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Thread: backfiring going up hill or under load

  1. #1

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    backfiring going up hill or under load

    well im going to give this truck one more chance, but its about to go. now on top of all the other problems its started backfiring when i was going up a hill going down the highway, it started instantly, no warning. down shifting doesn't help it starts back firing at 2500 rpms. lower gears like first and second it doesn't do it and it can be wound to 4000 rpms without a problem.
    what the heck happened? i'm going to be doing a compression check, but im thinking the timing chain may be the culprit since when i set the timing 50 miles ago i had to do it by ear since timing mark was jumping around so badly it was impossible to time with a light.
    this truck only has 60k miles on it, is that about when the original timing chains go out on these?
    this truck has me worried with all these problems coming up at once, i've never been much a fan of Mitsubishi until i got this truck and saw how easy it was to work on and how well it seemed to run for the first three to four hundred miles

    the ignition system seems fairly new, the wires look good and i just replaced a defective cap and rotor that were in it and the old car didn't look very old.

    one thing that could possibly be causing problems but i don't see why it would only do it under load is when i found the defective cap i was stuck out camping and it wouldn't start. so i took the cap of to check and the graphite piece fell out and i had to stick a twenty two shell in the cap to replace it to make it home. when i relaced the cap there were a few brass shavings in the bottom of the distributor and i didn't clean them out since they didn't seem to be bothering anything. i doubt thats the problem, but i'm going to clean it out and see if that helps.

  2. #2



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    Mine did that, next thing I knew I was rebuilding it because fuel was blowing by my rings at an enormous rate. Friggin oil smelled like gas right after changing it not 15 minutes later after restarting. Compression was 150 145 145 150 too. Just couldn't get it to idle smooth and seemed more like a jumped timing belt, but after taking front off 3 times and replacing timing belts, distributor, oil, etc etc. it reared it's head with a vacuum gauge connected to intake. Should of been around 20-21 psi at idle and was much lower. Poor truck sounded sick but everything else said it was ok. wrong!

  3. #3

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    Well that ticks me off it has 15 psi vaccumme at idle, compression is 125psi across the bord.
    What I don't get is why is it this bad at 63k miles that ridiculous! I've had subarus and Toyotas that were abused to hell and back and still made 150k!
    I was really liking this truck, until now. This is the last Mitsubishi ill own if it really is needing a rebuild, I'll go back to Toyota.

  4. #4

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    Just checked oil has a few hundred miles on it and it doesn't smell like gas at all. The low vaccumme and low compression could both be caused by late valve timing though. Spark plugs looks like its been running with a Rich mixture for awhile (makes sense) doesn't look like an oil burner by the plugs (I used to have a Suzuki sameri that burned oil like a two stroke I know oil rich plugs well) does anyone know how to check the timing chain? I just can't see it needing to be rebuilt this soon

  5. #5



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    oh that vacuum just about convinces me. Check this info I posted below out, good info.
    Not all trucks are bad or treat your wallet bad like you got, Who owned it before you and cared for it is what matters. I owned a 74 Celica that had 32k miles on it when I bout it and I went through the problems with it that it never should of had. I then looked at the prior repair records and a woman in Tracy, CA owned it and just trashed it since the first mile put on it. She even was in an accident with it.

    CHART OF VACUUM READINGS
    Indication of Engine Condition

    Smooth and steady idle
    (800 to 1200 RPM) Between 17 to 21 inches Engine is in Good Condition, but perform next test to be sure.

    1) Open and close throttle quickly Jumps from 2 to about 25 inches Engine is in Good Condition.
    2) Smooth and steady idle Steady, but lower than normal reading Worn rings, but perform next test to be sure.
    3) Open and close throttle quickly Jumps from 0 to 22 inches Confirms worn rings.
    4) Steady idle Intermittent dropping back 3 or 5 divisions and returns to normal Sticky Valves.
    If injection of penetrating oil into intake manifold temporarily stops pointer from dropping back, it's certain the valves are sticking.
    5) Steady 3000 RPM Pointer fluctuates rapidly, faster engine speed causes more pointer swing, Weak valve springs.
    6) Steady idle Fast fluctuation between 14 to 19 points Worn intake valve stem guides. Excessive pointer vibration at all speeds indicates a leaky head gasket.
    7) Steady idle Constant drop Burnt valve or insufficient tappet clearance holding valve partly open or a spark plug occasionally miss firing.
    8) Steady idle Steady 8 to 14 inches Incorrect valve timing. It must also be remembered that vacuum leaks and/or poor compression can result in a low vacuum reading.
    9) Steady idle Steady 14 to 16 inches Incorrect ignition timing.
    10) Steady idle Drifting from 14 to 16 inches Plug gaps too close or points not synchronized..
    11) Steady idle Drifting 5 to 19 inches Compression leak between cylinders.
    12) Steady idle Steady below 5 inches Leaky manifold or carburetor gasket, or stuck manifold heat control valve.
    13) Steady idle Floats slowly between 12 and 16 inches Carburetor out of adjustment.
    14) Blipping engine speed Quick drop to zero then return to normal reading Muffler is clear.
    15) Blipping engine speed Slow drop of pointer then slow return to normal reading Muffler or Cat is choked or blocked.


