MitchM

I'm going to run a temperature test on the cat con this weekend. we'll see what the difference is between inlet upstream of the cat and its downstream out let temp. not going to think about taking off the pipes just yet, we'll see what the temp test tells me.

Kael

Think '03 and later is much easier, not a big deal on my '05 other than rusted this and that.
Plan doing O2 sensors as well.

I had the same issue (P0300) and found a clogged cat. Replaced, still doing the same. At highway or 50+, when the code starts, can't tell any difference in the sound or response of the engine. I plan on chasing the crankshaft sensor, forget the "proper" name. It is what triggers the code, checks the speed of the crankshaft very closely to determine a misfiring cylinder. Unfortunately, P0300 means "random misfiring cylinders". Very helpful. The timing of the crankshaft is unique to each engine.

The sensor can be replaced, BUT, after doing so it has to be "re-learned", a procedure that can only be done by a really expensive GM-specific scanner, which takes 5 minutes. Mechanics may have this, one quoted me $170 to check the sensor and re-learn.

F Y I

MitchM

before you spend the bucks on the o 2 sensor ($150 plus labor )and/or a CkPos Sensor relearn (which cost me over $200 , plus 100$ for 3 re learns ) do the following : check each plug for fouling and each plug wire for continuity and no corrosion. ( if those were the case, you'd expect a P0301,2 3 4 etc code not a random misfire on all cylinders. ) put a good OBD reader like an ACTRON on and get some 48 freeze frames both at idle and at highway speed. (my ACTRON OBDII was showing an intermittent weird B1s2 sensor 'offline' code --but no o 2 sensor code --maybe had a loose wire on one o 2 downstream sensor, possibly causing my fuel trims to be showing some LTFT % unusual ratios and weird distributor timing from 2 to 18 degrees ) . currently investigating these. ) . the position of the o 2 sensors on my van makes it hard to get to them . and the 6/21 o 2 B1s2 downstream garage-installed sensor might have been improperly installed or come loose w w a intermittent loose wire. so I need to crawl under yr (cold) van, w or without rhino ramps, and check that no o 2 sensor wire is visibly abrading on something and that all o 2 sensors are screwed in tight. . also check yr distributor cap for crack . run some seafoam thru engine . clean you ecu ground.

some posters on internet boards recommend running CATA CLEAN or the DURATRON catalytic converter cleaner thru for a tank or 2 of gas, to see if the p 0300 goes away. ( sometimes it does. ) the catalytic converter ODB codes are set by the manufacturer to throw a cat lytic converter malfunction OBD II code.at a certain loss of cat con efficiency. my theory is that a partially clogged cat converter is causing the exhaust gases to not escape properly from the cylinders and this results in crazy signals to the ecu and the p 0300 code , not a cat con code or o 2 sensor code. the hot burn of the CATALYTIC CONVERTER CLEANER may take some clog out of the catalytic converter and reduce the back pressure . so I just bought some it, it is a lot cheaper to run a couple tanks of gas w this this cleaner stuff than to replace the timing chain for $1400 which is what my chevy dealer is proposing. (Curiously - the chevy dealer REFUSES to oscilloscope my van running hot and coding, OR to look at my ACTRON frames at idle and WOT. Curiously, I cannot replicate the p0334 code they claim they found (p0334 = cam pos sensor/ crank pos sensor mismatch- code which THEY claim they saw, to justify their proposal for a $1400 12 hour timing chain replacement. more on this curious circumstance LATER. ) stay tuned, I just bought scannerdanner's engine diagnostics manual after watching all his you tube videos. ) )

MitchM

update : now suspect this dealer timing chain stretch diagnosis is COMPLETELY WRONG.

local chevy dealer replaced cam position sensor 12/21, relearned etc $500. then said it was "still throwing codes p 0300 and p0334" " and said it 'needed a new timing chain.' b c " they found it was throwing 'p 0300 and P 334 codes. ' their estimate $1600 which I did nt have. plus also recommended to replace all the cat converter o 2 sensors (2 of which were pretty new--replaced by them . and note NO no o 2 sensors were throwing any codes either. )

dealer said it was safe to drive, come back when I wanted to spend the $$$.

drove It and recorded codes w my bosch actron. curiously I found NO stored p 334 code chevy dealer claimed. whatsoever. it was a p 0336 " which sets when p c m doesn't receive crank signal w/in a few seconds. "

a really good independent shop run by a master asc tech says next step is NOT timing chain replacement, but to to check crK position Sensor wiring and connector pins and voltage and resistance, they suspect weird waveforms may be due to intermittent interruption of primary current. . ' check the pins one may be shorting, check the green wire , is it making bad contact . ."


did the chevy dealer do any of that before giving me the wrong p code and diagnosing a $$$ timing chain replacement ???

more on this later . needless to say I've totally lost faith in the chevy dealer . . .

