My 2001 has been setting misfire codes on multiple cylinders for a couple of months if I leave it running at idle for long time. Finally went out and put in new plugs and my multiple misfires went away, but #4 stayed with me. Old plugs were all old with huge gaps, like 65 thou., so they were done. This happens from stone cold, so I don't thing it is the heat soak issue. Since you really can't check your spark with the coil pack, I unplugged the injector and no change, still rough, and got a misfire #4 code and open injector #4 code. Shut it down, got my noid light out and was getting a pulse on restart at #4, so I assumed it was the injector. Replaced the injector and what I'm finding is that on a cold start up, I get several pulses of fuel, then when it sets the misfire code, #4 injector goes dead, is that a feature of the ECM? I've even swapped the wires from #4 and #5 injector and the line for #4 is in fact dead. I'm about to order a new coil pack and plug for #4 and a set of "upgrade" injectors, just want to be sure I am not overlooking anything. Any input or suggestions? Thanks in advance!

 

Really A bit out of my league here. Till someone else chimes in...

It shouldn't be shutting off pulse to #4 me thinks. I'd be looking at the wiring and connections to the injector, myself. Got to mention here...the very rare times the puter' does actually seem to be shot is when one of the transistors? that work an injector go bad. (maybe one of the only things in there that deal with any real current). You could even jiggle the wires right to your PCM...at least one of them goes to that injector.

 

Very interested to see what kind of answers come up on this question. I'm having similar problems to the OP

 

Weekends can be slow. Let's see if Ken Or TJ or someone chimes in, maybe during the week.

 

I thought bad connection myself, but it seems to stop firing the injector in about the same time frame every time I try it. Went out after dark looking for stray spark, but found none. Even went so far as to spray some water in the area, but nothing. #3 seems to be firing fine, so I'm not so sure about the coil, it is a wasted spark system, so I would expect #3 to be skipping too. At 128K miles, I'm not sure that the coil could still be 100%. I may pull the plugs out tomorrow and see if I can get the miss to move by swapping them around.

 

check out all the grounds under the hood, maybe run a new one from the battery to the alt. Your pcm could have a shady ground therefore cannot supply ground to all of the injectors and everything else it has to ground to create pulse.

More likely you have a short or open in the pulse wire that runs back to the pcm. Check the ground pulse for injector 4 at the pcm by backprobing its pin on the harness connector whatever number it is i dont have a diagram for your year. If You dont drop pulse there then you know you have a bad spot in your wiring.

 

Could be a dirty injector or come carbon under a valve in #3. cylinder.

Get some BG44K and add it to a full tank of gas. Drive til 1/2 tank. Fill tank. Drive til down to 1/8 tank and fill again.

 

A very low impedance injector coil can smoke the PCM injector driver for that injector.


Injector impedance should be around 11-12 Ohms at room temp.


A driver wire shorted to ground could cause the same issue.


Inspect the wiring loom at the end of the fuel injector rail closely for chafing on the end of the fuel rail. There have been many cases of chafing here that goes through the loom and in to the injector wires.

 

ICK! That sounds pretty bad.

(Btw, he's loosing pulse)