misfire cyl #5

[tahoe nick]

Had misfire. Replaced all plugs,wires,distributor, and rotor.

Cleaned mass air flow and map sensor.

Cleared codes and ran fine for about 3/4 day. Hooked up my trailer that had crepe myrdle branches and other debris from trimming the shrubs and after only a mile nrazor two under just a little strain, miss came back and light back on.

 

[lesterl]

Run some Fuel injector cleaner thru it (some really good stuff and prepare to replace the fuel filter also), what year is your rig Nick?

 

[tahoe nick]

97. 125 k. I changed fuel filter and ran 2 cans of sea foam about a month ago. The miss went away for a day and a half after I did tune up. Then came back and light back on

 

[Ice98]

How did you run seafoam? if you tanked it then you likely did 2 things

1. cleaned out the system
and
2. stirred up more debris, which eventually made its way into your system/filter/injectors

You should always replace the fuel filter immediately after using anything like seafoam in your gas tank, its just a good idea

on the other hand, if you did 2 cans to a full 30ish gallon tank it could have also been marginally effective, as that is the severe limit of what a can will treat (I think it recommends 8gal?, cant remember)

 

[fjmichaels]

Dont forget the O2 sensors. Recently had random misfires. They occurred mainly when the weather was wet. Turned out to be a damaged wire on one of the sensors.

 

[lesterl]

Well if it is a cylinder 5 missfire, it is something related to that particular cylinder, Compression; Ignition; Fueling.

Common issues CAP, Plug, Wire, Injector.....

Compression check been done? How was #5? If low, put a tablespoon of oil in cylinder thru plug hole and retest, did pressure come up?

You said you replaced plugs, wires, and cap/ rotor, did you use an OEM ACDELCO cap/rotor? If not you may want to order one......

 

[tahoe nick]

Miss is still there. But scanner only shows codes p430 and p420. I don't have cats . it ran fine for 1/2 day then miss came back. So I know its able to run correctly,just chooses not to.

 

[AtekorSFR]

My son did a tune up on my 99 5.7L, Cap, rotor, plugs, wires, as I just purchased the vehicle. After that I had a misfire on 5. Was getting ready to pull the top intake off when we decided to check the power to the SFI. What we found is that he must have leaned on the connector to the SFI and Cyl 5 was not working properly after that. We sprayed the contacts with contact cleaner, reinstalled the cap, and now there is no problem.

 

[MO Viet Vet]

It is ok after the new parts for a while. Then the miss comes back. Like lesterl said, what is compression both dry and wet? But what I am really interested in is the condition of #5 plug compared to the others and what does it look like when you take #5 plug back out when miss returns?

 

[Randy911]

The popit valves used in this FI system are, well, garbage really. Sounds to me like you might have one stuck closed. These things protrude into the combustion chamber and are located in a very prone position. I ran seafoam through mine and had similar temporary improvement. I recently installed the Borg Warner MPFI conversion kit and it cured ALL ills.

 

[lesterl]

Correction Randy, the poppit valves protrude from the intake manifold to just above the Intake valve, they are plastic and would melt/ explode if they were in the combustion chamber..... My Original poppets are running fine at 300k miles.....

 

[Randy911]

Agreed about their location. Maybe I should have said they protrude CLOSE to the combustion chamber. That is great that yours are still in working order as mine were a mess. I had one stuck OPEN for cripes sake.

I am not here to cause undue stress, I am not here to lead anybody in the wrong direction. The fact that GM extended the warranty on this jewel of engineering excellence should speak volumes as they didn't want to do ANYTHING under warranty back in the day (rhetorical). There was a massive recall wherein these valves were cleaned at no charge, or replaced. The biggest issue I see, is that the internet is FULL of articles about these vortec's with the "random misfire code", driveability issues, no start issues, no start in rain issues. I had all of these, and I very specifically spoke to everything I did to alleviate the issues, the ONLY thing that worked was to replace the poppets with the MPFI kit. If this helps anybody then I consider it a service. Every situation is different, this is only my story based upon my experience and research.

This is a huge issue for these vehicles (1996-2003). A stuck poppet will cause misfires, no start issues, and reduced power. Understanding how the poppet works, the engineering, the prevailing bean counter attitude at GM are a must IMO. Then when you look at the the conversion to MFPI the benefits are obvious. Whatever ills were prevalent in the poppet valve tech are fixed in the reboot to MPFI.

I MUST ADD!!! I am in a locale that uses RFG which has been known to accelerate the gumming of these valves.

GM issued a recall (99066F) on 1996 to 2003 CSFI systems, and extended the warranty to 10 years or 200,000 miles (whichever comes first) to cover problems with the poppet spray nozzles. The recall covers free injector cleaning and/or replacement as needed to correct driveability or emissions problems.

GM Technical Bulletin #00-06-04-003B spoke to un-sticking poppets...with compressed or high pressure nitrogen......??.

My experience was confounding, now that I have installed the conversion I truly feel like I am driving a new vehicle.

 

[lesterl]

I plan on getting the upgraded MPFI kit when I get all the other stuff straightened out, but for now.... they work fine....