kicks and bucks

[05zx10r]

I am new to the site and was wondering if you guys could help. sometimes when i am driving the truck it will stumble and almost kick, if i get in to it hard sometimes it will kick and buck (cut out) but it wont allways do it. do you think it could be the APPS, i have a brand new pmd and good fuel press, no codes ever come on. i just dont have any idea

95 K2500
Cooling system upgrade
PMD upgrade
4L80E
Intake

[94bigdiesel]

Sounds like your lift pump/oil pressure switch to me. I had the same problem with mine. Found that my OPS was bad and wasn't turnin on my lift pump.

Quickest way to test is to crack your water/fuel valve by the alternator when the engine is running. If nothing comes out and after a short time the engine dies then you have no fuel pressure.

[05zx10r]

thanks i will try it

[05zx10r]

I did that this morning be4 work and it died. now how do i test to see what it is, it took like 10 min to start after so i would think the lift pump but i dont know if there is a way to test the oil press sensor

[okie65]

I believe that was the test and since it died then the OPS in bad and needs replacing.

[05zx10r]

Well on my lunch i tested the voltage and the lift pump and i have 12 voltes to it and you can feel it pump now im just at a loss

[94bigdiesel]

Well if the pump is runnin then I would have to say that it is prolly wore out and not actually moving fuel. If I were in your shoes, I'd replace the pump, or at least try a known good one in place of it before purchasing one. Are you sure that it was always running and you didnt happen to jocile a connection when you tested for power/vibes?

[trukdoc]

...have voltage to lift pump with engine running then replace the ops...when the ops starts to go it starts to operate with a wider range...sooooo when you let off the throttle and oil pressure drops back it{the ops}will momentarily cut off the lift pump when you get back on it the oil pressure comes up and pump comes back on, BUT you got air from the pump cutting,thus the missing and bucking...this is'nt b.s. this will really happen...change the ops...jd

[05zx10r]

thats helps a lot i will try the ops first and hope that will fix it

[JD_countryboy]

Change your ops. had this before. Had 12v to pump, but couldnt get the needed amperage (current) to the pump to operate it.

[05zx10r]

thanks guys i got the new ops in and it seemed to fix it thanks a lot guys

[Bazaromcmullen]

I installed a 2 dollar radio shack LED on my pump. I spliced directly into the wires at the pump and ran a mini LED that I mounted in the dash. Now I can always tell that the pump has voltage so when a problem surfaces again I can have a quick tell tale where to look.

[JD_countryboy]

Good idea. Now for the bad part. Not always does an ops go bad and quit completely. Sometimes the contacts inside it will deteriorate and let some voltage thru it, but wont let enough amperage (current) thru them. In the case of your LED light, it takes milliamps (way less than 1 amp) to light it. The lift pump on the otherhand takes a few amps, (im thinkin like 10 amps but not sure). So it would be possible top light your LED but not operate your lift pump. I had this scenario happen with my truck and bad ops. But i paid the $75 for a lift pump, found out that didnt cure my 0 fuel pressure, then found the gm bulletin addressing this issue, and then changed my ops and cured the problem.