So I HATE electrical issues....

Car (2000 M6 firehawk, stock engine just all bolt ons & tuned) was running fine, came out of work to drive 300 miles home & threw the following codes.

P0803 - 1-4 upshift (skip shift) (I have NO skip shift installed)
It now is hard as hell to get into reverse

P0102 - Powertrain Mass air flow low input
P0135 - Powertrain O2 sensor Bank 1 Sensor 1
P0155 - Powertrain O2 Senser Bank 2 Sensor 1

Drove it 300 miles home and it ran fine, just had SES codes & still got usual mpg. Got home installed two new Denso O2 sensors, new NGK55 spark plugs, had 42# injectors & replaced them back with 28# injectors.

Had my efi live tuner to come retune for the injectors. Still no maf reading & tuner says the O2 sensors are not reading, #1 cylinder is acting up (but no misfire code) AND it cuts out & pops & runs like utter HELL.

I checked all the wiring along the headers and no wires were melted or laying on the exhaust.

Where do I start? I cant see the MAF being bad & with new O2 sensors I don't see them being bad. Tuner says I may have a bad/glitched ecu. I do most my own work but when it comes to electrical... im usually totally lost!

 

Life was simpler when we only had bicycles...

The P0803 may be a red herring. I'm not sure if it triggers a MIL, so it might just be hanging out there. Do you have a skip sift eliminator installed, or is your cable just unplugged.

Your O2 issues could be caused or related to the MAF - so I'd start there and figure out what is going on with the MAF first. You could just have a very dirty MAF or maybe some contamination got on to the elements.

You haven't removed the MAF screen or anything like that, right?

 

No skip shift eliminator installed & checked the harness/plug in and all looked good.

Car has a descreened maf since before i owned it. Tried taking it out & cleaning it but it did not help. Im getting no reading from it at all. I agree O2 could be related to maf.

TEST A: Checked voltage with the ignition key turned to the on position, car not running. Checked the voltage on terminal B ground (black/white) and terminal A (yellow). There should be between 4-6 volts. (THIS TEST READ RIGHT AT 5V)

TEST B: Checked the battery voltage to the MAF with the ignition key turned to the on position, car not running across terminals B ground (black/white) and terminal C (pink). Should read 12 volts. (THIS TEST READ 0V)

TEST C: Checked the battery voltage to the MAF with the ignition key turned to on position, car not running across terminal C (pink) to battery positive. (THIS TEST READ 11.XX VOLTS)

TEST D: Went for a drive with maf unplugged. No change.

Gonna take injectors back out & try cleaning.

 

Hmmm. I haven't gone through the electrical diagnosis for the MAF before, but if you are supposed to have a voltage and read nothing, I'd expect that the test for unplugging the MAF may not reveal anything. (Because the PCM still thinks there is a deeper issue.)

Perhaps some MAF diagnostics experts can chime in?

 

Now throwing a P0200 inj circuit code, which explains the running like crap. Im pretty sure ive got a grounding problem. Uggghhh

 

the P0803 is the skip shift eliminator solenoid on the T56 transmission, it should have no affect on anything if it's disconnected or inoperable. It is not the reverse lockout solenoid which is completely different, the reverse lockout solenoid prevents you from shifting into reverse. but the t56 can often be hard to get into reverse for various reasons, bad clutch disengagement being one.

for you MAF sensor, the pink wire is hot when key in run position and should have 12-14 volts on it.
the yellow wire is the signal wire going back to the PCM, not sure what you should measure on it with a multimeter or if you should even try. for the MAF signal you should use a scanner in the obd2 port while engine running and observe the MAF real time and diagnose from there.
the black wire with white stripe goes to ground.

I would do the following, disconnect MAF connector and use multimeter to probe pins in wire harness connector,

1) with key off measure resistance between black w/white stripe wire to battery negative, you should have near zero ohm. can also measure voltage between battery + terminal and MAF pin for black wire white stripe, should see same voltage as measured across battery + and - terminals. if neither of these work then you have a ground problem in the engine wire harness between MAF connector and ground.

2) turn ignition key to run but don't start engine. measure voltage on MAF connector pin for pink wire between that and battery negative terminal or suitable engine ground, should see battery voltage. if not then pink wire is fed by 20A "ENG SEN" fuse in underhood fuse box, see if blown. if not blown then have wiring problem between MAF connector and underhood fuse box for pink wire.

once you get power and ground verified to the MAF, then with engine idling use an odb2 scanner and see what your MAF readings are. i don't remember what normal values are in grams/sec off the top of my head, but they should read constant at 800 rpm idle when engine is warn and in closed loop, and MAF reading should increase some with increase in rpm. how accurate it is then is the big question, and if you get P0102 which means MAF reading lower than expected for given engine operating condition then that's a likely cue you have a bad MAF. If the MAF is de-screened then you need a new one, or if you have run a K&N type air filter and have oiled it in the past then odds are you need a new MAF. i wouldn't get your hopes up on a can of MAF cleaner spray fixing it.

As for the O2 sensor codes, those two (P0135/55) mean the sensors did not start reading as expected because they did not heat up quick enough which is most likely due to the heater element in the O2 sensors not working. why they don't work can be they are bad in the sensor, the wire harness connector to the O2 is bad, not getting power to it which is fed by a fuse in underhood fuse box, or bad ground. the fuse according to my service manual is also marked ENG SEN and is 20A. so if it's the same fuse that's powering the MAF...

sorry for asking but you said stock engine and you were running 42# injectors. why?

 

42# injectors - well bad judgement, misinformation, not enough research - which is why I went back with 28#

So took it into Scoggin Dickey Chevrolet in Lubbock Tx: Found a broken wire in the harness going into the fuse block. I never would have found that!! Took care of the 02 sensors, maf sensor, reverse lock out issue.

They called said it was ready, picked it up went three blocks threw a inj 3 misfire. WAS NOT HAPPY & the service guy knew it! Waiting for next phone call.

 

After doing electrical work, (particularly after your emissions controls have been malfunctioning) you need to take the car for a leisurely drive at highway speeds so the PCM can go through the "re-learn" procedure. If you just tear off and drive aggressively, stuff like this will happen.

 

It's either a cylinder 3 misfire code or a injector control circuit code. No such thing as injector misfire whats the DTC number.

 

I took it for a 10 mile roundtrip nice easy drive for that reason just in case.

Sorry, yes it was a cylinder 3 misfire. Had a cracked spark plug.

All is good now!

 

It's always nice to find a easy fix very seldom are they easy or cheap