Is it time to rebuild the CIS fuel distributor? | FerrariChat

Is it time to rebuild the CIS fuel distributor?

Discussion in '308/328' started by dave80gtsi, Sep 21, 2020.

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  1. dave80gtsi

    dave80gtsi Formula 3
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    Nov 3, 2003
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    Dave Meredith
    I bought my 308 in 2003, and while I've done many DIY maintenance items, I've never touched the Fuel Distributor. And looking thru those maintenance records which I have which date back to 1980, no one else has ever done, either.

    So, now it is 40 years on. Thinking about pulling the F.D. this fall, and sending it to Larry Fletcher for a R&R. I have no genuine symptoms of mis-running, other than the appearance (and smell) of the car running rich. But that's pretty much the same as it has always done. All injectors are new and were flow-tested and matched (there's a thread here in the archives on this which I started).

    As F.D.'s wear with time, is their tendency to slowly start to run rich? Thinking that, as the various internal O-rings and seals age, their trend could be to allow excess fuel to pass by?
     
  2. miked

    miked Formula Junior

    Feb 7, 2001
    821
    Cincinnati, Ohio
    I rebuilt the CIS Fuel Distributor on my Audi ur quattro after it couldn't pass emissions. It would start normally hot or cold but had a soft or no reaction to small throttle changes. The main plunger becomes sticky over time from things in the fuel, similar to a carb gumming up. There really isn't much that goes wrong with these things, not much to do other than replacing "O" rings and cleaning the parts.
     
  3. Pero

    Pero Formula Junior
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    Apr 22, 2011
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    Peter R

    I might have a renovation kit for the FD in the garage. Can check tomorrow if interested.
    /Peter
     
  4. rjlloyd

    rjlloyd Formula Junior
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    Jun 19, 2014
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    Richard Lloyd
    I put a kit through my distributor not long after I bought it 6 years ago for all the reasons you describe. Car started and ran ok but had been poorly maintained in its life, so figured why not
    After putting the new kit in I cant say I really noticed any difference and car continued to run as usual.
    Anyway 2 months ago I decided to send it to a specialist for rebuild (just because) as they have the ability to measure/set flow rates etc.
    All I can say is it transformed the way my car runs, it starts easier, idles smoother, smoother power delivery.
    Whilst replacing 'o' rings and the diaphragm etc isn't particularly difficult, the ability to set them up on a flow bench appears (certainly in my case) made huge difference. best $700 Australian I've spent on my car, (this year at least :) )
     
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  5. dave80gtsi

    dave80gtsi Formula 3
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    Nov 3, 2003
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    Thanks for this - yes, this mirrors my own thought process.

    I've seen a video or two on rebuilding the F.D. While the process seems straightforward, I lack the experience to be able to recognize any faults which I might encounter. Better, I think, to place the unit into the hands of those firms who do this for a living.

    This will be a winter project, so I'll make it a point to report back after the work is done.

    Thanks - DM
     
  6. Banzairacer

    Banzairacer Formula Junior
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    Aug 24, 2017
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    Sanjeev Thohan
    if the set screws for the fuel mixture is ultra sensitive, a rebuild would be appropriate. I just had mine done for an 85 308QV that had never had it touched (Southern California shop). it made a world of difference, no more hard starts when warm. The fuel pump was fine but the vaccum return was weak and so it was probably flooding and bogging.

    Sanjeev
     
  7. SeattleM5

    SeattleM5 Formula 3
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    Jul 9, 2006
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    Ettore Palazzo
    The Bosch CIS system has intrigued me ever since acquiring my 328 over 10 years ago. It became an obsession of sorts and led me to build a test bench where CIS components (fuel distributors/WURs/etc) can be tested and calibrated. I have tested and rebuilt many distributors and I can tell you that CIS components in regular use generally remain well calibrated. That stated, cars that sit and are not driven frequently do suffer from fuel deposits which over time result in unequal fuel flow from the output ports which most certainly will affect performance. The performance difference when comparing a car with fuel distributor output flow variances of < 5% at idle/part load/full load to one that is out of calibration is quite remarkable. Note that the Bosch documented tolerance for flow variance between the ports is up to 16% at idle and 10% at part/full load. With the correct equipment and patience fuel distributor flow variances can be set to as low as 5% on most distributors. Performance enhancements are even more striking when you match a balanced fuel distributor with injectors that have equal opening pressures. A note of advice: For those sending their distributors off for rebuild, I would absolutely insist on pre/post rebuild testing data documenting exactly what the flow variance is between the ports along with system pressure and residual pressure documentation to ensure that the internal pressure regulator is set appropriately. Through the years I have been asked to test distributors which reportedly had recent rebuilds by well known 'professionals' and it is clear that they did not take the time to properly calibrate output flows.

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  8. waymar

    waymar Formula 3

    Sep 2, 2008
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    Wayne Martin
    I went the rebuilt exchange route. Best change/upgrade I’ve done along with rebuilt exchange digiplex units.
     
  9. 2cam

    2cam Formula Junior

    Aug 28, 2014
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    MikeS
    What are some of the key signs that a fuel disty needs to be rebuilt or needs a good calibration? My US market 3.2 Mondial fires right up when cold but becomes a bit more difficult to start once warm. It also idles about 500 rpm higher once warm than when cold. I'm wondering if this may be one of the potential causes.

