MitchM

MAF was cleaned, checked and found not so good so then was replaced. all new ac delco points, plugs, plug wires and each checked out fine . i'd expect a p030x code specific to a certain cylinder if i ahd one bad plug wire, i'd also expect rough runnning and loss of power which i definitely do not have. all fuel trims checked and all w/ in spec, that wa sone of the 1st things done. .

exhaust is the only item on the list that has not been examined. no smoke test yet.

will a topnotch obd we're using at the local pro mechanic's tell us with a code if it's a bad ecu or exhaust restriction? the only code we ever get is p0300 random misfire.

hanky

If possible, can you get the data stream info and post it here so we can examine it and maybe offer a useful suggestion?

Trying to diagnose over the net is not a good thing to attempt.
Need some info and direction which could be provided by data stream info.

There is a "Mode 6 function" that a quality scan tool will provide and this function will tell us which cyls and how many times the misfire is taking place. Until this info is acquired , we are shooting in the dark.

MitchM

we are going on a test drive tomorrow. the p0300 shows up randomly when engine is hot , running on freeway for an hour over 65 mph and rpm s are over 2000 and pressing gas pedal going uphill will throw the code p 0300. by the time a shop gets it engine is cold and not throwing ANY codes, the OBDII history does n't tell much. i need to see if 'data stream' was ever available but i doubt it b c every diag i have had begins with cold engine which is NOT THROWING codes anymore ( duh.. i bring it into shop, it sits for a couple days, they're not willing to run it hot fo an hour to throw the p0300 so it can be dynamic monitored with the mode 6 tool. 3 different p 0300 visits, never a hot run, just throw parts at it. .. = bad idea. i'm getting a mechanic willing to test dynamically but it is tough, no one wants to ride around for an hour waiting for p 0300 s to show . i now have a mechanic willing to do so so i will run it hot till it ' s coding its usuall p 0300 then drive it hot to his shop and we will monitor it driving on the road w his obdii gear plugged in and hopefully diagnose the misfire. it's driving me crazy, dont want to drive w a MIL and spouse is not happy w all the repair parts $$ that still haven't fixd it...

SteveROntario

there are a few videos on youtube about LS (LQ4) engine misfires as it is common. You may want to find a shop with a scope and an interest in troubleshooting. it could be a bad injector or connector

I have an Autel MS906BT scanner and my 2004 Roadtrek with the 6.0 happily pumps out misfire information for each cylinder but never gives a code. You can feel it idling rough and the tailpipe is black on the outside. One of these days I'll fix it.

MitchM

still chasing my P0300. i went way for about 3 weeeks, drove it hard and no DTC. then it came back : drove about an hour at freeway speed, came on. i pulled off the road nd hooked up my new foxwell 301 to get some live data. i was in neutral w engine running , steedy MIL p0300, data was:
freeze frame 700 rpm , engine in neutral , load pct of 21.2% air vol . fuel 1 CLR, ECT 195 F . fuel trims both god, MAF 6.97, short t2 0 to 2.3, long 9.4 . air intake 131. F MAP kPa 41. V= 0 mph as i'm parked and in neutral to read this data..

more data is available from the foxwell. basically i'm still throwing the a mil p0300 which is inetrmittent flash then steady then off then intermittent. i bought a foxwell 301 w live data and freeze fame since i have to be able to pull the live data myself. )i can' t get the van to do its p0300 when it knows i'm driving it to the mechanic who can put it on his $5000 obdIi w oscilloscope. ..)

if there's other data that might be helpful let me know and i'll try to pull it out of the foxwell...all thoughts welcome.

mountainmanjoe

Have you checked your fuel pressure? Check for vacuum leaks?

MitchM

hi Joe, and everyone else who chimed in: thanks for your thoughts.

