Fuel pump failure?

[jangell]

I ran out to do some errands today, and my car died just as I pulled into a parking space. When I got back out, it wouldn't start. It would crank and catch, and then promptly stall. I soon found that I had zero fuel pressure, thanks to the fuel pressure gauge I'd installed in the engine compartment.

I have DMCH's fuel pump/sender combo. The car has only been on the road for seven months, and the pump was used for testing before that, and has been installed soon after I bought it in 2013 (the car was not operational when the pump was installed, as I was doing an engine swap at the time). However, the pump has worked fine until now.

After some false leads, I found that the main fuel relay does have power. The relay is being energized by MegaSquirt (in a 3.0L EFI conversion, so no RPM relay). Once I finally remembered about the test mode in TunerStudio, I turned the pump on and confirmed that I'm getting 12v all the way to the pump connector, and that I'm getting ground from the other side of the connector that runs to the inertia switch. I also opened the tank and confirmed there was fuel in there (about half filled).

So, I'm fairly confident that everything is working up to the pump, and that the failure is at the pump or the white control box that feeds into the pump. The fuel gauge still moves when I try to turn on the car, so I'm thinking it's the pump itself, but I' m not totally sure.

delorean.com mentions that individual parts are available separately for this pump/sender combo, but how would I go about figuring out which part has failed? I'm well past the 6 month warranty, so getting just the part I need would be ideal.

Thanks!

-- Joe

[Patrick C]

My DMCH combo pump failed last year and wasn’t making enough pressure.

[CFI]

Sound like the pump. The white control box you mentioned is the microprocessor for the sending unit. I believe it adds a correction value in order for your fuel gauge to be more accurate.

[David T]

Once you pull the pump you can try putting 12 volts and ground directly to the pump and see what happens. Maybe a broken wire? It is possible the pump is dead.

[jangell]

I pulled the pump this morning and applied 12v and ground to the connector. Instead of whirring like a motor, it clicks like a solenoid. I'm guessing that means it's dead.

At least my filter looks reasonably clean, with just a bit of captured debris.

60799

Thanks!

-- Joe

[David T]

If it clicks it means the power is getting into the pump but it won't turn. As "Bones" would say in Star Trek, "It's dead Jim".

[Josh]

I had my dmch integrated pump/sender fail on me fairly quickly as well.

That filter looks very good

[opethmike]

The DMC-H fuel pump is dumb. You're dumb for using it. DeLoreans are dumb.

That filter is NOT dumb.

[jangell]

I have a replacement pump part on the way. I'm sure it'll work fine and I'll never have any problems ever again. :)

-- Joe

[CFI]

I pulled the pump this morning and applied 12v and ground to the connector. Instead of whirring like a motor, it clicks like a solenoid. I'm guessing that means it's dead.

At least my filter looks reasonably clean, with just a bit of captured debris.

60799

Thanks!

-- Joe

How old was the pump? How many miles on it?

[jangell]

Purchased in August 2013, but the it was only used for 5-10 hours of engine testing until January of this year, when it was finally back on the road. Since then I've put around 2000 miles on it, but I don't know for sure -- my car breaks angle drives within 5 miles, even though testing individual components and combinations of components along the speedometer chain all work perfectly. I have the hardware for a hall sensor based speedometer installed, but I need to build a UI for it still.

Point is, not too many miles on the pump, but it's six years old, and DMCH may have made improvements since then. In another thread it's claimed there's a 1% to 2% failure rate. I've also had to replace the water pump (which was new when I installed it four or five years ago, and has only 2000 miles on it) and alternator (ok, that one was used) recently as well, so who knows.

-- Joe

[Ron]

Ya never know, when one sits for years; Ds particularly. They punish you if you don't drive them every day.

6 months is a long time for a fuel pump to sit with fuel in it.
(Same for a, however slightly, used WP ;-)

With all you have done, it sounds like you are rounding 3rd base. :burnout:

[jangell]

I replaced the pump with a $50 one from Herko that is an exact physical match (as mentioned here: http://dmctalk.org/archive/index.php/t-3824.html ). It was a huge pain to get the plastic hose on and I had to resort to a hose clamp after applying too much heat to one end, but I finally got it, reassembled the unit, connected it and... nothing. Just a soft click. Damn it.