MitchM

NEW INFO on active fuel management problems causing p0300 s in a lot of models:

I got this from my independent mechanic. it did not show as a TSB to me, for my express 3500 using the online tab search in this forum. .
ask your chevy dealer for a copy of their tech service bulletin 10/15/2018 #P P4138R SES , misfire, DTC P 0300 , engine noises.
then see if your chevy VIN has ACTIVE FUEL MANAGEMENT.

"in certain Chevys from 2002 to 2021 , the AFM system shuts off fuel to 2 cylinders to save gas. the 2 shutoff cylinders don't get enough oil lube. loss of proper lube leads to big expensive mechanical problems. " (this is especially more of a problem if you dont change oil at recommended intervals or keep oil topped up. ) poor design of the AFM system has led to expensive repairs including failed lifter, damaged camshaft, destroyed cam lobes, even bent intake pushrods reported on various boards of this chevy forum..

there have been KNOWN poor - design mechanical issues on chevys with the AFM systems , reported as early as 2012 on this board for models with AFM. complaints are continuing as recent as thru sept 2021 even on young engines with only a few thousand miles..

symptoms: noise. valve train 'tick. ' chirp, squeak, or squeal. noise may increase w increasing load from idle. or may occur only at high loads or rpms or speeds. or noise may not occur at all.

AFM may cause lack of lubrication to the 'resting cylinders.' ' lack of lube to them may result in prematurely worn camshaft lobe or lifter roller. sticking valve. valve leak. broken valve spring. OR collapsed AFM lifter. some P0300 reports are as early as 2012 on engines w low miles miles. other engines start having problems at 60-80,000 miles .
the notice includes express vans 2002-2018, savannas, sierras. . .

determining how much damage an AFM caused, then fixing it is a lot of labor and expense, so my independent mechanic says.

as of 5/10/22, van is still throwing a p0300 . it's still idling and running fine, no excessive oil consumption, no noise, no loss of power. shows p0300 steady under high load at highway speeds especially when going up a hill. LT fuel trims look pretty high to me , that's the only odd thing in the ACton's live data.

more later, as the Independent who found this secret TSB thinks about what to do given the SI diagnostic options discussed.

trying to check which chevys have the AFM is nigh impossible and the chart of year and models in this TSB isn't specific in the updated P4138R of 10/15/2018. this was 'an update to PIP4138Q' which chevy says to now discard.

this is our family's 13th chevy/GM and 2nd express 3500. -- and the one we've had the most trouble with.

Triaged

I don't think GM ever put active fuel management on the V8 vans. I don't know anything about the new direct injection 4.3!

mountainmanjoe

They didn't. We already went through this at the beginning of this thread, and now we're back again.
He still hasn't told us which engine he has, but I think the only gas option for a 3500 in 2008 was the Gen III LQ4 6.0L.
Gen III engines do not have AFM.





He still hasn't mentioned trying the basic troubleshooting that was suggested to him since the beginning
vacuum leaks
fuel pressure
visually confirm spark
fuel injector test
exhaust restriction

MitchM

in fact Joe I have done all of the following you and everyone suggested . and have about $1500 of bills to show for it at 2 independent mechanics and my chevy dealer: 56,000 miles . p300 shows up under load at 60mph going up hills. doesn't show at 25-50 mph .

oil religiously changed every 4-5K miles and kept topped up. 1st mechanic did tuneup. no exhaust restriction. no vac leak. fuel pressure in range and good, checked sparks all fine, did wire continuity check fine, put in new plugs and wires anyhow. injectors tested fine but professionally cleaned by mechanic anyhow. crankshaft position sensor replaced and relearned, p300 code went away for a couple months to 9/21. came back driving 70 mph up hills. relearned CkPosS 2nd time, check and all grounds were cleaned and fine. no problem w CkPosS wire . no ecu codes. p0300 code went away til 12/21. i'm running OBDII live data from 6/21 to 12/21 , nothing was unusual in my live data or those by 2 mechanics. mechanic 1 had oscilloscope, could not see any cylinder misfiring . none of the 3 mechanics saw anything unusual. chevy dealer thought new cam shaft pos sensor needed, put that in 12/21 . refreshed w latest software. p0300 went away til march 2022 . I saw no unusual live data from dozens of runs over 6 months from 6/21 though 5/22. cat converter throwing no codes, and no o 2 sensor codes ever show . on 3/22 #2 mechanic examined crank sensor pulled it a 3nd time, verified AC Delco , housing cleaned of corrosion around tone ring, relearned CkPosS again . P300 code went away til 5/22 . more live data 3/22 to now show fuel trims and fuel pump pressure still fine . then of 5/10/22 when it started throwing p0300 again.

