1976 CIS troubleshooting guidance

[billh1963]

My '76 911S (all stock) would not start last weekend. I initially assumed the new Pierburg fuel pump was to blame. However, that may not be the case.

Here is where I am so far:
1. I know it's not ignition. Engine fires on a little bit of starting fluid
2. Cranking the engine (engaging the starter) results in fuel pump relay clicking
3. Cranking the engine (engaging the starter) produces voltage at the fuel pump and I can physically feel fuel pump run

Q1- When cranking the engine the fuel pump relay "pulses"..as does the fuel pump. Is that correct? Meaning, while the starter is engaged the relay clicks in and out and the fuel pump voltage fluctuates between 0 and 12v...is that the correct operation?

Q2- What's the best way to verify the pump is pumping fuel? Jumper the fuel pump relay out and pull the return line off the fuel tank and verify fuel is retuning or is there an easily accessible fuel line on the engine?

Thank you

[HarryD]

Sounds like a weak battery.

[fanaudical]

There are two attributes of fuel pump operation that you need to verify: Output pressure and flow rate. Generally, if these pumps are making sufficient pressure then they are also providing sufficient flow rate. The best method (my opinion) to verify pump operation is to temporarily install a CIS pressure test gauge set and get the pump to run. Do a system pressure test and verify the pump is working.

I don't think that you should be experiencing pump pulsing when cranking. This does sound like either a weak battery or some other electrical fault.

[pete3799]

Have you tried a new relay or swapped one of the black ones in and tried starting?

[psychoideas]

The red fuel relay has a diode in it that somehow works with the contact on the fuel sensor plate so that the pump stops if the car is upside down or somethong like that.

Turn the ignition on till the alt/guage lights come on but don't crank it. The fuel pump should at least start and run for a while. I'm not sure if it stops when pressure is reached. Go down the back take the air filter out and reach in and lift the fuel sensor plate gently off it's stop. You should quite clearly hear the injectors squirt and if the pump was off it should now start to run.

If you can't hear the injectors, then you have a pump problem.

Mine has a similar problem and I had to wiggle the red fuel pump relay a bit to get the pump to continually run.

[gomezoneill]

Did you bleed the fuel system after installing the pump?

[billh1963]

Originally Posted by gomezoneill

Did you bleed the fuel system after installing the pump?

Car was running fine for a couple of months after replacing the fuel pump. This is a new event.

[billh1963]

Originally Posted by psychoideas

The red fuel relay has a diode in it that somehow works with the contact on the fuel sensor plate so that the pump stops if the car is upside down or somethong like that.

Turn the ignition on till the alt/guage lights come on but don't crank it. The fuel pump should at least start and run for a while. I'm not sure if it stops when pressure is reached. Go down the back take the air filter out and reach in and lift the fuel sensor plate gently off it's stop. You should quite clearly hear the injectors squirt and if the pump was off it should now start to run.

If you can't hear the injectors, then you have a pump problem.

Mine has a similar problem and I had to wiggle the red fuel pump relay a bit to get the pump to continually run.

I think on the '76 the fuel pump only engages while cranking. The fuel pump won't run with just the ignition on.

[billh1963]

Originally Posted by pete3799

Have you tried a new relay or swapped one of the black ones in and tried starting?

I have a new red one on order.

[billh1963]

Originally Posted by HarryD

Sounds like a weak battery.

Originally Posted by fanaudical

There are two attributes of fuel pump operation that you need to verify: Output pressure and flow rate. Generally, if these pumps are making sufficient pressure then they are also providing sufficient flow rate. The best method (my opinion) to verify pump operation is to temporarily install a CIS pressure test gauge set and get the pump to run. Do a system pressure test and verify the pump is working.

I don't think that you should be experiencing pump pulsing when cranking. This does sound like either a weak battery or some other electrical fault.

You may be right. I did charge the battery. However, I don't know the age (was in the car when I bought it a couple years ago). That's worth checking.

[boyt911sc]

Originally Posted by billh1963

My '76 911S (all stock) would not start last weekend. I initially assumed the new Pierburg fuel pump was to blame. However, that may not be the case.

Here is where I am so far:
1. I know it's not ignition. Engine fires on a little bit of starting fluid
2. Cranking the engine (engaging the starter) results in fuel pump relay clicking
3. Cranking the engine (engaging the starter) produces voltage at the fuel pump and I can physically feel fuel pump run

Q1- When cranking the engine the fuel pump relay "pulses"..as does the fuel pump. Is that correct? Meaning, while the starter is engaged the relay clicks in and out and the fuel pump voltage fluctuates between 0 and 12v...is that the correct operation?

Q2- What's the best way to verify the pump is pumping fuel? Jumper the fuel pump relay out and pull the return line off the fuel tank and verify fuel is retuning or is there an easily accessible fuel line on the engine?

Thank you

Bill,

Perform the basic tests first and hook up a fuel pressure gauge. Stop guessing and everything you need to know about the procedures are well discussed in a thread by DKLever48. Spend a few minutes reading the thread. You will be well informed after understanding some of the post. Keep us posted.

Tony

[T77911S]

the FP relay could pulsate when cranking. if the sensor plate is pulsating due to the low RPM cranking that could cause it to open and close.

the easiest way to bypass this is to remove the connector on the top rear of the AFM. this runs the pump as soon as the key is on,

I would verify ignition with a spark plug and cranking it.

if it still will not start I would lift the sensor plate with the key on and prime the engine a little.
if ti starts I would look into the CSV.

make sure you have no air leaks

now comes the time when you have to have gauges. you need to verify CCP.

[billh1963]

Did the electrical test in DKlever48's thread and all is good.

Next step is to lift I want to lift the lever on the AFM described as the next step.
Three questions:
1. What does that lever look like?
2. How load will the injectors be when delivering fuel?
3. Will this procedure work on a '76?

Also, can the fuelressure gauge be bought as a complete unit or do I need to piece one together?

Thank you

[billh1963]

Ok...figured out the lever. Injectors squirt fuel when lever is lifted.

I also did the test (redundant) of lifting lever with the test light connected to positive and inserted in pin 85. Light goes out when lever is lifted

[billh1963]

Without a fuel gauge, what else should I test?

[billh1963]

CDI makes a high pitched squeal when ignition is on. But, i would like to test that as well because after flying lever t still won't start ( I heard gas go through the injectors). I'm working by myself.... Any suggestion on how I can test the ignition working solo?

[billh1963]

Car is running. Don't know why. Lifted lever a couple more times verifying fuel flow. Car started and died. Cranked again and started and is now running.

Car had only sat a week since I last ran it. It acted like it need to be "primed"

[gazzerr]

Might have been air in the fuel system. You have to bleed the injectors by lifting the sensor plate for 3 to 5 secs if it's been apart. No longer than that because you don't want to flood the cylinders with fuel.

[T77911S]

where are u located

[billh1963]

Originally Posted by T77911S

where are u located

Columbia area....

Update: Took the car on a 50 mile drive. All is well. Ran well. Let it sit a few hours, started it again and fired right up.

---------------------
Although I'm glad it's running again I find it interesting that the car would not start until I "primed" it. (at least that appears to be what happened).

The car had been running fine for two months or more after I replaced the fuel pump.

The car had only sat a week without being driven (that's typical) when the no start condition occurred. Any ideas on why this event happened? Anyone else experience this? Would a fuel leak or something similar cause this?