I went to O’Reilly’s and picked up a ‘98 Tahoe pump for $140, which Josh said he used in the other thread. Plugged it in and it runs just fine. I have some questions about it, though:

The sender arm rises higher than the DMCH one does, which means the tank won’t read full. I’m guessing I can bend the arm to fix that until it’s range of motion matches the old pump? Or just not care that the gauge never reads full.

I also have to figure out how to orient the pump so that the sender arm sits in the tank properly, since it points in a different direction than the DMCH one, so I’ll have to reroute the lines a little.

The base of the pump is taller. I still need to make sure it actually fits in the tank, but since it worked for Josh I’m guessing it will be fine.

I want to take the car somewhere tomorrow, so hopefully I can get this installed today.

— Joe

[Bitsyncmaster]

I run the Tahoe pump and the sender almost gives you the normal 240 ohms at full but I think the DMCH ECU unit is set up to read the 240 ohms at empty. Not sure but that is what I remember when designing my fuel gauge circuit.

[jangell]

I'll eventually do a digital dash and have the sender go into an Arduino.

But in the meantime, I did a test and I'm seeing exactly as you described -- ~40 ohms when full on the DMCH sender, but ~240 on the Tahoe sender. I guess I'll have a backwards sender until I get around to doing my dash.

Thanks for the info -- that would have thrown me off for a bit.

How did you orient your unit in the tank so that the float sits properly? To match the DMCH setup I'd have to have the fuel line connections point at the back of the car, which is probably fine (the lines would run between the body and the tank), but I'm wondering if there's a better angle.

Thanks!

-- Joe

[jangell]

Silly question: can I simply swap the wires on the sender to get it to read the other way? My knowledge of variable resistor is JUST enough to both say that it should work and say that it shouldn't work. :)

-- Joe

[jangell]

I came up with a solution. The Tahoe variable resistor rotates from left to right. I was able to flip the float arm so that the sensor now rotates right to left. That should make the gauge read correctly. Still have to actually put it in the car and try it out.

-- Joe

[Bitsyncmaster]

I came up with a solution. The Tahoe variable resistor rotates from left to right. I was able to flip the float arm so that the sensor now rotates right to left. That should make the gauge read correctly. Still have to actually put it in the car and try it out.

-- Joe

That should work.

I took my pump apart to make the unit sit centered under the mounting hole (rotate it into other holes). It would have worked I think with the offset pump (Tahoe unit) but another user suggested to do that. Doing that I had to pull a hose and re clamp it. The float arm has to go to the back of the tank to give it room to move.

[jangell]

Looks like we have slightly different pumps — mine is plastic, more like DMCH, but otherwise I expect they’re the same.

Pointing the sender arm towards the back ignore the car works well for me, since I’ve flipped the arm. The fuel connections now point towards the passenger side of the car, and I was able to slip the hoses between the tank and the floor of the trunk. Not that I really expect to be able to get the access cover back on over it...

I was going to disassemble my assembly, but I found that the three rods had been widened at the end so that it wouldn’t easily come apart, so I decided to stick with the stock alignment.

My current problem is getting the clamp in to hold the pump to the tank. It’s lije it doesn’t want to seat quite far enough down, or the rubber gasket is keeping it from pushing down far enough.

Thanks again

— Joe

[jangell]

Here’s a picture of the pump as I try to get the clamp seated.

https://uploads.tapatalk-cdn.com/20190801/067eb92474c13f39e78a2b723491563b.jpg

[jangell]

Finally got it secured. Of course, now the electrical connector doesn’t want to latch securely. Might have to replace it. But the car starts and the sender appears to be working, so that’s good.

Thanks again!

— Joe

[jangell]

Replaced the connector on the wiring harness and everything is good to go. As predicated, the access cover won't fit due to the way I have the fuel lines oriented, but that's something to worry about some other time. :)

Thanks again!

-- Joe

[CFI]

Good to hear.

What’s the blue zip tie doing on your fuel connector?

[jangell]

That was just to help me remember which line was fuel vs return. I didn't have a green zip tie for the other one. I guess they're different sizes, though, so I couldn't have screwed them up... probably.

-- Joe

[CFI]

That was just to help me remember which line was fuel vs return. I didn't have a green zip tie for the other one. I guess they're different sizes, though, so I couldn't have screwed them up... probably.

-- Joe

Lol if there’s a way to screw it up, I’ll find it:)

[jangell]

Today I confirmed that the low fuel light works (which makes sense, since that's just software handled by the DMCH box). I put more gas in the tank, but the gauge only goes up to 3/5 full. I'm thinking the arm is hung up on something. I foolishly tried to remove the old sender cap, forgetting that the filler is higher than the tank, and spilled gas everywhere. I'll try again once I've used a bit more gas.

