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93 sambar 2wd sc missing under load? im at a loss

Discussion in 'Subaru Sambar' started by Reese Chambers, Dec 10, 2020.

  1. Reese Chambers

    Reese Chambers New Member

    i was driving from a friends house in the early fall and it did a big backfire. I pulled over to give it a quick look over because i had nothing else to do and it didn't start (bad battery). after i jumped it off anytime i got hard on the gas it would stall but in an odd way (see later for description). I replaced the battery and also replaced the spark plugs, cleaned the wires (then replaced them), cleaned the engine with sea foam, and adjusted the timing. it got a lot better idle and runs great other than the stall.

    Now it idles ok but every 20 seconds or so does just a little tiny stumble (nothing that alone worries me.) I can drive it under half throttle almost entirely without issue, but if I mash the accelerator it stalls almost like when you throttle a two stroke before its warm. it just makes a whine sound from the sc and it gets deeper in pitch as it slows down. im not sure where to look next.
    also if im going down hill instead of stalling it does a huge flame producing backfire.

    what should the coil resistance be at?
    and yes the exhaust heat sensor im pretty sure is bad but i am running either too rich or its dumping fuel thinking its too lean. how would i find out which?
    Thanks guys i can post a video if needed but i dont like doing it in case its messing up something.
     
  2. Ratbago

    Ratbago New Member

    I am having a very similar issue however mine has the ECVT , i can drive it normally but as soon as the supercharge light / boost comes on the car splutters and starts to die . Let me know if you ever find out the issue
     
  3. banzairx7

    banzairx7 Active Member

    That is lack of fuel. You need to replace your fuel filter or fuel pump. The backfire was the truck going lean.
     
    Reese Chambers likes this.
  4. Reese Chambers

    Reese Chambers New Member

    i replaced the fuel pump less than a year ago and the filter about a month ago. Im all for replacing the fuel pump if that will fix it but ill test it first. should i just check for fuel pressure or is there something else?

    also i forgot the psi my memory is telling me 3-4 or something like that but i cant recall.

    I had to redo a lot of the wiring going to the pump when I installed the pump last so step one is making sure all of that is in good shape I think its ok but if that is the issue it will save me a bit of cash so ill just redo it again.
     
    Last edited: Dec 11, 2020
  5. banzairx7

    banzairx7 Active Member

    Fuel pressure will be around 40psi at idle, 45 or so at 0psi boost and should go up with boost pressure 1:1 above that.
     
  6. Reese Chambers

    Reese Chambers New Member

    that is exactly what i needed to know. I have a pump i know that is good in that range so I can just switch it out to diagnose!
     
  7. Reese Chambers

    Reese Chambers New Member

    do you think it could also be a fuel pressure regulator?
     
  8. banzairx7

    banzairx7 Active Member

    When regulators fail you'll get fuel coming out of the vacuum port. Pretty easy to just pull the vacuum line off of it and se if fuel comes dumping out.

    Which also makes me think this could be a MAP sensor problem. If the map sensor vacuum line was say broken it would read 0psi all the time and would probably run reasonable. That would be until you went into boost. Then it would start going really lean since the ECU wouldnt know to add fuel for the extra air volume. Moral is you should probably check the vacuum lines going to the MAP sensor. MAP sensor is located underside of the floor right behind the alternator.
     
  9. Reese Chambers

    Reese Chambers New Member

    its not the van but i believe the map is near the gate to get to the engine near the coil , but ill find it.
    how would one go about testing this, just check for change in voltage or resistance ?
     
    Last edited: Dec 11, 2020
  10. banzairx7

    banzairx7 Active Member

    They are usually pretty bulletproof. I've never seen one fail. If the sensor was faulty you'd most likely be getting a CEL. The more likely scenario is a broken or popped off vacuum line.
     
  11. Reese Chambers

    Reese Chambers New Member

    I cleaned all the connections for the maf and map. It still doesn’t like boost but it idles a lot better and sounds like it’s no longer missing at idle so I fixed something. I’m going to grab some vacuum lines at work and change them out because they are all dry.

    hopefully there is a leak in the line I can’t see or something and this just works out.
     
  12. banzairx7

    banzairx7 Active Member

    Our trucks don't have a MAF sensor. Did you mean throttle body maybe?

    Another thought I had was a split coupling or loose hose clamp on any of the intake manifold piping. I'd still also be looking at the fuel pressure and make sure you do it under load. Maybe have someone ride in the back looking at the gauge.
     
  13. Reese Chambers

    Reese Chambers New Member

    It was the sensor that comes out of the manifold. I don’t know what it was I kinda just always assumed it was some sort of maf or air temp gauge. Now that I think about it I don’t know why I called it a maf it’s clearly something else
     
  14. Reese Chambers

    Reese Chambers New Member



    here is a video of it. The smoke started the same time as all of this, but it only happens when I rev it hard. (There are no intake resonators so the supercharger is normally that loud.)

    mall I’m doing is flooring it in this video and letting off before it stalls. All vacuum lines are replaced all that’s left is the fuel pump but it’s been raining so I have been waiting on getting under it.
     
  15. banzairx7

    banzairx7 Active Member

    If that's not oil smoke then it has to be that it's running rich. If it's rich than seems like that could be a boost leak.

    Also this truck looks pretty modded? exhaust and intake at least? The ECU on these trucks has no way to adjust for any modifications, it just does what it does. That could be causing you issues too.
     
  16. Reese Chambers

    Reese Chambers New Member

    Ok I’ll keep tinkering with it I might just take the manifolds off and clean everything. I probably should check the cat. But it’s been modified for a year and hasn’t had even the slightest hiccup until now.
     
  17. banzairx7

    banzairx7 Active Member

    I'd say cleaning is the secondary task since it's very unlikely to resolve your problem. Keep an eye out for loose hose clamps, split hoses etc while you're in there. That is a much more likely root of the problem.
     
  18. Reese Chambers

    Reese Chambers New Member

    It is. I feel like cleaning is just the best way to make sure I see everything.
     
  19. NotSteve

    NotSteve New Member

    You should post a thread about this truck sometime. Looks like you've got an interesting truck with some unique mods. I wouldn't mind learning more about it. That clear engine cover is really clever idea.
     

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