[urq] Fuel Pressure leakdown testing CIS E III[wasWarning about Fuel Pressure Accum.]

[Ben Swann]

Good info. Pete - even I learned something new.  I am sure I have a leak somewhere, and wonder if running a pressure test will tell me anything other than indeed the system is leaking down injector side.

Since hooking up the guages is typically a PITA, I am incluned to just replace the injectors first now that I have them, and then run the pressure tests  IF AND ONLY IF the problem still exists.

I appreciate any other tips on methodology as I'll be doing this soon and even located my long unused guages and adaptors today.

With respect to the different points appreciate any clarification.

1. I assume my check valve is good as it is a new pump and AFAIK the valve is in the pump - correct?

2. Leakdown through the pressure regulator (we're talking about the cylindrical one located on the fuel distributor, not the Warm Up Reg. which my CIS-EIII system doesn't have.   Pressure reg.  - how does it leak, and  if so what is the fix?  Wouldn't a leakthrough system to control side occur at the needle/plunger valve located in the side of the distributor under allen screw fitting I think called system pressure regulator valve (my recall is from 5kt CIS distributor, so forget how it is on CIS-E3).

3.  This is where I feel my problem is, as I can run the pump and crank all day with no start.  I have seen the weepage that occurs in aged injectors on  3 of 3 cars using this type of injector that I checked because they were having hard start problem and subsequent replacement resolved  I am thinking this is what is happening and since CS injector is on same portion of circuit, I get no spray from this either due to reduce pressure.  

One question I have regarding this is why after charging the system with fuel pump and cranking for awhile isn't the plate rising enough to get the line up to pressure to start - or something to that effect?   I can't locate any intake leaks and everything is tight - completely new installation of hoses, etc.  

4.  Leakdown Problem possible here too - I guess removing the CS injector and checking not a bad idea.

5. Hmmm.

Just to confirm my thinking and help troubleshooting,  If there is a leakdown through an injector, but not in the supply side,  the system supply side should stay up to pressure - right.

Conversely, if there is a leakdown supply side (from the fuel pump) but not through an injector, the injector lines should stay charged, correct?

Or will any leak supply or injector side result in full system leakdown, including injector lines?

Ben

[From: a4kcstq at comcast.net
Subject: RE: [urq] Warning about Fuel Pressure Accum.
To: quattro at audifans.com
Message-ID: <012820041952.19285.7e84 at comcast.net>

The fuel pressure accumulator helps to maintain residual pressure by storing a small quantity of fuel under pressure.  It also damps pressure oscillations, as Ben correctly pointed out.
There is a specific residual pressure test (in Bentley) for CIS systems.  It's something like 35+ psi after 10min is OK.  Remember that there are 4-5 openings in a CIS system (excluding bad connections) and you need to check all 5 if your residual pressure is not OK.  Loss of residual pressure will potentially cause hard starting and/or vapor lock.
1.  Fuel Supply line (the fuel pump check valve)
2.  Fuel Return line (fuel pressure regulator in the fuel distributor or external)
3.  CIS injectors
4.  Cold start injector
5.  Frequency valve (if equipped)

You can lose pressure even if the accumulator is good, it just means you have a leak that's bigger than the storage capacity of the accumulator.

Some CIS systems (4kq in particular) have a fuel pump prime feature that bumps the system up to ~80psi just prior to starting.  This won't help prevent vapor lock, however.

-Peter Lines