no start after filter change

[rgrowan]

I just changed the filter in my '99 GMC 6.5, and now I can't get fuel to come out of the vent cap and obviously, she won't start. HELP!!

[simon]

OPS,and/or LP shot,check fuses too.

"Search" is your friend, lots of info there

Fill out your signature. we dont know what you'r driving. T-ford perhaps?

[rgrowan]

By LP you mean "lift pump", is OPS "oil pressure sensor"? I like to think I'm smart but my wife doesn't agree. And my ride is a '99 'Burb with a new "optimizer 6500" with about 10 000 miles.

[simon]

You are correct .
check for plugged fillercap (to much vac),or a leak in the fuel line from tank to LP.

My wife says I am smart only cause i get plugged into a genius (Her)a couple times a week.

[Robyn]

The lift pump should operate when the key is in the start position.

The OBD2 trucks of 96 and later had some changes made and the OPS
(Oil pressure switch) does not handle the load to run the lift pump as in earlier rigs.

The ECM controls the relay for the "run" time on the LP and the OPS just sends a signal.

Not sure about the 99 but my 95 will power the lift pump when the trans selector is in D and the key turned to the start position.

The starter wont go but the LP runs to charge the system.

Likely the LP is shot. This is an easy fix.

LP is in the frame rail on the LH side of the truck right under the drivers seat area.

30 minute fix max.

The relay in the junction box on the LH side of the engine bay could also be an issue so it might be a good idea to check them both.

First check to see if you have 12V to the lift pump when cranking.

If no 12V to pump then check the relay. These are not spendy and do fail on occasion

Once you get fuel to the filter and the air out the little beast will be a tad fussy to get going again but with some coaxing should come to life.

Purging air from the top hose (Upper front) on the IP will aid in getting things going quicker too.


Hope this helps

Missy Robyn

[rgrowan]

So I put in a new lift pump and she runs again! Only thing is it seems to be missing. If I rev it to 2500, it drops to 2250, then back up to 2500, then down to 2100, then back up to 2500, and so on. I can see the engine torque slightly with every miss. Any ideas? You've all been bang on so far...This site is AWESOME!!! And so is everyone on it!!! THANK YOU!!!

[john8662]

Sounds like air in the lines still. you need to prime the filter housing, open the top vent, and turn they key (you get a momentary lift pump operation). You want fuel to come out of the top.

Nice comment about being plug'ed in, haha.

J