Power Drop at Full Load

SD diesels were widely available in the US in the 1981-86 Datsun/Nissan 720 pickups, and in Canada through '87 in the D21 pickup.

Moderators: plenzen, Nissan_Ranger

Post Reply
jvoekel
Posts: 3
Joined: 8 years ago
Location: United States

Power Drop at Full Load

#1

Post by jvoekel »

Hi All,

I have an '82 Datsun 720 SD22, which I have been driving since '07 and absolutely love.

Recently, in the last year or so, I have been experiencing a loss of power under full load -- either going up a hill in 2nd or 3rd, or trying to keep pace on the freeway in 4th or 5th.

This is more than just that slow diesel feeling -- It feels like the engine is missing and the truck is being dragged backward.

The bandaid fix has been to use redline fuel additive, which typically works for a while. Recently, it's been less effective.

Because the redline did work, albeit temporarily, I am assuming I have a fuel problem and am planning to check/repair/replace the filters and injectors. Before I launched into it, though, I wanted to run the problem by the experts.

Any thoughts or suggestions would be appreciated.

Thanks,


John
John
User avatar
asavage
Site Admin
Posts: 5370
Joined: 15 years ago
Location: Duvall, Wash.
Contact:

#2

Post by asavage »

Some amusing fuel stores are here.

Unexplained loss of power with a diesel is usually the same ol' culprits: bad fuel, bad filtration, leaks in the fuel delivery lines (picking up air), restriction in the line(s).

All of which can be diagnosed with a hunk of clear fuel line (for air-in-fuel problems), an analog fuel pressure gauge, and some duct tape. See this post for more info.

You will likely find that, under load, the pressure at the fuel filter is dropping. If you plumb the gauge in before the fuel filter, and there's a restriction in the feed line from the tank, or a restriction in the tank itself, you may find a vacuum reading. See my Tale of Woe regarding a paper-element primary filter installed at the firewall where a mesh screen filter should be: I saw 11" of vacuum between the primary filter and the lift pump!

Hope this helps.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
jvoekel
Posts: 3
Joined: 8 years ago
Location: United States

#3

Post by jvoekel »

Thanks for the input, Al.

I'm going to start with the filter and then move to the clear line and pressure gauge... which, from the stories, sounds like a lot of fun.

I'll let you know how it goes...
John
User avatar
asavage
Site Admin
Posts: 5370
Joined: 15 years ago
Location: Duvall, Wash.
Contact:

#4

Post by asavage »

The Primary (cheap) & Secondary (expensive) fuel filters are definitely the place to start.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
jvoekel
Posts: 3
Joined: 8 years ago
Location: United States

Worked like a charm

#5

Post by jvoekel »

Thanks, Al. Changed the primary filter from a clogged old paper thing to a nice, wire mesh fliter and she has been running great.

Mileage is better, but still a little low. Averaging 27mpg over the last few months.

What do others out there average?
John
Nissan_Ranger
Posts: 267
Joined: 14 years ago
Location: Canada

#6

Post by Nissan_Ranger »

35 - 40 MPG (Imperial gallons)
N_R
The old 'six gun' was as popular as the cell phone in its time and just as annoying when it went off in the Theater.
dn29626
Posts: 249
Joined: 11 years ago
Location: Anderson, SC

#7

Post by dn29626 »

I do not know what filters are available to you, but wix 33972, which is diesel rated, is a great fit to the clip on the firewall.

Note: Most (if not all) paper filters are rated for gasoline, not diesel.
82 King Cab 2wd (nice)
82 Reg Cab (body damage)
Anderson , SC
Since Fall 2009
User avatar
asavage
Site Admin
Posts: 5370
Joined: 15 years ago
Location: Duvall, Wash.
Contact:

#8

Post by asavage »

Wix 33972:

Image
Wix wrote:Principle Application: Plastic Universal In-line fuel filter w/ 5/16" lines - can be used w/ gasoline or diesel fuel (33002 only to be used w/ gas)
Applications
Style: Fuel (Complete In-Line) Filter
Service: Fuel
Type: Full Flow
Media: Plastic Mesh
Height: 3.636
Outer Diameter Top: 1.828
Outer Diameter Bottom: Closed:
Burst Pressure-PSI: 58
Max Flow Rate: 1 GPM
Nominal Micron Rating: 50
It does look like the Wix 33972 will be OK, but last I checked, the Nissan 16401-36W01 filter is still available, and cheap. Plus, the OEM fuel lines don't have to be re-routed. But these are minor nits. Personally, I've never seen a whole lot of crap in the primary fuel filter, ever. The plastic becomes opaque, and that's a good reason to change it ;)

They don't wear out, and it's OK to backflush them.

