Broken down...fuel pump?

[asterix031]

Hi. My SC has broken down and I think its the fuel pump. Checked the spark side of things and that looks good.

When turning the key before firing the engine I'm not sure if I hear the pump. Fuse is ok. Do here a faint high pitched sound but not what I'd expect to hear and don't think its it or sounds right (though not that familiar with car).

As I can't get to the pump and the tow truck is hours away, is there anything else I can do/check?

Thanks.

[rusnak]

I'm not an expert on cis, but I think you can check it by opening the airbox lid (key on) and lifting the airflow sensor plate. You should hear gas shoot into the cylinders. If not, then swap out the fp relay with another, say the ac for example. Check fuses.

[asterix031]

Just tried it and it started. Swapped back and it started too... Then began to sputter and idle low/rough. Sticking to towing to be sure it gets home.

Something is on its way out or at least not liking heat.

[g_vaxed]

Originally Posted by asterix031

Just tried it and it started. Swapped back and it started too... Then began to sputter and idle low/rough. Sticking to towing to be sure it gets home.

Something is on its way out or at least not liking heat.

Have a friend who has an 87 that had the same symptoms as above. It ended up being a bad coil. Good Luck.

[asterix031]

Originally Posted by g_vaxed

Have a friend who has an 87 that had the same symptoms as above. It ended up being a bad coil. Good Luck.

Hmmm. I do have a temp coil in to run the car about until the correct one arrives. It was sparking fine though.

[RoninLB]

i'd pull an injector and lift the CIS flapper and see if it squirts even though the pump is triggered

pump on, no flow.... that's what happened to me on a Sat 2,000 miles from home on I-10 in NM

[asterix031]

Since its home and very very near a mechanic I'll work through it with him until I have a proper workspace. Thanks for the tip though. Now to that pesky window Its bringing back memories of the constant 928 electrical nightmares I used to have...

[juanbenae]

fuel pump relay? mine works its way out sometimes and its very evident due to the fact you can not hear the fuel pump run with the ignition in the ON position w/o the motor running.

[RoninLB]

if you pull out the relay and look at the pins you'll see each pin is two part

i use a razor blade to gently split the pin wider for a tighter fit

[juanbenae]

Originally Posted by RoninLB

if you pull out the relay and look at the pins you'll see each pin is two part

i use a razor blade to gently split the pin wider for a tighter fit

NICE! i guess i can get rid of the zip ties securing it in now.

[crustychief]

Originally Posted by car 311

fuel pump relay? mine works its way out sometimes and its very evident due to the fact you can not hear the fuel pump run with the ignition in the ON position w/o the motor running.

The fuel pump on an SC does not activate with the key on and the engine not running. Fuel pump activation requires intake air to lift the sensor plate.

[2.70Racer]

The fuel pump relay for CIS systems works opposite from what intuition would tell you.
As RoninLB mentioned in post #6, lift the air flapper with the ignition on, the fuel pump should come on and fuel will flow through the injectors.
A simple and correct test. Ron knows, he is a great source of correct info.
About the fuel pump relay, it is NOT energized when the engine is running.
Power to the fuel pump runs from the fuel pump fuse to pin 87a of the fuel pump relay.
pin 87a and pin 30 are the normally closed contacts.
This means when the relay is NOT energized, the power can flow to the fuel pump.
The fuel pump doesn't run until the ignition is on and cranking the engine.
Once the air flapper lifts, it de-energizes the fuel pump relay and the fuel pump gets 12 volts through pin 87a to pin 30 of the relay, pin 30 to the fuel pump.
It's all backwards until you study the electrical print.
Another simple test is to jump pin 87a to pin 30 of the fuel pump relay socket.
With the above jumper in place, the fuel pump will come on when the ignition switch is turned to the on (running) position.
Very briefly run the pump, not more than a second or two. Continous running can flood the engine with fuel.
Remember the fuel pump runs when the fuel pump relay NOT energized.
Not a bad idea to replace the fuel pump as preventive maintenance.
If it is the original fuel pump, it's over 30 years old.

[boyt911sc]

Originally Posted by 2.70Racer

The fuel pump relay for CIS systems works opposite from what intuition would tell you.
As RoninLB mentioned in post #6, lift the air flapper with the ignition on, the fuel pump should come on and fuel will flow through the injectors.
A simple and correct test. Ron knows, he is a great source of correct info.
About the fuel pump relay, it is NOT energized when the engine is running.
Power to the fuel pump runs from the fuel pump fuse to pin 87a of the fuel pump relay.
pin 87a and pin 30 are the normally closed contacts.
This means when the relay is NOT energized, the power can flow to the fuel pump.
The fuel pump doesn't run until the ignition is on and cranking the engine.
Once the air flapper lifts, it de-energizes the fuel pump relay and the fuel pump gets 12 volts through pin 87a to pin 30 of the relay, pin 30 to the fuel pump.
It's all backwards until you study the electrical print.
Another simple test is to jump pin 87a to pin 30 of the fuel pump relay socket.
With the above jumper in place, the fuel pump will come on when the ignition switch is turned to the on (running) position.
Very briefly run the pump, not more than a second or two. Continous running can flood the engine with fuel.
Remember the fuel pump runs when the fuel pump relay NOT energized.
Not a bad idea to replace the fuel pump as preventive maintenance.
If it is the original fuel pump, it's over 30 years old.

Doug,

You have presented many good information about the FP relay's operation but I beg to disagree to the above statement (highlighted). You could run the FP all day long and you won't flood the engine!!!! Fuel is delivered when the FD's plunger is raised or lifted up by the AFS (air flow sensor). Why do you think it would flood the engine? Please advise. Thanks.

Tony

[Flat6pac]

Just running a jumper from 30 to 87a will get the pump running and get you home if the pump isnt defective.
Bruce

[crustychief]

Originally Posted by boyt911sc

Doug,

You have presented many good information about the FP relay's operation but I beg to disagree to the above statement (highlighted). You could run the FP all day long and you won't flood the engine!!!! Fuel is delivered when the FD's plunger is raised or lifted up by the AFS (air flow sensor). Why do you think it would flood the engine? Please advise. Thanks.

Tony

By jumpering the relay you essentially bypass the sensor plate. When the pump runs the injectors inject.

[RoninLB]

[RoninLB]

Originally Posted by crustychief

By jumpering the relay you essentially bypass the sensor plate. When the pump runs the injectors inject.

check out "How to Tune & Modify Bosch Fuel Injection" by Ben Watson p105-6
it's easier to read than me explaining

or i can package together a few scans

[boyt911sc]

Originally Posted by crustychief

By jumpering the relay you essentially bypass the sensor plate. When the pump runs the injectors inject.

crustychief,

Did you have any direct hands on experience about running the FP or just read it? You could run the FP for hours and not get any fuel into the engine!!!!! I've been doing the WUR tests for many years now so I know it does not deliver fuel unless you lift the AFS/plunger. Where did you get such (mis)information? Sorry to disagree.

Reading pages 105-106 (Ronin's suggestion) would be very helpful and informative. Highly recommended.

Tony

[juanbenae]

Originally Posted by crustychief

The fuel pump on an SC does not activate with the key on and the engine not running. Fuel pump activation requires intake air to lift the sensor plate.

so now that ive got carb how does the fuel pump know when to come on? cant recall precarbs, but mine runs now with the ignition on, car not running. maybe what you meant to say was the fuel pump will run, just not deliver fuel until the plate is lifted??

[RoninLB]