Does an 87 convertible's MAF sensor need to have 12 volts at all times when the key is turned to the on position?

 

Check pin e for power , the maf gets power through the maf power relay

http://www.chevythunder.com/maf_code_33.htm

 

Thanks. I checked the MAF POWER RELAY. I have power on orange pin but not red which energizes the relay that allows current from orange wire to go to purple which provides power to MAF. I tracked the red wire to ECM and it does not have power. Should this red wire have power at the relay when the ignition switch is on the on position?

 

What ecm pin are you referring to ?

 

I believe it’s B2.

 

B2 is fuel pump signal voltage

 

The fuel pump relay and the MAF relay are identical and located next to each other. Make sure you are checking the correct one!

 

Hello addeleon, Welcome to the Corvette Forum!

Sometimes sensors will use what they refer to as a "Reference Voltage". It is frequently a 5 volt DC signal supplied to the sensor. The C4's ECM frequently will supply ground to activate parts like fuel injectors. Whenever the key is in the "start" or "run" position the fuel injectors are supplied with 12 volts dc and when the injector is required to inject the ECM sends a ground out to complete the power circuit to allow the injector to work. This is one of the reasons the Engine must be grounded very well, if a ground strap is missing be sure to replace them. I found a loose ground strap attached in the rear and after re-attaching it my power antenna started working properly. There are several ground straps on these C4's and they are all important to keep connected.

The relay you are looking for is identical to the ones used on the fuel pump and cooling fans as well on my 1988 C4. I keep a spare in the glove box for such an occasion, this was after my Fuel Pump relay was randomly turning off interrupting the flow of fuel to the engine while I was driving. A new relay and the problem went away.

On my car the relays were damaged by a serious close to 2 volt drop coming from the battery. Low voltage inside the car made lots of issues but was solved when I cleaned the connections where the Fusible Links get their power. That allowed my radio to see full battery voltage instead of close to 10 volts normally and everything worked better. It is easy to see if you have such a problem, measure the voltage at the battery and then measure it at the fuse panel. They should be very, very close. If not you need to solve that issue before moving on.

A lot of MAF sensors fail due to their required relays failing first. The burn-off relay is critical to a long lasting and working MAF sensor. I always suggest that people replace the relays when they replace the MAF. The wire that gives us the readings is 1/10 of a mm and needs to be kept clean, hence the burn-off relay heats the wire up to bright red and burns off the contaminants. I replace them before they break or fail, I try to avoid problems before they start.

Battery maintenance is very important on a C4, you need to be sure the connections are clean and the battery fully charged. This alone is responsible for a lot of Corvette no-start issues. I coat the connections with battery grease to keep oxidation from occurring. I remove the battery from both of my Corvettes for the winter months. I clean them and keep them charged and top off the electrolyte if needed (or applicable). Then in the spring they are ready for a another year of fun and no issues regarding the battery.

It sounds like you have a set of the Factory Service manuals for your Corvette with your knowledge of the ECM pin outs. If you don't have them be sure to put that on your list. It would be really hard to fix these cars without the awesome documentation of the service manuals.

If you have any more questions about your Corvette then you came to the right place! This Forum is awesome as it has a lot of very knowledgeable people here and they like helping others...

Best regards,
Chris