constant misfire

[jamodog]

Hi all

Please help
I have a 98 4.0 Explorer dual fuel and just had it serviced . Great on petrol now but constantly misfiring on gas,after a week of driving it now misses on petrol too ! Have changed the HT leads at AAs suggestion but still shocking on both fuels under load. Could it be a dodgy plug or should i concider the coil pack ??

Cheers

John

 

[NJMike]

Could be either, but if it is missing on more than one cylinder, or giving you a noticeable drop in RPMs when you nail the gas (like getting on a hiway) before responding, or if it happens more at high speeds than local driving, it is more likely to be a faulty coil pack. That being said, how long has it been since the plugs were changed? They last a long time, but do have a definite life span.

Mike in NJ

 

[chillyb0mb]

I had misfires on my 97. cause was plugs and leaky vacuum.

 

[NJMike]

Good point. I was going with the statement by the OP that it happened under load. Vacuum leaks will usually result in a poor idle as well. Of course there are exceptions to every rule. I had a Mustang II once that had a leak in the vacuum reservoir. The only symptom was when accelerating, the vacuum level in the reservoir would drop enough to cause the cabin air flow diverter to close so the air flow from the dashboard would change by itself to the windshield defroster output, and then back to the dashboard after you let up on the gas. It was almost like the car was haunted.

Mike in NJ

 

[jamodog]

Resolved

Thanks for taking time to help. But I
have finally found the fault tobe one of the new spark plugs fitted at the service had a hairline crack in the insulator , So replaced all 6 too be on the safe side and she runs like a dream .

Thanks Again.