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Author Topic: Engine stumbles around 4500 rpm - new distributor cap, rotor, wires  (Read 6238 times)

94daves

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  • Posts: 115
    • 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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Pappy T

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    • 91 base Capri
Re: Engine stumbles around 4500 rpm - new distributor cap, rotor, wires
« Reply #16 on: November 16, 2020, 11:34:13 AM »

Hi again all ! This issue ever get resolved ? Mine's still doing it , haven't messed it with it for a while either. Did put about 10-12 miles on it this year along with some fresh gas . Will be up for sale next spring too. Outside interests keeping us busy ! (RVing)
Have a good turkey day, stay safe and healthy too !



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94daves

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  • Posts: 115
    • 1994 Mercury Capri N/A
Re: Engine stumbles around 4500 rpm - new distributor cap, rotor, wires
« Reply #17 on: December 09, 2020, 06:45:43 PM »

Nope, was never resolved this summer.  Now it's in storage for the winter.  I will try again in 2021!  Hopefully someone here will have a few ideas over the winter that I can try next year.
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ZJCapri91

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  • Posts: 17
    • 91 Capri N/A 05 Excursion V10 06 F150 5.4 V8
Re: Engine stumbles around 4500 rpm - new distributor cap, rotor, wires
« Reply #18 on: December 27, 2020, 11:00:47 AM »

A suggestion:
When I got my car, it has a bad Ignition Control Module. I replaced it with the cheap one off rock auto, where the car then only revved up to around 4k RPM. I ordered the expensive Ignition Control Module, and it worked brilliantly after that.
Perhaps you replaced this part, and your experiencing this issue?
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Pappy T

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    • 91 base Capri
Re: Engine stumbles around 4500 rpm - new distributor cap, rotor, wires
« Reply #19 on: December 29, 2020, 03:11:20 PM »

Thanks for the suggestion . On it's 3rd distributor, no more cardone for me. Did replace  ICM with a good one and no problems with starting . Problem just came out of the blue one day and does it around 37-4000 rpm , levels out a little over 5000 . No codes except very faint check engine light that goes away about as quick as it comes on during sputtering . Quite a list of stuff I checked to no avail , stumped . Starts and idles great, only acts up at that rpm . Da heck  :-\  . 
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ZJCapri91

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  • Posts: 17
    • 91 Capri N/A 05 Excursion V10 06 F150 5.4 V8
Re: Engine stumbles around 4500 rpm - new distributor cap, rotor, wires
« Reply #20 on: January 02, 2021, 09:30:07 PM »

The only other suggestion I can offer is the main ignition ground. Its a ring terminal with a bolt straight into a bracket, right near the distributor. I had my ground come slightly undone, and the car misfired like crazy under certain conditions. If yours is on tight, maybe take it off and clean the contact surface. It only takes a little to create massive headaches.
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