12HT pump body pressure

[dousty]

I have been fooling around with my 12HT wagons measuring pump body pressure. In the workshop manual there are two references to this. One reference is during the lift pump checks at the start of the fuel section where is stated lift pump output pressure should be between 26-31psi at 600rpm whilst on a test machine, so I assume this speed measurement is pump speed and not crank speed. The other mention is during the pump body adjustment where it states that testing should be done with 28psi fuel feed pressure.

So I have removed the fuel bleed screw which is post fuel filter on my engines and measured pressure to find both running around 15psi. Pump body relief opens on both of them at 20psi. The pressure reading will also dip as engine speed is increased until eventually it recovers as engine speed climbs towards high idle. When I first discovered this drop I ran the wagon I was looking at out of a fuel container to eliminated posibble air/resitriction from the fuel inlet but found no difference in readings. Also both vehicles have new fuel filters, each of a differing brand.

So my question is, should I have/pursue 28psi pump body pressure? Or is this just a figure Toyota have used for testing purposes? Have any of you measured this yourselves?

Manual page for Lift Pump spec - FU-17
Manual page for pump body pressure - FU67

 

[roscoFJ73]

I dont have the answers,but is it possible to adjust the fuel pump pressure by diverting a lesser amount back to the tank?
There is also figures(around 900cc a minute) on how much fuel the pump should pull through,which it then diverts most of it back to the tank.
I think you can do this on the rotary pumps.

 

[dousty]

I could restrict it but I don;t want it overpressurising either. There are shims on the bolt that retains the spring and ball on the relief, I assume to adjust relief pressure. There are also several difference lift pump pistons in the parts breakdown but they are only recognised via some sort of colour coding. I stripped a lift pump fro a 2H auto pump I have and I can't see any colour on the piston at all.

 

[Tim-HJ61]

Interesting you are looking at this too. Any reason?

I have a permanent pressure gauge on the outlet of the lift pump so I can measure pressure going into the filter. I run WVO so use it to see when the filter is starting to block.

Over the last years, I've noticed the 'normal' pressure is dropping, yet the engine is running fine apart from a hesitation at highway cruise speed, sometimes.

I bought a brand new entire lift pump, and the gauge showed no difference.... Sigh.

My IP shop suggested the other place where pressure can drop is in the spring loaded ball bearing as you talk about. Whilst that all 'looks' okay, he said that the ball bearing seat can wear, so the solution is to replace the bypass as a unit. I'll do this soon. He says he'll need the number off the side of the IP as there are some variations.

I can't see and problems with too much pressure in the IP, not from the standard lift pump anyway. I wouldn't put a higher pressure aux pump inline, but the IP must be built to contain 2bar, as that's the spec. Remember the 2H does not have a bypass and the lift and injection pumps are pretty much the same as far as the top end of the IP.

The manual contains no reference to using the shims to adjust pressure, i see no harm in packing it to see if I makes any difference. Going back to the first question, is there a problem, or now you've got a gauge, you're wondering about things? Sometimes we know too much from gauges

Tim

 

[Tim-HJ61]

My error.

Just checked the manual and it talks about different pressures for the IP for the 2H and 12H-T

2H
Fuel feeding pressure to injection pump should be 0.5 kg/cm2 (7.1 psi. 49 kPal.

12H-T
Fuel feeding pressure to injection pump should be 2.0 kg/cm2 (28 psi, 196 kPal)


Fuel temperature for pump testing should be 40°C - 45°C 110°F - 113°F.

One the added complexities I have is that my fuel is 85°C to 100°C inside the lift pump and IP due to the WVO conversion, so any wear is multiplied due to the heating. Bottom line for me is, does it run well? Gauges can make us worry about things that don't matter in the end.

By the way, I converted the workshop manual PDF's into a searchable PDF and straightened all the pages, so they are easier to use. Find them at 60 Series Workshop Manuals

Tim

 

[dousty]

Thanks Tim. I was originally looking for a starting issue with the Sahara. When is has sat for a longer period....more than 8hrs...it will start immediately and then stall. It will continue to do this untill you just open the throttle on start-up. Once It has been run like that for even 5 secs, it will start normally..

So I was looking at fuel drain back, air in fuel etc and things went from there.

 

[Tim-HJ61]

Did you ever find the culprit?

Sounds like you've had all the important bits apart .. I'd be predicting an air leak, no doubt you did too....

If you put a pusher pump in front of the lift pump and see if that resolves it. This may show up fuel leaks too, which are hard to track on suction areas.

Tim

 

[dousty]

No I didn't. Running it out of jerry can stright into the lift pump removed most possible air leaks. Also if running on air it should be slow to respond and it's not. I am thinking that maybe the inlet check valve at the lift pump is sticking open or bypassing slightly allowing fuel to drain back and stopping the lift pump from creating enough positive pump body pressure at initial start up. I did notice the Sahara is fraction slower to make pressure compaired to my other wagon as well. This could also explain the lower pressure achieved although both wagon are achieving the same pressure.

Round and round and round and round and round and