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Possible lift pump issue -or something else ?

Danish Farmer

Danish Farmer

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Location
Denmark, Europe
My Silverado 1995 needs long cranking before starting up, and during acceleration it is lacking power, and stalls lightly, until the throttle is raised. It usually does not stall totally. Problem has gotten worser in a month, and here is what I have done so far.

-New fuel filter + cleaned the little filter screen in FFM
-Tigthned clamps on fuel lines under the FFM
-Replaced glows
-Injector cleaner in fueltank
-New PMD (Stanadyne on intake with heat zink)
-Cleaned four grounds so far
-Checked connections on OPS (looked good) Guage works, Power on orange vire.
-Checked fuses
-Now running the LP constantly with a bypass-wire
(LP Sounds loud the first seconds when been sitting for 15 minutes or more, and I seem to be able to bleed a little air from FFM every hour of sitting) -and IP sounds a little harder (Knucking) at idling when first started up.

I got a good stream of fuel on the FFM bleed valve ideling, and a stream from the t-valve.
No fuel leaks on the floor but some "sweat" arround some fuel lines under FFM
Engine RPM tends to switch rapidly between 900 and 600 a couple of times every time I move my foot from the trottle, going on the road.

Truck has been siting for two years at the former ovner, but ran ok for a week.

Folks, please help me being a new Silverado-ovner in a country with almost no US trucks. :)

Great forum, and thank you
Max Madsen from Denmark
 
Allright, I will inspect fuel lines from tank when i mount my new LP, and try to mount some clear tubing under FFM when i replace my oil pressure switch. Hope this operation will take me a step closer to the problem
 
Check the OPS instead of the LP. OPS can show Oil Pressure but the part that control the LP is bad.
When bad, LP will not run when engine is running. Test it properly.

When replacing OPS, make sure you get the ACDelco OPS.

Do a load test on the batteries one at a time.
 
Something else to consider doing is moving the PMD to the front bumper. Right now its in the worst place you can have it.
A fried PMD can show all kinds of symtoms, do you have another to try?
Have you checked fuel pressure while driving?
 
Hi folks

Thanks for your advice.
The OPS did nok look bad on the terminals, but I figured ordering a new one and a new LP to eliminate another two issues. (LP had a quite loud ticking at some points)
Will mount the things today, hoping that the LP will run allright when engine is running.
Guess that I will take off the tank, to clean it, and maybe to inspect fuel lines pre to the LP.

Vail 426---Its very easy to keep the needle steady at 2000 rpm. No have not put a guage on the fuel line
Burning Oli--- Yes I allready put on a new PMD which did not change anything.
 
She´s running :)

When i got things enough apart to reach the OPS for my replace, i figured raise the FFM like I have seen in this forum. Doing that i renewed the fuel lines and put in a clear one from FFM to IP.
Cleaned another two grounds, so like the big vire connector plugs behind FFM.
Had to try her before mounting the new LP, and she started right up after bleading FFM.
There were no bubbles in the clear tube, and she did not stall or misfire during hard acceleration.
Think my problem is solved, but don´t exactly know what was wrong. Maybe the old hose clamps were bad.

Anyway, I cut a hole in the bed to raise the fuel suction and inspect the tank, but lines looks so rusty and bad that I wont do that before i get a new top with lines ordered. Then I will replace it, and replace fuel lines at the frame with new rubber until the LP, and replace that with the new one.

One thing left to do is to measure if the new OPS deliver power to the LP. Until the still running the old LP with a bypass.

Thanks for your reply, and I can not believe how much I have learned about that truck from goint thru the 6,5 forum on this page. ;0) A V E some ;-)
 
Unfortunately she´s still not running perfect.

I got my new tank suction element mountet, cleaned the tank, and renewed hoses all the way forward until the LP. Put on the new LP too.

Truck still needs little longer cranking than normal, and after it´s been sitting thru the night, there is a four inches long area with no fuel in the tube from the FFM to IP. I guess it explains some, but where does it come in ? I can keep on bleeding but when it runs there is only clean fuel coming out.

While running there is no air in the line, but she will still misfire every now and the under acceleration.

Do you gyes have any more hints ?

--Could the diesel selinoid have a leak so it does empty the pump over night and cause slow start ?

--and what about EGR issues maybe?
A sticker tells it has EGR- but where are the lines from the exhaust to the inlet manifold ? Could a cloged up sensor or manifold make things act like this ? I dont see that mentioned much here, but I know that on newer tractors and many other cars they will cause troubles.

Thanks
 
Welcome to TTS!

Check the LP lines to the FFM. The FFM also has 2 O rings that should be checked. 1 is the water in fuel sensor the other at the bottom of the FFM is the heater.

Connections at the LP & the FFM. Clear tubing on the IP return line is helpful to determine if the IP is getting air bound after setting a while. This is the small hose that runs from the IP to the common rail that returns fuel from the injectors.

HTH's
 
If its still slugish/misfireing usually its fuel delivery. Do you have a scan tool? What year truck is it, don't remember if you said.
Have you checked fuel pressure while driving? The LP should give a possitive pressure at all times except maybe at WOT.
 
Check Engine light is not on. Is´s a 1995. Yes I just purchased a fuel pressure tester, but explored something this morning studying the diesel in the clear line between the FFM and IP before firing her up.
I saw lines of tiny small bubbles constantly mowing in the line from the FFM towards the IP.

Bying hoses to replace lines between FFM and LP, and trying to replace the O-rings in the FFM that crankme69 suggest. Hoping that I am getting close to where my problem is. Do you think so ?
 
If you are getting streams of bubbles in the fuel, it has to be coming from aft of the Lift pump.

Check all steel lines for issues.

As mentioned, replace the O ring on the inlet side of the LP.

If you still have issues, plug the line at the inlet to the LP and then lightlly pressurize the tank and look for leaks.

The FFM is under pressure so even if there is a leak it should leak fuel OUT.

Now, there can be an exception and this would be that the FFM is leaking some and allowing air to enter the system, then when you fire it up the air bubbles show up.

The FFM units have a bad habit of rotting out in the lower portion where the heater is.

Replacing the FFM with Racor is a good idea. I use a Racor 230R2 unit on my 95.

Made a little bracket that bolts to the same holes as the ABS (front bolts) and the filter sits right there in easy reach and can be serviced easily too.

These units use a spin on filter with a see through bowl on the bottom.

A very small amount of air can drive these things nuts.

Good luck

Missy
 
Our 95 Tahoe seems to be only having issues when parked nose up on the slope in front of our house.

Does anything about that make any sense or indicate where it's leaking from?
 
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