Codak

At a loss here with this misfire...

Just got in a different PCM from ebay and have no change with the misfire. I really don't know what else it could be.

I will go down the list here what i have done with no avail.

Diving into this more i do not have a check engine light on startup or idle. After resetting the codes with my scan tool and battery. The misfire is all the time. The check engine light comes on after driving for 10-15 minutes. The codes are P0300, P0303, P0305. There is a flashing check engine light when i drive before it goes solid.

After what is said above these are the checks i have preformed.

1. New 4 hole fuel injectors. All injectors have 13volts to the positive side of the injector circuit while running. I have swapped injector 2 and 3 and that did not change anything. (While the jeep is running i unplugged one injector pigtail at a time to narrow down the cylinder for change. Cylinder #3 is the only one where the misfire did not get worse as i unplugged it. So cylinder #3 is my problem).

2. Inspected wiring harness for #3 wires to see if there is a brake in the ground wire, did not see one. (Unless i missed it i think the ground wire is good in that circuit). (Also checked for resistance in the ground wire side with my multi meter, got no resistance reading). I do not believe there is a brake in this side.

3. Different PCM from Ebay to rule out ground driver in PCM, no change.

4. New Mopar CPS sensor.

5. Battery is new, along with spark plugs, cap and rotor and wires. I have already done the wiring upgraded replacing all the ground and positive wires from the battery. Cleaned all the grounds around the PCM and engine.

Jeep starts right up and sounds good running with no unusual sounds.

What i do not understand is i am getting codes for other cylinders but my misfire is on cylinder #3 so i believe.
Is there anything else that i should try? Thank you all for the help.

Dave51

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Dave51

A reading of 0.0 is actually bad, indicative of a short circuit. What kind of multimeter do you have? Check your technique and the resistance of the other wires.

Dave51

Or splice in a new wire.

Codak

i have a klein multi meter that has a setting just for resistance, i will try again but i remember i did get no reading at #3 for the ground side.

Also you said splice in a wire? So cut the wire at the injector ground pigtail and run a piece of wire to the pin on the PCM? Thanks for the help

J/D/S

Following because I'm having the same issues with number 4 injector.

Dave51

I might do some confirmation before I went to Hack n' Slash, but that's me...

Anyway, all wires have some resistance, even the probe wires (unless you use the REL button to subtract the probe wire resistance). Consequently, I'd check the other injector grounds to see if the correct range is being use and overall technique is good. If the other 5 grounds have some Ω and 3 still has 0.0 then there you go, bad wire.

BTW

You're welcome.

Seeing as how you've moved into the P0300 codes you really need to check compression and look into the electricity stuff-- plug, plug wire, cracked cap, etc.

Want to borrow the 'scope?

Dave51

Agree that plug looks like it got ++++ spark and zero fuel, but

I thought that plug could be steam-cleaned-- as in head gasket...

Codak

1. I checked resistance again this morning at cylinder #3 pigtail and PCM PIN 5 and got 0.2 with the (black probe side) of the multi meter) in the injector pigtail side, but if i switched probe ends to the (red probe side) into the injector pigtail i got 0.0. I don't know which side of the multimeter needed to be in which end so i stated both here.

2. Unhooked battery and i cut into the ground side injector #3 pigtail and wired in a direct wire to pin 5 at PCM (yellow/white stripe wire). Misfire is still there.

3. I then checked the positive side of the injectors again for 14volts. With the key on engine NOT running i got 4.5 volts to each positive side injector all 6. With the engine RUNNING i got 14.3 volts to all injectors. IS THAT A PROBLEM THAT I AM ONLY GETTING 4.5 VOLTS WITH THE KEY ON ENGINE NOT RUNNING? SHOULD IT BE 14 VOLTS WITHOUT THE ENGINE RUNNING?


Is there anything else that controls the injector circuit for cylinder #3? TPS? Cam position sensor? ASD? Thanks for the help.

Dave51

Not possible, but let's hold that for now.

I HAVE NFI. WHY ARE WE YELLING?

FOR THE 4TH TIME, CHECK COMPRESSION!

With a 300 and 305 code IMO you have to expand the search. A CKS/CPS sync issue might do that.

When you switched fuel injectors did you check patency of fuel rail? Like an O-ring was stuck in there?

Intake manifold and/or associated vacuum hoses near there intact?

Really thinking an o-scope is going to be needed to try to find the issue.

Dave51

Hold one.

Is that #3 plug? Or all the plugs?

exasemech

Again looking through this saga.Multiple cylinder misfire, parts cannon has been fired, have spark, plug(s) look like they do.It might be reasonable, considering it's not been done, to: 1)check fuel pressure2) look for vacuum leaks. I know you're focused on the ecm because you had that happen on another vehicle but you ought to look at ALLthe typical causes.

Codak

Just wanted to update this thread. Thank you all for the troubleshooting help. My misfire turned out to be the distributor pickup coil. I picked up a new Mopar one and the misfire was gone instantly. Again thank you all for the help.