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Scag turf tiger surge kawa 29hp dfi

Discussion in 'Mechanic and Repair' started by jdslucky, Jan 21, 2014.

  1. jdslucky

    jdslucky LawnSite Member
    Posts: 8

    Hello everyone. First time posting here, long time reader. I have been able to fix many machines off these threads and im hoping someone can help me with my issue.

    07 Scag Turf Tiger 1000hr
    FD791D Kaw 29hp DFI
    all maint, fluids, tune up done once a year no matter what

    My customer brought this machine to me after his regular mechanic was stumped. I do not work on mowers for a living. I do however run an automotive repair shop and very versed in fuel injection vehicles, that is why he brought it to me. I'm working on this thing at home and helping a friend.

    Issue: surges warm off idle up to wide open with no load. intermittent surge at idle when warm. runs great cold and any time deck is on up to wide open
    when surging governor is moving catching idle/changing rpm

    Before it was brought to me:
    new plugs
    air filter
    fuel filter
    fuel pump
    oil change
    fresh full tank of fuel

    Things I have done in this order:
    sprayed intake,throttle body with parts cleaner cold/warm for vacuum leaks
    volt olm check sensors using repair manual specs, IAT, coolant temp, map, ohm injectors
    removed throttle body/intake and cleaned
    check and adjusted governor when intake was off.
    adjusted "idle screw" at throttle body

    last night i put mower back together completely to test if cleaning intake/throttle body helped. Idled great surged off idle to wot. ran great with deck on.

    everything has checked out good and no change to anything that has been replaced or cleaned.

    my thought process points me to checking fuel pressure while surging to see if it fluctuates, and vent fuel cap when surging to see if gas tank is under vacuum.

    My customer is wanting to replace the fuel injection control module as a guess but nothing im finding is suggesting that to be the problem.

    also in the manual one section mentions an engine speed sensor. I cant find any parts diagrams or writing on such part....

    any help would be appreciated Thanks JD
  2. MRCo.

    MRCo. LawnSite Member
    Posts: 227

    Job one- make sure the plugs are exactly the right ones listed by the OEM. Not "it looks the same" or ones that for his other mowers. DFI / EFI need the right plug- kohler uses special radio frequency insult ted one, for example.
  3. jdslucky

    jdslucky LawnSite Member
    Posts: 8

    Will do, thank you for heads up
  4. MRCo.

    MRCo. LawnSite Member
    Posts: 227

    Well, to clarify, I know it seems fuel related, but two update schools I've been to stress it- if the customer changes plugs, make sure they are the right one. I had a trimmer presented surging, not revving to wot, high idea and dying. Seemed like textbook carb issues. Rebuilt it, same. Turned out it was the plug. Right plug, ran like a dream.
  5. ricky86

    ricky86 LawnSite Bronze Member
    Posts: 1,841

    Ck gov adjustment first. Engine must be fully assembled for that procedure. Then alter the gov sensitivity, ( try relieving tension) then set high idle. If there is NO change at all, I would look at the TPS and associated circuit. Control module would be the last part to replace. That's why he isn't working on it. It's fuel injected, so of course when you have a problem, it has to be the computer. Nothing is further from the truth.
  6. jdslucky

    jdslucky LawnSite Member
    Posts: 8

    The spark plugs are oem ngk R. I will mess with the governor again tomorrow and reset using info in the manual. This engine does not have a TPS. Thanks again guys
    Posted via Mobile Device
  7. pugs

    pugs LawnSite Gold Member
    Posts: 3,022

    First thing I would do is get a Tach on it and run it where it is surging. Grab the linkage with your hand and hold it at a steady RPM where it normally surges. If the surging stops and it runs fine, the problem is in the governor. If the engine dies or wont run steady while holding the throttle you have a fuel problem.

    Also I would check to see if you have any Fault Codes. There are only a few possible but if there are any...fixing those first would probably be a good idea.

    As for engine speed sensor...I believe that engine grabs a signal off one or both of the ignition coils to calculate engine speed.

    Kawasaki fuel injection shares very little with automotive fuel injection(at least modern automotive). Now Kohler on the other hand is a lot more automotive.

    I honestly know very little on the Kawasaki DFI. We are not a Scag dealer and they are probably the biggest user of that FD791D. It gets talked about a fair amount at update meetings...but hopefully a solid Scag guy can chime in and maybe help you a bit more.
  8. jdslucky

    jdslucky LawnSite Member
    Posts: 8

    yes pugs, the fuel injection is very primitive on these engines. That being said it actually makes it a little easier in that department. What is tossing me for a loop is the governor w/ efi. I can say that if you hold the throttle manually at the throttle body it runs good and steady in the rpm range that it surges. I will definitely wage a small war with said governor!
  9. pugs

    pugs LawnSite Gold Member
    Posts: 3,022

    If you can hold it and it runs steady then I think all the fuel system is going to be fine. Again I am no expert on the Kawasaki DFI but on all small engines with carbs thats how you figure out if you have a fuel problem or a governor problem so...

    Try redoing the initial governor setting before anything else. Other than that I really dont know what could be causing issues with the governor. I am not familiar with these enough to know if there is a governed idle spring or not as some engines have for low speed/no load conditions.
  10. BigFish

    BigFish LawnSite Gold Member
    Posts: 3,253

    I've not worked on any Kaw. dfi units, but, as mentioned, it sure sounds like a gov. issue. The part about running OK with the blades on ( loaded) is one symptom.
    Is the gov link spring in place? Its the small coil spring around the link rod and hooked into throt. and gov levers. It helps take up any slop in the linkage. Are you working with the Kaw. shop manual? If so, it has a pretty detailed gov section.

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