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Thread: Where to start...

  1. #1
    Join Date
    Mar 2016
    Posts
    6

    Default Where to start...

    First off, I'm new to the forum. Thanks for having me! Ive got a 94 K2500 6.5TD 5 speed. Ive owned it for about a year. Ive rebuilt a few small block gas gm motors in my day, but this diesel thing is relatively new to me.

    For the most part, my pickup runs great. I average about 16 mpg with the somewhat aggressive all terrains that I have on it.

    I live in a rather small town, no one here knows jack about these pickups. Not even the GM dealership, they told me that they didn't want to even deal with it (i appreciated their honesty). No one here has a machine that can read stored codes from OBD1 without charging me $200 to read them. SO, I'm hoping you all may be able to help. I'm just going to list some symptoms that i notice, and see if you all can point me in the right direction.

    - Check engine light comes on while cruising on highway. This is the only time it comes one, and it goes away. If I mash it, it goes away. If i let off, it goes away. If i continue to hold the throttle, it will go away. Doesn't run any differently than with light off.

    - When starting, its got quite the cackle to it for about 2 - 3 seconds, a decent amount of white smoke for 3 - 7 seconds. then it runs fine.

    - After pickup has warmed up, and I take off down the road, it acts like it is misfiring. only when above 1800 RPM, regardless of gear, until Ive gone a couple of miles down the road. No check engine light comes on when this happens. Summer, winter, hot, cold, engine up to temp, engine just started. every single time i drive it when it sits for more than an hour i would say.

    - This same 'misfiring' also happens if i jump out and pass someone on the highway. once i shift back into overdrive, it starts to miss for 5 - 10 seconds, and then it is fine.

    - Last, but most definitely not least, i have a coolant leak somewhere. it goes thru very small amount of coolant, maybe a quart in 3 weeks. New water pump, T Stat and coolant flush all done within last 12 months. I have pressure tested it, and it drops 2-3 PSI in around 10 minutes. (I verified that the gauge is not leaking) I have yet to find any external leaks, but cannot yet be 100% sure that i have checked everywhere. Aside from startup, I have never seen white smoke from the tail pipe. I have tried, but never smelled antifreeze in exhaust.

    - This pickup doesn't over heat, heater core is not leaking, heater blows hot and doesn't smell of coolant.


    I'm concerned. None of these are good things. I knew these 6.5s were kind of a bastard children of the diesel world, Ive come to discover that the 94s in particular have a pretty bad rap. The truck is in great shape, it was taken very good care of. PMD was relocated. I still owe $2000 on it ( I bought this 3rd vehicle just to build credit for a home purchase, because I haven't had any debt in years) and I am afraid its a ticking time bomb that I still owe on. If anyone can point me in some sort of direction, it would be greatly appreciated!

  2. #2
    Join Date
    Feb 2007
    Location
    Baja California Sur Mexico
    Posts
    2,806

    Default

    I'll begin, locate the code plug under the dash left side of the steering column, open a paper clip and connect the two top right connections with it. Turn the ignition to on, don't start the engine, the SES light will flash each stored code 3 times. eg 1 flash, pause 2 flashes, longer pause, does it 3 times, means code 12, means no codes stored. You can look up the codes at actron.com. Code 78 is common boost problem code for 1994. To remove the codes, while the clip is in place, press together the brake and full throttle for 15 seconds. Turn off ignition and remove the paper clip. Is the misfiring more like jerking while overtaking, that usually means the OPS controlling the lift pump has failed and needs to be bypassed. The Rattle and white smoke on start up could be a failed glow plug, or a cracked head that is also causing coolant loss, you won't smell a small amount from the exhaust. Fill in your "signature" with the vehicle mileage. I check posts each day, and have had many of your problems now cured.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

  3. #3
    Join Date
    Mar 2016
    Posts
    6

    Default

    Thanks for the reply! Ill get my sig updated sometime today. The pickup has 209XXX miles. I have a few corrections to make to my numbers after doing some re-checking last night with better light.

    I'm actually only losing 1 pound of pressure in about 20 minutes. Loss is loss none the less. I went over everything last night with a fine tooth comb and haven't found anywhere that looks to be leaking.

    I would say that jerking could definitely describe what i am referring to as a misfire. Another correction, it starts at about 2300 rpm, not 1800.

    Ill check codes tonight with the paper clip method and check back with you all. Thanks again!

