mountainmanjoe

as I explained earlier, the venting function can be tested by command the valve open and then checking for flow. This can be done with a diagnostic tool, or by just hotwiring 12V to it.
There's no use performing surgery to replace a kidney if it still works, and especially if the problem actually lies in another organ.
Check for leaks, blockages and faulty wiring first.

MitchM

the problem is that the 2 mechanics (1 a chevy dealer ) report that the vent control valve DOES open and shut when commanded by scan tool. During my vehicle 's being driven on the road, this VC solenoid (or other parts in the vent control solenoid valve system) fails, so as to trigger a P0449 DTC. so we do a voltage test and it's fine because it is intermittently working OK , that is only 1 piece of the 0449 puzzle. given that it's 1/2 day each way to get the chevy dealer to work on this and given a history of intermittent p0449 s , the dealer can replace this VC solenoid AND check all the other EVAP issues as described in the 2015 GM tech bulletin on diagnosing and fixing the notorious recurring malfunctions in the vortec vent control system.

our family, like most other vehicle owners with intermittent recurring problems. simply does not have infinite time to be without a working van. we cannot be taking this GM express back numerous times to mechanics and chevy dealers. we have already lost 7 days of its use and still don't have a fix to the problem. it now goes back to chevy dealer next week.

mountainmanjoe

Avoid stealerships like the plague.
Find a trustworthy independent mechanic who is local to you.

MitchM

I've been chasing a p0300 random cylinder misfire for 2 years now in my 07 3500 express vortec 6.0 8 cel no AFM. (4 crank position sensors, 1 cam position sensor, MAF, coil packs, plugs , wires , tuneup. ) found internet reference to bad E C M ground in GM TSB # 06 06 04 046: " intermittent or flashing P 0300 may be due to an E C M ground terminal that has corroded w rust over time. "inspect main wiring harness ground terminal G 103 for this condition. " RX replaced ground straps 7/22, mechanic noted fuel tank pressure sensor readings erratic, with key on engine off, 1.5 to 2.8 v range. after this was done , low signal voltages were still observed from fuel tank position sensor. . DTC p0300 disappears after 7/22 ground replacement.
Beginning 9/ 22 , P 0446 EVAP vent system performance, confirmed and 0300 pendingshows onafew coldweatherstarts (air temp 33 to 45 F. ) ( I can turn these DTCs off w my OBDII ii and neither recurs for the duration of the trip. Freeze data is unremarkable. ) p0446 alsoshows up when I resume driving right after a gastankfillup when engine is hot , and is very hard to fill when engine is hot .
In 10/22, chevy dealer did 58101 scan saw P0449 , EVAP vent solenoid control circuit. replaced the fuel tank pressure sensor and vent control solenoid. dealer also checked charcoal canister OK , vac lines looked fine, no MAF code or zero iac s or increase in idle rpms to suggest a vac leak. ) after 10/22 0446 and 0449 and 0300 pending went away.
now after 4 months of no codes, I'm seeing a new code P 0452 : " fuel tank pressure FTP sensor circuit LOW. "

found this thread on 5.7 Vortec: :from CHEVY FORUM :https://chevroletforum.com/forum/sil...ng-1324/page7/ Originally Posted by bcoolair [img]blob:https://chevroletforum.com/281c9e20-5308-4d39-aa21-519be2284078[/img]Post: ". . .I have 2000 chevy c2500 with5.7 vortec. Had fuel pressure regulator replaced . . Now have code P 1345. Replaced both crank and cam sensor, reset codes but still have code......PLEASE HELP

