Fuel sensor plate not moving. Too much fuel pressure?

[jim928]

Hi everyone, first time posting here.
Two years ago I bought a DeLorean with 17,000 miles, that was sitting for about 6 years and it had some hesitation and starting issues. Last summer I dropped the fuel tank and installed a new fuel pump, fuel accumulator, fuel filter and new fuel injectors. This fixed the hard starting problems but there still was the popping and hesitation issues if I pressed the accelerator too much. If driven easy it would not pop. The car also idled fine too. I put about 1500 miles on it this way. This past month I decided to finally tackle the hesitation issue and popping. I found that the plunger on the fuel distributor did not move freely and would get hung up so I swapped it out with rebuilt unit from Python injection. The rebuilt unit moves as smooth as silk. I also replaced all the fuel lines with stainless steel braided ones that are available on Special T Auto. To rule out any vacuum leaks I replaced all vacuum lines, gaskets, rubber seals and o rings on the intake manifold and mixture control unit. So after all this work done my new problem is the sensor plate on the mixture control unit does not move! The vacuum of the engine can't suck the plate down. It feels like the fuel pressure inside the fuel distributor is pushing the plunger down which keeps the sensor plate from dropping when rpms increase. Car will not hold an idle on its own but when the sensor plate is manually moved in conjunction to the position of the throttle the engine runs amazing and is super responsive. To me it feels like there too much pressure inside the fuel distributor. Has anyone come across this issue before?

[Bitsyncmaster]

A plugged return line would cause high pressure. You really need to check the pressure with a guage but I guess you could pull the return line at the tank and verify fuel is flowing with the pump running.

[Ron]

It feels like the fuel pressure inside the fuel distributor is pushing the plunger down which keeps the sensor plate from dropping when rpms increase.

Have you ever felt the plate at idle on a good system to compare with the way it feels now as you work it manually? ...It's normal for the plunger to push the plate -- I'm wondering if you need to adjust the CO screw (right = clockwise= richer) since you have a different fuel distributor, as usual.

[DMCMW Dave]

To me it feels like there too much pressure inside the fuel distributor. Has anyone come across this issue before?

Not too much pressure, but a case where the fuel distributor plunger and bore were gummy. Car would idle fine but lean misfire/backfire like crazy until the plunger finally moved. Then it would go down the road fine until you let it idle again.


Try the simple things first. Clean it.

[Ron]

He said he just put a rebuilt FD on this past month....

[David T]

Double check that you installed the lines correctly. Sounds to me like you have the feed and return mixed up. Pull an injector, run the fuel pump, and see what the pattern looks like as you push down on the air sensor plate.
David Teitelbaum

[jim928]

Thanks everyone for the help. I'll check the flow back to the tank and double check the lines again.

I found that the warm up regulator also affects fuel pressure in the distributor. From what I understand the pressure should be low when the engine is cold and as it warms up the warm up regulator gradually increases the pressure. The WUR may not be working correctly in my car. Since the orginal distributor was so gummed up, the plunger could never drop down, the faulty WUR sent full pressure to distributor and out to the injectors all the time. The sensor plate moved freely because the plunger was stuck up. I'll be testing the WUR tonight and see what the ohms are.

[jim928]

Update: The car runs perfect now!
WUR tested out fine. Readjusted the CO screw ALOT and sensor plate moves perfect and car runs great now. I'm thinking that the previous owner played around with the CO screw just to get it to run becuase the old fuel distributor was messed up so much. Even the air bypass screws were open bofore I changed everything. The fuel injection is functioning as it should now. Thanks everybody for the helpful info.