Resolving a DeLorean no start issue from low fuel pressure

Several years ago, in a project that started with a simple desire to change the old and failed motor mounts that evolved into pulling the motor and transmission, I also installed a modern fuel pump from DeLorean Industries so that I would have as reliable of a car as possible. During this process, I dropped the fuel tank for a deep cleaning, both inside and out, which I have written about before.

I have recently had my car off the road for a year while I tackled another project that snowballed, but this time it was for many things on the interior. I recently got it put back together enough to try and fire it up. It had been much too long since I had heard the motor come to life and I was excited to reach that milestone once again.

When I went to start it, it would fire immediately, but wouldn't stay running. It would cough, stumble, then die within a few seconds. I had a similar symptom as this a year and a half ago and felt like a fool when I discovered that it was just about empty on gas. I had to calibrate the fuel sender so it was more accurate, but that's a story for another time.

So I checked the fuel level, which was easy because I still had the fuel pump access panel off from when I had replaced the A/C lines, which I'll write about another time. I simply popped off the cap where the original fuel sender used to be and I could see that the tank had plenty of fuel with it being around half full.

It was acting like it would run when the cold start injector would kick on, but then not get any more fuel and die. To be sure it wasn't electrical, I verified the ballast resistor and coil were all wired correctly and that nothing was loose. Once that all checked out, I decided to dive further into the fuel. I decided I needed to verify that fuel was making it to the cylinders, so I pulled all six injectors and put them in glass mason jars.

On a Delorean, you can jumper the RPM relay so that the fuel pump runs nonstop, which is great for testing while the car is off. If you have the fuel pump running, you can then press down on the metering plate, and if everything is working, you should get fuel spraying from the injectors. I jumpered the RPM relay, but when I pressed down on the metering plate, I had zero fuel from all six injectors. I was stumped.

I removed one of the injectors and repeated the exercise just to see if fuel would come out without an injector in the way, and I did get fuel, so I knew the fuel pump was at least providing some pressure. Here's what that looked like:

I suspected that there may not be enough fuel pressure to open the injectors, but I didn't have a K-Jet fuel pressure gauge. I reached out to some local owners, and was lucky to have one volunteer to loan me their pressure gauge set. Once I got my hands on that, I saw that I only was seeing 40 PSI at the lines at the rear of the car. 

In case anyone needs any reference photos, here's how I hooked up the pressure gauge near the motor:

In order for the injectors in a DeLorean to open, they need to get ~50 PSI, and since mine was only pushing 40 PSI, it made sense as to why I wasn't getting fuel out of my injectors. I needed to determine if the low pressure was being caused by something in between the pump and the lines, or if it was the fuel pump. There was another fuel pressure kit in the parts I borrowed that allowed me to hook a gauge up directly coming off the pump, so I disconnected the feed line, put on the pressure gauge, and was surprised to see ~40 PSI coming right off the pump. 

Some other owners suggested that low pressure could be caused by a low battery, so I made sure the battery was charged, then checked the voltage at the connection. It registered right where I needed it to be, at around 12.7V, but I was still only getting 40 PSI from the pump when I jumpered the RPM relay.

I decided to bypass all of the wiring harness and see what happened if I hooked the fuel pump directly up to the battery instead of via the wiring harness. To my surprise, the pressure jumped up to ~60 PSI, which meant that something in the wiring was causing the low pressure.

After much head scratching, I couldn't figure out why I would have lower pressure from the fuel pump when the wiring harness was showing 12.7V, but with the same battery, pressure would jump up to normal if I hooked it directly to the battery. Someone suggested that I could be experiencing a drop in voltage once there was a load on the wires. I picked up a kit to backprobe the wires so I could watch the voltage when the fuel pump was hooked up to the wiring harness, and sure enough, as soon as power was sent to the fuel pump, the voltage dropped to only about 9 volts. The next question was why this was happening. 

