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MrSims

Tii Fuel Pressure

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Hello all, My Tii fuel prsssue is 24 psi at idle.But when I pinch the hose (dead heading the pump) it goes up to about seventy psi. Shouldn't the return valve keep the pressure at the recommended 28 psi or is the pump worn out?

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Yea that's what I'm trying to find out if the regulator/return valve should hold proper pressure or is the pump underperforming.Been chasing a hesitation for a while now.All ignition parts new, except dizzy and coil. Dwell and timming all correct.

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Exactly which hose are you pinching and where are you putting your fuel pressure gauge?  

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Exactly which hose are you pinching and where are you putting your fuel pressure gauge?  

+1 on this inquiry.  Here is how I hooked up a pressure gauge.

IMG_4654.jpg

IMG_4650.jpg

 

I believe the BMW factory fuel injection manual shows a special adaptor with gauge that mounts to the injection pump inlet.  With the gauge at that location, if you pinch the return hose at the back of the pump the inlet pressure will certainly rise since there isn't anywhere for the fuel to return to the tank.

Edited by jgerock

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Yea that's what I'm trying to find out if the regulator/return valve should hold proper pressure or is the pump underperforming.Been chasing a hesitation for a while now.All ignition parts new, except dizzy and coil. Dwell and timming all correct.

I've been down this road before.  I had a bad set of plug wires that drove me crazy until I checked their resistance value.

 

If you haven't checked the pump synchronization to the throttle body and made sure your linkages are in good shape, you need to do so before trying anything else.

 

When you have a timing light connected, does the flywheel ball bounce around?  This could be an indication of a worn out distributor.

 

It has been mentioned here many times:  Check your ignition system thoroughly before messing with the fuel (injection) system.

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Jim, Exactly what I was thinking and great photos.  

 

Slightly off topic but a tii-KF system related question (if this is allowed).  The cold start valve injects fuel on the air filter side of the butterfly plate.  Unless I step on the accelerator my butterfly is completely closed and it does not look like any air can get by.  I have not tried to start the car yet but will the "cold start process" open the butterfly?  If not it seems like a puddle of gas will just sit there an have no way to be drawn into the engine.  I have downloaded the BMW NA fuel Injection guide but did not see the answer.  Feel free to tell me to RTFM :-)

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Jim, Exactly what I was thinking and great photos.  

 

Slightly off topic but a tii-KF system related question (if this is allowed).  The cold start valve injects fuel on the air filter side of the butterfly plate.  Unless I step on the accelerator my butterfly is completely closed and it does not look like any air can get by.  I have not tried to start the car yet but will the "cold start process" open the butterfly?  If not it seems like a puddle of gas will just sit there an have no way to be drawn into the engine.  I have downloaded the BMW NA fuel Injection guide but did not see the answer.  Feel free to tell me to RTFM :-)

The air bypass hose that goes from the bottom of the intake manifold (log) connects to the KF pump warm up regulator.  Air is routed to the engine this way on start-up (coolant is cold).  Yes-  fuel will coat the throttle body but is drawn into the intake.

 

Graphic courtesy of CD (modified BMW diagram)

tiimotortransparent.jpg

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I connected the gauge at the kfish inlet.(24psi) Pinch the hose on the outlet right after pressure regulator.( aprox70psi) all 3 screens cleaned and new filter installed.So is the regulator not restricting flow enough to achieve 28psi or does the pump need to supply higher pressure.I'm thinking I need to do a volume test.If that's low then I assume increasing pressure via the regulator would just drop the overall flow rate.

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Good point, haven't cleaned the regulator yet.Anyone know what pressure thier fuel pump goes to against a closed return line?

Thanks.

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That is exactly how the system is designed to run. The fuel is supplied to the injection pump from the front of the valve body and the pressure relief valve bleeds off the excess pressure above 24 psi back to the fuel tank via the outlet at the back of the valve body(the relief valve is the fitting the hose is attached to). If you block off the outlet then the electric fuel pump will continue to supply as much pressure as it can ( in this case 70 psi) your fuel pressure is EXACTLY what it should be, AND the system is working as it should be.

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If that's the case then why isn't the specified pressure 24 psi.instead of 28. Is it more of an acceptable range rather than an exact pressure? Or maybe different for a 1974 vs. older models? ( 3 TD's and a field goal vs 4TD's ? Mmmmm ) Seahalks are killing it!

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Sorry I did not remember the exact pressure.  The spec is 2kp/cm2 (28 psi) 24 psi is well within the working range of the system.  The Kugelfischer injection pump needs some pressure to work correctly (it is what helps to push the plungers down to refill between each stroke) As long as the pressure does not drop and load and engine speed go up you will be fine.  The Injection pump does the fuel metering and delivery and just needs to be kept full of fuel so there is always as much fuel as it needs the delivery pressure (within reason) does not make much difference. 

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