What did I do wrong??

[Herman_Bolger]

I am getting ready put our 1993 dually back on the road shortly and in the process of doing a brake inspection , greasing the front end etc, we decided to change the fuel filter, we drove the truck into the shop, pulled the old filter off and put the new filter in, whent to try to start the truck and could not hear the lift pump come on?
maybe thinking it must have come on we started the truck and planned on bleeding the filter, it ran about 30 secs, then stalled. Tried again to hear the lift pump but could not, started the truck again ran for a bout 30 secs again stalled, did this about 3 times and finally had enough for today, finished painting the boat i was working on and went home.
Now when i go back to work tomorrow, what do i have to do so i can drive it out of the shop.

Thanks for any help, although i have had this truck for about a year(all my other dually's where gassers) i have not had to do any work on it. except for fun stuff like 4" exhaust, and an air ride suspension, but it allways ran after??

[MTTwister]

Did you get the new filter properly lined up? There's a recessed "keyway' for seating the filter.
2. did you open the filter air bleed screw and blead all the air?
3. I believe that on you year, '93? you can put the trans in "drive" ( Auto?) - anyway other than park or neutral, turn the iginiton key and you should be able to hear the lift pump run. That could eliminate that problem. Also helps to bleed the air out of the filter.

4. Sometimes coincidences happen - I'm sure someone else will have better suggestions.

Good luck

[bobt]

I have a '93 dually/auto and I've never heard the lift pump run when I turn the key on. I do hear the lift pump running when I shut the engine off after it has been running. It sounds to me like you didn't get the air immediately out of the filter housing. Getting it to run a couple more times should hopefully clear it up. If not, then oil pressure switch or lift pump may be culprit.
Bob

P.S. I've been a member since Mar 2000, but every time the fomat changes, I seem to start over listed as a "newbie"

[Bnave95]

This happened to me once also when I did'nt get the filter primed of all the air. It run as yours but stalled. Took a couple of time to get it running.
Thing is with the Elect. pump even after a injectors change you don't need to blead the injectors to get it running. Seeing how you have the Mech. injection you may need to bleed a couple of injectors to get the fuel flowing. Also I learned on my 95 I can turn key in drive to bleed filter. I like that.

[Hubert]

Any leaks? If no I would think seal is ok and or only further points to LP. If no positive pressure there might not be a leak.

You have to verify the LP is working and do the air purge on the filter after filter change.

The truck would probably work OK with a broke LP if fuel lines are leak and air free and filter is ok and fuel lines are not restricted. At least the electronic IP's do.

My LP broke once and I did not know it until I went to change the fuel filter and could not get fuel to flow out air purge step. I replaced LP before trying to start truck so I never had a problem.

[Herman_Bolger]

When I tried to bleed the filter, I had some fuel come out then truck stalled, I restarted the truck and opened the top of the filter, but could not get any fuel to come out again.
I did notice that the filter only fits one way, that took a few minutes to figure but we did figure that one, put new one in put lock ring on, does not seem to leak. did not have time to look at it today, but will tomorrow.
So I take it that the air will bleed out eventually by it self? Should I hear the lift pump run when I turn the key on in park, or only in drive? If I unplug the pump when should the be power there, to check with a test light?

Thanks

[Hubert]

1) Near the last step of fuel filter change is to power the LP and open bleeder valve at top to burp majority of air out of filter bowl and fuel lines from tank to bleeder. How did you do this? Some jump power to the fuse for LP I think yours you could put in drive and try and start engine. The safety neutral switch wont fire starter but LP will power up. Its better not to try to crank it until majority of air is "burbed". Fuel/air should spurt then flow out of valve then close it. It really helps to have a friend doing this if you use the key method. I spill fuel jumping out and running to shut bleeder valve.

The LP logic differs for some years maybe someone will confirm this. Yours it should power up with key on cranking/and or maybe when in drive key on run. Initially it will power LP for a few seconds. Then the oil pressure switch if it does not sense oil pressure will open the circuit.

Sounds like maybe your second attempt at bleeding air the LP was not powered due maybe to oil pressure switch not sensing oil pressure (The initial LP power on only lasts 5-10 seconds or so) or you weren't using the right trick to power it. Then when you opened air bleeder the second time you let fuel draining back to tank siphon more air into filter bowl making the problem worse.

IMHO You should NOT follow the GM instructions of pulling out old filter and dropping in new one. It allows a little dirty fuel to IP side of the new filter. You should clean out filter bowl and put in new fitler dry then purge air good before cranking.

There are several threads on changing filter and one just recent specifically on this.

[JohnC]

Fool proof way to power the lift pump:

Find red wire in one of the left hand corners of the ALDL plug under the dash. Apply 12 volts. Pump should run.

Once you have purged the air, start the truck. Open the vent on the filter. If fuel comes out and engine keeps running, the lift pump is running (powered by oil pressure switch).

Lastly, open vent and crank engine. If fuel comes out, cranking circuit for lift pump is working (powered by lift pump relay).

I'm not sure if the '93 pump will run with shifter in drive and key to start.

[Herman_Bolger]

Thank you,

We managed to get the lp powered up and you were right, spilt fuel over the top of the engine, but at least we have it running now. I did not realize that changeing a fuel filter was a 2 person ordeal.
Well it's done now and everything seems to be working fine. Judgeing from the look of the old filter it had not been changed in a while, this should be good for the year. I am looking into putting an inline spin on canister type filter in front of the factory one, later.

Thanks for the help

Herman

[moondoggie]

Good Day!

"I'm not sure if the '93 pump will run with shifter in drive and key to start." I started a topic about this a year or so ago. From the feedback I got, the 95's are the only year where this works.

Blessings!

[JohnC]

Good Day!

From the feedback I got, the 95's are the only year where this works.


My '93 was a standard and it did not work (start without depressing the clutch). However, the pump runs while cranking so you can purge the filter enough while cranking to get it running, then bleed the filter while it runs. This presumes the lift pump works correctly.

[moondoggie]

Good Day!

What I find really handy about this anomoly my 95's have is that I can test the lift pump system in cranking mode without actually cranking the engine. I find this much preferable to the alternatives that are unfortunately not available to non-95 truck owners. As much money as I've spent on starters for these 6.2/6.5 engines over the years, eliminating even a little cranking time makes me happy.

I still have to test running mode with the engine running, but that's quite easy.

Blessings!

(signature in previous post)

[RT]

There is an even easier way to power up the lift pump. There is a plastic cover on the firewall to the left of the fuel filter (passenger side) Remove the (3) plastic retaining nuts and pull the cover off. There will be a standard automotive fuse in an inline holder inside. There is also a positive, always hot stud under the cover. Touch the top exposed section of the fuse to the edge of the stud and the lift pump will power up. I open the bleeder on the filter and power up the LP until it spits fuel. Then close the bleeder and the truck will start and run normally. Thats how it works on my 93.... RT