high way speed severe hesitation .... occasionally !

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.

 

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

 

I changed plugs after first episode and before 2nd episode!
MY NAGGING PROBLEM IS WHY DOES THIS NOT HAPPEN EVERY TIME I'M ON A
LONGER TRIP OF 2 - 3 OR MORE HOURS?!
Thanks for the imput,
Bob V.

 

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.

 

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

 

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
electronics.

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
that?

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?!!!

Thanks,
Bob V.

 

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

 

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.

 

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.

 

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!

Thanks
Bob V.

 

Is it possible that the mechanic (dealer?) was referring to NOx (or O2)
sensor, not the knock sensor?