dbergair

hello all.
New member and first time corvette owner. Bought a 85 c4 project and it runs way too rich and wont take throttle. someone has changed the ecm (it has junk yard paint on it) and i dont know if the prom card is the right one. I am a aircraft mechanic by trade and have experience with older v8's. This car has had a tough life but i love it already. Any help would be appreciated. Thanks in advance.

Hooked on Vettes

1226870 was the original ECM used for a 85.
On the Eprom should be a sticker with some alpha letters on it which identifies what information is in the chip. Since the Eprom can be reprogrammed the only way to determine it hasn't been modified is to compare the information in the chip to an original file. That requires a device like an Eprom reader.

dbergair

thanks hooked on vettes. anyone have experience with a very rich running engine? i am going to check my prom code and go from there. one person suggested the mafs fpr and temp sensor. thanks.

Joe C

A&P - - got my license in 1966. (damn -- just realized that was 50 years ago - )

as for the 85, start with the basics. any codes? check for any codes. make sure all ignition components (plugs, cap and rotor, wires) are in proper order, timing at 6°BTDC - check fuel first - run a fuel system diagnostics per the factory service manual. baby steps....

if you don't have a FSM - make that your first purchase.

1985 is one of my favorite C4's - bought mine 21 years ago - 156K on the clock.

Hooked on Vettes

Short Pin A to Pin B on the diagnostic connector above the drivers right knee and turn the ignition On. The Service Engine Soon indicator
will blink 12 three times any codes three times and the cycle will repeat. Example for 12 which signifies the beginning of any codes will be Blink short pause Blink Blink long pause.

Can you tell if the fuel injectors are stock or have they been replaced?

Have you pulled the spark plugs and do they all look black?

Have you checked the fuel pressure?

Does the fuel pressure hold after you turn the ignition off?

Get the engine temp up to 210F then shut it off. Disconnect the two wire connector plug with the Yellow and a Black wire that plugs into the Engine Coolant Temperature sensor. With a ohm meter measure the resistance across the ECT pins. Should measure close to 186 ohms. The sensor is screwed into front edge of the intake manifold. This is one of the sensor the ECM uses to help determine fuel mixture.

Have you tried running the engine with the Mass Air Flow sensor disconnected?

dbergair

Thanks guys. i am on the troubleshooting. Plugs look dark like i suspected. i am working on getting some codes. zero fuel pressure on my gauge. I dont know if i can get the engine to operating temp the way it runs. ran it with the maf sensor disconnected. no change. anyone know where to get a reverse lockout rod? used preferably due to a budget. Thanks in advance. I love my corvette but the previous owners did not.

aklim

First thing I would do is determine what ECM is on it and if that is right, take the EPROM out and have it flashed so I know what I am working with. Next, I would get a scanner so I can see what the ECM sees. If you want to check the ECT sensor, find it and get an infra red gun on it and hook the scanner up to the ECM so you can see if the ECM sees what the thermometer sees. I don't place much faith in plug reading because the ECM changes the fuel ratio and we have no idea where it is lean and where it is rich so I prefer to rely on a good O2 sensor. That reminds me that I should change the O2 sensor since I don't know where it came from and how long ago. Scanner gives me a reading to see if it is running rich or not.

dbergair

hey guys. me again. Idont see where my check engine light is. i have a obd reader. when i turn the key on the whole dash lights up but i dont see any check engine light. the electrical system on this car is a mess. someone has hacked and cut wires and spliced wires. i have checked some of these things but am hung up on no codes.the wire in the mafs is broken but someone suggested to run it with it disconnected. I am also hung up on the fact that i have never seen any fuel pressure on my test gauge. could the fuel pressure regulator be stuck open? i replaced the leaky clutch cylinder but it still goes in and out of gears hard. I have the car on jack stands and have looked the linkage over. could the overdrive be engaged or something? I really appreciate all the help and cant wait to drive it. also i need a hood stop assembly and was hoping to find a used one. i saw a new one for about 100 but i am on a budget. thanks again for all the help.

aklim

Check engine light should be on the dash especially when the key is in run and you haven't cranked. You are going to need a FSM and a scanner. The code reader is a fancy paper clip that doesn't tell much.

cv67

If you got a fuel pressure gauge on it and it reads 0 thats one of your problems. Pull the vacuum line off the fuel regulator and see if its wet. See if your dipstick reeks of gas. may have an oil change coming after your repair
Could have failed, could be a stuck injector

Broken MAF wire problem 2. one thing at a time youll get it sorted out
cars with wiring like that scare me lol. If youre up to the task go for it otherwise get it running good dump it and wait til you find a sounder one tons of these cars were made so not like they are rare/hard to find.
Just hard to find one that hasnt been butchered to death.

Hooked on Vettes

The Check Engine or Service Engine Soon indicator is in the tell tale display. Could be Bubba removed the bulb or the bulb is burnt out.

When you turn the ignition On that indicator should be on solid.

If you connect Pin A to Pin B the radiator fan should come on?
If that works the ECM is probably in diagnostic mode but something is wrong with the bulb.

If you shine a light on the tell tale display you should see the wording Check Engine or Service Engine Soon indicating the location of the light bulb.

dbergair

ok me again. still struggling with engine running way too rich. a friend of mine found the part numbers for the ecm and prom. the ecm is from a cadillac and the prom is from a 85 firebird. how do i tell a corvette 350 from a firebird 305? the electrical system is a mess. the mafs has a small wire in it that is broken. its in the airflow. i have yet to see any fuel pressure on my test gauge. this thing has two coolant temp sensors on the front of the intake manifold. which one do i test? mafs? ecm? prom? fpr? if i replace the fuel pressure regulator should i do something with the egr valve? i really appreciate all the help. thanks

GUSTO14

You may have found your problem. If the filament wire in your Mass Air Flow sensor is broken the engine will not run well at all.

Is this wire the broken one you're talking about?

Good luck... GUSTO

dbergair

Sorry for the delay. life gets in the way of my corvette fun. I have ordered a mafs and it is definitely bad. my only concern is that a few people suggested i run it with the mafs disconnected. this leads me to believe that it might run ok with the sensor disconnected. i know this part is bad so it is getting replaced. i feel good knowing this car has been rescued. plus there was a womans top in the back and a half smoked camel cig on the dash. only good things can happen from here on out.

dbergair

ok new question. My 85 has two sensors on the front of the intake manifold. I know which one is the coolant temp sensor but what is the one next to it? thanks

Joe C

sensor on the left provides the signal for the cold start injector, right sensor, coolant temp sensor - signal to the ECM. coolant hose connect to the throttle body.

dbergair

thanks i really appreciate the info.