94 Chevy K2500 6.5 Multiple Codes Present

[IdDieselGuy]

Bought this truck from my work about 2 months ago. It was a trade in. Got it for $750. Ots a 94 K2500 long bed with a 5 speed. Awesome truck! Love this thing and dont ever wanna get rid of it. When I first bought it, it was pulling a code 29 for faulty glowplug relay and code 31 for wastegate solenoid. The wastegate solenoid was bad so I replaced it and it fixed that issue. Then it popped up with a code 36 but still had the 29. Wasnt totally sure what to think. It's now showing code 29, 36, 49, 57, and 62. The pmd is relocated to front bumper and has aftermarket 9 blade engine fan as well as straight pipe exhaust. No other mods yet. The check engine light sometimes comes on and then goes away. It does this intermittently almost everytime I drive the truck. Usually after its warmed up itll only come on at high speeds. Sometimes it wont come on and off at all. When I comes on, itll stay on until I decelerate then go off till I accelerate to a certain speed again. My friend seems to think it's the optical sensor. I removed the filter on the optical sensor and that seemed to help a little bit but still throwing the codes. The engine has been resealed and possibly rebuilt. Heads have been studded too I believe. There was also no nut or washer on the groundwire on the starter so I had to replace that because it wasnt starting. Fires right up now. Last night, the truck bucked about 3 times when I drove it. Never done that before. It did miss a few times at idle a month ago but has been absolutely perfect since. And in the mornings even when it's not cold and I go to start it up, itll smoke white/blue/grey for about 10-20 seconds and then be fine. Done that since I bought it. If I hit the accelerator itll go away quicker. Truck has 195k miles. I've talked to another guy in Northern Idaho about the issues I've had as he has built up several of these trucks and he seems to think it's the optical sensor or lift up but leaning towards optical sensor. I dont wanna rule anything out but I also dont wanna start replacing random things especially if they're expensive. As far as the grounds go, there looks to be a heatsink sort of thing bolted to the driver side fender well under the hood. It has a bunch of ground and positive wires going to it. The wires are not touching the metal all the way, they just look to be tightened down to where they wont come off. They are held on with a nut and washer. I can get a pic of what I'm talking about when I get home. Not sure if thatd have something to do with it or not. Also getting a really strong burning metal smell after driving the truck and shutting it off. Seems to be coming from the back of the intake or the front wheels. The front brakes were bad so I changed them out this last weekend but still having the smell. Clutch maybe? There is some grinding also in 1st second and sometimes third gear when I'm not stepping hard on the throttle and driving at lower speeds. Been like this since I bought it. I know the U joints are bad, could that be a possible cause of the grinding? Sounds like flywheel or clutch or something. Anyways, the multiple codes thing completely has me thrown for a loop. Before the other day, it has only ever pulled one or two codes at a time. Code 31 and code 29. Any info on this would be greatly appreciated as I am currently at a loss as for what to do.

 

[Wreckinball67]

I would remove and CLEAN all the ground wires and studs they connect to. Also, I would make sure that your charging system is fully charging good batteries. I would do this prior to worrying about the codes. As far as the smoke, I would check for a cracked block. Mine had the same symptoms (1998). The #8 cylinder had a crack. I have just replaced it with a GEP Optimizer. One way to check is to open the coolant reservoir and watch for bubbles while someone else starts the truck. Yours is older and not necessarily as prone to cracks as mine was but it's an easy check. If it is cracked, there's no sense in going any further, good luck.

 

[ak diesel driver]

First put a a piece of clear tubing on the return line coming out of the injection pump !/4" diameter bout 6" long. Look for air bubbles while it's running
Second open the water drain coming from the fuel filter while it's running and see if you get any fuel out of it. Your year truck the lift pump is controlled by the oil pressure sending unit (safety thing) and fails often. Consider making or buying a relay harness for the LP
Third does it have an EGR? I believe the code 29 is for the EGR
The others are electrical codes for ign and tranny

 

[IdDieselGuy]

Code 29 is glowplug relay fault. My 95 has an egr but my 94 doesnt. The other codes are saying other things besides tranny stuff. The truck has a 5 speed manual so I wouldnt think any of them would have to do with tranny stuff. I've looked for cracks. Have not seen any that are visible to the naked eye. Itll smoke and run rough. Doesnt do it every time I start the truck though. Only when it's been sitting overnight or for several hours. And like I said earlier it will only run rough and smoke for a few seconds or until I hit the throttle. And if doesnt always do it even after sitting overnight or for several hours, just most of the time. My gasser does have bubbles in the coolant while it's running though and it runs rough at idle but that's due to a faulty distributor and being out of timing. I will try the fuel filter thing for sure! I believe my truck does have the aftermarket relay harness for the oil sending unit. Theres supposed to be a small box with a fuse attached to that relay isnt there? My batteries are staying fully charged as far as I am aware but sometimes while driving the gauge will flutter just ever so slightly but it always stays at about 14. The truck has never died on me or overheated of left me stranded as of yet. Its actually been better than my other truck with the 5.7l has. Where on the block is a common place for it to crack? Would it be overheating at all? It doesnt use any coolant or anything.

 

[IdDieselGuy]

I did also remove the Optical sensor filter harness and plug the other end directly into the optical sensor. I think I read somewhere on here that doing so could solve some of the bucking issues. I had had a few small misses before i did that which is what lead me to do so as well as the guy in northern Idaho telling me he thought the optical sensor might be bad. I u plugged the filter harness and plugged the one end directly into the optical sensor and it seemed to be fine no more misses. But now its pulling all of those codes. Do I need to just buy a brand new filter harness and plug that in and see what it does?

