MTVette

My very first 'Service Engine Soon'! Was driving around last night and my SES light came on. Noticed that at WOT, the engine sputters above 4500 RPM and won't upshift until I ease off the gas. Did the paper clip thing and got a code 43. The SES light comes on 5 seconds after starting up and stays on. Resetting the ECM (pulled the ECM fuse) didn't change anything. With the exception of poor response under WOT at high RPM, the car behaves normally.

Other (possibly relevant, possibly not) factors: gf filled the tank with really cheap 89 octane gas the day before, and earlier that day I was wiping down internal engine areas for a cruise-in, and may have dislodged a connecter.

Suggestions?

nobodyunknown

I think code 43 is timing related,Im gonna guess here & say the knock sensors were activated by the low octane.
When you reset your computer it takes a few miles for the computer to completely get back to normal.Does the light stay off after resetting?
Mabey theres some eggshell from that cloud caught in the injectors?
Nice ride.

MTVette

The light went right back on after resetting. I suspect either the bad gas or a loose connecter. After driving the tank down 2/5 of the way, I refilled it with Sunoco 94 octane. I'll find out tomorrow on my drive to work whether that fixed anything. If not, I'll start looking for loose connectors.

Ruby_Roadster

It's the Knock Sensors - replaced mine and (touch wood) haven't had a problem since. When either one or both go bad, replace both - because if one goes it very likely that the other one will fail soon after.

ChrisB

Yep, it's the knock sensors. First thing to do is check for a short or loose ground, but probably you are going to end up replacing your knock sensors. If you recently changed the knock module in the pcm you might make sure it's seated.

MTVette

ChrisB said,

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:[/color]<HR><font face="Verdana, Arial" size="2">First thing to do is check for a short or loose ground[/color][/QUOTE]

The shop manual for the 92 Corvette discusses this in some detail, but leaves out some useful info. It discusses the voltages sent to the computer from the sensors, and how the unit will signal a fault code if the voltage is too high (bad ground) or too low (short or loose connector). I have a digital voltmeter, so testing both knock sensors shouldn't be a problem but my question is WHERE do I test the voltages? This woulc go a long way to resolving the problem. I drove the car in to work today and it seems to behave properly, although I didn't try acceleration at 5000 RPM. Power was good, though, at 1000-3500 RPM. Am I putting the engine at risk by delaying repair? For now I'm using hi-octane gas.

MTVette

ttt

I'm still trying to learn where I can test the voltages coming off my knock sensors - at the probe (from under the car - UGH) or somewhere convenient near the computer?

MTVette

Well, this weekend I poked around under the hood, looking for loose wires around the knock sensors. I couldn't even find them :( . Instead I bought a 3.5 ton jack and jackstands, so I can get under the car and look there. I want to check the voltage at the sensors - is this possible once I have removed the shields? Just in case the sensors are bad, I ordered another set from my friendly NAPA dealer, and I'm planning to replace them (along with the coolant and serpentine belt) next Saturday. Anybody done this before, and how easy (or hard) is it?

Raysur

This happened to me awhile ago but my knock sensors were fine. What happened was oil leaking from my intake got into the connections. So the dealer cleaned everything and put new sealent and gaskets.