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backfires in exhaust

Discussion in 'Mitsubishi Minicab' started by ccway, Jun 24, 2017.

  1. ccway

    ccway New Member

    2003 U62T with 3G83 EFI engine. Starts up ok but the higher the rpm the more it backfires in the exhaust. The injectors or firing and the coil packs or firing the plugs. All three cylinders had about 190 psi on compression test.
     
  2. Nathan Marshall

    Nathan Marshall New Member

    Have you got this figured out? I have a 95 3g83 that is doing a similar thing. Mine has now failed to start and no matter what ive tried i cant make it run
     
  3. ccway

    ccway New Member

    I don't remember where we were in repairing it at that point and ours is a fuel injected motor. We had bought it not running and it had a bad computer, a fuel pump at only 4 psi (it should have been over 40psi) and exhaust about stopped up. But your's should have a distributor and carburetor. Make sure you are getting fire to your plugs and are getting 3 to 5 psi fuel pressure to Carburetor and is your choke working.
     
  4. Nathan Marshall

    Nathan Marshall New Member

    Thanks for the response. I know yours is injected, just thought this issue may have been in another system that crosses over between them. I have spark at all plugs and they are wet whenever i pull them so im getting fuel. Ive pulled the lines from the carb and drained it and attempted to start from starter fluid, thinking it was over fuelling. It came closer to starting but still no dice. Ive verified cam timing (i think, although maybe off by less than 1/2 tooth), compression is at 200psi +/-. The choke flap is closed at rest and opens about halfway when thottle is floored. I dont know how to test the choke but since it wont start with closed choke and starting fluid, i assume this is not the problem. Ive been having running problems with this truck for 3 years now, seems related to weather/humidity. When its wet and cold, it intermittently misfires badly. Ive replaced coil wire, plug wires, dizzy cap and rotor thinking it was something getting wet. Each time i replaced a component, hours would have gone by and the truck would start and run again for days or weeks but would eventually act up again. Yesterday it died while i was in the store and would not restart. Did get it going with a boost to help with the extended crank times but would only run at light throttle and would immediatly rapidly back fire if i went past half throttle. Was able to get home but today i cannot get it to start at all. Alot of back fires from carb and some from exhaust as well. Sorry for the long wind but i really need this truck going and really appreciate any help i can get
     
  5. ccway

    ccway New Member

    Have you checked the coil? Before you wipe or clean on the coil unplug the coil wire and look for trace lines on the coil where it may be jumping fire. Are your wires going to the coil (not coil wire) in good shape and not grounding out when it is wet outside?
     
  6. Nathan Marshall

    Nathan Marshall New Member

    Well i got it running. Apparently a different issue than the wet weather issue tho. All my intake valves were tight. Strange that this would just happen with no obvious signs of compression loss or running poorly beforehand. Set to spec and fired right up. Just went for a short run and, I'll have to time the dizzy again but no backfires and running just about right. I have checked and sealed the coil previously. There was what might have been a crack but probably just a line in the casing. I sealed it anyway. Thank you so much for your help. Shes running but ill have to wait for the weather to change b4 i figure this other issue
     
  7. fmartin_gila

    fmartin_gila Active Member

    Many years ago I owned a 1964 Datsun pickup. It developed a no-run/very poor run condition depending on the amount of morning dew. I would just spray the dist cap with WD40 and it would run. I could not see a crack or spark trace but when I replaced the dist cap the problem disappeared.

    Fred
     
  8. Nathan Marshall

    Nathan Marshall New Member

    Ok so valves needed adjustment and that enabled it to start good and run good cold. Didnt fix the issue tho. Once the idle started to come down, the missing and backfires started and the warmer it got the worse it got. I found corrosion at the dist. connector, repaired and was slightly better. Replaced the cap and rotor with a really worn but OEM cap and rotor. Slightly better again.Really seemed like timing. I could advance the dist all the way and it would idle but still coughing. Pulled the advance hose off and put direct vacuum (had the wife sucking ) on it. Voila perfect. Off idle throttle response is there and it seems perfect, while hot at least. Thing is, it seems this truck runs a ported vacuum advance. Like no vacuum at idle only gets vacuum at slight throttle. It has run like this all its life. WHY DOES IT NEED MANIFOLD VACUUM NOW? Maybe im wrong though and there is supposed to be manifold vacuum on the plate between the carb and manifold. I have also noticed the aftermarket cap that i previously had was timed differently than the original mits cap. Not a whole lot but probably 5 degrees or more. I realize the rotor may be timed slightly different as well and i may have mixed and matched thru this ordeal. Just a heads up for anyone with aftermarket caps tho. Im too tuckered to put it back together and road test but im 90% confident that it is working great.
     

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