Gen III (3) MAF problem

[l michael wilson]

Hello all,

I have been working on tuning an LS swapped car and I've been running into issues with the MAF sensor. The car in question is a 89' BMW 325is that has been swapped with a LS1. I don't know all of the details of the engine, as it was bought complete however, we can tell it has 241 heads with a relatively mild cam, LS2 intake, new 90mm Holley DBC TB, Bosch 0280155868 36 lb/hr(@43.5PSI, car runs ~66PSI at idle and ~60PSI under load) injectors, a GM P01 PCM and a Wiring Specialties swap harness. and Sikky swap headers that are somewhere between shorties and true long tubes.

The issue I'm having as you can guess is with the MAF. Occasionally and without warning the MAF frequency drops from whatever it is currently running at (e.g. 3000hz, 10000hz, ect...) straight to 0hz. The car has a brand new 5 pin MAF (with the screen still in; new unit reads: Delphi Technologies AF10043 34021 old unit reads Delphi 25168491). Initially, the problem only occurred when the car was at WOT. Eventually I noticed that it was also happening at idle too. On some occasions, the MAF with hang at 0hz for approximately 10-15 seconds. I have not been able to notice any correlation between this and anything else that the car is doing other than it may possibly get worse when the engine is warm. Also, when the problem occurs at WOT, it seems to happen consistently twice during a pull; it seems to first do it at about 4500-4700 RPM and then again at approximately 4900-5100 RPM. The car has been smoke checked multiple times for vacuum leaks and should be as good as it can possibly get.

BTW: The car is a manual. All tuning has been on a Mustang chassis dyno with a WBO2. The wiring for the MAF has been checked for proper voltages and continuity/resistance between the MAF connector and the PCM; the MAF signal wire measured 0.5 Ohms between the MAF connector and the PCM. The ground on the back of the drivers side cylinder head was initially loose but has been tightened, the passenger ground is tight.

As a note: In the attached data log(s), when the MAF signal is at 0hz, the lb/min / g/min calculation will likely be higher that what it should be. This is the result of having the lowest (1500hz) MAF table cell being set way to high to avoid going too lean at WOT.

Attached is a log file including plenty of idle data, a drive train loss run on the dyno, and a WOT power pull on the dyno as well as the corresponding tune file and HPT Layout file and VCM scanner .cfg

VCM Scanner.cfg
bci gen 3 2.Layout.Layout.xml
89 ls1 swapped 325is maf issue 2.hpl
89 ls1 swapped 325is maf and ve 2.hpt

Please feel free to respond with any ideas, experiments, suggestions, or experiences that are relevant. Also please let me know if there is a piece of info/data that would help.

-Thanks

[blindsquirrel]

'0280155868' is possibly the most popular badly-counterfeited injector number in history, and, you have only updated the Injector Flow Rate table, while all the other (more critical) injector tables remain stock 2001 Camaro. But if you have the fakes instead of real ones there is no correct injector data.

[l michael wilson]

Hey blindsquirrel,

Thanks for the reply and the info. Just a few questions to follow up.

1. Would the injector data being wrong cause what I am seeing in the data logs? As far as my knowledge tells me the behavior should be slightly different if this is the cause.

2. How can I determine if these are in fact legitimate "0280155868" injectors?

3. Where can I find all of the correct data to input for these injectors?

-Thanks again

[blindsquirrel]

Injector data is the foundation all the other calculations are based on. It really does not matter if incorrect data is the cause of your specific problem or not, because any work you do on the tune will have to be undone later when it has real injectors with real data.

https://www.google.com/search?tbs=li...0&q=0280155868

^^^ How can you trust them when the maybe-real-to-probably-fake ratio is like that?

[kevin87turbot]

Based on the information that you've presented, I'd say that it's likely a problem in the PCM itself. I've had one do the exact same thing. I was able to get it dialed in with a proper SD tune on the dyno.

[l michael wilson]

Thanks for the replies, although I may still be looking for a diagnosis.

Injector data is the foundation all the other calculations are based on. It really does not matter if incorrect data is the cause of your specific problem or not, because any work you do on the tune will have to be undone later when it has real injectors with real data.

https://www.google.com/search?tbs=li...0&q=0280155868

^^^ How can you trust them when the maybe-real-to-probably-fake ratio is like that?

