When I unplug the plug at the battery for my computer the car runs better than when it's plugged in. Is my computer bad or maybe a sensor? It's funny it will run when it's unplugged but as soon as I plug it in it will run like crap backfire and stall. what's the problem? Please help!!

 

Reset the computer, drive around for a couple days, pull your codes and then post results and a clear description of your issue here.

 

I can't get it running long enough to get codes or drive it. I just replaced the knock sensor but I flooded it so I'll have to pull the plugs clean them and try again.

 

What plug exactly? If youre disconnecting the computer, the car should be shutting off....and the voltage spike from doing that or reconnecting it may very well short it. I think you're disconnecting something else, some kind of sensor hookup....maybe the EST connector, but that's on the passenger fenderwell IIRC...

Can you take pictures of what youre unhooking??

 

This connector Is connected to the battery. I can't take a pic right now because the car is being stored somewhere else but I can get a pic if that will help. You do know this is a computer controlled quadrajet right? It's not fuel injected. I know it's bad to unhook and hook the computer while it's running it was actually done on accident but it did run better. I even had the computer completely out and it ran better than when it was plugged in. With this car the timing plug is a 4 wire connector right near the distributor. There is also a spark control module on the drivers firewall thats connected to the knock sensor I'm starting to think that's bad If it's not the computer. I'm thinking the computer is screwing with the timing because it will fire but it won't start and stay running. I also have to pump the gas pedal to start it but now it's flooded so I have to pull the plugs and clean them.

 

Didn't realize it was a CC Qjet........hmm.....do you have any kind of IAC valve on that Qjet? If you do, try disconnecting it and hooking the computer back up, see if anything changes... My buddy's 84 with the Qjet had an idle hanging issue and it would diesel and backfire on shutoff, turned out to be a loose electrical connector on the carburetor....

 

Nope no IAC.

 

Well hell man I'm pretty decent at diagnostics but I gotta tell you, I know very little about those CC Q-jets. For most computers, here is what I CAN tell you....there's some kind of default value for everything in the computer, so try disconnecting sensors, with the computer hooked up, til it runs better.....works for most things.

 

Yea these things got me too. I like fuel injection myself but I can't afford to change it right now I hate carbs. I'll give it a try thanks.

 

My guess is that you need to check the base timing, adjust the mixture control solenoid, set the hot curb idle, then set the TPS voltage correctly. That should get the ECM back in control. All the procedures for those steps have been outlined in detail here. Try a search for each.

 

can I do all that without the car running?

 

You can set the TPS voltage with the engine off, and ignition on. After performing all the other adjustments (specifically the idle), you'll likely need to set it again, however.

You do not have to have the engine running to check the base timing, but it does have to at least be cranking.

The engine will have to be running and fully warmed to set the mixture control solenoid ranges and idle RPM.

As Red advised, retrieve the error codes. What you find may be very helpful.

 

Ok I'll check all that and I'll get back to you.

 

I've got the car running now. The computer was ok. It was the ignition spark control module that was bad. Thanks for all the help!

 

Thats very strange....usually when the ICM fails, the result is no spark....or no spark when the engine is hot.

 

It's not the module in the distributor. It's connected to the knock sensor. It retards or advances the timing when it hears a knock.