Engine/Transmission (1998.5 - 2002) Loping and bouncing tachometer

[SHobbs]

What can cause the engine to lope when coming to a stop? Every time I come to a red light or a stop sign I notice the tach bouncing and a definite lope from the engine. It only does it about three or four times before it settles down, sometimes it does not do it at all. It used to drop to about 950 r. p. m's before going to it's usual idle speed which I understand is supposed to be normal. Now it might drop below normal idle speed then bounce above that as I said three or four times before returning to normal. I have noticed that even at idle it does fluctuate a very small amount maybe 100 r. p. m's or so just enough to notice the needle moving. I have replaced the MAP, crank, camshaft sensors and the APPS ( TPS ) is just a few months old. The VP44 has around 80-85k on it. I was thinking maybe the fuel filter which I will change tomorrow to see if that helps, maybe barking up the wrong tree there though.



Thanks

Scott

 

[jhoughton]

I had bad fuel that did this to me once (water in the storage tank). I drained it out and replaced it problem went away. Just a thought.

 

[Sticks]

The only time I have seen that is on a 12v and either the governor was on the way out, or fueling issues (fuel pressure, air in fuel).

Start with the filter, then verify your fuel pressure. If both are good, check for leaks in the fuel system. Usually need to pressurize the fuel tank to about 10psi to force any fuel out bad connections. The number one culprit is the quick connect fitting just before the block mounted lift pump.

I'd also do a check for codes. Might be a timing issue, or the VP is going Tango Uniform.

 

[jgillott]

For what it's worth, I had a HR-VP in my former '01 that would do that when it warmed up. When it was cold, it would idle smooth as glass. Once up to temperature it would lope like a gas engine with a healthy cam. Not sure if it is the issue in your case, but it is a possiblility.



I sold that truck off over 3 years ago and from what I understand, it is still running on the same VP.

 

[ESwartzer]

Loping at idle

I currently have the same condition with my 98. 5 only when it starts to lope when hot it frequently stalls when shifting from park or neutral to either forward or reverse. I have read that a bad crank sensor could cause the problem, so that's what I'm going to try as a fix. It's only around 60 dollars so it's worth a try. Good Luck!

 

[ESwartzer]

Just re-read your post

And saw that you already replaced your crank sensor so that sort of negates my last answer. Maybe the electronics on your Vp44 are having an issue. Go to the Blue Chip site for some in depth diagnosis on your pump!

 

[NKenny]

My Hot Rod VP44 has loped exactly like you have described since I installed it in 2005. I installed a crank sensor and cleaned the IAT and everything I could think of when I installed the HR VP44. I pulled it and returned it to Industrial Injection within a week of installing it and it checked fine. It has worked for 5-years with great power... it just has a lope to it.