Gm Code 43 issues

[BrianF]

So I have spent some more time on my 1993 GMC K1500, 2wd, 4L60E, 375,000km. I recently replaced the cap/rotor/wires with United components, brass terminals and 8mm silicone wires. Plugs are correct ACDelcos CR43 (what ever the proper plug is), new ACDelco tstat, O2 sensor, EGR solenoid, Delphi knock sensor and new pigtail. Truck runs much better now but the fuel economy is still way, way down from expected. Hand calculating 10mpg unloaded light highway driving. Sure the cold weather does not help but the mileage has not improved what so ever.

It had intermittent code 32 that might just be the EGR valve itself (appears original). Even with the new solenoid, it has a crappy tip in stumble albeit much better than before. It also had code 43 for the knock sensor or ESC. Since replacing the sensor and pigtail, the check engine light is on right at start up and does not go away. Before it was intermittent once up to operating temp. Still code 32 and 43.

I was expecting some knock with out the sensor hooked but never detected any what so ever. I have straight pipe, true duals with no cross over. You can hear what the cylinder banks are doing and they sound strong and consistent. Previous to the new parts, the engine was down on power but while accelerating on the highway it sounded like the even bank would kick in, run smooth and a sudden surge of power. Now it runs good but still feels down on power.

In efforts of tracing this code 43 I am turning to the ESC but am unable to locate. It is not engine mounted nor can I find it on the firewall or behind the glove box.

I need to also get a timing light and check base timing and see what it is set at with the wire hooked up.

Any help is much appreciated and thanks for looking.

 

[das_peikko]

Which engine does it have? RockAuto gives you a choice of four engines for a 1993 K1500.

 

[joegreen]

Not positive but I think on the later trucks the esc was built into the ecm or something like that. You should post up on gearheadefi.com they can absolutely help you out.

 

[EricG]

Either completely rebuild or replace the distributor!

 

[mk378]

Your new sensor may be a dud. Code thrown before startup usually means a fundamental voltage or resistance check failed. If knock sensor code is active, it will constantly run conservative timing with corresponding low performance and mpg.

Base timing is important for mpg. There are some timing-related functions in the ignition module but mostly the problem with those modules is that they suddenly die completely.

"Tip-in" issue could be related to the throttle position sensor. It is a potentiometer type sensor that can be checked with a voltmeter. These PCMs are not very "triggerhappy" about throwing codes, so you can have some serious problems yet no code set. EGR code could be that the passages are clogged. If you force the valve open at idle by applying vacuum directly, properly flowing EGR should cause it to stumble or stall.

Also consider the basics like compression and is it firing on all 8 cylinders.

 

[Job]

I've done my share of replacing good parts due to codes. The code can be set by some other defect feeding wrong input to the part. From air leaks, to who knows what else. It isn't see the code, replace that part.

 

[BrianF]

Thanks guys, its a k code 350 in it. The weather is starting.... to warm up this week and will give me some time to start the trouble shooting: check the plug wires are actually on the right cylinders, test KS output, compression test, timing check.

 

[t1snwrbrdr12]

A leaking egr valve gives those older gms a lot of part throttle stumble off idle.

The egr fault is also often a failed driver within the ecm. Not too hard to go through the diagnosis and it's probably listed online somewhere.

Ignition modules throw faults for the est quite often. Aftermarket ignition parts typically fail far too soon so be careful in your parts selection

 

[BrianF]

So after much more reading, it appears Joegreen is correct that the ESC is now part of the PCM.

I am hoping to avoid rebuilding the distributor, unless that is the only option. Truck is just not worth it at this point in time.

 

[BrianF]

Further reading, PCM should be sending a 5 volt (thinking DC) reference to the knock sensor through the single wire. With the engine running the knock sensor should be sending a varying AC voltage signal back to pin B15 on the PCM.

I will need to check the new Delphi KS for resistance and AC output and hopefully get a 5V reference to verify the wire and new pigtail are actually working.

 

[clinebarger]

GM used 2 different resistance Knock Sensors in the '90's.....A 3,900 ohm & a 99,000 ohm, The 3,900 ohm sensor was almost exclusive to the Gen II SBC (L99/LT1/LT4) engines & had a Black tip. The 99,000 ohm sensor has a White tip & was used on all the TBI/TPI engines

 

[BrianF]

Thanks Clinebarger, that is reassuring. The white tip Delphi KS came back at 99.9k ohm, which was confusing as I was looking for the latter. I tested the pigtail. Key on/engine off came back at 4.95V. Engine running it came back at 5V even. I tested the KS for output as well while hitting the passenger side exhaust manifold. It varied. Very light taps resulted in .091V spikes. Giving the manifold some decent knocks and the output jumped to over 1V.

