I'm dealing with this same item on my 88. Code 33.....runs fine......no code, runs like crap......have to unplug MAF to start/drive it. Very interested in what your MAF experience shows, as I am 5 Cardone MAFs deep.

 

So here's an update...

My new Bosch MAF came in and the car's been driving a little sluggish when cold, but idle is always steady, doesn't stall, gas mileage is good, and once it's warmed up it runs perfectly. "Check" is still on, but it also ran very well when it was off once. I've been driving it for at least 20-30 minutes daily for the past 3 days to make sure the results are legit.

I'll keep you guys updated if trouble returns.

 

Sending PM.

 

Did you ever change injectors? i'm getting a lot of people pushing me that way too. Just wondering if rebuild MAF and weak injectors is the perfect storm here.

What code is throwing with the new MAF?

 

My injectors were replaced back in early 2012. I also kept hearing that from practically everyone and it frankly annoyed me, knowing that I have the paperwork and recently checked them myself. Thank god they were changed because worn out/crusty o-rings that seal the injector lead to engine fires which are common. If yours haven't been changed then I would do so just for safety. However, the process to remove the injectors requires removal of the intake plenum and there's a list of stuff I'd replace and inspect while that's happening.

Car's running fine, but still throwing a code 33. I've practically given up because it's comforting to see that little light. Plus this MAF has given me the best performance and MPG yet. Can't argue with that because it's an original unit.

 

I'm taking my car to a shop run by a tech that was at AZ Speed and Marine back in the day. They know TPI better than anyone, so I'm keeping the faith that they can find it and I'm hoping that it might be a combination of bugs unique to y bodies. The answer can't be to live with an SES forever! I'll let you know what they find!

 

From what I've read, I dont know if this problem is confirmed maf related. I can say that I experienced the same symptoms on my 85 many years ago. Turned out to be my ecm. I think this is a possibility.

 

I swapped ECMs a week back. No change. Did notice that the ECM was a reman GM part......prob years ago.

 

I searched for a member to lend me their spare ECM, but no dice. It still might be the ECM in some way, but for now it's running ok with the new Bosch MAF. Maybe one day i'll swap it for a faster unit or do a stand-alone and custom tune IF I feel the need to modify this motor instead of doing an LT or LS swap.

 

Why not troubleshoot the Code 33? It's very likely you had more than one issue. If you follow the Code 33 troubleshooting chart it leads to several possibilities. There could be a ground problem, ECM or the burn-off module. Since this code is related to the ECM signal voltage, a grounding issue is highly suspect. I would disconnect, clean and reconnect all the grounds. The one I suspect is ground Ckt 450. The ground attachment is on the front of the intake manifold on the drivers side. There are also grounds on the transmission bolts. There should be one on each side.

 

Its ALWAYS the harness. Always.

been more C4 parts bought and installed unnecessarily than the whole auto-parts industry combined when it was something very simple like bad connections in the C4 harness.
Plastic cars depend on the wire like you and I depend on blood vessels..

 

I'd say we are looking at multiple issues. The MAF was clearly bad. It was receiving power from the burn-off module but not lighting off the wire as it should.

The code 33 matches the symptoms. Code 33 indicates the ECM has seen airflow in excess of 90 grams/second (high voltage) with the TPS indicating less than half throttle and RPM less than 2200. If a code 33 is set, the ECM will use a default value and the check engine light will remain on until the next ignition cycle. So the engine may be running better using the default value.

A poor 450 ground could create enough resistance to cause a high voltage. It could also cause a wrong TPS voltage. In any case, checking grounds doesn't cost anything.

 

What brand fuel injector's? I have had failure brand new right out of the box!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!! Exact same problem. What's the miles on this car?

 

[QUOTE=A poor 450 ground could create enough resistance to cause a high voltage. It could also cause a wrong TPS voltage. [B]In any case, checking grounds doesn't cost anything.[/[/B]QUOTE]

Exactly.
I've said it a hundred times, these wire harness's are fragile and they are substandard for automotive use. They have poor insulation that is easily effected by common automotive chemicals and the plastic insulation hardens then cracks, then you get cross signaling and momentary grounding thats virtually impossible to pin point. I lived with a misfire that actually moved from one cyl left bank to another. Finally one day I jerked the harness with the engine idling and it ran right ! After more digging I discovered the damaged insulation and some very cheap splices in the harness under the wiper motor in the truck line on the firewall and ended up chopping out that entire section and soldering in new wire.
Problem solved.
I've also seen the connections on the jumper post cause an engine to misfire just from being corroded and dirty. These systems are fragile and need crystal clear signals and the levels of resistance that they started out with...otherwise, they WILL mis-behave.

