rideredcr

Hi everyone!


Thank you for taking time to read this post. If you have any advice, I would be greatly appreciative. I have 02 S10 4x4 4.3l vin W. I developed a misfire about 6 months ago while accelerating hard up a hill. The check engine light started flashing. I won't bore you with details, but as I attempted to fix this issue I found a multitude of other issues. Long story short there is not much left on this truck that has not been replaced with new oem parts. Engine performance is much better with all these new parts but the original issue persists. Misfires are fairly equal across all cylinders with #6 about 10% higher than the other 5
Anytime you accelerate, the engine misfires (I cant personally tell its misfiring except for the engine sounds like it has a bunch of marbles bouncing around in it. I verified the misfires via my SnapOn Solus Ultra)
The harder you accelerate the higher the misfire count. WOT will set the CEL off immediately. Turn the A/C on and it will misfire moderately. With the A/C off, once you maintain RPM/Speed the misfire count returns to zero regardless of RPM/Speed


The engine has 170- 180 #s compression on all cylinders.
Leak down test was <7% on all cylinders
New valve springs
Entire Ignition system is new
Entire fuel system is new-fuel pressure is within spec
MAF is new and clean


The vehicle is drivable without setting CEL as long as you do not accelerate to hard at any time.
I've been scratching my head on this one for a long time now. Any advice (other than selling the truck) or ideas on testing components or systems would be greatly appreciated.

tech2

maybe the exhaust has a restriction..ie clogged cats. remove both precat 02 sensors from the exhaust pipe and test drive. if it clears up; that is your problem.

it idles fine as there is little backpressue at idle. once you rev it up the restricted exhaust backs up. no air out = no air in. removing the 02 gives lets the exhaust exit out the 02 sensor hole.

rideredcr

Thank you for your response. I will try. Although the restriction would have to be in the muffler. After a tune up did not fix my issue I replaced the cat with a magnaflow cat system part# #49481. The original cat internals still looked like new to me.

tech2

if it has a braided steel flex pipe; can be a source for restriction...they collapse internally.

rideredcr

I verified no blockage in the exhaust system with a boroscope.


I disconnected the battery to reset my long term fuel trims, ran it around town for a bit to warm it up and then took it out on the highway for a 30 min trip-1 way
At idle the #3 cylinder misfires
off idle to 2000 rpm there are no misfires on any of the cylinders
Above 2000 rpm the #6 cylinder goes nuts with an occasional misfire in the remaining 5
Long term fuel trim is +10 on both banks under normal driving conditions and rises to +15 if you WOT.


I did learn that when the computer detects a misfire it doesn't allow your TCC solenoid to activate which explains my poor fuel mileage and why I never detected a lack of power

tech2

at wot the vehicle is going into open loop and ignoring the 02 sensors and fuel metering is based on set programming.

fuel trim will not be accurate during misfire conditions. +10 is borderline rich

are you viewing the misfire counters on the scan tool? Just wondering how fast the rate #3 is accumulating

rideredcr

I'm viewing data on a snap on solus ultra.
#3 cylinder @idle will misfire in the range of 3-10 misfires per cycle. I think I've read somewhere that 1 cycle consists of 200 complete engine revolutions.

rideredcr

Let me make a clarification to my previous 2 posts
#3 is the only cylinder that misfires at idle.
Engine does not misfire from just off idle to 2000 rpm.
After 2000 rpm the engine begins to misfire prominently in the #6 cylinder (counts are in the 25-65 range). All other cylinders w/ engine above 2000 rpm typically misfire in the 0-10 range.

The above numbers are under normal driving conditions. If I'm pulling a trailer, going up a hill, the a/c is on, or the TCC solenoid is active: the misfire numbers listed above can almost be doubled.

SBchevyfan

When you say the entire ignition system is new, does that include the coil pack?

rideredcr

Here is a list of ignition components I have replaced:

Ignition control module
Coil
Rotor and cap 3xs
Distributor w/ cam sensor
Crank sensor w/ shim
Plug wires
Spark plugs 2xs

I'm a bit embarrassed to say I've fallen into the trap of throwing new parts at it to see if it fixes the issue.