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Username Post: Code 43 issues '93 c1500 sub        (Topic#348496)
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
11-30-17 09:06 PM - Post#2716485    

Hello all, I'm new here and was hoping I could find some help with my problem that I'm having with my suburban. It's got the 350 5.7 and about 150k miles.
I recently bought it in hopes of fixing it up to use for the family and dogs etc. It has a code 43 on the CEL, which is the knock sensor. I've done a LOT reading about it, but at this point I'm stumped.

I took a look at the knock sensor and the wire was broken, so I ordered a new connector and soldered it on. No change. I took the knock sensor out and there was so much gunk that the coolant wasn't even coming out so I cleaned all that out and reinstalled. No change. New knock sensor, no change.

So I was reading and saw that the timing could be off so I checked that. The timing was so far off to the left of the 0 that I couldn't even see it, so I unplugged the brown wire and set the timing to zero. That helped the idle a little (it was idling high, about 1k rpm, now at 900). I know the knock sensor code will retard the timing a little, so I hooked the brown wire back up and the line on the harmonic balancer was just off to the left of the whole timing plate. So I don't even know how many degrees that is. Funny thing is now the truck smokes like crazy, and my CEL is still giving me code 43.

I also recently rebuilt the tbi and checked the iac and the tps. New pcv valve. They are both fine. There are no vacuum leaks. I've checked with both a gauge and by spraying starting fluid around everything.

I know there can be other things that will make the knock sensor throw a code, but I don't know what else to check! If anyone could help me with this situation I would greatly appreciate it. Thanks!



 
Low priced Genuine GM Auto Parts
someotherguy 
Moderator
Posts: 28464
someotherguy
Age: 47
Loc: Texas
Reg: 08-01-03
12-01-17 07:05 AM - Post#2716516    
    In response to Mjricha

Welcome to Chevytalk,

I may be misunderstanding you, but I think you may be going about setting the timing the wrong way.

Any reading you get from the timing light while the tan/black wire is still connected is going to be off the marker. It will generally be quite a bit advanced until the wire is disconnected.

So you start the process on a warmed-up engine, disconnect the tan/black wire, then check the timing. Adjust to zero. Reconnect the wire - and you can check again, but what you're really checking is just to see that it indeed is advancing past zero, could be 12 degrees or more, easily.

Are you 100% sure you bought the correct knock sensor for your application?

What kind of smoke are you getting, and you're saying this is a new symptom since replacing the pigtail, sensor, and setting the timing?

Richard

06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-01-17 07:25 AM - Post#2716521    
    In response to someotherguy

Yes I am pretty certain I bought the correct knock sensor. I got it on Rock Auto and it looks exactly the same as the one I pulled out.

The truck used to smoke on startup for about 5 minutes then would clear out. Now it's smoking continuously.

This is the one thing I didn't understand about the timing. Yes I pulled the brown wire and set timing to 0. When I plugged the brown wire back in and checked the timing it was way off to the left of the timing plate. Is this advanced or retarded? I thought it would be retarded because it's to the left and advanced would be to the right but I could be wrong.

I did a bunch more reading and im going to test the voltage on the knock sensor. It should read 5v from what I read. If it doesn't I want to test the knock sensor wire at the pcm but I can't seem to find which pin it goes to. I tried to trace it but there are 3 dark blue wires going into the pcm.



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
12-01-17 07:36 AM - Post#2716522    
    In response to Mjricha

Welcome to the board!


If the timing light shows that the line is off the passenger side of the timing tab then the timing is advanced.

After the set timing wire is plugged back in the timing should be advanced.

Here are some code 43 threads that may help you.
http://www.chevytalk.org/fusionbb/showtopic.php?ti...

http://www.chevytalk.org/fusionbb/showtopic.php?ti...

http://www.chevytalk.org/fusionbb/showtopic.php?ti...

This link has a great photo by Richard (Someotherguy) of the timing tab
http://www.chevytalk.org/fusionbb/showtopic.php?ti...

http://www.chevytalk.org/fusionbb/showtopic.php?ti...

http://www.chevytalk.org/fusionbb/showtopic.php?ti...


For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
12-01-17 07:40 AM - Post#2716523    
    In response to Mjricha

  • Mjricha Said:


I did a bunch more reading and im going to test the voltage on the knock sensor. It should read 5v from what I read. If it doesn't I want to test the knock sensor wire at the pcm but I can't seem to find which pin it goes to. I tried to trace it but there are 3 dark blue wires going into the pcm.



