[allezgrand]

Hi All,
I've been chasing a misfire on Cylinder 3 of a 2001 IS300. It's constant and entirely obvious.

Backstory:
I purchased the car from somebody who had broken the ignition casting and the car was stranded in his car port. He had disconnected the wires which sense the physical key presence (and make it beep) and was pressing those against the key and against the metal box of the RFID module (sorry, I forget the proper name of that box), misunderstanding how the security system worked. I had the car towed to my place, replaced the ignition switch, fired it up, sprayed down the engine at a car wash to clean off the oil from old oil leaks, let it sit a day or two, then drove it to emissions testing. It drove just fine to the emissions testing facility, passed without any problem, then as I was getting on the highway to go home, began missing on cylinders 2 and 3 and had the random misfire code.

So far I've:

• Replaced one coil pack with OEM Denso and replaced plug wires and plugs - only cylinder 3 missing after this
• Swapped coil packs - no change
• Checked compression: clearly worse on cylinder 3 than the others, but not enough to be missing 100% of the time

6 - 175​

5 - 180​

4 - 180​

3 -155​

2 - 185​

1 - 180​

• Replaced spark plug wires again after previous replacements were visibly arching in the dark - new wires not visibly arching and cylinder 3 still misfiring
• Removed fuel rail, manually cleaned and flushed injectors, swapped injectors 1 and 3 - no change
• Replaced spark plugs one more time with OEM Densos - no change
• Purchased techstream cable (https://smile.amazon.com/dp/B0977HJB42) and tried 3 different versions of techstream - when I run "Health Check" every version crashes when it gets to ECU 2 of 9.

I'm suspecting it may be an ECU or Igniter issue at this point. Or possibly a wire somewhere. Any suggestions for the best way to diagnose from here?

Thanks in advance for any help!!

 

[jesve]

Wow. I was going to say injectors. At 155 comp that shouldn’t cause a misfire. I would check the igniter and wiring. Correct me if I’m wrong, but cylinder 3 and 4 use the same coil, with the wasted spark style ignition system our cars have this would mean that cylinder 4 would be missing as well if it had something to do with ignition. If you can get an igniter for cheap give that a shot. I would check fuel pressure too. Wouldn’t hurt. Start with that and see what happens 🤷‍♂️

 

[Hodgdon Extreme]

Checked compression: clearly worse on cylinder 3 than the others, but not enough to be missing 100% of the time

What do you mean "missing 100% of the time"? Does cyl 3 have a dead miss?

I'm suspecting it may be an ECU or Igniter issue at this point.

I don't see how it could be the ignitor or ECU considering the issue does not effect cylinder 4. Cyl 3 and 4 share a coil, igniter signal and ECU signal...

 

[allezgrand]

Yes, it appears Cyl 3 probably has a dead miss. It certainly feels that way and has a super high fault count on Techstream.

So how does the igniter work? Does the coil pack fire both 3 and 4 at the same time and is always just wasting a spark on one? Or does the coil somehow alternate? It looks like there is only 1 ground and 1 signal wire to the coil, so I'd assume it's always firing both.

Fuel pressure looks like a PITA to measure on these and hard to imagine that that would be the issue with no misses on any other cylinder when monitoring on Techstream.

If not the igniter or ECU, then I'm back to either mechanical or it's one of the things I already checked roughly one bazillion times.

Would it be helpful to post Techstream logs here?

 

[Thatblueis]

On a scan tool you should be able to pull up misfire load %. This will show that lack of power in a % form. If its 100% then you have a dead miss and somethings wrong. If it's not 100% I'd say a compression issue.

 

[Hodgdon Extreme]

how does the igniter work?

It preps/charges the coils, awaiting a signal from the ECU to fire/discharge them.

Each coil has two terminals, each going to its own spark plug. On an inline 6, cylinders 3 and 4 go up and down together, so they share one coil, which discharges when they are both at TDC so one spark is wasted during the exhaust phase while the other is used for ignition.

So cylinder 4 running properly implies the igniter is charging that coil correctly and ECU is triggering it discharge correctly.

With LS and Hemi V8s using displacement on demand systems, the lifters often fail which wipes out the cam. At first its a tick, then develops into a misfire once the cam lobe is really worn...yet they'll pass a compression check. I guess the valves let enough air in to create compression at low speed but not enough to actually run right at normal operating rpm...

Seems unlikely, but a look under the valve covers might be a good next step to ensure cams and buckets are all in order with proper lash.

 

[allezgrand]

On a scan tool you should be able to pull up misfire load %. This will show that lack of power in a % form. If its 100% then you have a dead miss and somethings wrong. If it's not 100% I'd say a compression issue.

I'm using v17 Techstream. It gives the load in units of g/rev. It shows 0.53 g/rev. To test your theory, I unplugged the spark plug from Cyl 3. It still showed 0.53 g/rev and there was no noticeable difference in how the engine ran.

