P0302 Cylinder 2 Misfire. Any ideas? **SOLVED** (1 Viewer)

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Oct 14, 2005
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5
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1995 FZJ80, 230K mi.

Sorry in advance for the long post but I’m trying to document all my troubleshooting to date. I was heading home from a trip and the truck began running rough and the CEL came on. The CEL light would blink under heavy throttle indicating serious misfire. I plugged in the code reader when I got home (30 miles later) and got P0302 (misfire cylinder 2). I figured it wasn’t bad gas or a fuel pump / pressure issue since those would affect all cylinders. The plugs, plug wires, and cap/rotor had been replaced 5 years (only 5,000 miles) ago. There is no apparent water in the oil or oil in the coolant. I pulled the #2 plug and it looked tan (not oily) and basically normal. Based on research here, I suspected either a bad injector or melted wiring by the EGR.

I pulled off the wrap on the wire bundle and inspected all the wires. Nothing was melted but I re-wrapped with heat tape anyway and re-routed away from the EGR so it’s nice to have that done. Not finding any issue with the wire bundle, I removed the intake plenum and checked continuity on all injectors. All were within spec but, since I was all the way in there, I decided to pull all the injectors and send them to FIS to be cleaned. All injectors were cleaned and all flow tested fine. I checked continuity to chasses ground at each of the injector connectors and they all tested exactly the same (no continuity on one lead, and about 500 ohms on the other lead which is presumably the ECU) so it doesn’t seem shorted anywhere (like by the glovebox for example). I also drained the fuel tank just to make sure there was no bad gas / water in there.

I re-installed the injectors (with new gaskets) moving the #2 injector to another cylinder in the process. I replaced all the small water and vacuum hoses while I had the plenum off and also bypassed the rear heater and replaced the heater valve. I got it all put back together and started it up. It immediately idled rough (about the same as before). No CEL immediately (probably reset from having the battery disconnected for 2 weeks) but CEL came on within a couple minutes. It has the exact same code P0302 for the exact same cylinder.

I’m now at a loss. I could try replacing the plugs / wires / cap again I guess but it kinda seems like I “just” did that. I don’t have a compression tester. It may be time to drop it off at the dealer and just bend over unless somebody here has something else to check. Any ideas?? Thanks in advance for your help!
 
For all the work you've already done, buy a compression tester and leakdown kit and check it out.
 
Thanks for the responses. I've ordered compression and lead-down testers. Unfortunately (or fortunately??) we're leaving for vacation for two weeks so I won't be able to test it before we leave. Now I'll have to worry about it the whole time.....

The truck sat un-used for over a year before this. It fired right up but ran a little rough (no CEL) and I figured it was bad gas. I filled up with fresh gas and the problem immediately went away. So, that was probably the problem and un-related to this issue. Following the gas re-fill, I drove probably 100 miles and it ran fine before this issue. It runs worse with this issue and has a CEL. I just mention the vehicle sitting and the previous rough running in case there is a clue there. Maybe rust has caused a stuck valve? Seems a little weird that it ran good for 100 miles if it was rusted / sticking.

I don't think its fuel since: 1. The other cylinders are firing fine 2. The injectors are cleaned / tested 3. The injectors have been moved and it's still cylinder #2 4. The harness continuity on #2 tests the same as all the other cylinders. I have a mechanics stethoscope so I'm going to just verify injector sounds today just to fully rule out a fuel issue.

I'm also going to pull the #2 plug and check for spark with the fuel pump fuse pulled. If good spark, that should rule out a bad plug / wire / cap issue.

Then I'll try the compression / leakdown testers after we get back. If its a stuck / burnt valve, I guess it's time to do a preventative HG replacement? I'm assuming it's original unless it happened to be replaced during it's first 5 years of life. I've owned the rig for the last 20 years and it hasn't been done under my watch.
 
Thanks for the responses. I've ordered compression and lead-down testers. Unfortunately (or fortunately??) we're leaving for vacation for two weeks so I won't be able to test it before we leave. Now I'll have to worry about it the whole time.....

The truck sat un-used for over a year before this. It fired right up but ran a little rough (no CEL) and I figured it was bad gas. I filled up with fresh gas and the problem immediately went away. So, that was probably the problem and un-related to this issue. Following the gas re-fill, I drove probably 100 miles and it ran fine before this issue. It runs worse with this issue and has a CEL. I just mention the vehicle sitting and the previous rough running in case there is a clue there. Maybe rust has caused a stuck valve? Seems a little weird that it ran good for 100 miles if it was rusted / sticking.

