car bucks 1st few miles.....
 

OK, here is my problem.....

Car sits overnight (12 hours). Start engine put it into gear and drive away. No problems at all.

Get to work after a 20 mile drive around 6:45 am. Leave for lunch at noon. Car bucks and jerks for about 3 miles. Even after the engine temp has hit the mid mark. Goes away.

Leave lunch 45 minutes later. Same thing but not as bad and for not as far.

Leave work at 5pm and same thing again. Jerks and bucks then goes away.

Again. Leave for work in morning and engine runs fine.

Has been doing this for about 2 weeks not. Does not matter what the outside temps or if it's sunny or raining.

Things that have been done to the engine within the last 6 months.

new plugs, wire, cap rotor, fuel system o-rings, all hoses both coolant and emissions (ALL OF THEM!) water pump, air filter and full oil and fuel system cleaned with seafoam.

I regapped and installed my old plugs and double checked the wires and cap. still jerks.

Could it be the O2, fuel filter or EGR?

Car runs fine afterwards and still getting great gas mileage.

Thanks everyone. I know it's a long post but wanted to be as complete as possible.

P.S. I wired in a tach about a month ago. 2 weeks prior to this problem occuring. Double checked my connections for loose wire to ignitor. Seems fine to me. Still tight and no corrosion.

I'd place my bets on the fuel filter. The o2 sensor would just give you worse gas mileage. The EGR might be it, but I doubt it.

i am just curious; why would it jerk at first if it was the fuel filter wouldn't it keep doing it while you drive?

I second the fuel filter. When it sits over night or while you are at work, all the junk in the filter has a chance to fall back into the tank. After driving a bit the pump sucks it back up and the filter clogs again.

If it is independent of throttle then it is not the fuel. If it runs smooth with light throttle then bucks with more throttle it could be spark breaking down. Wet distributor cap is often the problem if it clears up with temp.

It bucks in all gears while appling throttle. If I rev it while out of gear than it spools up fine.

It did it this morning on the way to work. It usually doesn't do it then. However it was very light bucking. it feels as if there is no power at all then I fell a short (1/2 sec) burst of power than no power. Repeats a few times and goes away.

I just remembered that my jeep would do this. A friend was under the impression that it might be a clogged catalytic converter, or a clogged exhaust system.

Just an idea.

Could be possible?

The truck is a 1992. I had the head rebuilt 2 years ago but the exhaust has only had a muffler changed.

I hear that when the cat gets clogged it will run VERY hot! So far the cat seems to be running at a normal temp.

I have been thinking about running 2 cats anyway. So I might just change it?

The fuel filter needs changing. Been putting it off because my filter runs $30!

After I do that I'll see what happens.

Check your PCV valve - I heard once that the engine block pressure vented into the poor seals of the distributor blowing moisture up into it - a poor PCV valve would do this. Also when it starts doing it just stop and pull the distributor cap off. Also check on the ignition connections to make sure you get good grounding to the distributor or else you could be misfiring the coils or not firing them at all when you loose power. Check for the smell of gas in the exhost too since that would indicate a failing spark - smell that all the time when I hear a car go by skipping a lot. Soot in the tail pipe would indicate a cat problem too. Spark plug gap too big can cause problems with high voltage wiring breaking down under less than ideal a/f mixtures.

After it's been driven awhile and bucking, what is the combustion looking like? Any smoke? What do the plugs tell you?

The plugs are gapped at .028 just as the manual reads. The plug was grayish white. No build up are splatters. There was however oil on the threads for all four plugs. Wasn't heavy by any means. Really light oil.

I'll pull the cap off and look in there. All of it's brand new. But they are cheap Advanced auto parts stuff.

I have never onced walked behind my truck while it was running. The tailpipe does exit on the driver's side. Have never seen smoke out the rearveiw mirror and when I washed the truck there is no bloack soot on the bumper or in the pipe. Looks really clean.

I'll also get a PVC. I think it was changed 2 years ago when I had the head rebuilt but can't remember?

Thanks guys!

I put a new cap on my rabbit one time and it was cracked within a week - new does not mean working or better sometimes. What happens is as the engine warms up moisture would leave the engine and condense in the cap until the cap warms up and burns off the moisture.

OK, stopped by the local auto parts store and bought a new fuel filter and PVC.

The old Filter looked old but was not the original as far as I could tell. I have the screw in style PVC and when I removed the old one I noticed a lack of thread sealant. Old one seemed fine but I could have had a small vacuum leak?

Anyhow, took it for a drive and MOST but not all of the hesitation was gone.

I came back home and hook the timing light back up. I had just set the idle and timing about 3 weeks ago and marked my distributor.

Timing was set at 8 degrees but after only 3 weeks it dropped down to 5 degrees!

Nothing had moved according to the marks I had made. So I reset it back up to 8.

The thing I have noticed was the pinging. Even at 5 degrees it pinged under acceleration.

My dad had rebuilt the head 2 years ago and said while he had the head off he cleaned all of the crud on the piston domes and intake runners and ports.

For the life of me I can not figure out why it's still pinging. The head was never even shaved? The machine shop said it was perfectly straight and only cleaned it up, changed the valves and machined the seats.

Should I try a higher octane or look for some other possible cause first?