2003 navigator 5.4 had thrown code p0308 cly 8 misfire, replaced Cop and all plugs and also all fuel injectors, # 8 plug was a little darker than the others. After all that it still has a low rpm vibration from the engine and after driving for a few days the same code went back on.
Please let me know if you have any ideas...

I also hear a rattle occasionaly on start up not sure if that has anything to do with it.

Thanks.

 

The rattle could be a worn cat,or cat cover, is the injector ticking( power to it ,can be checked with a hose to it), does the engine change when you unplug the injector running, and or also unplugging the cop running, next any coolant loss, cylinder 8 is where the coolant port is blocked off by the intake with the gasket, its possible coolant is leaking into the intake port,or plug hole, fouling the plug, next would be compression check and valves not seating on that cylinder

 

Well I unplugged the cop while idling and saw no change with the engine , I assume I have a electrical problem with the cop or the injector supply wires?

 

No coolant loss and I can't get back to #8 to hear the injector, had the upper intake off and didn't see any sign leakage.

 

Ok tested the power and pulse to the cop and was good then checked the power the the #8 injector and that was good but had no ground pulse as compared to other cylinders
Now what a broken wire? Or could it be a bad control module.

 

Lower matters for that too. Pull the coil and plug it in. Leave a plug in it and check for spark. Don't hold it though. Just look at it...

You may know that, but just in case. If it shows spark, you know that's not it. Next is compression check. Do the whole bank for comparison...

 

Back probing or unpluged for the injector voltage? check for broken wire inside the installation on the section of wire from the connector until it goes into the loom( just roll the wire bent it in your fingers so see if you have a soft spot....

Injector not ticking?

 

I'd swap #8 injector with #7's, #8 coil with #6's, #8 plug with #5's.
Then see if the problem moves. If it moves, you know which component is bad. If you still get the P0308, ohm out the ground side of the #8 injector and #8 coil wires back to the PCM connector.

 

Yea did the swap and had the same result , with #8 being so hard to reach I can't tell if its ticking but am assuming its not since I am getting no ground pulse, can't really get at the wire to follow it to the loom, is it possible to test the wire at the other end wherever that is?

 

I hear ya if you dont have a long piece of hose, any kind , to put against the injector and to your ear to listen for the ticking , and its hard to feel the wiring since it wraps around the back side of the intake, its even more of a pain to trace the wiring thru the loom to the pcm, are the wires on the injector red and the other light blue and you have no pulse on the light blue at the connector ,even on the back of the connector where the wire goes in the connector, or get a pin out diagram and ohm the wire for 8 like pdqford said

but i would get a injector noid light tester before i attemped all that to test for your pulse

 

I would make sure there was ground and no pulse before condeming the pcm for a bad injector driver, well remans are about 250 and then the install and flash from the dealer thats another 150

Could maybe borrow a good scanner or have it scanned and look at the injectors pulsing see if 8 is dead

 

I attached an old injector to the #8 plug and seem to get about 8 clicks then it trails off to nothing after 15-20 seconds, I then hooked it to #6 and get constant clicking, would this be a sign of a bad pcm - since I'm getting some pulses at each start up?

 

The pulse actually looks normal for about 5 seconds after starting then dies out

 

I think the ground side of injector #8 is a light blue wire. Check the middle connector on the PCM - pin 6 should be the same light blue wire. (Also look to see if there is any crud (trademark ) growing on the pin.)

 

Ya it is light blue, Do you have a pin diagram ? I can't figure out what you mean by pin 6.