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Author Topic: Engine stumbles around 4500 rpm - new distributor cap, rotor, wires  (Read 4347 times)


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  • Posts: 114
    • 1994 Mercury Capri N/A
Re: Engine stumbles around 4500 rpm - new distributor cap, rotor, wires
« Reply #15 on: June 19, 2020, 02:10:06 PM »

It could be a faulty cap/rotor or plug wires.

If the plug wires were in the wrong order the vehicle would barely run if it all. But, double check. Cylinder #1 is on the passenger side.

Does the car stumble when revving in neutral?
Have you tried revving the engine at night in a dark area to look for arcing on the plug wires?

A common problem with the N/A is the plastic intake tube - it cracks and opens up creating a vacuum leak. Often on the underside where it is not visible. It may be that your engine is moving enough at 4500rpm to cause the issue. Just spitballing on that one. Will need to remove to do a visual inspection.

Thank you for this info.  The plugs are in the right order, thanks for telling me where Cylinder #1 is.  The car does stumble when it's in neutral.  It will stumble sitting in the driveway.

Car sounds great idling in neutral in the driveway with the parking brake on.  No issues at all, no surging.  Very steady.

I haven't checked it at night.  It's past my bedtime when it's dark now in the summer!

New development - it doesn't stumble at 4500 rpm when shifting from 2nd to 3rd, nor from 3rd to 4th.  It will stumble from 2nd to 3rd but I can't tell exactly when it does it.  I haven't driven it around much lately to notice a repeatable pattern but I think it's higher than 5000 rpm.
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