Twenty Thousand Degrees Advanced

[ericburgundy]

Hi, I'm new to the forum.
I have a problem I haven't been able to find a solution for.
94 GM TBI 7.4 Truck. 395 ECU BHDF Moates G1 adapter, Tunerpro RT.
I can rev up moderately just fine, but if I WOT from idle, it instantly reads 6375 RPM and 23000 degrees spark advance.
(about 1200 RPM by the external tach) It then backfires through the throttle body.
It does this with the stock $OE bin, I also tried a stock $OD bin with the same results.
This is in Open loop, map reading of 80, TPS 2.1 volts.
I replaced cap/rotor/wires to rule out secondary ignition misfire, but this seems more of a computer issue.
Could I have a bad ECU?
Could I have a bad Memcal?

other unrelated issues:
ECU reads the O2 constant 446mv, but I measure varying .90-.93v at the pin.
On hot restart, it struggles against the timing. Even though it's reading 0 degrees advanced.
If I reset the ECU by disconnecting the battery, it starts up with ease.
Has anyone seen this before?

[Fast355]

Hi, I'm new to the forum.
I have a problem I haven't been able to find a solution for.
94 GM TBI 7.4 Truck. 395 ECU BHDF Moates G1 adapter, Tunerpro RT.
I can rev up moderately just fine, but if I WOT from idle, it instantly reads 6375 RPM and 23000 degrees spark advance.
(about 1200 RPM by the external tach) It then backfires through the throttle body.
It does this with the stock $OE bin, I also tried a stock $OD bin with the same results.
This is in Open loop, map reading of 80, TPS 2.1 volts.
I replaced cap/rotor/wires to rule out secondary ignition misfire, but this seems more of a computer issue.
Could I have a bad ECU?
Could I have a bad Memcal?

other unrelated issues:
ECU reads the O2 constant 446mv, but I measure varying .90-.93v at the pin.
On hot restart, it struggles against the timing. Even though it's reading 0 degrees advanced.
If I reset the ECU by disconnecting the battery, it starts up with ease.
Has anyone seen this before?

I wouldn't rule out a bad Memcal or ECM, but I would start by locating the ECM grounds and cleaning them as well as where they attach to the block. I am not as familiar on the 454 with their location, but on the same truck with a V6 or smallblock V8 the grounds are on the thermostat housing and on the rear of passenger side head.

[ericburgundy]

Good call on the ground, and thank you for your response!
o2 is working and now i've discovered i was extremely rich.
I leaned out the VE tables and also rerouted the #7 plug wire away from the wiring harness in case it was causing interference. This has nearly cured the misfire.
I still have the hot start issue which feels like i'm overly advanced although I'm reading 0 degrees.
I'll have to get the wife to crank while I check with a timing light to be sure.
My gut says the memcal is faulty, even though I don't know exactly how it works.

[1project2many]

You might have a mismatch between the ADX and the calibration. There's really no way the ecm should be sending a message for 23k degrees timing.

[JeepsAndGuns]

I remember something like this happening to me once. If I remember correctly, I changed a spark advance setting, maybe a bias setting, and did not reset the ecm before I installed the chip and run it.
I just remember the spark advance number on my ADX jumping to some crazy stupid number and it running like doo-doo.
I have no idea if this has anything to do with your issue, but just figured I would share.

[RobertISaar]

i get the feeling that the spark is being reported as a 16-bit value but someone never set the box for signing.

23,000/.35 = 65,714, which is right around the 16-bit limit, indicating spark is happening negative to reference(or TDC, i don't know the late TBI code too well).