CIS Tuning

[jimavey]

76 911 CIS 2.7.
Replaced a leaking fuel pump. I think I fixed a problem and uncovered a problem(s).

The engine hunts at idle. And cuts out at first 5Krpm and over the last few days progressively lower - now I get misses at 3Krpm or worse.

Start when cold. But doesn't run very good.

After reviewing some archives here I ordered the LM-1 gas analyzer, and am picking up a can of carb cleaner to go vacuum leak hunting while I wait for the Lm-1 to arrive.

Oh - we live at 8500' elevation and a cold start around here can be 25 degrees or warmer. (I don't even think about it below that temp.)

What else should I be considering?

[76911]

I had the same problem last summer missing at higher RPM,s. Everything was go with ignition, and made so I made a fuel pressure gauge and found out I was only running 35 to 45 psi of fuel pressure. Replaced the fuel pump and It ran at 75psi. That was the problem. Cis needs that much pressure to run right. My car is a 76 2.7 So I would check the pressure

[MotoSook]

You are leaning. Sounds like you are starving for fuel. Sounds like a progressive problem which is likely to be the fuel filter and/or the pump.

Don't spend money on the LM1 yet (although it is a great tool). A better tool for you is the CIS fuel pressure tester. And if you haven't replaced you the fuel filter or know if it's replacement, plan on it.

[sammyg2]

The LM-1 will tell you a great deal (I've got one and really like it), but it won't tell you if you have ingition problems.
In fact it might give you the wrong indication.
If your engine is missing due to ignition, you will have excess hydrocarbons as well as excess O2 in the exhaust because they won't be burned up in the engine.
Since the wide band O2 sensor only measures O2, it will tell you that the engine is running lean when if fact that is not the case.

My point? (besides the one on my head) is that you need to make absolutely sure the ignition is in perfect condition before trying to tune the CIS.

The old jokes goes that 90% of all CIS problems are ingition related

[bigchillcar]

i agree that if you don't know when the fuel filter was last changed, by chance, then definitely replace. typically with a dirty fuel filter a car will start fine, but then begins to cut out after say, 5-10 minutes of driving as the sediment particles in the filter begin to get stirred up and enter the mixture. also, like sammy mentioned, baseline your ignition system. if you use points they could be dirty or starting to close up..points are about the cheapest porsche part there is..get a dwell meter and check them out. also check timing and the operation of what i think you have as a vacuum-retard mechanism like my '74, but am not 100% sure of this. anyway, eliminate the ignition question..and how long has it been since you replaced distr. cap, rotor, plugs, wires? know their history?
ryan

[stlrj]

What else should I be considering?

Heard somewhere that 99% of CIS problems were ignition.

[sammyg2]

LOL, yer right, 99%.
I toned it down to be conservative

[stlrj]

Even at 99% it's hard to believe that the first place most look into is the CIS.

[jimavey]

Good thoughts all. I've had the car 6 mo. The points, cap, plug wires "look" good. The car ran pretty good until the fuel pump leak. So the only apparent change is the fuel pump replacement. That is why I zeroed in on the CIS.

The LM-1 will be useful for this and other cars too. So I'm glad I ordered it. (I like tech gadgets anyway).

I have a replacement fuel filter (from Pelican of course) waiting to go in the car. I'll search Pelican for a CIS fuel pressure tester.

Thanks for the ideas. This is a great forum!

[bigchillcar]

jim..when you say 'look' good, i guess you know that would come across as mighty subjective. you've gotta have good eyes to discriminate hundredths of an inch differences that can make a substantial difference in points gap - dwell meter time. need an ohm meter to venture a 'guess' as to the condition of plug wires..they don't have to show dry rot on the rubber to be in poor working order. anyway, good luck with the troubleshooting and be sure to let us know what you discover!
ryan

[jimavey]

That's why the "look" was in quotes. I knew it was a suspect observation as I typed it. But my deductive reasoning made me think fuel related because the only change I observed was the fuel pump leak and subsequent replacement.

I am impressed with the 99% of CIS problems being ignition. That sounds like a sure thing. So I guess I have to move the ignition parts from my project list on Pelican over to the shopping cart. And... I have to "dwell" on where the timing light is hiding.

