cableguy47

i have a 1978 928 it runs but no throttle response what should i look at

crushingday

try moving the throttle by hand under the hood. perhaps the cable is off

cableguy47

nope checked that it is on it will start but will not respond wide open it still just idles

elgy

Has it been sitting for awhile? Mine would only idle after not being started for 2 years. I let it run for awhile and was able to give it a bit of throttle, than a bit more and it finally ran well enough to take it out and the road where higher revs seemed to clear the cobwebs out of the fuel system. Runs fine now.

cableguy47

It has in fact about 9 years

tailpipe

warm up regulator is prolly full of sediment and the pressure is to high.

The Deputy

Does it have fresh fuel? After sitting for that length of time, probably should have drained tank and fuel system and flushed with clean fuel. Fuel manifold/delivery system is probably all gummed up, too. Since you have no throttle response, but runs, I'd definitely focus on the fuel system.

Brian.

cableguy47

Yes i did drain and put fresh fuel in.

Rob Edwards

At the risk of visual overkill, here's an annotated schematic of the '78 fuel system, it starts at the tank in the upper right at #1 and the fuel flow circuit from and back to the tank is all in the right half of the image.




Jim Doerr has an excellent summary on the CIS fuel system here:

http://928classics.com/4/post/2014/0...ide-78-79.html


In the '78 that I helped refresh, the fuel pump was bad, the accumulator was bad (long cranking on hot starts), the fuel distributor was clogged, the fuel lines to the injectors were clogged, and the injectors were clogged. At the risk of sounding negative your safest bet is to assume the same thing, and start from the back of the car and go through each item sequentially. You can at least verify that the fuel pump is putting out the correct volume and that the accumulator, filter, and feed/return lines are not blocked by running the fuel pump volume test - spec is 1120 cc in 30 seconds:

cableguy47

Thanks for the info do you know what the fuel psi is supposed to be at the inlet for injector body

Rob Edwards

Spec for system pressure at the warm-up regulator (which is where system pressure is measured) is 65 to 75 psi.

cableguy47

Cool thanks

jpitman2

You need to tell us some more data please. When you open the throttle AT THE ENGINE, does its running change at all? eg if its getting more air with the throttle open, but no more gas, it should run very poorly, roughly, struggling to keep going IF THE THROTTLE is really wide open. If it keeps idling the same, I cant believe the throttle is really open.
To check for fuel pressures you need a CIS gauge set (talk to Roger at 928srus.com) to measure system and control pressure. System should be around 65-75 psi, cold control (depending on ambient temp) as low as 10-15psi, rising to 45psi when hot. Also check fuel delivery rate as above - approx 1350cc in 30 secs. The fuel filter should be changed asap. If it starts well the cold control is probably OK, but a high hot pressure will kill throttle response and power.
If it has been sitting a LONG time there may be crud everywhere. Some of it may be cleared by loading the tank with something like Berryman's or Marvel Mystery Oil, and bridging the pump relay and letting it run for an hour or more. If the injectors are blocked in any way they will need to be cleaned (back flushed) - a good 911 shop should be able to do this, or advise replacement. The short brass MB injectors seem to be available where the originals are not, and are reported to work fine.

jp 83 Euro S AT 57k

cableguy47

Well it does start but first start of the day is doesn't start well but when it gets warmed up it starts fine but when you open throttle starts to back fire through the throttle body and wont get above 1400 rpm . i have put new pumps and filter on and drained tank i dont know if the fuel accumulator is bad and dont know how to check it i do know that i can pull injector lines off i don't have much for pressure coming out. I am new th the porsche world and i got this one for a steal couldn't let it pass by i have always wanted one .there is alot to them, im a pretty good mechanic but never worked on or owned a foreign car. Thanks for any info i can get to get her back on the road. Thank you again and merry Christmas

The Deputy

Like Rob mentioned, you need to find out fuel pressure and go from there. Most likely, after sitting for that length of time, you are going to have plugged up components.

Just be sure to look at the two rubber fuel lines (along passenger side exhaust manifold), really, really good before you get an engine bay fire going on...or just replace them now and avoid the whole situation.

Brian.