Fuel delivery issue - Only new injectors not firing

[RobotMartian]

I'm trying to hunt down a not firing on all cylinders issue. When I removed the injectors to run a mason jar/spray pattern test I found that 3 had good pattern, 2 were weak, and 1 (cylinder 5) had no spray. I replaced 1 weak and 1 good with fresh injectors and neither new injector fired. I moved them around the distributor and no matter which of the ports I attached them to, the new injectors won't fire. I also switch fuel lines to confirm the lines aren't blocked. I can tell that the port for cylinder 5 is weak, so I'm guessing distributor? My question is, if my fuel pressure is weak, would that cause the new injectors not to fire with their fresh springs? When a distributor fails, is there a general lack of pressure or is it variable by port?

Within the last year I have replaced: 9 Fuel lines, fuel pump, CPR, removed the Cat (was melted inside), and dropped and cleaned out the tank.

[David T]

No way to know what pressure the injectors are opening at unless you test them. It is possible the distributor is plugged up. At this point you should send the distributor/mixture unit out along with the injectors to be cleaned and tested. Send the old ones too and maybe they can clean you up a good set. Look up Special T. If the tank was dirty (you said you cleaned it) you probably have all that dirt throughout the fuel system so you should flush the lines and reclean the tank before you put the clean parts back in. If the cat was melted inside that means your mixture was way too rich and your cat was turning red from the fuel burning inside it.

[RobotMartian]

That makes sense, thank you. I'll call John. I wasn't sure how wide the pressure difference would be. I should clarify that when I cleaned the tank there was almost no contamination or dirt in it. I had removed it to do some frame cleanup and figured I'd clean what little there was while I was in there. The car has been driven regularly for the last 10 years, but I think a year or so ago one full tank lasted 9 months. I hoped that wouldn't be enough time for the fuel to go bad, but I guess it may have been.

[DMC-81]

Because all 6 injectors fire at the same time, I think it is good practice to replace all 6, just like replacing all spark plugs or doing brakes at least in pairs. The other parts are worn and if you change them out on a piecemeal basis, I think you will always be chasing poor performance. The spring rate will be different on these injectors because some are worn (with an unknown life) and 2 are new.

Just like a lawn irrigation circuit, a blown sprinkler head causes the other ones not to pop up and spray as the water pressure is wasted on the on the blown head (an extreme example, but hopefully one gets the point). That's why your new injectors with strong springs don't open even if you change them around.

My advice is to treat the car to 6 new injectors before potentially wasting money on a fuel distributor rebuild, especially since you said that the fuel system was cleaned well. I bought new injectors when I got my car, and the engine runs smoothly... highly recommend.

[DMC-81]

Because all 6 injectors fire at the same time, I think it is good practice to replace all 6, just like replacing all spark plugs or doing brakes at least in pairs. The other parts are worn and if you change them out on a piecemeal basis, I think you will always be chasing poor performance. The spring rate will be different on these injectors because some are worn (with an unknown life) and 2 are new.

Just like a lawn irrigation circuit, a blown sprinkler head causes the other ones not to pop up and spray as the water pressure is wasted on the on the blown head (an extreme example, but hopefully one gets the point). That's why your new injectors with strong springs don't open even if you change them around.

My advice is to treat the car to 6 new injectors before potentially wasting money on a fuel distributor rebuild, especially since you said that the fuel system was cleaned well. I bought new injectors when I got my car, and the engine runs smoothly... highly recommend.

Sorry, one more thing: Along with new injectors, I would advise to start with a fresh tank of gas (i.e. pump out the 9 month old gas), and then have your fuel pressure tested. You may need some PPR washers to bring the pressure up to spec.

[RobotMartian]

I appreciate the analogy, that makes a lot of sense. I went ahead and replaced the full set of injectors and swapped out a functional distributor. I also put in another fresh fuel filter just to be safe and the fuel is fresh. Now I get no spray at all from the injectors. If it is a fuel pressure issue now, would I be adding or subtracting shims from the PPR?

[dmcnc]

You would add or subtract shims on the PPR based on your fuel pressure reading (should be between 72 and 75 PSI).

Also, every Fuel Distributor has to be reset every time it is installed on a new (or different) Mixer-control Unit. Essentially with a fuel line disconnected at the fuel distributor, jump the RPM relay and turn the CO screw clockwise (richen) until gas starts coming out - at which point you turn counter clockwise just to the point where gasoline stops flowing out the fuel line connection. Once reset, (assuming all your injectors are good and you don't have ignition issues) you can turn the car on, wait for it to warm up and adjust CO once your O2 sensor kicks in.



