I just bought my stepdads 85 corvette. Well maintained, but rarly driven the past few years, only 37k However, after we pulled it from the garage we discovered more than one problem, some of which Ive already fixed, others I'm completely stumped.

1st, when the car is started it sounds like it's running fine, but once you put any pressure on the gas it either chokes up or cuts off. It does this until the engine hits about 150 degrees. Then it runs like a champ.

The second problem, which may be related to the first, is a code 33 MAS high voltage. Ive already tried 2 new MAF's, just in case one was faulty, and Ive cleaned all the grounds, not that any of them needed it. I also cleaned the connections going to the ECM but nothing has worked thus far.

Honestly, I'm not sure what else to do and I want to avoid the dealership at all costs.
Thanks

 

The code you have can certainly give the problems you describe. My suggestion is to purchase a 85 factory service manual. It will tell you step by step how to trouble shoot the code you have. The 85 has a MAF burn off module located in the passenger side dash. Hard to get to, but could be causing the code.

 

"Code 33 indicates: That the ECM has seen air flow in excess of 90 grams per second (high voltage) with TPS indicating less than half throttle and less than 2200 rpm."

Translation: The MAF is feeding the ECM data that isn't possible for the throttle opening and engine speed. Your problem could be a short,an open,a bad ground, a bad ECM or a bad burn off module. The FSM gives you a step by step guide to isolating the problem.

 

There are a few things that can cause a code 33 including a high MAF signal. Other Code 33 related issues could include a) an open wire or terminal at or to the MAF; b) faulty relays (or installed backwards and with this I mean there are two different relays, one for power and the other for burn off, and if they are switched I have seen them throw a code 33, don't know why but I have seen this even though they seem to be the same relay with the exception that one comes with a shock absorbing strap and the other one does not. Accordingly, one thing can be to just swap relays and see if that helps); c) faulty MAF sensor and the last possibility being; d) the ECM.

PROME REVISION - I want to point out that Chevrolet has come out with a revised PROM for the 1986 Corvette due to code 33 problems. Now before you go off and order the revised PROM we need to find out a little bit more of the problem you are having. This is not a hard code to fix but you may have to do a little looking.

WIRING - Wiring is not a common code 33 problem but if you have an intermittent problem that could be a sign of a poor connection of one of the terminals at the MAF sensor. If the light comes on right away that could also be a sign of a broken wire. If one of the MAF sensor wires becomes open it will set a code 33 but, this condition would happen all the time probable shortly after start up. If you have access to a scan tool I would hook it up and read the airflow; when warm it should be around 6.0 grams per second. Then try wiggling the wires and if it shoots up you having a wiring problem. If it's high all the time then you could have an opening in the wiring. I would suspect that seeing how you tried a new sensor that would not be the problem but I would check it anyway to begin with.

ECM Upgrade - I suspect that you have a #1227165 ECM in the car and that could be the problem. This is the original style ECM used in the 86 to 89 Corvettes. Chevrolet has had a real problem with the internal circuit board cracking on these original units and when this happens there can be all kinds of problems including code 33, 36, 34, 15, 51 and a few more. Drop down the ECM and see what the service number of the unit is and if it's a #1227165 replace it, if it's an aftermarket rebuilt painted black one replace it as I do not trust that old style ECM at all and I have found that just about all aftermarket replacement ECM units are of the old style. The GM number you need to go back in the car with is a #16198259 it is the GM replacement for the original #1227165 and is much better.

 

This may be way out there, but if the car has set alot, look closely at the wiring for damage caused by mice. Also, have you drove the car a few hundred miles and refilled with fresh gas? Cars that have set alot can sometimes run better after being driven awhile and fresh fuel.

 

Actually I have found a few mice droppings, but have checked diligently for any signs of damage, but have found none. I drove the car from NY to NC. So the gas has been flushed a few times over.


I copied and saved the service manual page for this problem I'm just trying to make sense of it.
Ill look into a new ECM any idea what they $. Ive already tested for shorts and bad grounds.

 

pmihaltin, excellent discussion for an 86 but his is an 85. Different ECM/ MAF burnoff entirely.

 

I've dealt with this same problem on my '85 as well. Contrary to what others say you dont need to convert to a later ECM. You will need to remove the dash cap and the passenger side "breadbox" to get to the MAF module. Its bolted just behind the breadbox. There's is a strong possibility that some of the connections on the circuit board inside the module are broken. Thats what was wrong with mine and I had even replaced my MAF twice. Make sure you check all the wiring as mentioned before. If nothing obvious is broken, remove the module and take it to someone you know is good at working on circuit boards. Have them look at the connections under a magnifying glass and repair as necessary. I had an electrician fix mine and it has ran great ever since.

 

[QUOTE=Demonic85;1564245357]I've dealt with this same problem on my '85 as well.


Just out of curiosity did yours also have problems when it was cold?

It would be nice to kill two birds with one stone.