    You might of jumped a tooth on the chain?!?!. The belts last about 60k then they need to be changed. My Celica had a chain and 80k was time for new sprockets and chain. If you need to check the timing I think the cover has inspection holes that really aren't worth a crap to look into, but front cover doesn't take long to take off and do a full inspection. Your mileage is at a time when timing parts need to be inspected. I hope you don't have more problems then it should have at that mileage amount. Could squirt a bit of oil into cylinders to test again, if it climbs up then I think rings are a good guess.
    Check cat for clogs also. Burning rich and all might leave crap in it and shrink the passages.

  6. #6

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    I was thinking the cat as well but, all in all there is no way even being abused (wich judging by the interior and the internals of the engine I have seen it hasn't been) that It should be worn out yet, that shows me that these aren't built to last. I'm driving a Subaru with 130k that's been abused badly, it sat for ten years in a field then was fired up and driven for three years with a oil pump that's bypassing the filter and with no Tstat plus ive been driving it for about a year and have put a good 5k miles on it and is still going strong. Any engine even abused should make 100k if its made to last

  7. #7

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    Okay, I really don't think it's in my rings since #1 the oil doesn't smell like gas #2 the plugs weren't oil fouled #3 at 60,000 miles I just can't see the rings going out unless its been badly abused.
    The trucks condition shows me that its been somewhat taken care of since the dash isn't cracked, the dash hasn't been hacked into for various reasons, and since I could eat of the top of this engine (literally the cleanest head I've seen, absolutely no sludge in it)

    ive been thinking about it and if for some reason the chain and sprockets have worn out and caused slop, it could result in late valve timing wich could cause low compression and low vaccume. It could also be a bad tensioner (I'm assuming hydrolic)

  8. #8

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    also i apologize for my responses, everything is deciding to break down at once and of course right before winter. im going to do an inspection of the timing belt, but i cant do to much right now because its the only truck that runs at all and i still have to get firewood in.

  9. #9

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    i meant timing chain

  10. #10



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    there is an adjustment of the timing chain guide you can make from the front of the cover. There is also a hydraulic tensioner that comes into play. The whole timing chain system is oiled with 1 tiny hole that squirts on the chain - it takes very little to resrtict oil flow and burn up the chain.
    Pennyman1
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  11. #11

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    Nice! That's what I was looking for thank you penny man, ill check out the timing chain and see if I can make an adjustment, then ill do a motor flush

  12. #12



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    rather than use motor flush, run a quart of Rislone in place of one quart of oil - its a super detergent that will clean out the sludge without causing major issues with worn bearings and rings
    Pennyman1
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  13. #13

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    i was thinking of draining a quart of oil out and adding a quart of atf

  14. #14

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    ATF is a BAD Idea. That will ruin any good engine. Why not use the Rislone or do as I always have use a high quality DIesel truck ol. ie Rotella, Delo 400, etc. Cheaper and it will clean any sludge with NO damage, or chance of engine damage as ATF DEFINITELY can (and I KNOW does in some cases)!/ Also if something is blocking the chain oil hose, you need to remove the restriction as its probably not sludge but a bit of gasket, sealer, or metal... Sounds like a timing issue to me. Take it to the dealer for testing on a computer and or see what codes its throwing. It could be something easy and simple. DOn't throw a GREAT vehicle away because you haven't explored all info. There is a guide in here somewhere that will tell you how to read the codes and what they are. Backfiring is a timing (or valve possibly) issue. Hav you set/checked your valve clearance yet?

  15. #15

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    umm ya your totaly wrong about atf damaging the engine, unless you drained all the oil out and ran straight atf then tried to haul a trailer. im an auto tech, so i do know what im talking about, one quart of atf with four quarts of oil will clean the sludge out and will not dmage anything.

    im going to pull the ttiming cover of though since i found the drivers side chain tensioner is loose and i think that be the whole problem

  16. #16

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    also i work in a shop with the snapon diagnostic computer than can pull up any codes but seeing as this truck has the weber conversion it will tell me nothing, besides its more likely a mechanincal problem and the computer cant detect mechanical problems

  17. #17

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    update, the timing chain went out so bad it broke of the bolt the holds the drivers side chain guide and the tensioner for the balance chain and skiped a tooth. i bought a new timing chain kit but i need the bolt to put it back together.

  18. #18

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    Weak valve springs will cause backfiring under engine load or going up hills.

  19. #19

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    Your problem is due to weak valve springs.

  20. #20



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    You need to read what he found - the timing chain guide bolt broke and caused the timing chain to jump off the gears. It is true weak valve springs will cause issues like this, but the chain is the main culprit here. Welcome to the forum - we always like to see pics of new members rides - condition not important.
    Pennyman1
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