#6 misfire, looking for experience. (1 Viewer)

[thestunts]

So within the past few months I did plugs and wires. Wires were original, woo ! Now they are new NGK. Plugs are NGK as well.

Before doing that, everything ran fine, just felt like doing it to do something. It has had a EGR code for a little bit now and O2 sensor code as well. All running fine even with those codes.

Now I have a misfire on #6. Runs rough, but runs. No smoke of any color out the exhaust. No crap/gunk under the oil cap or radiator cap. Did a cold start looking for bubbles in the radiator with no bubbles.

Pulled the plugs one at a time @ the dizzy to find that it was #6 that was unaffected. I can see spark on all plugs @ dizzy.

Checked the plugs and #6 gap was at .22, so got that back to .31 & no different.

I'm thinking fuel injector ?
maybe HG ? but at this point, no real signs of it.

Is there an "easy" way to check the fuel injector ? and/or tips/tricks to doing so ?
Is there an "easy" way to check the wiring harness ? and/or tips/tricks to doing so ?

And I'll be checking the compression tomorrow, any tips/tricks to that ? I've read on direction to remove all the plugs at the same time, then some say remove only the plug for the cynlinder your testing ...

As for as how it runs. Idles rough, as you accelerate it's still rough. If I get up to 45mph it kind of smoothes out, then at 50mph+ its rough. If I open it up I cant feel any roughness but seems like its lacking some power .. If I let off the gas while moving its smooth as well at any mph letting off.

Thanks in advance.

Thanks in advance.

 

[DIXIESLEDPULLER]

check the engine harness at the egr tubes. the heat in close proximity to the harness causes issues with the injector wiring breaking down, and ive actually seen some come in melted.

 

[elprup87]

I came across something like this when I ran the engine after a HG rebuild. I had issues with #6 and #3. My problems were that the plug wires did not deliver a good connection while in their normal position. I had the a bad wire on those two wires. My plug wires were about a year old. I had a fortunate case of borrowing a set of wires to confirm that the plug wires for #3 and #6 were not giving as good of a signal to.

If your truck was running normal before you changed plugs and wires (and didnt touch anything else), chances are that either the plug or wires are faulty.

 

[jeph]

One of the simplest ways to check the affected cyl. for the cause of a misfire without expensive diagnostic equipment is to move cylinder specific items to a different cyl one at a time and seeing if the problem follows the component. eg. move the spark plug from cyl 6 to cyl 1, if the problem is now on cyl 1 it's a deffective plug. Repeat this for the injector as well as plug wire. also check for vacuum leaks at the intake gasket near the problem cyl.

 

[thestunts]

Cool, I start digging around and swapping stuff I guess.

After changing plugs and wires, it ran fine for a few months and is now causing this rough ride and idle.

 

[RescueU]

turned up anything so far in your investigation?

 

[Bob_Garrett]

I had a very similar problem with a intermittent #6 misfire and since plugs, wires, distributor cap and rotor were all replaced 6 months ago, I assumed that it was an issue with the wiring harness. However, an initial inspection of the harness revealed no obvious issues. Also, I could not find any correlation between moving the harness and the miss.

Today, I decided that I would rule out any problems with the plugs, wires or distributor before diving further into the wiring harness. With a fresh new set of plugs in hand, I set about removing the current set. An initial inspection of the old plugs revealed no issues. Gaps were correct, all looked pretty much the same. However, closer inspection of the #6 plug revealed what at first just looked like a small mark or scratch on the porcelain insulator was actually a small hairline crack.

This resolution of the picture isn't good enough that you can see the crack, but if you look closely below the E of Denso and just about the 6, you'll see a small black spot. There is also another one on the other side. I think that is where the plug was arcing to ground.

 

[thestunts]

turned up anything so far in your investigation?

Nope ... I swapped the #6 plug & wire w/ no change.

Been monitoring the oil & coolant w/ no loss or so minimal I can't tell.

