2000 Ranger 2.5L Intermittent Misfire

[Fern Fries]

My truck has recently started misfiring.
I’ve replace the plugs/wires and have cleaned the MAF Sensor with appropriate cleaner.

My truck starts to shake hard after a 5-10min drive. The misfiring is mostly consistent but it does go away for about 10 seconds at a time then keeps misfiring after that. No misfiring on cold starts but definite misfire on warm starts.
The truck stays on when unplugging the MAF while running, but runs rough nonetheless.

Note the first misfire happened weeks ago 130mi from home. Check engine light came on. I pulled into a nearby autozone and their code reader said cylinder 3 misfire. I changed out the passenger plug and reset the computer. I was able to get home without any misfiring.

I could use some help. A list of parts i can check would be helpful. My Ranger sounds like a lawn mower. Thanks in advance.

 

[tomw]

The computer generally provides a richer fuel mix when the engine is cold, and leans it out as it warms up. I would look for an intake manifold leak, such as a vacuum line that is split or loose fitting, or even a loose throttle body or intake manifold bolts.
If you had a failing injector, say on #3, in most cases it would not work so well when the engine was cold and fail when hot, unless it was stuck closed, but then when cold it would run poorly. If stuck open, it would/could flood all cylinders, and you would have black smoke out the exhaust.
tom

 

[RonD]

+1 ^^^

You can also unplug either Coil Pack and start engine, yes it can/should run OK with 4 spark plugs working, and see if all 4 spark plugs on that coil pack are working OK
Then switch coil packs, plug one back in and unplug the other
This may tell you if one of the spark plugs is marginal

Dual plugs are for better performance, this engine ran on 4 sparks and a distributor for 14 years, 1974-1988

If misfire is after warm up then do the test after warm up

 

[sgtsandman]

If I remember correctly, one bank of spark plugs on the 2.5 Lima runs at a lower voltage and wasn't intended to create more power, just clean up the emissions of the engine. If I'm wrong, I'm sure I'll be corrected.

 

[RonD]

No, that would be wrong
Dual spark plugs are strictly for more power, which is why Dodge Hemi used them, but hard to get the space to do it, and the advent 4 valves per cylinder makes more power so better use of the space

The 1989-1994 2.3l used a spark inhibitor circuit for the intake side coil on start up, no spark on intake side spark plugs.
Never did find out why they did that, maybe for stronger spark on 4 remaining plugs when voltage drops while cranking engine, but 1995-2001 Limas have full spark on both coil packs all the time

 

[Fern Fries]

The computer generally provides a richer fuel mix when the engine is cold, and leans it out as it warms up. I would look for an intake manifold leak, such as a vacuum line that is split or loose fitting, or even a loose throttle body or intake manifold bolts.
If you had a failing injector, say on #3, in most cases it would not work so well when the engine was cold and fail when hot, unless it was stuck closed, but then when cold it would run poorly. If stuck open, it would/could flood all cylinders, and you would have black smoke out the exhaust.
tom

Thank you Sir. I will inspect the intake and vacuum lines when I get a chance.

I drove my truck home from work the other day without any misfiring issues. I was sitting in traffic for an hour and nothing happened. The following day I ran the truck pretty hard for 10 minutes going to the grocery store and I did get some misfire right before I got back home.

Thanks in advance if anyone has anymore ideas.

 

[scotts90ranger]

Also look at the wires going to the coil packs, if one of the 3 wires going to the coil are grounded sparks will happen at the wrong time. If memory serves the center wire is power and outer wires are triggers for 1&4 and 2&3. Chaffed wires are annoying and hard to find and cause ridiculous issues like this...