I had this code a couple years back. It ended up being an open on the wire going to the injector. I accidentally damaged the wire when running another wire through a boot. Have you checked continuity?

Nope hasn't crossed my mind. I'm guessing ignition on multimeter set to volts test the tabs that plug in to the injector? I can tackle that this weekend when I do the vacuum hoses since a few are cracked...including the one that connects at back of drivers side valve cover ( it's near cylinder 6...hoping its just been a vacuum leak I missed).

injector plug checks out at 12 volts. Am I crazy here? I know normally clogged fuel filters and bad A/F sensors will throw codes for the. fuel system or the sensor itself normally. And when they cause misfires they typically cause random misfire ( a fuel filter has no control over which cylinder it starves, or and A/F sensor can only tell how much emissions the entire engine is putting out). However they do play a role in fuel mapping potentially. Therefore changing my old, possibly original, fuel filter along with my 10yr old, with unknown mileage in that time, A/F sensor may allow ECU to collect info that will correct what seems like a sporadic misfire.

One thing I should add that I may not have stated previously is I can now feel the shaking of the vibration at higher speeds and hold it steady till it triggers a CEL and code. But once I resume normal driving it smooths out some, but will still stumble occasionally at idles then correct again.

You replaced everything and still the #6 missfire.

Do you have any antifreeze loss?


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Is there a way to check for fuel volume? Wondering if cyl 6 is starving for fuel. Fuel line goes into the passenger side of the rail near cyl 5, then goes transfers over to the driverside of the rail. Cylinder 6 is the last cylinder to get
fuel from the rail before dumping through the regulator and returned back to the tank. Wondering if it's a ever so slightly sticking FR?
I'm just thinking out loud as you have tried almost every possible way already.

Maybe a double dose of Techron would help.


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I'll go out on a limb and suggest an Intake Manifold Leak.

Just a side thought, the original pic of the #6 spark plug looked like the gap was really small. You mentioned you changed this plug though. Maybe double check that all the gaps are within spec just to cover your bases.

@HiLife that is something to think about. And does make sense to me.

@19963.4lsr5 I have done multiple tanks of techron and Lucas prior to tackling the injectors and no changes.

@Whakeen and intake manifold gasket leak crossed my mind as well which is why I wanted to do a leak down test. No leak that I could see. Also no notable coolant loss.

Now the gap on cylinder 6 plug looks so small due to corrosion and build up from enduring the misfire. All plugs have been replaced with OEM from dealer.

Thanks for responses. I did order a OEM fuel filter and A/F sensor today. So waiting on those to come in. Grabbed another 6er of OEM spark plugs as well in case I need em. I may try @phattyduck A/F scan gauge code he uses on his 99 to see what mine is currently reading at, then if it changes once new parts are put in.

Had an issue getting the nuts off the front o2 sensor since they were rust puddles and had no shape to get a socket or wrench on. However the front o2 sensor being swapped, as well as new OEM fuel filter, as well as recleaning the MAF has yielded 2 hpr more at idle and what seems like slight improvement in fuel economy. I should also correct that since my rig is federal emission the front sensor is labeled as an o2 sensor ( i previously referred to it as a/f sensor) unlike the CA emissions which label the front as the a/f sensor. Either way the front sensor on either version plays a role in the air to fuel ratio. However I was creeping along on the freeway on ramp at about 15mph this morning and engine was misfiring and stumbling but no code thrown. Smoothed out once throttle was pushed. Still shakes at freeway speeds too. I'm thinking swap ecu at this point...what's your folks thoughts?

I'm with this guy ^^^ - unmetered air or lean misfire.
Engine Misfires - Finding And Fixing Them The Easy Way

Today I did what I'd call the poor mans leak down. Let me know I did it correct. Pulled plug from 6. Took ratchet extensions linked together and placed in cylinder 6 spark plug tube. Rotated crank pulley with breaker watching the extensions go up and down with compression cycle. Marked extensions with paint pen notating what I feel is tdc. Removed extensions and place compression tester hose into cylinder 6 with Schrader valve removed. Rotated crank pulley until I felt air pushing out the top of hose( compression stroke). Removed hose and swapped extensions in. Continued rotating crank pulley till tdc mark on extension was in sight. Replaced the compression hose and attached to my on board air (ARB compressor)...

No bubbles at radiator
No noise at exhaust tail
Hissing when opened throttle body...

Intake valve leak. Makes sense with noisy lifters I hear from drivers side valve covers I guess. But did I do it wrong?

Let's test. Removed compression hose. Dropped extensions in again. Rotated crank pulley watching them go down and back up until tdc mark is seen. Reconnect hose setup...

No bubbles at radiator
Audible hissing noise from exhaust tail makes sense since I'm now on exhaust stroke.
No noise from throttle body

Cool so now I know my head gasket is good. And I seem to have my strokes correct on the cylinder. So I put extensions back in and rotate again to tdc. Swap back to hose setup. Reconnect air one more time...

No bubbles at radiator
No noise at exhaust
Hissing when throttle body is open.

Cool so intake valves it is...unless how much room for error is there to actually not being tdc? How do I know I wasnt near tdc?

There is definate ticking from back side of drivers valve cover that follows rpms. It was pretty obvious hissing at throttle body.So I think this could be intake valve issues.

I still get engine shaking vehicle at hwy speeds felt through the driveline. I still get intermittent stumbles and misfires. Nothing consistent enough to have a code thrown though since injectors were swapped.

I've also been tracking mpg and its terribly down. 10.7mpg solid city driving tank. And 15.6 mpg solidfreeway. I'm on 285s regeared to 4.88 armored and winch upfront but I should be getting better mpgs still.

So now what? Valve adjustment?

All I can think of is disconnecting the battery for a bit to reset the ECU...

Did a leak down today with OTC tester and onboard air. Used ARB cmka12 compressor which puts out a max psi of 100 per their site. However multiple attempts at getting it to run that hard at tdc did not work. Tested a variety of psi and average 16% loss all from intake valves ( heard at throttle body). Funny part is I forgot to connect my spark plug wire, and could feel the difference but it wasn't alarmingly different then how the motor normally runs. I guess I'll do a valve job...

Also this is plug 6 again. What is building up on the electrodes? It doesn't look like oil ( which I'd expect with leaky valves) . It almost looks like over heating and ash? What are your thought.

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Confirmed with a shop today. Compression 175 (getting worse vs difference in gauges) no change with wet compression vs dry compression. Leak down again confirms intake valves. Suggests intake valves burnt or bent so head job needed but lowering of compression on cylinder with no change wet vs dry leads us to believe piston ring starting to fail...so rebuilt 5vz ordered from yota 1. It'll be February by the time it's done so this thread will go silent until then...Thank goodness @mtbtim just did a motor swap vid series.

If I'm reading this correctly, you are saying that the dry compression is the same as wet compression? If that's the case then that tells me that piston rings are in good condition. When a piston ring fails you will have low dry compression and higher wet compression (depending on how damaged the rings are). The added oil helps seal the piston rings.