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94 Chevy K2500 6.5 Multiple Codes Present

Painful compared to stock. Iirc he sells them ebay now. Seen 2 sets from him- top quality. Hummers come stock with big boy cables, so I got lucky there.

My suggestion is use top post rather than side post. Only advantage of side post is manufacturing cost for gm. All electrical and mechanical advantages are to top post. Maybe someone here has a number for him?

I am assuming someone hacked apart your factory cables to do the isolator btw. If not and you can go back to stock easy enough for free, do that for now. There is alot of other things that justify $ before batt cables.
 
It's a pickup... and may have been used for pulling an RV. The "assumed" battery isolator may have been for the RV wiring so the RV didn't drain the battery while camping overnight. Follow the wires and see where they go before making any changes. The breaker is consistent with a trailer power plug. Just a Wild Ass Guess as maybe there was a stereo system involved or other high power drain stuff installed.

I suggest you have an electrical problem that needs to be solved before you throw even one expensive part at it.

Codes are listed here:

OBD I Codes

OBD I Codes DTC 12 - No Codes Present DTC 13 - Engine Shutoff Solenoid Circuit Fault DTC 14 - Engine Coolant Temperature (ECT) Sensor Circuit Low (High Temp) DTC 15 - Engine Coolant Temperature (ECT) Sensor Circuit High (Low Temp) DTC 16 - Vehicle Speed Sensor Buffer Fault DTC 17...
www.thetruckstop.us

You noted the following codes (One step ahead of the game here, congrats! We don't have to ask.) :woot:

DTC 29 - Glow Plug Relay Fault
DTC 36 - Injection Pulse Width Error (Time Long)
DTC 49 - Service Throttle Soon Lamp Circuit Fault
DTC 57 - PCM 5 Volt Shorted
DTC 62 - Turbo Boost Sensor Circuit Low

Start with grounds by taking them apart and cleaning them. Load test the batteries separately. Check the positive and negative battery cables. Yes, they are coming apart for a total clean and inspect or you can do job right later after wasting a bunch of time on other things while missing a dirty connection.

Then you need to concentrate on the short. Shorts piss off the ECM like no day tomorrow and a bunch of other avalanche codes pop up from the short. Your biggest clues are the Boost (MAP) circuit low code. Then the glow plug/ STS lamp. It is suggesting something on the MAP sensor wiring is shorted somewhere.

The STS lamp may be removed or burned out.

Unplug the MAP sensor, reset the ECM via battery pull for 30 seconds and see if the code is gone. Trace the wires. Inspect under the intake manifold for wire problems like rubbing through on things, burn up, etc. If the code is intermittent moving the wire may temp solve the problem until it shorts again.

If the code 36 continues and only after the MAP short is fixed:
Check for air in the system including a INOP lift pump as suggested already. Again Testing For AIR IN FUEL is step Number One in the GM flowChart.

Replace the PMD extension cable with a Made in USA one. And then the PMD.

Last replace the DS4 with a DB2 and get rid of the unreliable PMD screw up GM let out the door. :p

If electronics are not your thing I suggest looking for an auto electric shop and pay them to hunt down the short/wiring problem. Trons can be a real time consuming PIA even for those who "get it". Just saying this is one of the few frustrating things that it can be worth renting experience to get fixed and out of your hair.

@IdDieselGuy I rarely grammar police anyone, but, if you lean on the enter key it would be a helluva lot easier to read than one chunk of text. Mixing up your blown head gasket cracked head etc. gas rig in with the diesel rig and wondering about timing causing it is confusing to read in one paragraph. Bad news is bubbles in the coolant are expensive tear the heads off combustion leaks unless it's burping air or boiling over. There is a little known water pump failure for 1995 or so years where the flow is/becomes so unbalanced the passenger side boils over on 350's (5.7L gas engines) while the driver side with the temp probe says everything is fine. This gas engine water pump failure/defect/(whatever I forget) is above and beyond the known 6.5 Diesel balance flow problems.
 
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I did do the lift pump test and it is fine. STS lamp does work and is not burnt out. I checked that. PMD extension cable is USA made. I'll try what you said. Wish there was an easier way to do this stuff. Mice had chewed thru the wires to the wastegate solenoid so I fixed the wires. It has power to it i do know that. If I unplug it I dont hear a turbo whistle but if i plug it in I hear one.
 
I'm also getting a burning metal smell from the front of the truck after driving it. Cant tell exactly where it's coming from but it's only been doing it the past few weeks. Thought maybe it was the front brakes but I just changed those last weekend and I'm still getting the smell.
 
Mice... Squirrels... Last one we had was an $800 vandalism insurance claim because the engine shut down. Electronic throttle gas and the throttle stuck open from air filter debris going through it. So the ECM shut the engine down. Tow bill and wiring damage that took 3 trips to find and fix it all. Who checks that the little pisser chewed the washer pump wires off till later anyway?

Looks like you are going through the harness looking for more insulation the mouse chewed off. Code 62 Boost is really a MAP, the square sensor on the top manifold... The MAP wiring is a good place to start. Of course the 5 Volt is used for several sensors so short one and loose several. Thus my ECM gets pissed off comment. You are going to have to check the entire engine harness because a 5V short isn't for sure on the MAP. The MAP is but one light in the Christmas tree strand.

Should be a slam dunk: 1) disconnect MAP and 2) probe harness connector pins to see if there is 5V reference to engine ground on one of the pins.

