Lurching at low speed and throttle, HELP

[desertsky]

I am out of town taking my son back to college and I have the strange lurching. '99 Explorer XLT 4.0 SOHC, 4WD.
Here is what it is doing.

Idles fine.
Apply normal throttle and it acts like someone has a light switch and turns the engine off and on every 1/2 second.
Apply very little throttle and truck will accelerate with 1/2 second hesitations.

Get it over about 20-25 MPH and you can give it a bunch of throttle and it goes good. Normal throttle and it lurches.

Freeway speeds, light throttle and you can feel slight lurching. Give it some stick and lurching goes away.

Lurching is 1/2 second intervals regardless of speed, throttle or gear.

First time it happened, I thought it was out of gas and filled tank. It went away for a few weeks. Came back today on I-40 in northern AZ. Got lean bank 1 and 2 twice during this.

It went away for a while and ran fine, then back again.

I am leaning towards a fuel injection control problem because it seems to coincide with a timing event (every 1/2 second), or possibly a throttle position sensor, but no error codes other than the lean banks. I did a search on the forums and didn't find anything quite like this. I really don't want to drive it all the way back to Colorado Sunday without knowing what this could be.

Any insights would be appreciated!

 

[desertsky]

No help for this one?

Went out this morning and the truck is running great. Drove all over town today and not a hiccup.

Oh well. Leaving for Colorado tomorrow. We'll see what happens.

 

[fex98]

dirty fuel maybe

 

[desertsky]

I thought that maybe, too. Problem is, It happened as I got down near 3/4 tank and I continued until I got to 1/2 tank. I filled up with some mid-grade Chevron and the lurching continued unchanged for another 150 miles.

Now that it is running fine again, no point in taking it in for a checkup. No codes were stored other than the lean bank one and two.

 

[fex98]

change the fuel filter and a bottle of fuel injection cleaner in the tank try that.

 

[desertsky]

Changed the fuel filter last month. Put in a bottle of Techron this morning and the lurching started again about 100 miles into the trip. It went away after about 20 miles. So far, 450 miles and all is well.

I believe it is an electrical problem because it switches off and on in a regular 1/2 second cycle regardless of other parameters.

 

[waskly]

maybe wires you can feel misfire on there trucks with light, tip in throttle and on damp days. try using a spray bottle and see if the wires arc.

 

[javedjee77]

Very interesting story, I like it.

 

[desertsky]

Well, no problems for over a week. When it happened, it was warm and dry so I don't think moisture had anything to do with it.

I may hook up my oscilloscope to the computer and see if there are any timing circuits that operate at the frequency of the on-off rate. Its hard to troubleshoot when it is intermittent like this.

 

[storlied]

Lmfao... WTF ^^^

 

[2000StreetRod]

lean condition

I would focus on anything that could cause a lean condition. The engine will stumble under load when lean which could occur at a regular interval. Since you've replaced your fuel filter and added Techron I suggest measuring your fuel pressure. It should be around 65 psi for all engine conditions. Have you cleaned the MAF sensor with MAF sensor cleaner? I agree that testing the TPS is a good idea: TPS Test Procedure