2003 CTS consitenty random misfire on bank 1 resolution
Posted to Technical Discussion Forum on 12/12/2016
13 Replies
Because it was so long ago that this was initiated and not
sure on the notification process on who replied whether they
will be automatically emailed of an update as I never posted
this in Tech help and I want to give anyone who follows this
a chance of what the cause was. A brief rundown on what was
the issue and what I was theorizing on for anyone who may be
interested , but missed the post:
The engine presented from another shop that had replaced a
cat on bank 1 in attempt to repair the misfire. I was told
that it ran better and most misfiring was gone, except for a
slight misfire on bank 1 at idle and it was random, but
would code. Cyl 1 was the main one then 3 and very rarely
you would see 5 count 1 if you let it idle long enough.
Raise the idle just a touch and the misfires would cease.
Both long terms would at zero and bank 1 ST would hold
around - 3-4 and bank 2 ST would be +2. Shop had swapped
injectors bank to bank and misfires did not move. Coils and
plugs had been replaced.
I have disciplined myself to check mechanicals first short
of a visual inspection for the obvious on misfires. Cranking
relative compression indicated nothing suspicious, however
cranking vacuum and exhaust had something to say as the vac
pulls were almost even, yet every other one had a push that
was almost twice as high. Move forward with doing an in
cylinder compression on bank 1 cyl 1 and bank 2 cylinder 6
suspecting something was going on with bank 2, and cyl 6
that may be effecting cyl 1 given the cranking vac pattern,
i.e., a little EGR effect. Found exhaust on bank 2 cyl 6 was
opening about 32* BBDC and bank 1 cyl 1 was at about 48*
BBDC. With no cam specs to go off of I informed the shop it
was my opinion that bank 2's exhaust cam was opening late.
They informed me that they had purchased the tool set to set
it up and it was correct. I returned the vehicle (it didn't
drive bad, but felt like it did not have all the power it
should have) and asked them to call me over when they had
the front cover off. I witnessed it was dead nuts on, -
ouch. I did count the teeth of the cam gear and came up with
a value of 15.6 degrees of crank rotation per tooth which
still supported my theory of valve timing. We removed the
bolt on the exhaust cam and looked to see the pin deformed
or missing, yet it was perfectly centered and square in its
alignment slot.
I retrieved it once it was reassembled and started digging
deeper. I did forward my screen shots to one of my
instructors who has taught me just about everything I know
on in cylinder testing among other things and he responded
that he did not think I had a valve timing issue causing
misfire. Re-verified all my testing and would come up with
some slightly different numbers on valve opening/closing
events but still supporting a bank to bank difference. I
then posted it here, in this forum for some more eyes on my
problem. I also put out to the shops I service, that I was
looking for one of these products to base line off of, which
I received the day after Thanksgiving. No codes, fuel trim
was actually almost identical to mine and both EVO's were in
the mid forties, so again I'm looking at bank 2 as the
culprit. While I appreciated everyones input, I have to call
out Shannon Lindsey for doing most of the heavy lifting the
entire time I was wrestling with this. He discovered that
there were multiple cam positions depending on what product
the engine ended up in along with the engine displacement
variations. I then returned the vehicle to the shop and they
removed the cam covers and discovered that bank 1 had both
exhaust cams installed and bank 2 had both intakes.
I never had a chance to hear it ,but the shop assured me
that it idled like glass and no more coding for misfires and
given I have known good from the loaner, I didn't feel the
need to get it back. The vehicle owner was pleased as this
had been to four other shops prior to the one I was helping.
Again thanks to all who gave their advice and especially
Shannon who made himself so available.
You can probably seek all the shots and uploads if
interested through the title ,but be fore warned as I'm
deeming the above as brief summary compared to all the
correspondence and details, screen shots. Feel free to
contact me if you are interested in something specific.
Paul Sanders Owner/Technician Parkway Auto Rebuilders Harvey, Illinois, USA
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