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EVAP System or Transmission Problem?

Home Forums Stay Dirty Lounge Service and Repair Questions Answered Here EVAP System or Transmission Problem?

This topic contains 5 replies, has 4 voices, and was last updated by Ronald Tylor Ronald Tylor 1 year, 10 months ago.

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  • #659705
    Adam Hosey
    Adam Hosey
    Participant

    So, I recently bought a 2004 Montero Sport LS. It had 155,000 on it, so I was expecting a few issues. One of the things I’m having problems with is the way the car behaves going uphill.

    When I’m driving up hill, SOMETIMES (maybe 1/5 hills) the car surges up and down about 200 RPM. Basically, at, say, 1/2 second intervals, the engine will rev up and down between 1500 and 1700 RPMs, despite the gas pedal being depressed at a consistent pressure. This is also coupled with, say, one in every two hills, I’ll start to lose acceleration on my way up the hill, and then I’ll push the gas, it will hesitate for a split second, then jump from, say, 2500 to 3100 REALLY fast, then it shifts and the shift is sort of rough. I can’t describe it as jarring, but more just a generalized bump in the car that you can feel. And it only does this occasionally.

    The engine recently threw a P0455 code. I changed the gas cap to no avail, so I figured maybe the purge valve was sticking and I changed that. No luck.

    So I can’t figure out exactly what it is. And it does it in any gear I’m in. For instance, if I’m driving slow-ish up a real big incline, and I’ve got it in 3 instead of D, and it needs a little more power, it’ll downshift into second and produce the same hesitation, surge, and then bump on the downshift. It also did this in 2. It most commonly does it in D, but that’s probably because I am most commonly driving in D.

    Now, I don’t think it’s a transmission thing. It’s not like a jarring feeling when it shifts. If I’m accelerating on flat ground, it is perfectly fine and shifts completely smoothly. There are no problems downshifting when I’m decelerating, although sometimes I do get the same response trying to pass somebody. Given that I’ve still got this P0455 code lingering around, I can’t help but feel like it’s something in the EVAP system.

    If I were to go PURELY on speculation and conjecture, it feels sort of like when I step on it, it’s not delivering more fuel to the engine right away. Then, when it surges, it feels like the engine got blasted with fuel and the hard shift comes because the tranny is trying to act quickly to catch back up. But I’m really at a loss at this point.

    Also, I should note, although I don’t imagine this is relevant, that I noticed after replacing the purge valve (probably just because I wasn’t paying attention before that) that there’s a VERY faint clicking sound when I accelerate that sounds almost exactly like a playing card in a child’s bike spokes, only really really faint.

    Any ideas on this? Does it sound like a transmission issue or something else? Dear God do I hope it’s not a transmission thing.

Viewing 5 replies - 1 through 5 (of 5 total)
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  • #659712
    A toyotakarl
    Its me
    Moderator

    You may have to have that vehicle tested with a smoke machine to find that EVAP leak. Sometimes they can be very small and impossible to find without pumping smoke into the system.

    About the lag, May be due to fuel pressure regulator not working properly, when vacuum goes down (rpms up quickly, like going up a hill), the regulator should allow a slightly higher fuel pressure.

    I would put a fuel pressure gauge on it and observe it when driving in those conditions and see what is going on with the pressure when it bogs down.

    JMHO

    -Karl

    #659713
    Adam Hosey
    Adam Hosey
    Participant

    Okay, I’ll give that a shot.

    It sounds to you like a fuel system thing, then, and not a trans issue?

    #659722
    A toyotakarl
    Its me
    Moderator

    [quote=”ahosey01″ post=132515]Okay, I’ll give that a shot.

    It sounds to you like a fuel system thing, then, and not a trans issue?[/quote]

    Can’t say exactly right now…. But I would start with a fuel pressure gauge on it…

    -Karl

    #659735
    Andrew Phillips
    Andrew Phillips
    Participant

    The clicking sound you hear is probably the purge valve operating. If your old one wasn’t working (you did say you replaced it) then it would be a new sound you didn’t hear before, or maybe the new valve is just louder because it is new, lol.

    +1 on Karl’s advice.

    Also, did you check the trans fluid for proper color, smell, and level? It should look like cherry cough syrup and smell like chemicals and oil, but no burned odor. And, you may also need to check your shift solenoids to make sure they are clean and not binding up. Test their resistance also with an ohmmeter, you should look up the exact resistance specs in the service manual, but they are normally somewhere between 12-25 ohms from voltage pin to ground. They should click noticeable when you connect 12v directly to each voltage pin. On most cars the wires to the solenoid are all hot and they get ground through their mounts, but check your wiring diagram first to make sure.

    #989706
    Ronald Tylor
    Ronald Tylor
    Participant

    PURGE VALVE ON GM 3800 AFFECT HARD SHIFTS ON TRANSMISSION mine does this on my 03 Buick lesabre it never shifts hard when the purge valve is not not rattling

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