purplezee

I have a 1993 Z28 LT1 with 144215 miles, recently had to replace head gaskets so the complete top end was gone through....when I bought the car it had a miss in it and has gotten worse after getting it back from the garage. It runs really rough under a load and has started to back fire and while following the car you can smell fuel real rich. They said the computer needed to be replaced due to the quad drivers. I have scanned the computer and received the following codes....

12
26
44
55

Is there anything that can be done to fix or do I need to replace the computer? Any and all help will be appreciated.

bobdec

26 (quad driver #1 or QDM #1)says you have an air pump, EGR solenoid or EVAP solenoid open or shorted. 44 is an O2 left side reading lean and it s/b related to the 55 lean fuel condition. You probably have some loose or bad connections causing the 26, 44 and 55. The 12 is not a valid code for '93 F-body. You can get help here if you want to proceed. At this point I would not change the ECM.. Do you have air, egr or evap deleted, have fuses been checked, air pump is prone to bind up and blow fuse.

purplezee

Im not for sure what all has been deleted in the chipping process but I do know that they disabled the traction control when they chipped it.

Injuneer

"12" is a valid code - its the "handshake" code that you get when you short the ALDL pins, indicating the ECM has entered diagnostic mode.

There was no traction control available in 1993. It was not available as an option until 1995 model year.

I wouldn't write off codes 44 and 55 as being due to loose wires. They are closely related. One indicates that the Bank 1 O2 sensor is stuck in the lean position, the other indicates that an O2 sensor is indicating a lean conditon in power enrichment mode.

Since it apparently seems to smell like its running rich, I would check the O2 sensors first. One of them may be producing a false lean condition, as a result of a faulty sensor, or as the result of an exhaust leak or misfires.

purplezee

when you say loose wires are you talking about the conection to the O2 sensors?

purplezee

I found a square plug under the throtle body that has the clip broke off but appears to be making good tight connection. the fuse to the air pump had a 10 amp in it and was blown....put a 20 amp back in that it calls for and while messing with the sensors and unhooking them to see if it changed the running of the car i noticed that the fuse to the air pump was blown again.??????????????

Injuneer

The AIR pump rusts up due to the water vapor in the exhaust leaking back through the check valve. Once it rusts enough, the motor can't turn the pump, draws too much current and blows the fuse. The AIR pump does not affect the way the engine runs. Its just there to run for a couple minutes at startup to help the cat heat up faster, then it shuts down.

Pull the harness connector back off the AIR pump, then replace the fuse. Do not plug the pump connector back in. That will get rid of the DTC 26.

pkincy

You say "garage". A GM facility or a local auto shop?

What did they do to the top end?? simply the head gasket?

Did they do what you asked or did they diagnose the car.

If they are competent they would have diagnosed the car and fixed what was wrong. If not they would have replaced one thing and returned it to you with 4 outstanding codes, which it appears they have done.

Sometimes paying $120/hour for labor is cheaper than paying $70/hour particularly if the cheaper rate doesn't solve your problem.

Computer controlled cars are sophisticated enough that it sometimes pays to have a quality Chevrolet dealer diagnose your car for you. Once that is done you always can tell them you can't afford the fix and drive off with the car and than do the repair yourself. However you have spent about $150 to get a good diagnosis which could save you thousands of dollars of throwing parts and labor at the car.

Now I do say "quality" dealer. I have had GM dealers think I was a 20 year old girl and try and feed me s**t like I didn't know any better so you do need to be a bit careful.

As it was a Dealer with lots of locations I will call them out here. It was Bill Heard Chevrolet in Las Vegas, but they had other locations as well although I recall they went bankrupt soon after this incident.

I had a problem with the speedometer and the A4 not working together smoothly. There were 5 different potential causes. Not wanting to diagnose the particular cause I dropped it off with them as they were very near work at the time. Well they called several hours later and told me that it was going to be thousands of dollars to repair the problem, and named all 5 possible factors as needing replacement.

Well, I had about 3 of the 5 covered with spares in the garage, so picked up the car (yes I had to pay them $100 for the "diagnosis") and replaced 3 of the 5 (one was a new pcm they had said I needed and yes I carry a spare). Well still no luck. So I was down to 2 choices and got the car up on jack stands and pulled the VSS port on the tranny and low and behold the press fit gear on the tail shaft that drives the VSS gear has shifted. Slid it over 2-3 inches with a pry bar and voila! it was working. Cost = $0.

However every other GM dealer in every other town I have dealt with has given me what I thought was an honest diagnosis for a very reasonable cost.

And those diagnosis have saved me untold amounts of parts cost. (BTW, I think I have 2 or 3 working Optis in the garage, because I replaced it thinking it was the problem when it wasn't prior to me developing this philosophy of "let the experts do the diagnosis and I do the repairs").

Sorry for being long winded.

Perry