Question: Knock Sensor

[boomdriver]

Grounds.....check all the grounds. All these things you describe are common c-4 wiring issues. They ALL have rotten wiring harnesses and broken plugs...

A "lean exh" code does not always mean that there is a bad injector. It can easily mean that there is a RICH condition that the ECM tried to compensate for with shorter inj pulse bandwidth. It can mean air leak, vac or intake. These codes are not direction that take you straight to the problem, more like a road map that shows you the many ways how you can get there....


This comes from experience,
Its far more economical to slow down and fix it right. Been there, done that.

There are new wiring plugs available,fairly cheap, and there are dozens of vette salvage shops that sell pieces of wiring harness. I bought spare plugs/pig tails (used) for as many things as I could at around $5-$20 each. I have replaced many that have deteriorated from age, like myself.
J&D corvette used to have a pile of butchered C-4 harness that they sold chunks of. XL auto parts has delco pig-tails listed. Ecklers has many of them. I'm watching for a replacement fuel relay plug myself, and aux fan relay plug.
More effort will go into a jury-rig, so why not get a replacement plug, solder it in place and plug it in and forget it? If that does not solve the problem then a bypass certainly won;t either. A bypass will simply put your motor at risk. You just can't eliminate sensors on computer cars because you don't like them or can;t fix them properly. The motor was designed to run with that KS and it'll bite you hard for applying old school mechanics to a complex modern design. Not trying to be an ass, just trying to save you LOTS of grief. Retarding timing happens INSTANTLY to save the pistons. It only takes a second to break one. I'll send pictures if you have doubts. Installing a resistor will probably send the motor into open loop operation and thats not good long term.

I keep my broken piston and the bent valve on a shelf so I can see it everyday. That reminds me what it cost to make mistakes with 20th century motors.
Good Luck.

 

[boomdriver]

I remember it. It was called performance ping.

Yes...we all did it that way. But, that was before these cast aluminum hypertheuritic (sp?) pistons that seem to hate beating the walls..

 

[aklim]

toptech
Thank you for the offer of the injectors. I will keep that in mind but first I want to just put a resister on the right bank knock sensor. I was just out looking for the common wire in my case dark blue wire from both knock sensors to the ecm connector. It occurs to me that if I only put a resister on the ks that the electrical connection has turned to dust I will still have one working sensor so the impact of the ecm not being able to retard the spark should not be as bad as if I disable both ks in effect I would have only removed one half of the sensors. I can see why most people would put the resister in the wire close to the ECM because it is so easy to get to but when they do that they do remove all ks protection because that wire is the common wire for both sensors.

What are your thoughts on this thinking. I also was thinking that I could have an injector that was intermittent in how it works causing the code 64 Lean 02 sensor on right bank.

If we were closer, I would run over there and help you with it. I have done it on my own car and would definitely not recommend disabling any part of the system. Is there someone nearby who can help you with running a wire? Someone that can trade a favor or just "paying it forward"?

I am kinda skeptical of that theory

 

[aklim]

I will play devils advocate.
While not disputing the reason for the existence of the KS , for those of you old enough to remember; in the good 'ole days, the hot tuning trick for street engines was to screw dist advance up and load car up in gear until audible pinging was heard then back off dist slightly.
That was the most advance a particular engine could handle.
Given the advances in engine materials quality I don't see our engines being any more " fragile" than any previous SBC .
A KS will sense knock ( real or false ) a long time before anything is heard

Do those SBCs make as much power and did they have the same low quality fuel that we have today? I know my ancestors used leaves to wipe their butts and they lived. I once used snow when I was hunting and forgot to pack butt wipes. Doesn't mean I want to do that when I can get my hands on Charmin.

 

[Hib Halverson]

If your engine is running lean and then you relocate the KS to a non-standard place, you're in double jeopardy because lean AFR tends to cause a higher level of detonation so you need the protection the KS and EST offer.

If you're worried about the effects of lean AFR on pistons and valves, if the engine detonates, any damage will be increased.

