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Testing lift pump.....

Odlaw

Odlaw

Redneck
Messages
577
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40
Location
Deep in the woods - near Waldo, FL
I'll be replacing my lift pump and finally getting new injectors - my originals only lasted 178k miles..:smile5:

I noticed when I shut the truck off last week I didn't hear the familiar hum of the lift pump. Not really thinking much about it at the time, the next morning I tried to start the ole girl and she didn't just bust right off like normal. I had to bump the starter about three times and then she cranked, idled a little rough, and the RPM's went up from 700 to about 900 until the idle smoothed out then it dropped back down to 700. I shut it off, and no lift pump hum again...so, I jumped 12v to pin G(IIRC) on the OBDI port and still no lift pump. I just did this a couple of weeks ago because I thought the pump was starting to sound 'weaker" and it would run.
Finally, my question. By jumping 12v to pin G is that bypassing the relay (I'm guessing there is a relay) and putting power straight to the pump or do I need to troubleshoot both the pump and the relay?

Thanks
Smitty
 
Do you have a dedicated/separated fuel pump relay on the passenger side firewall? I have jumpered the lift pump by putting 12v to the pin E on the harness, which is the center pin of the connector closest to the firewall.

If the pump works when you do that then your OPS must have failed. Usually there is oil pressure in the switch after the truck turns off so it keeps running after you shut down, so there is fuel pressure waiting in the morning. The lift pump otherwise is powered by the firewall relay when cranking which doesnt help a whole lot if your truck fires up quick because of the fuel pressure the OPS left after shut down, but is better on OBD-II where it turns lift pump on with the ignition when the PCM is powered on, before cranking.
 
Rule out the relay first. I replaced the pump on my 92 and it was the rely that was shot.Ops isn't as failure prone as newer trucks.
 
You have to open the t-valve after the jump and see if there is any fuel. If not, the LP is bad.

In a 95, relay is not a big factor as in 96+. It is mostly the LP and OPS. If you have a new Delco OPS, chances are your LP is bad.
 
..having just discovered that my six month old Carter replacement pump is now dead..:mad2:
Have you got a test light? I crawled under the truck and put the test light on the wire to the pump because I thought my OPS was going bad. Got a good bright light (power to the pump) but no pumping.

The diesel gods are telling me I needed a Walbro FRB-5 to begin with. Now go buy one! :nono:

Mike
 
How many wires are coming out of the lift pump relay? I pulled the cover on the firewall and all thats under there (left to right) Fuel pump fuse, terminal block, and a huge relay. The cover is labeled (left to right) Ground, Fuel pump fuse, terminal block, fuel pump relay, optional relay and ground. The relay thats under there has 5 wires coming out of it and does NOT look like the replacement relays I've seen on some of the supporting vendors websites.

BTW the fuse was blown and I connected a circuit breaker type fuse to it for testing and the pump will not run. I only left it plugged in for about 2 minutes and it didn't trip. Still need to crawl under the truck and make sure there is power at the pump......it's been wet here and I need to find me a redneck creeper (cardboard).
 
That huge relay is the correct one with 5 wires, make sure your circuit breaker fuse has continuity with a multmeter or test light. I figured you knew to open the T-valve to see fuel pumping, thats why I jumper at the relay to watch the fuel pump out into a jar to check for water. You should do that at least with oil changes.

So putting 12v from the battery to the middle pin of the connector towards the firewall that goes to relay pin E should make the fuel come out with an open T-valve
 
Thanks guys. Great info.
TD, I'm guessing that when you were very young, you were one of those kids that couldn't help but dissemble everything you laid hands on. :D
....I'm very glad you continue to do so. very informative!

I noticed that the relay was not OEM brand....then I remembered a box of crap I cleaned out of the truck a couple of years ago when I purchased it from my uncle....guess what? a couple of spare relays new in the box and one of them is a lift pump relay. yea!

I ordered my new injectors, air intake, and HD lift pump from one of the supporting vendors today.....man I hate waiting on UPS ground shipping.....and I'm too cheap to pay for anything else.

Thanks again guys.
Smitty

EDIT: I stand corrected......well I least I think so, not sure if I purchased from a site vendor or not.....

I must be blind because I can't find a link to see 'who' the vendors are for DTR.
 
Last edited:
Odlaw said:
Thanks guys. Great info.
TD, I'm guessing that when you were very young, you were one of those kids that couldn't help but dissemble everything you laid hands on. :D
....I'm very glad you continue to do so. very informative!
Click to expand...

You been talking to my mom ???? :D sometimes stuff still worked when I put it back together, but then again times it didn't :eek:, but I learned from those experiences what not to do the next time :mad2:
 
Does that mean your relay wasnt working before, did you try jumpering it?

You came to the conclusion the LP was just broke?

Alls TDs thread needs is pictures of LP relays and fuses like ours. Maybe I'll do that when it stops raining.
 
buddy said:
Does that mean your relay wasnt working before, did you try jumpering it? Yes, I jumped the relay - still, pump would not run.

You came to the conclusion the LP was just broke? yes

Alls TDs thread needs is pictures of LP relays and fuses like ours. Maybe I'll do that when it stops raining.
Click to expand...

I replaced the relay today just as a precaution - supposedly, it's highly recommended to swap the relay when you replace the LP. The lift pump is the original with almost 180k miles on it.
 
I think it is wise to replace the relay and LP at the same time especially after 180K. When I bought mine, it was already on the way out and it only has half of your mileage.
 
Well, there is another way to tell if your LP is bad...if you loosen the clamp that holds it to the frame rail...and as soon as it is loose enough to separate from the pump...and you smell some awful, burnt, stinch.....your pump is probably hosed. No wonder it blew a fuse. Check out the picture. I thought I was going to have to throw away the shirt I was wearing....even after washing it I can still smell the burnt dielectric goop.

picture.php
 
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