Based on the information that you've presented, I'd say that it's likely a problem in the PCM itself. I've had one do the exact same thing. I was able to get it dialed in with a proper SD tune on the dyno.

I understand how critical injector data is for the tune however, I do not see how it would cause the specific problem I am dealing with. The car hits target AFR(verified by an external wideband O2 sensor welded into the exhaust approximately 1ft after the collectors) in all situations until the MAF acts up. I can try to find better injector data, or even swap them to a set of injectors with known data but I do not think that is the root of the problem. I need to figure out why the MAF decides to randomly and intermittently decide to stop working/give not data to the PCM/PCM stop getting data/ect... The rest of the tune can be adjusted later if the injector data is incorrect, that is no problem.

BTW:
-The MAF has approximately 1ft of straight tube before the MAF and in between the filter, along with approximately 6in of straight and a 90 degree elbow after the MAF and before the throttle body.

- The PCM has thrown several codes repeatedly:
P0102, which I am confident is only a symptom of the MAF falling to 0hz randomly
P0121, which I have no clue as to the cause
p1637, which I assume is due to the car being an engine swap, the car does charge fine

-Thanks

[l michael wilson]

Thanks for the reply as well,

Based on the information that you've presented, I'd say that it's likely a problem in the PCM itself. I've had one do the exact same thing. I was able to get it dialed in with a proper SD tune on the dyno.

Would you give some more details? It would be great to hear about your experience.

I would really like the leave the MAF tuned on, turning it of and doing a SD only tune is somewhat of a last resort.

-Thanks

[Alvin]

Are you absolutely positive there are no corroded pins? I know you said you checked wiring. It's failing in a odd way.

I'd say the new MAF is bad out of the box or like someone else said it's a PCM issue. I've had faulty PCM's do all sorts of weird things. One of them would go -40 on the IAT any time you floored it.

[Hondaeater]

Thanks for the replies, although I may still be looking for a diagnosis.





I understand how critical injector data is for the tune however, I do not see how it would cause the specific problem I am dealing with. The car hits target AFR(verified by an external wideband O2 sensor welded into the exhaust approximately 1ft after the collectors) in all situations until the MAF acts up. I can try to find better injector data, or even swap them to a set of injectors with known data but I do not think that is the root of the problem. I need to figure out why the MAF decides to randomly and intermittently decide to stop working/give not data to the PCM/PCM stop getting data/ect... The rest of the tune can be adjusted later if the injector data is incorrect, that is no problem.

BTW:
-The MAF has approximately 1ft of straight tube before the MAF and in between the filter, along with approximately 6in of straight and a 90 degree elbow after the MAF and before the throttle body.

- The PCM has thrown several codes repeatedly:
P0102, which I am confident is only a symptom of the MAF falling to 0hz randomly
P0121, which I have no clue as to the cause
p1637, which I assume is due to the car being an engine swap, the car does charge fine

-Thanks

P1637 are you using the original Camaro alternator or the 1989 2-wire alt.? If the later put a 0 in the systems tab under Alt L-term.
The L-terminal circuit from the generator is a discrete circuit (a discrete circuit has no splices and only one source and one destination) into the Powertrain Control Module (PCM). The PCM applies ignition voltage to the generator L terminal circuit. A small amount of current flows from this circuit through the generator windings to create a magnetic field which starts the generator process. When the generator is at operating speed and producing voltage, a solid state switch for the L terminal circuit in the generator opens and the PCM detects that the initial startup current flow has stopped.
The PCM expects to detect low voltage on the L terminal circuit prior to the generator rotating at operating speed and conversely expects the circuit to be at ignition voltage potential when the generator is operational.

P0121, which I have no clue as to the cause Set the the Engine Diag P0121 field Error MAX to 100kPa and Min MAP to 0

P0102 look for connector corrosion as mentioned. Separating the IAT wires for a stand alone IAT (open Element style is best ... $25 @ DIY autotune Megasquirt https://www.diyautotune.com/shop/sen...ssure-sensors/) and install into manifold will be better long term anyway as the heat-soak can be a PIA.
The tune file DTC is NOT set to fail on first error for P0101, P0102, P0103 so it may be getting mixed signals.

Good luck and hope this helps.