If indeed it is a dead miss, it seems most likely that it is a spark or fuel issue. Then again, the fact that cylinder 4 is not missing would suggest that the only thing that could cause that would be a bad spark plug itself, which seems unlikely given that I'm on the 3rd set and I've swapped them around as well. It seems highly unlikely that it's fuel given that the miss was the same when I swapped injectors and low fuel pressure seems highly unlikely given that injector 3 is in the middle of the fuel rail and no other cylinders are missing.

It's hard to see anything pointing to an obvious cause which is an indication that there's something I'm missing. I read about a case where somebody had a similar issue and it turned out to be that the plug wire boot on cylinder 3 was arcing to the throttle body above it. I specifically checked for that in the dark, but perhaps there's some other similar issue?

My plan is to pull off the throttle body again and pull the plug on cylinder 3. If it's wet, it's probably a spark issue, in which case I have no idea where to look next. If it's not wet, I'll follow Hodgdon's suggestion and pull the valve cover and check lifters, buckets, cams, lash, etc.

Any other suggestions? Thoughts?

 

[Hodgdon Extreme]

I can't remember if #3 has a plug wire or if the coil installs directly onto it...

If it has a plug wire; you might wanna hook up a timing light to that cylinder and see what you get.

Another thought: If for some reason the #3 plug isn't making good electrical connection to the cylinder head - you'll get no spark despite the rest of the electronics working correctly. Usually, a plug having good conductivity to the head is a given... But because your situation is a head-scratcher, I'd make sure you don't have something funky going on with it.

 

[allezgrand]

Thanks for the suggestion Hodgon. The timing light is a great quick and dirty way to confirm that I'm at least getting spark to cylinder 3. And yes, that's the wire - the coil plugs into cylinder 4.

When I did the compression test, I first blew out the recess where the plugs goes in with compressed air, then vacuumed out the ridges where stuff was still remaining, then sprayed carb cleaner in the port to thoroughly clean the seat so I didn't have any leaks around the o-ring of the compression tester. Then I used anti-seize (with metal flakes) when I installed the plug, so I feel pretty confident that the conductivity is good through there, but that's a good suggestion. I'll take another look when I go in.

 

[allezgrand]

I pulled the plug again and it was wet.
I then connected the plug to the spark plug wire and used a jumper wire to connect the plug body to ground (off to the side to avoid fuel spray), then cranked the motor. The plug sparked.

Photos of the plug:

I cleaned it off, reinstalled it and started it up to find the same problem.

Maybe the timing from the ECU is bad on cylinder 3 but not 4?

I'm stumped.

 

[ill_mannered]

You have a mechanical problem. Even at 155psi of compression. It is far off the other cylinders. I recall seeing someone post here recently (maybe KrisOK) and his compression numbers were good but one cylinder had a misfire like this one does. Believe he pulled the head off and had it gone through and found a problem. You should do a leak down test as well to find out where the air is escaping.

you have fundamentally tested and replaced everything you could and you still have a misfire. Something is wrong with the valvetrain or bottom end (not likely)

 

[Thatblueis]

You have a mechanical problem. Even at 155psi of compression. It is far off the other cylinders. I recall seeing someone post here recently (maybe KrisOK) and his compression numbers were good but one cylinder had a misfire like this one does. Believe he pulled the head off and had it gone through and found a problem. You should do a leak down test as well to find out where the air is escaping.

you have fundamentally tested and replaced everything you could and you still have a misfire. Something is wrong with the valvetrain or bottom end (not likely)

That was a valve sealing issue after a valve job. That plug looks pretty oily wouldn't be surprised if you had some ring leakage causing oil to leak onto your plug causing it to run rough.

 

[ill_mannered]

Could be a valve problem. Or bottom end. It’s definitely mechanical and should be looked into.

 

[allezgrand]

Yeah, something's not lining up here. I did a leak down test a while back at 150 psi from my air compressor. There was a very slight hiss from the exhaust side, but nothing major. I couldn't feel any air coming out of the oil cap either, indicating nothing major on the bottom end. Even if there were poor compression, the plug shouldn't be wet if it's getting spark.

I pulled the valve cover on the exhaust side today and checked with a feeler gauge. Both exhaust valves on cylinder 3 were at 0.012", squarely in the recommended region of 0.010-0.014".

I ran the engine with the oil cap off and nothing more than the normal, slow expansion of coolant as the engine warms up.

I'm perplexed and I don't have the time to tear down the engine in hopes of finding something that may be because I missed something simple.

Anybody ever heard of the ECU signal pegging an ejector open on these? What about a valve guide leaking oil on the intake valve?

I have a few Techstream logs. Any suggestions for where I can post those to get another set of eyes on them in case there's something obvious that I'm missing?

 

[ill_mannered]

Did you perform the leak down test with both valves shut (ie compression stoke) if not then you should redo it.

If you did do it on thé compression stroke, and you heard air coming from the exhaust then you could have a bad seat or seal on the exhaust side.

 

[allezgrand]

Yes. Both valves were closed. It held pressure quite well. Before I got the balance right, the 150 psi pressure rotated the engine, then I found TDC and the pressure held quite well.

