Karpedmman

Compression tested fine so we now know it is not a valve. Module 019 & 020 on "Engine"-rosstech showed "0" misfires across the board. At this point I'm almost certain it is the ECU. If there is No spark at the plug and all the connections have been cleaned and tested that leaves only one last item-The ECU! Has anyone ever changed their ECU? Does it need to be programmed at the dealer? Anyone know what part number/s will work?
TIA

PaulW

Now I don't know if I agree with you.

When you pulled the injector, did you do a flow test to see if it is flowing fuel?

I would even consider pulling the coil pack for cylinder number 3 and attaching one of your old spark plugs to it and grounding it out and make sure it sparks.

Did you do the LED test for the injector?

pw

Karpedmman

Flow test was positive-Same amount of fuel sprayed out for the entire left bank.

Did take the spark plug out and grounded it to the head-Negetive. Switched coil packs onto the #3 coil pack plug-Negetive-No spark. If the ecu is bad then that could be why we are not seeing the misfires on the rosstech software-right?

Paul- is the ECU basically "plug and play"?

gondar

Once you have checked the conductor/connections leading from the #3 pack to the ECU, and the EUC connector, I guess you are left with the ECU. If you want to get tricky, perhaps you could determine what cyl is 360 crank degrees from #3 in the firing order, then run a jumper from that ECU-to coilpack-wire (from the other coilpack) to the #3 pack and see if you can get the bare grounded plug to spark as you have tried. Just for a second or two. If you have spark, then I think you are confirmed.

gondar

Otherwise the ex stroke will blow combustible mixture out in your face near the spark. Best to burn it inside the engine.

PaulW

Yes, it's plug and play for the 97-99 as far as I know.

When you put your analog meter on the input to the coil pack on voltage, does it show any voltage spikes? I take it the answer is no.

If no, check for continuity from T4b/2 (power output stage) to terminal 1 on N158 (ignition coil 3). Should be less than 1 ohm.

If that's good, swap power stage outputs, because you know the one is good. Do you still have the "no fire" on cylinder 3? If no, then it's the power stage, if yes, it's something upstream of it.

If it still has a problem, perform a continuity check from (the first number is power output stage terminal, the second is the ECU terminal):

T5a/5 to B16
T5a/4 to B15
T5a/2 to B13
T5a/1 to B14

All should be less than 1 ohm.

If they are all good, then open the ECU and perform a visual inspection of the circuit board. Do you see any burned components? Carefully inspect where the B13-16 come in and attach to the circuit board, anything obvious?

If yes, you most likely have an open circuit on the cylinder 3 circuitry.

If no, you still probably have an open circuit but just can't see it, probably an output transitor that went bad.

So my question is, did you swap the power stage outputs? Did you check continuity from the input of the power stage outputs to the ECU?

Funny how something in the ECU could fail from sitting deenergized for 3 months at the repair facility. Just doesn't seem right. But you never know. I would focus on the wire runs between the power stage outputs and the ECU and the actual power stage output itself.

pw

escapA8

Had one day of misfire again last weekend. Put in a (big) bottle of Techron in a half full tank. The problem was gone when I started the engine after a 5 minutes drive. Unfortunately your problem seems to be tougher to fix. Good luck!

gondar

Those detergent additives take a while to work and 5 minutes would not run enough through the injectors to clean anything.

I think you scared it.

escapA8

Actually I think it just wanted some added flavor like some people like toffee flavored coffee. ;-)

Karpedmman

LOL!