high way speed severe hesitation .... occasionally !

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.

----------------- The SnoMan

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?

1. 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.