With MY93 Vin P engines, DTC55, 63 and 64 all present at the same time means this engine has serious fuel system problems. :nono

DTC55 typically sets when the engine is lean at WOT. Those three codes mean you need to troubleshoot, per the FSM, all the way from the pump strainer to the injectors, in that order. Running the engine like that and with a disabled or desensitized KS is just asking for major engine damage. If the car is one of your few enjoyments and you are having a hard time fixing it, you need to weigh the lack of enjoyment because of a blown motor vs. the expense of having a professional repair it.

DTC43 is, as you know, is a fault in the knock sensor system. There are two sensors, one to sense detonation from each bank, wired in parallel. You could run with one sensor but then the opposite bank would be more in danger of engine damage.

Bottom line, the mix of lean AFR at WOT and disabled or desensitized KSes is a recipe for engine failure.

I'm sorry to be the bearer of bad news.

Good luck.

 

[aklim]

There are two sensors, one to sense detonation from each bank, wired in parallel. You could run with one sensor but then the opposite bank would be more in danger of engine damage.

On my 91 there is only 1 sensor. Is there a benefit to wiring a 2nd one in parallel or will the ECM freak out?

 

[boomdriver]

On my 91 there is only 1 sensor. Is there a benefit to wiring a 2nd one in parallel or will the ECM freak out?

Is there a hole in the block somehwere that could take another sensor on the opposite side in a water passage? hmmmm..Now I'm curious and want to look. As long as the signal values did not change, it seems like the ESC & ECM would not care. Either way, with these engines today and what our fuel is, I would not drive to the end of the street without the KS or EGR.

 

[Hib Halverson]

On my 91 there is only 1 sensor. Is there a benefit to wiring a 2nd one in parallel or will the ECM freak out?

Because the engine controls systems in a 91 and a 93 differ so much, I think it might be difficult to adapt an L98 to two sensors. Also, I think the practical advantages of doing so, while measurable, would be limited.

As to why a 93 LT1 has two sensors? Well...I surmise that GM felt the LT1, due to higher output, needed to have knock sensing of more consistent sensisitivity across the engine. It is also possible that GM was just "planning ahead" for the switch to SEFI in 94, a system which had more of a need for two sensors.

 

[aklim]

Is there a hole in the block somehwere that could take another sensor on the opposite side in a water passage? hmmmm..Now I'm curious and want to look. As long as the signal values did not change, it seems like the ESC & ECM would not care. Either way, with these engines today and what our fuel is, I would not drive to the end of the street without the KS or EGR.

IIRC, there is a plug there.

 

[John Robinson]

Update

Thank you everyone for your input on this question. Due to a very generous offer of some used parts I have now got the codes down to just code 55. I worked on the car yesterday and had the battery disconnected so the codes were cleared. When I took the car for test drive I only went until the temp was up to 208 and then I mashed the go peddle. That was when I got the code 55 and the car had a slight flat spot in the RPM about 3K. After that It did not recur. I read somewhere that when the battery is disconnected it takes the ecm about 30 miles to relearn so maybe I caused the code from my not being inpatient. The code only appeared for about 30 seconds then it went away.

 

[aklim]

That was when I got the code 55 and the car had a slight flat spot in the RPM about 3K. After that It did not recur.

I read somewhere that when the battery is disconnected it takes the ecm about 30 miles to relearn so maybe I caused the code from my not being inpatient. The code only appeared for about 30 seconds then it went away.

I would use a scanner and check the TPS. Turn the key so the engine is in run position but DO NOT CRANK. Check TPS voltage. SLOWLY depress the skinny pedal and watch. It should go up smoothly with NO flat spots. If there are flat spots, toss it and get a new TPS.

I don't think so. Your long and short fuel trim might not be in place but that should have no effect on a code 55 which is ECM problem. Could be you have an intermittent ECM which is causing the problem

 

[toptechx6]

Delighted to hear you have made some progress John. I think my next step would be to clear the code, install a fuel pressure gauge and tape it to the windshield then drive to see if code 55 returns, keep a close eye on the fuel pressure at WOT to see if it remains within spec.

 

[aklim]

Delighted to hear you have made some progress John. I think my next step would be to clear the code, install a fuel pressure gauge and tape it to the windshield then drive to see if code 55 returns, keep a close eye on the fuel pressure at WOT to see if it remains within spec.