    2cam
     
  10. SeattleM5

    SeattleM5 Formula 3
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    There are a whole host of symptoms that can be traced back to unequal fuel distributor output flows. On cars with Kjet with lambda (which I assume your car is as a US market 3.2) one of the first symptoms is often an increase in idle surge variation as the closed loop feedback system attempts to fine tune adjust the control pressure to maintain the AFR at the stoichiometric ratio. Note that Kjet with lambda systems all demonstrate some degree of idle surge variation but on a car with a well balanced fuel distributor it is very minimal.

    Warm start challenges on 3x8 cars are often CIS related but more likely the result of inadequate residual fuel pressure after shut down. Many will look to the fuel accumulator first as a potential culprit for failure to maintain residual pressure, however, there are multiple CIS components that can fail and cause lack of residual fuel pressure after shut down. In sequential order from the fuel tank to the engine of potential component failures affecting residual fuel pressure: Fuel pump non return valve --> fuel accumulator --> fuel pressure regulator plunger o-ring (installed in the lower chamber of the fuel distributor) --> fuel distributor diaphragm (diaphragm compromise) --> injectors (leaky). The first thing I do when encountering a warm start issue on a CIS car is to perform a fuel pressure test with particular focus on the fuel pressure after shut down. Your workshop manual calls out what fuel pressures should be maintained based on time after shut down.

    Hope this helps.
     
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  11. 2cam

    2cam Formula Junior

    Aug 28, 2014
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    MikeS
    That's great info. Thanks Ettore! I've been leaning toward the accumulator but the OPs post about the fuel disty had me wondering if that could be a cause as well. Thanks for the additional suggestions.

    2cam
     
  12. Brian Harper

    Brian Harper F1 Rookie
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    Feb 17, 2006
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    Really? Do you understand what the accumulator does?
     
  13. SeattleM5

    SeattleM5 Formula 3
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    #13 SeattleM5, Sep 24, 2020
    Last edited: Sep 24, 2020
    Brian, I'm curious what your understanding is of how the fuel accumulator works. If the internal diaphragm in the accumulator fails, residual pressure can not be maintained after shut down which can affect warm starts. Note that I'm referring specifically to 2cam's comment regarding warm start challenges. I don't believe that his comment regarding higher idle issue is related to this. That is an entirely different conversation.

    One final comment, . . . there is an easy way to determine if accumulator diaphragm failure is the cause of lack of residual fuel pressure after shut down. On US cars just pull the hose off of the atmosphere port/nipple on the end of the accumulator shortly after shutting the car off and see if fuel is leaking out from this location. On non US cars I don't believe there is a hose on that port and you can see fuel leaking directly on the ground from that location.

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  14. 2cam

    2cam Formula Junior

    Aug 28, 2014
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    My apologies - I didn't mean to conflate the two issues. You're correct - the accumulator wouldn't impact the high idle. I was looking at it from a hard start perspective once the car is warm. The car still starts - just not with the instantaneous pop that it does when cold. The high idle is definitely caused by something different. Just not sure if there's a common link between the two somewhere within the system.

    Thanks Ettore! I'll check that this weekend.

    2cam
     
  15. tbakowsky

    tbakowsky F1 World Champ
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    Sep 18, 2002
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    I had a rolls cornish in the shop not too long ago for a hot start issue. The accumulator as usual was the issue.

    However..on this car the usual vent side of the accumulator was fed direct fuel from the main outlet line for the fuel tank which gravity feeds the fuel pump.

    Changing the accumulator turned into a complete mess of fuel running down my arm and all over the floor. Why did Rolls do it this way? I have never seen fuel being fed to the vent side of an accumulator ever..yet this car had it, and the car ran like a champ after..no more hot start issue..customer very happy..but I'm confused..can you explain?
     
  16. SeattleM5

    SeattleM5 Formula 3
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    Hi Tom, I'm not sure if this question was directed to me or others on the thread but I'll give it a shot. I have never seen the atmosphere port of a Bosch CIS fuel accumulator plumed in the way you describe. It most certainly peaked my interest and I tracked down a Rolls Royce Corniche workshop manual which shows exactly what you describe (see attached diagram). It looks like the atmosphere port of the fuel accumulator (#22 in the diagram) is connected to the return line from the fuel pressure regulator on the distributor which travels back to the fuel tank. It looks like the accumulator also communicates with a separate line connecting the lower chambers of the fuel distributor to the fuel tank which carries an inline fuel damper (#12 in the diagram) and a fuel pressure control valve (#13 in the diagram). As I understand it, many countries required the atmosphere port on the fuel accumulator for Bosch CIS equipped cars to be connected back to the fuel tank in the event that the fuel accumulator diaphragm failed thus preventing raw fuel from being released to the environment (this was the case with US bound Ferrari's with Bosch CIS). On all of the cars that I have worked on this was an isolated line directly from the accumulator back to the fuel tank. Perhaps for efficiency sake Rolls/Bentley decided to plumb this line into an existing fuel tank return line. It certainly makes replacing the fuel accumulator a much more challenging task as you noted.

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