I don't think its fuel since: 1. The other cylinders are firing fine 2. The injectors are cleaned / tested 3. The injectors have been moved and it's still cylinder #2 4. The harness continuity on #2 tests the same as all the other cylinders. I have a mechanics stethoscope so I'm going to just verify injector sounds today just to fully rule out a fuel issue.

I'm also going to pull the #2 plug and check for spark with the fuel pump fuse pulled. If good spark, that should rule out a bad plug / wire / cap issue.

Then I'll try the compression / leakdown testers after we get back. If its a stuck / burnt valve, I guess it's time to do a preventative HG replacement? I'm assuming it's original unless it happened to be replaced during it's first 5 years of life. I've owned the rig for the last 20 years and it hasn't been done under my watch.


A number of things can cause a stuck valve

Could be sumthin as simple as a busted valve spring

In my case, it was a burnt valve (also on cylnder #2)




At around 400k miles, she had started consuming oil to the tune of about half a quart every 1000 miles due to worn valve seals

This caused excessive carbon build up, which led to the exhaust valve not seating properly and eventually burning an edge

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In the end, I replaced all of the exhaust valves and freshened up the head as a PM

Original HG still looked fine and I'm kicking myself for not doing the valve seals earlier when I noticed the oil consumption

You'll know right away once you get the leak down tester hooked up

Just get it to TDC, connect about ~50psi and listen for leaks

If you hear a leak from the intake side, then the intake valve is leaking

If you hear a leak from the exhaust, then the exhaust valve is leaking
 
Found it!

I've already wasted enough of your time, and THANKS everybody for the responses. But, I'll document the rest of the troubleshooting in case it helps somebody else someday.

I figured I'd test the last few remaining things before the compression tester arrived (and before vacation). Tested the injector sounds with a mechanic's stethoscope. Injector #2 sounded exactly like #1 so that pretty much ruled out the injector connection (injectors themselves had already been ruled out with the cleaning).

Then I figured I'd verify spark. I tested the #2 cable for resistance and it measured 8.7 Kohm. Removed the #1 wire (since it is easily accessible) and measured that at 7.5Kohm. Those are both within spec and, from my research, the wires should be approx. 1Kohm per inch so the difference between #1 and #2 made sense since #2 is slightly longer. So, it's not the wires. Next I removed the #2 plug and it was wet with fuel. Removed #1 (since I could access it easily) and it was dry / tan. I disabled the EFI, inserted the #2 plug in the #2 wire, grounded on the intake, and had my wife crank it over. NO spark whatsoever. Inserted the #2 plug in the #1 wire. No spark whatsover. DOH! Just to verify, I inserted the #1 Plug in the #2 wire and had good spark. Crap. After all that work taking apart the entire intake plenum it was a bad plug the whole time! A quick trip to Toyota for a $2.22 plug (well, 6 of them), installed it and it absolutely just purrs!

The old adage "check the easy stuff first" definately applies here. The plugs were only 5K miles old so I assumed it wasn't that but that was obviously a bad assumpion. And do they just quit suddenly mid drive? I've heard of fouling or wearing but just flat-out quitting all of a sudden? I don't think I've ever even heard of that. Anyway, I'm so glad I don't have to spend my entire vacation reading head gasket threads! Plus, I've got nice clean injectors and a bunch of new vacuum and water hoses so I guess I've got that going for me! I'm going to keep the old girl in the shop tonight so she doesn't see the Amazon guy deliver that compression tester. I don't want her getting any ideas.......

Thanks again everybody. And, check the easiest thing first!
 
What brand was the defective plug? Country of origin (OEM or aftermarket)? Any noticeable damage, cracked insulator, broken electrode, ---??

If you still have the plug you could send it to the manufacturer for evaluation.
 
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I've still got it. It's hanging on a magnet above my workbench as a constant reminder to me not to make assumptions when troubleshooting......It's a Factory Toyota "Denso". 6 years old (purchased from Toyota in 2015). 5,500 miles ago (yeah, I know, I've been busy!). I didn't see any obvious cracks / skid marks on the outside of the plug to indicate that it had decided to just be a "plug" and stop doing the whole "sparky" bit. I was just going down the highway and boom. Done. CEL and misfiring.

I'm not home right now and this is the only picture I have on my phone. Sorry, you can't see the jacket / markings due to the socket. Wet with fuel (but otherwise looks good to me). I didn't try to clean it or anything. I wouldn't trust putting it back in there so I just replaced it.

Plug.jpg
 

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