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81 720 diesel looses power


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I'm looking at a 720 diesel 5spd. It is in great condition, runs good, but when under load, like climbing a grade, it looses power. Current owner said a diesel mechanic said it needed a fuel pump to the tune of $800. Since I have no knowledge of diesel's, are we looking at a fuel pump or an injector pump. I could use some education about what to look for before I decide to make the purchase.


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The SD22 has about the same torque an an L20B but at half the RPMs

I agree with this statement, out of the hole hauling weight they are about the same, but the similarities end there, the L20b will haul ass everywhere including the hiway, the diesels top speed is about 70mph @ 3000rpm The L20b will haul weight, but get terrible mileage but still move along pretty good, the diesel will get pretty good mileage everywhere(city 25mpg, hiway 36 mpg @ 60 mph approx.) and will still get 22mpg hauling another diesel behind it, but you will only be moving about 60mph on level roads, and be sometimes down to 40mph on the hills towing that other vehicle. wayno

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Mechanic also told the guy that it may just be rotted fuel lines and it may be sucking air.


it also could be either the inline fuel filter or the spin on as well if it is partially clogged or the diaphragm in the fuel pump I know I have to go in second going up my mom's hill when I visit that house but then again I am doing a complete rebuild this summer hopefully they are a beast but not fast anything above 70 is going to shake rattle and roll even down hill lol but very underpowered 40 hp at lowish to mid rpm and about 60 at about 3800 rpm and unfortunatly no turbo available for them how many miles on it ? and how does it start I know mine even during the summer had to use the glow plugs on a cold start

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it also could be either the inline fuel filter or the spin on as well if it is partially clogged




I bought my '82 with similar symptoms as the OP's. Ran great in town with good power, but would bog down badly at anything over 40 MPH or so. Hills on the highway would take me from about 70 MPH to 40 MPH in short order. I knew it was fuel-related when I got the truck, but it took me a little while to diagnose. The previous owner had taken the truck to Firestone to have it serviced, and they changed the fuel filters. BUT, they installed an incorrect in-line filter on the firewall. These in-line filters are made for gasoline engines (paper filter element) and do not allow quite enough steady fuel pressure for the diesel. Got the new (correct) primary (firewall) filter from Nissan, and it drives like a completely different truck. Don't know if this is your problem, but hopefully it helps. I seriously doubt it's the injector pump, though. If not a filter problem, then a fuel line problem is possible. Read here for more info on fuel filters:



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