CIS questions
 

Hi all,

I have tried searching but really need some specific answers from the CIS experts. I have a 77 2.7 911 which is hesitating under any load, but not at idle. My mechanic has done a full service but couldn't fix this problem. he has presure tested the injectors, and adjusted the mixture as best he can. He says it is either the fuel distributor, or the injector lines are blocked / full of gunk. It idles ok but a bit up and down. He also says the WUR is leaking, but said this should not affect the running / hesitating.

I would like to know if this sounds correct and what else to check. The engine is healthy otherwise with good leak down, and all ignition has been renewed. He says there are no air leaks in the system.

A second problem is hot start. The car will not start when hot. Can someone please assist in the diagnosis of this problem, i believe it is quite common.

TIA
Chris

Hesitation under load sounds like timing. Is your advance working?
If your idle is going up and down, that most likely means it's running rich. The most common reason for running rich is an air leak. This causes the car to run lean, so the mechanic turns up the amount of fuel so it will run fairly normal, except at idle, where it's now just rich. It is possible that you don't have air leaks, and have too much fuel coming in from somewhere else, but the most likely problem is an air leak.

How familiar is your mechanic with these cars? Air leaks can be difficult to trace - especially if you don't know the problem areas.

Aside from what Walter said, has he checked the control pressures? It's interesting that you said he tested the injectors but thinks there might be a blockage. Was this because the fuel pressures, delivery or spray pattern were bad?

The WUR affects the entire running condition of these cars. What kind of leak did he say there was? It's hard to think that a leaking WUR wouldn't have a negative effect, or be dangerous, depending on type of leak.

Since he did a service, then can we assume points, plugs, wires, cap, rotor, and timing are all good?

Finally if the car fails to start warm have him check the fuel accumulator. He might as well check the fuel pump check valve too. They are the most likely causes of this.

hey walter, you must have made a typing error. air leaks cause a lean condition.
as you said in your second sentence.

it sounds like the thermo time valve (TTV) may be bad. also, you said, "he adjusted the mixture as best he can", that does not sound encouraging.
is steady speed driving ok? is the problem just when you try to accelerate?

if the TTV goes bad, like mine, it blocks the vacuum to the WUR. this will cause stumbling and bucking when you try to accelerate.
follow the vavuum line on top of the WUR back to a small device with another vacuum line and an electrical connection, (it is connected right?). you can bypass the TTV to see if it is bad by connecting the 2 vac lines together.
also make sure there is 12v on the connectors to the WUR, TTV, and aux air regulator (AAR)

these are easy checks, plus it sounds like you do not have a pressure gage. if these are all good, then you need to look deeper as said above.
WUR leaking? if it is a fuel leak, that is not good at all, and where is it comming from, the connections or the WUR body. if the WUR is leaking internally, that could be realted to the vacuum problem and also change your fuel presures. if the body of the WUR leaks, then it will cause the problem you have due to lack of a vacuum seal. i would investigate the WUR more closely

CIS Issues............
 

Ignition could also be contributing to your running problems. Try replacing the coil wire and see if that helps. You can check for cross firing by parking the car in a dark spot, open the engine lid and start the engine. If the plug wires or the coil wire are arcing to ground or cross firing, you will see blue or yellow "lightning" bolts. A bad coil wire can cause misfires while running above idle and under load.
Good Luck!

I'm with Rex on this. It sounds like you're running too rich. Before you do anything too complicated I'd adjust your mixture (at the fuel distributor) as follows.....

(respectfully borrowed from this thread.... )

http://forums.pelicanparts.com/porsche-911-technical-forum/437101-cis-mixture-tool.html?highlight=CIS+rich

"right to richen (CW). always turn it from lean to rich for final adjustment. if you do not have a way to check CO, here is how i set mine. turn it CW until it surges at idle then back off a tad. blip the throttle and if the RPM's dip down then come back up to idle, it is too rich. turn it CCW about half a turn then back CW a little less than how far you turned it CCW. blip the throttle again. repeat until it no longer dips down when the RPM's come back down. mine is set so it has just a hint of wanting to dip down when i let off the gas. drive it and check again. i later had mine checked and it was dead on 3%."


PS....your problem may or may not be compounded by an air leak, but it is always a possibility and is a common problem...to paraphrase Rex's point...If you have an air leak (lean), often people will compensate for this by adjusting the fuel distributer to run rich, which results in a hunting idle (it will hunt up and down) hesitation, etc.

No typo - I just haven't quite got the hang of getting my point across in cyber space. Thanks Al, for straightening out my rambling thought.