Answer: I hope this info will help you out:
The Ignition Control Module (ICM) has independent power and ground circuits. The circuits between the ICM and the Powertrain Control Module (PCM) consists of the following circuits:
-The ignition control (IC) timing signal
-The IC timing control
-The low resolution engine speed signal
-The medium resolution engine signal
-The camshaft position signal
-The low reference
The ICM sends 3X signals to the PCM, and controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions occur:
The PCM receives the second 3X signal
The PCM applies 5 volts to the ignition control (IC) timing signal circuit.
The ICM monitors the CKP sync signal when the engine is cranking. The CKP sync signal is passed from the CKP sensor to the ICM on the CKP sensor 2 signal circuit. The CKP sync signal is used to determine the correct cylinder pair and initiate the ignition coil firing sequence. The 18X reference pulses are passed from the CKP sensor to the ICM on the CKP sensor 1 circuit. The 18X reference pulses are used for fuel injection and ignition control. After the ICM receives both signals, the ICM passes the 18X and 3X reference signals to the PCM. The CMP and the CKP sensors share a 12 volt reference and low reference circuit. The CKP sensor consists of the following circuits:
-A 12 volt reference
-A low reference
-A CKP sensor 1 signal
-A CKP sensor 2 signal. . .

MINE: 6.0 Vortec, bad FTP low signal voltages still measured as of 7/22 and are still continuing after installing new grounds, fuel tank position sensor and vent control valve solenoid.

I'd like to read GM #PIP 5628 E ' diagnostic aids for engine misfire.'

possibilities:
bad ignition control module? how to diagnose?
bad PCM? how to diagnose ?

all thoughts welcome, as usual. no money to fix right now. i need to know how much to save up for next round of firing the parts cannon.

mountainmanjoe

Diagnostic scanner of course.

MitchM

thanks . back to The Independent Mechanic and his $$$ bi directional scan tool. he thinks it's a signal voltage] problem which is throwing the new code and does not want to put in a new $$$ p c m til he is sure of that . it will be interesting if it turns out that the the misfire p0300 and all the EVAP system problem codes P0455, P0446, p0449 have been due to a bad PCM intermittently not receiving proper voltage signal then sending proper air-fuel mix for over 2 years.

MitchM

I need opinions on the latest suggestion from my local mechanics' forum on curing my recurrent random misfire in my 07 Vortec 6.0 (without AFM): :

on a recent check, my mechanic found the timing in my engine is off by 7 degrees. advice from a local mechanics group:

6.0 L Vortec in 07 3500 express: " Cam Retard needs to be within 5 degrees of 0. 0 or slightly positive is desired. If its off by 7 Degrees it will miss fire. its the most common intermittent misfire with the GM Flat top Distributor engines. look at scanner data. To set it you turn the distributor like you are setting the ignition timing on a carb engine. Some are not Adjustable. (Most Aftermarket Distributors that are not adjustable will be off brand New. I have never gotten one from Autozone that did not have to be sent back. ) When your setting new distributor , you have to rev the engine above 2k rpm for the PCM to register it. (snap throttle). . I've seen 3 of these vans that the MAF was dirty/faulty that would cause this. These vans use the Load Percentage from the PCM to determine Shift Points. The biggest contributor to the Load percentage is the MAF. . .. suggestion: go with high quality new distributor like aluminum from summit racing. plastic parts in older oem distributors can have tiny hairline cracks which mis up timing . . ."

​​​​​​​summit racing offers aluminum body distributors that avoid the plastic disintegration age- vibration deterioration seen in the plastic components of the oem plastic distributor parts.

all opinions welcome, ( especially mountain man and gm tech. ) what's another $$ on a new distributor and reset of cam retard, if it's possible to do and fixes the longtime p0300 problem?

mountainmanjoe

I wouldn't waste money on that fancy stuff. Just buy a new ACDelco cap & rotors and call it a day.
But pull out the vent screen and throw it in the garbage. It just causes moisture and problems.
https://www.chevytalk.org/fusionbb/s...hp?tid/154365/

MitchM

hanks Joe. The aluminum distributor caps from Summit are 2x the price of ac delco s. I'll go with ac delco .

when this 3500 was at the chevy dealer for the p0300 random misfire problem, 12/22 for their replacement of the cam position sensor, (after 3 new crank position sensor installs and re learns ) they did NOT mention any possible adjustment to cam retard . or propose that they re adjust cam retard on the existing distributor. after their cam position sensor install the added new code code was p0336 more than 3 second mismatch between CPS and CkPS. chevy s till did nt mention the cam retard, just said 'drive it for a couple months. . . '

mountainmanjoe

dealerships are scumbags. They only want your money. Avoid them whenever possible.