Help diagnose this CIS problem

[Aurel]

Here are the symptoms:

1. Does not start well in cold weather (takes at least 10s cranking)
2. Sometimes will stall with a pop a few minutes after driving cold. Will not restart unless I give it more gas by lifting the air meter.
3. Gas mileage is down by about 2 mpg.
4. There is a very annoying vibration noise linked with the throttle, when the car is under load. Same rpms in with clutch in makes the vibration go away.
5. Still good power an running well besides these annoyances.

I am suspecting that all these symptoms can be caused by one of the CIS components going bad, but which? WUR, CSV...? I would be especially interested to know if the sound I am hearing can be attributed to failure of one of these.

[1990C4S]

CIS diagnostic step #1. Fuel pressures....do you have gauges? Measure cold and warm pressures, as well as your pump pressure.

[mca]

Interested in #4. I have a strange rattle exactly as you describe. For the life of me I can't find it. Can only be heard faintly with windows up and is tied to throttle (not when clutch is depressed). Linkage sounds like a good place to look though.

[ossiblue]

#1. Agree with 1990C4S, check your fuel pressures.

"10s" cranking? Does that mean you are cranking the engine for 10 revolutions, or the engine is cranking for 10 seconds? Either way, you should get an immediate firing if your cold start valve is functioning so check that next for operation. (If you are cranking the engine for 10 seconds you are risking flooding and hydrolock--be careful.)

#2. Stalling with a pop when cold indicates lean mixture--related to high pressures or air leak. Check all the usual suspects. Having to lift the air meter may indicate the meter plate needs to be adjusted--this could account for hard start also.

Do you have a pop-off valve? Maybe the valve is sticking open when there is a backfire and when you remove the air cleaner to move the air plate, it snaps shut--this can happen if the valve is installed incorrectly, with the hinge facing toward the front of the car.

[47silver]

The main cylinder injectors should NOT operate when the air sensor is at rest. When you lift the sensor you can hear them operate, that is how they should operate not until the sensor is raised.
On my car the fuel pump starts when the key is on. My injectors do not spray (i adjusted them as detailed in the Haynes manual). The manual says to pull an injector and put it in a container. then activate the fuel pump. adjust the fuel mixture 3mm ccw 2 turns. then adjust the mixture screw until an injector just barely starts to operate then turn it ccw 1/2 turn so it is off.
Since the injectors dont add fuel when the car is starting the designers added a cold start valve and the cold start valve only operates when you energize the starter. If you see the wiring diagram on here you will note that it gets power from the yellow wire off of the starter.
On a 75 the power is sent through a switch on the throttle body. When the switch is made the power flows to the CSV. The ground side of the valve is sent to the thermal time switch. On my 75 this ground wire is red/black. The red/black wire on the TTS is open to ground if the engine temp or the electric heater element is above a certain temperature. If the temp is below setpoint then the ground is made and the valve can work. The other contact on the TTS has 12VDC when the key is on...

I tested my CSV by pulling off the throttle body, and I put 12vdc across the valve. I turned my key to ON which starts the fuel pump and I heard a faint click and saw the spray in the air box from the CSV. I knew it worked with direct power so I was able to trace my problem to a bad contact in the connector at the CSV.

Some CIS cars have a switch located on the air sensor. This switch starts the fuel pump when the sensor is raised. Since My 75 fuel pump starts when the key is on the pressure is always high. If yours has the switch on the air sensor then
jumper the fuel pump to on and then test the valve again. If you have spray then your cold start valve is ok.

If you dont have spray then I would guess that the check valve that is located on the fuel pump is bad because it will not keep the pressure in your supply line high enough to let the cold start valve injector work.
With gauges you can test the leakage of this pressure.

The CSV is necessary to get initial fuel to the system as the cylinder injectors are designed not to work when the air sensor is at rest. The main reason I believe that the cylinder injectors dont work until the engine is running is to prevent hydrolock.

So here is sequence:
1. turn key to start.
2. power flows to throttle switch to cold start valve to ground at tts.
3. Cold start valve sprays fuel.
4. then the engine starts.
5. when the engine starts the air sensor raises.
6. then the fuel pump starts.
7. then then injectors operate.

