MitchM

update: per my 1/2/23 post: the one time code p 452 'low sensor voltage on FTP sensor' has now disappeared. the p 0300 only showed a couple times after the f t p sensor and vent control solenoid were replaced fall 2022, but p 0300 is now GONE !! too. we're just watching and waiting to see if p 0300 is gone FOREVER. so The Independent Mechanic isn't looking at replacing an ignition control module or a PCM replacement now .

I did see a thread recently that explained that in the manufacture of modules like the fuse/relay control panel (or PCM?) , a pin can be misaligned during manufacture but not deleted by quality control. then the misaligned pin can cause all sorts of weird electric problems years later that are very hard to diagnose. there 's a thread right now on a chevy with a NO START problem. It discusses design of the Chevy underhood fuse box . a misaligned pin on the control board where the fuel pump relay plugs in can cause a current arc resulting in failure of the relay and a no start. rain water leaking into the fuse box past its cover can corrode a pin such for the fuel pump relay, and the corrosion then interferes w proper current to the fuel pump resulting in a no-start. bad pins on the fuel pump relay circuit causes all kinds of hard to diagnose electric problems ( vehicle being hard to start or no starting at all.) the owner discovered the bad pin because he saw burn marks around the fuel pump relay which he had already replaced once. )

BETurner

Hi MitchM,

Did you ever solve the issue with your van? I have a 2006 Express 3500 with the exact same issue. Throws random misfire code but runs fine. I likewise tried new plugs, wires, coil packs to no avail. No clear path forward to fix. Mine started throwing the misfire code a few years ago at about 75 mph, has progressively gotten worse to 65 or lower now. I seriously wonder about AFM, it seems to me when my engine throws the code it is trying to change regimes, almost feels like it is downshifting, but I don't believe that is the case. No issues when running at slower speeds.

mountainmanjoe

Try my suggestions mentioned throughout this topic.

For the 3rd time there is no AFM. Read the whole topic before replying.


again, measure fuel pressure. The pump might not be able to keep up at higher speeds/loads

BETurner

Thanks for the reply! I'm certainly not a chevy expert. I would think if fuel pressure was the issue, it would manifest during acceleration. But there is no issue when accelerating, where the engine is presumably at higher RPM and power than when the random misfire codes are thrown. The problem is only at speed + load, and seems to me like the engine is trying to do something. I did read the entire thread and your insistence there is no AFM, but it seems if there were AFM, this could possibly explain the behavior I am observing (I don't have any direct experience to know how AFM actually functions). Otherwise I am at a loss to explain. There is no noticing of actual misfiring. I suspected a bad sensor, but MitchM has tried to replace any and all suspects on his van to no avail. By the way, my van has an LQ4 6.0L. Great engine.

mountainmanjoe

But there isn't because that generation didn't have it. Period.
There's your LQ4 engine


so if you don't have information suggesting otherwise, you can stop suggesting it.
Waiting to hear the results of all the tests you performed

MLockheed

I think it was in 2014, when they started putting the 6.2L into the express. I may be wrong on that tho

MLockheed

all you have to do is just look at the cam valley cover which in afm engines is replaced by the valve lifter oil control manifold

mountainmanjoe

You are wrong. Vans never had a 6.2L engine

MLockheed

ya got that confused with the 6.6 my bad

MitchM

my 07 3500 express has been plagued by P0300 random misfires for going on 2 1/2 years now. (62,000 miles on it. ) starting in June 2021 to March 2022, 3 different mechanics each claimed it needed a new crank position sensor (and each blamed the previous mechanic for 'not using OEM ac-delco ' CKP parts. ) Codes P0300 and P0336 continued occasionally after each of the 3 CKP replacements. The chevy dealer claimed in 12/21 it also needed a new cam position sensor too as 'the old cam sensor OEM install 2007 and the new crank sensor (#2) installed 8/21 "don't work well together. " (It did NOT ever have a code P0341 for CKP--CPS mis match. ) So a new CPS cam position sensor was installed in 12/21. but the P0300 s and P0336 continued, the chevy dealer said 'just drive it. it's now 10/24. I've been 'driving it. ' it's still misfiring P 0300 about 1x a month only when engine is hot and only at highway speeds 65 + mph. occasionally I get the P0336 'CKP sensor signal incorrect for more than 3 seconds . ' 'it never misfires when cold, or at lower speeds.

In desperation I decided to watch every you tube that mentioned any CKP code fix. I found one
for "random p0300 misfire still occurring after a new CKP was installed ":

See: Schroedinger's Box YouTube, You Tube Title:" "New crank Sensor, Still has P 0335, P0336"

this 1/2 hour YouTube discusses his repair of a Chevy with intermittent P 300, P 335, 336 codes still
happening after a new crank sensor was installed.

author: Schroedinger's Box.

YouTube outline: he found a bad green signal reference wire to CKP and replaced it..

at 16:45 to 17:52: car ran OK cold, then mis fired occasionally at engine operating temp.

at 17:52-- when driver hits the gas, engine loses rpm s and misfires. he noted LTFT s were "suspect and high. "

at 20:00 he starts back probe of GREEN CKP signal wire.

at 20:21 he checked wires and went under the vehicle , used his light . Then ran a jumper into CKP . 3- wires are there ( GReen = the signal ref NOT the ground wire.) and also checked yellow and other wire too.

at 22:59 he is under the car using a test lite. because ' his VOM won't fit. '

at 23:40 he did a crank sensor bypass , he suggests using a scope w 2 channels.

he found the green sig wire to crank sensor 'occasionally coming loose . ' he did some more tests. he verified a it was loose green signal wire . his fix ; was to replace that green wire.

27:30 he 'believes he fixed it ' by completely replacing the hot green signal wire to CKP. he then did a crank relearn/ reset.

he says 'it is now running fine. '

He suggests to diagnose this problem with a light or a scope running 2 channels.


Questions: should mechanics test for a bad or loose green signal wire to the CKP before replacing the CKP ?

and do they then test the NEW CKP after install to see if its green signal wire is good ?

All comments welcome. ( thank Schroedingers' box, not me )

Subject: Schroedinger's Box repair of Chevy with intermittent P 300, P 335, 336 codes still happening after new crank sensor install and relearn

by: Schroedinger's Box.
You Tube Title:" "New crank Sensor, Still has P 0335, P0336"

Summary he found and replaced a bad green signal reference wire to new CKP crank position sensor..
symptoms :
at 16:45 to 17:52: car ran OK cold then mis fired occasionally at engine operating temp.

at 17:52--when you hit the gas, car loses rpm s and misfires. he noted LTFT s were suspect and high.

at 20:00 he starts back probe of GREEN CKP signal wire.

at 20;21 he checked wires --he went under the vehicle , used a light . Then ran a jumper into CKP . 3- wires there ( Green = signal ref NOT ground) and checked yellow and other wire too.

22:59 under the car using a test lite. ' his VOM won't fit. '

23:40 did crank sensor bypass , suggest use a scope w 2 channels.
found green sig wire to crank sensor occasionally coming loose . did some more tests. verified loose green signal wire . RX was to replace that wire.

27:30 'believes he fixed it ' by replacing hot green signal wire to CKP. Then did crank reset. says 'it is now running fine. '
(suggests to diagnose with light or scope running 2 channels. )