Surging and bucking while driving

[JO9816]

Hey guys. I've got an early 99 7.3 that has been surging pretty bad lately. If I'm trying to accelerate normal (1/4- 1/2 throttle) the truck will rev like crazy, and the rpms will jump spastically even though my foot is in the same spot on the pedal. I'm thinking it might be a throttle sensor of some sort because it only does it when I'm using the pedal. On cruise control, it runs smooth as glass. Any ideas?


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[ghohouston]

Several things possible. Cps would be the first thing. On my obs, i had the exact same jerking/bucking, and eventually found out my selector valve failed between the front and rear position, and not really letting any fuel past it, up to the fuel pump or injectors. It would idle fine, and run okay with partial throttle, but full throttle in the higher gears, it would buck and or die. I would definitely check fuel pressure under a load. And of course, could be tps related too. Have ypu scanned for codes?

 

[JO9816]

I brought the truck into a reputable shop near me and they scanned it and no codes popped up. However, about a week later I checked the "diagnostic" feature on my edge monitor and code p1211 popped up and said the engine had "lower or higher icp than desired". Also, at wide open throttle, it runs fine. It might be the cps, but I thought the truck would die completely if the cps screwed up.



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[Arisley]

What oil are you running and how long has it been since an oil change?

Let's start with the simple stuff.

 

[JO9816]

What oil are you running and how long has it been since an oil change?

Let's start with the simple stuff.

Mobil delvac 15w40, and last change was about 2000 miles ago


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[JO9816]

Here's a little update. I just drove from the outer banks in NC back to my house in VA, about a 3 hour drive. I let the truck warm up for about 10-15 minutes this morning and then started on my way home. For 2 hours, there was no bucking or surging at all. The last hour, it came back. So I put it on cruise control and the surging and bucking stopped. Then I got on some back roads and had to use the pedal and the bucking came back. I was pretty annoyed at this point with it, so I floored it on a long stretch of road. Get to a stop sign and start accelerating normally, and the surging and bucking has stopped. This has me thinking that a throttle sensor or something is getting partially stuck which causes the bucking...


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[Arisley]

Contact cleaner on the throttle assembly.

 

[firehunter]

I have had a similar condition on and off for the last 18 months or so. I feel it most when keeping the throttle steady (light throttle) and it feels like the engine is switching back and forth between two different tunes. Use cruise control and it is smooth.

I switched out my grey CPS for another grey CPS and the same thing came back in just a few weeks.

I was researching CPS in general lately since I have used my last black one and noticed on a website that the Dark Blue CPS was called for in OBS trucks. I have a SD but with A codes in it and figured what the heck? The grey ones work fine in my wife's SD with split shots in it, try the dark blue for my truck with singles? MAGIC. Truck has never run so smooth. Fires up consistently and predictably. Jumpy running is no more. EGT's are down, smoke is down, fuel mileage is up. Towing is noticeably easier and even shifting is smoother. I have had the dark blue CPS in there for a few weeks now and am over the moon happy with it.

I have gone so far as to do compressions tests and pull the injectors to inspect...and the fix was a CPS...just like in the first response in this thread.

 

[bruce]

I would mount a fuel pressure gauge. I had one doin that and I just mounted a mechanical gauge under the hood. Eventually the fuel pressure went to zero so I dropped the tank and the mixing chamber was full of what looked like black tape.