Drivability Issues '77 CIS

[rwest]

Hello,

Here are my symptoms: cold start takes 5-10 seconds to start (used to be quicker), very flat acceleration up to about 2500RPM (been this way for 27 years), very slight to moderate bucking/hesitation/studder when at steady speed (recent change).

I did a partial engine drop last year, removed and replaced just about every wear item, gaskets, hoses, seals and the air box.

Ignition components are all recently new except the actual distributor, timing is on and steady- I'm still suspicious of the distributor and most likely will get it rebuilt.

I decided to start testing systematically and then post my results and ask for suggestions; first thing was to try and find vacuum leaks. I started a post on that Smoke Testing, Did I Do It Right? and I would like to believe I am "leak free".

Next step is fuel pressures, which I'll list out in the next post to avoid making each post too long.

Thanks in advance for any help and suggestions.
Rutager

[rwest]

Did the fuel tests this morning and here are my results:

FD 0 438 100 006, WUR 0 438 140 033

Temperature was 75 degrees F.

WUR heating element 26 ohms

System pressure 4.9 bar
Cold Control Pressure 1.3 bar electrical disconnected.
Warm Control Pressure 2.8 bar after 3 minutes electrical connected.
Warm Control Pressure vacuum applied 3.6 bar.

Residual Pressure:
.9 bar after 5 minutes.
.5 bar after 15 minutes.
.2 bar after 30 minutes
.1 bar after 60 minutes.

It appears to me that only my residuals are out of spec.

Here's a picture of my gauge set up and factory listed specs.

[Bob Kontak]

Guessing you have tried seafoam in the gas tank to scrub out cooties.

Your rest pressure should not cause the operational issue.

[rwest]

Hi Bob,

Never put any type of fuel system cleaner in it. I almost exclusively use ethanol free gas. Only exception is on road trips, but them I burn through it pretty quick.

Rutager

[75 911s]

How old is the accumulator / fuel filter?

Is there lateral and axial play in the distributor? Why do you want to rebuild it? (I think this is a good idea and something I want to do too) When you say ignition components are new does that include points? Is the dwell and timing set? Does it run hot at all? just some additional questions.

-Edit I see you set the timing.

[ossiblue]

I'm with Bob in that your test pressures would not account for the running problems nor the cold start issue. (BTW, I think you typo'd the fuel results--the second and third measurements should be warm pressure readings, correct?) If you cold start valve is working, you should get at least a brief firing/quick dying of the engine upon cold start. Is that happening, and have you tested the CSV? Regardless, that will not result in the problems in running.

Assuming your air leak results are correct, your symptoms look more ignition related to me, especially the flat acceleration you mention. Still, you may have a problem with fuel flow. It might be a good time to check the volume put out by the FP and pull all the injectors to perform a test to measure their spray patterns, possible leaking, and volume of fuel delivered by each.

[rwest]

Hi Duane,

Fuel filter was installed last year along with all new engine fuel lines. Accumulater is not original, but can't remember when I replaced it, likely ten years or more.

I had an issue with my points (tiny piece of wire broke down!) last fall leaving me stranded, so I replaced them this spring. Strangely I could get dwell to set, so just gapped with feeler gauge to spec.

Distributor looks pretty clean, although I did remove a black piece of something out of it recently. Side play seems minimal; up/down seems like a lot to me. Watching the advance with revving the engine seems smooth. I just feel like that thing has been spinning around for forty years and a rebuild couldn't hurt.

Rutager

[rwest]

Hi ossiblue.

Yes, warm pressures, I referred to them as electrical connected, which then heats up, I'll edit to avoid me confusing people.

Car takes awhile to crank, but once it starts, it stays running. Hot starts are immediate though. Car will start every time under all circumstances.

I will say that it on occasion idles low for a bit- running while the starter is still operated and if I let the key back, it runs on its own and then idles at 950 or so.

Thanks,
Rutager

[ossiblue]

Originally Posted by rwest

Hi ossiblue.

Yes, warm pressures, I referred to them as electrical connected, which then heats up, I'll edit to avoid me confusing people.

Car takes awhile to crank, but once it starts, it stays running. Hot starts are immediate though. Car will start every time under all circumstances.

I will say that it on occasion idles low for a bit- running while the starter is still operated and if I let the key back, it runs on its own and then idles at 950 or so.

Thanks,
Rutager

If the CSV is working, you should not have excessive cranking upon cold start. Have you checked it out?

Can you clarify the last bold portion in your post? Is the engine running while you still have the starter engaged? I can't really understand the situation you describe.

[rwest]

Just for kicks, I did residual just on the system (4.9 bar) and when pump is turned off, it dropped immediately to 2.9 bar then at ten minutes it was at 1.8 bar, twenty minutes 1.6 bar.

Of course, the tester might be faulty too?

[rwest]

Ossiblue,

It's like the engine hasn't caught fully, but if I stop cranking it will run- so the revs are low enough that it doesn't out spin the starter. This is not every time or even that often.

One reason that ignition is suspect to me is that when I was trying to get the dwell set and at certain gaps, it would start up real fast, so I'm pretty sure the cold start valve works, but I will verify- just need to get a helper.

It also seems like when I time to spec, it doesn't run as well, so I have it at halfway between the timing mark and Z1.

[ossiblue]

Originally Posted by rwest

Ossiblue,

It's like the engine hasn't caught fully, but if I stop cranking it will run- so the revs are low enough that it doesn't out spin the starter. This is not every time or even that often.

