2.7 CIS Loping - Need Help
 

I'm relatively new to the scene with a silver '75 Targa with what appears to be a stock 2.7 and CIS. I've brought it back from the brink of the crusher, and just had it repainted.

I am having a problem diagnosing an issue. The car runs rough at idle which I believe to be injectors. I have started replacing them as I identify which cylinders aren't running properly at idle. It accelerates like a dream once over 3000 RPM, and decelerates without popping, missing, or backfire.

At lower RPM, especially 1700 to 2500 it bucks like a horse regardless of being hot or cold, and regardless of gear or speed.

I've ruled out electrical as it should break down under load vs the other way around. That leaves me at fuel, but don't understand why low RPM would cause the loping. When driving, I have to downshift or accelerate beyond this RPM band.

Any thoughts appreciated.

Blowmeup,

Have you checked your ignition timing?

Rex

I have not checked the timing. What is your thought; too much advanced/retarded, or lack thereof?

Thanks
Bob

I 2nd the timing, either way could cause that I think.

Timming slightly retarded, and a minor mixture adjustment( just did one last week, same issue)
What number did you find so far is running bad???

Check timing, clean/replace your points. Injectors could be bad- you can test these by pulling them out and watching the spray pattern. Also your WUR could be out of adjustment or malfunctioning, which affects mixture, although the mixture screw is a better place to start.

Sounds like your fuel mixture might be to lean.

A sick idle and rough run out started me down this path initially. The car sat at the body shop for close to a year and came out barely running. #5 was not running but had good spark (I changed all the plugs with no improvement) and the injector was in rough shape.

I compared it to #4 and it wasn't right. So, I changed #5 and then #4 after I saw what a new one did. It runs much more smoothly now, but still has rough idle and this loping issue. I am convinced that I will renew the other injectors as they are OK under load, but don't have the fine mist at low volume like the new ones which probably accounts for my poor idle.

I'm glad that 'lean' is coming forward from your experiences as the old plugs were telling me this when I removed them i.e. white deposits.

The points are also another area of suspicion. I think that I will just replace them.

Since I have replaced the two injectors and earlier added Techron to the tank, it has started a new trick. It runs the best it ever has, and then dies completely. On the way to a dead stall, it backfires through the intake. Once dead, I can restart until the next time it repeats. Is this air in the fuel system, or would points do this also? Coil?

Thanks
Bob

I'm thinking points, too. Also, check to see if your dizzy turns and springs back easilu (use the rotor). How does the car start/warmup from cold? Do you have a popoff valve? Check the usuals: air leaks, WUR, AAR.

Finally, see my recent thread on broken head studs. You may have a pulled one on your 2.7.

Bob,
It is best to do this one thing at a time.
1) Check your timing/ points
2) Change fuel filter (buy 2)
2) Check your cis fuel system pressures
3) Check each injector
4) Check fuel dizzy

Did you drain the fuel first, or is this 1 year old gas+crud? You may be better off draining the tank, cleaning the in tank screen, replacing rear filter, then filling up with fresh gas. It sounds as though there are multiple issues, and bad gas is the easiest to fix, then points, timing. It took me about a month to get mine right, but it is RIGHT. Fires right up, no sputtering etc.

I will check the dizzy. The car used to start cold without issues, but since it started the stalling routine, it's hard to tell. It seemed to improve with time, so I'm also thinking that perhaps some debris came loose via the Techron and was plugging the fuel distributor and is now working its way out.

I was also thinking AAR, but how to access it without taking the entire fuel system off the car. It's in the back and impossible to see/access? Any tips?

Thanks
Bob

How about that plunger thing for the CIS air intake regulator? I've read it could stick when old and brittle.

http://members.rennlist.com/jimwms/CIS/CIShome.html

I didn't drain the tank as I completely drained and cleaned the tank/filter just before it went into the shop. The fuel level was very low going in (intentionally) and I have put two tanks through since getting it back.

I agree with limiting the hunt. I will complete the injector replacement (needs it anyway), points, and timing. Should be in a better position to diagnose once these are completed.

Thanks for the pointers.

Bob

Kach22,

I read this also, and it is not stuck. It did lead me down the mixture path, however, and also leads me to believe that it is running too lean.

I think that I will do the injectors, points, and timing before I start messing with the mixture as poor fuel flow through the injectors will also have the same leaning effect.

Thanks
Bob

Keep us posted..

I replaced the points and rotor today, and took a ride. The stalling/backfiring was the points on the way out. The new points provide much better ignition than the old ones ever did.

I retarded the timing a little, and the loping is less of an issue, but it is definitely still there.

I have a dist. cap and more injectors coming for Friday.

BTW, I can't seem to get the idle to adjust higher. It wants to live around the 500 rpm level regardless of what I do. Once I get the cap and injectors in, I will let you know what's happening.

