Battle of the 35 year old fuel injection system CIS 1973.5 2.4L

[confused]

I am hoping a CIS expert can chime in here and help me out a little. Trying to keep this short and sweet but detailed enough. I pulled a 1973.5 2.4L CIS car out of a long slumber. The car is now restored and with much aggravation runs and moves under its own power. It still does not run well enough to go out on the open road.


Problem
The power comes on slowly, the transition from idle to speed is lackluster and soggy. Idle is perfect - although sometimes it surges and searches for idle. I think I can hear subtle popping as the car accelerates - like the engine is leaning out.



The last fuel distributor that was in the car made the engine backfire through the intake (pop pop) - the piston in that distributor looks like it was mangled - possibly welded to in order to free it. I had to file some of the piston cylinder to get the piston to move freely. This fuel distributor idled, popped wildly during acceleration, I think the piston is just not moving freely - hanging up and not allowing the air flow plate to move the way it should during acceleration - creating a lean condition.

2nd fuel distributor. I bought one on eBay, it showed up with a slightly aged Bosch Rebuild sticker on it. The piston was stuck, after some penetrant oil the piston freed. I doused the unit with carb cleaner, cleaned the piston an piston cylinder as well as I could and now the piston moves well....

this new fuel distributor runs the car well at idle. Revving the engine by hand you can hear and feel a stumble. I was thinking this is a lean condition, so I then revved the engine and gave a little assistance to the air flow plate to make the engine run a bit richer (it is very tricky to give just a little bit more plate movement while simultaneously opening the throttle). This seems to wake up the engine, you can hear a distinct positive howl out of the engine as if it is finally making the power it should.
So a big question is should I try cleaning the piston more to free up movement or is this distributor just bad.....
One cylinder not firing properly will drag the rest of the engine down sooooo thinking that I decided to pull the injectors and see how much fuel is coming from each injector - preliminary tests show that one cylinder so far is getting less fuel than the others. I plan on trying this test again in a more measured way.

Does anyone have any advice so far? Particularly looking for knowledge on fuel distributors as they mystify me. I have been told by a good mechanic friend that he does not trust rebuilt units. A rebuilt unit is going for a little over $1200 retail right now, I do not plan on buying a rebuilt unit unless it will guarantee a solution. Some of what i have done is listed below:






You have to love a 1 year only car when trying to find parts, how about a 1/2 year car, I have noticed that many 2.7L CIS parts are the same overall but most will not physically bolt onto the 2.4 car. Here is what I have done to the car in the last year:

Engine: compression numbers are ALL within 140psi +/- 5 psi. A leak down confirms the engine is good with numbers all 5% leakage or less. The engine block is sound and should make good power.

Gas tank - this is a half year only gas tank unlike any other early gas tank, you can not switch gas tanks with other years. My tank was full of old fuel mess, it was boiled, cleaned and resealed by a gas tank guy

Fuel pump - replaced with a good used tested used unit. Seems to provide plenty of pressure

New fuel accumulator

Fuel injectors - all the injectors were junk when sent out to be cleaned. New injectors have been installed.

Warm Up Regulator - I think it works fine

Cold start injector - was leaking into the plenum when it should not have. I changed it out with another used one from a 2.7 and it sprays only when the starter is engaged. The engine starts up immediately from cold now.

Fuel distributor from a 2.7L engine - the original 73.5 distributor is gone although it seems the 74-77 are identical.

Distributor Bosch 001 - cleaned well, the advance mechanism is moving well, dwell is at 34 degrees, timing set at 35degrees total advance with vacuum line disconnected, new cap/rotor/points.

Also installed- new injector seals, intake tube seals, pop off valve, Carrera pressure fed tensioners, Platinum plugs recommended by Pelican, new Bosch spark plug wires, valve adjustment, numerous seals, etc

[moneymanager]

Fuel distributors are a bear. My 73.5 got three before it ran well. My guess is that anything that requires force to move is pretty much junk...they are an extremely precise device. In your shoes I'd buy rebuilt only from Vertex or someone who will take it back if it doesn't work properly. Buying used is a real crap shoot.
I don't see anything about setting pressures in your note. Assume these are perfect? If they aren't, the car will run badly. Ditto for the air flow plate...perfectly aligned and free to move easily?

