Engine/Transmission (1998.5 - 2002) intermiitent surge ?

[BarryG]

My truck has developed an intermitent strange surge (by intermitent I mean may do it today then not again for a week). It only does it sometimes, it only does it (can only hear it anyway) above 55mph best heard at 65-70mph. The tach bounces sometimes when it does it but only bounces 25-50rpms which it sometimes does even at idle. I can't feel it but definitely hear it. It has done it for 100 miles at a time and it has done it for 5 miles. Stopping and shutting off the truck does not get rid of it, it just stops doing it when it is good and ready. The truck runs fine even when doing it no loss off power or drivability it accelerates fine even when doing it (can't hear it while accelerating only while cruising at steady speed). Does it with cruise on or off. It sounds like you are tapping your foot on the go pedal It is a steady 1 second cycle up down , up down, up down. It sounds like about 100rpm change but the tach doesn't really show it (though it does bounce as mentioned above sometimes). I have done a search and can find things about surging but nothing like this. By the way fp seems to be ok. It is driving me crazy when it does it. Any ideas VP44? CPS? TPS? I am at a loss and with its intermitent nature reluctant to take it to a dealer since it can't readily be replicated.

 

[RustyJC]

Will it surge on cruise control? If so, since the fueling signal is being sent out of the PCM based on speed without referencing the TPS, you could pretty well rule out the TPS as a culprit.



Rusty

 

[BarryG]

Yes it will do it with the cruise engaged. But I will double check next time it does it.

 

[ihegdal]

Barry,



My engine also frequently makes a surging sound when the RPM is between about 1800-2000 rpm. I have been told that it sounds like the injection pump timing is varying. This usuall most noticeable at low power levels in drive and overdrive. Happens both with and without the EZ attached.



Other than this all is well.



Ian