Totally, Completely and Utterly Baffled

[Robert]

OK....I hope I do not post another thread on this topic.

I bought an 84 and drove it home 100 miles. Ran great. Got it in the garage and the plugs looked rusted so I figured they needed changed. They did. While I was at it, I changed cap, rotor, wires and PCV. Also installed new valve cover gaskets. It needed them too.

I took it out for a drive and it ran even better. I then decided to install a K&N filter because it needed a filter too. I then sprayed 303 Aerospace Protectant lightly all over the engine compartment. I did that on my Astro van and it looks brand new under the hood.

Next day, I take the Vette for a spin and after starting within 10 seconds or less...Check Engine comes on. Code 42....EST. It has done this for 3 weeks. I have read everything I can about code 42. I finally gave in and took it to a reputable mechanic. He did the flow chart twice and it both times came down to ECM. I went to Advanced Auto Parts in Urbana, IL and they had one for $96.00 no core. I asked if I could bring it back if I still had code 42. They said OK.

So I kept my old ECM which was fortunate because most places charge $50.00 to 150.00 for core.

The new ECM threw a code 42 also. Out it comes and in goes the old ECM.

The Vette runs fine with the Check Engine light on. I get 23-25 mpg at cruising speeds. It runs as good as it did when I bought it. But...I keep looking at that darn light when I drive it and it makes me crazy!!!

Sorry for long post, but this has me completely at my wits end.


Robert

 

[Ken]

I can't remember, but I assume you checked all connections, both at the sensors and at the ECM itself. I can only think it would be a loose or corroded connection (or a ground) at this point.

 

[redvet]

Have you checked if there is a PROM update?

Also, keep in mind that your problem could be coindidental (in other words, none of the things you did may be the reason why your CE light is coming on/you're setting a DTC).

 

[Robert]

Ken, I checked all the connections. I might add that I put dielectric grease in most of the connections. I am wondering if I put too much it might short across?? I will pull them tomorrow and see if maybe there is an excess.

 

[geekinavette]

There are no PROM "updates" for 84...none that would have anything to do with EST anyway.

Check your EST bypass wire...it's a single (brown, w/ black stripe I think) wire connector that'll be hanging somewhere in the area of the brake booster. You unplug that connector to set the base ignition timing (disables EST), and it sets a code 42 in the process. One end goes to pin C of the HEI 4-wire connector, the other end to pin 10 of the black ECM connector, check continuity between those two with an ohm-meter.

Bill

 

[redc4corvette]

Did you disconect your battery for 90 seconds to clear all codes.
It could be throwing what is called a ghost code?

 

[Robert]

Did you disconect your battery for 90 seconds to clear all codes.
It could be throwing what is called a ghost code?

I bet I have had the negative battery cable unhooked about 50 times the last 3 weeks. Sometimes for several days.....!!!!!!

I am going to check all visable connections. It's raining and I have nothing better to do.:cry

At least by buying and installing a new/rebuilt ECM and still getting the same code, I have a pretty good idea that it is something I did when I installed all the tune up stuff. I HAD to have messed with a connection somewhere. Just gotta find it.

Robert