have you ever found a solution to this problem? My car is doing the excact same thing, and I just replaced the wires and plugs and its still doing it
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Old 03-11-2008, 02:11 PM   #7
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We had this; It was vehicle wiring connected to the ignition coil. Wires broke at the back of the connector due to relative motion from the engine.
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Old 03-11-2008, 02:57 PM   #8
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I had this same problem but it was cracked porcelin of the spark plug.

But i see that it could be the ignition coil not groundig properly.
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Old 03-11-2008, 03:30 PM   #9
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Yup, few things it could be.
Common things to check are,

spark plug wires - visually check for arcing, test resistance with a DVOM (vs other wires, Ohms increases with length)

spark plugs - verify correct gap (more gap = more resistance), make sure plug is good, no cracks/corrosion/submersed in water/oil

ignition coil pigtail - pretty common to see these crack and fail, there is a how-to in the stereo section of this site (don't ask me why it's there)

fuel injector - easyiest way to test this one is to move the injector, if the miss follows the injector, well ...

mass air flow sensor - if it is dirty or has an oily coating it can not burn off it may be giving the ECU a foul reading, under light load you may not notice it (lean and light timing) but when you put your foot in it (rich and heavy timing) you may notice it, use a specifically for MAF cleaner

PCV - the elbow specifically, if there where a tear in the tube you may be running lean and that would give a miss (most likely not your problem but it's one of those commonly overlooked things)
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Old 03-16-2008, 04:38 PM   #10
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i have the same problem, replaced pcv hose, and the pigtail, also checked the spark plugs any idea?
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