'74 914 Throttle Issue
 

I'll try to keep to the pertinent details on this question. I bought 2 '74 914's from my dad recently, one for parts. The 'good' one, a 2.0, has been sitting for 18 years due to a bad trans. I've got it up and running, trans swapped, cleaned fuel tank thoroughly, cleaned fuel lines, replaced fuel pump and filter, removed and cleaned injectors and tested them with a battery and some carb cleaner. 3 spray a nice pattern, one is iffy but the engine doesn't miss at moderate speeds. If you start up and take off and try to go over about 60% throttle in any gear it acts like its running out of fuel. You can be running 80 down the interstate just fine and then go to pull a hill and it has the same symptom, feels like you're running out of gas. When this happens, I discovered you can clutch it, turn the key off, count to 3, turn the key back to run or crank it and let out the clutch and you can floor it with no hesitation clear to 100+ mph. I probably did this every 2 miles in a 20 mile stretch the other day, then it ran ok for a few miles. I'm guessing this is a reset for the fuel injection computer. I suspect the throttle sensor as it seems to be throttle/rpm related. It also runs rich all the time and the idle speed varies. What is the wiring pattern to check the throttle sensor, and what else should be checked? BTW, my dad bought this car from the original owner in 1984 and it ran great until he parked it in 1995 when the trans went out.

The FI computer is not sophisticated enough for a reset to do anything. I am thinking that you might still have something going on with the fuel supply--some leftover crud in the tank, a fuel line that gets pinched or collapses under suction, or similar.

Rich running can be quite a few things. Too much fuel pressure, too much resistance in the CHT circuit, a leak in the MPS, and other things as well.

Varying idle is often a lean mixture (a "lean hunt"). It can also be due to varying timing--how is the distributor?

The throttle sensor can be most easily tested by unplugging it. The idle may get worse, and acceleration will really suck, but the engine should still run without misfire. More involved checks mean looking for continuity on the idle contacts when the throttle is closed, and at no other time, and listening for 10 "clicks" from the injectors when you open the throttle with the key on.

Also look through the D-jet bible, here: Brad's '70 914 2.0L

--DD

If it were me, I'd dump some Marvel Mystery Oil in the tank and drive it around, repeat for three or four tanks of the mix and I would imagine the engine will be okay. I know if I laid around that long I'd have troubles to..........

Thanks Dave and John, will try these suggestions. Dist was in good shape, no shaft wobble. Btw, it ran great Tuesday until last stop making errands. Will let you know, thinking CHT sensor would be good investment.

Whats the fuel pressure like @ the engine after the fpr?,have you gone thru the engine loom looking for possible bad connections?,the engine looms in these cars really degrade because of heat and old age,they go so hard the wires can just break.
I would replace or get that bad injector cleaned,is your ignition system ok,you have a lot of work ahead of you if the car has been unused that long,its about checking everything and eliminating as many possible issues as you go.
Hope it goes well;)

The pressure regulator works by acting as an obstruction to flow. The pressure on the inlet pushes against a spring, when it overcomes the spring pressure the fuel bleeds off until the spring closes the valve again. So you want to measure the pressure somewhere "downstream" of the fuel pump, but "upstream" of the fuel pressure regulator.

On some fuel rails there is an extra unused fitting. You can remove the bolt that plugs it and hook a gauge up there. Or, if you have the type of cold-start valve that only has one fuel hose going to it, you can take the hose off the CSV and instead hook it up to your gauge. Failing that, you'll have to make a 'T' fitting up and put it in the middle of one of the high-pressure hose runs.

BTW, Jeff Bowlsby sells "rebuilt" D-jet injection harnesses. I put the "rebuilt" in quotes because it's about 97% new parts, and is probably better than the originals were in the first place. Replacement Porsche 914 Wiring Harnesses

--DD