94LT4Corvette

So I've been getting an intermittent code 43... and completely random whenever it feels like it seems. I have replaced the knock sensors and I'm still getting the code. Usually I see the SES come on after driving a bit on the highway and then it goes off and on randomly... sometimes after 30 seconds or less... sometimes it last more than a few mins at a time. Also lately now the SES light also seems to be already on as soon as I start the car, but will usually disappear after a min or so and stay off for a bit, but like I said... completely random it seems on how long. Car has been running rough before the SES light comes on... I can smell either exhaust fumes or just more gas being burnt... but car does idle better at lights afterwards. Car has also been running rough just when turning on A/C, but it was doing that before I started just randomly getting the SES light with the code 43. I've been reading about every forum I can and I seem to have way too many answers for my problem... everything from replacing knock sensors again because the ones I got could be defective, replacing the ECM, replacing O2 sensors, checking wires (which seem fine, but I could do better looking if need be), checking the connectors (which are clean), etc.

Has anyone run into this issue before and figured out exactly what causes this? Any insight would be appreciated on this... driving me nuts trying to figure out what it could be so I don't spend a fortune replacing everything I don't need to.

vetteoz

The PCM does a self check of the knock sensor when the engine is first started; it advances the spark to create
knock ( to show the KS is working ) and if it doesn't see the knock then it throws the code.
If the KS is not seen the PCM retards the spark advance over 1500 rpm? to prevent the engine blowing up

http://shbox.com/1/4th_gen_tech2.html#knock_sensor

http://forums.corvetteforum.com/1579063220-post8.html

94LT4Corvette

Okay so pretty much even though I had a mech change the sensors once already... I still got a problem either with the new ones... the wires... or that module it mentions... I need to find that then... thx

Update... 50 min later... lol
Okay I now know that the module resides in the PCM... good good... I didn't know it existed before like I said... so thank you very much on that... I will probably replace that first if the new knock sensors I put in are reading within limits... it should clear my problem... and if not... then I got a bad wire elsewhere probably... but hoping for the best that the module is what is causing my issue!

gerardvg

This might not be of much help for 94 but i have come across this with a friends 87 vette that some work done and the mechanic put the distributor in one or two teeth out, it could not be set to 6 btdc correctly and was badly retarded and throwing knock sensor codes. We checked the timing and put the distributor in and set to 6 dbtd and the knock sensor codes went away. No problems since so i would recommend you double check the timing is correct.

Can you hear the engine pinging (knocking) during acceleration?

Remember the ecm will try to counteract for any problems it encounters and disconnecting / reconnecting the battery to clear the codes can solve most bad running issues after a problem has been rectified.

vetteoz

Cant adjust the timing on a LT1 ,the Opti only goes on in one position

richauto

I have seen this before on other Chevy engines. I replaced the after market knock sensor with o.e.m. I found out the resistance was alot different between the two . Installing the o.e.m. part was the fix. I hope this helps

94LT4Corvette

Okay yeah thats probably it also... I did put aftermarket... well anyway... I ordered the module... I will do that first... if anything it will "knock" out that possibility on the list... lol. As far as hearing the knock goes... I really don't hear it at all... so idk... but I will do module... and I guess recheck those knock sensors since they are aftermarket and not OEM.

94LT4Corvette

So I replaced the module today... and immediately it felt like it idled better and was smoother. I test ran it up and down the highway for about 20 min... gave it the gas... and so far the error has stayed gone... of course my only thing is that normally the error has remained off when its cold and stays on constantly when its warmer... so I'm gonna give it a few days... normal driving like I do... and see if it pops again... I will update in a few days if confirmed or not that this worked... but like I said... so far it does seem a lot better and feels like it has its power back. Also no error on startup... but then again I didn't this morning before I replaced the module... so we'll see on that too.