I pulled out my borescope today. I checked to make sure that the valves visually appeared to open and close properly from the inside (they did), then I used a 9v battery to manually open the injector on cylinder 3. Once a puddle of gas had formed in the cylinder, I brought the piston to TDC and, using a rag to absorb it, blew out the fuel with compressed air. It was exceptionally dirty with plenty of oil. I repeated this until the cylinder and top of the piston was pretty clean. Then I swapped one of the spark plugs for good measure and reassembled everything. I still had a miss on cylinder 3, so I pulled apart just enough to scope it again. Here's the oily mess that I saw:

It certainly appears that a substantial amount of oil and a bit of debris is getting in from somewhere. So before I tear it apart:

What areas would you imagine the oil could be coming from?
Piston rings
Leaking valve guides
Head gasket leak from an oil passage

Would anybody be able to show me on an image of a cylinder head where the oil passages are??

 

[Thatblueis]

Oil passages are further out. The only thing that can leak into the cylinder through the head gasket is coolant. You still need to find your base problem before you rip it apart. By manually firing the injector you know that works. Use a noid light to verify the injector is being fired by the computer. If you can get the tools an oscilloscope would be best. Next, I would pull that plug and wire and ground it out on the valve cover or head and watch it visually spark. 155psi is bad but not your problem. I've seen engines run fine at 100psi, no power but they still fire.

 

[ill_mannered]

Rings or valve seals. Is the car smoking bluish smoke while idling?

 

[allezgrand]

SOLVED!!!!

The backstory:
When I bought this car, it had a broken ignition casting and I had it towed home. The previous owner said that he had recently replaced (or had a friend replace) the valve cover gaskets. He also mentioned that the power was low at higher RPMs and he thought it might need a new VVT solenoid. After I replaced the ignition casting and I managed to start it up, it ran a little rough at first. I cleaned the MAF sensor, fixed a vacuum leak, and everything seemed to run just a small amount better. I took it to the car wash, cleaned off the oil from the previous valve cover leak, then drove it to emission testing. No problem getting there. On the way home, it started missing all of a sudden after WOT for a few seconds. When I got home the DTC's showed misses on Cylinder 2 and 3. I replaced one of the ignition coils and swapped the other and now only Cylinder 3 was missing. Jump ahead..... after lots of troubleshooting, it wasn't lining up. I had spark on cylinder 3, I had fuel going to cylinder 3, and cylinder 4 was firing.

I ran a borescope into the intake down the runner for cylinder 3 to get a visual on the misting action of the injector before I tore the engine apart. Something fuzzy was visible....

I've never been so happy to fish a rag out of an intake manifold! I put everything back together and it runs like a champ.

So apparently, the person who replaced the valve covers must have blocked off the intake manifold with a rag and somehow forgot about it (I'm guessing they turned over the engine to test something). When it was running poorly, the rag was likely still near the mouth of the intake and restricting every cylinder. When the miss started happening after emissions testing, it must have been split between cylinders 2 and 3, causing a greater restriction. At some point, it got sucked way into the runner on cylinder 3. When I tested the cylinder 3 injector and got an oily mess with debris in the cylinder, the rag was getting a nice cleaning.

I'm quite thankful to say that it's running quite smoothly now. Thank you all very much for your ideas and advice! This was definitely a very unique one...

 

[Thatblueis]

SOLVED!!!!

The backstory:
When I bought this car, it had a broken ignition casting and I had it towed home. The previous owner said that he had recently replaced (or had a friend replace) the valve cover gaskets. He also mentioned that the power was low at higher RPMs and he thought it might need a new VVT solenoid. After I replaced the ignition casting and I managed to start it up, it ran a little rough at first. I cleaned the MAF sensor, fixed a vacuum leak, and everything seemed to run just a small amount better. I took it to the car wash, cleaned off the oil from the previous valve cover leak, then drove it to emission testing. No problem getting there. On the way home, it started missing all of a sudden after WOT for a few seconds. When I got home the DTC's showed misses on Cylinder 2 and 3. I replaced one of the ignition coils and swapped the other and now only Cylinder 3 was missing. Jump ahead..... after lots of troubleshooting, it wasn't lining up. I had spark on cylinder 3, I had fuel going to cylinder 3, and cylinder 4 was firing.

I ran a borescope into the intake down the runner for cylinder 3 to get a visual on the misting action of the injector before I tore the engine apart. Something fuzzy was visible....

I've never been so happy to fish a rag out of an intake manifold! I put everything back together and it runs like a champ.

So apparently, the person who replaced the valve covers must have blocked off the intake manifold with a rag and somehow forgot about it (I'm guessing they turned over the engine to test something). When it was running poorly, the rag was likely still near the mouth of the intake and restricting every cylinder. When the miss started happening after emissions testing, it must have been split between cylinders 2 and 3, causing a greater restriction. At some point, it got sucked way into the runner on cylinder 3. When I tested the cylinder 3 injector and got an oily mess with debris in the cylinder, the rag was getting a nice cleaning.

I'm quite thankful to say that it's running quite smoothly now. Thank you all very much for your ideas and advice! This was definitely a very unique one...

Nice Glad you're good as new. Sometimes you gotta keep it simple. Air, fuel or spark.