Some helpful DeLorean owners suggested that the wires were corroded, burned from heat, or there was a bad connection further up the harness, like where the wiring is connected near the windshield washer reservoir. The wiring harness looked good near the fuel pump. The wires were still very flexible and not at all crusty. 

 I saw no evidence of corrosion on the connector, so I decided to go upstream and check the connection near the washer fluid reservoir. I just wrote a blog post about the headache of getting the reservoir cover off as I had several bolts that spun the rivnuts. 

I did eventually get that taken care of and found the wire on the connection that supplied power to the fuel pump. Here's the connector near the washer fluid reservoir:

 I removed the fuel pump, put it in a bucket of gas, and hooked it up directly to the connection that supplied power, and to my surprise, I still saw a big drop in voltage and the fuel pressure was not as high as hooking it directly up to a battery. That meant that something further up the line was causing a voltage drop. You can see the voltage dropping in a video I took during all of my testing:

I then stumbled upon a write-up during all of my head scratching that the ground may need some attention. The ground for the fuel pump is tied to the inertia switch, which makes sense as the inertia switch would kill power to the fuel pump in the event of a collision. The inertia switch is located near the clutch pedal inside the car. Visually, mine looked fine, but I thought that I didn't have anything to lose. 

The process of adding a more reliable ground involves cutting the ground wire coming off of the inertia switch, then running a new ground wire from both ends of the cut wire, under the carpet, and to one of the bolts that holds the tub to the frame. I followed the process that I found outlined here. I then tested the fuel pump pressure using the wiring harness and was so pleased to see it shoot up to nearly 70 PSI. The problem this entire time was a weak ground. I'm glad it wasn't a bad fuel pump or a cooked connection, but it was still frustrating that something I hadn't touched or messed with created this problem.

Next, I needed to confirm that the fixed fuel pressure would result in fuel coming out of the injectors, so back to the mason jars I went.

I was extremely happy when I pressed on the mixture plate and heard the whistling of fuel coming out of the injectors.

I was getting a pretty inconsistent spray pattern and volume from some of them, so I swapped some around to see if the problem followed the injectors. I decided that they could all use a good cleaning, so I took them all out. The injector seals were a pain to get off as the rubber was super hard and inflexible. I figured I might as well replace those while I had the injectors out. I found replacements from Advanced Auto for $2 a piece and they arrived within just a couple of days, which was awesome.

I put all of the injectors into a bucket of Berryman B-12 and was blow away with the amount of gunk that came off the injectors. They went in looking quite nasty and came out looking brand new after less than 30 minutes. But I knew that what I really needed to do was to force cleaner through the injector with pressure. I don't have a K-Jet injector cleaner and didn't want to wait around for one, so I created a redneck way to get cleaner through them by using an air compressor fitting, some foam to create a seal around the injector, and I was successful in getting a little bit of cleaner at a time through all of the injectors. I then connected the injectors back up to the fuel lines and tested the spray patterns and volume.

As you can see below, volume was a little bit of a hot mess. I swapped some injectors around and did several rounds of testing and saw a little improvement.

Ultimately, I took out a couple of injectors and put them through another round of cleaning. I had previously heard that a good rule of thumb is to get 5oz of gas out of each injector by pressing the mixture plate down for 30 seconds. I marked 5oz on the far-right bottle and tested to see where things ended up. It wasn't too far off of that number, so I called it good and installed the injectors back into the engine.

Here is one of the new injector seals before putting the injectors back in the engine. Check out how nice and clean the injector looks:

After putting in all the injectors, the moment of truth came when I went to start the car. It started and ran for the first time in a year after stumbling for a bit at first. I blew out all of the cobwebs and it ran beautifully. I got it up to temp while I got air out of the new radiator that I had installed during the year's nap and now I need to wrap up the rest of the interior before I can get it back on the road.

Here are some clips of the car running once again. I'm so pleased to have gotten past this no start headache.