dead like a dog on the side of the road!

[bigwingnut]

1985 4+3 with no mods:

Driving down the interstate, on cruise at 75 mph, 200 miles into a 500 mile trip. Cruise trips off, car falls on it's nose. Coasting to the side of the road. Gas pedal has no effect, but idles at 1400 rpm. Temps, volts, pressures normal. Suspect throttle position sensor.

1400rpm in 4th overdrive is 51mph, so I got off to a parking area. Shut off the engine, jump the connector for the codes, and it says Code 12, 22, 33. Parked under a street light, but it's shining in the wrong place. Try to start the car to move it so I can see the throttle position sensor and vacuum line to MAP sensor...it cranks perfectly, shows no codes and I finished the trip with no problems. Any of the Techies out there got any ideas what the problem is??? The last Vette I had was a 65, and I understood it...but the new "electronical" ones have me bum-fuzzled! Thanks!!

 

[Ken]

I'm not going to be of much help here Rip, except to maybe give you the code's meaning (According to the Haynes manual for my '87, because I can't find it quick enough in the GM manual :L).

• Code 12: No reference pulses to the ECM...Probable Cause: This code will flash whenever the diagnostic terminal is grounded with the ignition turned on and the engine not running. If additional trouble codes are stored in the ECM they will appear after this code has flashed three times. If this code appears while the engine is running, no reference pulses from the distributor are reaching the ECM.
  
• Code 22: Throttle Posiition Sensor...Probable Cause: Check the TPS adjustment (0.54 +/- 0.075 volts). Check the ECM connector. Replace the TPS.
  
• Code 33: MAF Sensor...Probable Cause: Check terminal C on the MAF sensor--it should be about 0.5-volts at idle and 4.7-volts at wide-open-throttle. Trace the wire from terminal C and look for an open. Replace the MAF sensor.

I know what you mean by be "bum-fuzzled" by it all nowadays.

I hope this helps you.

 

[bigwingnut]

Thanks Ken! I got the same stuff from my Haynes manual too. What I don't understand is why 2 simultaneous error codes, that go away when the engine is shut down. What are the odds of two components gettin sick at the same instant, and then "healin' up" together too? I'm tryin to figure out what they have in common. The only component the two Haynes code explanations share is the ECM box...and I replaced that less than a year ago to fix a cruise control problem.
"'Is a puzzlement!!"

 

[vigman]

Well it's actually easy

The GROUNDS for both circuts might have failed.


Vig!

 

[bigwingnut]

Vig, I hate it when a possible explanation is that obvious!! Especially when somebody else has to point it out to me!

I'm back in South Carolina now, but when I get back to Florida next weekend I'll check it out. I appreciate it, and will let you know what I find. I've already ordered an new ECM and chip...I'll have them on the shelf just in case. I drove the car about 400 miles after the incident, and so far it's been just fine. An intermittant ground could very well be the problem.

 

[vigman]

The weak link

IS the braid ground from Block to frame and all the little grounds at the tranny bellhousing.

Do a search "Getting Grounded" by yours truly!

Vig!

 

[bigwingnut]

Yuppers, Vig, I had the same problem with both the MG's and a Suburban too. When I get back to Fla. this weekend I'll check it out. Thanks for doin' my thinkin' for me. I'll read your "Grounding" post before I start!