Engine misfire, and I have no hair to pull out. (1 Viewer)

[Equinsu ocha]

In need of some advice.

Backstory: I’ve been chasing a P0401 code. Took intake off, replaced all vacuum lines, cleared my vacuum port through the intake and relocated my VCV switch. Put it together and my light comes back on. No big deal. I kind of expected that. Vehicle ran fine.

Fast forward a few days to this past Friday and it starts running super rough just after filling it up. Code comes back as a cyl 6 misfire, and later 5 and 6 + random misfire codes. I did a full tune up to see if that would remedy the issue, but it did nothing. I did some research and I assumed the harness next to the EGR pipe had damage. I was working in that area, loom is melted, and it just made sense that that was the issue. Harness looks like it’s taken no damage in the area. Connector to #6 injector looks fine, no corrosion to it or the injector itself. Before I took it apart, the injector sounded like it was firing while listening through a stethoscope. I’m just at a loss of where to go next. Should I just throw an injector at it and see what happens? Could the EGR issue be causing my cylinder 5 & 6 misfire? Should I pull the valve cover to see if I have an issue with the valve train?

Some guidance would be greatly appreciated.

 

[Equinsu ocha]

I’ve got everything out of the way, my next step will be to pull the valve cover to rule out valvetrane. The tube seal for cylinder 2 is seeping a little anyways.

 

[Jeff Elliott]

I had similar issues but it was #4. Chased it forever. My loom was also melted and, on first inspection, didn't appear to be compromised. However, when I dug into it, it was obviously enough to short out the #4 injector and thus cause the rough running / loss of power. Not saying that's what is happening with yours but I'd have a very close look at the wires if you haven't already. FYI, mine shorted enough that fixing the wires didn't fix the issue - it had shorted the ECU which also required replacement.

 

[Equinsu ocha]

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I had similar issues but it was #4. Chased it forever. My loom was also melted and, on first inspection, didn't appear to be compromised. However, when I dug into it, it was obviously enough to short out the #4 injector and thus cause the rough running / loss of power. Not saying that's what is happening with yours but I'd have a very close look at the wires if you haven't already. FYI, mine shorted enough that fixing the wires didn't fix the issue - it had shorted the ECU which also required replacement.

will definitely dig into it more. I guess I assumed it would be obvious. May have to pull more loom back.

 

[Equinsu ocha]

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[bajaphile]

Check wiring harness again I suppose. I'd also check spark plugs in 5 & 6, see if there's oil, fuel or coolant remnants. Ensure you've re-seated the plug wires correctly onto the plugs and distributor cap. (Unless your full tune up included replacing the spark plugs, I guess you've already addressed this). It is a little concerning that both 5&6 are misfiring though. It is a PIA to get a compression gauge onto #6. I'd try testing #5 and #1 and see if there is difference in PSI.

Annndd... I hate saying this one, but try disconnecting the battery for a few minutes to clear your ECU. It's worked for me once during a misfire issue I was pulling my hair out on (for me it was one of the injectors dumping fuel).

 

[Equinsu ocha]

I did replace spark plugs. 6 was super black, and 5 was pretty close to 6. All pugs are seated. I have the battery disconnected now, so if the ECU is the issue and needs to be cleared, a few days unhooked should clear it up.

 

[Equinsu ocha]

Valvetrane looks perfect. Cams look new and no sludge. No sign of any coolant in the oil. Hopefully this rules out a head gasket. Will pick up a compression gauge today.

 

[inkpot]

I have never seen a valve train problem on a 1fz yet. I have seen wiring damage by the egr that is hard to I D and even harder to repair. You need small fingers and lots of patients.

 

[Equinsu ocha]

I just did a pretty in-depth inspection of the wires. I can’t find a single break, or a wire that’s been burned. The tape and loom did a great job protecting the wires. It was pretty thin, though. There’s no telling how much longer it would have lasted.

 

[Equinsu ocha]

I just want to be sure, Cylinder numbers start at the front at 1, and at the firewall at #6, correct? So 5&6 would be the cylinders closest to the firewall.

 

[whaler]

Clean up the wiring harness, remove further back too. Seems like that isn't your issue but you never know.

Also, your oil looks due for a change. Looks dirty to me and your valve train doesn't seem to have oil coverage.

 

[Tools R Us]

Did you check the harness at the ECU? It can rub on the glove box support and short in that area.

 

[Equinsu ocha]

#5 on the left and #6 on the right.

 

[Equinsu ocha]

Clean up the wiring harness, remove further back too. Seems like that isn't your issue but you never know.

Also, your oil looks due for a change. Looks dirty to me and your valve train doesn't seem to have oil coverage.

Harness was removed back to where the wiring looked new. I’ve got a 10” section exposed. I’ll take it back a little further as it gets closer to the motor, just to be sure.

The oil has about 500 miles on it. I used 10W30. Motor has been sitting for 3 days. Probably why there is no coverage.

 

[Equinsu ocha]

Did you check the harness at the ECU? It can rub on the glove box support and short in that area.

I’ll look at that now. Thanks.

 

[Equinsu ocha]

Wiring behind glove box is unharmed.

 

[BILT4ME]

Spark plugs 5 & 6 look like fuel fouling if anything.

Again, it leads to injector wiring, bad injectors, or bad O2 sensors or temp sender telling the engine it's too cold and not going into closed loop and dumping fuel into it.

Make sure you do Spark Plug tube seals and PCV grommet while the VC is off. When there are hard, crusty, and shrunk, they allow in unmetered air and it causes the engine to run rich. (Too much O2 seen by the O2 sensors adds fuel to compensate)

Also do the bypass coolant hose to the TB under the intake manifold while that's off. It's a lot easier to get to while you're in there.....

 

[Equinsu ocha]

Spark plugs 5 & 6 look like fuel fouling if anything.

Again, it leads to injector wiring, bad injectors, or bad O2 sensors or temp sender telling the engine it's too cold and not going into closed loop and dumping fuel into it.

Make sure you do Spark Plug tube seals and PCV grommet while the VC is off. When there are hard, crusty, and shrunk, they allow in unmetered air and it causes the engine to run rich. (Too much O2 seen by the O2 sensors adds fuel to compensate)

Also do the bypass coolant hose to the TB under the intake manifold while that's off. It's a lot easier to get to while you're in there.....

Do you think I’d be able to rule out the temp sender and 02 sensors since it’s only cylinder 5&6? Isn’t the temp sensor for engine control and temp sender for the gauge? I get them mixed up.

I did the PCV and grommet when I did the tune up. I can rule that one out.

Good thinking on the coolant hose replacement. I hadn’t thought of that. That would be a booger with everything back together. Thank you!

 

[BILT4ME]

Agreed, it SHOULD be all cylinders, but maybe 5 and 6 are already running rich or those injectors are being problematic.

If 5 and 6 are dumping more fuel, it could be they have a bare ground wire.

Remember, Toyota switches the GROUND side of the load and not the HOT side of the load, so, if there is a failure to ground, it's on all the time.