94LT4Corvette

Okay well the SES light came on today... of course it was a lot warmer and humid today in Houston. The car still seemed to idle better and the light wasn't on during startup... but eventually did come on and did its random off and on like it does. So now... module is done... I can recheck the knock sensors as well now... but AC Delco knock sensors were used when they were replaced, so I don't believe that would be it. Anybody hear of the O2 sensors causing a problem like this, but hiding under a code 43? Anyway... open to any more suggestions here... I hope its not something with the engine itself, but it runs too damn good for me to believe something is wrong with it causing a random knock. The only other thing I can think of is the damn optispark causing a knock and doing the code 43... but that is the only error I am getting.

red89c4

fought the same issue with a friends 87 ss monte. he bought the parts and i changed them at his request, 2 knock sensors. 1 ecm, 1 dist ign module, 1 new dist assm, and 2 esc,s. finally i convinced him that the esc could not advance the timing far enough to produce a knock due to the 93 octane that he was using instead of the recommended 87. after 2 tanks of 87 the code has remained absent for 4 months. check the octane value of your fuel.

disconnect the knock sensor and go for a drive and try to produce a knock. you should get some valve pinging after the engine warms up and you accelerate moderately under load. this will determine that the system is working. it will set the code again and need to be cleared.

94LT4Corvette

Yeah I run 93 octane and no less all the time... I guess I can give that a try... but I haven't done anything to the distributor yet... and it still has an old OEM one in there... it probably is going bad at 150k miles on the car... but anything short of me having to pay $1000 parts and labor to fix that... I'm gonna do first... lol

pcolt94

This is what I have heard and been reading about also. Resistance is not a good indicator of a good or bad unit. Even with a known good unit the resistance may differ between units.

It's a possibility a scanner may give you a clue as to if you are getting knocks and will set a code in reguard to what the PCM indicates.

Check for anything (lose) what may strike the block or that may make a noise that may simulate a knock.

94LT4Corvette

The only code I've been getting is a 43... Knock Sensor Circuit

94LT4Corvette

Would a starting to go bad Opti or plugs and wires cause an issue like this without any other code? That's what I'm trying to narrow down to... what problems that would only be causing code 43 that I haven't already replaced right now... lol

Knock Sensors
Knock Sensor Module

I haven't messed with wires since the code is just so random and does it while sitting at lights sometimes, so I know it's nothing being joggled around causing it like if I was hitting bumps on the road and seeing it pop up. It still seems to be on more and stay on more when it's wet and lots of humidity outside here in Houston.

rtracy

Mine has been doing the same thing. The service manual says to check the sensor wire for voltage with the ignition on and you should have 5 volts present. If not you could have a short in the wires or bad pcm. But check both sensor wires first.

don hall

Read through all the posts, and may have missed the torque setting
you used to tighten the knock sensors. !4 ftlb is the correct torque for the
knock sensors ....... + / - from that setting may cause an erroneous code.

94LT4Corvette

Well I wouldn't think it'd be the PCM... she runs fine when not erroring out... lol... seems weird that'd be the only thing bad the PCM is doing. I have yet to check voltages... been going to college so been driving my Pontiac last 3 months... I'll pull it out of storage at the end of March and start working on it again. Keep this updated so when I find what fixes it... I'll post it.


As for torque on the sensors... I had the mechanic do it... so he should know better... but I guess it never hurts to ask what torque lbs he used... although I was getting the code before replacing as well... just seems like that's probably not it... lol

rtracy

It does seem weird and if it were the pcm why wouldn't it do it all the time? But thats what I read out of the FSM.
I have a log of this happening if anyone with experience is interested?

aminnich

94lt4corvette - is that correct? You runnng an LT4 in a 94 instead of an LT1? If so be sure you are using LT1 knock sensors with the 94 ECM.

94LT4Corvette

hmmm good point... I know the knock module in the PCM is for the LT4 motor... sensitivity reduced due to the extra noise the LT4 made.... read all about that stuff... but the sensors... yeah I don't know... and the ECM thats in there has already been tuned by the ZR1 Team in Kentucky... so I imagine they didn't do anything wrong on their end... lol. I did just put those sensors in though and I didn't even think to check that... I just know I already had an issue before that... and it just continues I still thinking its more than likely an exhaust leak since I was starting to have multiple cracks in the pipe right before all of this happened. Could just be bad spark plugs and wires / optispark as well... which is why I hate this code! I know I can replace the knock sensor harness from NAPA auto for around $45 or so last time I checked... so I will probably do that as well... god knows electrical issues on a 19 year old car is bound to happen with the lil puny wires GM used back in the day.