Missfire - cylinder 4

[WICruiser-97]

I have a 1997 5.0 L Votec with the spider fuel injection system.

The engine experienced a lower intake gasket failure that filled the crankcase with coolant and then sat for 6-7 years.

I rebuilt the engine, replaced the fuel pump/sending unit, fuel filter, and all of the typical tune up parts (cap, rotor, plugs) and it runs/drives. It had a tendency to have a light load misfire, not at idle but slight uphill grades at speed, and occasionally on acceleration from a stop but the only code was related to CMP Offset. Now I have the CMP Offset adjsuted the missfire seems a little worse and it therw a code for cylinder 4 missfire.

I suspect that the injection system is still dealing with issues related to the long term storage, only about 130 miles so far. However I am concerned that from other posts I have read the injection system may need to be replaced.

I would appreicate any insight from others if fuel injector cleaners have helped this situation or if I should just bight the bullet and replace the injection system.

Replacement systems appear to fall into 2 categories - original or retrofit.

I would also appreciate feedback on which route others have taken if they replaced their injection system.

 

[Schurkey]

Virtually everyone on this forum with an opinion, says to use the upgraded electronic injector spider, rather than the poppet-valve spider.

I would use the electronic-injector unit. However, I've never owned a small-block Vortec so I have zero actual experience here.

The single downside to the electronic-injector system is that it supposedly benefits from updated computer programming according to one member--it's not "really" a 100% compatible upgrade. Maybe 95% compatible, even though GM says it's validated.

Have you verified the spark plug, plug wire, distributor cap (and rotor), and cranking compression pressure? There's more than just fuel that can cause a misfire.

 

[WICruiser-97]

Other than the plug wires other ignition related parts (spark plugs, distributor cap and rotor) are new. However, the code only appeared after I had done work on the distributor that would have moved, but not disconnected cylinder 4 spark plug wire. I plan to recheck the wire connections etc.

I am thinking it is fuel related because the miss only appears to occur at light load accelleration. At idle, and heavier acceleration no miss is evident (seat of the pants determination).

Prior to this episode I was dealing with a CMP code and while there were no misfire related codes there was a similar seat of the pants misfire detection under light load acceleration. I hoped it was related to the CMP offset not being set but it may have just been masking the problem.

 

[WICruiser-97]

Cleared the code and have driven it multiple times without code returning.

However, it does seem to be running rough at time and a little sluggish.

Considering if it may ba an EGR problem. I have had the EGR valve off multiple times to resolve EGR pintle codes, finding metal pieces that appear to be from the replacement EGR tube that runs from the exhaust manilfold to the from the of the intake.

I will disconnect the connector to see if it affects the run quality but if the valve is leaking exhaust gas into the intake that may not make a difference. ALso concsidering plugging the port in the valve that does not have the pintle so that no exhaust can get into the intake but not sure how to do that in a way that can be undone easily.

 

[Schurkey]

Defeating the EGR will set it's own code(s). Also promotes detonation if the EGR is not removed from the computer programming.

If the EGR tube is coming apart, you'd best look into a replacement. I'd expect exhaust leaks as the tube fails. Dorman had them for the small-blocks; the big-block tube is no longer available except as a Treasure Yard find so far as I know.

Have you tried a fuel-injection cleaner to potentially remove deposits from the injectors? I dump a bottle of Chevron Techron Complete Fuel System Cleaner in the gas tank at every oil change, (6000--13000 miles depending on vehicle) and most of my fuel fills are with Top Tier fuel having additional detergent compared to EPA minimum levels.

 

[WICruiser-97]

I realize disconnecting the EGR will set a code, just a test to see if the performance changes.

The EGR tube is new, not sure why it is shedding materials into the valve other than if it was not cleaned after build. I am blaming it on cheap aftermarket parts for now. No leaks detected. The pieces were fairly small and appeared to be from cutting the flex tubing.

I did run one bottle of Techtron through with the first fuel installed after the tank was emptied to replace the pump. I just added a second bottle to see if that will help. I am also using Top Tier fuel.

 

[WICruiser-97]

Still no codes but it seems like there is a missfire or at least poor combustion happening occasionally, primarily at ligth-moderate accelleration. Seems to clear up it I accellerate faster and/or get the rpms up.

I still have not tried to disconnect the EGR, trying to get a consistent picture of the performance to compare when it is disconnected.

 

[WICruiser-97]

Disconnected the EGR and it set a code immediately (as expected).

Seat of the pants it seems to run better but do not want to leave the EGR disconnected such that "service engine soon" light is on.

Removed EGR valve and it appears that the is a leak across the gasket by[assing the control provided by the valve. It isn't much of a leak path but maybe under some intake vacuum and exhaust back pressure conditions it is enough to cause a problem. A new gasket will be installed to see if that changes anything.

 

[WICruiser-97]

Replaced the EGR gasket but no real change in performance. I did check and the only code set was related to the EGR and it was cleared and did nto return (EGR valve connection restored).

I am convinvced given the incosistency of the problem that it is related to the injectors but for now I am going to let it go and see if it gets better or worse over time.

 

[GoToGuy]

The old pooppet injection system may have been good in its day. But Much better is the new upgrade. You did all this major tune up good decisions. Did you think about replacing the O2 sensors, all 4 could be old and tired. And are important as the pcm looks, adjusts mixture through O2 sensors.