I will go get a manual and look it up.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-01-17 07:40 AM - Post#2716524    
    In response to Mjricha

The knock sensor read 4.95 volts, so I know it's not that now



 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-01-17 07:45 AM - Post#2716525    
    In response to Mjricha

Thanks chevytech, Ive read all of those threads except for one, which says I need to test the knock sensor KOEO for 2.5 v and test the resistance as well. I'll do that now. Thanks for all the help so far!



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
12-01-17 07:53 AM - Post#2716526    
    In response to Mjricha

You're welcome.

I looked up which wire is for the knock sensor at the computer and it is terminal B15 which is circuit 496 and the wire is Dark Blue and it is it the second cavity from the end of the PCM connector.

If you look very closely the connectors have the letters and numbers on them.


For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-01-17 08:23 AM - Post#2716528    
    In response to Chevytech

Ok I tested the pcm and got 5v, tested the connector with koeo and got 5v. The other thread said it would be at 3600 ohms so I set my multimeter to 20k and got nothing. Then I set my multimeter to 2000k I got 100. So did I get a faulty knock sensor?



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
12-01-17 08:55 AM - Post#2716533    
    In response to Mjricha

  • Mjricha Said:
Ok I tested the pcm and got 5v, tested the connector with koeo and got 5v. The other thread said it would be at 3600 ohms so I set my multimeter to 20k and got nothing. Then I set my multimeter to 2000k I got 100. So did I get a faulty knock sensor?


Your truck's knock senosr should have 3900 ohms.

My guess is they sold you the wrong sensor.

If it had a manual transmission with separate ESC module the spec would be 100K ohms (100,000 ohms )

The parts people do this all the time. Many of the manuals are very unclear about this topic.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-01-17 09:12 AM - Post#2716536    
    In response to Chevytech

Ok they're saying theres no difference at the parts store when I called so I'll go pick that one up and test it before I buy it.



 
someotherguy 
Moderator
Posts: 28464
someotherguy
Age: 47
Loc: Texas
Reg: 08-01-03
12-01-17 09:24 AM - Post#2716538    
    In response to Mjricha

  • Mjricha Said:
Ok they're saying theres no difference at the parts store


You should ask them why there are so many different part #'s.

Richard

06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
12-01-17 09:30 AM - Post#2716539    
    In response to Mjricha

  • Mjricha Said:
Ok they're saying theres no difference at the parts store when I called so I'll go pick that one up and test it before I buy it.


Have a different parts guy look it up when you go because what they are telling you is not correct.

A 1993 C1500 with and automatic transmission uses and computer that is a PCM that also shifts the transmission. That PCM runs at a 8192 baud rate and has the spark control built into the PCM.

A 1993 with a manual transmission uses a separate spark control module and a 160 baud rate ECM like the older TBI trucks.

These are two very different systems with different sensor specs.

Note:
Knock sensors are more fragile than they look. I like to only tighten them by the hex on the base on the sensor, not by the hex on the plug end of the sensor.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-01-17 09:59 AM - Post#2716545    
    In response to someotherguy

  • someotherguy Said:
  • Mjricha Said:
Ok they're saying theres no difference at the parts store


You should ask them why there are so many different part #'s.

Richard



Lol right? So I called advance and AutoZone and they both say they only have 2, the acdelco one and their own off Brandon one. Both stores say the both brand sensors are the same. Either way they have to order one so it'll be later today before I can go pick it up.

Also, I saw the note about only screwing the sensor in by the base. This is the old one I took out and there seems to be only one place I can use to screw it in at. The replacement one looks the same.






 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-01-17 11:45 AM - Post#2716556    
    In response to Mjricha

Ok so I got one from AutoZone that tested 3700 ohms. Put it in an the CEL is cleared! Now since this is fixed should the timing change at all? I just read that having no knock sensor will seriously retard the timing that's all. I don't know why but the smoke cleared up too. It just does what it did before, smokes for a couple of minutes then clears up. The idle is still high though, around 900 rpm in park. I was hoping that once I got the timing issues fixed the rpm would be lower.



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3715
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
12-01-17 12:11 PM - Post#2716558    
    In response to Mjricha

You are making good progress quickly.

The photo does not look like and original equipment part.

The timing should be where is was without having to reset it. When you have no knock sensor the timing gets retarded because the code is set and the system reduces the timing advance to protect the engine because it cannot determine if it is pinging or not. When the set timing wire is unplugged you take the electronic spark timing out of the picture and are setting the base timing.

Drive it a little bit and see if the idle comes down by itself. The system will relearn the idle after being driven at speeds above 45 MPH and meeting other criteria.