Do you have an IR temp gun? You can spot check temps of the front diff (if 4x4) brakes, hub bearings, belt drive stuff including "did the vac pump lock up, again?" Did anything get chewed and fall on the manifold?

Sometimes things that go "thump" on the road can hang up on the crossover. Blown tire tread parts and grocery bags for example. Aluminum foil on the manifold just means someone been cooking and may have forgotten their lunch. 🤪
 
I've inspected everything and havent noticed anything on the manifold or crossover. My only other guess would be clutch or flywheel. It sometimes grinds in 1st and second gear with my foot off the throttle and just barely going. Other than that its fine. Pretty sure my U joints are bad though. I can move my driveline back and forth more than a person should be able to.
 
Well I think I figured out part of or most of the issue. The plastic connector part around one of the prongs on the pigtail for the boost sensor is broken. Fixed it and pushed it back up and now it's fine no check engine light...for now. Still burning metal smell though after shutting the truck off.
 
So the check engine light still comes on but only intermittently and only in the morning when it's cold outside or the truck hasn't been driven for several hours. When the truck is up to operating temp it's perfectly fine and I get no check engine light at all. I drove it all over this weekend and it did great. No issues whatsoever. Gonna fix the ground on the intake and the pigtail for the boost sensor and go from there. Still getting the same codes. When I went to warm it up this morning it started up and SES came on and went off like usual after I started driving but the glowplug light flashed for a brief second as well and I am still getting the code 29 for glowplug relay fault so I'm guessing that's why or cause it's cold out maybe?
 
What did you do for the codes to be gone? (Nothing means intermittent and clues to problem still.) You didn't say so I am guessing...

Code 31 Check the firewall, driver's side, for one of those rectangle MAP sensor looking devices. That's the baro sensor OR it doubles up and uses the MAP as a baro sensor. I forget, but, recall the diesels may have used a separate firewall mounted MAP as a baro sensor.

DTC 31 - EGR Control Pressure/Baro Sensor Circuit Low (High Vacuum)

Your initial post said WG solenoid for 31 and that's confusing me. Does the truck have an EGR valve on top of the intake?

So you still have an electrical problem. If you just have the MAP and not a separate Baro sensor I suggest replacing the damaged connector. They sell new connectors with pigtail wires coming out of them... If you have a Baro sensor on the firewall check it's wires for mouse nibbles and connector condition...

Not sure the damage to the connector, but, any reason the sensor side conector itself is damage free? It needs a close look.
 
I didnt clear the codes they just went away I guess. I wiggled the connector on the MAP sensor and I think it helped. I will check the baro sensor as well. No mouse nibbles as far as I am aware of. I am going to replace the pigtail for the MAP sensor. This truck doesnt have an EGR but my 95 6.5 does.
 
Replaced the fuel filter. Old one was literally black. Probably stock honestly, would not be at all surprised. Ran and drove great for about 30 minutes then it went back to its usual bs of the SES light coming on and going off intermittently. I'm getting alot more white smoke at startup too and SES light is coming and and off intermittently more than before.
 
Also when replacing the fuel filter, I noticed there was no fuel strainer inside the fuel filter manager. I figured that was probably an issue. Looked inside the filter too and didnt see one. Could that be causing the codes or the white smoke?
 
Just curious, did the clear hose on the return side of IP show any air ? It will appear as sort of a white foam if there is. It should look like clear liquid.
 
No, the screen wont cause any issues noticeable changes. That is a secondary safety catch for debris. Many hot rodders or heavy towing guys remove it completely after ensuring their tank is perfect on the inside and adding a spin on fuel filter.

Any bubbles in that clear return line? This is SO HUGE and should have been first thing done. Most of us simply never remove the clear line, just replace it with another clear line in 3 years or so depending on how it weathers in your area because it is like $3 and 3 minutes to change- and is SO important to start there.

The next thing after that I push is a fuel pressure gauge you can read while driving tapped at the ip inlet.

But in your case- I agree with WarWagon that is sounds like your rodent issue got ahold of something else in there.
 
I dont have the clear return line. I bled the fuel, replaced two of the battery terminal screws, replaced the baro sensor, cleaned the MAP/Boost sensor, and noticed one of my glowplug wires wasnt fully on my glowplug so I put it on all the way and then hooked the batteries back up and no more codes. All im getting now is the normal code 12. The truck has been blowing quite a bit of black smoke lately though which is a little concerning.
 
Go to any hardware store around you.
1/4” diameter clear tubing sold by the foot. DO NOT ask for fuel line - it is not fuel line. You need a 6” piece. So you will have the replacement for in a few years if you store it out of the weather.
Get 2 screw style hose clamps to fit over the tubing.
Seriously if it costs $10 and takes more than 5 minutes to replace you have set a record.

When mentioned above that it is the first step in the GM manual, that was not an exaggeration, It is literally the first thing you are supposed to do.
 
I got this cheap Hurst fuel pressure gauge from off the innernet, made a simple bracket and hosed clamped the bracket to the gauge and mounted it under the dash. Got the fuel pressure bleeder screw kit from Leroy Diesel and now at a glance can verify that I have good fuel pressure.
A fuel pressure gauge should be the number two item on the list of necessities when owning a diesel anything.
But for now get the clear plastic hose installed and verify that there is or is not air getting into the fuel system, then We will go from there on to the rest of the black smoke diagnostics, which by the way may or may not trip a code. These engines do not have an O2 sensor like the gassers so not much info in the ECM codes about emissions.
 
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