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Thread: 6.5 Diesel Stutter and Defueling

  1. #21
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    Quote Originally Posted by DmaxMaverick View Post
    The vibration is normal. ECM boost control is not on/off, but is modulated and will allow wastegate opening at a gradual rate. 17" is a little high, but within the margin of error. 15" is ideal at sea level at any "full closed" RPM, with 11" the minimum. Less than ideal variations could be a matter of a well seasoned solenoid, or aftermarket programming adjustments. If you have an aftermarket power program, it wouldn't be unusual to have increased wastegate actuator vacuum, as a means to compensate for increased exhaust back pressure against the wastegate.

    Ok, I will hook the trailer up tonight and take it for a spin after I get my boost bolt in so I can monitor boost again. I relocated my AIT back to stock as mentioned. As far as the boost solenoid goes, to my knowledge it is the original from new. I do not have a chip or anything to increase power. Just a PMD relocate, straight pipe exhaust and a not so cold air intake.

  2. #22
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    Well, I installed my boost bolt last night and did a check with the new boost solenoid to see how it compared to the one on the truck. Both resulted in a vacuum reading at the actuator of about 19" Hg. So I left the stock one in place and took it for a drive with my 850 lb 4 wheeler in the box and a 3400 lb trailer on the back. It would still build boost as I was accelerating until it hit about 10 psi then would drop down to about 8 psi, which it appeared to hold. It appears to be working, but with the load I hooked up I did not get the engine temp up to about 200-210 like when I am pulling hard, so I will have to wait till next weekend when I take the camper on a trip to see if it actually works when under heavy towing.

  3. #23
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    So I took the truck on a trip this weekend pulling the camper. I still get either a defueling symptom or an inability to control boost. It seems to happen when I drop below 60mph but as soon as I get to about 50mph it straightens out again (when in 5th gear). When it acts up I tried downshifting into 4th and that would not cure the problem it would continue to defuel/surge the boost.

    I did have something else happen as well. I pulled the camper for 2.5 hours and then parked the truck for the weekend. When I went to start the truck after 3 days to hook the camper up, the truck would crank and crank but not start. It would not even try to start. No smoke out the tailpipe or anything. I was getting fuel to the fuel filter, but it seemed like nothing was going to the engine. I then went and unplugged my relocated PMD and plugged in the old one on the side of the pump, but nothing. Then I plugged in my relocated PMD and it started. Then about 10 miles down the road I had a huge miss in the motor, so I am putting money on my PMD is about to fail.

    My last question is could a failing PMD cause my other symptoms of the defueling/boost surging? I would think that it is a definite possibility.

  4. #24
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    The PMD is always on the hit list.

    The PMD is the big weak link in the injection system on these engines.

    What brand of PMD are you using ???
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  5. #25
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    And how good is your extension wire for your remote PMD?
    Maybe clean connector pugs with electrical contact cleaner and spray a little di electric grease in them.
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  6. #26
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    Quote Originally Posted by Robyn View Post
    The PMD is always on the hit list.

    The PMD is the big weak link in the injection system on these engines.

    What brand of PMD are you using ???
    I have the relocate kit from Heath Diesel. I cannot remember what brand PMD it came with as it was like 6+ years ago I did the install. I have a new one on the way from Leroy Diesel along with the #9 resistor.

  7. #27
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    Quote Originally Posted by 6.5_Diesel View Post
    I have the relocate kit from Heath Diesel. I cannot remember what brand PMD it came with as it was like 6+ years ago I did the install. I have a new one on the way from Leroy Diesel along with the #9 resistor.
    Well I took the truck on another trip with the camper and it happened again.....a no start. I found out the no start is from my harness going to the relocated PMD. To make it back home I go lucky that the pig tail off of the pump was just long enough to reach the PMD by setting it on the intake. The original PMD is a Dtech with a No. 7 resistor. I have ordered a new cable and will be mounting my new PMD with a No. 9 resistor onto the heatsink. I will be keeping the Dtech that was on the truck for a spare.

