and just like that.....42 was gone.

[Robert]

I posted here about 8 months ago that my '84 was throwing a code 42. EST.

I had just bought it and tuned it up (cap, rotor, plugs, wires, PCV and new valve cover gaskets), then sprayed the engine compartment with 303 silicone spray. I had pulled loose some connectors that I could get to and put dielectric grease on them. I then installed a K&N air filter, started it up and code 42 popped up.

I tried everything I could think of to get that code gone. I took it to a Corvette mechanic and he said it was a bad ECM. I installed a rebuilt one and still code 42.

So, I decided to just live with it. The car ran great so I figured why let it bother me.....but it did!!!

Anyway, tonight we take the Vette out and it sounded different.....it felt different and the read out for instant mileage was way up.....it had been 25-27 mpg at 55 mph at 1700 rpm. Now it was 35-40 at 55 at 1600 rpm. I looked over and said to the wife....HEY!!!! NO Check engine light!!!! And sure enough...just like that it was gone.

I pulled over at a school parking lot and turned off the engine. When I turned the key the check engine light came on as did the seatbelt light then went out when it started.

Amazing.....just like that it was gone.


Robert

 

[geekinavette]

Problems that go away by themselves tend to come back by themselves.

42 is a problem with the EST circuit (as you know). That code is set when the EST bypass is disconnected (to set the base timing)...a single brown wire connector near the brake booster. If that gets disconnected you won't have electronic control of the spark advance...and it will run horribly retarded. Check that and make sure it's connected good. Also check the 4 wire connector behind the distributor.

Bill

 

[Vettefan87]

Yes I threw that code when I set the base timing with it unplugged. I wonder could it have maybe been loose? I would probably assume if that was not connected all the way the fuel economy would be worse, as performance like said before. Any check engine light should be diagnosed and fixed ASAP, whether it affects driveability or not.

 

[geekinavette]

That's correct, fuel economy and performance will be drastically reduced, since the computer is not able to advance the spark timing if the EST bypass is disconnected.

Bill

 

[Robert]

Believe me, I have agonized over this for months. I have checked and rechecked. I have gone the library and read everything I could on code 42. My next step was to replace the spark plug wires with GM Corvette wires that match exact length.


After I posted this I remember that I did do something else. The other day I was sitting in the garage and saw the Electronic Spark Control module and remembered that I had put dielectric grease on it too. I pulled it loose and wiped a little of the grease off. The next time I started the Vette the code was gone.

Also, after I posted this I disconnected the ground cable to clear the code. Then I started the Vette and the code popped back again!!! So I pulled loose the ESC module again and again wiped the contacts. Started the Vette....No Code!!!!

So, in about 15 minutes from this posting, the wife and I are taking off on a day trip. I hope the code is gone all day. It is amazing how much better it runs now.

This is my first Vette and for that matter first sports car.....so even throwing a code 42, it seemed pretty fast to me.


Robert