Upgrading / changing CIS components

[teveo]

Hello, I have a 78SC that is a little thirsty, but most of all its not running very nice.

The idle and cold start is poor, the WUR have "the allen screw" and it does not look too work very well. Having read up on the CIS development in the 911 it seems like alot of people is in favor of using the 2.7 fuel distributor and air metering unit.

I was thinking about interchanging with parts from one of two CIS systems I have, a CIS taken off a 1977 911S (it ran very well) and also a 1974 Carrera CIS system.

The 74 Carrera CIS is very lively, it almost has the same response as the "MFI"(not quite but well more responsive than the later CIS).

Initially I was going to follow an advice which involve using the air metering and fuel distributor from the 2.7, but my carrera is getting an RS style engine so that CIS is also becoming available.

I would be happy for any advice on what parts to put on my 78 SC.

[Alan L]

I dont know what you mean by Allen bolt mod.
But the symptoms are diagnosable and fixable. The system is capable of running well if you track down the faults. What is wrong with the idle (warm ,or cold).
There are many places to start looking - need more info. Air leaks would do all the above.
Alan

[boyt911sc]

Originally Posted by teveo

Hello, I have a 78SC that is a little thirsty, but most of all its not running very nice.

The idle and cold start is poor, the cold start valve have "the allen bolt mod" and it does not look too work very well. Having read up on the CIS development in the 911 it seems like alot of people is in favor of using the 2.7 fuel distributor and air metering unit.

I was thinking about interchanging with parts from one of two CIS systems I have, a CIS taken off a 1977 911S (it ran very well) and also a 1974 Carrera CIS system.

The 74 Carrera CIS is very lively, it almost has the same response as the "MFI"(not quite but well more responsive than the later CIS).

Initially I was going to follow an advice which involve using the air metering and fuel distributor from the 2.7, but my carrera is getting an RS style engine so that CIS is also becoming available.

I would be happy for any advice on what parts to put on my 78 SC.

teveo,

The first thing I usually do when performing CIS troubleshooting is hook up a fuel pressure gauge and check the control and system pressures, followed by residual pressure. You could check your WUR, AAR, TTS, CSV, TV, FD, FP, injectors, etc. without even running the engine.

In your case, I would check the CSV and TTS to facilitate start-up. Once you get your engine fully warm-up, check for vacuum leak. Remove the oil fill cap and observe the engine RPM slightly go down after the removal of the oil fill cap. If the engine RPM does not change a bit, you have symptom for unmeterred air (vacuum leak). Keep us posted.

Tony

[teveo]

Thanks for the advice, the WUR has had the following fix which does not seem to do much good .. (allen bolt)
http://www.pelicanparts.com/techarticles/911_warmup_reg/911_warmup_reg.htm

I read a post about the 2.7 CIS being a better choice and having 2 good systems left over I would like to see if one of those would make my engine more responsive.

Shall check the WUR and TTS today, earlier I checked my car driving with thr LM1 and the AF seems ok, the car runs very fine on throttle so that was not a surprise.

[teveo]

Installed the air flow sensor (unit) from a '77 2.7 today, I was going to install the 2.7 fuel distributor as well but I could not find the 2.7 WUR ( maybe I sold it ) so it would not work. The 3 liter has a tube from the fuel distributor down to the WUR, the 2.7 has an Y-pipe which will do the job but i could not find that one tonight either..

I also installed a new FPR and filter, it may cure the warm start problem but it did nothing much to the idle and cold start..

+ 30 minutes.. ... just drove home from my hobbygarage, car run like sh***,.. well so much for mix and match. Tomorrow I will reverse to the original air flow sensor and do it by the book.

Check the fuel pressures
Check all connections for vacuum and clean out the WUR ( took of the oil cap on idle, no change in Rpm's )

Will also test the A/F ratio under various rpms and under driving condition, for what it is worth it does not seem to be possible to get a steady A/F ratio with the CIS system but if it gets around 14 - 14.7 under normal operation it would be nice.

[cmonref]

You will drive yourself nuts enroute to the poorhouse by swapping parts, until you methodically check the CIS system as suggested by Tony above. A CIS is not tunable until you check and adjust everything -- and intuition based on other injection systems' performance and foibles is worthless. There is a wealth of knowledge on this board to assist you along the way, but you gotta decide to do it.

Brian

[Alan L]

+1.
There is a systematic approach to dealing to this problem, and in the long run, it is the quickest route.
It is still not clear what the symptoms are. Your earlier ref to the allen head mod referred to the CSV. I now gather you may have a tunable WUR via the allen screw mod.
You need to be precise with the information, and I would start by measuring your WUR pressures - cold/hot/system (since that has been modified).

[teveo]

Correction, initially I wrote cold start valve but was referring to the WUR, could not get the name from the back of my head..

Swapping the parts for 2.7 pieces are recommended by many a specialist and I was going to tune the car afterwards, but yesterday I could not get any decent reading on the LM2 and that was after I had gone through all potential vacuum leaks. Later on the car drove very "non satisfactory" to the least. I never got a good relation to CIS, either a car work fine for years or it is a constant struggle to make it run nice..

