CIS riddle
 

After 800 miles of highway driving, the engine would not hold idle - zero. What would cause this? Adjusting the idle screw put idle back to 950 rpm, but now it has a hot start problem. Any ideas?

1. Cold pressure, and Hot Control Pressure, chech them first. WUR is likely the culprit if they are off.

2. Vacuum leaks, so many hoses to check.

3. Idle mixture is way off, but you need good fuel pressure before you even attempt a mixture fix.

So many things can be off with CIS and the are all interelated, you need to start from sratch with the fuel pressure check.

Try the usuals in hot start threads.

Hot Start Problem:
The hot start problem could be related to one of two components. The check valve (at output of fuel pump) or the pressure accumulator. Both components are designed to keep the pressure on the system after the car is turned off. Keeping pressure on the system prevents vapor lock.

Idle Problem:
Check for vacuum leak by removing the oil cap with the car running. Idle speed will change if there isn't a leak.

Primary role of the WUR and Aux Air Regulator (AAR) is to rapidly adjust the mixture of a cold engine. When you start the engine a rich mixture is required (cold engine requires more energy to turn over) but with in 5-20 seconds a leaner mixture is reuired (or the engine races). The WUR accomplishes this through an internal electric heater wrapped around a bi-metalic strip. As the strip heats up the diaphram changes position which reduces the control pressure leaning out the mixture. (If the element is bad the mixture stays rich to long - several minutes or until the physical temperature of the engine warms up the WUR)

The AAR allows air to bypass the air metering plate and into the intake during an engine cold condition. The valve closes as the engine temperature increases. This is accomplished by a bi-metalic strip with an internal electric heating element. If the valve stays closed a cold engine won't idle. If the valve is stuck open then the warm engine will have a high idle.

The Idle Adjustment screw performs a similar function (as the AAR) in that it allows air into the intake bypassing the metering plate.

I had a cold start idle fluctuation that I tried to fix with a 1/4 idle mixture to the left, then the hot idle dropped, so the idle screw went up a few notches, then the warm idle started to act up.

So, back to the beginning looking at fuel pressure. Found that the cold fuel pressure was always high (like it's hot).

Pulled it, adjusted it with the CIS fuel test guage, put it back adjust the idle mixture to 0.8%CO, and adjust the idle speed to 1000RPM.

Now, it starts right up when cold, runs well when hot, starts and idle smooth when warm. Could not have guessed what the problem was unless I had the fuel pressure test done. Start from the fuel pressure test, it will tell you a whole bunch about your fuel pump, check valves, wur, accumulator. Then go on from there.

Opening the fuel line above the fuel filter usually works, but didn't last night. However, after the car sat all night it worked.

If it's not pressure related, could it be temperature related?

after 800 miles? is that three or so tankfuls? if it acted up at a nearly empty gastank, check for vaporlock. remember the CIS system sends back unused fuel back to the gastank. so as it get empty, the "heatsink" gets smaller and smaller, so the fuel get warmed up. put your idle screw back to original setting, get the tank full and try again. but this time keep a can of compressed air in the car (dust blower for computer keyboards) and when/if it acts up. turn the can upside down and get coldmiser all over the lines, FD, filter acummulator. see if that clears things up. dont freeze your fingers or face? personally, i keep my tank at half tank and up. i dont have any problems.

My car will start up fine sometimes and then a nhour or two laterr won't start after cranking it over and over....Then for know reason at all I go out 30 minutes later and it starts? What would cause that to happen...it is driving me crazy!!!

This is the hot start problem that we were discussing today on another thread.

Basically the Pressure Accumulator and the Check Valve (output side of Fuel pump) work to gether to keep pressure on the system and this prevents vapor lock.

actaually, my problem is cold start...I crank and crank and it won't start, but after a while it will again...after two hours, after overnight....when hot it starts areat.

Carl, we agree that it's a hot start problem that should be the fuel pump or pressure accumulator, but what I don't understand is why opening the fuel line after the fuel filter doesn't make the problem go away. I also read that lifting the air flow sensor should solve the same problem, but that is not working for me. It could be the fuel mixture, warm-up regulator, or aux. air regulator. Anyway, I'm going to take it in on Tuesday. This has been an off and on problem for too long now.

Cold Start Valve (Injector) isn't working.

The Cold Start Injector is automatically activated on a cold engine and is turned off by a thermal switch. (So if it is real cold out it is active longer.) It injects fuel directly into the intake manifold. (Kind of like a Chevy TBI Or like pumping the gas pedal on a carb car.)

First make sure the cable is connected.

Injector o[eration is easily tested by removing the injector and placing a suitable container under it. (Disable the actual starting of the engine. Don't want any surprises.) Then turn the engine over as though you were starting it. If the injector is working it will squirt fuel into the container.

It is an electronic fuel injector so you can measure the voltage . I believe the thermal switch interrupts the ground line. So you can check for ground on one of the pins before you try starting the engine.

The injector is not required when temperatures are above ~95 degrees.

Good luck

Ha. Nobody got it and it was so simple.

The fuel mixture adjustment went rich during the 800 mile drive. I increased idle, but now it won't start when hot.

Simply leaning out the fuel mixture increased the idle and fixed the hot start problem, too.

So my CIS riddle question to you is how can an 800 mile drive cause the fuel mixture adjustment to richen????

Yelcab1 got it!!!!

Yelcab1 got it!!!!!
 

RazorRacer,

So what did you actually do to correct your problem. I was a little bit uncertain about YelCab1's instruction. So could you help us understand the steps you did? Thanks.

TD

He probably stuck a long 3mm allen wrench down the adjust port and gave it a 1/8 turn counterclockwise.

Razor,

I am not sure your mixture went rich. It may be your 800 mi version of an Italian Tuneup cleaned things out enough so that you did not need such a rich mixture.

Also, I usually lean my mixture slightly each year as warm weather approaches, and then slightly richer in fall. Of course, our temp extremes are different from yours: I will use my car from approx 15F to 100F. Winter temps are colder still but that's when the car is sleeping.

Paul

Well, there is still a hot start problem and I have ordered a pressure accumulator, but the problem is not nearly as bad as it was before my wrench leaned out the fuel mixture. Yes, he used an allen wrench and turned it counter clockwise. The idle would increase so he would lower the idle. Then he turned it in some more and the idle increased so he lowered the idle again. He did this about three times. He says he doesn't need to measure the CO and that he can tune it by sound. Any ideas what the correct sound is?

"He says he doesn't need to measure the CO and that he can tune it by sound.":rolleyes: Keep an eye on your oil temp gage!
http://forums.pelicanparts.com/porsche-911-technical-forum/164612-tell-me-what-you-think-ive-done.html?highlight=smoke
Jim

I may not know how to tune by sound, but I do know when the engine is in it's sweet spot and it's definately there now. My wrench is a 25+ year veteran and I trust him with my life (err car).