I appreciate the analogy, that makes a lot of sense. I went ahead and replaced the full set of injectors and swapped out a functional distributor. I also put in another fresh fuel filter just to be safe and the fuel is fresh. Now I get no spray at all from the injectors. If it is a fuel pressure issue now, would I be adding or subtracting shims from the PPR?

[DMC-81]

I appreciate the analogy, that makes a lot of sense. I went ahead and replaced the full set of injectors and swapped out a functional distributor. I also put in another fresh fuel filter just to be safe and the fuel is fresh. Now I get no spray at all from the injectors. If it is a fuel pressure issue now, would I be adding or subtracting shims from the PPR?

Cool. You would be adding shims to increase the pressure.

Here is a good thread on the topic: http://dmctalk.org/showthread.php?12373-Fuel-Pressure-Regulator-Shims

[David T]

You should not have to adjust the PPR but you will definitely have to set the mixture screw. Since you should be checking primary pressure anyway you might have to make a small adjustment with shims. Make sure to verify you have the correct mixture unit. They all look similar but the numbers tell what the specs are and the specific application. The internals are set up differently for each car. There is no exact cross/over to a Delorean. Same for the CPR and the fuel injectors. You MUST have the Delorean specific parts.

[Jonathan]

I'm curious, and a bit confused, with the chronology of your car and what happened up until now. While nothing you said jumps out as being the culprit, I'm wondering if maybe one or more of those things you mentioned or changed is the issue?

Could you lay out a timeline of what you worked on or replaced, when and why? Going back to when the car was running fine. Have you owned the car going back long enough to when it was fine?

What makes me think there's something else to this is reading how you had to replace your cat because it was melted inside. Sounds like the car ran very rich for some time to do that and maybe there's something else needing attention we aren't thinking of?

Again, list out what the original problem was and then the steps you took to try and correct it, and I think someone on here will be able to spot where the real problem is or was.

[RobotMartian]

Thanks for all of the help so far. As an update, and to answer some of the questions asked, the swapped distributor has identical numbers to the one I removed, and the injectors are new numbers correct units.

I've had the car for around 11 years now and when I first purchased it everything from the VoD up was in boxes in the cabin. I put a whole new fuel system in it at that time, rebuilt it, and it ran great for years. It sat for 9 months a couple of years ago, and I'm guessing that's when the whole thing started.

I have since the last post; verified that the new fuel pump is pumping the correct direction. I couldn't get the fuel filter to seal properly after swapping it out, so I gave up and moved it to the engine bay. Now I can watch it leak more comfortably. I still can not get the main line from the filter to the distributor to stop leaking. I've installed new crush washers, put my old fuel line back on, and tried new banjo bolts. Both ends keep leaking. Is there something obvious I might be missing here? I assume that the slow drip (1 drip/2 sec) leak will keep the pressure from getting high enough to fire the injectors? Right now only two are going.

[David T]

You can't run the fuel system and the motor if you have any fuel leaks. It is just dangerous. Use new crush washers, make sure you aren't missing any and if you have to, use teflon tape. It can be difficult to get the fittings around the fuel filter to stop leaking.

[RobotMartian]

Oh, I would never intentionally run the engine with a fuel leak. I should have clarified that I'm jumping the RPM relay and doing the Mason jar test. It's the line from the top of the filter so I can't tape it. If I attempted to resurface the banjo fittings, what would be the best way to do it?

Hopefully the pressure gauge will arrive soon and that'll tell me more on the other issue.

[DMC-81]

Oh, I would never intentionally run the engine with a fuel leak. I should have clarified that I'm jumping the RPM relay and doing the Mason jar test. It's the line from the top of the filter so I can't tape it. If I attempted to resurface the banjo fittings, what would be the best way to do it?

Hopefully the pressure gauge will arrive soon and that'll tell me more on the other issue.

Is the leak point the area around the 12 mm hollow bolt in the banjo fitting?

I had some experience with this. Mine had a thicker section at the top:
http://dmctalk.org/attachment.php?attachmentid=41625&d=1461368395

When I took it off there was a 12mm copper washer on the bottom as normal, and a larger 13mm washer at the top because this apparently this earlier design has a larger upper section. I couldn't initially find the 13mm washer, but both vendors confirmed that there shouldn't be a need to use a washer on the top of the bolt... Just the bottom.
I omitted the top washer and it sealed fine, but I also procured 13 mm washers just in case.

Anyway let us know what version you have. If the fitting is dirty, I cleaned it up with carb cleaner and 1000 grit sandpaper.