3B varying power - What is going on here? (1 Viewer)

[MrMoMo]

For starters... 1984BJ60, Stock3B (veggie/diesel) Running 33's & 3"OME. ~250K km

OK... over the past few months I have been experiencing an odd phenomenon.... Sometimes when I drive, everything is normal, other times when I drive, I have a significant loss of power - and can't maintain 100kph (adjusted for 33's)

Now, I'm sure someone is going to say that I screwed up my whole engine by running veggie. Thing is, it's not that I've had an overall loss of power - it's intermittent - and it happens if I'm running veggie or diesel. I've been running veggie for about a year (10k km), never forgot to purge, my veggie is clean, dry (HPT verified) and I never switch over before reaching full op/oil temp.

Things I've checked;

- Filters?, new diesel & new veggie filters - didn't solve it.
- Tire pressure? - was 35psi, tried 38psi - didn't make a difference.
- Dragging brakes? - don't seem to be dragging (all new front end)
- Drag in front axle? - disengaged hubs (in 2hi) - a bit quicker overall - but still varies between full and reduced power.
- Butterfly in intake? - opens all the way and not past.
- No black smoke
- No white smoke
- No fluid losses
- Cold days? - It can be fast in the cold, slower in warm & vice versa.
- Headwind? - Happens with head, tail & side winds!

The engine runs fine/smooth when I seem to be down on power, and I only notice it when on the Highway (trying to do 100kph!) When I don't have the power lacking, I can easily maintain 100 for 95% of my drive to/from work - save a few hills that I have to drop to 4th. When the power is lacking, I can barely maintain 90, sometimes down to 80, even down in 4th. When I have "reduced power" - it's for the entire trip - not a few minutes here or there. I can drive in to work in the morning and be fine, drive home and have reduced power, or vice versa. I can go a few days with full power, or a few with reduced power. I can't find a constant!!!!! does not seem to vary with fuel load, or weight.

So - my question is - what else is there??

-can the injection timing change?
-can the fuel pressure vary?
-could an air/fuel leak cause a reduction in power, without a noticeable "roughness" of running?
-how can I find if my brakes are dragging, if it's only intermittent? maybe they just are not dragging when I check 'em (on the hoist)

Any thoughts are worth exploring at this point! - I'd like to sort this out before I slap the turbo on!

Thanks!

 

[maximBJ70]

?This happens to me fairly often. In my case its a good headwind. Is that a possibility? I know I can do a certain trip and sometimes do 120 and other times barely reach 90.

 

[Freewheel]

You can figure out dragging brakes by feeling your rotors and drums after driving - If you haven't used them during the drive and they are hot - They've been dragging.

I would make sure you're not getting air into the system - This can lead to erratic power. Crack an injector nut and see whether the fuel is foamy - If yes, then track your leak down. Look for wetness everywhere in your fuel hoses and connectors. (a common leak is the return hose out of the injectors)

My truck was also more erratic before I changed the governor diaphragm and emptied the engine oil out of the reservoirs on either side of the diaphragm.
I also had the injectors rebuilt - so it's hard to say what exactly caused the erratic power - or what fixed it.

I can say though, that all those things I've talked about above were happening at different times and probably had some effect.

 

[cruiser_guy]

The rear drums have a tendency to drag. Have you checked those? The bellcrank will occasionally freeze in the pivot and "hold" the brakes on. If the bellcrank doesn't move freely check that first.

 

[John Hatchett]

I had a similar symptom and finally realized my clutch was ready for a rebuild. Some days it would engage just fine without too much slipping and other days I would notice problems getting up long climbs. Didn't find a way to inspect the clutch but figured it wouldn't hurt to rebuild it so I pulled it apart and sure enough the clutch was worn out.

 

[Turbo45]

im not sure how the "veggie" fuel part works? do you use the same fuel tank for regular fuel and veggie?
mabey there is somthing in your fuel tank that is getting in your suction like a wrapper or a fuel line comming apart on the inside and restricting fuel flow to the engine
sounds to me like some kind of restriction in your fuel from the tank to the engine

 

[MrMoMo]

Thanks guys - I'll re-check some things again.

