Alright, so its been a while since I've been on, just real busy with the farm and logging and school and blah blah blah.

Here's the deal. My 99 4x4 5-spd is idling pretty rough once its warmed up and been running a while. Now, its stock besides the XZT, including the lift pump, I just haven't had time to change it yet. I sold my Airdog to my buddy who needed it for his truck and couldn't wait to have one shipped. I'm thinking now that I'm gonna just put on a PPE billet pump and plumb it through the stock lines, then bypass the stock pump (I'll leave it there just incase the PPE fails). I'm thinking the injectors could be worn out, I'm at 210K miles roughly, and a busted injector is what killed my 97 (melted down the #5 cylinder when one stuck open), so I'm hesitant to keep running it, but its my only registered vehicle at the moment.

So... Lift pump? Injectors? VP? Whatdya 24v guru's think?

 

whats your fuel pressure at?

 

I would check fuel psi if thats good. then your lift pump is ok. when is the last time you adjusted your vavles, If you havent adjusted them that would be a good start. to check your injectors get a temp gun and go down the exhaust manifold and see if on is colder then the other,

 

Well, I'd check the fuel pressure, but my X-monitor seems to have reprogrammed itself again, and the fuel press is back to trans temp, so I don't know what the fuel pressure is at. Also, it has an updated fuel filter canister, so my old schrader valve psi tester doesn't work anymore (not compatible).

I adjusted the valves about a year ago, so it is time, but its about 35K miles. Would the valves really cause that lope at idle?

One more thing... Is the lift pump supposed to come on every time the key is turned to "ON"? Because mine doesn't, its sporadic.

 

it will come on for a 4sec then shut off, turn the key on and just tap the starter for not even a sec and you will here it run for 30 secs

 

Your valves would have to be way out for them to do much more then lower fuel mileage and chatter pretty good.

As far as the LP. Even if you hear it runnin don't assume it's pumpin anything cause that is not always the case. One of the common things to go wrong with them is the overflow valve sticks open and just keeps the fuel spinnin in circles not goin anyplace.

To check it out real quick till you get a gauge you can do a flow test. Pull the line going between the Injector pump and the fuel cannister and run it into a jar, bucket or whatever, then bump the starter. It should flow a pretty good amount of fuel, as in at least a few cups full or more before the LP shuts off. Not the best way to test but will do in a pinch.

Also don't forget to check for codes, they may tell the whole story.

If I was a bettin man though I'd be puttin my money on one a the three sensors being dirty, bad or out of adjustment.

 

flow test
Lift Pump Diagnostics

make sure your lift pump is good, overflow valve is not bad, IAT and MAP sensor are clean, check codes

 

Don't forget to check the APPS sensor also in addition to the ones listed above.