[MURF]

THROW THE CIS AWAY GO TO
www.bitzracing.com very user friendly weve done several every thing you need comes in the box.........porsche spoken here

[confused]

I would go EFI if the factory appearance of the engine could be retained. This car is too original and nicely restored to go with an aftermarket system. I wouldn't argue what is a better system but I would argue of what is original in a collector car.

[Paulporsche]

Have you tried richening the mix now w/ the new injectors and FD?

Have you checked your fuel and control pressures?

Have you verified that the sensor plate is set @ the right height?

Some on this BB don't like the platinum plugs. I have had some in my CIS car for years.

If the FD plunger now moves freely, I would leave it for now and try richening the mix first. Let us know what happens.

[MURF]

go to the web site and look at the pictures of the cars..will speak for them selves
more performance ,no ethenyl issues.turn key cold starts.just more modern technology..i'm not involved with them just super satisfied customer..murf

[911quest]

Not to sound like a broken record but you need to put some gauges on it. I would also do a volume test on each clyinder with and without the injectors.

Send me a PM I have an extra 73.5 fuel dist. if want to try it.

[jac1976]

Off topic, but what size tires are you running? Sharp looking 911.
Thanks,
jac

[Mysterytrain]

Are you saying that a rebuilt fuel distributor is not available?
I was searching for you and found this:
http://specialtauto.com/fuel-distributors.html
http://www.jaytanindustriesinc.com/PorscheFD.htm

[Sunroof]

I have been hearing so many opinions as to who has the best reputation on rebuilt fuel distributors? Has anyone used any of these folks?

Confused: can you let me know the serial number on your 1973.5T CIS distributor? I understand that the one for the 73.5T is specifically calibrated for that model and that one, say from the 1974 will screw up performance? Might be something there!

Places like those listed claim that the 73.5T cores are hard to come by, so they have to rebuild your unit.

I have a 1973.5T and have just about replaced every CIS componment but the distributor. The BIGGEST issue thus far is that built in check valve in the fuel pump (only on the 1973.5T pump mind you) SUCKS!!!! I replaced all my fuel lines, replaced the airbox, intake runners, cold start valve, fuel injectors, accumulator, WUR, refurbished the fuel tank, replaced the fuel pump and my old lawnmower starts up better then my car! Folks say "change the therotime switch", but we know better! It does not exist on the 1973.5T CIS model. Once warmed up though it runs like new. I think CIS defies physics!!

I would say that you may have a myriad of things going on but certainly start with a fresh fuel filter................often thats all the difference in the world.

Bob
1973.5T Sepia of course

[confused]

Thank you guys for the responses, trying to cover all areas and answer all questions.


I tried to richen up the air/fuel mixture and it does not want anymore fuel. If I increase the fuel adjustment at the Fuel Distributor the engine dies off.


I do not have a recent fuel pressure and control pressure test, I did check pressure about a year ago when I first put power to the car. I will try to get my friend over with his gauges to check pressure.


I have had the car running on 2 different Fuel Distributors both with the last 3 digits of the part number being 006. I have seen 5 or 6 different FDs so far, there seems to be many different part numbers. I did notice when comparing FD pistons that some are different length and you can not move one piston into a different FD. There could be something to a 73.5 only Fuel Distributor, however, note that Pelican has a FD listed for a 1973.5 2.4L engine AND they have one listed for the late 2.7L engine BOTH with the same part number and price. The car is running in a way that it feels like in needs only slight adjustments.


How do I align and check the air flow plate? I was wondering if it could be off.


