And here's another photo that would be a good addition to this thread and my earlier reference to "sucking on a hose" to test your diaphragm:
3B diaphragm replacement
- Thread starter lynchmob
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RufusTheDufus
SILVER Star
Sucking might help if there's serious issues. A vacuum gauge is very helpful and far more accurate.
FSM provides a test for the diapgragm: put a vacuum gauge on it at 36.8 mmHg. It should take longer than 10 seconds to drop below 35.3 mmHg. My vacuum gauge isn't that sensitive but it's close enough to be able to see if there's a leak in the diaphragm.
FSM provides a test for the diapgragm: put a vacuum gauge on it at 36.8 mmHg. It should take longer than 10 seconds to drop below 35.3 mmHg. My vacuum gauge isn't that sensitive but it's close enough to be able to see if there's a leak in the diaphragm.
- Thread starter
- #23
And here's another photo that would be a good addition to this thread and my earlier reference to "sucking on a hose" to test your diaphragm:
View attachment 213419
Whatever you do - DO NOT remove the line on the right side in this picture while running. I did this once and the engine races to max RPM. I quickly shut it down, but it scared the crap out of me.
The lines cross over each other so it is hard to tell which one you're referring to Lynchmob.
But I would think it must be the "vacuum" line that connects from the LH side of the intake-manifold-throat to the RH side of the diaphragm because removing that one would make the injector pump think your foot was "flat to the floor - and then some".
I don't think I'd be game to try that
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Trying to understand this phrase makes my brain hurt.
Sorry. I'm not too good at explaining things sometimes. My years spent in refrigeration/air-conditioning (where pressures/vacuums are studied in detail) probably means I've left stuff out of the explanation. Try this:
When the butterfly valve is wide-open, it is like a "wide-open tap" within a water pipeline. The pressure either side of the tap is roughly the same. But when the "tap" is closed - you normally have "supply pressure" on the upstream side and "little or no pressure" on the downstream side. So the valve "closing" has increased the "pressure-drop across itself".
So I was trying to say that closing the butterfly valve increases the pressure drop across the "venturi tube" and this forces a higher air speed through the venturi. (A higher pressure drop across a tap would force more water through it.)
A Venturi is also used in a paint spray-gun (where the "pot" hangs down below the gun). The air speed through the gun (when you pull the trigger) then sucks up the paint from the pot by means of the vacuum produced by the venturi. Pulling further on the trigger further increases the air speed and this further increases the vacuum/suction to suck the paint up faster.
In the air intake of a diesel engine the "supply pressure" is "atmospheric pressure" and downstream of the butterfly valve, the engines pistons and valves are together trying to pull a vacuum (below-atmospheric pressure).
My apologies
- I used to teach in a polytech and maybe writing all this sh*t is just me "playing pretend" at being a teacher again. (I'm fully aware that I'm IGNORANT in comparison to many others who post on MUD.)
rchalmers3
I speak Toyota
My apologies
I think you did a great job of explaining pressure differentials and how they are used. Thank you for your willingness to contribute. No more apologies needed!
Rick
has anyone who has done this repair found there is a loss of power?
i did this repair and have noticed a small drop in power. As we all know, the 3b needs as much power as it can get!
i did this repair and have noticed a small drop in power. As we all know, the 3b needs as much power as it can get!
I was kinda hoping someone else would reply but since it has been a while since you posted this question Kon -----------.....................
I didn't experience any change (increase or decrease) either time I renewed my diaphragm. (Gosh I feel like a woman talking about an IUD
) If you are experiencing a loss of power immediately after having the diaphragm renewed - I would think something may have been done incorrectly - or perhaps the new diaphragm was of poor quality.
But if the loss of power is minimal - then I can understand that you may be unsure about whether it is worth delving into it. (I would be uncertain too.)
That's why I like doing ALL work myself. When I do it myself, I have a much better idea of what has gone wrong (if anything).
- Thread starter
- #30
I wouldnt say I experienced a loss of power, but the engines I have done do have different power characteristics. They both just seemed to run better over the entire driving rpm range whereas before the diaphragm was changed there was probably a little quicker throttle response from start and between gears. I also had black smoke while there is none now.
Neither of the ones I changed were so bad that I had the high idle condition described by others. I suspect mine were just worn and stretched which allowed more movement and more fuel by moving the rack farther.
If you have a pyrometer maybe you could turn your fuel up a bit to get some power back?
Neither of the ones I changed were so bad that I had the high idle condition described by others. I suspect mine were just worn and stretched which allowed more movement and more fuel by moving the rack farther.
If you have a pyrometer maybe you could turn your fuel up a bit to get some power back?
thanks guys!
well the old girl is up for sale now.
time to upgrade!
well the old girl is up for sale now.
time to upgrade!
my idle just rose about 150 rpm and i now have a wierd shudder as soon as i let off the pedal (from lots of throttle straight to idle idle drops to aboot 450 then back to 650 which just jumped to 800 in a day or two) this all makes me think the diaphram anyone else had this problem?
also my vac lines are not crossed like in the pictures in this thread theyve been this way since ive had the truck would this affect power or anything else?
thanks for any repy
also my vac lines are not crossed like in the pictures in this thread theyve been this way since ive had the truck would this affect power or anything else?
thanks for any repy
Hi Big Blue
I'm at work otherwise I'd copy and paste the photo here. (The work computer is very user-unfriendly.) But Watrob's thread on his build shows photos of his engine. And his hoses don't appear to cross either. So perhaps "crossing tubes" is just peculiar to B diesels like mine. (His injector pump is on the opposite side of his engine to mine too.)
When was the diaphragm last replaced? And does the exhaust produce more smoke than before? Depending on answers to such questions as these, it sounds like your problem could indeed be a leaking diaphragm.
yeah i can get her smoke now just by adding more throttle and if i givver a nice big black cloud comes out so from what i gather the diaphragm is on its way out
but its the shudder that worries me a little its never done this before and im hoping when i replace the diaphragm it will go away (the shudder)
thanks lostmarbles for clearing up the crossing of the tubes (makes me feel better that im not alone lol)
but its the shudder that worries me a little its never done this before and im hoping when i replace the diaphragm it will go away (the shudder)
thanks lostmarbles for clearing up the crossing of the tubes (makes me feel better that im not alone lol)
Here's the photo that I couldn't post last night. I'm sure there must be other suitable photos on MUD (showing those tubes) but I went to Watrob's build thread because I remembered he was fitting a diesel and did some good photography.
PS. Of course Watrob's engine is a 6 cylinder 2H.
We know that my "B" 4-cyl diesel has its tubes crossed and that Big Blue's "3B" doesn't. Anybody out there able to say what the "2B" engine's tubes do? And is this "tubes crossed" or "tubes uncrossed" feature specific to the engine models or does it even vary within the same engine model? - Just interested - That's all..............
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thanks for the pick yep thats the way the vac hoses are hoked up in my truck (except dirty not all shiney and nice)
what would happen if one were to cross the tubes on the 3b or 2h (ide immangine the engine would rev out or am i wrong)?
what would happen if one were to cross the tubes on the 3b or 2h (ide immangine the engine would rev out or am i wrong)?
Well the air-intake butterfly would still have some control over the engine rpm - but only through varying the engine's air supply.
The fuel would never move away from the "maximum pedal-to-the-floor" setting.
(Very smokey I would imagine and it certainly wouldn't idle smoothly or at the normal revvs.)
makes sense as there still would be preassure in the intake
next step replacing the diaphragm for me thanks again
next step replacing the diaphragm for me thanks again
What's the cause of them ripping besides age?
