Engine/Transmission (1998.5 - 2002) Truck bucked hard from a stop light

[BKeence]

While pulling our fiver over the weekend the truck jumped or bucked real hard pulling away from a light. We just started moving, maybe 1 or 2 mph, I really don't think the truck was trying to shift into second. I let off the throttle and then accelerated and it did it again. I then accelerated gently and everything was okay. It did this at 2 different lights. It has not done it since.

I am running a superchip in "Tow Safe" mode. I do NOT have a boost fooler. I have seen boost as high as 24 psi. Never had a CIL from over boost. I also checked for codes in the computer and found none. I was thinking maybe the truck defueled quickely or something. Is this possible? The very last time it bucked I looked at the boost guage and noticed it was only about 7-8 psi. Boost usually hits 21 or higher when I accelerate pulling the fiver.

Right before the truck did the bucking we had pulled several steep grades, but EGTs never got too high.



Thanks

 

[BKeence]

Anyone have any thoughts to the truck jerking like it did? I still don't think I had picked up enough speed for it to be shifting yet.



Thanks,



Brian

 

[JMetzger]

You didn't say if you had a limited slip diff or not. I have had my truck do that a couple of times while pulling our trailer & all it was was rear wheels trying to spin. It did it on a damp road & the limited slip would be locking the other wheel. It also did it on my 92 with auto transmission. I don't know if that is what yours was doing but that is what I found on my two trucks.

 

[RAJohnson]

Your signature does not mention a FP gauge, Do you have one?



My first thought when I read your post was your APPS needs to be reset.

 

[BKeence]

Yes it has limited slip, but the roads were dry and I'm sure the tires didn't even come close to slipping. I mentioned defueling, I'm not sure I could recreate the jerking by letting off the throttle and then accelerating again. It is very hard to explain.

I don't have a FP guage, however I replaced the APPS recently due to the dead pedal.



Thanks



Brian

 

[RAJohnson]

Well I would guess you have lost your Lift Pump possibly. Due to your statement of (I replaced the APPS recently due to the dead pedal).

And what you may be experienceing is a dieing VP. Or bucking due to loss of fuel pressure. Which will injure the VP.



How many miles on your truck?

Are you on your original VP and LP?

 

[BKeence]

I have less than 10,000 miles on the new lift pump, vp44 and apps. I will have the fuel pressure tested this weekend if I can get there in time.

I have 132,000 on the truck now. I hope to figure this out soon. It has only done it on two different occasions.



Thanks!!





Brian