Code 55 is an ECM fault code isn't it?

CODE 55
Trouble Code 55 indicates that the Analog- to-Digital (A/D) converter in the ECM timed out. The ECM checks this by initiating a conversion and timing how long it takes to complete. If the converter, for whatever reason, fails to signal the End-Of-Conversion (EOC) before a timeout counter runs down, the ECM assumes it is bad and sets this code.
Possible causes for Code 55 are limited to:
1. Defective or incorrectly inserted MEM-CAL
2. Defective ECM
If replacing the ECM, be sure to transfer both the PROM and the CALPACK from the old unit. If the old-ECM also indicated PROM failure (Code 51) or a bad CALPACK (Code 52), be sure to verify these components are fully operational in the new unit. If they are not, they too will have to be replaced.

 

[toptechx6]

Code 55 is an ECM fault code isn't it?

CODE 55
Trouble Code 55 indicates that the Analog- to-Digital (A/D) converter in the ECM timed out. The ECM checks this by initiating a conversion and timing how long it takes to complete. If the converter, for whatever reason, fails to signal the End-Of-Conversion (EOC) before a timeout counter runs down, the ECM assumes it is bad and sets this code.
Possible causes for Code 55 are limited to:
1. Defective or incorrectly inserted MEM-CAL
2. Defective ECM
If replacing the ECM, be sure to transfer both the PROM and the CALPACK from the old unit. If the old-ECM also indicated PROM failure (Code 51) or a bad CALPACK (Code 52), be sure to verify these components are fully operational in the new unit. If they are not, they too will have to be replaced.

Not on a 93, see this link

Recovering the C4 ECM Codes - www.c4vettes.com

 

[aklim]

Not on a 93, see this link

Recovering the C4 ECM Codes - www.c4vettes.com

My bad. If it is a "Engine Running Lean" condition and not "Rich Exhaust" or "Lean Exhaust", it might either be fuel related or maybe even the MAF. I would wonder how long ago he has had the injectors and fuel pressure checked.

 

[John Robinson]

Code 55

I think I have found my code 55. When I ran my test drive I did not look at the fuel gauge and today I noticed there was only one bar showing. I suspect I simply was accelerating so hard that the fuel was low and pushed away from the pick up screen momentarily causing the pump to drop preassure and the ecm to set the code. At least I hope that is the case. Only time and a full tank will tell for sure.

 

[aklim]

I think I have found my code 55. When I ran my test drive I did not look at the fuel gauge and today I noticed there was only one bar showing. I suspect I simply was accelerating so hard that the fuel was low and pushed away from the pick up screen momentarily causing the pump to drop preassure and the ecm to set the code. At least I hope that is the case. Only time and a full tank will tell for sure.

Somehow I doubt that. While I have a 91, I have always driven my car down to the bottom of the fuel tank

 

[vetteboy86]

If I can I try not to allow my fuel tank under 1/4. However the other day I drove it to work for the first time in a month or so, and planned on getting gas on the way home. I tried a few hard accelerations with only 3 or 4 bars, and absolutely the car simply ran out of gas. Topped the tank off and no issues.

I thought there were provisions in the tank to prevent fuel starvation from cornering and accelerating. This has been an issue whenver the car is under 1/4 of a tank. Never an issue more than 1/4.

 

[navy2kcoupe]

John, you might also want to run some TECHRON fuel system/injector cleaner thru it to dissolve any crud or varnish in the fuel system. I use it regularly in my C5 to get rid of the "pucker factor" that hits when the gas gauge drops to zero like a rock and the check gauges message comes up on the HUD. I've only heard good things about TECHRON, and never anything bad. Of course, it goes without saying to follow the recommended instructions. Keep plugging, you'll eventually get it all sorted out!
Andy

 

[aklim]

I thought there were provisions in the tank to prevent fuel starvation from cornering and accelerating. This has been an issue whenver the car is under 1/4 of a tank. Never an issue more than 1/4.

There might be a baffle there to stop some of the sloshing around. I would think that unless your sender is reading wrong or something, you should have more than enough fuel. That or your pump might be weak.