    On the trip down camping, I still had the defueling/boost surge issue when I got between 60 and 55 mph (in 5th gear), so when I was at the camp ground I threw in the new boost solenoid I had to see if on the way home it would still do it. It still does the defueling/surging when I hit just the right speed ranges in both 4th and 5th gear. I have a new boost sensor that I am going to try, but after that I am out of ideas on what it could be.

    Also, I noticed an oil leak coming down the passenger rear side of the bell housing. When I look up top, I can also see some oil in the valley under the intake. Any ideas on what could be leaking? Could it be the oil pressure sending unit?

  8. #28
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    I seem to recall issues with surging when I was experimenting with a #9 resistor, about 18 years ago... IIRC, mine was calibrated for #4.
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  9. #29
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    Quote Originally Posted by JohnC View Post
    I seem to recall issues with surging when I was experimenting with a #9 resistor, about 18 years ago... IIRC, mine was calibrated for #4.
    I was wondering if the resistor change could mess up the air to fuel algorithms and how the ECM responds causing the issue. I have read that the computer can be very picky when it comes to maintaining proper air to fuel. What is the stock resistor for a 3/4 ton F VIN engine? Is it still a #4? I remember reading somewhere what it was but I cannot remember.

  10. #30
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    The resistor is to calibrate the individual injection pump to the software. (Don't know how to better explain it). So, the resistor goes with a particular pump, not a vehicle. IIRC, 5 is the target setting, so if you're not sure what you should have, 5 is a good guess.
    The Constitution needs to be re-read, not re-written!

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  11. #31
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    Quote Originally Posted by 6.5_Diesel View Post
    I was wondering if the resistor change could mess up the air to fuel algorithms and how the ECM responds causing the issue. I have read that the computer can be very picky when it comes to maintaining proper air to fuel. What is the stock resistor for a 3/4 ton F VIN engine? Is it still a #4? I remember reading somewhere what it was but I cannot remember.
    There is no such thing as a "fuel to air ratio" when talking about a diesel. A diesel should always have an excess of air, with fuel-rate determining engine speed/power/emissions. A turbocharger just allows more fuel to be injected, to make more power.

    Most fuel injection pumps use a #5 resistor. The resistor is used to calibrate the fuel-rate of the injection pump. Due to mechanical tolerances, some pumps need a little more help than others, which explains the need for a calibrating resistor. Can't go wrong with a #5.

  12. #32
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    Quote Originally Posted by More Power View Post
    There is no such thing as a "fuel to air ratio" when talking about a diesel. A diesel should always have an excess of air, with fuel-rate determining engine speed/power/emissions. A turbocharger just allows more fuel to be injected, to make more power.

    Most fuel injection pumps use a #5 resistor. The resistor is used to calibrate the fuel-rate of the injection pump. Due to mechanical tolerances, some pumps need a little more help than others, which explains the need for a calibrating resistor. Can't go wrong with a #5.
    Interesting. I was always under the assumption that during the combustion process you look at your stoichiometric ratio of air to fuel and you always wanted to stay slightly above that ratio in order to ensure completeness of combustion. If you dive below this point you will not consume all of the fuel resulting in an inefficiency or incomplete burn. I was under the assumption that all vehicles even diesels had to monitor this and used air (boost) and fuel curves in order to ensure the engine didn't enter a fuel rich or fuel deficient stage.

    Learning something new every day.

  13. #33
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    Quote Originally Posted by 6.5_Diesel View Post
    Interesting. I was always under the assumption that during the combustion process you look at your stoichiometric ratio of air to fuel and you always wanted to stay slightly above that ratio in order to ensure completeness of combustion. If you dive below this point you will not consume all of the fuel resulting in an inefficiency or incomplete burn. I was under the assumption that all vehicles even diesels had to monitor this and used air (boost) and fuel curves in order to ensure the engine didn't enter a fuel rich or fuel deficient stage.

