Loss of power...briefly

[boneheaddoctor]

Here is situation. 1979 300SD W116, if I drive 60mph or more I abruptly lose power where I can barely maintain 50-55mph. this occurs about ever 10-15 minutes. if I pull over and let car idle a minute or three I can pull away with full power for another 10-15 minutes. Like there is a fuel restriction. But main filter has 8,000 miles on it, just replaced the prefilter because it looked dark. Turns out it was dirty outside clean inside. I did a shock of BioBor a week ago, no change, zero debriss making it to pre filter.

Tomorrow I will drive without cap on tank to prove its not a tank vent issue.

Any ideas. I though if it was algea I would get debris at prefilter. Car runs wonderful outside of this.

This started abruptly a week ago and I see no signs of an air leak.

sounds like algae in the tank strainer, if you pump the hand primer pump quickly does it pull back down? the algae creates a vacuum on the hand pump
which is a good indicator if it is plugged.
Ray
mercedessd@cox.net

[boneheaddoctor]

Originally Posted by carson356

sounds like algae in the tank strainer, if you pump the hand primer pump quickly does it pull back down? the algae creates a vacuum on the hand pump
which is a good indicator if it is plugged.
Ray
mercedessd@cox.net

I'll give that a try tomorrow afternoon. Too dark outside right now. I had assumed if I had algea I would see signs in the prefilter. Filter and fuel are very clear, but yes it does seem like its burning more fuel than it can pump at 60+ mph, and it sucks the main filter dry and untill it fills it up it gets only enough to maintain about 50 on level road.

It occures very suddenly its not a gradual loss. I'll let you know if the primer sees a restriction in the manner you said.

[JamesStein]

This could also be an air leak under high demand. I.e. a leak not visible at idle, but only under high fuel loads.

At idle the engine isn't demanding a whole lot of fuel. So any air in the system is purged through the return line to your tank. Which would explain why idling seems to temporarily fix the problem. As you get up to speed, eventually your fuel demand will start sucking air through a leaky connection somewhere that eventually increases until you don't have enough fuel to systain the demand of the engine.

My wifes WVO burner was having this problem. I tightened all the clamps on the fuel lines and the problem went away.

[boneheaddoctor]

Originally Posted by JamesStein

This could also be an air leak under high demand. I.e. a leak not visible at idle, but only under high fuel loads.

At idle the engine isn't demanding a whole lot of fuel. So any air in the system is purged through the return line to your tank. Which would explain why idling seems to temporarily fix the problem. As you get up to speed, eventually your fuel demand will start sucking air through a leaky connection somewhere that eventually increases until you don't have enough fuel to systain the demand of the engine.

My wifes WVO burner was having this problem. I tightened all the clamps on the fuel lines and the problem went away.

Well I will look closely at all connections again very closely tomorrow when I get home from work. Including looking at the rubber lines for any age related cracks.

[Brian Carlton]

I think that you have no choice, at this point, but to change the secondary. To simply guess that it is OK when you have a fuel delivery problem is not acceptable. 10 minutes and $10. rules it out.

I had the SDL missing on the highway, like a gas engine. Most thought it was the tank filter. Well, I was not about to change the tank filter unless I was at the end of my options. Primary and secondary and the problem was eliminated.

[Palangi]

I have been dealing with algae on one of mine for the last few months. I would say that if you have algae it is almost guaranteed that you will see it in the prefilter. I am currently running a paper element prefilter ahead of the regular prefilter, and it plugs with black crap in about 600 miles.

This may sound kinda obscure, but it's easy to check. Make sure the hood pad isn't coming loose and squeezing the crankcase ventilation hose.

[boneheaddoctor]

Originally Posted by Palangi

I have been dealing with algae on one of mine for the last few months. I would say that if you have algae it is almost guaranteed that you will see it in the prefilter. I am currently running a paper element prefilter ahead of the regular prefilter, and it plugs with black crap in about 600 miles.

This may sound kinda obscure, but it's easy to check. Make sure the hood pad isn't coming loose and squeezing the crankcase ventilation hose.

Its positively not that Hood pad is tight and was new last year, lines from that to a oil seperator and back to the turbo are new.

There is not so much as a single dark fleck in the prefilter. And fuel is quite clear.

[boneheaddoctor]

Originally Posted by Brian Carlton

I think that you have no choice, at this point, but to change the secondary. To simply guess that it is OK when you have a fuel delivery problem is not acceptable. 10 minutes and $10. rules it out.

I had the SDL missing on the highway, like a gas engine. Most thought it was the tank filter. Well, I was not about to change the tank filter unless I was at the end of my options. Primary and secondary and the problem was eliminated.

Well, if I find no loose conections, no cracked rubber lines and driving it to office without the fuel cap doesn't solve it I will replace the secondary filter too. This is agrivating..........

It doesn't miss, just has an abrupt loss of power every ten minutes of 60+ MPH driving. Only resolved by slowing down a LOT or stopping with motor running, then its fine for another 10 minutes. Power loss is steady as long as I keep going and don't do anything.

[Palangi]

Any chance of a dragging alternator, water pump, A/C compressor, etc?

Leaky primer pump? Dying lift pump?

[boneheaddoctor]

Originally Posted by Palangi

Any chance of a dragging alternator, water pump, A/C compressor, etc?

Leaky primer pump? Dying lift pump?

A/C = nope its off. Not hot or damp enough to turn it on.

Alternator = no symptoms are totally against that.

Water pump = Again no, no coolant leaks and its new less than 3,000 miles ago.

Primer pump = ? hasn't been disturbed since I bought the car so who knows.

Lift pump = ????????? I would think it would be more constant. But its not beyond the scope of possibility.

May I add, temp remains normal, so is oil pressure during these eppisodes.

[boneheaddoctor]

Well whatever it is is getting worse. Had to turn around and take car home this morning and get my honda. I replaced the secondary (main) fuel filter along the road, no change. Also drove the car without the tank cap, so its not tank vent blocked. Primer was tight, still zero crud in the primary filter, still clear and clean, this is really getting on my nerves.


after reading the "air leak" thread I have the black primer pump not a white one.

[Brian Carlton]

I think you have done a good job covering all based on the easy stuff.

The next step should be the tank strainer. It may be full of gunk that slows the flow of fuel at high speed, and, after 10 minutes or so, the engine begins to starve.

Jim recently posted a photo of one of his strainers. Unbelievable that the damn thing ran at all. He did not have any algae in the primary that was apparent.

[boneheaddoctor]

Originally Posted by Brian Carlton

I think you have done a good job covering all based on the easy stuff.

The next step should be the tank strainer. It may be full of gunk that slows the flow of fuel at high speed, and, after 10 minutes or so, the engine begins to starve.

Jim recently posted a photo of one of his strainers. Unbelievable that the damn thing ran at all. He did not have any algae in the primary that was apparent.

Trying to figure out how to get to it on the W116. Time to dig into the service manual and figure out what has to come apart. And figure out what to dran a half tank of diesel into.

[Brian Carlton]

Can't help you with the W116, but, you might want to siphon, or pump, the fuel out the filler pipe into a couple of five gallon jerry cans. You certainly don't want too much in there when you pull the strainer.