Vehicle: 1991 XJ Laredo. 4.0L, 168k miles with original engine and transmission.
Relevant Modifications: Upgraded headlight harness, MSD Ignition Coil, Aftermarket security/alarm system
Symptoms: When accelerating (25% pedal or more) and cycling the high-beams off the engine will stutter for a split second (completely die and jolt the entire vehicle)

When driving around town at speed or sitting idle at a stop I can cycle my high-beams on and off without seeing any drop in my idle speed or engine what so ever, but if I'm accelerating, for some reason there is something that happens to cause the engine to stutter a full cycle or more. It will even do this in neutral if I'm at 25% or more throttle and cycle the high-beams on, then off. This will even happen if I'm driving a distance with the high-beams on then turn the high-beams off (so it's not about a momentary spike in voltage consumption from cycling them on, then off).

Any help would be appreciated as I cannot seem to find the problem.

 

See Cruiser54's site and clean up your grounds.

 

I'll take a look and make sure they are all still good. I just did the ground refresh about 6 months ago though.

 

Double-checked all my grounds and no change... Any other thoughts?

 

This is a weird one. I might start looking at that high beam switch, perhaps.

How is your MSD coil connected to the existing wiring?

 

MSD coil is using the existing wiring, yes. It had a lose connection that I had to fix by pinching the plugs internal to the connector on the vehicle side just a little so it had better contact. High-beam switch is in the column right? I replaced my indicator lever about eight years ago but didn't look at that switch when I was in there.

 

Had that problem with my 97 once. Gave me random misfires, often pretty bad. Took a while to run that one down. Can't hurt to check that connection.



Yes, that's the guy. Maybe some corrosion in there?

 

do you lose all electrical power..ie lights dim ?

my previous XJ started doing that, (just before someone smashed into it)

had tried a few things like new coil, but when i noticed it dropped all power for a split second, I began to suspect main battery cables/connections

it was very hard to notice the dropping of lights cause it was so brief

( I repaired that XJ enough to drive it up to my property in the mountains, started it up and used it for the 1st time in a few years on the weekend)

 

For fun, disconnect the security system power.

 

I suspect the problem might be in the new headlight ground. Did the new head light system involve the light ground? Is that ground near other grounds?

maybe move the headlight ground? Double check that ground point is perfect, make sure that ground point is not shared with other grounds i.e. ecu sensor grounds