I just replaced an air box, so i reviewed a million pieces of info to find out how this stuff works. you need gauges, a good vom and wiring diagrams and you can figure out most problems.
After replacing the air box i am an advocate of removing the CIS system for maintenance to replace any seals, hoses, gaskets and suspect fuel lines. it is easier than you think.

[boyt911sc]

Originally Posted by 47silver

The main cylinder injectors should NOT operate when the air sensor is at rest. When you lift the sensor you can hear them operate, that is how they should operate not until the sensor is raised.
On my car the fuel pump starts when the key is on. My injectors do not spray (i adjusted them as detailed in the Haynes manual). The manual says to pull an injector and put it in a container. then activate the fuel pump. adjust the fuel mixture 3mm ccw 2 turns. then adjust the mixture screw until an injector just barely starts to operate then turn it ccw 1/2 turn so it is off.
Since the injectors dont add fuel when the car is starting the designers added a cold start valve and the cold start valve only operates when you energize the starter. If you see the wiring diagram on here you will note that it gets power from the yellow wire off of the starter.
On a 75 the power is sent through a switch on the throttle body. When the switch is made the power flows to the CSV. The ground side of the valve is sent to the thermal time switch. On my 75 this ground wire is red/black. The red/black wire on the TTS is open to ground if the engine temp or the electric heater element is above a certain temperature. If the temp is below setpoint then the ground is made and the valve can work. The other contact on the TTS has 12VDC when the key is on...

I tested my CSV by pulling off the throttle body, and I put 12vdc across the valve. I turned my key to ON which starts the fuel pump and I heard a faint click and saw the spray in the air box from the CSV. I knew it worked with direct power so I was able to trace my problem to a bad contact in the connector at the CSV.

Some CIS cars have a switch located on the air sensor. This switch starts the fuel pump when the sensor is raised. Since My 75 fuel pump starts when the key is on the pressure is always high. If yours has the switch on the air sensor then
jumper the fuel pump to on and then test the valve again. If you have spray then your cold start valve is ok.

If you dont have spray then I would guess that the check valve that is located on the fuel pump is bad because it will not keep the pressure in your supply line high enough to let the cold start valve injector work.
With gauges you can test the leakage of this pressure.

The CSV is necessary to get initial fuel to the system as the cylinder injectors are designed not to work when the air sensor is at rest. The main reason I believe that the cylinder injectors dont work until the engine is running is to prevent hydrolock.

So here is sequence:
1. turn key to start.
2. power flows to throttle switch to cold start valve to ground at tts.
3. Cold start valve sprays fuel.
4. then the engine starts.
5. when the engine starts the air sensor raises.
6. then the fuel pump starts.
7. then then injectors operate.

I just replaced an air box, so i reviewed a million pieces of info to find out how this stuff works. you need gauges, a good vom and wiring diagrams and you can figure out most problems.
After replacing the air box i am an advocate of removing the CIS system for maintenance to replace any seals, hoses, gaskets and suspect fuel lines. it is easier than you think.

Gary,

I'm impressed with your CIS diagnostic but I tend to disagree with your theory about the injectors (6) not adding fuel during the start phase. If that's the case, how do you explain when the engine is warm/hot? The CSV is inactive when the engine temperature is around 60°F or higher. Once you crank the engine during a START phase, it sucks air and displaces the AFS plate causing the injectors to squirt fuel. I'm no CIS expert and would be much obliged to be educated and informed about your findings. Thanks.

Tony

[47silver]

I did not think of that, it is 30 here so in the cold mode.

So the problem with his hard start may not be a cold start valve it may be an air leak causing him to run lean.

I tested the vacuum on mine with a shop vac, i dont know how accurate it is but seemed ok to me.
Here is how i did it: i have a vom that measures current. I sealed the intake end of the shop vac and turned it on and measured the current.
I then sealed the throttle body intake with a tennis ball and rubber glove and the exhaust the same way.

I put the shop vac into the popoff valve hole and sealed it in. I turned on the shop vac and let it run and measured the current to the motor....It was very close.
I noted that the rubber glove in the exhaust and tennis ball was being sucked in and so was the rubber glove on the throttle body. If i would have had some of those 4th of july smoke bombs i would have set them off in the engine compartment to see if any smoke came out of the shop vac exhaust, next time i will.