This style of filter, with inlet/outlet on top/bottom, is probably a drop-in replacement for 1983-on with SD25, where the OEM filter also has that configuration.

I'm going to go update the SD fuel filters post to add the Wix number. Thanks for the info. If/when the OEM becomes NLA, that'll be good info.

BTW, I just discovered that Wix no longer supplies a Secondary fuel filter for the 1982-on SDs (33224). It's been discontinued. What are people using in its place? Will we need to convert our filter heads to something else?
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
User avatar
asavage
Site Admin
Posts: 5370
Joined: 15 years ago
Location: Duvall, Wash.
Contact:

#9

Post by asavage »

I was getting 33-35 US MPG in my '82, driving fairly leisurely. Philip could get 40, but he took extraordinary measures. If you have to drive above 60, 27 may be the best you can do.

Sadly, my '82 Maxima Wagon with LD28, a much more powerful Six cylinder Nissan diesel, would get 27 with automatic and A/C. It's probably the same weight as the 720 with SD, though more aerodynamic. I never got less than 25 in it.
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
dn29626
Posts: 249
Joined: 11 years ago
Location: Anderson, SC

#10

Post by dn29626 »

Al
I went to the 33972 after being told by my local Nissan dealership that the 16401-36W01 was not available. I tried to prepay for an order and he repeated-not available.
I suppose he just did not want to fool with them.
82 King Cab 2wd (nice)
82 Reg Cab (body damage)
Anderson , SC
Since Fall 2009
charmalu
Posts: 166
Joined: 10 years ago
Location: Soquel, Calif

#11

Post by charmalu »

Iam using the Wix 33393 for the Secondary filter.

I replaced the Primary small screen filter to a Racor 200FG, and us a 2 micron replaceable filter I buy a West Marine. I like the Racor because it has a large bowel to trap any water.

I have been using this set up for the past 30+ years and has worked just fine.

Does anyone know what micron size these Wix Filters filter down to?

The Mercedes uses the same sort of set up, Primary mesh filter and a small screw on Secondary which filters down to 10 micron. I always thought the mesh filter was a joke, and like better filtration. I have the Racor set up on my 240D.

As far as my mileage goes, I just took a trip to Portland Oregon, from Santa Cruz, Ca. fueled in Lathrop, Ca about 100 miles from here.

Lathrop to Yreka, Ca, ...336 miles and 32.41 mpg
Yreka to Portland, Or.....348 miles and 30,36 mpg
Portland,......................361 miles and 33.84 mpg
this was mixed city freeway driving all week
Portland to Medford, Or,.304 miles and 35.86 mpg
Medford to Lathrop, Ca...376 miles and 35.50 mpg.

Milage actually got better coming back home, and I was hauling a SD-22 engine, two Mercedes 4-spd Transmissions, two MB Flywheels, two front sections of the Drive Lines, 4 manual window Window regulators, 8 gallons of Amsoil engine oil and one gallon of the gear lube. Picked up a new after market Turbo set up for a MB 240D, Turbo, manifolds and other related parts. me my wife, all our luggage etc... and my tools.

There is one long grade coming over the Siskiyous climbing up to 4300ft, that I as in 3rd gear for 4+ miles, and still got the good mileage.

I use to always get in the 36 - 39mpg range, but she is getting a little tired.

Charlie
82 Datsun KC 483K lost #2 cyl blowing blue smoke :cry:
83 Nissan LB 134K SD-25 as of 10-21-13
78 240D Mercedes $300 Parts?
80 240D 360K
80 240D Parts? $750
82 240D Parts? $440
84 300SD 270K
85 300D 363K
86 Ford F250 6.9 Diesel 221K
Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest