Greetings everyone it's me again. I would like to start by thanking all of you for helping clear up the CYLINDER 5 MISFIRE CEL ( SEE THREAD " CYLINDER #5 MISFIRE"). After 3.5 months of running smoothly with no issues, I get another CEL stating the #6 cyl is misfiring. I can feel the lope in the idle and I knew it was coming but I thought it would have been the #5 since that has always been the culprit but it's 6 this time. To save time everything ignition wise has been replaced recently thinking this was the cause of the #5 problem. I also have a new fuel pump and i only use name brand gasoline (ie. Exxon, Shell, Chevron, etc.) and have been adding the Seafoam, Techron Concentrate, and Berryman's Chemtool fuel system/injector cleaner. Now I don't this next part has anything to with the problem however to cover all the bases I will mention that a couple of days prior to the #6 cyl issue I replaced the straight exhaust pipe between the cat and the tail pipe with 3'' pipe. This was about a 5 ft section. I do not run mufflers but that cat is still in place, although I might need a new one. If it's the injector I would be stunned given the amount of fuel system/injector cleaner I've run through the system in the past 3 months. Also I cannot get rid of that stumble the engine has during warmup when the computer is gradually bringing down the RPM's. It takes about 2 -3 minutes of stumbling then you can hear the TB or the IAC valve opening up allowing more air in to correct the stumble. Any help would be greatly appreciated.

 

When's the last time you changed the plugs, wires, cap, and rotor?
Used dielectric grease on the plug, coil, and cap tips?
Cleaned the Throttle Body?

Stop with the cleaners for a bit, running too much isn't a good thing either, especially if it starts to break down the fuel line.

Try those listed things first as they are the cheapest and easiest and won't do anything more than help performance.

 

Check the spark plug and plug wire at #6. Inspect the plug wire for fraying in the jacket and either end to see if the connectors are broken. If the cap and rotor were an issue, the misfires would be occurring on other cylinders as well.

 

might have crud in the top of your #6 injector too. There's a small cone shaped screen in there that acts as a last defense of debris entering and destroying an injector.

If the fuel rail doesn't look clean when you pull it, go to a local school band music store and ask for a Trombone or Tuba cleaning snake. It's a flexible spring-wire cleaner with bristles that will easily bend 90* or more. The bristles also aren't as abrasive as wire or brass bristles like you'd get with a gun cleaning rod so you won't mar the rail's finish inside and lead to rusting/corroding.

 

Longshot, but if you are not running a muffler there is very little if any back pressure in your exhaust system. That means the exhaust gases are passing the exhaust valves very quickly and with no-lead gas the valve seating surfaces could be getting burned away and causing poor compression around the valve seat. I know racing engines do not use mufflers, but are being regularly torn down and rebuilt so that does not become a problem for them.
As I said a longshot but a possibility.

 

Hey Aim thanks for the tip. Yes all of the ignition parts you mentioned has been changed when I was having the #5 problem. You helped me with that one as well. This weekend I removed all of the injectors and fuel rail. I sprayed the fuel rail with 2 cans of carb and choke cleaner and the injectors as well. I got a 6 volt battery with 2 wire leads and used the current to open the injector pintle then I blew htru them in the opposite flow direction to clean that top screen. I replaced all of the "O" ring gaskets, lubed them up and reinstalled the entire system. So far no CEL and no rough idle. If I have to remove it again I will use that band instrument cleaning tool you mention. Thanks again for all of your help.

 

Yeah I heard about that too. I want to run the old school cherry bomb as a muffler but I'm getting different opinions on that as well. What do you think? Suggestions?

 

Hey VW those are all in good shape as they are new. I went ahead and checked the connections because the #2 spk plug wire had unseated itself off of the cap so I snapped it back on.Thanks again for your help.

 

How does the truck know exactly which cylinder is missfiring? Where does it get it signal from i guess is what i'm curious?

 

The fuel injection systems are sequetial, so the computer knows which cylinder is supposed to be firing. I assume that it uses the signal from the crank sensor in some fashion to determine misfire.... as there is no knock sensor......