One reason that ignition is suspect to me is that when I was trying to get the dwell set and at certain gaps, it would start up real fast, so I'm pretty sure the cold start valve works, but I will verify- just need to get a helper.

It also seems like when I time to spec, it doesn't run as well, so I have it at halfway between the timing mark and Z1.

Okay, got it.

IMO, get the ignition/timing issue settled once and for all--eliminate one of the variables. Once you are certain the ignition is in spec and cannot be a problem, move on to the fuel delivery if the issue remains. Keep us posted.

[rwest]

Ossiblue,

The ignition thing is troublesome to me, because it "seems" fine, but not being able to get dwell and another thing that happened is that now after I put new points in, the distributor had to be moved to the farthest side of the slot when before it was in the middle?

Any ideas? Should I just send it out for a rebuild and advance curve check to be sure?

If so, any suggested shops?

As for residual dropping off, should I test before the accumulater to see if it is the pump check valve or something else?

Thanks,
Rutager

[rwest]

I will add that when I accelerate anywhere in the 2500 to redline area, it goes great, no issue. Doesn't shudder up to 2500, just doesn't pick up and go.

Only poor running is at steady speed

[ossiblue]

Originally Posted by rwest

I will add that when I accelerate anywhere in the 2500 to redline area, it goes great, no issue. Doesn't shudder up to 2500, just doesn't pick up and go.

Only poor running is at steady speed

Steady speed=constant, relatively low-volume fuel flow. Acceleration=increase in fuel flow. If poor running at steady speed was due to inadequate fuel flow, one would not think you could accelerate smoothly, as you need even greater fuel flow.

On the other hand, poor pick-up to 2500rpm could be an advance issue, and poor running at steady rpm could also be erratic timing.

Still pointing to ignition/timing advance issue, IMO.

[rwest]

Ossiblue,

I was just looking around at Partsklassic since they rebuild distributors and found some videos and they showed one that had points bounce and what it looked like on an oscilloscope. I have an automotive scope, so I might just see if I get a proper wave, although I'm not sure what kind of resolution mine has and if it is enough to see.

I know of a couple rebuilders, so I'll try and figure out if they do a good job and send it to one of them.

Thanks,
Rutager

[boyt911sc]

Rutager,

You are doing great in your CIS troubleshooting. Things I like to see are:

a). Are any of the injectors leaking? Including CSV.
b). How is the spray pattern? Jet like or mist like pattern?
c). Remove all injectors (except CSV) from their fuel lines and place the ends in suitable vessels or containers. Then test run the FP. Look for any premature fuel delivery. A good FD should not deliver fuel nor drip when the plunger is at rest. CSV test with the engine installed is quite cumbersome due to accessibility.

Your cold control fuel pressure is rather low @75°F. How old is your CIS airbox? Focus on your ignition components. And finally, have a shop test your exhaust using a gas analyzer. Keep us posted.

Tony

[rwest]

Hi Tony,

Airbox is new last year when I renewed just about everything that I could as far as gaskets, seals and hoses.

When I put it back together last summer, I did the factory baseline FD set up with injectors in mason jars. At that time, the patterns were good, no leaks and equal quantities delivered.

I've not checked the CSV as it seems that adjusting timing/dwell would get me different quickness in starts.

I have an LM-2 AFR meter and here are my numbers I posted in another thread a couple months ago:

"I've been trying to get my car running as well as possible; 1977 911S with CIS. I did an extensive refurb last year of the CIS and at the time my WUR and fuel distributor where in spec and I also tested as many of the other bits that I could and they tested out as well.

I still think there is room for improvement; it feels like a very, very slight bucking sensation at low RPMs and a steady speed- really hard to tell if it's the engine or bumpy roads, that's how slight it is.

I had a bit of ignition trouble last fall and I now believe that I have it all sorted, so I hooked up my LM-2 with the tailpipe adapter and headed out on a 50 mile drive in 80 degree temps.

Car never got above 200 degrees. Here are my observed AFRs, what do you think?

Idle 12.8 cold 13.1 at the end of the trip.
Full acceleration 13.8.
Steady cruising on flat road at 55 mph 14.4 to 14.7.
Slight acceleration 15.4 to 15.6.

Thanks for any input or suggestions."

[T77911S]

i would look at
ignition- advance working properly, set correctly. try a little more advance
injectors. very often over looked. I am not one for just replacing parts as a guess but you might consider replacing all 6.
you can test them. compare volume of all 6. do 2 tests, one that would simulate an idle, run it for about min. you need a battery charger on the batt.
another test for WOT. you might repeat for consistency.

check intake bolts, injectors sleeves and injector Orings for air leaks.

mixture may need to be richer.
for my 77 I would adjust It so it was on the edge of surging at idle or the RPM's dropping down then coming back up if you rev it and let off the throttle. mine liked to be on the rich side.

[Bob Kontak]

Originally Posted by T77911S

i would look at.........................- advance working properly

I am going to throw something in the pot for grins. Vacuum pod.

On my 81 there is vacuum advance (and retard). The vacuum advance kicks in off-idle and assists the mechanical advance.

What I don't know:

- Does the vacuum advance assist max out at a certain RPM?
- Is the vacuum advance and mechanical advance additive at full advance?
- Does the 77 have vacuum advance?
- Can you fit and suck on a hose and make the inside of the distributor move?

Another thought is if you only have a retard port, suck on the hose and see if it moves the inside of the distributor.