COLD START Bob, the 73.5 does not have a Thermo Time Switch - it does have a cold start injector that is powered by a yellow wire on the same circuit as the Starter solenoid. The ground for the cold start is activated by the micro switch on the throttle body. In order to start the car you pull up on the hand throttle - thus activating the ground to the cold start injector, then and only then the cold start injector will fire while the starter is engaged. It took me a little while to understand this system but now it is cake! Its just an early manually controlled cold start rather than a temperature/automatically controlled cold start.


I know that rebuilt Fuel Distributors are available but I would rather not spend the money if that is not the problem, they are not cheap.


Jac, I think the tires I have on that car are 205/60/15 - on early 911 cars I like 205 or 195 size tires with a 55 up to 65 series. My fav tire on my 914-6 is a 205/55/15 Dunlop SP although I do not know if it is the best tire but it looks very cool and has a rubber lip to protect my Fuchs.


I will attempt to measure the volume of the fuel flow from each line - with and without injectors. I will also read up on the plate adjustment.

[moneymanager]

I believe that the 73.5 fuel distributor may have been different, but has been unavailable for years. Most people use the later one, which someone once told me then needs a 74 or later WUR and a tiny bit of rejiggering. However, I think you've jumped right to the most complex part of the problem without checking at least two simple basic things first: air flow plate alignment (put your finger under it and lift, let it drop and be sure it doesn't hang up anywhere, do it two or three times) and system and control pressures (knowing what they were a year ago before you made a bunch of changes is pretty much useless. If they are off, the car will run like it has 3 cylinders.) Good luck.

[911quest]

I just got done battling a 74 which is very similar to the 73.5 it had a few different problems one thing to check does the warm-up regulator have voltage? It is wired different then the later CIS cars. It has a relay back on the relay panel in the engine compartment....

[confused]

Control pressure is around 42psi

I did the injector test - or I put all 6 injectors into equal plastic containers. One cylinder (my injector to #3) has less fuel volume. You can see in the side by picture - the container on the right is the affected line.

I tried this volume test multiple times, I switched injectors, cleaned out the affected line - Always the same line has significantly less fuel volume than the others. It seems to me that the one particular port in the fuel distributor is putting out less fuel. Looks like rust or ???? is clogging one of the outlets.

[confused]

I put a rebuilt fuel distributor from Jaytan Industries the other day. Car revs perfectly now. Power all the way up to redline.

The ****** fuel distributor was the problem all along

The rebuilt unit I got was a 006 or a 2.7L Fuel Distributor.

For future readers I do not believe the 73.5 only fuel distributor is required for a 2.4L. The 2.7L unit works fine. The 73.5 WUR works fine with the 2.7 Fuel Distributor. The 017 FD for the 2.4 is a hard find, the rebuilders can fix your if you have it. I only had a 006 2.7 unit so thats what I got in exchange. Only time will tell if the rebuilt unit works indefinitely.

When you think about it a 300cc displacement difference is not much - a 2.4 vs 2.7. I think most all the parts from a 2.7 system would work but most of the parts simply will not physically fit the early 1 year only engine.

If anyone has a problem in the future with 73.5 CIS systems then feel free to email me as i have learned quite a bit on these systems. allaircooled@yahoo.com

[Sunroof]

Confused.

Glad to hear you finally nailed the problem and back on the road. When researching Fuel Distributor rebuilders their is a handful around. The big question is who is the best or most dependable? Was JAYTAN your first choice here? Obviously you recommend them, but I am curious to know if you checked others out before making your choice. By the way, what did you pay for the rebuild?

Thanks
Bob
1973.5T/CIS

[confused]

It is hard to do research on rebuilders. I can't call them up and ask "are you guys any good?"

I chose Jaytan because they offered a 2 year warranty, they were lower cost at $314 w/$100 core. The person I talked to was friendly and they are only 75miles away with a real address so in the worst case scenario I can show up at the shop if something goes wrong that they won't fix.

[Paulporsche]

Great work! Let us know how things work out.

[Sunroof]

Good information............many of the other rebuilders are asking $400.00+ for the rebuild. Two year warranty ain't too shabby either.

Bob
73.5T in Sepia