I just recently finished installing a wideband O2 sensor. My car ran fine before the install, but afterward wouldn't run without pedaling it. Turns out that the alternator went bad (I guess on the ride home from the muffler shop). I replaced it and got the car running after giving the battery a charge. It gave a code 33, so I replaced the MAF and burn-off relays. After replacing the relays, I connected the laptop and the MAF readings seem to be where they should, but the BLMs are floating at or just above 110 at idle. Still getting the SES light with the engine running. Could the old alternator have been making such low voltage that I tuned around it adding more fuel that it really needed? Otherwise, any other plan of attack you would recommend?

To start with, while getting the BLMs at idle of 110, the wideband gauge was showing 7.6. I made one change in the chip and now my idle BLMs are sitting at 158 and the wideband gauge still shows 7.6. I also still have a code 33, but the values in TunerPro still seem to be where they should.

I'm tempted to buy a new MAF but have a feeling this won't cure my problem.

I'm getting very frustrated with it and contemplating parting the car out, because I refuse to go back to a carb and don't want to spend the money on aftermarket electronics. It's been a year and a half and the farthest drive I've had is a 10mi round trip. Still haven't been able to step in it because the tune sucks.

Edit: I just looked through the log file I made and noticed that the MAF raw input is static at 254. Should this be the case?

You could have tuned around a low battery voltage. Or even worse around a fluctuating voltage (ripple from a bad diode).

For low/high voltage there is an injector compensation table in the calibration that are based on battery voltage. Once hte tune is OK at the nominal 13.8 - 14.4 volts, you can disconnect the alternator, start the engine, and drive around data logging.

Then using the BLM value make changes to the injector compensation to adjust the PW. But this type of tuning is typically a final touches kind of thing.


The code 33 is important, as the ECM will then create a default airflow based on engine RPM and throttle position (n-alpha mode). You can't tune with that code being active.

Which year TPI system are you using? And which ECM and code mask?

And what type of modifications have been made to the engine? I note the 383, HSR, and AFR, but the XFI I am note sure about (only in the context of a FAST XFI ECM).

RBob.

The heads are AFR 180 Eliminators , and the XFI is in reference to the 268XFI cam. The ECM is a '165 running 6E with a modified AUJN bin.

I went ahead and ordered a new Micro-Tech MAF to see if that will stifle the code 33. Should I look at replacing the ECM next?

From what I've read here and at other boards, the aftermarket MAFs leave a lot to be desired. In both calibration and in reliability.

There could also be an issue with the connectors involved.

At the same time the code 33 could be caused by the MAF reporting a slightly higher airflow then expected. This is because a 383 with a cam pulls more air then a stock engine. So it is basically a false error.

At location $210 in the calibration is the high MAF airflow trip point. Stock in ARAP is 45 gms/sec. Try setting it to 60 gms/sec and see if that clears up the error.

If the MAF has the screens I would first try the tune with the stock MAF tables and scalar values.

RBob.

I doubt the MAF is reporting higher that it should. I've made quite a few chips while tuning with this MAF. The code 33 just happened this week. I've picked up the new one, I'll try it in a bit.

Edit: installed the new MAF and she fired right up and pured with no SES light. Of course, I used the chip I was using before I made the pulse width changes.

RBob, thanks for all the help and advice. I hope if something similar happens again later that I can remember this post.

Okay, one problem right after another. Now the car wants to overheat. It got to 270 on the way home according to the Equuis gauge I picked up at O'rielliys. My computer locked on me so I don't know what temp the ECM was seeing.

I've come to the conclusion that this engine can't be tuned. It went from running very rich after the new MAF (but steady, BLMs 108 at idle) to running a bit lean at idle (BLMs 134ish) and running 240 degrees (at least) either way. Idle spark advance is 26 degrees, so timing shouldn't be the issue.

RBob, I really appreciate the help, but think it's time to part it out. A year and a half and have only driven the car a max of 10mi round trip; that's not getting to enjoy it at all. I've put more money in this engine and tuning that the whole car is worth.

The saga continues. I wish I had the ability to just leave something alone.

New TPS at the end of August, installed wideband and Equuis water temp gauge last week. After the gauge installs, I had to replace the alternator, then I replaced the MAF and Burn-off relays but found out that a new MAF was the problem there. What I thought was overheating was just a faulty gauge or sending unit (not sure which). Tried to get a datalog this morning and noticed that the MAT reading is 392 across the board. I bought a new sensor and ohmed it against the old one to find out they read about the same. I just fired up the car again and, no dice, still have a reading of 392.

Now, the MAT sensor is brand new, the engine harness was bought new from S10Wildside about 4.5-5 years ago as well as a reman ECM from the parts store. The jumper harness that goes from the main harness to the MAT sensor ohmed fine. Any ideas where my problem could be?

392 degrees is a short to ground.
with the ECM thinking the air is that hot, it ignores the MAT sensor.
i know for coolant temp it drops onto a default mode for fueling and spark advance, im not sure if it does the same for MAT or not.
whats the MAT read in TunerPro with it unplugged?
it should be around -40.
with the MAT unplugged, you can check the voltage at the MAT connector. it should be around 5 volts on the reference side.

I haven't checked with it unplugged, but my guess is it will still read max.