Need help with OBDI code 41!

[CAChevy]

Hey Gang. The saga continues with this truck. It's a 1984 CA emissions equipped with a new GM 350 crate.

Finally got it firing on all eight cylinders and the miserable CCC Quadrajet is as tuned as I can get it with a dwell meter and a vacuum gauge.

I took the truck out today and ran it. Other than being disappointed in the "get-up-and-go" that this truck is lacking, it seemed to run pretty good. However, I did notice slight pinging under semi-hard acceleration. Base timing is set at 8 deg BTDC, 87 octane gas. I may try to set it back to the recommended 6 BTDC and see if that helps.

I got it home and for giggles put it in diagnostic mode to see if there were any codes. The check engine light wasn't on but I pulled a code 41.

41
EST circuit
No distributor reference pulses to the ECM at specified engine vacuum.

I have no idea where to start. The ignition module is new, the MAP sensor is new. I don't know if the original parts were bad or not, I just replaced almost everything under the hood during the rebuild.

I did accidentally momentarily ground the tach lead of the distributor when I was setting my idle. Just a quick spark. Don't know if I messed something up in doing that. The lead is still providing a tach signal.

[beamn7]

That quick spark may have shorted out the reference side of the ign module in the dist.... When you replaced the MAP did you make sure it was actually a Baro sensor and not a MAP? These use a Baro sensor that looks exactly like a MAP and has the same plug but functions opposite of a MAP....

[CAChevy]

You know, the thought hadn't crossed my mind about having the wrong sensor. I put the old part back on and so far, the code has stayed away. The two MAP sensors look identical other than the original still has the "GM" stamped on the back. I took the "new" one with me back to the parts store where I got it and asked the guy for a MAP sensor for my truck. The one he brought out to me was the same part I had in my hand. Then I asked him if he had a Baro sensor for my truck. He looked it up and couldn't find a sensor listed as that.

Got me. I'll just keep running the original until I absolutely need to replace it. Thanks for the response beamn7!

[CAChevy]

Oh, and the lack of "get-up and go"??? Solved!

I put my son in the driver seat and had him push the accelerator pedal to the floor as I checked to make sure both the primary and secondary butterflies of the carb were opening all the way.

The primaries were only opening 3/4 of the way with full throttle and the secondaries weren't opening at all. Apparently the TV cable for the 700R4 didn't self adjust correctly and was keeping the throttle from opening all the way. I released the adjustment tab on the TV cable and looky there, all 4 butterflies opened. So, with the accelerator pedal to the floor, carb fully open i released the TV cable adjustment tab and pushed the cable as far as I could towards the firewall then locked it in place.

[beamn7]

Good deal! As for the Baro sensor, I was able to get the correct one from RockAuto. May give them a try if you want to replace it. Glad she's up and running good now!