Edit: Forgot to add, while engine running, the KS was kicking out less than a volt but was steady. I did not record the exact numbers unfortunately.

Now I am always getting that Code 32. I pulled the line to the valve and while the engine was running I applied some vacuum (just me giving the vacuum line some love) and the valve easily opened and bogged the engine down. There is a bit of insulation removed from both wires right at the solenoid connector so I will do some research to see what voltage it is receiving.

Also of note, if it matters but this was all done with a cold engine, possibly at 10C ambient.

 

[clinebarger]

I decided to do more research on your issue, Looking through my 1993 light truck FSM & I hand wrote a note @ 25 years ago......
"Check Knock Sensor Tip Color & verify with parts department per VIN on ALL '93-'95 4L60E/4L80E equipped TBI vehicles."
White Tip 99,000 ohm part# 10456288
Black Tip 3,900 ohm part# 10456549

*I'm sure these part numbers have changed by now, But I'm sure they will cross......AcDelco started using 6 digit numbers for stuff like this a few years ago.

I wrote the note right on the Code 43 diagnostic trouble tree page, It specifically states 3,900 ohms! But the note means I must of had some problems with it being correct for ALL models. I wish I remembered all the details.....But I've worked on so many different systems since then!

So what I posted earlier isn't necessarily true.....It's just the way I remembered it

, Getting old sucks!

Short of visiting a Chevy parts department armed with the VIN.....You may want to try a 3,900 ohm sensor!!

 

[BrianF]

I saved the old sensor as it came out easy. I will check resistance. I know it had output when I tested it in block. Perhaps the code 43 was associated with the garbaged original pigtail. I did have the new pigtail attached to the old sensor for a few km as I was waiting on the new one. The connection was a bit loose so I will put a wrap of tape on the tip to secure it.

Thanks for the insight as the learning continues.

 

[BrianF]

SO the original KS was a black tipped one that reads 3.9k ohm. In it goes next available date.

 

[clinebarger]

I've ran across Knock Sensors that ohm within spec & still set codes.....
A couple years ago.....I was working on a 2006 C1500 4.8L & replaced both knock sensors & jumper harness with OE parts, Came back with with DTC's for one of the sensors. Ohm'ed out fine. As this one uses 2 sensors I was able to swap the wires & cull the faulty sensor without much drama.

Generally.....GM PCM's self-check Resonant Knock Sensors by advancing the timing 'til knock is "heard" during initial cold start, The very reason they started using two sensors later on.

 

[wtd]

Years ago I had a 93 S-10 with the 4.3L/4L60E that developed this code 43 at about 54,000 miles. I replaced the knock sensor and pigtail going to it with no results. Mine was intermittent and the CEL wouldn't usually stay on.

I ended up trading this truck off on my 98 K1500 soon afterward and I never got the problem fixed or knew what had caused it. I know it drove me crazy.

 

[BrianF]

So I spent some time today and swapped the old KS back in. I did a few tight wraps of electrical tape around the KS nipple (lack of a better term) as this helped the new pigtail have a tight fit. It was a bit finicky but once it was seated on the KS it was a tight fit. This only took a few minutes with a 7/8 socket and short extension but the steady [censored] of coolant on your arm lasts much longer.

Got it buttoned up, had the negative terminal disconnected to clear the codes and took it for a drive. The code 32 was intermittent but the 43 was gone. It appeared to run great but I really need to get it on the highway to eliminate the grid road noise and get some miles on it to hand calculate the mileage.

 

[BrianF]

Put a couple hundred Km on the truck thus far and code has not returned. With the EGR vacuum completely hooked up I have no codes but the slight low rpm stumble, which I believe is solely the valve.

Going to pull plugs, inspect and check gap as well because they are cheap and the previous owner figured they were new....

 

[BrianF]

Pulled all 8 plugs, which are the correct CR43TS. They were all in great shape and all had a beautiful, even tan color. Checked gap and all were .045. According to the emissions sticker and internet searches, .035 is where they should be. Gap changed and will see how fuel economy pans out.