Intermittent injector driver failure

2008 Ford explorer 4.0 V6.
Intermittent cyl 2 misfire. Using a lab scope, I'm seeing system voltage between computer control and batt ground. It will fire the injector for a few minutes then fail to pull it to ground, but mostly it misses. Seems to be worse when engine is warm. Computer is located in engine bay on passenger side firewall.

It also fails when cranking, so I don't think the computer is shutting off the injector. I can touch the tpin at the computer with a test light and make the injector fire. Is there anything I should check before condemning the computer?

The only thing I didn't do was check pin fitment, but I either get steady 12v or a good injector waveform. No glitching. Wiggling the wire doesn't change anything.

Been a while since I've been on here. Hope everyone is well.

To be clear, while #2 is misfiring, there's no attempt by the PCM to field the injector?

It sounds crazy, but I have seen these injector wires short to each other inside the loom. :silly: Happened to me recently on a '10 Explorer 4.0:

www.scannerdanner.com/forum/post-your-re....html?start=17#46996

This is what I eventually found. There was no external damage to the loom.



Not saying you're gonna find this, just something to keep in mind.

That's messed up. I recently fixed a transmission that was randomly shifting from D to manual 2. After the owner replaced the range switch, I found the harness had fallen against the EGR tube.

I'm an engineer. This is just a hobby for me, but it wouldn't take much effort to make it full time.

Correct. Just steady battery voltage. Not even a blip. Same signal at computer and at injector. Power feed is steady and will power a test light when it's missing.

This one has been a saga. It came to me with a P0300 and several P030X after another shop put in plugs, wires, and a Dorman coil pack. I put in a Motorcraft coil and returned it with no misfires.

It came back with a P0302. The connector on #2 injector was broken and loose. I could make the miss come and go by pushing on the connector. I replaced that and appeared to have fixed it. Oddly, it never gave a circuit code.

The P0302 returned which is where we are now. The miss has gotten more constant as this has gone on. As the truck warms up, it comes and goes. When it's hot, there's a dead miss and it never fires, even when cranking. After all of the previous repairs, I never brought it up to full operating temp.

Side note, several of the injectors on both banks had a lot of engine oil in the connector. All of them had some oil. No idea how it got there.

PDM wrote: The P0302 returned which is where we are now. The miss has gotten more constant as this has gone on. As the truck warms up, it comes and goes. When it's hot, there's a dead miss and it never fires, even when cranking. After all of the previous repairs, I never brought it up to full operating temp.

Well isn't that interesting. :blink: Do you have a scope? It might be interesting to watch injector current ramps during a warmup to see if one injector starts drawing less or more current than the others. That might give a clue as to what's going on in the circuit during the driver shutdown.

I'd be checking wiring...and probing/scoping at the ecu connector itself in case the problem lies at that end

I'd be surprised if an ecu driver was intermittent

Tyler wrote:

PDM wrote: The P0302 returned which is where we are now. The miss has gotten more constant as this has gone on. As the truck warms up, it comes and goes. When it's hot, there's a dead miss and it never fires, even when cranking. After all of the previous repairs, I never brought it up to full operating temp.

Well isn't that interesting. :blink: Do you have a scope? It might be interesting to watch injector current ramps during a warmup to see if one injector starts drawing less or more current than the others. That might give a clue as to what's going on in the circuit during the driver shutdown.

I'll check that out. The voltage waveform doesn't change. One anomaly is this extra firing event that occurs at random and has a very short on time. See anything else here to be concerned with?

stevieturbo wrote: I'd be surprised if an ecu driver was intermittent

That's exactly why I'm asking the question.

Does anyone know of an input that would cause an intermittent shut down on a single cylinder?

Even more interesting. The only time I see additional injector pulses like that is during snap throttle conditions, for fuel enrichment purposes. You're obviously not snapping the throttle during that capture.

I'm starting to wonder about a cam/crank issue? Like a nicked tooth on the CKP wheel or the like. Only drops the amplitude low enough to cause a problem when hot. I could be way off. :silly:

Now you're coming around to what I'm thinking.

Like I said, this is just a hobby. I only take on about one car every couple of months, but I come across some of the weirdest intermittent stuff.

I went and looked everything over again. The signal drops out when cold or hot. It may or may not be missing while cranking. When cold, it comes and goes. When hot, it rarely fires at all. Other than that, I can't make out any other patterns.

The ckp signal is perfectly fine, and I just unplugged the cam sensor. The injector voltage and current waveforms never fluctuate. They look good every time it fires and are identical to the other cylinders.

If no one has any more ideas on what I can check, I'm calling the pcm. Does an intermittent driver fault make any sense?

what does the current look like? Those injectors with less voltage are pulling to ground perfectly fine so I’d want to rule out a power feed problem. Provide it a good power feed and see what happens.

Reading further up I see you say it’s failing to pull to ground. Intentional shutdown is something that is used to protect a catalytic converter but it would shut down until the next startup cycle. Sounds almost the exact opposite of what a cracked solder joint would be doing on an ECM. Very curious to see what you find.

John Curtis wrote: what does the current look like? Those injectors with less voltage are pulling to ground perfectly fine so I’d want to rule out a power feed problem. Provide it a good power feed and see what happens.

Reading further up I see you say it’s failing to pull to ground. Intentional shutdown is something that is used to protect a catalytic converter but it would shut down until the next startup cycle. Sounds almost the exact opposite of what a cracked solder joint would be doing on an ECM. Very curious to see what you find.

I ruled out a power feed problem early on by using a test light in place of the transistor. The injector fired every time.

On startup when cold or warm, it's about 50/50 if it fires. Once it's hot, I have zero firings at startup. Also, intentional shut down wouldn't come back on without cycling the key. That's why I came here asking about any possible inputs affecting injector control. Firings are also always at the correct time.

One thing I didn't mention is it comes and goes in periods of 5s to a minute. Never just one or two. That and worsening with heat really sounds like a bad trace or solder on the board. It's either the transistor, transistor control, or transistor ground

I'll report back after I open up the pcm

Also, I did check the other cylinders, and they all have those extra injector firings.