Cyl 6 misfire only at idle (1 Viewer)

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OklahomaOvrland

OklahomaOvrland

Joined
Jul 12, 2016
Threads
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Location
Oklahoma City
I have checked spark plus and tried 3 different coils. I get a misfire at idle only. It is not bad enough to throw a code most of the time but is a rough idle.
About 2 weeks ago I replaced Cyl 5 coil pack due to code and flashing check engine light. I suspected low fuel pressure due to it seeming like if was not getting enough fuel to start and stay running on the second start of the day, several days in a row. Replaced the fuel filter and ran Techtron in the next tank of premium. When I replaced the fuel filter I rinsed the engine bay to deal with any spilled fuel. On start it threw a P0300, P0306, and the c1201 code on the abs vac circuit. I cleared the codes and changed the Cyl 6 coil pack. It’s only thrown those codes once since. It was at a red light. No flashing check engine just rough idle.
Today I swapped in another coil pack and watched the live pids for misfires on my scan tool. Right after start it is still picking up misfires on Cyl 6.
Anyone fought a problem like this? There are no obvious vacuum leaks.
 
I'm chasing a similar cylinder 5 misfire. I've been super busy at the shop wrapping up a few projects before the holiday closure but going to go in while it's quiet and do some diag.

In my case I have had a slowly progressively worsening miss that wouldn't throw a fault. I first thought it was a bit of driveline play or trans shudder as it only happened on a slow accel from a stop. within a few days it would occasionally mis at idle and continue to about 1600 rpm in first gear.

Last weekend I had a little time and swapped coils; no change. Swapped plugs; no change. Even swapped injectors; no change. I have finally been able to log live data, thought techstream is a bit slow with its live data; and I finally got a misfire to register on cylinder 5. The only component that is not up to snuff seems to be the MAF as it will read below the min suggested 4.5 g/sec. I find it odd, and hard to believe that only one cylinder would register a mis from a faulty MAF.

Dynamically, an intermittently faulty reading MAF makes sense though since the mis is random and intermittent itself. It will run like a rapped ape for a period of time, followed by running like pooh the next. The only other intermittent low load fault could be in the fuel pump ECU delivery, but the numbers look to be well within spec at all times. And again, a faulty ecu/ecm can't cause a single cylinder fault. Fuel delivery would cause a random/multiple misfire fault, like I would assume the MAF "should" too.

An intake leak at that cyl might suggest a possible idle/low rpm miss as at higher rpm/load could result in more fuel and air to overcome the leak. But the intake runner were sprayed with a combustible and resulted in no change of rpm at idle.

Once I get some time to get into the shop to continue to diag and probably a smoke test, I'll post up if I come to a conclusion as it may help guide you along.
 
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So I may have isolated my idle/low rpm mis. Probably won't help your situation, but I just learned today that I am a moron!
I went off 25 years of working on german marques with every one of them having the same cylinder configuration.
I was very unaware that Toyota happen to have an even and odd cylinder/bank configuration. My diag was going nowhere
and out of the chance I could be wrong in assuming what I was accustomed to all the years I decided to search Mud and sure enough
I discovered to never assume.

I'll follow along with your diag and maybe I can offer some direction.
 
Fuel pressure? Any of you verify with a gauge? Sounds like most of the basics have been covered already. I've had bad fuel pumps give me lean codes and multiple cylinder misfire issues, not just 1 cylinder though.....if fuel pressure checks out I'd be running compression test next..
 
Moparsncruisers said:
Fuel pressure? Any of you verify with a gauge? Sounds like most of the basics have been covered already. I've had bad fuel pumps give me lean codes and multiple cylinder misfire issues, not just 1 cylinder though.....if fuel pressure checks out I'd be running compression test next..
Click to expand...

True, but looking into Techstream live data and injector duty cycle will show a pressure drop, if the numbers are out of range. And, fuel pressure/pump pressure should/would typically result in all cylinders misfiring. Duty cycle should rise and fall with the MAF signal, any deviation would point to pressure loss.
 
Also, there is one knock sensor per bank. Could it be related, maybe? If it were a single cylinder mis then no, not likely. But a full bank, possibly.
Should throw a fault though. Small vac leaks ( inj cups, mani gasket, etc) can be overcome by inj DC. My injector seals leak like a sieve but has no effect on idle or mis. You'd have to have a big leak.
 
I think I’m at the point of looking at the possibility of a timing jump. I did it 60,000 miles ago with quality parts. But I guess it could have happened. On my last drive today I had a couple of misses on 4 a ton on 6 and quite a few on 8. I’ll get the injector duty cycle pids added to my live dashboard on my scan tool and see if I see anything up with that.
Compression test is on my radar.
 
