I have a terrific mechanic but he seems a little stumped by my 31k 1992 Lt1 Coupe (manual). Last winter the car was stored while running nicely. I made the mistake of taking it out and running it through some deep puddles that were filled with salt from the melting icy roads. Almost immediately it started missing, bucking and backfiring and would only run on about 6 cylinders at about 2500 rpm. I parked the car and next day it was fine and drove home. Parked for a while and tried to start no luck. Tried many times and could get it barely moving on 6 cylinders with terrible backfiring and bucking.

Enter the noble mechanic. New battery, plugs, wires, dephi distributor and waterpump from partsladi. Cleaned throttle body and new serpentine belt. When he put the new distributor in, the car started on the first click and he drove it for a couple of days and said it was perfect as good as new. I went to pick it up and he said the same problem had returned on his last drive (althought not as bad). Hard to start, missing, backfiring. I asked him about the codes and he said the when the ignition is messed up the engine will throw so many codes that they aren't really useful.

His current analysis is that it could be:

1) faulty new distributor
2) an aftermarket chip that my car has
3) bad ecm

I am lost to see how the new parts can work perfectly but only for a couple of days.

All I had done prior to this was to replace the open cut air filter housing with the stock one

Any help for this guy who is realy trying to fix it.,

Thanks for any assistance.
Chris

 

Where are you (& your mechanic) located?

Jim

 

Here is how I view the situation.
The problem was never fixed with all the parts you replaced, it is still in there. I don’t think the chip is bad because it would probably not ever run good if defective.

Your right about that many codes are of no use here. But the common thread I see is the ECM. In those years its known that they go bad and cause a wide amount of weird problems and symptoms. It monitors lots of items and generates the codes if something is not measured correctly. It probably can generate false codes to if defective.

Seems like if a MAF, TPS or other item was bad it would generate one code if all electronics were working properly. The ECM controls the injectors and the drive for the spark.

Just another thought, I would say check the fuel pressure during all of this but that would not relate to the codes unless you have separate problems.

 

I'm located in Vancouver, B.C. Thanks for your help.
Chris

 

Get a new mechanic!

 

Well, there goes THAT idea! I was hoping you were a little closer as I was willing to bring my spare ECM over and let your mechanic try it on your car.

Jim

 

Why don't you tell us what is wrong with it? The mechanic sounds competent to me.

 

Stored Car=Bad Gas

Do you still have the 6+month old gas in there?

 

This could be it, especially if it's got 10% or more ethanol.

 

Thank you Jim for your kind offer. You guys are great. The latest word is that the mechanic unhooked the battery for an hour (to let the electronics all drain). He hooked it back up and it started first click and ran perfectly again.

The mystery continues does this help the analysis?
Thanks again
chris

 

Once the problem returns, ask your mechanic to check injector pulse. Also what is the fuel pressure when the problem occurs. He needs to figure out what cylinders are misfiring and then why.

 

Any chance the coil and module were soaked too? Were those checked?

My 96 has them mounted on the passenger side cylinder head (front) area which would put both of them right in the path of splashing water.

Jake

 

did you reinstall the iat plug back when you change the air filter housing?

 

Lastest is that after a hour of battery disconnect the lt1 starts perfectly and runs normally for a short period of time. Won't start a second time without a disconnect of the battery.
thanks again for your help
Chris

 

That would lead me to believe that the ECM is the cause of your problem. Nothing else in the system would be affected by disconnecting the battery.

Jim

 

I'd be looking for a mechanic with a scanner! A couple of my thoughts.

That road salt is very corrosive, I'd take a look at the knock sensor connections, because it's down low...just a thought. Second, when he disconnects the battery he's clearing any stored codes, starting new again until the problem re-occurs and scews the info the ECM is getting. He should be reading those codes...plain and simple.