L300 fuel pump failure?

blackbrent · Post by **blackbrent** » Sun Jun 21, 2020 7:51 am

Hi folks, this is my first post so please forgive any error in format.

I'm having trouble on starting my '92 L300 (4D56) turbo diesel automatic. The vehicle is always on block heater when parked and up until recently would turn over with virtually no cranking / minimal cranking. A few months ago I noticed some diesel dripping from the front fuel tank but didn't deal with the problem immediately. Eventually the fuel leak got worse until this past week I patched the tank with steel reinforced epoxy - no more leak. Because of the leak (which was on the top side of the tank) I had been keeping minimal fuel on board and letting the tanks get quite low. I'm also someone who for years has been driving till empty / till fuel light is on, which I know can be hard on fuel pumps. Just before I did the tank repair last week the motor was idling low then dying at stop lights (electrical still working) and becoming increasingly hard to get started - having to crank way more than usual.

Now here's my question / problem : Since patching my tank I've noticed I have to crank quite a bit to get the motor to turn over. Even if the van has been sitting for a few minutes or hours it doesn't seem to be holding fuel pressure or feeding the motor as needed on startup. I have to crank it much more than previously even when on block heater (it's summer now, plugs replaced less than a year ago). I'm thinking the extra abuse I've likely put on the fuel delivery system because of the leaky tank with low pressure and low fuel has strained the diesel fuel injector pump or some other part and I'm trying to narrow it down. In looking at the pump /schematic of the pump itself I'm thinking it could be the issue. I've taken the pump out a few times previously to fit new filters and I can definitely replace the pump myself. I guess what I want to know is : what is it exactly that 'pulls' fuel from the tank to the injector? And : can the fuel pump fail? In looking at it I have a hard time understanding what could cause it to fail, maybe I just don't understand how it draws fuel from the tank. I don't want to spend the money / time on a replacement if I should be looking elsewhere. Is there a way to test for fuel pressure before/at/after the diesel fuel pump? Is there something I should be troubleshooting at the injector? The van runs perfectly once started, no longer dies on me or idles low, patching the tank solved that.

For now I'm going to keep the fuel tanks as full as I can to see if having tank pressure helps on starting. I've always noticed the van is sluggish on hill climbing and am thinking maybe the pump has been dying for some time and is just done. Given how simple the design is - would that be likely / possible? It looks original, so that's almost 30 years.

Any assistance or experience with diagnosing L300 fuel pressure / fuel pump issues is hugely appreciated.

sk66 · Post by **sk66** » Mon Jun 22, 2020 5:56 am

I think there's an error in there somewhere... no-one in their right mind would pull the injector pump in order to change the fuel filter. I think what you are meaning is the priming pump on the fuel filter mount.
The injector pump is next to the engine and connected to it by a pulley/belt and hard pipes to the injectors. It is what pulls fuel from the tank and sends it to the injectors under high pressure. And I highly doubt that you have strained/hurt it unless you've run it dry.

IMO, the most probable issue is a restriction, especially if the tank was open to gathering additional crap. I would start with the easier things. Replace the fuel filter, and check the injection pump inlet/outlet screens in the banjo bolts (may have one or both). If you don't find/fix the issue there, then I would probably guess the pickup screen inside the tank; which can be pulled/cleaned.

Actually, before doing any of those things you might want to crack an injector and see just what kind of fuel flow/pressure you are actually getting. You can also run the IP inlet line directly to a fuel can; that will isolate the fuel filter and pickup screen/plumbing and give you an idea if the issue is before/after the IP inlet.

helibrian · Post by **helibrian** » Tue Jun 23, 2020 9:46 am

Could be your rubber fuel lines. Sounds like your loosing prime.

blackbrent · Post by **blackbrent** » Tue Jul 07, 2020 1:38 am

Ok, so I've done a bit of narrowing down the past few days but still looking for suggestions or thoughts.

I checked both banjo bolts / screen filters on the injection pump and they were clean as a whistle. Decided to isolate the fuel injector pump and injectors to test them independent of the tanks / fuel filter. I ran straight Seafoam motor treatment directly into the injection pump and cycled it back through the tank return line to my supply bottle containing the Seafoam. Ran for about an hour total - no gunk, debris, discoloration was visible and the motor ran perfectly. No hunting, stumbling, hard starts - nothing unusual. In fact the tach stayed pinned steady to where I had it set to idle, van turned over first turn of the key every time. So I think it's safe to say that my issue is back of the IP / injectors.

swapped out the old fuel filter for a new one, just to be safe. the old one was 1 year old but looked totally fine. I run seafoam treatment from time to time, occasionally add lucas injector cleaner and habitually run Shell 'V-Power' diesel with higher cetane. Seems to be keeping everything clean so far, makes for easier starts in winter and generally better performance.