Moparsncruisers said:
Fuel pressure? Any of you verify with a gauge? Sounds like most of the basics have been covered already. I've had bad fuel pumps give me lean codes and multiple cylinder misfire issues, not just 1 cylinder though.....if fuel pressure checks out I'd be running compression test next..
Click to expand...
Failed to mention that I also replaced the fuel pump.
 
I've been seeing some D vibration and some misfires lately (multiple 4.7L). They seem, to be fuel related.
In one:
Coil swap and new Denso coil. DTC did not move, and came back.
New plug, same.
Check spark, comparing look, with good firing cylinder. Looks good.
Check compression while plug out. Good.
Use NAP gas to check for vacuum leak, for change in idle. None.
Pulled injector wire housing block. No change in idle. Confirmed by pulling injector wire, from cylinder without issue. Idle drop.

Having 4 backup fuel injectors tested, cleaned and rebuilt now. Will be replace bank one's FI.
forum.ih8mud.com

When to Clean or Replace fuel injectors

Please post your experiences and thoughts on the subject. I’ve been considering cleaning or even replacing all 8 fuel injectors, is this wasting time and money. I understand keeping fuel injector clean by adding a can of additive to the gas tank, now & then, is a good practice. This keeps them...
forum.ih8mud.com forum.ih8mud.com
 
2001LC said:
I've been seeing some D vibration and some misfires lately (multiple 4.7L). They seem, to be fuel related.
In one:
Coil swap and new Denso coil. DTC did not move, and came back.
New plug, same.
Check spark, comparing look, with good firing cylinder. Looks good.
Check compression while plug out. Good.
Use NAP gas to check for vacuum leak, for change in idle. None.
Pulled injector wire housing block. No change in idle. Confirmed by pulling injector wire, from cylinder without issue. Idle drop.

Having 4 backup fuel injectors tested, cleaned and rebuilt now. Will be replace bank one's FI.
forum.ih8mud.com

When to Clean or Replace fuel injectors

Please post your experiences and thoughts on the subject. I’ve been considering cleaning or even replacing all 8 fuel injectors, is this wasting time and money. I understand keeping fuel injector clean by adding a can of additive to the gas tank, now & then, is a good practice. This keeps them...
forum.ih8mud.com forum.ih8mud.com
Click to expand...
Looks like my bank 2 fuel trim is setting at above 9% at idle. It is the same on both sides while driving. Reading some of your other injector threads that is sounding like injectors may be the issue. What do you think?

IMG_0461.png
 
I like to see RPM & MPH w/LTFT & STFT. On HWY ~65 MPH steady (no hills, no change in RPM or MPH)

I'd, also go through all I did above in post #12. Gathering all the clues first!
 
I don't think -9% LT is causing your misfire...sure it's taking away fuel, MAY cause a rich code eventually but not taking enough fuel away to cause a miss......at least I don't see it.
 
Tried so far.
1. Fuel Filter and then pump
2. Multiple coils including known good coils from opposite bank.
3. Tested for vacuum leaks with unlit torch.
4. New spark plug.

Remaining tests to be tried.
1. Swap fuel injector to other side.
2. Check timing marks on belt to see if jump has happened.
3. ????????????

Any other suggestions?
 
OklahomaOvrland said:
Tried so far.
1. Fuel Filter and then pump
2. Multiple coils including known good coils from opposite bank.
3. Tested for vacuum leaks with unlit torch.
4. New spark plug.

Remaining tests to be tried.
1. Swap fuel injector to other side.
2. Check timing marks on belt to see if jump has happened.
3. ????????????

Any other suggestions?
Click to expand...
Yes.

First I'll say, I've seen many bad Denso coils and spark plugs, from Parts stores. I suspected, their returned bootlegs. So many, I now only buy direct from Denso distributors or Toyota.

Make sure wires to cam & crank sensors in good working order.

Check spark. Hold coil w/plug in it, to a ground. Watch for spark. Compare with good cylinder spark. While plugs out check compression.
Note: kill fuel pump power (*safety & no extra volume in cylinder), by pulling EFI fuse. Hold gas pedal down, opening throttle body butterfly fully. So air not restricted. Also make sure, air not restricted in air pipe/box.

Pulling wire housing off fuel inject. To see RPM change or no change. Difference from a good cylinder, points to injector. No RPM change, very likely bad fuel injector or wire to. But, if a bad wire, should see DTC.

If everything checks out as good. I'd check T-belt.

Check fuel pressure & leak down. BTW: Long crank to start, is typically leaking fuel injectors, in a well turned engine.

If all good still issues. I'd back check wire to and ECM also crank & cam sensors..
 
Last edited:
Compression test solved the mystery. 55 psi on Cyl 6.
 
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