I tried all your suggestions, Joe, and those by 2 independent mechanics and the chevy dealer . I'm trying to avoid a $1400 timing chain replacement . we've all about run out of ideas.

note please my 2nd mechanic was the one who supplied me 2 days ago with the 2 chevy P- printouts on the a f m possibility which I quoted above. it took me 1/2 an hour and three phone calls on the phone w my chevy dealer to MY whether my express 3500 engine had a f m -- BECAUSE GM' P #d documents I quoted from above , as supplied by my mechanic, claim that SOME chevy express vans have a f m. Joe apparently has access to better data than my mechanic who's been in business since 1954 does. ( or what I can find as a mere loyal 13-time GM/chevy owner family, trying to get info from GM and my dealer. ( no reason to yell at me, Joe--I'm just quoting what the GM chevy's a f m documents they make available to average human beings like me and my mechanic say. )

i

mountainmanjoe

Nobody is yelling. But you waste people's time when you leave out the vital information.
Did you run a cylinder compression test?

If your mechanic of 70 years knew what he was doing, he could tell you in 5 minutes if you had AFM by just look to see if the equipment was there on your engine. But really the VIN digit 8 is all you need.

MitchM

chevy 07 3500 express, v8 vortec, no AFM. 57,700 miles. previous issue" P 0300 DTC 'random cylinder misfire' 'confirmed' , and intermittent since 11/20 . p0300 code thrown only after driving 1/2 hr at highway speeds 60 mph +, code throws when going up a steep hill at high speed. ( No p0300 ever thrown when driving at lower speeds around town. ) P0300 random misfire has occurred intermittently for almost 2 years (and I've had done every mechanical repair suggested by previous posts on this board--CkPS,(4x) CPS, replace grounds, coil packs, wires, MAF , air filter, tuned up, o2 sensors cat con and smoke test all OK. ) (No symptoms of loss of power, hard start, stalling, or drivability problems noted. P0300 continued intermittent despite these repairs.)

freeze frame for P0300 confirmed 8/29/22: left 8:40 am driving on I 76, interstate, 65 to 70 mph lots of hills. air temp 89, sunny and clear. P 300 Code shows after 20 minutes, while going uphill at 62 mph.

FUEL 1 : CL

Fuel 2 : CL

LOAD 31. %

Coolant 194. f

STFT 1 % (-.80)

LTFT1 % 5.5

STFT 2 % o.o

LTFT2 5.5

MAP"HG 10.9

ENG SP 2280

VEH SP 62

IGN AD 38.5

IAT f. 82

MAF 4.32

TPS% 23.1

When the MIL lite appeared on the dash, I hit 'record on the OBDII . I pulled off the road, stopped and recorded the freeze frame which was auto stored, also looked at the PIDs and their graphs which I manually recorded, then cleared the p0300code . ( I hand record the freeze frame w paper and pencil. The PID data is recorded when I press a button 'record data' on the OBDII which I do as soon as I see the MIL lite on the dash. The PIDs can be viewed, and some have graphs. ) After clearing the p0300 code on this trip, the p0300 does not reappear for the whole rest of the 1 hour high speed trip despite driving up steep hills. .

NEW CODE P0446: EVAP emission control system vent performance" & 'pending' P0300: FREEZE FRAME #5 FRIDAY 9/23/22 ******************

43 degree air temp. left Pgh. 8 am for Erie on interstate 65-70 mph with hills. no codes though driving up steep hills at 65-70 mph. . brief 9 am 10 minute coffee stop (gas tank not filled up it was 1/2 full) . got 1st ever P 446 Code within 3-4 minutes while entering I 79 on- ramp at 6 mph..

fuel sys 1 open

fuel sys 2 open

LOAD 39.6%

coolant 100 f

STFT1 (-10.2)

LTFT % 8.6

STFT 2 (-5.5)

LTFT 2 9.4

MAP HG 13.9

rpm 711

speed 6

ign adv 8.0

IAT 68

MAF #/M 1.79

TPS 14.1
******FREEZE FRAME NO 6- SAT 10/1/22 **********************

van was started up from cold, sitting overnite in driveway at 55 degrees. MIL came on, with DTC P0446 while idling, after 3 or so minutes. van had not yet moved.

fuel sys 1 OP

fuel sys 2 OP

LOAD 31.0%

coolant 79 f

STFT1 (-2.3)

LTFT % 6.3

STFT 2 (-1.6)

LTFT 2 6.3

MAP HG 11.2

rpm 719

speed zero

ign adv 18.5

IAT 50

MAF #/M 1.43

TPS % 11.
***********
The EVAP vent system is described in Haynes Manual p. 6-22 as:. . " When engine is warmed up and vehicle is at moderate or heavy load, the PCM opens the canister purge solenoid which allows fuel vapors to be drawn from the charcoal canister into the intake manifold to mix with the air-fuel mixture. . .'

Is it possible that an intermittent failing solenoid or vent control electric part in the EVAP system has finally failed so badly that p0446 is finally showing all the time as the main code both on a cold start ,and on starting up a warm engine after a short fuel stop ?

is this solenoid or electric part now failing more often, causing the PCM to not be able to properly open the canister purge solenoid, so there is a misdiagnosis of the proper fuel-air mix, which bad fuel-air mix is causing the random cylinder misfire ' p0300' all along ? ?

so do I just throw a new EVAP canister purge solenoid and canister vent valve onto it ?