I just did about 3 hours of research and can't find an answer to this. So here it is:

1989 Camaro IROC-Z LB9 all original, 21k miles, like new condition. OEM .BIN with only mods for MAF voltage reporting.

On cold starts and sometimes on hot restarts, the engine dies seconds after starting fine. If I rev-up upon starting, it runs fine, drives fine and idles fine after for the reminder of the ride.

NO CODE or SES

Scan tool shows something unusual:

MAF voltage = 0 (???) It'll take up to 60-90 seconds to finally see a voltage on scanner. Once voltage appears, it is normal range and MAF g/sec reported is consistent with MAF tables..
MAF g/sec = around 11-10 at 1150rpm. All normal range. 1150 RPM is 1000 RPM from idle table + Hot Restart adder of 150 RPM.
MAF Raw = 5... weird!!!

When MAF g/sec is at around 11-10 g/sec, car idles smooth in open loop like supposed to. But at some point, it drops to 5.77g/sec which seems consistent with what the MAF table #1 calls for at 0.00V. When this happens, it kills the engine as it lowers the injectors BPW calculation by almost half (see attached file at sample #89-90).

What I don't understand is:
if the MAF is not reporting a voltage, why I am not getting a code?
if the MAF is not reporting a voltage, why do I get 11-10 g/sec when the table says 5.74g/sec. Furthermore, from other similar test I have done, if I rev the engine upon start-up, I get 0 voltage from the MAF but let's say 50-60 g/sec. Is there a default MAF table if ECM sees 0 volt?

Now I thought about upping the MAF table#1 at 0 volt to let's say 8 or 9 g/sec to resolve the problem. However, it does not address the issue of no reported voltage.

Does the MAF sensor need a warm-up time to report voltage like an 02 sensor?

Thanks

UPDATE 1:
After reviewing the $6E hack, I figured out that the ECM, for some reason, enters the MAF Default routine but does not not throw a code 33/34. The default relies on the IAC, TPS and RPM (0x21E, 0x21F, 0x220, 0x223) to produce a calculated (estimated) g/sec for injectors BPW. If for some reason, the ECM exits the default routine, with a MAF voltage of 0.00, it returns the values from the MAF tables. In my case that is 5.7g/sec, which kills the engine by fuel starvation. I can see the MAF g/sec reported moving in tandem with the IAC when TPS is at 0%. If I applied the throttle, the MAF g/sec reported appears to be calculated from a table with %TPS * table value vs RPM (Default air flow offset per pct TPS vs RPM 0x223). As soon as the MAF starts reporting a voltage, the g/sec are extracted from the MAF tables and the engine runs great for hours.

So now that I know that, I will temporarily modify the MAF table to prevent stalling on start-up. Then I will investigate the MAF circuitry to see why it is not reporting a voltage to the ECM upon starting or restarting.

UPDATE 2:
Bench tested all 3 relays (Fuel pump, MAF and burn off) - all good
Inspected all wires at relays, MAF and ECM - all good
Ohm tested all wires MAF to relays to ECM - Good continuity
Burn-off relays works after engine shut-off
Inspected MAF, looks like new
Back probed B12 on ECM connector and did a start-up test with AFR gauge and data logger - All good. This time, I have a voltage reading from datalogger and voltmeter. The engine stumbled for a fraction of second as voltage dropped but went back up. Voltage was within range.

I could not get the MAF to not send a signal. I tapped on it while engine running and nothing. I played with wires and nothing. This is the kind of mind boggling problem one can have. I did increase MAF table 1 at 0.00V to 9g/sec to avoid stalling on startup. This is a temporary solution.

 

I had a very similar issue with my L98, Cold start, idled up a few secs and die but second restart was no issue and it was intermittent. I chased my tail on it forever until getting lucky and having it happen when I had a scanner hooked up and data streaming, turned out the wiring from FP relay was not great at the pigtail. Spliced in a new pig tail and no more problem. That being said I would check your MAF wiring closely and the condition of your MAF. My original Bosch would heat soak and on hot start up would have off readings and seemed to dump fuel...once again on the scanner it showed way off reading when heat soaked. When the engine was cold it was fine, a used Bosch MAF cured that issue.

 

Yep!
I read your entire thread about it. https://www.thirdgen.org/forums/tpi/...art-issue.html
I will go over the entire MAF circuitry when I get a chance. Everything looks so new as the car was garage kept for decades and barely driven

I will convert to heated O2 sensor as it contributes to a somehow rough idle. Sensor voltage won’t swing when sitting idle for a while. It’s something I randomly caught on the data logger. It’s intermittent. The 02 voltage will go flat for a while when idling. Have to rev the engine and it comes back.

Also the entire APYS oem .bin is a mess. I will write a post on it once I’m finished tweaking it.
Overly rich in PE with injectors working at 95% DC
Too lean on startup and open loop
BLM way too rich, had to back off MAF tables by 5%
BLM boundaries made no sense
SA was way too high in PE creating knock retard
PE TPS threshold was too low
HWY mode is a farce an inaccurate, that was disabled
SA Latency was off, had to be readjusted
Fan came on too high
SAM was disabled as it threw off open loop
And finally the knock attack/recovery had to be tweaked
Car runs way better now

I used an AFR gauge. I disabled AIR temporarily to get accurate reading

 

That is a beautiful car in what looks like outstanding condition! Really has eyes!

With that low a mileage/condition MAF wiring should be good but maybe a loose ground or connection...

