If gasoline is allowed to sit in a gas tank for around three months or longer, it will slowly change composition into something resembling, and smelling like, furniture varnish. When this happens in a DeLorean, it not only ruins the fuel pump and the ancillary parts in the tank, but also the fuel injection components in the engine bay.
When dealing with a car that has sat unused for many months or longer, start by pulling the fuel pump assembly out of the tank. You can find the pump under the access cover in the spare tire well at the bottom of the luggage compartment. The opening that the pump mounts to is the only access to the inside of the tank, so there is no reason to remove the tank from the car. More detailed instructions are found in the Fuel Tank Access article.
Siphon the old gas out as completely as you can, then wipe the remainder out. Clean the inside of the tank with a strong solvent, such as Kreen or Seafoam. Let the solvent sit overnight to help dissolve any accumulation of sticky residue, then scrub the tank with a metal brush and wipe it clean. Be rigorous about this - don’t leave any residue behind. Just a small amount will re-contaminate the new gas you put in and will likely ruin your new pump. Replace the pump and associated bits with the 107000 Fuel Pump / Sender Module by following the included instructions - it also includes a new external fuel filter.
Before installing your new fuel filter or hooking up the feed and return lines on your new fuel module, remove your old fuel filter and fuel accumulator and flush out all the hard lines on the car. This will ensure that there will be no debris left in the system that can work its way back into the fuel tank and contaminate your new components. Spray through each hard line with brake clean, attaching a hose to the other end of the line to guide the used brake clean into a bucket outside of the car. This lets you gather debris easily and also allows you to monitor the color of the brake clean as the line gets cleaned out. Repeat this process on both ends of each hard line until everything comes out clear. Then you're ready to install your new fuel filter, a new fuel accumulator kit (K100519), and attach the feed and return lines of your new fuel module.
At the engine, install a set of new braided stainless fuel injector lines (K102318A) and a new braided stainless fuel feed and return line (102365A and 102359A, respectively). The car's original fuel lines are major fire hazards at this point due to the age of their inner nylon cores - handling them WILL cause the nylon to split and you will have fuel actively dripping down onto your engine as it runs - it's not worth the risk. Replace the fuel injectors, injector clips and injector seals (6 each of 102742, 102346, and 102631), then move to the fuel distributor and the control pressure regulator (also called a warm-up regulator).
While the lines are removed from the fuel distributor (102807B) and control pressure regulator (102353), inspect their ports for corrosion and debris. There is a screen on the inlet (larger) port of the control pressure regulator that will clog with ethanol gum and cause severe pressure-related running issues. This area can sometimes be flushed but generally requires a rebuild for proper cleaning. If you remove the three retaining screws on the fuel distributor and lift it up, you may find that the plunger protruding from the center is stuck. If the plunger is only slightly sticky and not firmly stuck, there is a good chance that you can free it up with a little care and persistence. Grab only the narrow tip of the plunger with a non-marring tool and gently twist and pull to remove it. The polished surfaces of the plunger must never be touched with tools or abrasives. They may be cleaned with appropriate solvents (brake cleaner works well) or in an ultrasonic cleaner. If the plunger is firmly stuck, the entire unit is likely so gummed up that a rebuild is required.
We do not recommend that the fuel distributor or the control pressure regulator be disassembled for cleaning or DIY rebuilding as doing so can render them unable to be properly rebuilt. We offer in-house rebuilding and testing services for both! We moved this service in-house after repeatedly poor experience with other professional rebuilding services. We have the expertise to restore these components to optimal condition and set them up to a DeLorean-specific calibration.
Once all of the new / rebuilt fuel components are installed and you're ready to start the car, fill the tank with about 5 gallons of fresh gas - regular unleaded is all the car requires. Make sure the car has a good battery - we use Interstate MT-78's here in the shop - don't purchase any kind of gel battery, the car's electrical system will kill it. If your car has an old or bad battery in it currently, take it with you as a core so you’ll avoid a core charge at the parts store. With the fuel system complete and a fresh battery installed, prime the fuel system by bypassing the RPM relay - this is accomplished by unplugging the RPM relay and jumping the brown wire to the white w/purple wire on the RPM relay connector. This will cause the pump to run at all times until the jumper is removed, even with the key out of the ignition. Thoroughly check for fuel leaks at every connection point on the car. Depress the metering plate in the center of the air metering assembly 3 times. This should be sufficient to prime the injectors for starting. Remove the jumper wire and reinstall the RPM relay. Attempt to start the car by cranking for 5 or more seconds at a time. It is rare that a DeLorean being brought back to life will start with less than a second of cranking like a modern car.
If the car will not start or starts but runs very poorly, it is possible that the base fuel mixture requires adjustment at the "CO Mixture Screw" (the small hole just in front of the fuel distributor). If your factory plug is still in place please refer to the “Removing a Factory CO Plug” knowledge base article. First, remove the injectors for cylinders 1,2, and 3 from the engine but leave them attached to their fuel lines. Place the tips of these injectors into individual fuel-safe containers. Bypassing the RPM relay as before, prime the system with one or two depressions of the air metering plate, and observe flow from the injectors. It should be a conical-shaped spray pattern with fine atomization. Now check the drip rate from each injector without depressing the air metering plate. It should drop at a rate of approximately 2-3 drops per second. If the drip rate is less than this, use a 3mm Allen wrench or T-handle to turn the CO adjustment screw clockwise. If the drip rate is more, turn counter-clockwise. This will establish a baseline for the fuel mixture but more adjustment will be required once the engine has started. If you need help dialing in the fuel mixture from this point, reach out to us at techhelp@classicdmc.com.