1981 BJ40, B engine with fresh rebuild. I'm not through the break in period yet, but it seems low on power across all RPMs. (1 Viewer)

Joined
Apr 29, 2020
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Cuenca, Ecuador
No trouble starting, or at idle, but just won't generate the power it had, even before rebuild. It seems almost certainly a fuel pump problem. I mean, it's timed pretty close, and there's practically no smoke, but it seems fuel starved. I'm going to have a pump pro go over everything, but my question is this: should I continue to break in the engine, or wait until the fuel is dialed in. If running it now on a wonky fuel system will cause long term damage due to a crummy break-in, I'll park it for now, as the fuel guru is off til August.
 
Joined
Jul 22, 2003
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18,018
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Perth Western Australia
 
 
 
You wont hurt a diesel engine with a bad pump, certainly not in the short to medium term. How many klms since the rebuild? They are usually a bit tight and run hot for 1-2000klms.
Have you tried turning the fuel up? An 1/8th or 1/4 of a turn usually is all they need.
 
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Mar 4, 2012
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Adelaide, South Australia
 
  • Are the two hoses from the throttle body to the injector pump intact and in good order?
  • Was the pump rebuilt as well?
  • Did the engine sit for a long time after rebuild (if so it'd be worth checking the operation of the lift pump)
 
Joined
Apr 29, 2020
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Cuenca, Ecuador
Thanks to both for your input.
It's been fewer than 100 km since rebuild...really fresh. No abnormal temps. I'll inspect the vac hoses come daylight. The pump was rebuilt as well, but not by the same shop. I'm reluctant to touch the fuel screw until the guy who put it together gets back, in case he blames me for messing with it. And, it sat no time at all prior to running.
 
Joined
Apr 29, 2020
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Cuenca, Ecuador
Well...no. I just thought if I were to have put something together, and the customer came back to say I'd done it poorly, I'd prefer to have a look at it before it had been fiddled with. But I guess that's nonsense, and I should turn it up a bit...see what happens.
I should add that he wasn't around when we started it...made a good bit of black smoke at first. He came around after I'd gone, and cleared up the smoke issue, but maybe all he did was cinch down on the fuel flow. It looked to me that he'd adjusted the timing, too, but that's just from eyeballing the timing mark.
This is all a very steep learning curve for me. Until now it's been 100% gas engines...now suddenly I've got to learn a whole new animal.
 
Joined
Mar 4, 2012
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Adelaide, South Australia
 
It looked to me that he'd adjusted the timing, too, but that's just from eyeballing the timing mark.
There is no timing mark.. I know there's a line on the pump and timing cover.. but you cant eyeball this line to get the timing correct, it doesnt work like that. It has to be spill timed in accordance with the factory procedure if the pump has been off/engine rebuilt etc..
 
Joined
Apr 29, 2020
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Cuenca, Ecuador
Ok. That's something I'll read about today. I have no real idea what he did. On top of my ignorance, I have a bit of a language barrier, here in Ecuador. And a cultural barrier...small town...I ain't from around here...treading carefully as not to sour things. I doubt the fuel guy has ever read a manual...his shop is a small step better than a shade tree. But his work is driving all around here, and I know he can dial things in if I'm patient.
Thanks for the help.
 
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Sep 12, 2020
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Victoria BC Canada
I had a similar issue with my last rebuild on my 78 BJ (B engine), until I adjusted the tappets properly. The mechanic was a gas guy and felt that having the exhaust valves open a bit longer would give it better performance. Not !
 

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