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Lift Pump - wont run.

D

DMDK

Diesel Obsessive
Messages
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1
Location
PSL,FL
Need help please. Just went to insall a new LP b/c mine was on way out, then it died recently- (0) pressure on mechanial gauge.

Before undoing pluming I plugged in the new Lift Pump and it started the engine and LP started for a second then stopped.

The OPS was replaced 4 months ago, or 8kmi.

I have +12V at the Fuel Pump Relay, and at the LP plug on the harness.

Fuses are good. Grounds are good.

I've searched the old threads and troubleshooted-jumping 12v to pin G on OBD1 port. -Nothing (jumped the new LP and made sure it was working-Yes)


Also dont know if this is related but ever since I changed the timming belt it shows high oil pressure 60-70. Just thought it was another fine gauge by GM. Because I ve got a wacky fuel gauge when it goes below a 1/4 tank.

Thamks all!!:grouphug:
 
I just triple checked the new Lift Pump and with it plugged in the harness while i was holding it in my hand- the new LP turned on only during the cranking period.
 
It will only run when oil pressure is @ 4lbs and above.Mine would work until the switch got warm and would quit.During cranking,your switch allowed it to power up.Is it quitting while the engine is running?
 
OPS switch is what powers the LP after cranking perioud on 1995's. Test power coming out of OPS, or if its unknown age, just replace it. Not expensive. Get ACDelco. (others are specced too low and blow).

Or rewire to eliminate OPS. (Not recommended, OPS turns off LP If accedent, or any other No Oil Pressure situation. (Key OFf).

Its a Safety device that causes problems. On 96up they gave LP Power from PCM (which monitors Engine), and OPS switch.

Test lights are dirt cheap, that will verify for sure power.
 
Try jumping wires to it and give if direct power. Test drive. Make sure it runs good with plenty of fuel pressure.

If they works, try another OPS switch or just safely permanately re-wire it.
 
DMDK said:
OPS was replaced, not AC Delco.
Click to expand...

There was a 'typo' or soemthing from GM's side on the specs of the OPS current. So Other brands are building them to spec, but the wrong spec, and they don't last long as a result. Too much current passing thru them.

Be sure your verifying LP Power. It may pressureize and 'feel and sound' like its stopping. Only because it has reached its max PSI.

Eesiest cheapest way is to work backwards. Temp wire LP. Verifiy runs/drives/works. Then figure out what you want to do to fix it after she's alive agin.

Or test power coming from OPS. Verify that is coming out. If it is zero power out of OPS when engine is cranking. Bad OPS.
 
Check Post #9 from TD's post:

http://www.dieseltowingresource.com/showthread.php?t=6872

One of the picture shows how to jump the LP using 12V to ALDL connector.

After you jump it, see if there is any fuel coming out of the t-valve. If not, LP is bad. If yes, OPS is bad.

Change to ACDelco OPS even if you have to wait.

Also read this one from reference:

http://www.dieseltowingresource.com/showthread.php?t=2647

The best solution is to put in a relay to override the OPS part that switch the LP. I don't have that thread handy.
 
Did the jump from batt-pin G. And it does not run with the NEW Lift Pump plugged in.
 
DMDK said:
Did the jump from batt-pin G. And it does not run with the NEW Lift Pump plugged in.
Click to expand...

OPEN THE FUEL FILTER BLEEDER, and jump the lift pump, tell us what happens.

Perhaps if nothing happens the wiring to the LP has been damaged.

IF nothing hapens by jumping the batt-pin LP method. Give the LP direct 12v and see what happens out of the fuel filter bleeder, when its open of course.
 
Also check the cables around the LP. Make sure it is not chaffed.

There was somebody recently with a non running new LP. Turns out his cable was bad. So it has unnecessary grounding.
 
Problem Solved

Got a new OPS and installed with new 92' LP and now gauge shows 7psi @idle. (also Oil Pressure went to the normal range 40-60)
The funny thing was that my autometer fuel pressure gauge took a dump too.

Buy AC Delco= Less Headaches THANKS ALL:grouphug: for the help to keep provin the naysayers wrong; and gettin those dirty cuimmins thoughts out of the head.

rockauto.com -great source
 
Just FYI the OPS is also your oil pressure sender unit for the guage.

If you want to jump the LP, like for draining water out of t-valve, you can put 12v battery to pin E of the LP relay harness, which if you unplug the harness is the middle contact closest to the firewall.

I think you have the same as me, on the passenger side firewall, the only relay there is for Lift Pump, and a lift pump fuse.
 
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