I think it may be a method of checking vacuum with some refinements. Maybe an actual vacuum gauge would be best.

An alternative would be to reverse the flow of the shop vac and pressurize the system,, seal the exhaust etc and then use those smoke bombs to pump smoke into the shop vac intake and then into the system.

[Wyvern]

Did this condition come on slowly or just start all of a sudden.

I ask because one of my pals looked to me after I had many issues (now all good) as issues just kept getting worse ..
To get back on track I did the fuel filter and accumulator then started checking pressures ... something was off.. (high pressure when cold)
I found a ton of S**t in the screen on the WUR. cleaned that and ALL WAS GOOD.

just be methodical and you will get it .

I am NO expert but with all I have learned from the "brain trust" here feel comfortable and capable with our little friend CIS ...

[stlrj]

It is sounding more like an ignition problem than a CIS issue.

[T77911S]

Originally Posted by 1990C4S

CIS diagnostic step #1. Fuel pressures....do you have gauges? Measure cold and warm pressures, as well as your pump pressure.

sorry, ALWAYS, start with looking for air leaks. if you jump into it with gages, you are likely to end up compensating for an air leak even if the pressures are off. someone will adjust their CP's, reset the mixture and not even think about air leaks. you do want to check pressures before adjusting or replacing anything.

when was the last time you changed the plugs, cap and rotor? i forgot this simple rule just recently thinking mine were still ok. fires up first hit now. this is another basic problem area to rule out early.

one way is to check for air leaks is with smoke. the other thing is to just replace all the places it can leak. the car is 30 years old, it would not hurt. this rules out everything. injector sleeves, injestor O rings, the rubber boots on the runners, intake gaskets, rubber hoses, replace it all. also check that metal pipe on the rear that goes to the aux air valve. paulporshe found a hole in his and mine has been rubbing. another place is the hose that goes to the brake booster. JW did a post about this. i checked mine with a hand vacuum pump. i pulled a vacuum, not with a shop vac, and let it sit for a few minutes.

check the thermo time valve, it should be closed, no vacuum, when cold, after 20 sec or so it should open and let vacuum through.

that procedure in the haynes manual is just a starting point for a rebuild, after the car is running, the mixture should be checked with an analyzer and reset.

i would think as the car is starting, hot or cold, the injectors would have to spray fuel or it would never start.

[1990C4S]

Originally Posted by 47silver

Since the injectors dont add fuel when the car is starting the designers added a cold start valve and the cold start valve only operates when you energize the starter.

I don't believe this is correct, the fuel injectors will supply fuel once air is sucked into the engine. As pointed out by boyt911, the cold start valve is only for temporary enrichment when the engine is cold.

Originally Posted by T77911S

sorry, ALWAYS, start with looking for air leaks. if you jump into it with gages, you are likely to end up compensating for an air leak even if the pressures are off. someone will adjust their CP's, reset the mixture and not even think about air leaks. you do want to check pressures before adjusting or replacing anything.

I might agree if his car was running lean, from his description of the issues I am not sure it is/was (although point #2 could be a lean issue). If he has gages and knows his previous settings, then he can diagnose the issue better knowing the fuel pressures have not changed. If he doesn't know his previous settings he should still confirm they are within spec before moving on. It is easy to do, a lot easier than getting a smoke test done.

I admit you are correct in general, ask Paulporsche, he had a long thread on a CIS issue he couldn't solve. I eventually diagnosed (and fixed) his vacuum leaks. But the vacuum leaks were deduced when the car wouldn't run with proper fuel pressures. Same outcome, just worked from a different direction. I don't advocate changing CIS pressure settings to just get the car to run better, but the three basic pressures are the diagnostic starting point in my mind.

[Jim Williams]

47silver wrote:

Some CIS cars have a switch located on the air sensor. This switch starts the fuel pump when the sensor is raised. Since My 75 fuel pump starts when the key is on the pressure is always high. If yours has the switch on the air sensor then
jumper the fuel pump to on and then test the valve again. If you have spray then your cold start valve is ok.

On the cars equipped with the safety switch ('76 and later CIS cars), the fuel pump, as well as the cold start valve, operates during the entire time the starter is operated and so provides fuel pressure to the CSV. This operation is provided by the fuel pump relay. The CSV doesn't need to rely on residual fuel pressure to operate during startup.

