high way speed severe hesitation .... occasionally !

Discussion in 'General Motoring' started by bvannatter, May 18, 2006.

  1. bvannatter

    bvannatter Guest

    Believe this story and give me an answer, please!

    1998 SW1 250,000km
    New fuel filter @ 238,000 km ( I change it @ 100,000 KM intervals)

    Travelled on a trip of 3,000 km and problem started. Short story: car
    could not pass highway truck because of severe jerking hesitation.
    Seemed like starving for fuel. Got passed the truck finally and by
    being gentle on gas peddle, I gained a bit of speed. While just
    cruising, no problems appeared. Next truck, the hesitation was so bad
    that I aborted passing him. Stopped car, looked under hood for plug
    wires off, etc ... but nothing. Started driving and all OK !!! Went
    for 1/2 hour and same thing. I was going up a good sized mountain hill
    and could not keep 60 km / hour even though I fethered the peddle as
    best that I could!! Stopped car ... nothing ! So started car and
    started off and all OK. Now the car has torque to spare .... going 100
    to 140 kph at the drop of a hat!! Headed to next city and within 1/2
    hour the problem is back. Stopped car and nothing for mechanic to see.
    By now, I realize that turning off car cures problem until 1/2 hour
    of travel has passed. So went to next city stopping car every 1/2 hour
    and talked to mechanic. He had no time to look at it but said it
    idled and reved up nice so not likely fuel, or at least not without a
    high demand for fuel. Decided to travel last 4 hours by turning
    ignition off for 1 - 2 minutes to cure the problem and finally get
    home!! Did this one time and tried skipping it the 2nd time.
    Wouldn't you know it, it kept going!! In fact, it made the last 4
    hours with no problems. Was it bad fuel? Well, the other day after 2
    hours of travel, the hesitation during high speed and heavy
    acceleration started again. I did notice that heavy acceleration at
    low speeds other than 5th gear also had a slight hesitation. Several
    times I talked to Saturn over the last 2 months and they said few
    service codes DO NOT make the engine light come on. One code was
    spark, so I changed the plugs 1000 km ago. One mechanic said the
    ignition module needs only 2 - 3 seconds "off" to cool down and run
    right again. So what's my problem?

    Bob V.
    bvannatter, May 18, 2006
  2. bvannatter

    Bob Shuman Guest

    When were the ignition wires and plugs last changed? Bad wires could give
    the behavior you are seeing, but more likely it is fuel delivery. Not
    likely the filter given it was recently changed, but very well could be a
    bad fuel pump or clogged pickup screen not delivering the pressure you need
    at high volume. Less likely, but also suspect is the ignition coil pack.
    Make sure there is no corrosion on the wire towers.

    Bob Shuman, May 18, 2006
  3. bvannatter

    bvannatter Guest

    I changed plugs after first episode and before 2nd episode!
    Thanks for the imput,
    Bob V.
    bvannatter, May 19, 2006
  4. bvannatter

    SnoMan Guest

    My nickel is on the fuel pump. They are know to act like this when
    they get close to end of service life. (act up after while and then
    work for a while after it sits) I would focus my effort there given
    age and mileage on vehicle if it has never been changed before.
    SnoMan, May 19, 2006
  5. bvannatter

    Private Guest

    Do the easy (and cheap) stuff first.
    1 - Check the air filter and air intake for obstruction.
    2 - Check the plug wires for resistance with an ohm meter.
    2B - Change the plug wires for a known good used set.
    3 - Remove coil packs- clean mounting surfaces and bolts - reinstall using
    nevr-seize grease to prevent corrosion - clean electrical connections and
    seal with dielectric grease.
    4 - Install new plug wires (if you have not changed them in the life of the
    car they are probably due) use dielectric grease on the wire boots.

    Good luck YMMV
    Private, May 19, 2006
  6. bvannatter

    bvannatter Guest

    Thanks to YMMV, Bob S., and the Snowman.
    Actually, I've done literally all that!! ... including a new fuel pump!
    That's why I'm looking outside my own expertise! The car is well
    serviced even after 250,000 km.

    Remember some facts:
    1. key off for 2 minutes solves the problem !!
    2. restart car and I have the power of a V-10 !!, again !! 130 k/h in
    no time!
    3. problem is at 'high demand', therefore either fuel (like a stuck
    pressure valve in the
    '98 fuel filter, even tho' it is new) .... or ... ignition

    What I need expertise on is:
    1. what about the mechanic that claimed the ignition module needs only
    3 seconds
    to cool off and work again? (That was experienced by himself)
    .... any rational for

    2. what service code is so insignificant that it won't light up the
    engine light and yet can
    cause such havock?

    ***** I just got back from my nearest city (54 miles) and was able to
    get Saturn to put his diagnostic equipment on it and a new code
    registers: the "engine knox" code. He thinks I need a new Knox Sending
    Unit, even tho' there are only 4 in all of Canada and they have never
    sold 1 yet !!!! I know the job of this unit, so the question is: What
    engine failure makes the Knox unit go off and yet does not register its
    own code or set off the engine light? Also, if it is simply the
    sending unit glitching, on occasion, why so seldom and why the serious
    hesitation and jerking? I'm willing to buy the thing, but there needs
    to be some rational!!

    Has anyone EVER replaced an engine knox sending unit, ever?!!!

    Bob V.
    bvannatter, May 20, 2006
  7. bvannatter

    Bob Shuman Guest

    Never heard of a Knox sending unit ... perhaps they suspect the Knock Sensor
    is bad? This detects pre-ignition ... I think there is one on the vehicle
    near the rear of the engine and it may retard the ignition timing which
    could give the sluggish performance ... It can be reached from underneath by
    the firewall. This is a pretty simple part to swap out so labor should be
    minimal at the dealer. I don't know the cost of the part, but it might be
    worth a try if they suspect it is bad.

    Good luck and post what you find.

    Bob Shuman, May 20, 2006
  8. bvannatter

    Private Guest

    1 - The knock sensor could be at fault, I would think that shutting down
    would reboot the computer and reset the timing? how much is the part worth?
    Most computer startup problems are connection related and temperature
    related failures are often silicon.

    2 - The computer cannot be relied on to always set an error code for every
    problem or to set the correct code when it does. Think ME$Window$.

    I would suggest installing a fuel pressure test gauge. If you can route it
    into the car it would be possible to monitor the fuel pressure in operation
    under load at the time of problem. CAUTION, depending on how you accomplish
    this you may have a safety issue.

    Good luck, it is a trial and error problem. As always do the easiest and
    cheapest things first and only make one change at a time. YMMV the good
    thing is that you are still mobile.
    Private, May 20, 2006
  9. bvannatter

    BläBlä Guest

    Risky yes. Best to pull over and check it when its acting up.

    If you rule out the new fuel pump, which hasnt changed the symtoms, this
    sounds a lot like a failing Crank Sensor to me. It would have to be
    checked with an O-scope to know for sure. A bad crank sensor can set a
    knock code as it confuses the timing and fires at the wrong time. A
    crank sensor problem is also hard for the ECM to notice and often it
    wont throw a code.
    BläBlä, May 20, 2006
  10. bvannatter

    bvannatter Guest

    Well, folks, thanks for the info. I ordered an engine Knox (Knock)
    sensor and I'll put it in upon arrival next week.

    Neither you nor I will probably won't hear if it works or not for 2 -3
    months! I'll get back then!

    Bob V.
    bvannatter, May 20, 2006
  11. bvannatter

    ns Guest

    Is it possible that the mechanic (dealer?) was referring to NOx (or O2)
    sensor, not the knock sensor?
    ns, Jun 8, 2006
Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.