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Thread: Truck jerks and lunges violently no rpm or speed change?? Mk2 v6 mm

  1. #1

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    Truck jerks and lunges violently no rpm or speed change?? Mk2 v6 mm

    So my truck has been running fine for the past 1000k since I rebuild the heads and yesterday I was pulling out of a ditch and hit one of the supports for the frame on some concrete but I checked and it just scraped it no serious damage at all I thought at first it hit the rear axle but there is no obvious damage at all. So I drove home around thirty miles or so and stopped at the bank, left the truck running and I came back out and drove it away and it started lunging violently in gear if you give it more than about 10% throttle. It seriously feels like when your pulling a trailer and the trailer yanks on the back of the truck. Weird thing is, the rpms and the speed do not change at all when it lunges??? Any ideas gentleman? 94 mm v6 5 speed. O and when I got home I checked the oil in the diff and it has plenty no issues.

  2. #2

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    I it's a 4x4 to my bad.. And changing it into 4 wheel drive does not help the issue at all.

  3. #3



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    check your rear u bolts - sounds like the axle is moving back and forth. Also check the roll over valve near the tank - it is there to shut off the fuel flow in a rollover, and may have been shocked by the impact. Make sure the driveshafts are seated in the transfer case and move freely.
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  4. #4

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    Quote Originally Posted by pennyman1 View Post
    check your rear u bolts - sounds like the axle is moving back and forth. Also check the roll over valve near the tank - it is there to shut off the fuel flow in a rollover, and may have been shocked by the impact. Make sure the driveshafts are seated in the transfer case and move freely.
    Checked the u-bolts. doesnt look like they have moved since the day it drove off the lot



    Im assuming this thing is the rollover valve you spoke of? I'm not really sure how to check it. in the L shaped thing there is a little ball that rattles around and the other seems to be a one way valve that seems to work.


    Weird thing i found though. i put the truck in neutral and 2wd and jacked the rear end up and spun the wheels by hand. the drivers side wheel spins freely with very little effort. the passenger side wheel seems to catch on something almost like its catching on the drum pad. but i had my wife help and we spun both wheels in the same direction at the same time and the passenger side wheel then gets very difficult to spin the drivers side remains easy though. they both spin the driveshaft with no noises or clicks. the driveshaft seems to be fine, not loose at all as far as i can tell.

    Thank you for the help!

  5. #5



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    Pull the dif cover. Sounds like a rear end problem When you lunch a ring and pinion they feel like that before they start to make noise. Also try moving the pinion around up down side to side. It should not move.
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  6. #6



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    +2 on the diff - neither side should bind like that. Those are the parts I was referring to for the gas tank btw
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  7. #7

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    Can you guys tell me what kind of diff is in the back and the gear ratio?? I have a ford explorer rear end and a 87 mm extended cab rear end to get parts from. Will either of those match?

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    Did you pull the cover yet?
    Without finding the problem you can't move forward.
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  9. #9

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    Quote Originally Posted by camoit View Post
    Did you pull the cover yet?
    Without finding the problem you can't move forward.
    The cover is on the side where the drive shaft comes in. Doesn't look as simple as on other trucks from what I can find its a 4.222 ratio? But what kind of axle? Is it just like a Dana something or something proprietary?

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    it is a mitsu 8" rear - the 87 MM carrier will work, but you need to swap the ring and pinion to keep front and rear gears matched. You have to pull both axles before you can pull the center section out.
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  11. #11

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    Quote Originally Posted by pennyman1 View Post
    it is a mitsu 8" rear - the 87 MM carrier will work, but you need to swap the ring and pinion to keep front and rear gears matched. You have to pull both axles before you can pull the center section out.
    How about the axle from a 94 montero? Same same? I'm just trying to think if I can't source out the parts for what's broken I'll just swap another axle in. Parts for this truck haven't been the easiest to find.

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    I may have misspoke - the V6 is a 9" rear - the 94 Montero rear will work, but the gearing may be different.
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    Got the diff out and took a look at it and nothing seems wrong. all the gears are intact and functional, there are no metal shavings or other noticeable signs of wear anywhere. what exactly am i looking for?

  14. #14

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    Today i finally got a analog multimeter and i read the codes on the truck and i got "Airflow Sensor" Airflow Temperature Sensor" and "Barometric Pressure Sensor" I know the first two are the MAF but where is the third sensor located at?

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    They are all part of the MAF
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    For the MAF, I'd check power and ground at the MAF connector before messing with the sensor itself. That doesn't sound like your problem though. Bad signals from the MAF usually manifest as poor idle, loss of power and stumbling.

    Since it sounds like your axle is ok (aside from the odd binding symptoms...wheel bearing maybe?) I'd look at the fuel tank. Drop the tank and look at the pump pickup. Also, when was the last time your fuel filter was replaced? Momentary loss of fuel pressure at the rail could be causing the symptoms you're describing. I got a new pump and filter from O'Reilly and it made a huge difference in how my truck started and ran.

  17. #17

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    if you do get a new fuel filter go with o'reillys house brand. they are wix filters and seem to work really well. avoid autozones, ive put both on and you will notice a slight loss of power with the autozone filter. I replaced the old one on my truck with the autozone filter and noticed a loss in performance. i new this is was not right so i picked up an o'reilly filter and immediately noticed a difference once installed.

    hope you figure out what is wrong.

  18. #18

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    im not a 4x4 expert but could it be something to do with the hubs?

  19. #19

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    Fuel filter and pump where replaced brand new less than a thousand miles ago. I also dropped the tank and cleaned it out. The fuel pump does make some weird sounds though. Like after the issue starts happening, the fuel pump like whines in a pattern like high pitch low pitch high pitch low pitch. I that's another thing. If you let the truck sit for 20 minutes or so then drive it around it works fine for about 10-20 miles then the issue comes back.

  20. #20

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    Quote Originally Posted by Jeff V. View Post
    For the MAF, I'd check power and ground at the MAF connector before messing with the sensor itself.
    Can you get me a pin out of the MAF connector please sir?

  21. #21

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    Quote Originally Posted by finalfighter View Post
    im not a 4x4 expert but could it be something to do with the hubs?
    As in locking hubs? It seems to be a issue with the rear. And as far as bearings, when I say it lunges I mean your head almost smashes into the window it is incredibly brutal not subtle at all. I don't think a bad bearing could cause that?

  22. #22

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    Quote Originally Posted by Chyrio
    Can you get me a pin out of the MAF connector please sir?
    I've got the factory 92-95 books at home. I'll try to get posted tonight.

    Your description of the fuel pump noises make me wonder if it's a bad relay somewhere? It's odd that it'd be tied to throttle input though.

    Does it make a difference what gear you're in when this happens? Can you free rev it in neutral without problems?

  23. #23

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    are your real brakes locking up? i dont know if you can do this but remove the rear drums and put the tires on and take it for a quick spin and see what it does.

  24. #24

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    or remove the rear pads and see what it does

  25. #25

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    my truck would kind of lunge when the ecm went bad but i have a 4cylinder. try checking the ecm and post some picks of the inside. sometimes the caps inside go bad.

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