Fuel Pump Check Valve
08-20-2002, 05:33 PM
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Fuel Pump Check Valve
Did all 928 models with the CIS K-jetronic systems have a fuel pump check valve.
When I was working through the tests in Ben Watsons Bosch Fuel Injection book my 928 (1982 Euro 4664) failed the residual pressure test.
At present I have flow from the tank to the fuel pump, to the fuel filter, to the fuel accumulator to the CIS head. No check valve to be seen, also when turned off the pressure drops from 30-33 lbs to zero after about 60 seconds when you hear the accumulator clunking.
May be causing one of the problems I have been having?
When I was working through the tests in Ben Watsons Bosch Fuel Injection book my 928 (1982 Euro 4664) failed the residual pressure test.
At present I have flow from the tank to the fuel pump, to the fuel filter, to the fuel accumulator to the CIS head. No check valve to be seen, also when turned off the pressure drops from 30-33 lbs to zero after about 60 seconds when you hear the accumulator clunking.
May be causing one of the problems I have been having?
08-20-2002, 07:31 PM
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Based on my experience, the original fuel pump has an integral check valve built into the output port. If that fails, a stand-alone check valve can be installed immediately downstream of the integral one.
Very possibly the fuel pump on your car was replaced at some time with a later version without the integrated check valve, and the additional valve was not installed.
Very possibly the fuel pump on your car was replaced at some time with a later version without the integrated check valve, and the additional valve was not installed.
08-21-2002, 01:05 PM
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Paul,
Failure of this check valve should only affect things like warm start - it will allow vapour lock to form readily. Steady state engine running should not be affected.
Have you been able to find any other pressure related problems - system, control etc?
jp
Failure of this check valve should only affect things like warm start - it will allow vapour lock to form readily. Steady state engine running should not be affected.
Have you been able to find any other pressure related problems - system, control etc?
jp
08-21-2002, 05:14 PM
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Hi JP
I got the book and the test kit, i ran all the tests and they seem fine apart from the fact the control pressure is actually a little low when cold and hot and when the car is revved violently warm the control pressure drops, rises and then goes back to normal (all within 1 second or less).
I ordered a set of leads and a coil!! from Devek, should have been hear but will arive in the next few days and we will see.
Everything seems OK on paper but reality is very different.
Will let you know when the next batch of new parts is fitted!!!
Paul
I got the book and the test kit, i ran all the tests and they seem fine apart from the fact the control pressure is actually a little low when cold and hot and when the car is revved violently warm the control pressure drops, rises and then goes back to normal (all within 1 second or less).
I ordered a set of leads and a coil!! from Devek, should have been hear but will arive in the next few days and we will see.
Everything seems OK on paper but reality is very different.
Will let you know when the next batch of new parts is fitted!!!
Paul
08-24-2002, 12:38 PM
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Paul,
To lift control pressure, try tapping the regulator body (iron part) INWARDS into the die cast body - with gauge fitted so you can see changes. Do it hot first. Mixture should lean out and run better.
jp
To lift control pressure, try tapping the regulator body (iron part) INWARDS into the die cast body - with gauge fitted so you can see changes. Do it hot first. Mixture should lean out and run better.
jp
08-24-2002, 03:16 PM
#6
As Randy mentioned, you probably have an original style pump with the internal check valve. If the pump is still good, you should be able to add an external valve from any of the big three for about $18. Other reasons for bleed down could be leaking injectors (including the cold start injector) and the fuel distributor leaking into the lower intake plenum.
Concerning the low control pressure. If the system pressure is within the correct range and control pressure is low, it should be adjusted at the WUR as JP suggests. If both the control and system pressure are low, the adjustment is at the relief valve by adding a shim(s).
Dennis
Concerning the low control pressure. If the system pressure is within the correct range and control pressure is low, it should be adjusted at the WUR as JP suggests. If both the control and system pressure are low, the adjustment is at the relief valve by adding a shim(s).
Dennis
08-24-2002, 03:54 PM
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Thanks for the info,
i have discovered that the guy who changed the pump fitted a later pump so there is no check valve at all, will order one!!
Also although I had a new set of injectors fitted??? two of them gave very little fuel which seems to unbalance the others, i have just fitted two to replace these and now the fuel delivery (the way the book says, bypass pump and lift the flap) on all 8 injectors is now even and it was far from even before.
One thing I noticed, with all the injectors out and still connected but placed in glass tubes to measure the output when the fuel pump relay is bypassed and the pressure build up all the injectors fire occasionally - is this normal? They make a little chirping noise, no drips just a little puff of petrol mist
Will try and run the car again in the morning and see if its any better now (it should have some improvements as now all cylinders get an equal amount of fuel). <img src="graemlins/c.gif" border="0" alt="[ouch]" />
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
i have discovered that the guy who changed the pump fitted a later pump so there is no check valve at all, will order one!!
Also although I had a new set of injectors fitted??? two of them gave very little fuel which seems to unbalance the others, i have just fitted two to replace these and now the fuel delivery (the way the book says, bypass pump and lift the flap) on all 8 injectors is now even and it was far from even before.
One thing I noticed, with all the injectors out and still connected but placed in glass tubes to measure the output when the fuel pump relay is bypassed and the pressure build up all the injectors fire occasionally - is this normal? They make a little chirping noise, no drips just a little puff of petrol mist
Will try and run the car again in the morning and see if its any better now (it should have some improvements as now all cylinders get an equal amount of fuel). <img src="graemlins/c.gif" border="0" alt="[ouch]" />
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
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08-24-2002, 06:59 PM
#8
Jackin,
with the pump relay bypassed the injectors should spray continuously. Hence the "C" in CIS. I would put the check valve on and see if it will raise both pressures into spec.
Dennis
with the pump relay bypassed the injectors should spray continuously. Hence the "C" in CIS. I would put the check valve on and see if it will raise both pressures into spec.
Dennis
08-24-2002, 07:24 PM
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Ordering it tomorrow, will take 7-10 days!! but I am used to waiting
Thanks and I will get back to you on this when its fitted.
This car is going to run as it used to one day and that day is getting closer
<img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> <img src="graemlins/yltype.gif" border="0" alt="[typing]" />
Thanks and I will get back to you on this when its fitted.
This car is going to run as it used to one day and that day is getting closer
<img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> <img src="graemlins/yltype.gif" border="0" alt="[typing]" />
