MAFs wont go above 1599hz, starts bucking and backfiring at 4500rpms

[DROOPY209]

Ok guys, this problem started about 3 months. At first, I had a lot of boost leaks. I found a huge one at the 14b outlet pipe. I fixed it then I found out that the lower injector seals were toast(Thanks soapy water test!!!) Timing is set at 5*.

At idle, my boost gauge is now at 20hg vacuum, where before I started fixing the boost leaks it would idle at 15-16hg of vacuum. I no longer have boost leaks. No exhaust leaks. I used the ultra coppper sealant and sealed up all the exhaust leaks that I found when I seafoamed it. The idle is dead solid now. No misfiring, idle surge or anything. exhaust has a nice deep note, thanks to my Thermal R&D 3" exhaust. Greddy EGT gauge says 550* Celcius at idle.


No matter what I do while driving, in boost or out of boost, the car will now backfire at 4500 RPM everytime without a doubt. It used to buck and backfire at 5187 RPM, everytime. Plugs are new, gapped at .028, plug wires are new. I can rev it up to redline while in neutral, but once the car is moving, 4500rpms is the max before it starts backfiring and bucking.

On my logger after this happened, I saw 255 counts of knock, and the O2 sensor voltage went up to 4.98v. Yes that is correct, the o2 went up to 4.98v.

Another issue, when I have the key in, ignition ON, but car off, the ISC makes a very weird noise the whole time. It will stop when I turn the key OFF, or unplug the harness connector.

Im running the GM MAF-Translator setup in blowthru. Fuel trim low is at 118% Fuel trim Mid is at 111%, and Fuel Trim high is at 101%. I can turn the Mid and WOT knob on the translator all the way rich +35% and the MID and High fuel trims wont change. No matter what, the car NEVER gets above 1599 Hz. It stops right there and the bucking and backfiring starts.

I relocated my battery to the trunk. My logger says voltage is at 14.2 volts.

What should I do to fix this. I have an EPROM Ecu that I'm thinking about trying out. I was also thinking about putting on the stock MAF

 

[Gromit]

On my logger after this happened, I saw 255 counts of knock, and the O2 sensor voltage went up to 4.98v. Yes that is correct, the o2 went up to 4.98v.


Im running the GM MAF-Translator setup in blowthru. Fuel trim low is at 118% Fuel trim Mid is at 111%, and Fuel Trim high is at 101%. I can turn the Mid and WOT knob on the translator all the way rich +35% and the MID and High fuel trims wont change. No matter what, the car NEVER gets above 1599 Hz. It stops right there and the bucking and backfiring starts.

I can address a couple issues you're having. With respect to the 255 counts of knock & the 4.98v O2 reading...Are you using MMCd to log? If so, have you verified it's set up for 1g - the default settings are for the 3000GT/Stealth cars. Also, is the 4.98v for the O2-F? If so, you actually want the O2-R reading, which actually corresponds to the front O2 sensor on a 1g. These are just a couple typical things that turn up with MMCd.

As for your MAS reading of 1599 Hz, that's the max it'll show on the logger. If you had an EPROM with a custom chip, 1 of the options is to be able to display double the MAS value. Are your MAS values erratic at higher rpms's when the bucking starts? Do you have a log of a 3rd gear pull you could post?

 

[Wizard]

I've had this happen on a few cars before.....ECU was toast on them. Open her up and take a whiff imo.

Wiz

 

[DROOPY209]

I can address a couple issues you're having. With respect to the 255 counts of knock & the 4.98v O2 reading...Are you using MMCd to log? If so, have you verified it's set up for 1g - the default settings are for the 3000GT/Stealth cars. Also, is the 4.98v for the O2-F? If so, you actually want the O2-R reading, which actually corresponds to the front O2 sensor on a 1g. These are just a couple typical things that turn up with MMCd.

As for your MAS reading of 1599 Hz, that's the max it'll show on the logger. If you had an EPROM with a custom chip, 1 of the options is to be able to display double the MAS value. Are your MAS values erratic at higher rpms's when the bucking starts? Do you have a log of a 3rd gear pull you could post?

Yes, Im using MMCD. I have it set up for a DSM instead of a 3si. Im using the O2-R for the O2 sensor. I will post a log as soon as I figure out how to do it easily, Im a newb at posting logs.

 

[DROOPY209]

I've had this happen on a few cars before.....ECU was toast on them. Open her up and take a whiff imo.

Wiz

Will do. I know for a fact the caps have not been replaced in this ECU.

 

[DROOPY209]

Here are some pics of the ECU that I know for a fact has not had the caps replaced. I took it out about 5 minutes ago and snapped some pics. The ECU was not an EPROM.

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[RvlutionMtrsprt]

Ouch, I think that's an injector driver board.... and the root of your problems. Dave Mertz can probably fix it, Terry Posten should be able to if he's got the parts. Or at this point you could score yourself a good eprom ecu!

 

[DROOPY209]

Ouch, I think that's an injector driver board.... and the root of your problems. Dave Mertz can probably fix it, Terry Posten should be able to if he's got the parts. Or at this point you could score yourself a good eprom ecu!

So, do you think the leaking caps took out the injector driver board? I have an EPROM ecu laying around in my garage, but I can see that the caps bearly have started to leak.

The ECU in my red 1gB awd is CLEAN. No leaking caps at all.

Should I swap that GOOD ecu into my car?