First I have to get my original pieces in place. I will try out the cold start valve from the 2.7, that piece looked new but the rest will be the original 3 liter pieces.

I'd love to see A/F ratio curves from anyone that would happen to have it.. my curves for hot engine were good but on cold start it is only the pop valve that has saved my airbox (its backfiring).

I'll take out my tools and start on Tony's checklist then..

[boyt911sc]

teveo,

If you want to run your CIS engine, you need to know and understand how CIS components work as a system. You could mix and match CIS parts if you have the know-how to measure the individual performance of the substitute component/s otherwise, you'll be doing a lot of guess work.

Establish your baseline data. Start with fuel delivery and pressures. The heart of your engine is the FP. So knowing your control and system pressures would tell you a lot about your CIS (FP, FD, and WUR). So your main objective is to make the engine start and run after one turn of the ignition switch. Then you could concentrate later on setting the mixture to stoic (14:1).

Provided you don't have a significant vacuum leak, all CIS components in good working conditions, correct ignition timing, and a decent compression, your engine should start and run!!!! CIS troubleshooting is easy and fun!!!!! It's basically fuel pressures and vacuum..........keep these under control and you'll enjoy driving your car for a very long time. Keep us posted.

Tony

[teveo]

Yes, I have a teoretical knowledge from the Bosch FI book, however putting this to practice is a little harder. I was really confusing myself with the FPR and CPR on top of this.. everyone talk about the WUR but the Bosch litterature only mention the CPR..

Anyway, we hooked up the CIS tester and here's the results.

Test 1: original WUR with Allens screw mod
---------------------------------------------------
System Pressure 5.0 bar
Cold Pressure 3.3 BAR
Warm pressure 3.5 - 3.6 bar

Test 2: 1981 WUR but with the bottom parts from the 1978 WUR ( no vacum on the 81 wur)
---------------------------------------------------
Warm pressure 3.1 bar
.. I will have to check the cold pressure on that one tomorrow obviously

So, we could assume that original and modified WUR is crap, the 81 WUR I have to check tomorrow on dead cold engine.

[cmonref]

the 81 WUR I have to check tomorrow on dead cold engine

Not really. If you take the WUR apart and remove the bimetal device, then put it back together and reinstall it, it will give you the "cold" pressure.

"Cold" is specified to make sure the bimetal device is not in contact with the operating mechanism. Remove it and you have achieved the same thing.

When you reassemble the WUR, use a spot of grease to hold the little operating rod in place -- it has to stand up with no means of visible support while you put the bottom plate back on.

Brian

[teveo]

Yes, thats a good idea, I could do that but I just put it together so I'll do it tomorrow on cold engine..

I did run the engine with the LM2 and received 13.9 - 15.2 air fuel ratios and the engine seem to be more happy with the current setup. The AFR seem to be good.

[Alan L]

Your cold pressure is way too high. This will cause much of what you are experiencing.
I have a friend with a 2.7 who has the same problem - hard cold start, backfire.
So far we have checked the pressures, and the CSV and thermo switch. I assume your CSV and TTS are working - if you have not checked them, the good place to start. His Cold Pressure is around 1 bar. I could check a list of graphs I have, but his is closer to where you need to be than 3.3 bar.
The next place we are checking are his injectors - we are running out of options. But if you have differential/poor injector performance particularly at low opening, this could cause the engine to run on 2-3 good injectors and run poorly on the others. One way to check would be to put your hands on the headers if you can get at them, after trying to start it for a few cranks. See which ones are warm. You could try again later and see if same ones are cold. At that point I would pull the cold injectors and check them.
That is what we plan next. But knowing your CSV is actually delivering fuel at crank over would help too. Have a look at the wiring - you can dummy this to work by putting power to one of the TTS terminals from a battery and earthing the other (from memory). The TTS is just providing an earth for the CSV and then heats an internal contact which eventually breaks the earth and CSV shuts. You should hear/feel it click on/off.

Your information would suggest there is something wrong with the WUR bimetallic finger setting. You can pull these things apart. It should be fixable. I'm not sure 'cold ' means absolutely no contact with the disc - on the ones I've fiddled with, it is always a partial pressure on the disc. But if you pull it apart, you should be able to identify the problem - understanding the finger heats and bends towards the disc to raise control pressure.
Alan

[teveo]

Status .. car is running much better and have good cold start and cold engine driveavility.

The CPR (WUR) must have been trashed, I have not had time to do the cold pressure but it must be good now.

Car is still hunting/pulling a little around 1300-2100 rpms be so hot or cold engine and my next step is to ultrasonically clean the injectors.

I already installed a new FPR and filter so that rule out clogged filter. Reason to change the FPR was a really annoying hot start problem, car left for 20-40 minutes with hot engine would need lots of cranking. After I installed a new FPR this has never occured...

I recommend reading the "Bosch Fuel Injection.... " book by Probst ( Bentley publ. ) and of course to discuss with the knowledgable guys in the forum.

[Alan L]

Typical symptom of faulty accumulator is poor hot start - looses rest pressure over 20 mins. Easy to check.
Regards
Alan