NEED HELP with misfire

[fubar62172]

I have a 99 2500 truck..i'm have a misfire on cyl 1..plenty of spark and compression. No vacuum leak. Pulled off valve cover and spring,rocker and valve ok..installed new fuel injector...still missfirring!!
What am I missing???
Thanks

 

[SportRam00]

What does your spark plug look like (oily, ash covered)? Did you try swapping the wire with cylinder 2 to see if the wire is bad? What does your cap/rotor look like? Any vacuum leaks? Did you check your plenum gasket for failure? Burning coolant or oil at all?

Just some things to check...

 

[dudeman2009]

Sportram has a good list to start, but I'd add swapping the cyl 1 Spark plug and wire with cyl 4 or 6. It's rare but I've experienced in newer cars cyl 2 acting up and throwing codes on cyl 1. So 8 never assume the cylinder across the engine to be good since they are so close on the crank and can affect each other more.

Might not be an issue on these older trucks with real crank shafts, but I won't dink around with it anyway.

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[fubar62172]

What does your spark plug look like (oily, ash covered)?
Wet
Did you try swapping the wire with cylinder 2 to see if the wire is bad?
Yes..didnt follow
What does your cap/rotor look like?
Only month old just did another full time up..same issue
Any vacuum leaks?
Nope
Did you check your plenum gasket for failure?
Not yet
Burning coolant or oil at all?
Has always burned about a at between oil changes

Could it be computer related?

 

[Yeret]

If the plug is wet, it will short and not fire. Replacing the plug will temporarily fix the problem but obviously the only real fix is to fix whatever is causing the plug to become wet.

When you say wet, is it wet with oil, gas or coolant? If you're not sure, post a picture of the plug. A picture's worth a thousand words, especially when it comes to spark plugs. If it's wet with gas, it's easier to tell by sniffing it since gas tends to have a rather distinct scent.

 

[dudeman2009]

How much oil does it eat? If the plenum is bad right near cyl 1, it can allow oil to get sucked into the cyl and foul the plug. Usually it's cylinders 7 and 8 that have that problem, but any cylinder can be affected.

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[fubar62172]

How much oil does it eat? If the plenum is bad right near cyl 1, it can allow oil to get sucked into the cyl and foul the plug. Usually it's cylinders 7 and 8 that have that problem, but any cylinder can be affected.

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about 3/4 a quart between oil changes

 

[fubar62172]

If the plug is wet, it will short and not fire. Replacing the plug will temporarily fix the problem but obviously the only real fix is to fix whatever is causing the plug to become wet.

When you say wet, is it wet with oil, gas or coolant? If you're not sure, post a picture of the plug. A picture's worth a thousand words, especially when it comes to spark plugs. If it's wet with gas, it's easier to tell by sniffing it since gas tends to have a rather distinct scent.

gas

 

[fubar62172]

Mechanic just did a full tune up and ran fine...hooked up scanner to clear code and truck wouldn't register it (did before), he disconnected battery to clear code...went to start and misfire is back!!!
What am I missing???
Am I looking at a computer issue on truck?
Thanks

 

[fubar62172]

Can I get a used computer and install in truck or will it need to be programmed?

 

[dudeman2009]

I highly doubt its a computer issue. You'll have to have it programmed, but most places that sell them will program them if you supply the VIN.

Are the spark plug wires crossing or touching? They shouldn't be unless they're ultra thick insulation. Check the offending cylinder spark plug wire for white ash looking deposits.

Try this, while the engine is running pull the fuel pump relay and let the truck die. Pull the offending cylinders spark plug, spray carb clean or seafoam into the cylinder. Let it sit for a minute or two. Crank the engine for 5-10 seconds then reinstall the spark plug and fuel pump relay. Start it up and let it warm up. See what happens. If it improves, seafoam the thing and replace the plenum gasket. If not, you might be looking to replace the spark plug wire.

 

[fubar62172]

I highly doubt its a computer issue. You'll have to have it programmed, but most places that sell them will program them if you supply the VIN.
its really the only thing left to try except plenum gasket everything else has been replaced

Are the spark plug wires crossing or touching? They shouldn't be unless they're ultra thick insulation. Check the offending cylinder spark plug wire for white ash looking deposits.
not touching and not deposits

Try this, while the engine is running pull the fuel pump relay and let the truck die. Pull the offending cylinders spark plug, spray carb clean or seafoam into the cylinder. Let it sit for a minute or two. Crank the engine for 5-10 seconds then reinstall the spark plug and fuel pump relay. Start it up and let it warm up. See what happens. If it improves, seafoam the thing and replace the plenum gasket. If not, you might be looking to replace the spark plug wire.

Ill try this


Thanks

 

[SportRam00]

I highly doubt the computer is bad. A bad computer would manifest itself in other ways... and is an awfully expensive part to throw at a problem. Are you sure that the injector you replaced was the correct model/type and that it was good? Could be the injector is leaking or sticking open and flooding that cylinder with gas. Try swapping injectors with another cylinder and see if the miss follows. Also, double check your wiring for that cylinder (spark wire and injector wire) and make sure it isn't grounding out anywhere.

 

[fubar62172]

I highly doubt the computer is bad. A bad computer would manifest itself in other ways... and is an awfully expensive part to throw at a problem. Are you sure that the injector you replaced was the correct model/type and that it was good? Could be the injector is leaking or sticking open and flooding that cylinder with gas. Try swapping injectors with another cylinder and see if the miss follows. Also, double check your wiring for that cylinder (spark wire and injector wire) and make sure it isn't grounding out anywhere.

Mechanic did a full tune up , went to start it and it started right up and sounded great with no skip, went to attach scanner to clear the code and for some reason the truck would not reconise the scanner ( like it already has prior )..he could read but not change anything...so he disconnected the battery to clear the code...reconnected and started and misfire was back
Only thing I can think of is computer

 

[Yeret]

Hmm, if the computer won't connect to a scanner, it could indicate an issue with the diagnostic module which warrants replacing the unit. However, it's not impossible that the scanner used was indeed unrecognizable. My folks had an '04 Expedition that had a misfire and they took it to a dude's shop. He had one of those multi-thousand dollar scanning tools and the Expedition wouldn't recognize the scanner. However, I went and hooked up my two hundred dollar scanner and it worked just fine...

Have you switched the plug wire with a different cylinder? If the misfire moves, you've found your problem.

Also, have you re-routed your plug wires via the TSB? If you're using 10mm aftermarket wires, this isn't so much a problem, but most replacements are 8mm and they tend to crossfire if they run parallel to each other.

Finally, what plugs are you using? Anything other than plain ole copper tips can cause plenty of running issues on these engines.