Isolated stall issue (not PMD)

[DennisG01]

Last night, the engine "slowly" stalled. Was driving about 20mph through the neighborhood and over the course of about 3 seconds, I started losing engine power and it then died. It did NOT turn off "like someone turned the key off". It was gradual. It took a few minutes, but I was eventually able to restart it. It stumbled a bit for a minute or two (every 10-15 seconds or so) and eventually cleared up and then drove just fine. I'll check the fuel filter, as my first thought was some type of fuel blockage... but if it was the filter, it wouldn't of cleared up on it's own, right? Maybe a piece of dirt caught somewhere else? Somewhere between the tank pickup and the filter? Just looking for any ideas/info that anyone might have.

[Warren96]

How about opening the bleeder on the filter and see if air comes out? An airleak can come and go! If you crawl under the truck can you smell fuel? Can you see oily spots near any of the fuel lines.......

[DennisG01]

Sorry Warren, I didn't initially see your response, even though I logged on yesterday and the say before.

I had another "stall-n-go" today so I logged on to explain it better and then saw your post. Earlier today, the engine idled fine in the driveway for about 5-10 minutes (went Christmas tree "hunting") and then took off with the family. The same as a few days ago, I got about 100 yards away from the house and the engine slowly died over the course of 3-5 seconds. After about a minute of intermittent cranking, it stumbled to life and had a few small hiccups over the course of a minute or so while I let it idle. After that, it was all good.

So, just now I went out to the truck (FYI, the lift pump runs nice and loud) and...

-- Checked fuel filter. A little brown, but not slimy or horrible. Noticed fuel was lower in the bowl than I expected, but I don't do this check every day so it might be hard to compare. Reinstalled filter.

-- Started the engine and opened the bleed valve slowly (with rags stuffed all around) a few turns. Nothing came out. Opened it more and more and still nothing (just about completely unscrewed at this point. After about 20 seconds the engine started to die out so I quickly reclosed the bleed valve, but the engine still died. Tried to restart with no luck. Tried more cranking than the other times but could not get it started.

-- Next, I removed the filter and jumped the lift pump and after about 30 seconds of watching for fuel to enter the bowl, nothing appeared.

-- I then had my son watch the bowl while I went under the truck and looked for anything obvious in the fuel line with the lift pump still jumped. Nothing that stood out at me.

-- I also could not find any indications of fuel leaking at the engine or in the lines coming from the tank. There are never any drips on the driveway and the frame rail is dry.

Question... Does the output side of the lift pump go directly to the filter bowl?

Question... Can a lift pump fail, but still make noise?

Oh... I did try a round of LP jumping with the fuel cap removed. No dice.

EDIT: Thought of something that might help. I totally spaced on this and forgot about it. Over the last few weeks, I've noticed that the LP (upon initial start, waiting for GP's to finish) sounded a little funny. Sort of "inconsistent" or "not constant" in it's sound over the 10-15 seconds of glow time. And, now that I think of it, I think the current sound that it's making - while very consistent/constant - is also louder than I'm used to hearing.

[DmaxMaverick]

Noisy pumps, even sounding "normal", can be bad. If the pump is running but no fuel is getting to the filter, either the pump is bad, there's a significant restriction, and/or a serious leak between the tank and lift pump.

There's nothing but fuel line between the lift pump and filter. If it leaked there, it would be messy, but it would still supply fuel to the filter (unless it was really bad, and you'd know that right away).

[DennisG01]

Am I thinking about this logically...

Given how/when the stall occurs, does it make sense that a failing/failed LP is more likely the culprit? I mean, if it was a major restriction, isn't it too much of a coincidence to have stalled twice within 100 yards (literally pulled over at EXACTLY the same spot in our neighborhood!) of driving after a warm-up in the driveway? There would of been enough fuel in the bowl to support what the IP needs at idle, but once I started demanding more fuel (driving), now the IP was starting to starve.

The other times that I've been driving, I haven't had anywhere near as long as a warm-up. From everything I've read, the IP can pull enough fuel on it's own (although it's not something you want to make a habit of). But, maybe at idle, it can't pull enough on it's own to keep the fuel bowl full.

I've seen AC Delco and Delphi LP's for $60-$80. As much as I'm not a fan of "throwing parts" at something to fix it, I think I will do just that. It's probably been 6 or 7 years since I last replaced the LP, anyways. Certainly would be a much easier/faster fix... and likely less $$ since I don't think I have the time to lower the tank from the Suburban on my own.

[DmaxMaverick]

I wouldn't call replacing the LP "throwing parts at it", unless you have some diagnostic evidence that it may be something else. The diagnostic result calls for it. There's more you can test, but the likely suspect is the LP, which will likely enter the picture in the very near future if it isn't the problem, this time.

At 6-7 years old, it's likely due for replacement. The IP can, and does, pull fuel and is able to run under light load with a bad LP. However, running the system under a suction condition will exploit any opportunity for an air leak (one that won't leak fuel under pressure). Many seals are designed to manage pressure in one direction, and often "leak" when in an opposite condition.

[DennisG01]

I wouldn't call replacing the LP "throwing parts at it", unless you have some diagnostic evidence that it may be something else.

Only that I didn't 100% eliminate all other variables. I suppose I could disconnect the pump on the tank side and see how easily the fuel flows out. FYI... when you replace the lift pump, don't do it with a full tank of gas and the vehicle parked with the back end higher than the front end. Figured that one out the last time I changed the LP...... a little bit too late..... :eek:

But, you're right, we're probably close enough and even if it turns out that the LP isn't the culprit, it's good PM.

With my vehicle (a Schoolcraft build, Kennedy ECM, playing with bigger turbos)... do you think it's worthwhile to get a Walbro FRC-10? It's not much more than a stock LP through Leroy Diesel. I know there's other options for LP's, but most of those are also a bigger jump in price that I don't want to do right now.

[DmaxMaverick]

Unless you have a specific need for greater fuel volume and/or pressure, I suggest staying with an OEM pump. They really are much more reliable than any aftermarket. Really.

[sctrailrider]

I think a fuel pressure gauge is in order, and a LP....

I like the FRC-10, I use it with my DB2 but I have a regulator to keep the psi at 8*... very handy to know when filters get dirty also....

[DennisG01]

I do have a fuel pressure gauge - not a permanent one. I just attach it to the fuel drain hose and then tape the gauge head to my lower windshield. Last time I checked, I was getting between 1-2psi at WOT. I think for now, I'll just get another AC Delco. I'll see what happens with these bigger turbos and tuning and then revisit this. I can always add the LP to the "spare" pile!

[DennisG01]

Stopped by NAPA on the way home today and picked up a LP. Took the old one off and diesel freely flowed from the tank-side line so there was no obstruction there. Popped the new LP in, went up to the filter bowl and powered up (remotely using that wire by the fuse box) the LP... and we're good to go! All is well again in 6.5 diesel world. Thanks guys!