loss of power after new fuel filters

[darksheep85]

I just bought my first deuce back in march of this year. Its a 1971 AMG M35A2 w/w. I bought it from a private party who had it as advertising for his business. He said that he had the oil changed every year seeing as how it didn't get much use ( less than 3k miles a year ). But when I asked when was the last time he changed the 3 fuel filters, he gave me the "confused dog" look.

When I got the truck home I started going through it as much as the wallet would allow. First was oil and filters. Then replaced the fuel lift pump that wasn't lifting fuel. Then checked the primary filter only to find it was the OE style reusable filter. But there was no other hardware in the can besides the filter. No spring, no cup washers, nothing. Just the stud and the filter. So, the filter wasn't doing anything because it wasn't against the housing. It was covered and filled with what can only be described as a mixture of rust, mud, and a gelatin-like substance. I found a new reusable filter to install and rigged a spring from a stretched out carriage spring.

Some time passed after this and I was driving it to town a couple days a week. Didn't seem to have any problems and had plenty of power. I finally got around to changing the secondary and final fuel filters this past weekend. I used Napa 3512 (10 micron) for secondary and 3540 (6 micron) for final. The filters I removed were in about the same condition as the primary. They were the same filters by part #'s and had no shielding around the elements like the new Napa filters did. Also, both canisters had a wonderful mystery substance in the bottom of them.

After struggling with the new canister gaskets for a while, I finally got it all buttoned up and excited to go for a test drive.

Upon purchase, it had very good power, did not smoke at idle, puffed a little cloud on takeoff, and only left the faintest trail of smoke going down the road. But now that it has all new filters (and I run diesel fuel with a gallon of rotella dumped in with every fill up) it seems to have lost considerable power and it won't smoke at all (idle, take off, or cruise). It doesn't rev as fast while in neutral. Although it well rev higher now. It would only rev to about 2300 before but now will rev past 2500. ( I know, I know, don't do that). And this power loss didn't gradually happen, it was right after changing S&F filters.

Could the new, tight filters be restricting fuel flow?
Do I need to change the final filter to a 10 micron like the secondary?

 

[jatonka]

It would probably be a good idea. You could find a bunch of junk has already plugged it. Let us know how it turns out, JT

 

[cranetruck]

Could the new, tight filters be restricting fuel flow?
Do I need to change the final filter to a 10 micron like the secondary?

The original secondary and final fuel filters are 6 microns, should be no need to change to 10 micron. (The primary is basically a water trap and is about 40 microns (original equipment)).

 

[FloridaAKM]

The Deuce I own had horribly filthy filters when I bought it last year like yours. The water seperator was also bypassed from the military by leaving out the brass dome fitting, but it ran amazingly well for being so dirty. After a major cleaning session for several hours, the red varnish (an acetone soak removed the varnish) & several cups of rust later; the new filters were installed & it ran quite well again. You need to check your new filters & see if they have gotten dirty again from use. Have you cleaned your fuel tank @ all? You said that you replaced your lift pump, so that should have given you a good view of if it was clean or trashed like they so often are. The varnish in your fuel lines will break loose & plug your filters as time goes on from clean new fuel running thru it. Carry on!

 

[darksheep85]

When I changed the lift pump there was a light film of scum on it along with some rust. The previous owner had his own biodiesel business which I'm sure he ran 100% for fuel.

After I changed the primary I ran a bottle of Cetane's diesel cleaner and algae killer through it. Thinking it would catch anything in the primary and I could clean it. After that tank of fuel was gone I checked the primary and it was actually clean. So I figured "good to go, let's do the secondary and final". I have 1 air purge on the top of the housing and I did that too...for quite a while actually.

I don't get any water draining from the primary. And I haven't ever drained the tank. Its so strange that new filters, and a loss of power.

BTW, when I say immediate loss of power, I mean I bled the air out, fired it up, and power and smoke were gone. Instantly.

Could the sudden surge of fuel through the lines from air purging have knocked a bunch of garbage loose in the lines and passages? Also the engine is a Hercules LDT-465, FDC still hooked up for now, and data plate on block says manufactured 3-91

 

[jasonjc]

I'd check all the filters again. What you are saying sounds like clogged filter/s. Also check the tank for crud.

 

[FloridaAKM]

Your tank, from your description, sounds clean. The in tank pump is new, so that problem is out; check your filter closest to the firewall for more trash & goop. If it is clean & the water seperator are clean, the second one should be clean also. Usually it takes time to figure out the bugs & then, they sometimes work them selves out. Take her out for a good hard run of 30 to 40 miles & see if anything changes. Good luck with your problem & keep us posted with your results!