Okay, the 1985 corvettes HAVE a burnoff module, correct?

My car’s MPG is S*** and the cars RPM’s are ALL OVER the place. The car has a knocking noise (someone told me possibly backfire) and sometimes the car will just turn off in the middle of the driving.

i think it’s the burnoff module and I’m about to replace it. I replaced the fuel pump, spark plugs, relays, etc.
so I think it’s my best bet.

let me know if this is a good move

 

The burnoff feature will not work with a bad module but this will not affect the car like you are seeing unless the MAF is totally fouled. Also you would get a code 36 if it were not doing the burnoff function.

 

any suggestions as to what’s wrong? Someone else told me it is most likely the burnoff module. Or could it be my MAF all together ?

 

Have you pulled codes? It can be both, generally if the MAF dies there will be an SES light showing a code. O2s are the ones that die without setting codes soon enough.

Tried disconnecting the MAF to see if it runs/idles better?

 

Is it setting any codes? The SES light will be on if it does. If you don't have a factory service manual get one and follow the troubleshooting for drivability.

check Fuel-Air-Spark

You can disconnect the MAF when it's idling and if it doesn't change then your MAF is bad plus it will throw a code while it's disconnected.

If it is not setting codes there could be a few things that might be wrong:

• Bad distributor cap/rotor - plugs, wires
• Bad Fuel Pressure REgulator - There will be fuel in the vacum line to it if it is bad. Also the FPR leakdown will happen pretty fast... should be more than 20 - 30 minutes.
• Fuel injectors are bad or leaking ... will fail the leakdown test.
• Check the fuel injector fuses ... there are 2.
• Bad injector drivers in the ECM ... get a noid tester and check that there are pulses on each injector.

That's all I have for now.

Good luck

 

it does the same thing with the MAF disconnected

 

A couple things I will throw around.

The ICM(under the rotor) needs computer cpu thermal paste under it. You can check the wires to it are in good connection.
Redo the thermal compound. ICM from standard motor is cheap.

Clean the maf and connector with cleaner, I use only this one

https://www.ebay.com/itm/CRC-QD-Elec...frcectupt=true

Also if you take a pencil you can make sure relay wires are not contacting each other because sometimes the covering shrinks down.

Good luck

 

i have thermal paste . I work on computers a lot.

is this true ? First time I ever heard of this

 

Yeah, it probably is. I never changed one on a C4 HEI, but it was true for all previous years that I know of.

 

What I am saying is when you have strange problems off and on , and if you are changng things out it needs to be looked at along with the condition of the plastic. Be carefull it can be brittle. It is there under the rotor trust me. Dont overtighten it back on also. When I was getting terrible gas milage it was because one of my injector connectors was corroded and not firing. Every once in a while unplug the battery to force computer to reset.
I used Arctic Silver 5 under my new ICM(I build computers too).

 

so signs of the bad thermal paste there would be bad gas mileage and what I’m describing ?

 

The burnoff cleans the MAF wire.. You could try spray cleaning it and see if that helps.

I saw a youtuber who took the cover off his burnoff, activated the relay by hand, and see if that helps.

I am running an autozone MAF that doesn't appear to HAVE a hot wire?

I posted pics of it once.. Looks like a thermistor or something? It's just a board inside.

It works fine, and I am not at all sure my burnoff even works every time.. Sometimes I hear it click? Sometimes not?

Not sure it needs it with no wire?

Perhaps you could try that?

 

There's pics of it on the AZ site, btw.. They show you right inside it.

 

AZ site?

 

"Auto Zone"

 

No bad thermal paste will not be directly affecting gas milage, but if you are shooting for reliability those are things to address. The ICM is known to get hot and shut down when going bad. A redo cannot hurt. Or at least check it out and apply new paste. It can be tested. If the wires are not fully seated(5 of them) on the ICM you can get a misfire,ask me how I know.
I am assuming you did the wires and they are fully pressed on, Diesn't hur to check and clean connectors wit the said electrical cleaner I mentioned.

 

Just a heads up
I had been sent one of those NO HOT WIRE MAF sensors from corvette central, the car didn't want to idle.
Turns out you need the ecm chip modified to run those maf sensors, i got a proper bosch hot wire MAF and all was ok again.

Remember if the burn of module (a one off 85 only item fails a code will be set so check that check engine light code.
I got a spare one years ago when they were just 20 or 30 dollars, now they are priced like their weight in gold .....

I would disconnect the battery and reconnect after 10 seconds, to clear the ecm codes and rough running from the ecm perceiving a fault.
That restores most rough running issues, also check timing retarded timing will cause high fuel consumption and rough idle.

 

Check the basics first. Set your timing at 6 degrees, make sure your fuel pressure is correct at 39 psi. Then trouble shoot. Pull codes to see what the computer is telling you.

 

I would go with basic things as well. Backfiring usually indicates a spark/timing problem, fouled up plug, plug wire on the wrong plug, distributor cracked, etc. Ignition control module will just die, and once its dead its usually gone forever and won't fire the engine at all, but if you didn't put the thermal paste on it then I don't know what it would do, never not put it on mine.

Fuel pump will do the same, but will work intermittently if its problem is actually in the bulkhead wiring, which is going bad more often on these cars nowadays, a FP gauge at the rail should show about 40psi and hold there, if its not then theres a problem with the fueling. Regulator can go bad. Injector connectors don't really go bad often, but its a possibility. Injector drivers CAN be fried if youre messing with the ECM and not careful, that I have done as well. But it won't run at all if one of those gets fried. A noid light will indicate a problem. You can usually rent a set from Autozone or wherever.

Vac leaks would cause it to run rough idling but wouldnt really backfire much.

If the MAF being disconnected makes no difference, most likely the MAF is bad. In other years we'd recommend replacing the burnoff module at the same time as the MAF, but 85 is unique with the burnoff buried inside the dash (and more expensive) and its not strictly necessary.