I’m all out of ideas. 04’ b2300.

It started having an intermittent misfire a few months back. I had done plugs and wires as part of a overhaul/service last year, so I put a coil on it. That fixed the misfire, but it came back after maybe 2 months. Crank sensor replaced. Fuel pump and filter done last summer.

Last week it started up and was running good, so I took it to run an errand. On the worst hill in town it starts misfiring again, huge power loss. Somehow got up that hill and got it home. Found that it was running on 2 cylinders (2 and 3).

Pushing in the valve on the fuel rail shows there’s pressure, I haven’t put a gauge on the rail to check the actual value yet.

noid light on injector #1 shows there’s signal to the injector.

noid light on both coil primaries shows signal to both coils.

timing light on plug wires 2/3 show spark. Timing light on wires 1/4 show no spark.

I put another coil on it just to be sure(denso)(I know, probably not necessary but I’m running out of ideas. I did plugs and wires too...) I still see signal to both coil primaries. I still only see spark on one coil.

like I said, I’m stumped. Anyone have any idea what could be going on? Could it still be the ECU even though o have good signal to the coil primaries?

 

Welcome to the forum

Love all the testing

Now do one more, 50/50 test
50/50 test
Spray fuel into the engine
Gasoline, ether(quick start), even carb cleaner
Try to start engine
If it starts and then dies your spark and compression are good, but no fuel delivery
If it doesn't start then no spark or no compression
50/50 instant results
(test has been around since 1890's and first gasoline engines, always the first test to do with a crank/no start)

In your case engine should start but run rough on only 2 cylinders
And should stay running if its getting fuel from injectors

Its possible the transistor in the PCM(computer) for coil 1/4 has failed, but should be codes coming up for that, and it would be a very very odd failure, possible, but long odds against it
I would pull off the PCM connector and have a look for any corrosion inside that large connector
Also if you have a OHM meter test the 2 Coil wires from PCM to Coil plug
Pins 26 and 52 on PCM are for the coil pack
Numbering here: https://easyautodiagnostics.com/imag...99/image_1.jpg
Tan/white wire is usually 26 and tan/orange wire 52

Code list here, P0300's is where spark system codes are: https://www.therangerstation.com/tec...II_codes.shtml

You can get Bluetooth code reader, like ELM327 for $15, works with smart phone as the display

 

Hi Ron, thanks for the reply and suggestions.

here’s the update:

before I got your response I was trying to dig deeper. I.....

-confirmed that the new spark plugs were not DOA and that they’re internal resistance was within spec. They’re good.

- did the same thing with the spark plug wires. They too are good.

-assembled both cool circuits w/ the plugs removed from cylinders to make sure there wasn’t a bad connection anywhere. Electrode-wire-coil secondary-wire to electrode shows the expected resistance values, for both coils.

-removed the ECU and checked the transistors that fire the coils. No shorts, everything within spec. No obviously melted transistors.

-checked resistance in the wires between the ECU and the coil plug. Also made sure they weren’t shorted to each other or ground. All good.

Then I got your response. I considered your 50/50 test unnecessary because it was already running on 2 cylinders, it had just stopped wanting to start. But I know it wouldn’t hurt, so I buttoned everything back up, sprayed some started fluid into the intake manifold aaaaaand it started right up! No misfire. Nice and smooth.

this has me thinking either the connections at the ECU plug are bad, or the coil connector has work out...

anyway, it was running, so I ran some errands with it. Put maybe 50 miles on it that day. Everything was working. Flash forward to Monday morning, I decide to drive it to work. It started up OK, but about halfway to work while accelerating away from a stop sign, it starts misfiring. I limped it to work (and back home 🤷‍♂️)

so I’m back where I started this thread.

One positive is that on the way home, I had my code reader with me. I never got a check engine light, but there is a pending code that came up: P0351.

based on what I’ve tested and observed: ECU, coil, plugs and wires are good.

my unknowns are the ECU plug(unlikely culprit in my mind), the wires to the coil(I check for shorts between them and to ground but they could still be shorted to some other wire), and the coil plug itself.

I may go ahead and bypass the wires in the loom from ECU to coil and splice in some external wires and see if that makes any difference. After that, I would replace the plug on the coil. Thoughts?