Hi all, new to the board.

My buddy has a 1986 C4 that he's asked me to help him with. I've done quite a bit of search on the forums here for info. What a great resource! Already saved money in not having to buy a code reader. So here is the problem:

After sitting all winter, the car started up fine and I drove it down the road for a bit. It started stumbling a little, but I was able to get it back home with some slight rough idling. The next day, I drove it again, and this time it died in a parking lot, would not start back up. It cranks just never lights off. After letting it sit all day, it started back up, but had no power, and would die if I gave it too much gas. I limped back home, where it has sat since (about 1 month).

We put in a new fuel filter and some fuel treatment and octane booster just in case the gas was bad. I checked fuel pressure, and it is getting about 8psi. The gas smells good, so I don't think we are dealing with bad gas here, but my nose is hardly a calibrated gas tester. For the last couple weeks we played with it. It would start up after sitting for a while, but die in about 5 seconds. Then, it wouldn't even start up unless you let it sit for 30-40 minutes.

So, we started looking at it deeper yesterday. We shorted the ALDL to get codes, and it had none. That battery had died, so no surprise there. So, we hooked up some jumper cables to my truck to charge up the battery. We tried starting it again, however, the ALDL was still shorted because we forgot it was and it started right up and idled smooth. It was a high idle (1200 rpm), but it was smooth. So, we let it warm up in this mode and then un-shorted the ALDL. We tried to start it back up, and it ran barely. Rough idle, but at least the check engine light came on, so we read the codes:

34 and 43

So, we started diagnosing the 34 code (MAF sensor). After reading some posts here, and finding a copy of the FSM page relating to it, we unhooked the MAF sensor and tried starting it again. It started but would only stay running if we gave it a little gas. It coughed and popped badly, so we shut it off. I shorted the ALDL again, and it started up fine. I unshorted the ALDL and completely removed the MAF from the air intake. This time it started up fine, but wouldn't idle. It would only stay running if I gave it some gas. It sounded good, but died immediately if I let off the gas. After running it for a couple minutes like this, we checked the codes again and got: 33. According to the FSM this means we need a new MAF sensor.

I'm just checking here before we spend a bunch of money on one. Could this be something more simple? Money is tight for my buddy, so I don't want him to have to buy this if it isn't needed. Thanks for the help, and thanks for these great forums. They have been a huge help already just with the archives.

 

This fuel pressure is way too low for the engine to run on it's own. If 8 psi is correct, you either have a kink in the fuel lines, a dying fuel pump, bad FPR, or the fuel pressure gauge was not connected good. I would start with that. You should have ~40 psi of fuel pressure. Fix that and then clear the codes by disconnecting the neg cable on the battery for 30 seconds or pull the ECM fuse. Looks like you have a fuel delivery problem.

Never try and start the engine with the ALDL (terminal A and B) grounded. You will eventually ruin the ECM or the wiring. You can ground the ALDL and turn the key "on" to pull codes or ground the ALDL after the engine is running to put the ECM in Field Service Mode to roughly monitor the O2 sensor.

Welcome to Corvetteforum.

 

Thanks for the point in the right direction. We put in a new fuel pump, and the car is running great. Started right up, and we are getting a good 45psi of pressure now. That was a lot cheaper than a MAF sensor!

 

Another job well done!

 

Glad to hear it was an easy fix.