Page 1 of 4 1 2 3 4 LastLast
Results 1 to 10 of 31

Thread: New to me M936A2 engine idle / load issues

  1. #1
    Private
    Join Date
    Sep 2019
    Location
    Rogersville, MO
    Posts
    16
    Thanks
    0
    Thanked 1 Time in 1 Post

    Default New to me M936A2 engine idle / load issues

    I have a 1991 M936A2 that I recently acquired. I bought it knowing it had an issue running correctly. It will start only when given a little accelerator. It will only run from about 800 rpm up. From there it seems to run fine. Below that it stumbles and dies. If you let it idle down to about 800-1000 and then hit the accelerator it will stumble and die. It is usually then really hard to start after it dies this way. I have read many posts on this site that have helped me greatly to get things in better order but still have the same issue. Here is what I've done.


    • Drained fuel Driver Side tank - It was horrible, like varnish
    • Cleaned 1" of "tar" out of tank using E85 (this worked amazingly well) - Ended up with 7.5 gallons of what looks like road tar
    • Replaced fuel filters - they were horrible. The spin on was rusted and pitted inside and had varnish in it
    • Checked air filter it was ok
    • Still same issue
    • Replaced Injector Lift pump - old one was leaking when hand pumped
    • Replaced injector pump check valve
    • Still same issue
    • Ran fuel line directly from Lift pump into fuel tank bypassing all the old lines / switches and big filter
    • Still same issue


    One thing I have noticed is everything I have taken off or apart is just incredibly varnished up. Carb cleaner will clean it up but only with some work.

    I'm running out of things to try. Only thing I know to try now is injector pump adjustment and or fuel injectors. Those are beyond my knowledge. Does anyone have any ideas?
    Last edited by dcowan; 10-04-2019 at 09:43.

  2. #2
    Former SSG 98G's Avatar
    Join Date
    Aug 2013
    Location
    AZ/KS/MO/OK, varies by the day...
    Posts
    4,312
    Thanks
    6,606
    Thanked 3,554 Times in 1,645 Posts

    Default

    Run the fuel line into a jug of diesel. This will tell you if your problem is with the fuel tank.

    Edit - also check all your lines and fittings between the lift pump and the small filter on the block.

  3. #3
    Private
    Join Date
    Sep 2019
    Location
    Rogersville, MO
    Posts
    16
    Thanks
    0
    Thanked 1 Time in 1 Post

    Default

    I have completely eliminated everything to the injector pump including the lift pump and all hoses by temporarily taking a new line from the lift pump to the tank through the fill hole in the tank.
    Last edited by dcowan; 10-04-2019 at 11:52.

  4. #4
    Colonel Nomadic's Avatar
    Join Date
    Oct 2016
    Location
    Nevada
    Posts
    236
    Thanks
    139
    Thanked 52 Times in 43 Posts

    Default

    Can you bench test the fuel injectors?

  5. #5
    Private
    Join Date
    Sep 2019
    Location
    Rogersville, MO
    Posts
    16
    Thanks
    0
    Thanked 1 Time in 1 Post

    Default

    I don't have any way to do that. I could probably remove them and take them somewhere to test.

  6. #6
    I'm the dude, man! Steel Soldiers Vendor simp5782's Avatar
    Join Date
    Jun 2011
    Location
    Memphis, TN
    Posts
    7,568
    Thanks
    108
    Thanked 7,544 Times in 3,334 Posts

    Default

    Most places will not test injectors unless its after rebuild. They do not want to contaminate their equipment
    2008 F-250 6.4L Powerstroke
    1979 AM General M920
    1984 AM General M915A1 (Big Cam III, HT3B Turbo, Brushless 24v Alternator with equalizer, A/C, Rear 20,000lb winch. 11R24 rear tires and 395s up front.)
    1984 AM General XM923A4 ( Big Cam III NTC-400, HT4B turbo, Intercooled, #10 button, Dual fuel Line setup - MRAP Aluminum Radiator - 7" Ram Air Intake system - Dual 115 gallon tanks - Air Conditioning - 145amp alternator - Puradyn Oil Bypass system, CAT 7155 16speed transmission, riding on 16.00 AT-3s on HEMTT wheels. )
    M923A1
    M931A2
    M1083
    M1078
    M796 Bolster
    M322 Equipment Trailer
    MEP-804A


    901-318-8353 for Help in and or around the Memphis area or transporting in the southeast. Text me first before calling.

    Tires (HMMWV, 395s, 1600s) and Transportation Vendor

    Wes

    Videos at https://www.youtube.com/results?search_query=5782simp

    https://www.youtube.com/channel/UCTd...D4dOJidPFnmYGA

  7. #7
    Former SSG 98G's Avatar
    Join Date
    Aug 2013
    Location
    AZ/KS/MO/OK, varies by the day...
    Posts
    4,312
    Thanks
    6,606
    Thanked 3,554 Times in 1,645 Posts

    Default

    You took a good hard look at the threads where the fuel pressure sensor attaches at the top of the lift pump?

  8. #8
    Private
    Join Date
    Sep 2019
    Location
    Rogersville, MO
    Posts
    16
    Thanks
    0
    Thanked 1 Time in 1 Post

    Default

    Well that is an interesting question. This lift pump just had a bolt in the spot were the fuel sensor went. It apparently had it removed at some point.

  9. #9
    Former SSG 98G's Avatar
    Join Date
    Aug 2013
    Location
    AZ/KS/MO/OK, varies by the day...
    Posts
    4,312
    Thanks
    6,606
    Thanked 3,554 Times in 1,645 Posts

    Default

    Was the lift pump new?

  10. #10
    Private
    Join Date
    Sep 2019
    Location
    Rogersville, MO
    Posts
    16
    Thanks
    0
    Thanked 1 Time in 1 Post

    Default

    Yes the lift pump was brand new. I would hate to count how many times I've pushed the prime button on the lift pump during all of this.

Page 1 of 4 1 2 3 4 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •