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Discussion Starter · #1 · (Edited)
Engine missing (especially when cold)

The last couple mornings has been fairly chilly (-5 to -10 C) and I forgot to plug the block heater in.

Still fires up with no problem but when I go to back up the driveway, it starts missing pretty badly. Will continue to miss under power until the engine warms up a bit (actually registering on the gauge anyways).

Any ideas where I should start looking?

Thanks in advance
 

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Infinity FX35
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When an engine runs rough or misfires only when it is cold, generally it means the fuel mixture is not rich enough. Many things can cause this but a good starting point would be to look for vacuum leaks. For example a loose or cracked vacuum line. Unlikely, I think, but possible is a loose throttle body or intake manifold. Don't forget the PCV valve hose.
 

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Discussion Starter · #3 ·
I'll check it out!

Can't really tell for sure yet, I'll give it a go tomorow morning when it's cold again, but it seems like it "might" be fine when it's in neutral.

Any chance the clutch might be slipping when it's cold? Never had a clutch go on me in a car, I have no idea what happens when it's starting to die.
 

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It's not your clutch.

The vacuum leaks check etc. is a good idea. If you think you've isolated a small vacuum leak you can confirm by giving it a small squirt of WD40. It will temporarily stop the leak and the engine may smooth out. You should also check carefully if it's still missing after the engine is warmed up. It won't be as bad but a slight miss is usually detectable by listening to the engine and at the exhaust.

My previous vehicle had low compression on one cylinder. It ran awful when cold but it smoothed out as it warmed up. I guess as the engine warms up the clearances tighten up and compression gets better. I could still detect a slight miss though even when it was warm but it had adequate power. Also, plugs and plug wires really do make a difference. If you haven't replaced them in a whilie you should consider that. Another thing to do is check your ignition coil. If it's failed you may hear a snapping sound under the hood if it's shorting out. You may also be able to see a spark arcing at night. Again, this may go away when the engine warms up.

Back to the clutch. if you want to test it, warm your car up and then get it up to 40-50 mph in 5th gear and then step on it to the floor. If the engine bogs a bit and the car accelerates (speeds up) as it should, the clutch is okay. If the RPM's shoot up and the car doesn't actually move any faster, your clutch is slipping and it's on it's way out. You may also smell it burning at that point. Once it starts to slip, it usually deteriorates rapidly.

Good luck!
 

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Discussion Starter · #5 ·
cheesep said:
It's not your clutch.

The vacuum leaks check etc. is a good idea. If you think you've isolated a small vacuum leak you can confirm by giving it a small squirt of WD40. It will temporarily stop the leak and the engine may smooth out. You should also check carefully if it's still missing after the engine is warmed up. It won't be as bad but a slight miss is usually detectable by listening to the engine and at the exhaust.

My previous vehicle had low compression on one cylinder. It ran awful when cold but it smoothed out as it warmed up. I guess as the engine warms up the clearances tighten up and compression gets better. I could still detect a slight miss though even when it was warm but it had adequate power. Also, plugs and plug wires really do make a difference. If you haven't replaced them in a whilie you should consider that. Another thing to do is check your ignition coil. If it's failed you may hear a snapping sound under the hood if it's shorting out. You may also be able to see a spark arcing at night. Again, this may go away when the engine warms up.

Back to the clutch. if you want to test it, warm your car up and then get it up to 40-50 mph in 5th gear and then step on it to the floor. If the engine bogs a bit and the car accelerates (speeds up) as it should, the clutch is okay. If the RPM's shoot up and the car doesn't actually move any faster, your clutch is slipping and it's on it's way out. You may also smell it burning at that point. Once it starts to slip, it usually deteriorates rapidly.

Good luck!
Great, thanks for the tips. That clutch test will definitely be handy to know eventually!

Once it gets dark tonight I'll fire it up and look for any lights that shouldn't be there and check for vacuum leaks tomorow.

If no luck, I'll give it a tune up.

Thanks again!!
 

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Discussion Starter · #6 ·
Been getting a little worse the last couple days, missing quite a bit more, especially under heavier loads (going up hills). Even missing once in a while when it's warm, but it's not a regular miss.

Checked for vacuum leaks and unwanted sparks, didn't find anything out of the ordinary.

Changed out the plugs, no change. I'll try the wires/dist. cap next (who's bright idea was it to make them into one piece and charge $120 for that?)
 

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My spark plug wires are seventeen years old with 145K miles. They still check out fine.
Check the wires for damage first. Cracks, burns etc. If they look good, check resistance with your Ohmmeter. (buy one most anywhere for less than $15. An analog is useful for extracting eec codes. A digital is useful for testing sensors.) Check resistance through cap and wire together. Anything under 25,000 Ohms is good.
It won't hurt to replace them anyway except your ass pocket. If they look good and test good, don't get your hopes up that a new set will fix your misfire.
 
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