I've done a lot of work on this code 33 business but I still haven't got the problem solved. I am now able to reproduce the problem at will.

It happens at low RPM( < 2000) with MAF flow greater than 50gm/sec and with a TPS voltage less than or close to 1 Volt. Sounds like right out of the GM manual doesn't it? I have trapped the error in my scanner and is consistent with the above numbers.

The problem is I already had a custom PROM made that has the 2000RPM limit set at about 150gm/sec. My TPS sensor has had the bottom end set at from .52 volts to .60 volts. WOT is at 4.4Volts.

I have pulled/tugged on the wiring, changed the MAF and MAF burnoff relays, cleaned connectons and cannot get the error to trigger except under the previously listed running conditions.

The car totally rips when the code isn't set. I have had it above 100mph on two recent occasions, full acceleration, etc.. High acceleration, deceleration, nothing will make the error set, except lugging it at low RPM.

The group that made the PROM has offered to reburn it at max values for MAF over the whole RPM range. They have also suggested that I set the TPS as high as possible, like .6+ volts. At some level it will set an error (21 or 22).

Any insight would be appreciated.

Thanks



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88 IROCZ28
ZZ4, Big Mouth, Lg. runners and BBK 58mm TB. 700R4 w/ corvette shift servos, 3.23 Borg Warner & posi.
B&M 2400 Hole Shot and MegaShifter. Random Tech Hi Flow Cat and 3" Catback system, Edlebrock headers - jet coated.

 

They didn't change the right table.....You need to change the MAF high diagnostic (error 33) threshold. That is found under the ECM constants. There is no "rpm" to that. In the 6e code there is a table that has rpm- Mass air flow vs. rpm (diag.)BUT, that will not change the parameters for setting the code 33. Hope this helps.



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86 406

 

Thanks. I'll call them tomorrow and see if I can get this across. I'll let you know how it turns out.

 

Told you I'd get back:

When I called the chip folks, they informed me that they already had it (the MAF limit)raised to 250gm/sec. They insisted that I had a loose wire or short. There was no way the PROM could be causing this problem.

I have found a workaround although I don't know exactly what it means. By adjusting the TPS to 0.8V, the problem disappears. Now I think that the MAF limit is still at 45gm/sec, that they are working in the diagnostic location (6e) you had mentioned. One of the conditions to set the error is that the throttle position is less than 25% (I assume this means 1.2 Volts). At first I set the TPS at 1.2volts, the error went away. The downside was that the idle is commanded high - like 1500RPM with the tranny in neutral. I kept working it down. At 0.73V the problem was almost gone, at 0.8V I can't get 33 to set. The car is very drivable with a 2400 stall TQ but I would like to get the idle back down to 800 for smog testing.

Has anyone ever attempted to slide the idle control table (I'm assuming there is one)? I would like the desired idle speed to be 800RPM with the TPS at 0.8Volts.

Bottom line, I don't think I have a loose wire or short. Just a big ported throttle body and intake that draws in a lot of air with a little movement of the butterflies.

Thanks for your help, at least I can now drive the car in closed loop without that light.

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88 IROCZ28
ZZ4, Big Mouth, Lg. runners and BBK 58mm TB. 700R4 w/ corvette shift servos, 3.23 Borg Warner & posi.
B&M 2400 Hole Shot and MegaShifter. Random Tech Hi Flow Cat and 3" Catback system, Edlebrock headers - jet coated.

 

Resolution for now:

1. Set the TPS at 0.8V.
2. MAF 33 has been fooled - ECM thinks car
is at >25% throttle. (I started at 1.2V and worked it down to the minimum. In my case at .73V the MAF33 still came on but rarely)
3. Back out the screw on the Throttle Body
enough for satisfactory idle. (I like about 700RPM for the rumble.)
3. Car goes like hell - this phase of the project is complete. Next phase suspension.

To all who helped - thanks, my turn now.

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88 IROCZ28
ZZ4, Big Mouth, Lg. runners and BBK 58mm TB. 700R4 w/ corvette shift servos, 3.23 Borg Warner & posi.
B&M 2400 Hole Shot and MegaShifter. Random Tech Hi Flow Cat and 3" Catback system, Edlebrock headers - jet coated.

 

Man,I have the exact same problem(posted 12/2)maybe thats my answerraising the tps setting.I've always thought that lowering it
would give better results with long duration cams.I to have recently changed to a 58mm t.b.but didnot have this problem previously.
please let me know of your findings.

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87 IROC WITH 409(.040 OVER400) MINIRAM,NOS(125HP)TRICK FLOW PORTED HEADS,C.C.CAM,FLOWTEK HEADERS,CUSTOM PROM,MODIFIED 700R TRANS,2400 B&M CONVERTER,3.73POSI REAREND.
LOOKING FOR THE 11 SEC. ZONE.current ets.12.39@114 mph