 

I'll need a list of grounds to check out since that last time I went digging for wires in a car the radio and interior lights stopped working properly...

Think interior lights turning on whenever you took a turn. Hah... memories.

Not in a hurry to check this out, but I'll need something to do when I have time.

 

Someone that can scan and post a pic will be able to provide the FSM page that has them listed...
I can give you the high-lites...

get under and look upwardtoward the oil filter. Look along the bellhousing and block toward the driver side valve cover. You will see a bundle of 5 wires on a bolt....
have fun !
I didn't put it there....

Then after you recover, get up and above and find that upper end of that where it runs to the trunk-line under the wiper motor. IIWM, I would pull what ever and split that harness and look closely at the splices. They often pull apart and loose the connection.

These are the most important of ANY grounds onj the entire vehicle.

Next, jumper post and fusable links behind battery. Take battery out, clean the entire area, wires and harness.

After that simply search the frame rails in the engine bay for grounds bolted to anything. Remove and clean. Wire brush, dremmel with wire wheel is best. You WILL see or feel a difference in the way it runs just by doing this. These cars are absolutely 100% dependent on good clean elect connections since the computer data is sent in measurements of resistance..

 

1. Circuit 450 grounds the ECM, Burn-Off Module, Fuel Pump Relay and ALCL connector. The common ground point is G103 and is located at the water neck bolt on the intake manifold. The schematics show another smaller 450 ground but I can't find where it attaches.

2. Ignition and Electronic Spark Control are grounded through common ground point G104. G104 is located and the rear of the driver side cylinder head.

3. As mentioned before, another ground point is G140 on the driver side transmission bolt. It grounds the instrument panel, A/C, and wipers.

If cleaning the connectors and attach points doesn't clear things up you may need to do some continuity tests to verify the integrity of the wiring.

 

Thanks again guys.

Took a drive this morning, "Check" is back, but performance and everything was fine, as it was. Car sat for about 5 hours, started it up, "Check" was off, but it was running normally. Same code as before, but with "Check" off it's running on a different memory.

I honestly beleive it's a ground now... idk what else causes such sporadic results.

 

You have to remember that when you see the CHECK lite...the ECM is bypassing 90% of all sensor input and running the engine off of a program. Thats the emergency method of operation and will not pass a smog nor will it provide the optimum performance. Its designed to get the car home...thats about it. Thats the LHM (limp home mode).

The system can cycle in/out of LHM and norm run until the conditions are met for another code that sends the ECM back to OL (open loop--a break in sensor input or something out of range) and sets the CHECK ENG lite again. Normal (no lite- CL-closed loop, all sensor input) has a fairly wide window of operation and will stay there until something goes beyond that range or parameter.
So, as long as you see the LITE...its going to run ok, it does not have a choice. Thats the program that GM wrote for general operation. It'll run ok. BUT, its not good to run it like that for very long...its like a bad tune up.
IF its running like crap and refuses to go to OL, pull the MAF plug. That sends a major fault to the ECM and forces the shift to OL so it will run better in LHM or OL.
With what you describe, it does sound to me like its connections. As I said before, start with the grounds, do the power distribution node,(jumper) then search the harness by wiggling, gentle twisting (to locate breaks while its idling) and you will find the point of failure.
These things are totally dependent on the quality of the electrical signals. In Resistance values for reference to the ECM, a dirty contact is the same thing as the far end of the sensors value...so sending the ECM a signal from a temp sensor for example, that says extremely hot (far end of the scale)while the car sits there key ON not running @ 160* and the ECM will be confused and respond by attempting to compensate but there is only so much it can do with impossible data its seeing. End result...it runs like crap or is very difficult to start.

Good luck...
we tend to forget just how easy these systems are. We over think the problem because we are unfamiliar with the electrical. It seems complicated at first.
Its easy. It really is. The fun part is finding the exact failure...wire or a sensor?

telling the difference between a mechanical failure like a burnt valve and a bad injector isn;t that difficult with the right tools and a little back ground on the engine and its systems. telling the difference between a bad inj and a bad wire TO that inj can be more....interesting.

They say that "patience" is a virtue.
If that is true, then by default, owning and driving Corvettes you are already full of it...

 

Hey Ziggy- Tony at Tempe Performance troubleshot the code 33, and tracked it down to a bad power wire from the MAF relay to the MAF. He replaced the wire and no more 33, although I now get an intermittent code 36 now. I'll live with the 36 for now, as its running great and it's every once in a while. Old cars!