    Learning something new every day.
    This is essentially true for all internal combustion engines. However, only recently (2001 M/Y for GM/Duramax) is air by volume measured and fuel adjusted accordingly to more efficiently combust Diesel fuel. Unlike gasoline and other volatile fuel engines, a Diesel engine simply cannot have "too much" O2 (it simply passes on what it doesn't use). Too little air/O2 for the (attempted) combustion of fuel results in black smoke (old school).

    In regards to the resistor, it's a nothingburger. Minimum to maximum extremes won't yield any appreciable "power" or efficiency. Perhaps something that can be realized with a laboratory dyno, but even then, gains/losses will still be within the margin of error. You'll never feel any real-world difference on the butt-dyno or MPG's. Use a resistor that doesn't cause the PCM to complain, and life is good. Problem is, IP's are rarely calibrated such as they were before original delivery on a new vehicle. Once a pump is rebuilt, the original calibration spec goes out the window, and we're then shooting from the hip. Very few distributors (if any, anymore) include the correct/calibrated resistor with a new or reman IP. If you're using a #9 and it works, stick with it. Same goes for a #4.
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  14. #34
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    Quote Originally Posted by 6.5_Diesel View Post

    On the trip down camping, I still had the defueling/boost surge issue when I got between 60 and 55 mph (in 5th gear), so when I was at the camp ground I threw in the new boost solenoid I had to see if on the way home it would still do it. It still does the defueling/surging when I hit just the right speed ranges in both 4th and 5th gear. I have a new boost sensor that I am going to try, but after that I am out of ideas on what it could be.
    I'll mention again what I did to my '95: I removed the vacuum pump and associated plumbing, installed a Turbo Master wastegate control, and Kennedy Diesel's chip in my ECM. I've never had a defueling problem since, and I can drive by the EGT gauge now. These upgrades made a tremendous difference in the towing capability of my rig.

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  15. #35
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    Putting a #9 resistor on a pump that should have (say) a #4 tells the PCM that the pump delivers less fuel for a given command than it really does, so, when the PCM commands a specific rate the pump actually delivers slightly more. This is the basis of the "hot rodding" idea, but, as Dmax said, it's barely a measurable amount. What it does do, however, is make the PCM's commanded fuel rate transitions more dramatic than they should be, hence (I believe) the surging issues.

    It is my recollection (could be wrong) that the resistor isn't actually part of any control circuitry. Rather, the PCM reads the value of the resistor to determine which fuel map it should use for a given pump. That value is stored in the PCM's memory and stays there until you perform a TDC offset learn, even if you change the resistor or pump. The proof is, you can remove the resistor, without any effect on performance, and a month later the PCM will still report the same resistor value.
    The Constitution needs to be re-read, not re-written!

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  16. #36
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    Quote Originally Posted by JohnC View Post
    Putting a #9 resistor on a pump that should have (say) a #4 tells the PCM that the pump delivers less fuel for a given command than it really does, so, when the PCM commands a specific rate the pump actually delivers slightly more. This is the basis of the "hot rodding" idea, but, as Dmax said, it's barely a measurable amount. What it does do, however, is make the PCM's commanded fuel rate transitions more dramatic than they should be, hence (I believe) the surging issues.

    It is my recollection (could be wrong) that the resistor isn't actually part of any control circuitry. Rather, the PCM reads the value of the resistor to determine which fuel map it should use for a given pump. That value is stored in the PCM's memory and stays there until you perform a TDC offset learn, even if you change the resistor or pump. The proof is, you can remove the resistor, without any effect on performance, and a month later the PCM will still report the same resistor value.
    The resistor value remains in memory and isn't checked again until an IP diagnostic condition exists, or a specific number of starting/warming cycles. If you drive your truck once a day, week, or infrequent, it may be months/years before the resistor value is updated. In this case, it doesn't matter which resistor you have installed. It will map fueling according to the last value read until it reads it again (and will set a DTC at that time if something is amiss).
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