Actually I think Walter stated it correctly:

1 Lean from an air leak

2 Mixture is richened to compensate and

3 It becomes too rich.

As others have said, this may or may not be the cause of the symptoms however, and ignition items should always be verified prior to attacking the FI.

+1

With all due respect, it doesn't appear that your mechanic is too familiar with CIS. As you have read from these posts, there are many possible reasons why your CIS car has these symptoms. Start with the basics as Paul states, in diagnosis before chasing your tail--confirm the ignition first. Then, start with control/system pressure checks which it sounds like have not been done. Only if the ignition and pressure systems check out should you then move on to other possibilities.

One step at a time...

Thanks all for your input here. I think the summary is basically that there are lots of possibilities and few concrete results as yet. I am thinking of taking it to someone with more experience with these issues. The hesitation / surging is quite bad, so I am not yet comfortable taking it all apart at this stage.

I will post again with more questions or answers as they come to hand.

Thanks,

Chris in Australia

to follow up some of your questions, it had a major service so all ignition has been renewed. The injectors have been flow tested and are apparently all good, the suspected blockage is the fuel distributor or the injector lines.

I do not know which part of the WUR is leaking, or if it is fuel or air.

Chris

I't be careful with a WUR leak if it is fuel. Depending on the part number on the WUR it should not leak fuel since it will have an effect on the warmed up pressure. It could leak vacuum and that would cause a leaning or richening condition depending on the WUR #.

Try the cheap stuff first. If you can get Chevron Techron of Ventil Stauber (Wurth?) run a can in at 1/4 tank. Performance will suffer but it may free up the components from the gum and residue. Do a couple of tanks of gas this way.

Then check the WUR out with a pressure test, pulling the necessary Vacuum depending on the serial number of the WUR. If that's ok then it's mixture and Vac leaks. The intake runners being the most difficult to fix (Phenolic sleeves and o-rings in them so you have to remove the FI from the engine.)

There was a thread on the brake booster vac line from the engine rotting and causing a massive leak. Check that out. I think is was by Formerly Steve Wilkinson.

Best wishes!

My success with the CIS system:
1. learn how all the components work and how they work together as a system. This is definitely a mechanical injection system meaning components like the AAR and WUR (CPR) work off bi-metal springs controlled by heating elements along with the fuel distributor that riches and leans out depending on the temp of the engine OAT in response to the WUR.
2. air leaks are critical in the operation of this system making many strange performance problems that "disguise" themselves as other problems (had an AAR that wouldn't close all the way so the engine ran lean and to fix the problem the A/F mixture was richened. this caused the car to stumble above 4000 rpm looking like a ignition problem but it only took an adjustment on the AAR to fix it and the A/F mixture was leaned out and now runs great)
3. test equipment... CIS fuel pressure gage set, A/F mixture allenwrench, multimeter, 12v power source, vacuum leak finder (carb cleaner, propane, starting fluid, ect.. (use caution!)
4. check each and every component of the system and verify that they are working correct. this might mean disassembly and adjustment, electrical checks, operational checks, cleaning, ect...( most of the components are repairable/adjustable and it's free!)
5. operational check from cold to proper operating temp recording all the pressures and atmospheric conditions and verify that everything is working.
6. double check for air leaks (external and internal), set A/F mixture and idle
7. enjoy!!!!!

Short and quick and not too bad to do. but l am a mechanic (never worked on one of these systems prior to purchasing mine).

Key is finding ALL OF THE AIR LEAKS and properly adjusting all the components so they work right when there supposed to, easy.........http://forums.pelicanparts.com/support/smileys/wat6.gif

...also, the "history" of your injection system may be in play. Has the car sat unused for some time with old, crappy, gummy gas? CIS system parts are very sensitive to bad gas and gunk or debris in the fuel. Even if all the parts are "ok", if your fuel distributor, or lines (or pretty much any other part), are full of gunk - you're gonna have trouble.

Thank you all very much for your help. It is a car that has sat for some time, so I am leaning (pardon the pun) towards gunk in the fuel / or innopperation equipment due to missuse. Sounds like it is worth taking a few bits and pieces apart but i am first going to take the car to a mechanic whos knows CIS well. Hopefully he can narrow it down for me before i start taking bits apart.

I am not afraid of removing and testing equipment, but like everyone was hoping to find a quick fix.

they never happen..!!!!

Thanks,

Chris

i was just being nice, i know, thats not like me. i know you new what you were talking about, i figured you just got your fingers crossed.

CIS issues when the car is running are invariably the fuel pressure, mixture or advance. Or a combo of all three.....