mack600 Posted October 29, 2017 Share Posted October 29, 2017 85 r686 is surging at lower rpm between 1000-1200 is the worst. smooths out ok above that but very annoying driving around the yard when almost any throttle will start a surging/bucking show. throttle linkage is tight and return spring on pump is intact. I seem to remember a service bulletin about the ambac pumps with governer/flyweight issues, can the governor assembly be separated from the pump while still on the truck? and any idea what parts need to replaced? the number off the pump is GVB250/850E-7507A1 any input would be appreciated -thanks Quote Link to comment Share on other sites More sharing options...
david wild Posted October 29, 2017 Share Posted October 29, 2017 smother foot is needed driver, your not driving some numb brand X, your driving high performance very touchy equipment, keep at it you'll get better. Quote Link to comment Share on other sites More sharing options...
fjh Posted October 29, 2017 Share Posted October 29, 2017 (edited) I know you have said the return spring on the pump is intact however is the throttle lever worn at he cantilever springs near the throttle shaft if these have worn notches in the actuator the engine will surge on light pedal! Just something to look for! Edited October 29, 2017 by fjh Quote Link to comment Share on other sites More sharing options...
mack600 Posted October 29, 2017 Author Share Posted October 29, 2017 That's possible as I've only driven this truck a few times but I think there are further issues As it also does it in neutral with the throttle set Quote Link to comment Share on other sites More sharing options...
david wild Posted October 29, 2017 Share Posted October 29, 2017 and the rest of the story ??? Quote Link to comment Share on other sites More sharing options...
Truck Shop Posted October 29, 2017 Share Posted October 29, 2017 Tread light on him, I sent him this direction. Truck Shop 1 Quote One ping only Link to comment Share on other sites More sharing options...
theakerstwo Posted October 29, 2017 Share Posted October 29, 2017 many times cab mounts can cause a tricky throttle at low speeds but if all other things stated here has been checked then its time to pull the pump.I have replaced the linkage with a cable pull and helped some. Quote glenn akers Link to comment Share on other sites More sharing options...
fjh Posted October 30, 2017 Share Posted October 30, 2017 If it is surging at idle as well the you likely have internal issues in the pump how ever do check the lever.just in case. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.