You could also check for a leaking gasket making a vacuum leak right under the TBI unit.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-01-17 12:20 PM - Post#2716560    
    In response to Chevytech

Yeah the new knock sensor that worked actually had a black end not a white one. But other than that they look similar. The original owner shoved a piece of copper in there and soldered a wire to it. I just couldn't get it out/didn't feel like trying to get it out. I just replaced all the tbi gaskets as well, and checked for leaks and couldnt find any.

Ok, I will take her for a spin as soon as I get the seats back in(also replaced carpets a/c and dash). Thank you for all your help I'll let you know how it turns out.



 
rain_man_rich 
Contributor
Posts: 124

Loc: Grants Pass, OR
Reg: 02-09-14
12-01-17 06:07 PM - Post#2716597    
    In response to Mjricha

"This is the one thing I didn't understand about the timing. Yes I pulled the brown wire and set timing to 0. When I plugged the brown wire back in and checked the timing it was way off to the left of the timing plate. Is this advanced or retarded? I thought it would be retarded because it's to the left and advanced would be to the right but I could be wrong."

LOL your intuition is correct but the logic is wrong. So looking at your flywheel from the front of the vehicle, the engine spins clockwise. When you hooked up the timing light after you plugged the wire, in the mark showed up on the left. That means it's firing before it hits top dead center. In other words its firing IN ADVANCE of top dead center.

I seen this confusion before and it stems, I believe, from the words "retarded" being somewhat synonymous with "before" and "advance" being somewhat similar to "after". Glad to see you are on the right track to getting it fixed. Good luck!



Edited by rain_man_rich on 12-01-17 06:09 PM. Reason for edit: No reason given.

 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-01-17 07:45 PM - Post#2716607    
    In response to rain_man_rich

  • rain_man_rich Said:
"This is the one thing I didn't understand about the timing. Yes I pulled the brown wire and set timing to 0. When I plugged the brown wire back in and checked the timing it was way off to the left of the timing plate. Is this advanced or retarded? I thought it would be retarded because it's to the left and advanced would be to the right but I could be wrong."

LOL your intuition is correct but the logic is wrong. So looking at your flywheel from the front of the vehicle, the engine spins clockwise. When you hooked up the timing light after you plugged the wire, in the mark showed up on the left. That means it's firing before it hits top dead center. In other words its firing IN ADVANCE of top dead center.

I seen this confusion before and it stems, I believe, from the words "retarded" being somewhat synonymous with "before" and "advance" being somewhat similar to "after". Glad to see you are on the right track to getting it fixed. Good luck!




Thanks! This makes a lot of sense. Very good info, I feel dumb now because I didn't realize it before!



 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-06-17 07:13 PM - Post#2717129    
    In response to Mjricha

Update:

I got everything put back together and drove it around today.

I ended up also getting a new iac and that solved the high idle problem. My iac tested ok but it was stuck open so it was letting to much air in I believe. Park rpm now at 800 drive rpm at 550-600.

No more knock sensor issues either. The cel light is off and it's staying off.

However there are some new issues now and I'm dealing with those.

Since I got the new knock sensor and the new iac, sometimes on startup when the truck is warm it will rev high then low ( to almost stalling out) in very rapid succession. Up down up down etc for about a minute, then it evens out and runs fine. I tested my tps and it's fine (good ground, 5v on grey and smooth voltage increase on blue). With a new iac and the tps being fine I don't know what else it could be. I've checked for vacuum leaks 10 times and can't find any.



 
CowboyTrukr 
"6th Year" Silver Supporting Member
Posts: 3821
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
12-06-17 08:31 PM - Post#2717141    
    In response to Mjricha

Throttle body base gasket? Mine had the factory one installed wrong.

Greg

'95 K1500 Z71 EC Short Step 5.7L+0.040/NV3500
'00 Explorer XLT 4.0 V6 Auto
'94 K2500 5.7 NV4500 ECLB - SOLD

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke


 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-06-17 09:04 PM - Post#2717146    
    In response to CowboyTrukr

I just installed the tbi rebuild kit that came with all new gaskets for everything. I've checked vacuum with a gauge and it's fine and I've also sprayed starter fluid around everything and nothing. I can take the tbi back off tomorrow and check the gasket again though. Would it cause any issues to use gasket sealant when I put it back in?



 
Mjricha 
Forum Newbie
Posts: 18

Reg: 11-30-17
12-06-17 09:06 PM - Post#2717148    
    In response to Mjricha

This is starting to drive me nuts. It's like I fix one problem and two more pop up in its place. In getting the infamous 1-2 whiplash shift now too.



 
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