  4. #4
    Join Date
    Feb 2007
    Location
    Baja California Sur Mexico
    Posts
    2,806

    Default

    While the engine is running, listen under the vehicle below the drivers seat to find if the lift pump is running, it is inside the chassis rail, put your hand on it to feel if it is vibrating. If it is not working, remove the plastic cover on the passenger side of the fire wall, there is a fuse there, pull it out and then with ignition off, connect a wire between one of the live bolt threads near it, to the fuse holder, rt side I think. If the lift pump runs, the the OPS has failed, let me know if this is the case and you want to bypass it.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

  5. #5
    Join Date
    Mar 2016
    Posts
    6

    Default

    Well, i pulled codes and got 2 in relation to cruise control ( 71 and 76 if i remember correctly) as well as code 78. I ended up just ordering wastegate solenoid and am going to install with new lines this weekend. I vacuum tested solenoid and it is holding pressure fine.

    I couldn't hear lift pump running. I opened up water drain hose, no fuel and it died. Ive yet to confirm 12V at plug but I will tonight. I went ahead and just ordered lift pump, OPS, lift pump relay and #9 resistor from SSDiesel, because i would like to know that these are all good. I have not a clue when lift pump was last replaced.

    I imagine between lift pump, as well as associated parts, and the wastegate solenoid i should notice quite an improvement all around.

    THANK YOU for pointing me in a direction. I feel just from your help, Ive already gained a tremendous amount of understating of the 6.5. I will come back with updates once new parts are installed!!

  6. #6
    Join Date
    Feb 2007
    Location
    Baja California Sur Mexico
    Posts
    2,806

    Default

    You must have lots of spare cash. When code 78 comes up, there are often erroneous codes, and none of them are true. A lot of us modify the various systems to prevent further problems and cost. I will wait for the results.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

  7. #7
    Join Date
    Mar 2016
    Posts
    6

    Default

    I wouldn't say a lot... but I did have a couple bucks laying around. Pump/relay/OPS/#9 resistor was like $160 with shipping.

    I did replace wastegate solenoid and lines, i saw an instant improvement. I tested wastegate actuator with vacuum gauge and it wouldn't hold pressure, so i have another one of those coming too. I chose to keep it stock VS something like a turbo master.

    I ordered these parts probably prematurely because I want to know that they are good. I'm going to keep replay/pump that is currently in pickup as spares once replaced. I plan on making the 300k mark with this pickup if possible. I don't tow or haul a lot, mostly just DD.


    On a complete side note to all of this. There was a, what appeared to be new, PMD in my glovebox when i bought the pickup. Stanadyne. Looks new. SO i plugged it in yesterday, and my pickup wont fire?? The PMD that is on and works has no name on it. It is physically a little different that the Stanadyne. Thoughts? I am also not able to see a resistor in it. Does that mean it is calibrated inside of the PMD? Will the #9 resistor work with this? Again, it has no name on it, just a barcode and some numbers, i looked them up and nothing comes up for it.

  8. #8
    Join Date
    Feb 2007
    Location
    Baja California Sur Mexico
    Posts
    2,806

    Default

    The spare PMD is probably fried. I have not heard of a PMD without an external resistor, the resistor is to calibrate the injection quantity, no resistor will be equivalent to a a #1. Before replacing the OPS and lift pump, run the test from the fuse, to work out what has failed, no point in saving the failed parts. A replacement PMD that I took off my truck, has only a bar code and Made in USA on it, it has a resistor. I'm unable to see the brand on the ones installed on both vehicles, but hey have resistors.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

  9. #9
    Join Date
    Mar 2016
    Posts
    6

    Default

    Oh yeah, I'm definitely going to test parts, no point in having a broken spare!

    Maybe ill try my new #9 resistor in that PMD that doesn't have one, it looks brand new. I tried to get the resistor out of the PMD that is working, and i couldn't get it out. Is there a trick to it? Ive got to get it out in order to put the new resistor in, right? New WGA will be here today, I'm really looking forward to that being resolved.

    Thanks for being patient with my ignorance!

  10. #10
    Join Date
    Feb 2007
    Location
    Baja California Sur Mexico
    Posts
    2,806

    Default

    You are doing fine. Another job for a paper clip, make it look like tweezers, and bend the ends inwards, short hooks to get the resistor out.
    Grant H.
    1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
    1994 6.5 turbo GMC K2500 4x4 suburban "F" VIN #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, Positrac 3.73 diff, 17 mpg highway.
    1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, 21 years.

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