I have never seen any evidence that any fuel is provided by the injectors during startup, as a certain amount of airflow is necessary to raise the airflow sensor. I'll be the first to admit that I don't know if the engine, just powered by the starter, provides enough airflow to raise the sensor plate. However, the first few "power spins" of the engine doubtless provide enough airflow, and fuel to the injectors, to keep the engine going after the starter is released.

[1990C4S]

But a car with no functioning CSV will start, so I think you can assume that fuel is injected when the engine spins on the starter.

Not a definitive statement, just a supposition....feel free to contradict, I'm not sure about this.

[E Sully]

I would start by pulling the spark plugs and checking their condition to see if they are all firing correctly. It could be a bad spark plug or one of the injectors might not be flowing properly. The vibration under load doesn't seem to be related to a cold engine.

[T77911S]

C4S, #1, a cold car will be harder to start lean, as in an air leak. rich is more forgiving starting cold.

a cold car is VERY hard to start without a CSV, i would think longer than 10 cranks, much longer.

if the plugs are old, just replace them along with cap and rotor, these are cheap and could save you time and money.

perhaps even check residual pressure.

[Jim Williams]

Originally Posted by 1990C4S

But a car with no functioning CSV will start, so I think you can assume that fuel is injected when the engine spins on the starter.

Not a definitive statement, just a supposition....feel free to contradict, I'm not sure about this.

I suppose that there are some cars that will eventually catch and start without a functioning CSV, but I know they weren't designed to do such. I've never tried to test your statement, so I don't know that I would feel comfortable saying this.

I've also learned from experience not to just assume things with CIS operation. I've already admitted I didn't know the answer, so I won't contradict your supposition....

[47silver]

The CIS is a pretty robust system except for air leaks. As was stated an air leak can be over come with adjustments but that is not how the car was designed and will eventually cause problems.

I removed the CIS without droppign the engine. I realize it is easier on a 75 than others but i would not waste another moment on finding the problem i would take it off and replace:

fuel injector sleeves and seals. If the injector sleeves are good just replace the seals.
Fuel injector seals.
Breather gasket
tstat oring
throttle body oring
fuel distributor gasket.
intake runner gaskets
intake runner rubber sleeves.
new breather hose and clamp.
new vacuum hoses on the back of the throttle body and air box if any.
these parts you can get for < 100 bucks i suppose...
a couple of 1/4 inche flexible extension and a good 12 mm socket and torgue wrench for your intake runner nuts.

[1990C4S]

Originally Posted by 47silver

The CIS is a pretty robust system except for air leaks. As was stated an air leak can be over come with adjustments but that is not how the car was designed and will eventually cause problems.

I removed the CIS without droppign the engine. I realize it is easier on a 75 than others but i would not waste another moment on finding the problem i would take it off and replace:

fuel injector sleeves and seals. If the injector sleeves are good just replace the seals.
Fuel injector seals.
Breather gasket
tstat oring
throttle body oring
fuel distributor gasket.
intake runner gaskets
intake runner rubber sleeves.
new breather hose and clamp.
new vacuum hoses on the back of the throttle body and air box if any.
these parts you can get for < 100 bucks i suppose...
a couple of 1/4 inche flexible extension and a good 12 mm socket and torgue wrench for your intake runner nuts.

So your suggestion is to do this first? After a leak has been diagnosed, yes, but not now..

[1990C4S]

Originally Posted by T77911S

C4S, #1, a cold car will be harder to start lean, as in an air leak. rich is more forgiving starting cold.

a cold car is VERY hard to start without a CSV, i would think longer than 10 cranks, much longer.

if the plugs are old, just replace them along with cap and rotor, these are cheap and could save you time and money.

perhaps even check residual pressure.

I agree completely, but I think we are getting off track. If the CSV is a suspect it can be tested when we determine that is appropriate.

I still say the easiest thing (assuming he has gages) is to measure his pressures and post the results.

[Aurel]

Thank you all for the replies and ideas. My feeling is that the mixture is set too lean, and maybe also an air leak. I am still wondering what is causing the rattle that I hear in the throttle. Hopefully it will go if I richen a bit...