cis problem pump runs no pressure to injectors

[Alan Cottrill]

I have a 1977 911

my fuel pump runs but I don't get any flow through the injectors.

I have pulled an injector, jumped the FP relay and ran the pump, and lifter the air sensor plate and get no flow through the injectors.

if I let my pump run for a minnute or two I will hear the pressure build up in the engine compartment and then when I lift the sensor plate I will get flow.

I hate to throw parts at a car.

any ideas?

[jason2guy]

you could start with the fuel filter and the accumulator, they could be clogged.

[IROC]

Yeah, like Jason says, verify you have flow out of the pump and then start checking components downstream from there.

Mike

[MotoSook]

Buy a CIS pressure tester. Costs less than an hour's labor charge by your favorite wrench. That's a start..and it will save you a lot of head scratching.

[Superman]

That's unusual. remove the fuel filter and the fuel accumulator, next to each other on the left side of the engine compartment. Toss the filter. Blow gently through the accumulator, to make sure it is not plugged. Also remove the fuel pump and the fuel level sender. This gives you access to the screen that is probably at the bottom center of the fuel tank. Make sure the screen is not clogged, and that gas flows easily to the fuel pump. Blow compressed air through the line that moves gasoline from the FP to the engine area. Disconnect and blow compressed air through the lines in the engine compartment and the line that returns fuel back to the tank. Then put it all back together.

Check fuel pressures with a pressure gauge. If residual pressure leaks down faster than spec after engine shutoff, then put a check valve onto the fuel pump. If residual pressure still falls too fast, replace the fuel accumulator.

Even if residual pressure leaks to nothing, your FP should be able to recover that pressure in just a few seconds. Certainly less than a half-minute unless a line is clogged or the pump is toast. Clogged lines are very common on older cars. Very common. When buying a car that is 20+ years old, blowing out those fuel lines is probably as important as changing filters and doing a tune-up.

[Alan Cottrill]

Thanks for the info. Sounds like I'm going to be busy this weekend.

[juanbenae]

the fuel filter can go south real quick like, i had one go from running fine to barely running with in 5 miles on the freeway. it did not come on slowly as you might imagine, i changed the filter and presto! there was no noticable difference from the time just before it went south to the new filter install. in otherwords its a quick trip from fine to bad.

[Alan Cottrill]

Thanks for all the good advice

I invested in the CIS pressure tester. Great investment! Buying the right tools always saves money in parts.

"since I was there" and had the tool now I made my WUR adjustable.

I also pulled the filter, tossed it, and pulled the accumulator and checked to see if it was plugged, it was. Replaced both.

disconnected and blew out every line. It took some time but it was worth it. The return line to the tank seemed to be the worst.

waited till morning, about 50 degrees out and adjusted my WUR and fired it up.

It's never started that easy! I tweeked the mixture to get a good idle and she runs great, and starts better than ever, hot or cold.

Thanks to everyone for sharing your knowledge and experience. I've only had my 911 about 2 months and am very greatfull to be able to participate in this group.