1978 SC Intermitent Power Loss and almost Stall
 

Hi All,

Thanks in advance for your help.

I have had an issue last few times I have taken the 78 911SC for a ride. She will start up fine, first twenty minutes of driving no issues she runs good. Then all of a sudden I get a loss of power, when I slow down she tries to stall on me, I put it in neutral and give her gas and she does not stall. I continue to drive and the problem goes away, then after a while it happens again. Strange

I do look at the guages when the problem occurs and they seem to be OK. I thought perhaps vacuum leak, but why would the problem come and go like that?

Note: Spark plugs, wires, cap fairly new. Fuel filter changed last year. Air cleaner fine

Thanks

Mike

Sounds like you might be losing fuel pressure. Tough to diagnose but if you consider a fuel pump preventative maintenance, you may want to look at replacing it.

Of course when you say loses power I am assuming it is losing power when you try to give it gas, and not just the coming close to stalling when you slow down.

Hi IceMan,

Thanks for replying, yes I will be in third or fourth gear and the engine sounds like it is straining, and losses power. If I push on the gas it will strain to pick up speed.

Is there any way to test a fuel pump?

FP test run.........
 

mfiazzo,

Check the volumetric flow rate or use a pressure gauge to measure your system pressure. Two (2) liters per minute is the minimum requirement or a system fuel pressure between 68 - 74 psi will do it. Keep us posted.

Tony

Hi Tony,

Is it possible to use my CIS test kit to test the fuel system pressure? If so, is there a procedure I should follow?

Thanks

FP test run.........
 

mfiazzo,

A simple and direct test for the FP is using a pressure gauge. Connect the 'gauge' before the FA (fuel accumulator) or after the FP. The shut-off valve should be after the gauge, away from FP. With everything properly connected, run the FP long enough to get a good reading. Depending on your FP (type/size), a typical CIS FP could deliver from 85 to 100 psi fuel pressure. Typically in the 90+ range. Don't forget to close the valve when doing this test.

Tony

Tony, thanks, i will keep you posted on the outcome. Wont have a chance to work on it till next weekend

Hi Tony, quick question. Can I unhook the hose at the inlet to the fuel accumulator to perform the test? Would that be the best spot or is there another?

Update:

I received my new FP and installed it today. The project took me about 1.5 hours and went without a hitch.

A couple of observations and questions:

1. The belly pan was much more beefy than I anticipated. I thought it would be a relatively thin piece of metal. It also seems the belly pan is helping to hold up a torsion bar, is this the case or is something wrong with the bar?

2. The new FP is much quieter than the old one which leads me to believe this may (hopefully) fix my intermittent issue with power loss.

3. Something I found shocking, it appears one of the PO changed the FP at some point in time as the PO used zip ties instead of clamps to hold the rubber tubing from the gas tank to the inlet of the FP. I put clamps on and also changed the clamp holding the fuel pump to the chassis.