What is the effect of diagnostics mode on the pcm

[pman92]

Does diagnostic mode force open loop?
A bad O2 sensor creating a lean condition in closed loop?

Try disconnecting the oxygen sensor to force open loop

[Dylan]

Has this problem been happening since you brought it 4 months ago?
Use flash tool and do a get bin. If it's been tuned possibly worth a look.

[Cameron9595]

Thanks for replies, it has been running fine for the 4 months before this happened and also good on fuel when driven sedately, about 10 to 12 L/100.

I will try disconnected O2 sensor tomorrow. Correct me if I am wrong, the 02 sensor is for fuel trim not main fuel supply calculator. If it was main fuel reference you could wack in huge injectors and a standard tune pcm could adapted the in hector plus to run any size injector to stich. Anyway so you think in diagnostic mode the pcm ignores the O2 sensor?

With the fuel pressure I don't have equipment to test it, the fuel pressure cold be good or reasonable or even bad, but what I mean is if It can idle and run smooth in diagnostic mode and up to 2500rpm I would assume it has enough fuel pressure to do the same out of diagnostic mode.

[Cameron9595]

How would I get the bin file? New to this, can this be done with tuner pro conected through adl plug?
But if did run good before can the chip be come corrupted? Or some part of pcm burnt out?

[Dylan]

Use this program with your aldl plug to get the tune

http://pcmhacking.net/forums/viewtopic.php?f=3&t=82

[blownvp]

still runs closed loop in diagnostic mode.the check engine light flashes to show open or closed loop fast flashing open loop slow flashing closed loop.runs fixed 10 degrees advanced till 2000 rpm then i think normal advance map takes over.i had a factory fuel pressure regulator go low pressure on a v6 commodore drove ok to about 2000 to 2500 rpm then started to miss and splutter.checked leads coils everything ok then checked fuel pressure it was down 100kpa 200 instead of 300 new pressure reg fixed.could be really lean and the 10 degree timing is masking the problem lean mixture needs higher voltage to jump plug gap and takes longer to burn.if the fuel filter was bad pump could have punched a hole in element and all the crap ends up in the fuel pressure regulator or injector filters or the ecu or memcal is faulty.

[Holden202T]

it is an odd one though for sure, because as soon as the throttle is let off it pretty much just stalls, I would expect to see it kinda of struggle for longer before stalling.....

I tend to agree its probably not fuel pressure because it shouldn't make a difference diag mode or not it should still struggle if that was the issue.

did anything happen when it just decided to not run properly ? like start it one day fine, then stuffed next drive ? did it overheat etc anything that's happened just before this issue ?

also have you removed the battery power to the PCM to reset it ?

[Cameron9595]

Hi all and thankyou for your thoughts and time.

Car had been starting to lack power, so changed fuel filter. Checked and adjusted timing as it was at 5 deg, adjusted to 10 deg in diagnostic mode, out of diagnostic idled at 10 deg. Car went the best it ever had on way home heaps of power crusading on expressway car started surging and died as if run out of fuel. Put fuel in was not issue, checked no fault codes, pulled engine fuse and wait, then disconnect battery and waited 15 minutes. Nothing helped. Noticed could run in diagnostic mode so drove home that way.

Just a thought after reading blownvp I will have to see what happens to timing in diagnostic mode above 2000rpm. We have ruled out cas in dizzy as it will run in diagnostic mode with smooth and stable timing. Tuner pro shows timing jumping low teens to 22 deg while engine struggles in normal mode as rpm jumps up and down as well. Uncle noticed with timing light on it that sometimes he said it is firing when no timing mark present in normal mode. Does the pcm actually know when a spark has actually fired to give a reading on the tunerpro graphs or only when pcm has told it to fire? We tried swapping ignition module and no different.

So If pcm holds 10 deg to 2000rpm (ish) than uses tables, could the pcm or chip be corrupted?

[Jayme]

The spark shown on tunerpro is the spark that the ecm is trying to run ... it has no visibility of what actually happens. above 2000 rpm it will definitely drop out of diag mode spark and back onto tables. have you checked inside the dizzy? could the rotor button or dizzy cap be damaged? perhaps running 10 degrees is helping work around a damaged or misaligned rotor button?

[Holden202T]

yeah certainly what you said above sounds like it could be spark related issue.....