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Topic: Spark Control Issue Solved

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Spark Control Issue Solved (1/2)
 3/28/20 5:29pm
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Steelton, PA - USA

1992 white roadster, removable glass top, red leather.

Joined: 7/8/2019
Posts: 13


I haven’t been in touch at all since joining the registry many months ago, but with ample time now on my hands due to the nationwide virus scare, here’s an update.

Last time I wrote, I was having problems with my 1992 LT-1. I was getting an occasional SES light—a code 43 (spark control). I’d start the car and the SES warning would come on. Then, after the engine was warm and the thermostat opened, the SES light would go out. Otherwise, there was no problem; the Corvette (“Stormy” by name) always ran like a champ.

If you haven’t had problems with spark control, there really isn’t much to the system. It consists of two knock sensors, one installed on either side of the lower engine block, the vehicle processor or ECM (electronic control module), and the wiring connecting the sensors to the ECM. That’s all there is!

Figuring the problem had to be the sensors, I had my mechanic, Rob Jackson, in Camp Hill, Pa., replace them, which he did while I was right by his side. But after restarting the engine, the SES came back on and this time stayed on, unlike before, when it would go out after the engine was warm. Rob checked all the wiring but could find no breaks or faults of any sort. Okay. Must be the ECM, we decided.

I pulled the ECM and sent it to a shop in Illinois that routinely repairs old car computers. Cost was $166 and change, not extreme. Got a call a week later from one the technicians telling me he had discovered a number of breaks in the soldering that were consistent with the problem I was experiencing. As he explained over the phone, the heat from the engine eventually weakens the solder, causing the ECM to operate improperly or sporadically. The fix was to reflow the solder, which he did. When they bench tested the ECM afterward, it tested correctly. I paid the bill and the ECM was mailed back to me; I reinstalled it and started the engine. But once again, I had an SES warning, same code 43. Frustrated, I telephoned the tech and asked if he had tested the ECM’s removable microchip. He said he had not, that they used one of their own chips during final testing. He said this was company policy because a bench fire had once melted a customer’s microchip. And as the chips are expensive and somewhat hard to find, they now always removed the customer’s chip and put in storage and used one of their own during testing. Unfortunately, this raised the possibility that my original chip could still be causing a problem, and I said as much to him. Yes, he agreed, it could.

I shopped around on the web and managed to locate an original AC Delco chip from a parted out Vette that matched the component number of the one in Stormy. When it arrived, instead of installing it myself, I took it to Rob Jackson and let him install it, just to be sure I didn’t botch the effort. With the new chip installed, I started the engine . . . and yes, once again, an SES warning, same code 43.

Now Rob was annoyed. He put Stormy up on the garage lift and retested the knock sensors with his meter. He checked one, then the other. Then he walked around, looking puzzled, and checked them again. He shook his head and said, “I think we have a knock sensor problem.”

“But these are new sensors,” I pointed out.

“Yes,” he agreed. However, he noted that they could still be faulty or maybe not even the correct sensors—they could have been incorrectly packaged, which he assured me happens more often you might think in the aftermarket parts industry. So, that being said, I ordered another set of sensors, this time getting them from Zip Corvette instead of the local aftermarket company. When they arrived, Rob bench checked them before we installed them, and then we fired up Stormy and held our breath.

This time the SES light came on, then went out . . . and stayed out! At long last, mission accomplished!

Since then, I have driven Stormy frequently, without a problem. Elsewhere, I’ll give you the full story on how and where I purchased my Corvette, and the work I have accomplished on the car since purchase.


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Re: Spark Control Issue Solved (2/2)
 4/3/20 5:52pm
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Joined: 12/7/2011
Posts: 219

Most curious and good to know. The board soldering is very interesting, something to file away.

96's are programmable and for some time I did with my laptop. Then came the problem that it would crash part way through uploading the new tune. Figuring it was my cable I returned it for verification and purchased a second ECM which they programmed with my cable. "Red Queen" lives again! But to be safe try some down loads... fails. Now, I have a lot of changes, the current tune is good but rich when I get after it. So I eventually, I find in the manual that the battery hot for the diagnostic port is on the dome light fuse!! #@!! So, I'm running a dedicated power and ground from the battery (now located behind the rear diff) to a fuse panel where the battery used to be. Both the ECM and diagnostic will be powered there with little else (to keep the power clean). Hopefully I can get back to logging and correcting. But, a Holley Dominator ECM is on the shopping list. It might be time to abandon 25 year old electronics! The only real hesitation is the other stuff the OEM is tied into.

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