Ford Ranger, 3.0

Misfire on cylinder# 5
- changed plug on # 5
Still misfiring on # 5
- noticed a squirrel had been chewing some of the plug wires - replaced plug wires
Still misfiring on # 5

Suggestions for diagnosis?

I know it has to be either a fuel-air mix, compression, or fire issue. I just don't know the most reasonable step from her.

 

It is limited to one cylinder. Test the fuel injector. Use a stethoscope or a length of garden hose and listen to the injectors. If #5 is making no noise check the electrical circuit.

The coilpack may be shot. If you have 100K + that would be my first guess.

What year and mileage on your Ranger?

 

2000
154,000

THANKS! I'll try your idea once I figure it out completely. Can a coilpack be bench-tested.

 

Tested the injectors. #5 is clicking just like 1, 2, 3, 4. Can't reach #6 with the stethoscope, but no mis-fire is indicated on 6, so ignoring for now.

Of course I guess clicking doesn't mean they're clean ...

I guess it's on to the coil pack,

 

carphead
Junior Member
Join Date: Feb 2009
Posts: 5



2000
154,000

"THANKS! I'll try your idea once I figure it out completely. Can a coilpack be bench-tested." ?

Yes, check U-tubes for a pictorial on how to test COP's.
The problem is getting down to the COP.

skip.

 

Using a spark tester, I'm getting sparks from all 6.

While I've got time on my hands, I think I'm going to grap a compression tester.

 

Compression was fine - all between 165 and 172.

... but I think I found the problem when I pulled the plugs to test comp. All plugs showed signs of heat, high speed glazing, and worn to a nub electrodes.

The one in #5 that had been replaced 60 days ago had actually been replaced with a 32 (edit: I mean replaced with a 22) which is for the 4.0 - a miss on my part.

I'm going to try using a slightly cooler plug, if I can figure out which one.

Thanks for all your help. Should know within 50 miles if it's a fix.

 

Nice going Carphead!
Let us know how it goes. Get OEM plugs or some plugs that are very similar. Stay away from fancy stuff.

To skip1930; This is just a clarification: Carphead's engine does not have COPs (Coil on Plugs). It has a coil pack and wires from the coil pack to the plugs. Coil packs can develop internal shorts. Also there can be shorts at the towers where the wires attach.

A coil pack:



COPs: