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This is perfect, and I greatly appreciate you uploading these charts.
However, I do have one question. When examining the diagram, I still don't see a MAF power relay And when looking at the area you suggested where it would be, there is only the fuel pump relay?
The relay is what you're missing. I got an 88 and a 85 TPI. My bad. HERE IS THE CORRECT ANSWER. I have too many cars!
Several modifications have been made to the TPI system introduced in 1985. The 1985 system used a GM Part #1226870 ECM and had a Mass Air Flow (MAF) sensor and a MAFS module to control the power and burnoff functions for the MAFS. In 1986 two relays replaced the MAFS module and the Electronic Control Module (ECM) was changed to a GM part #1227165. In 1989 the cold start injector was deleted from the system. The primary injectors were used for cold starts via a fuel enrichment program in the newer EPROM calibrators. In 1990 GM introduced the speed density system. In essence the MAFS was replaced with a Manifold Air Pressure(MAP) Sensor. This system uses a ECM GM Part #1227727 for the Corvette and 1227730 for Camaro.
I have tested 3 MAFS and no progress.
Tested Voltage from Burn-off module and there's 12V going to the MAF, so its getting power.
Computer still indicates low voltage from CKT 998 to terminal B11 to ECM (Code 34). When I test voltage from CKT 998, I get 5v with key on.
Question: Shouldn't I be able to keep the car running with the MAF disconnected? Even with it disconnected it will not stay running and stalls as soon as I let off the throttle.. I Do get code 33 (which is correct) indicating that the burn-off module IS working..
After many hours of reading and contemplating, it clicked as to HOW the MAF system works.
I followed the wiring charts and tested cables, and they all tested correctly. I tried 3 different MAFs with the same results. So even though I was getting code 34, the problem was NOT the MAF sensor...
Code 34 is the ECM telling you that the voltage on Circuit 998 going to terminal B11 is low (it wants to see 0.8v - 5v). The level of volts on CKT 998 indicates how much air is going through the MAF. More air through the MAF, the more voltage the ECM should see. I realized that if the MAF is working properly, air is somehow getting in the intake after the MAF.
So in order to get the engine to run, I opened the idle adjustment screw quite a bit to make it easier for air to get in through the throttle body, thus allowing it to run. I then listened for any hissing air from lines coming off the plenum. And sure enough, a plastic three-way splitter had deteriorated from the plenum to the cruise control unit. I replaced the splitter and readjusted the IAC following the procedure and BOOYA!
I hope my experience helps anyone in the future! I spent $150 to solve a $1.50 problem. But, hind sight is 20/20 eh?
08-04-2015, 11:15 PM