 

[ak diesel driver]

Ditch the filter harness. To test the OS unplug the crank position sensor and then try to start it. It will take alot of cranking and when it starts it'll be in limp mode. Should run nice and smooth no glitches at all. If it acts up at all replace it. Do the reverse to test the CPS

 

[IdDieselGuy]

Okay. Where is the crank sensor located? I've tried to look for it before but havent seen it. Yeah I completely ditched the OS filter harness. Will be taking it off of my 95 and ditching that as well. It bucked for the first time ever last night. Only 3 times then it was fine. Truck runs and drives fine otherwise. And then about a month ago it missed at idle 2 or 3 times and has not done so since. So it's like intermittent. But the issue is still there. From what I'm reading the code 57 is pretty serious? I'll definitely try what you said and let you know.

 

[Wreckinball67]

Mine cracked inside the #8 cylinder. My year (98') was more prone than yours. Mine too had the same symptoms which is why I mentioned it. It would start and run rough for 10 seconds or so after leaving it overnight. And, like yours sometimes it wouldn't do it at all. I have since determined that the reason it would sometimes not run rough, was because the piston would stop on the crack and in a sense plug the crack. Of course you can never tell where the piston would stop. I'll include a pic of my crack in the #8 cylinder. Once I pulled the head the piston was low in the cylinder, there was a bit of coolant on top of the piston and the crack had what looked like perspiration. So it wasn't a huge crack. I drove it for about a year til finally it was parked for 2 weeks and when I went to start it, it hydolocked on me. When I pulled out the glow plugs and cranked it, it blew coolant out of #8.

 

[Will L.]

@IdDieselGuy the cps is on driver side of the timing cover down low. The connector is about 5” up from it, 3 wire weatherpack.

@Wreckinball67 sux about the #8. Yours cracking so high in the cylinder is proof for some of the hummer folks on here about the “at risk block” thing being wrong. There is a theory that a bad casting spot was the cause for the #8 cracks, but most happened about the middle of the cylinder and they blamed it on a casting issue for that 1” area.
Truth is both cylinders 7 and 8 have issues there- note ring gap, piston to wall clearances, etc. The #8 goes more often from the imbalance of flow from the older waterpumps, and the coolant eddy currents in the block.
If you take measurements of that damaged cylinder, the issue of warping stands out pretty good.

Temps kept always below 220, and almost always below 210 made all the difference in the world in the fleets.

 

[IdDieselGuy]

Do you think it's possible that mine is cracked then? I've gone a week or two without driving it once or twice and it's been fine. Hasn't hydrolocked as of yet. No telling how long it's been like that either. The previous owner resealed it from what it looks like as well as studded the heads. Possible the actual engine was even rebuilt too but I'm not 100% on that. No leaks though. But it does have one small steady stream of oil running very slowly down from the top of the timing cover. I guess if all else fails I can always throw in the engine from my 95 6.5 but it's an S VIN and has egr. I had another 94 several months ago that smoked lots of white smoke on startup and then went away after awhile. It was also very cold outside everytime I started it up so I dont know if that had something to do with it or not. That truck had 293k on the odometer but the previous owner told me the engine wasnt stock and had been replaced. It was mostly bulletproofed as well.

 

[IdDieselGuy]

I've attached pics of the ground thing I was talking about as well as what i think is the aftermarket oil sending unit relay.

 

[IdDieselGuy]

I started up the truck and unplugged the baro sensor, map sensor, and ect sensor. Made no difference at all in the way the engine ran. I unplugged them each individually one at a time. Could this be a ground issue still or possibly a short skmewhere? Checked all my fuses and they look good.
Checked the fuel filter. There was fuel spraying out of the top of the fuel filter bleeder when I opened it so that rules out the lift pump.

 

[ak diesel driver]

When you unplug the ECT sensor it should have gone to high idle

 

[ak diesel driver]

That blue thing looks like a battery isolated or something like that. That last pic is just a fuse

 

[Will L.]

Yup that is a battery isolator. Do you have 2 batteries or 3? If 2, you should eliminate that and run 2 batteries like normal.

 

[IdDieselGuy]

Oh okay good to know on the battery and fuse thing. In the second to last pic, the wire to the ground is showing towards the metal thing that goes around the bolt. That might be an issue. Noticed it the other day. As far as the ECT goes, there was no change in anything when I unplugged it. Same with the Baro and MAP sensors. Just drove the truck about 6 miles and it ran fine like usual. But it had the usual intermittent check engine light at certain speeds, mainly about 45mph. If I accelerate or decelerate, itll go off like usual. Cruise control will work for a few seconds then the truck will buck and cruise control will go off and check engine light will light up then go away after a few seconds. Done that since I bought it but it was only pulling code 29 and 31 before. And Will L, I only have two batteries. How would I eliminate the battery insulator? What is it even there for?

 

[IdDieselGuy]

The engine does blow a good amount of black smoke when I really get on it though. Pretty thick. Have the #7 resistor in the PMD. Not sure if that's part of it or some of the codes maybe? It blew a ton of black smoke before I fixed the wastegate solenoid and straight piped it but it still seems to blow quite a bit. Air filter is clean.

 

[Will L.]

You should pick up a new battery cable set from pt wiring solutions if you can afford it. Afaik his are still the best.

I really doubt the isolator is the cause of you issues, so maybe solve that first. Keep following AK DIESEL DRIVER’s lead here. Make sure to hit all the steps and report back.

 

[ak diesel driver]

I forgot to say only the ECT sensor in the coolant crossover should make it go to high idle. the one in the head is only for the dash guage

 

[IdDieselGuy]

I know I unplugged the one in the crossover. The other is for the gauge. Had the same issue recently on my gasser. I'll definitely clean up the grounds and report back to yall. Thanks for the info! And Will, how much do those battery cables run? Are they side or top post?