That heated o2 sensor was on my list and I just saw a thread where Vader mentioned you could use the cold start inj. purple wire IIRC for a power source...seeing as how mine is deleted, as it runs 89' cold start program, and could be a use for that wiring. Tuned Performance did my tune and the car runs great! No complaints. It sounds like you really have a handle on tuning these cars so when you dial it in I bet it will be much improved. It was almost night and day with my car.

That o2 sensor sounds like its gotten lazy and not reading as fast? I have heard that happens and can cause problems.

 

Thanks for the info and compliments!

 

Well, I thought I would give a final update on this thread. The MAF sensor has been sending a signal to the ECM ever since I unplugged and tested everything. So the car starts and runs smooth. I have a new Delphi MAF as a back-up.

This is the kind of trouble TPI systems can give you. A signal that is not being sent to the ECM... Intermittent. Good luck chasing that one without datalogging.

 

Well, now it's throwing a code 36 but not acting up. The MAF is sending voltage to ECM while running. So I'll change the MAF and report back.

UPDATE:
Try changing the MAF with a Delphi #AF10320. It fits perfectly. However, car ran overly rich and stumbling at idle. Figured out that the Delphi MAF has a voltage range different than the OEM Bosch. It seems to stop at 0.80v at the bottom of the scale and won't go further down. The OEM was at 0.60-0.65 at warm idle (800-750 rpm). That added up over 20% fuel!!!! It seems like the voltage scale is off by about 0.12-0.10 volt on average. It's worst at idle since it won't go under 0.80volts. Threw the old MAF on and car runs smooth and BLM are decent, no code. The higher the air flow, the less impact the voltage offset has.

Re did all testing on Burn-off circuity to see what was causing code 36. Could not find anything at fault except the voltage peeking for a fraction of a second at around 2.10volts (on the blue wire during burn off cycle). ECM will trigger code if voltage is over 1.90volts after 6 occurrences. So I decided to change (0x22E) to 2.49 volts to see if it would make Code 36 go away.

MAF could be responsible for code 36. It has been documented on TGO. But retuning the MAF tables, open loop and PE-WOT is not in the cards right now (lots of work). So I'll keep the old MAF until it gets worse.

 

MORE INFO:
Just ran an airflow test on the Delphi MAF. With no airflow, it is stuck at 0.80volts. This is definitely an inconvenience to say the least. The OEM BOSCH has a voltage of 0.04volts with no air flow. That means that for a stock LB9 305 it will mess-up idle big time with OEM tune. I'm not even sure I can tune the MAF table since the Delphi MAF reaches 0.80 volts at 850RPM idle. Between 750-850 rpm warm idle it is stuck at 0.80 volts. MAF tables would have to be retuned starting at 850 RPM (0.80volts) and let the BLM/INT compensate under 850 rpm. WOW!

 

Well, code 36 returned but car runs fine.

Retested all MAF circuitry again. This time when manually activating the MAF burn off relay, the MAF wire element was not glowing. Voltage on green wire (MAF input B12) was between 0.26-0.31V which would trigger code 36 after 6 occurrences. Voltage has to be higher then 0.39V. After cycling the MAF burn off relay a few time, MAF wire element started glowing and voltage peaked at 4.91V, again, outside threshold of 2.49V. MAF wire element would glow intermittently.

So I need a new MAF!

I will remove burn off relay for now and temporarily disable Code 36 in BIN until I get around to changing the MAF for a reman. So I won't have that annoying SES light in my face!

 

New MAF installed
BSE remanufactured #27854
Did a data log before and after and I get the exact same voltage for same engine conditions. Car runs great.

Reactivated code #36 in BIN

We'll see if code 36 comes back.

 

Hello everyone new member but third gen owner for years. Great info on here! I too am having a similar issue with my 86 IROC. it started having cold start issues bad idle etc so I changed a lot if the sensors o2, IAC, coolant temp. Seemed to help a little but symptoms would come back. Codes were 34 and 42. When I did the troubleshooting per manual I determined I had a bad MAF. Purchased a delphi one and again when installed it seemed to help, but shortly there after idle issues. While I was at it I figured I would changed the injectors because it couldn't hurt so again it helped a lot. Figured I was done. Then idle issues started again, I had to keep my foot on the gas to keep it running. When it catches on its own the idle was horrible. Initially I assumed injectors but they are new and not leaking. Fuel pressure is good. It sounds like an airflow problem??? Could it be the Delphi unit? Where do I find a new Bosch for our cars???

 

Welcome aboard, you might want to start your own thread to get more looks by ppl. That being said there is no option for a new Bosch MAF unless you find a NOS and that will likely cost a small fortune. Your best bet is a good used one (can be a pain find a good one) or try one of the reman Bosch ones at Rockauto or parts store. The reman Bosch ones are easy to spot as they still have the original Bosch markings and are hot wire inside instead of the Delphi style with the board inside. Another member also reported the Delphis had problems with calibration IIRC and were giving ppl issues.

Also if you want to work on these cars yourself a factory service manual, which it sounds like you have access to, and a scan tool that works on OBD1 are really essential for trouble shooting. Without those things it’s really tough to find out exactly what’s going on and what the ECM sees.

Just going on what you mentioned have you checked your MAF Burn off and power relays and wiring to that and the MAF? Throttle position sensor voltage? Deep cleaned the throttle body and IAC passages? Check timing ( factory spec is 6 degrees BTDC) and distributor? A smoke test for vacuum leaks works well too and can be done with a cheap cigar and harbor freight fluid exchanger( nice video on YT) and lastly checked the grounds on the back of the cylinder heads? Hope some of this helps.

 

Rockauto.com

 

This might shed some light on some of the potential causes:

https://www.thirdgen.org/forums/tpi/...ml#post6461102