Code P0304

[Flingarrows]

Code P0304 - Resolved

I have a 99 ranger with a 4.0, auto trans, with 91,000 on the odometer. Ive had the truck for about 2 months now.

Last night the truck started missing under load and the check engine light came on. I went to autozone to get the codes read: P1405 DPFE and P304, cylinder 4 mis-fire.

I nosed around and found a split hose on the DPFE and changed that.

I pulled the drivers front plug (#4?) and it looked clean, possible even lean. I put the plug back in and put a plug test in line with the wire. It appears to be firing fine. The plug wires look newer.

I removed the battery cable to clear the codes, then went for a ride. Same thing: missing under load. It idles good.

Does that sound like an injector issue, or would the coil fail under load. Any other things to check?

Here is a picture of the plug:

 

[Flingarrows]

I ordered a coil. I'll update if this fixes it, in case someone else has this issue

 

[chazz79]

likely an injector. Those coils fail in pairs of two. I don't recall the paired cylinder to #4 but the post directly beside it would be dead too because they fire at the same time. Bad coils toss a good deal of unburned gas into the exhaust, truck will run poorly and toss multiple missfire codes along with rich upstream 02 sensor codes. If the injector plug is accessable on #4 you'll be able to verify condition by unplugging it while the engine is running. No change=bad injector.

 

[Flingarrows]

Thanks Chazz, I appreciate the tip.

The coil did not arrived yet, so I haven't changed it. I also haven't driven the truck since last weekend, until last night.

I only went a mile to my daughters school and back. The truck never warmed up. The check engine light was not on, and it wasn't bucking like it had when the engine was warm. It had a very slight hesitation, but that is it

 

[Flingarrows]

Just to add more info, the bucking last weekend only happened under load.

If I backed off of the pedal it smoothed out

 

[Flingarrows]

Well, I changed the coil and the wires yesterday, and had no change.

Today I took off the upper intake and changed the #4 injector. Now I have a different symptom: rough idle, but smooth surges under power. I disconnected the #4 wire, just to be sure that I didn't leave a connector or wire loose on another cylinder. It appears to still be on the #4 cylinder.

I am going to have my son stop at autozone again tomorrow, to get the codes read again to see if it is still a P0304

 

[Flingarrows]

It appears yesterdays maintenance has set me back even further.
I have 3 codes now:
P0174-fuel trim bank 2 condition
P0304-cylinder mis-fire - cylinder 4
P0171-fuel trim bank 1 condition
Any ideas guys?

 

[Flingarrows]

I changed the # 4 plug, now idle idles well and smooth under power. I had never seen a plug go bad, especially since the plug tester was lighting when it fired.

I think the lean codes are a leak at the egr tube. I'll mess with that this weekend