[bigchillcar]

i personally think the 99% thing is 'tongue in cheek'..in reality i'd bet the actual figures are closer to 50/50..it's just that cis gets blamed for everything..everything except the issue of the ports deal and the uae..the administration's acting president is catching that..
ryan

[sammyg2]

LOL, yes the ignition comment is exaggerated, but for a good reason.
Lots of folks spend big bucks chasing CIS problems only to find out part of the ignition system is at least partly to blame. It is easy to mis-diagnose the cause if ignition is contributing to the problem.

In fact, here is a direct quote from the factory manual:
"CONTINUOUS INJECTION SYSTEM (CIS)
General Checkout Procedure
Prerequisite for the CIS checkout is a properly functioning ignition system and proper mechanical condition of the engine."

[bigchillcar]

lol..sammy..even the porsche factory manual tries to 'first blame' the ignition!
ryan

[Dan in Pasadena]

Originally posted by Souk
You are leaning. Sounds like you are starving for fuel.....

A better tool for you is the CIS fuel pressure tester.....

Souk, Ryan and others,

I will try not to hijack jimavey's thread but I have a few questions.

First, I HAVE searched CIS threads and have a sketchy picture of what I need to do but... I suppose the first question is about this "CIS pressure tester". I hate to be stupid but is there some standard test setup to make or buy? I looked but didn't see anything like it here on Pelican.

Even if it already exists, where would I find an "Idiot's Guide" on how to use it and properly interpret what it is telling me? It is obvious to me that I'd better get competent with CIS if I'm going to own my '76S at a reasonable cost.

Last, my car has fresh plugs, cap, rotor, new braided factory plug wires, new fuel filter, new distributor and rebuilt fuel distributor. So the ignition system "should(?)" be fine. I had the airbox swapped w/ new pop off valve installed as it blew (over 6 mo down time while being painted, it backfired on first attempting to start, I didn't know not to touch the gas pedal when starting, I do now!). After overnight cold, I've got to crank a little to get it to "kick", sometimes stay on the starter a couple of times to get it to actually start. Then it sputters for a few seconds, idles up to maybe 1200-1300rpm momentarily before settling back down to 900-1000 rpm. Idles smooth then, though not at elevated rpm while cold - AAR, right?

Can pull away smoothly when cold with a little extra blipping of throttle. Runs great when warm but my overall impression is that it is rich, it even smells some of fuel. All this would be okay I suppose - I'd rather it started sharply, idled high reliably until warm then, settle down to normal idle. But the problem is if I have to drive along at low speed in traffic it is awkward to try to drive at 25-30 mph as it wants to "buck" if I shift into second. My buddy's perfectly running SC runs fine in second at this same "in between" 1st-2nd gear speed. Is it just a little extra torque from his 3.0 or do I have a problem?

[stlrj]

The engine hunts at idle. And cuts out at first 5Krpm

The first part sounds like a too rich mixture issue which is easy to correct, but the cutting out at 5K is ignition.

The points, cap, plug wires "look" good.

Unfortunately, looks don't count when dealing with ignition components. High on the suspect list are the highly problematic and expensive to replace shielded Beru ignition cables which rank high in the "looks good" department while hiding from view any evidence of shorting.

Cheers,

Joe

[jimavey]

I searched the Pelican search engine for CIS fuel pressure tester and got this link.:
http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&make=POR&model=911M&section=TOLtol&page=5&bookmark=26&part_number=PEL-PP910450

It is the Bosch CIS Tester. So I ordered it.

I also ordered the CIS fuel Enrichment wrench (Pelican # UN-120-1334) I read in the archives that it is a 3mm allen wrench but 5" long.

I also ordered plugs, wires, and a cap. And a Ignitor electronic Ignition (PEL-PT1867) Anyone have a history with this?

I'm looking forward to getting my stuff!

Dan in Pasadena is describing my low rpm symptoms too.

STLRJ's observation about the high end cutting out being ignition is taken note of. MY new plugs/wires/cap, etc should fix that.

[Dan in Pasadena]

jimavey, Thanks. Not sure how I missed that, Dan

[stlrj]

The best way to really nail this ignition issue is to stay away from copper core ignition cables (Beru), they give CIS a bad name. Go for carbon core wires.

Cheers,

Joe

[jimavey]

I ordered these wires: http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&make=POR&model=911M&section=UPrc91&page=15&bookmark=20&part_number=CE-9192-28-R

I can't tell from the description if they are copper or carbon - anyone know?