I'm pretty sure it's not the clutch - it's got plenty of grab - and it's not revving up when I have the loss of power.

Turbo45 - The veggie comes from a separate tank, so I don't think its the fuel pick up, the only common parts in the fuel system are a valve just ahead of the lift pump - and everything from the lift pump on...

I'll check the fuel return line - I do seem to be going through more fuel than I would expect - but I don't smell any raw fuel around. I'll check though!

Thanks guys!!

 

[crushers]

install a 12V feeder pump near the tank
they are cheap and easy to install, i have found this helps smooth out the engine performance.

 

[MrMoMo]

Slow on the way home today. Checked wheel temps when I got home... Rear drums stone cold, front hubs - less than luke warm. not enough to concern me at all. No wind today - so it wasn't a headwind issue.

I know it wasn't my imagination, because after pulling onto the highway, and still attempting to get up to 100kph... Moosecruiser passed me. He pulled on behind me, and outright passed me. His truck has over 100K more than mine!! Bastid!.

Will check for fuel leaks on the weekend.

 

[Radd Cruisers]

Sticky governor/rack in the pump?

Bad diaphragm?

Not enough fuel?

EDIC not working properly?

HAC or spring binding?

~John

 

[lostmarbles]

Just finished driving a bus that mimicked this behaviour exactly. Good power and perfect running one minute. Then a distinct lack of power the next.

However it had the added symptom of "dying on me and doggedly refusing to restart until it felt ready to". (Whereupon it ran fine till it decided to randomly repeat the exercise.)

I wrote the symtoms in the logbook for the mechanic and added my amateur diagnosis of "fuel restriction".

And I was later told (a few minutes ago) that this bus has previously suffered from "a fuel bug" which was turning good clean diesel into "filter-clogging muck".

Anyway - Hope you don't have the same thing.

(Just thought it was worth mentioning.)

 

[KOOTENAY KRUZER]

Just finished driving a bus that mimicked this behaviour exactly. Good power and perfect running one minute. Then a distinct lack of power the next.

However it had the added symptom of "dying on me and doggedly refusing to restart until it felt ready to". (Whereupon it ran fine till it decided to randomly repeat the exercise.)

I wrote the symtoms in the logbook for the mechanic and added my amateur diagnosis of "fuel restriction".

And I was later told (a few minutes ago) that this bus has previously suffered from "a fuel bug" which was turning good clean diesel into "filter-clogging muck".

Anyway - Hope you don't have the same thing.

(Just thought it was worth mentioning.)

If it is a bacterial contamination there is a product called "Prist" which should be available at any airport that fuels jets and other turbine aircraft. It is designed specifically to combat this very problem.

 

[smack]

Hey
got a 3b in my girl get the same problem some times normally sits on bout 100kmph
wit 33's but every now and then i will start her before work and she will feel underpowerd all
the way to work and back in the arvo same problem but next day fine..
when she is feeling underpowered wont sit on 100km in 5th back to 4th nd feels like she labouring
usually runs warmer and uses more fuel no smoke tho as i hav a side pipe on drivers side so easy to tell.
also when feeling underpowered she is quiter in the exhaust not as much of a growl?? and not as responsive in the throtle??

but its funny cause when i first start her i usually just drive her dont really worry about warming her
up lol but when i start it and drive it easy till its warm thats when it feels underpowered for the day

sorry for the long post

cheers

 

[MrMoMo]

Well I am glad to see I'm not the only one who has had this problem!!! - Still hunting down problems, though now I have to fix the alternator....

 

[tmarx]

Well I have now joined this "club". Could my pump have gone into a "limp mode" somehow eg from over-revving her when I repeatedly tried to crest a sharp dune ?

 

[tbailey4]

suck side

did you move both your filters to the suck side? with my veggie set up it took a long time to track down all the air leaks it was at both filters. Did not add a dc pump but it would be nice. I have also heard of instead of using a valve to switch fuel just using two pumps and check valves making the filters on the blow side. but for now filter wrench and almost all I can give it.

 

[VTCDN]

MrMoMo= N44 W76 Is watertown in USA.
This thread is over a year old.

tmarx , start your own thread , and state your year model engine , location etc.

VT