How in the hell do you check the #6 injector wiring ? I had my head smashed up against the hood ... Anyone got some tips on that ?

 

[72rockcruiser]

Is #6 the back one? I had a bad miss I coulnt figure out, and the heater valve hose clamp was broken, and just barely leaking coolant into the spark plug tube, somehow(?) causing it to miss.

 

[thestunts]

Is #6 the back one? I had a bad miss I coulnt figure out, and the heater valve hose clamp was broken, and just barely leaking coolant into the spark plug tube, somehow(?) causing it to miss.

I had a leaking heater control valve awhile back that I changed out ... Not it though as it is misses as soon as it starts up ...

Rough idle in park. While in park, I slowly pressed the accelerator today & at 2k rpm it smooths out completely, then at 2500 rpm back to rough ... While driving it doesnt do that but instead smooths out at 45mph, and anything past 50 is pretty rough & 65mph or higher its pretty nasty.

No smoke on the tail pipe though ...

All I have left to do is a compression check and/or radiator sniffer test to rule out HG.

Otherwise from all the posts I've read with similar issues ... its looking like a bad injector and/or the wiring ...

 

[thestunts]

Update: Checked compression this morning ... 180-190 across all cylinders.

Guess it's pointing to the fuel injector like most have suggested or found in this similar situation.

Can EGR cause this much trouble also ?

 

[chap79]

I went through this over the past summer and ended up replacing a bunch of stuff, including the engine wiring harness and two injectors that had broken frogs on the connectors allowing them to vibrate.

Ultimately to rule out the head gasket I would send an oil sample to blackstone-labs. When mine finally went there really wasn't any signs other than a little bit of occasional coolant loss on hot afternoons.

 

[thestunts]

I've used blackstone for years ... I've still got about a case of sample bottles I could use ... Good point though.

Thanks for the reminder

 

[grizzlygibbs]

Nope ... I swapped the #6 plug & wire w/ no change.

Been monitoring the oil & coolant w/ no loss or so minimal I can't tell.

How in the hell do you check the #6 injector wiring ? I had my head smashed up against the hood ... Anyone got some tips on that ?

This helps keep your head jammed against hood!

 

[Crawdad]

I rewired #6 injector from about 4 inches up from the injector, to about 12 inches after the wire organizer in the center of the firewall. Worked to resolve the problem. The original wire is buried in the main harness and had fried from the EGR heat. I carefully wrapped the wire bundle with insulating stuff and routed the new Injector wire away from the EGR to keep it safe.... good luck. Probably not an injector or plug issue, just a wire.

 

[thestunts]

@ Grizzlygibbs - Havn't had the allowed down time to do such a thing. But when I get in there to work on it, I'll definately do that ... just gotta "call a friend" since I don't have nice rafters like that ...

@ Crawdad - If it's just the single wire thats screwed up, I'll have to do the same ...

 

[Brentbba]

My $.02. Had what's been diagnosed as a lean idle misfire at 1-5-3 ever since a HG job January, 2010. No apparent wiring harness. Shook the hell out of it at the EGR tube. Timing fine. Distributor fine. New plugs. Ignition wires about 1 year old. No coolant in the oil but was still loosing coolant tho no leaks anywhere.

Finally gave up and took it to SD Trux in San Diego. They found a cracked head at #5. That explains the coolant. Unfortunately, it meant another HG, plus a new cylinder head. While doing the job, they found a pinched wire to a coolant temp sensor and repaired it. Finished the job and it still had the misfire. Long story short after much diagnostics, head scratching, etc. that found the ECU pushing too much fuel to the 2-6-4 cylinders and the ECU adjusting constantly causing a misfire from too little fuel to 1-5-3. Injectors are grounded to the ECU. Ultimately, they found one of those injector wires right where the pinched coolant temp sensor wire had been to be exposed causing a ground fault. They patched that wire, wrapped the harness up nicely with heat tape and she runs as smooth as when I drove it off the lot 16 years ago...if not better! Kudos to John and his staff at SD Trux.