I moved on from the fuel filter to the fuel tanks/lines to have a look and diagnose. Drained both tanks and got an inspection camera inside the rear tank to check the condition of my pickup screen. It's spotless, no buildup whatsoever. checked the condition of my fuel lines. They're not new but they don't leak. I'm considering swapping them out if my issue persists. As of now the van is hard starting - unpredictably (sometimes turns over first kick, sometimes a few seconds of cranking, sometimes takes 3 tries to get it to turn over - even if the engine is warm or has just finished running and I start up again just to test). Also stumbles while idling (when drawing fuel from the tanks) and will often idle so low that it dies at stop lights or when I decelerate - especially if I've just accelerated and then backed off. None of this happens when the tanks are full to the top with fuel, symptoms start around 3/4 full and get progressively worse as fuel levels drop from driving. Drives fine, just has trouble starting / decelerating / idling when fuel goes below 3/4.

I got the inspection camera up around the back/top of the rear fuel tank and noticed quite a bit of corrosion on the metal lines coming out of the top of the tank - from what I understand these are the return lines from the injector pump and the line that feeds to the fuel filter housing mounted in the engine bay. I feel like whatever I do I'm going to have to deal with the corrosion I see either now or later, it's eating away quite a bit of material.

Am I missing something obvious here? Is there any way to test for air leaks? Should I just go ahead and swap out these fuel lines? I had removed those lines and refit them just prior to this stumbling/hard starting issue beginning and I'm starting to think they need replacing. Would worn our fuel lines make sense given what I'm describing?

Looking at the corrosion on these tanks I feel like they're going to need replacement / refurb sooner than later. Would that corrosion on the lines feeding my fuel lines be the culprit? letting air in? I guess I can put clear lines on there and just watch what happens, but also open to other suggestions/ideas/experiences. The tanks don't leak, all the filters are clean and everything runs fine ahead of the fuel filter. really want to nail this down and get back to having confidence on longer hauls.

deskinthewoods · Post by **deskinthewoods** » Tue Jul 07, 2020 3:37 am

It's easy enough to put a clear tube between the fuel filter and the IP and see if you have any bubbles...

blackbrent · Post by **blackbrent** » Tue Jul 07, 2020 5:47 am

deskinthewoods wrote: ↑Tue Jul 07, 2020 3:37 am It's easy enough to put a clear tube between the fuel filter and the IP and see if you have any bubbles...

Yeah that's my next try. I'll give it a go in the next few days.

blackbrent · Post by **blackbrent** » Fri Jul 10, 2020 10:14 pm

Alright so I tested each segment of fuel line to figure out where it was suckling in air. Using clear vinyl line it wasn't hard to find where the issue starts - at the rear fuel tank where the top of the screen filter / outlet assembly meets the fuel line supply to the filter housing / injector pump.

I've attached a screen shot from a video below, the fuel supply is about half full of air.

The top of that tank and outlet assembly is wretchedly inaccessible without dropping the tank. I've done my best to clean up the area for now and am going to try patching the metal outlet line with Permatex fuel tank epoxy. Has anyone got a part number for that outlet assembly? Current price from CCA is $300.94 and its back ordered a month. Here's a link to the part I need - photo attached. Would love to source it elsewhere for cheaper and / or faster!

http://www.ccautos.ca/l300-auto-rear-fu ... uine-part/

Ralph in Winnipeg · Post by **Ralph in Winnipeg** » Sat Jul 11, 2020 9:49 am

If you have the part number try partsouq or amayama.

blackbrent · Post by **blackbrent** » Sat Jul 11, 2020 4:38 pm

Ralph in Winnipeg wrote: ↑Sat Jul 11, 2020 9:49 am If you have the part number try partsouq or amayama.

I don't have the part number, am hoping someone here has it.

blackbrent · Post by **blackbrent** » Sat Jul 11, 2020 7:14 pm

Update: I used 2 sticks of Permatex 'ethanol resistant' Fuel Tank Repair to cover that outlet line from the back tank feeding my fuel line - finished applying it before 9am and just took a 1hr drive now - no issues. Considering I had the sketchiest drive of my life earlier today (van died 3 times in town, in a roundabout and on highway) I'd say I'm confident I've found the issue. Going to keep watch on that patch job, and probably try to source a new filter/outlet assembly for a late summer fuel tank drop & refurb.

deskinthewoods · Post by **deskinthewoods** » Sun Jul 12, 2020 4:26 am

Yay!!!