CIS FD CrAzInEsS

[Wyvern]

Hello.

I am working on a 75, 2.7
All pressures are in spec, timing is set and advance is working

I have been fighting the CIS battle and the last part is the FD.
I have uneven and improperly metered fuel (too rich when cold and low revs - Too lean when warm and high revs)

The PO did tell me that in his efforts he did take the system apart and his method of sealing the WUR, fittings, and YES the FD was to use copious amounts of silicone

I did take the FD apart (not much to loose) and cleared out all the junk, it was clean and did seal but no new O rings ... just cleaned all the silicone out (did new injectors at the same time) the car runs "OK" after all the things I have done. But just OK.

I have sourced another FD . Same Bosch # (0 438 100 006) even got the Plenum and that is the same # (different stamped secondary #s)

These FDs are VERY different.
Please any insight ???
The FD on the car now does NOT have the allen screw (adjusters).
Why would the same Bosch # ... clearly be a different unit ?
One thought of mine is that the unit on my car now, may point to a 1975 CA item ..? but just thinking out loud on that one.
My thought was to replace the FD after cleaning (not disassembly) as it came off a running car)
for your viewing pleasure ...

this is on the car now. Note no allen adjusters


Note the RED tag


This is the unit I have off a "good running car"
The duct tape is how it was shipped to me ..It is holding in the pin.


Thanks for any insight ..

[Dr J]

The mixture adjustment is not made with the allen screws on the FD. You shouldn't have to touch those. There is a small hole just to the left of the FD (on the air mass flow sensor) to adjust the mixture. You insert a 3mm long allen wrench (ccw to lean and cw to enrich).

However, the problem you mention is not fixed by that. Are the vacuum lines to the warm-up regulator properly attached? Is the electrical connection to the WUR working?

[Scott R]

Yea, don't open those allen's up. Can you post your control pressure readings? I can see you have a CIS tester hooked up in your picture there. I know you said they are in spec but it would be easier to see the delta between cold and hot.

[Wyvern]

I will post ALL the stats.

My bigger question is why are 2 Bosch FDs the same # so different.
Is the one on my car correct or is my "new" one correct ?

[Jim Williams]

Here is the story on the two fuel distributors: As far as I know, the one without the external adjusters is the type that came on the cars up through the 77 year models. The one with the adjusters is a later style that came as a replacement type from Bosch for the 006. The specs should be the same, unless someone has changed the later one. The earlier one was adjusted with internal shims. So in a technical sense they are both "correct"'.

[Wyvern]

Great info Jim.

I installed the new to me FD (the one with the adjusters)

At last ... a nice even spray at all 6 injectors.
Tested with the key on and did tests with just slightly pushing up on the plate and then with a bigger push and hold it there. all 6 bottles filled to the same level both times.

System pressure 4.7 bar

cold pressure this morning was 1.7 bar I woke up early and tested at 68 deg F

warm pressure 2.7 bar as temp was around 90 deg F after a drive around the block was still 2.7

leak test 10 min 1.2 bar
20 min 1.0 bar

no longer have irregular idle at startup and at temp.

Without a CO or AFR meter I am now working by the good 'ol headache / sniff / another trip round the block method ..

In the garage I can blip the throttle , slowly raise engine speed and it seems ok.
Does not like load at all ....

Thoughts ....
My understanding is that CW on the mixture screw and even CW on the idle both richen (and vise versa).
I have tried the mixture screw up to 1.5 turns in both directions and adjust the idle to let it run smooth.
seems about the same.
I think I am mixing rich and lean cues.

Perhaps ... right now ... I should stop and go th a shop that understands CIS and has meters. I just am not one to give up.

[Wyvern]

well I didn't stop ...
I played a bit with both the idle and the mixture ....
I discovered that if I moved the "plate up" (off of the spring plate stop . decided to do this as I noticed that the bellows were being sucked in as i reved the engine). just a bit that I no longer had the issue with load. but was very rich at idle 1/2 and full. so I then leaned it out ... set the idle and I HAVE IT.
Never run so well ... cold and hot start up from outside the car, NO flat spots, no back firing. Maybe just really lucky but I really understand what the system does (school of hard knocks)

Thank goodness for my years with very odd Brit and German cars and motorcycles ...

On a 50 mile test today everything was perfect. what a joy.
Can you see the smile ?

Inspired to now start the rest of my "things to do list"