Thanks
Bob

What did you set the timing to? Idle issue is probably a vacuum leak. I just replaced all mine instead of messing with it. You can get the hose at any autozone, napa etc.

I didn't use the strobe light, but rather marked the position and tried going either way to check the result.

I just couldn't seem to bring myself to run it up to 6000 rpm to set the thing. Is that really what needs to be done on these things? I don't even go that high when out for a thrill.....

Next time your points start to go, you might consider replacing them with the Petronix Ignitor (available from our host). I did this upgrade a couple of years ago and highly recommend it. It is easy to install and totally eliminates the hassle of dealing with points.

Jack Mansfield

Throttle Operated Control Regulator
 

OK, after considerable reading I realize that I am missing the TOCR listed on this link Item #28 on the diagram.

http://members.rennlist.com/jimwms/CIS/CIShome.html

This would explain the lean operation. Can anyone advise where I can get one and/or how critical it is to 75 2.7 operation?

Thanks
Bob

Bob,

Sorry - what's a TOCR? I looked at the diagram and #28 looked like a connector for the fuel line to the WUR.

My 1975 CIS system is very simple - but I think that they are not all the same. I have a hand throttle - so no AAR or AAV. I have a WUR, a decel valve, and a cold start injector. No other CIS controls - it's pretty simple.

Explain your inability to increase the idle above 500 RPM. Is that with the idle air bleed screw all the way out? If so, that could be an indication of a rich idle.

An idle that hunts up and down (you say lopping) could be an indication of a vacuum leak.

If the car has been sitting, I would clean the fuel system (drain the tank), new fuel filter, look for vacuum leaks, and check that the advance weights in the distributor are not gummed up - and a good tune up is always a good idea.

Let us know how you are getting along - you have some really good help and suggestions on this thread already.

Rex

Item 28 appears to be a fuel line adapter fitting on the WUR; are you saying the system is missing the WUR (item 27)?

Sorry for the confusion...It's the Throttle Operated Control Pressure Regulator and is Item #20 on the Pelican Diagram and is item #28 on the photo shown at this site when clicking on the part name under the CIS components heading.

http://members.rennlist.com/jimwms/CIS/CIShome.html

It's part of the throttle body.

The 'loping' that I am describing is more like a miss and at 2000 RPM seems to build on itself up to a buck and then escalates to a serious herky jerky. The only way to make it stop is to accelerate or rev up in a lower gear. It then goes away unlike an electrical miss would.

The idle issue is rough/poor idling, again like it's running on 4 cylinders. Adjusting the idle screw and the linkage doesn't seem to do much if anything. It doesn't hunt, it just doesn't speed up.

My next move is mixture adjustment. The lack of the throttle regulator and symptoms to this point lead me to believe that it is running extremely lean.

Again, any idea where I can get a throttle regulator?

Thanks
Bob

I am voting for the wur (problem)

Scraps point go with Pertronix, check ign wires at night & replace if arcing, check for hanging distributor weights (erratic advance), may be lean. BTDT bucking with each of the above

http://members.rennlist.com/jimwms/CIS/CISparts_ID.jpg

Someone mentioned reconditioned WUR's for about half the price of the new ones from Pelican. Are they worth the risk of a redo? Will you have to reset the CIS mixture settings when replacing a WUR? Or is is plug and play?

Guys,

I am unclear. So if I don't have item #20, does this mean that I don't need it? Do your '75 2.7's have it?

Thanks
Bob

The throttle valve (TOCPR) was used only on the '73.5 and '74 911 CIS systems; '75 on did not use them. Several of my local Porsche SC 911 buddies have recently had their WUR's rebuilt (systematic trouble shooting including CIS system pressure measurements indicated the WUR's were the problem). The rebuild turn around time was short (a week or so) and the rebuilt WUR's solved the CIS running issues.

Likely candidates include your WUR and AAR, as others have mentioned. There is a lot of info on these available via a search. You should check your control pressures w/ a fuel gauge. This will tell you a lot about the status of your WUR. Quite often these merely need to be adjusted, rather than changed or rebuilt.

I have recently tracked a bad warmup idle to a broken head stud. This is not so likely in your 75, but a pulled one may be indicated.

Check Mystery Train for his threads on the AAR.

Try disconnecting the vacuum line #25 that goes to the WUR and see if that helps. Seems I read sometning about that line that was the cause of the jerky problem at 2000 rpm.

Joe

Problem Solved
 

Well guys, I took several of the easiest suggestions and did the following today:

1) Lubed the weights/lobes on the distributor.

2) New dis. cap at the same time.

3) Adjusted the mixture 1/4 turn richer.

Everything came into line. Did some minor idle changes and set the timing back to where I had it.

It's better than it has ever been.

I LOVE IT!

Thanks for all your help.

Bob