Question about early cold start enrichment solenoid and throttle bodies
 

Regarding the cold start enrichment solenoid, it is my understanding that in 1969 models (E and S), the solenoid was located directly on the MFI pump, and in 1970 Porsche moved the location of the solenoid to the fuel filter console. However, the fuel spraying were still into the same place (airbox) until 1972 with the introduction of plastic stacks.

Why did Porsche move the solenoid to a different location in 1970?

What are the pros and cons of the 1969, 70-71 and 72-73 cold start systems? Which is the best in terms of performance and safety? Are they interchangeable?

Throttle bodies - what are the differences between 69, 70-71 and 72-73?

Thanks.

You are correct about the 69 being different.
It did have a second solenoid on the pump for enrichment.
It was a complicated system of sensors and wiring...and sometimes it would either not activate on cold starts...or would on hot starts (there is a little box with a relay and electronics involved).
I ripped out all the extra wiring on mine...and used a button on the dash to feed +12V to the solenoid on the pump for starting.
It made it a lot more positive in control.
Also...the thermostat on the pump...it takes warm air from the exhaust jackets to activate...and the tubing and hoses were a mess...soo...I removed it and put a plate over the end of the exposed shaft with an adjustment device for enrichment (worked like a charm).
In all other MFI systems...they seem to have used some sort of direct pipe feed enrichment system (shooting raw fuel down the throats)....(very dangerous in the case of a backfire).
Bob

So, do you think the reason Porsche moved the solenoid to another location in 1970 was to tidy up the wiring and hoses - a more simplified version?

Regarding shooting raw fuel down the throats, I think 1969 E and S did that as well - not just 70-71.

Am I right thinking that the only difference between 2.0S and 2.2S MFI pumps themselves is the removal of the cold start solenoid? Same performance otherwise?

On my 69...there was NO direct down the throat fuel injection.
It only had the enrichment solenoid.
As to the changes for 70/71/etc ... who knows? The factory may have had second ideas about the costs involved with the more complicated 69 pump.
If you try to second guess a factory change...you have to consider that perhaps a personnel change was involved.
When new people come in to a position...they may keep or discard any or all of the previous designs and ideas.
All you have to do is look at GM when Duntov came to power...he changed everything! (most for the good).
Bob

69 also has the solenoid on the fuel filter console, I believe.

2 liter pumps can be modified to flow more fuel I believe, and are preferred for making an RSR pump clone. 2.2 and later pumps have a different space cam follower (ball vs. point type) and I think a move complex mapping. At least this is my understanding.

Speaking of a fuel consol...I found my old one on the shelf the other day.
Since the car is gone...I suppost I should sell the thing to someone who needs it.
Bob

So, where did it squirt fuel when cold starting?




I've just had a look at the PET. Yes, that's what it says, apparently. So, does it mean that 69E/S models had TWO cold start enrichment solenoids? :confused:

The one on the pump would force the rack full rich and the one on the fuel console would squirt fuel down the stacks.

I went through all the pics I took of the system before I took it apart...and I could not see a direct tube or pipe leading from the fuel console to the air filter housing or top of the throats.
Seeing as the new system worked so well for cold starts (applying power to the pump enrichment solenoid)...I can't see any reason for the original system to pour more fuel down the throats....it would flood the engine.
I may be wrong...but after my mods...the cold weather starting (even at -20F) was just fine....I would push the button...fire it up...keep pressing the button for a few more seconds...then release....then maybe give it a couple more shots as it warmed up.
Bob

According to the PET, the 69 has the same steel airbox and spray bars as 2.2 models (same part numbers). Maybe yours were removed before you bought the car?

I've just remembered that I have a MFI brochure inside the box of my workshop manuals, so I went to have a look. Found some good info!

COLD START ENRICHMENT SOLENOID
1969 2.0 MFI
Primary - Located on the MFI pump
Thermo time switch operates between -25°C and +10°C

Secondary - Located on the fuel filter console
(injects fuel into intake pipes)
Thermo time switch operates between -10°C and -30°C

2.2 MFI
Located on the fuel filter console
(injects fuel into intake pipes)
Thermo time switch operates between 0°C and +45°C




I have taken a couple of pic of the relevant pages:

http://forums.pelicanparts.com/uploa...1387729545.jpg

http://forums.pelicanparts.com/uploa...1387729578.jpg


For 69 models, I agree the best way is what Bob did - delete the secondary system (who'd in their right mind drive their early 911 in weather temperatures below -10°C? :eek:), and for the primary system - remove the thermo time switch and install a driver-operated 12V button on the dashboard wired to the solenoid on the MFI pump for starting. :cool:


For 2.4 models, there was no diagram. However, it states:
Characteristic features:
Thermostatically controlled device.
Intake manifolds make of synthetic material.
Vacuum-controlled ignition distributor.



Sorry if it's a stupid question but aren't 2.0 and 2.2 distributors vacuum-controlled?

My 69 E has both systems as described above. It was not uncommon to remove the direct squirters due to fire hazard. Mine lived in FL so never had a really cold start.
Dave

For performance applications we found that eliminating all of the factory equipment in lieu of a hand operated device was the answer for many applications both street and race.
First, no need for a heat riser system, making the use of aftermarket headers far easier.
Second, eliminating the cold start injector makes intake fires a thing of the past.
Third, putting the cold start system under the command of the operator meant that you never have an issue with over rich running when enrichment was not called for.
Our cable operated system also eliminates a plethora of wiring and fuel plumbing.
BTW: all of our modifications are bolt on requiring no change to your pump and is completely reversible.

http://forums.pelicanparts.com/uploa...1387814610.jpg
http://forums.pelicanparts.com/uploa...1387814714.jpg
http://forums.pelicanparts.com/uploa...1387815026.jpg

Stolen from another forum:

http://forums.pelicanparts.com/uploa...1387827960.jpg

Bob,
When you ripped out all the extra wiring and used a button on the dash, did you also remove the 2-second time limit relay?

Henry,
Your device looks very interesting (thanks for the pics :) ). However, I'm a little confused bacause it appears to be attached to the warm-up thermostat rather than where the solenoid was, next to it. So, can you please explain what's difference between cold start (full rich) and warm-up thermostat?


p.s.
Those trumpets look good. Are they stock?

All the various devices attached to the MFI pump ultimately act on the rack, but through different linkages. All you need to do is connect to the rack and you can do that with the thermostat port, which is present on all MFI pumps, rather than go through the one-year-only cold start solenoid port and need to make and stock a separate part number that will have a much more limited market.

Even though the pump is a twin-rack? (if that what 'twin-row' means).

The rack has teeth on both sides and goes down the middle of the rows.

http://forums.pelicanparts.com/uploa...1387831124.jpg

Thanks for the clarification. :cool:

Our intention was to eliminate all the factory cold start devices in favor of one hand operated device. Because the thermostat system would accomplish that task without any modification to the pump we chose this access point.
The trumpets are PMO 52 mm trumpets installed on a set of our modified mag stacks. 41.5mm at the butterfly end and 52mm at the top of the stack.

Blue...yes...when I removed the cold start stuff...I pulled out everything.
Like I said before...I just found the console assembly on the shelf....so possibly I might still have the rest of the equipment that was removed.
I though I sent everything with the car when I was forced to sell it (health reasons) but some stuff keeps turning up.
Bob