91 Service Engine Soon light code 43
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Joined: Dec 2006
Posts: 72
Likes: 1
From: Jacksonville NC
91 Service Engine Soon light code 43
I have a 91 vette with the SES light that comes on for about 2-5 minutes, when first starting up, then goes out. Car sputters like it has bad fuel when I get on it (but it's not bad gas). I read the codes and it had a 12 and 43. Everything under the hood looks normal. Had the fuel injectors, gas filter, plugs and wires changed @ 3 months ago. Read on the forum that a code 43 is usually a knock sensor - will the knock sensor make the car sputter as well? Thanks!
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Joined: Jun 2004
Posts: 56
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From: Fort Worth Texas
The knock sensor will cause hesitation. I'm going through the same thing right now on my 93. The FSM manual says to unplug both knock sensors and see if that helps. If it does, then one or both are bad. here's the check for them. Using a digital multimeter, set it to two volts and place the positive on the terminal of the knock sensor and ground to chassis. tap on the exhaust or engine block and see if the voltage jumps, if not...replace knock sensor, if so, check/replace prom or ecm.
Oh by the way, to remove the connector from the knock sensor, squeeze the sides and pull and it should pop off. I spent 10 min. trying to figure that one out. Depending on your fingers and hands, you may be able to get the connector off without removing the heat shields, but they are only held on by a couple of 11mm nuts.
I'm waiting for my k.s. now from zip corvettes.
Good luck.
Last edited by 93_vette; Sep 9, 2009 at 12:42 PM.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
The knock sensor doesn't cause anything. It's function is to sense detonation. Depending upon the severity, the ECM will retard timing until the "knocks" are at an acceptable level.
The act of retarding the spark may cause the symptoms you describe.
Are you running Regular or Premium? You say it is not the fuel. How do you know? It is easy to get a "bad" tankful.
Check the base timing. It should be a 6 BTDC. Be sure to disconnect the EST wire between the brake booster and the rear of the engine. Disconnect the neg batt terminal for 30 secs to clear the code cause by disconnecting the EST.
Let us know what you find.
The act of retarding the spark may cause the symptoms you describe.
Are you running Regular or Premium? You say it is not the fuel. How do you know? It is easy to get a "bad" tankful.
Check the base timing. It should be a 6 BTDC. Be sure to disconnect the EST wire between the brake booster and the rear of the engine. Disconnect the neg batt terminal for 30 secs to clear the code cause by disconnecting the EST.
Let us know what you find.
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Joined: Jun 2004
Posts: 56
Likes: 0
From: Fort Worth Texas
did you fix your sputtering? For me, my K.S. was the problem, although mine never threw a code, it only acted like it was going to throw up a times.
Anyway I replaced the K.S. today and it runs great. Hope you got 'er going.
Marlon
Anyway I replaced the K.S. today and it runs great. Hope you got 'er going.
Marlon
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Thread Starter
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Joined: Dec 2006
Posts: 72
Likes: 1
From: Jacksonville NC
It was the Knock Sensor the threw the SES light! Light is out - I haven't driven it much since replacing the sensor so don't know if it's still sputtering - hasn't sputtered since taking it out for a quick drive. Thanks all for your help! 
