Stumbling and loss of power on the highway

[spark3542]

A question for all the diesel wizards.

I've owned my diesel for about a month now, so I'm still very new to diesel operation.

I'm making my own homebrew biodiesel, and have put about 28 gallons of the stuff in it over the course of the last two weeks (yes, I know... recipe for disaster)

It ran fine for about 400 miles, then all of a sudden it coughs and sputters when I'm up on the highway doing about 70 (2500 rpm). I move over to the shoulder and find that I can maintain about 42 mph, so I limp on to the next exit. (idle is smooth, but motor just didn't seem to have any power)

I'm assuming fuel filter is clogged, since I was told this is the first thing that will happen as biodiesel cleans the lines. I carry a spare filter, so I swapped it out. I don't have the appropriate knowledge or tools to purge the air from the lines, so I made sure the filter cup still had as much fuel as possible when I inserted the new one.

It took maybe an extra two seconds of cranking and the engine fired right up and idled smoothly. I jumped back on the highway, and went smoothly for about 10 miles, then stumbled in an identical fashion. I once again limped to the next exit, found a diesel station, and topped off the tank with 15 gallons of petroleum diesel, figuring a blend should only improve things. It didn't. The truck continued to stumble and not exceed 40-50 mph the entire 40 miles home.

After I let the truck sit for a few hours, I started it. It started, then ran VERY loudly for about 4 seconds, and quieted back down.

The SES light is on, and I haven't procured a code reader yet, so I'm still in the dark. Upon initial turning of the key, I see the water-in-fuel light during the test cycle, so I know the bulb is good, but that light has never come on during this entire time.

My questions: Do the symptoms sound like water in the fuel, poor quality fuel, air getting into the system somehow?

The engine running extremely loud at times...what is that an indication of?

Have I done any permanent damage by not properly purging air?

Thanks for your help.

Mark in MA

[brianblack138]

First off, i'm assuming you have a 6.5, but what year is it? Any specific information about the IP?

The first thing I would do is install a pressure gauge and a clear glass sight valve before the IP. I run WVO and I did this to make sure the fuel is at the right pressure (4-5psi) and is clear with no air leaks. If you are at a really low pressure, it's likely a clogged fuel filter or bad lift pump. Make sure the sight valve is one that has an inline filter in it, since as you said the biodiesel will act as a detergent and clean out your lines and you don't want any gunk or degrading pieces of fuel line getting into your IP. The second thing I would do is test the lift pump to make sure it is running.

As far as the check engine light, i'd be curious to see what the codes are... if it is an older 6.5 (mine is a 94) you can do the paperclip trick (just do a search of the forums for reading codes and you'll see what I mean) and then write down the codes (each code will repeat three times) and post them on here.

With the biodiesel, do you generally get a pretty clear liquid or is it foggy? Do you make sure the water has settled out or somehow dry the fuel? I don't know too much about biodiesel since I just use WVO but it would seem to me that you would want to treat it pretty much the same way when it comes to getting the water out.

As far as bleeding the air out, you don't need any special tools. When you replace the filter, just loosen the plastic "cap" on top and turn the ignition a couple of times. You should start to see diesel coming out of the hole in this cap. Screw the cap down tight and the diesel will stop coming out. You've just successfully bled the air out of the filter cup that got in when you changed the filter (tada!). As far as draining the water and sediment from the bottom of the filter cup, just open the petcock for the fuel drain line (located next to the water-neck on the thermostat housing) and start the engine (after putting a bucket under the truck to catch the fuel/water/gunk that comes out) let a bit of fuel run out and then tighten the petcock up. Go back to the cab and make sure the "water in fuel" light is now off.

[spark3542]

Thanks for the info, and sorry for not providing the background info. I have a 97 Suburban k2500, and was disappointed when I found out I can't read the codes by shorting the connector (which I could on my 93 gasser).

I read a little on the lift pump in my Haynes manual, but it was somewhat vague. Do I have an electric or mechanical lift pump?

Could a bad lift pump be causing the 'starvation' and I don't, in fact, have a fuel problem at all?

The first batch of BD was clear and I had no problems. The second batch was thoroughly washed, but perhaps not dried completely, because it was slightly cloudy. That's why I was quick to assume fuel was the culprit.

There's a brass valve with a small t-handle near the front top of the engine. Is this the petcock for water in the filter cup?

When I began troubleshooting, I took the new fuel filter out, sucked out everything that was in the cup, and put it in a glass jar to examine it. A fair amount of dirt/rust/particulates in the bottom, and perhaps 1/4 to 1/2oz of water in the bottom of the jar with about 10oz of fuel.

Again, I never got a water-in-fuel message. Should I assume the water sensors are working or should I assume otherwise?

Thanks

Mark in MA

[brianblack138]

You have an electric IP and the lift pump is electric as well. That brass T handle is the petcock i was talking about. The dirt/rust/particles are normal (that is what the filter is there to stop) and you probably just didn't have enough water to trigger the water in fuel sensor (if you hadn't cleaned it out, it would eventually fill up with enough water to trigger the sensor).

I would run on petro for a while and see if that fixes the problem. If it does, then you know it was bad fuel. If you are still getting the same results, then it isn't the fuel. (I'd still put in the sight valve and the pressure gauge since they cost about 25 bucks and are well worth it)

[BrentN]

Sparks,
Go to an Autozone if you have one close by. They will read your codes for you. Just write them down and then consult the code list.

If you just bought this diesel recently, dont rule out that you have have a PMD starting to go. But I have found on mine that all it takes is one load of questionable fuel to plug up that filter and cause a stumbling issue. Definately check your pressure as suggested and your filter. If you are running Bio or WVO as I intend to shortly, having a prefilter would be a good idea since our filters on the engine arent very cheap.

Good luck.

[spark3542]

Alright,
At the risk of sounding like an idiot, what does PMD stand for? I did a search on it, and found lots of conversation about it, but can't find anyone with a definition.

Thanks

Mark in MA

[DmaxMaverick]

PMD = Pump Mounted Driver. It is the FSD (Fuel Solenoid Driver), if it is mounted on the IP (Injection Pump).

Have look at THIS (http://www.thedieselpageforums.com/tdpforum/showthread.php?t=20598) thread for other abbrev.

[TJ Moose]

Bill Heath at Heath Diesel (heathdiesel.com) also has a blog on his site with general info and discussion of why it matters. PMD (pump mounted driver) discussed there along with other good info. Sure - Bill uses the info to sell stuff - but why not? Everything I've bought from him has worked like a charm.