after replacing the cheap knockoff crankshaft position sensor with an OEM ac delco , and cleaning the injectors, and cleaning and dielectricing the ECU ground, the MIL P0300 'flashing' went away for a couple weeks. then it came back, 1st as intermittent flashing 'check engine' and now is a steady MIL . (my cheap FIXD threw the p0300 each time.) I drove around for the past couple weeks trying to get van to throw the steady MIL code and it wouldn't , because my mechanic was willing for me to bring the van to his shop while it was hot and throwing the P0300 code so he could put it on his hi quality scan 6 mode scanner with oscilloscope to try to see the gull wings for each cylinder . (the van knew this so it never threw an y code for 3 weeks.) since i could never get the van to throw the code at the times the mechanic could look at it 'hot', i bought myself an OBD II scanner that pulls live data and freeze frame. with constant MIL P0300 now, steady not flashing , on even when engine is cold, i pulled my own live and freeze frame data. (some is posted below. )
i checked the p0300 youtubes of problems w/ the 6 cyl chevy vortecs random misfires. opinions were this steady MIL now is showing because there is a mismatch between crankshaft speed and cam sensors. (crankshaft positiion sensor is new ac delco, was replaced first time w cheap with chinese knockoff,.). after this crKpos replacement and re learn, , the P0300 went away for a while. ) ( the cam position sensor is old and OEM , it was suggested to always replace cam position sensor at same time as crankshaft position sensor or the mismatch will cause the steady MIL on the dash if the ecu senses a certain number of mismatches.) (I haven't replaced the cam position sensor but i intend to as next RX along with vacuum leak test. )
my new OBDII scanner unit cannot do oscilloscopes and gullwing stuff but claimed it can pull the important fuel trims and o2 bank sensor data. so fuel trim data and o2 sensor data was pulled but the results are spotty . scanner said couldn't read ANY SHRTFT B1S2 at all. it takes spotty freeze frame data too. (i'm pretty unhappy w the foxwell 301 and returned it for a new ACTRON by bosch which i'll run on road tests tomorrow. ).

this foxwell data is after a 1/2 hr drive at 62 mph w a lot of steady uphills, then at flat paking-lot idle at 2 mph . . I have a P0300 and a steady yellow MIL on the dash at all times. : Engine Cooling temp T was 192 degrees F. , all OBD readings are in 'closed loop '( CL= warmed up engine ) mode. OBDII was plugged in to data port under dash at left as i drove at 62 mph then went to flat parking lot at 0 to 2 mph. data was pulled by the scanner as follows. there was no sign of running rough, no shake or shudder, no loss of power, steady acceleration from the gas pedal , and throttle seemed to be operating normally.

LIVE DATA TEST 1- at idle - load per cent was 22 at 550 rpms , on the road at 62 mph went to 71 percent at 2554 rpms . spark advance was 15 at 550 rpms idle, went to 28.5 at 2554 rpms. the fuel trim data STFT1, 2 and LTFT 1, 2 and and o 2 sensor banks data are as follow:

o2 bank 1 s1 (upstream sensors, before cat converter ) 1 is right t side cylinders , 02 bank 1 s2 is left side cyls.
02 bank 2 s 1 is downstream sensors, after cat converter on rt side. o2 b2 s2 is left side .

obd took 48 frames of live data but it cannot be printed out (the foxwell scanner i bought has a virus and print software can't be loaded. ) so i will summarize by copying data from the OBDII for 6 of the 48 frames it took at low RPMS:

SHRT FT B1S1 varies + .8 to 1.6 to 2.3 .
SHRT FT B1S2 --- says ' N/A no data available'

LTFT 1 steady 8.6 and LTFT2 steady 9.4

by frame # : 13 15 30 45 47 48

o2b1s1 .54 .61 .60 .73 .69 .78

02b1s2 .08 .10 .08 .10 .10 .095

SHRT B1S1 0 to 1.6 to 3.9

SHRTFTBIS2 N/A-

TEST 2 FREEZE FRAME ONLY , LIVE DATA DIDN't TAKE, AT 60 mph : spark advance 28.5. rpm 2554, load % 71
FRAME 1 8 15
SHRTFT1 % -2.3 - - some readings seem to be missing ...

LONGFT1 % 1.6 -3.1 - same

LONGFT2 % +3.1 - same

sorry that this foxwell data is so bad. i am disappointed in the foxwell 301 because i cannot print data ,( it has a virus preventing printer app upload,) and the readings seem to be spotty and missing . i am returning the foxwell and have a new ACTRON bosch OBDII ($100) which i will run to get live data and freeze frame tomorrow, and post the results.

if there are particular live or freeze frame results that would be helpfu;l in this long and disappointing diagnostic effort, let me know ?

Kael

Was the new crank sensor re-learned? If everything is running well, I'd chase that first. Unfortunately, a specialty $$$$$ scanner/device is needed for this (not happy GM), ie mechanic level.

MitchM

1 st crank position sensor was a cheap autozone knockoff . relearned. but the MIl did disappear for about 2 weeks. was back in for another relearn. didn't fix the problem. then was replaced w an OEM cCkPos sensor from AC delco. that was relearned. after that OEM acDelco replacement both the flashing and steady MILs w code p300 started showing up within 50 miles.

hanky

Sometimes the only way to pin down what is really going on requires first, a scan tool that can show mode 6 info which will tell which cyls are misfiring.
The next thing that can be done is to graph what is happening with crank sensor, cam sensor, and injectors. If there is anything going on there you will see it.
Until you have some definite info to examine , everything is up for grabs and replacing a lot of good parts can get disappointing and expensive..