DIY PROMDo It Yourself PROM chip burning help. No PROM begging. No PROMs for sale. No commercial exchange. Not a referral service.
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I've been working on a TPI swap on the 350 in my Jeep for some time now. After a lot of searching and reading I got running. I went with 6E code on the 165 ECM and I'm having some trouble with the MAF.
I started with the AUJL bin and tweaked the injector constants until the BLM's would hover around 117-124 in closed loop idle. I thought I was headed down the right path so I took the MAF off to install an open element cone filter on the intake side before getting it out on the road. After I reinstalled the MAF the engine would run as usual for about 2 minutes then I would get a code 33 MAF high. I used that pdf file that has a flow chart to trouble shoot the code 33. I went over it twice and came up with bad MAF. So I sent it off to www.siaelec.com to get rebuilt.
Since getting the sensor back I still get code 33. So to take care of that I just set the MAF high Diag. error threshold as high as it would go. So no more code 33. However since my MAF has been rebuilt the engine runs worse than ever. In a word - rich. As soon as it goes CL the INT races to 80 and the BLM follows. And I can see a cloud of exhaust all around.
I didn't do a log on it because I was rather disgusted, but I could see right off what the problem was. The rebuilt MAF was reporting much higher flow now than before. Pre rebuild it reported 6-7 Gram at 675 RPM idle. Now it shows like 15-17. Much more air = so much more fuel I can see it in the air.
I had read somewhere in the past that different MAFs read different and the MAF tables must be changed. Ok no problem, or so I thought. I went to MAF table 1 and took the G/sec that I had, the 15-17 range and reduce them the the 6-7 range like I used to have before the rebuild. No good still high. I then took a more drastic step and took MAF table 1 and 2 and reduced the G/sec in each field on both tables by dividing them by 10. I thought that would make a huge difference. It made no difference. What am I doing wrong here?
The only way I could get the G/sec down is Maximum airflow vs. RPM. I made the max like 7 at idle RPM. But I don't think this is a good way to tune so I just quit. I really thought a rebuilt MAF was gonna put me on the right road but I'm worse off now than before.
Sorry this post was so long. Thanks to anyone that is still reading and feels like helping a lost newb.
For the record the engine is a 74 model 350 stock rebuilt with an 86 TPI base. Timing is 6 degrees. No more vacuum leaks. Heated O2. No EGR.
If changing the MAF table calibrations does not affect the MAF signal, then the ecm is likely using the default airflow calculation instead (due to your previous fault history).
To verify that the MAF signal is being read and used, check the MAF raw input signal on byte 38. This should closesly correspond to the normal 16 bit filtered MAF signal.
If not, recheck your connections and/or disconnect the battery temporarily to clear any existing fault or SAM history and try again.
To verify that the MAF signal is being read and used, check the MAF raw input signal on byte 38. This should closesly correspond to the normal 16 bit filtered MAF signal.
Mind explaining in layman's terms how to do that in Tunerpro? Thanks.
Okay, we're getting somewhere now.
I'm using v4.14 and it has the raw maf I just never paid any attention to it until now.
No matter what it reads 254. Key on engine off, running, revved up alittle always 254. I even looked back at a log I made pre MAF rebuild and it was 254 then too. So surely this is the root of my problem.
I do not, however, know where to go next. You mentioned wiring, I'll double check it over the weekend. I was also wondering about the MAF power and burnoff relays. They are the ones that came with the TPI setup used when I bought it, perhaps originals. Could they be the problem?
Another note worth mentioning, I just noticed. The MAF G/Sec reading will sometimes flash a real high number. Even with engine off key on it will go from 5 to like 128 or some other 3 digit number, I can't really tell it's so fast. Just a quick little blip. Any connecton to the problem or just normal with these systems?
The MAF signal input circuit has a 5 volt pull-up resistor in the ecm. So an open circuit on the signal wire will result in 5 volts at the ecm or a raw input reading of 254 or so. You may simply have an open circuit on the MAF signal wire.
While loggind data with the MAF disconnected, you can try shorting the MAF signal wire to ground (green wire). This should bring the MAF raw input signal down to zero. This will test if the ecm side is working.
You may need to key off and key on while doing so in order to get the ecm to process the MAF input signal again.
If the ecm checks out and responds to grounding the signal wire or by inserting various resistances to ground (if available) to get some different values on the raw input signal, then you have issues with either the MAF itself or with the MAF power relay or associated wiring.
Okay, grounding the green signal wire gives me a raw MAF reading of 0, so the ECM must be okay.
I then started looking over my MAF power relay wiring. My meter reads full battery voltage on the red power wire for a few seconds when the key is turned on and then again after the motor is running. Looking over the schematics I followed when I done the swap I think I have the power side correct.
The two grounds have continuity to ground that's all I knew to check on them. And I assume the blue burn off has nothing to do with this problem. Please advise if there is more to look for in these areas.
Did I overlook some key points in my wiring I could check? The MAF gets 12v when engine is on, the signal will go low when grounded, and the two grounds go to ground. What else could I check?
I just got this MAF back from getting rebuilt, could it still be bad? Or bad again, could I have messed something up some how? I dunno, thanks for any help.