If I had to pick which part of the gauge I'd want working, though, it would be the low side.

-- Joe

[jangell]

A quick follow up: my Tahoe sender was definitely hanging up on something. I finally got around to taking it out again and rotated it so that it matched the orientation of the DMCH pump, and the sender arm worked perfectly. I just had to bend it a bit more so that it actually reads full properly, while also making sure that it still makes goes all the way to empty. I was also able to put the access cover back on once I clipped off a couple extra pieces of plastic from the top of the unit (they probably were used to hold something in place on the Tahoe).

-- Joe

[CFI]

A quick follow up: my Tahoe sender was definitely hanging up on something. I finally got around to taking it out again and rotated it so that it matched the orientation of the DMCH pump, and the sender arm worked perfectly. I just had to bend it a bit more so that it actually reads full properly, while also making sure that it still makes goes all the way to empty. I was also able to put the access cover back on once I clipped off a couple extra pieces of plastic from the top of the unit (they probably were used to hold something in place on the Tahoe).

-- Joe

Thanks for the update. I just recently installed a Tahoe unit on my car. It works fine but I’ve got a few minor things to clean up. The fitment of the access cover for one.

[jangell]

My cover still hits the very top of the "R" fuel connector a little, but you can still push it into place well enough to get the screws in. Before I fixed the sender arm and rotation this weekend, I just kind of threw the cover over the pump and stuck the spare tire on top and called it a day.

Admittedly, I haven't gone through a full tank of gas yet, so it's possible that I bent the arm too much and it doesn't actually get to empty, which I'll find out when either the gas light comes on or I run out of gas one day. :)

-- Joe

[CFI]

I just kind of threw the cover over the pump and stuck the spare tire on top and called it a day.

Lol, that’s exactly what I’m doing (minus the spare. I’ve got tools and extra fluids in there instead).

[jangell]

Most of my trunk is filled with a tool kit, a box of assorted small parts, fluids, a small floor jack, spare belts, multimeter, and a few other odds and ends. And there's about a 1 foot square area where I can put something that isn't a tool. :) I have been wondering if I should just get rid of the spare and use that space for storage too. It might be neat to make a kind of repair kit case designed to fit in the spare tire cavity.

-- Joe

[David T]

Even if you leave the spare tire there, if you turn it over you can fill the center of it with small stuff. I keep a large plastic bag and a bungee cord in there just in case I ever need to use it to put the flat tire in (the flat won't fit in the well) and the bungee cord is if I put the flat on the engine cover, I can hold the sunshade down with it. If you have a passenger you can't put the flat on the passenger seat. Try not to overfill the trunk. Very easy to exceed the weight capacity of the car. If you look at the label in the driver's door jamb for weights, figure gas, passengers and stuff, you can quickly exceed the weight.

[jangell]

I have my spare tire in place with the cavity down, mostly because I don't have that piece of wood under the carpet, so it flattens out the carpet a little.

I've heard before that the rear wheel won't fit in the truck, but I haven't had to worry about that problem yet.

I've been curious about the weight capacity. What happens if you exceed it? Does it damage the fiberglass or the body, or overload the suspension, or reduce the handling and braking characteristics? I'm not going to fill the trunk with lead, but the tools, fluids and and a jack do add up.

-- Joe

[Ron]

My D didn't have enough clearance for the new style pump no mater which way it was turned. I didn't want vibration to wear a hole in either one. I wound up laying a 1/2" x 6" disk of wood on top of it, installed some of the fasteners then pressed the cover down while using a heat gun on it. I pitched the disk and it left ~1/4" gap.

[David T]

I have noticed many Deloreans overloaded, especially if you are going on a trip like to a club event or overnight. Really haven't seen any bad effects except that it will increase your gas consumption and probably affects the braking and handling. It might also show up in decreased life of the suspension and tires. A flat tire won't fit anywhere well. 3 choices, leave it on the side of the road, put it on the passenger seat (and leave the passenger on the side of the road) or on top of the engine cover under the sunshade. If you put it in the trunk there usually isn't any room for any of the other stuff in the trunk and the trunk won't close.

[CFI]

3 choices, leave it on the side of the road, put it on the passenger seat (and leave the passenger on the side of the road) or on top of the engine cover under the sunshade. If you put it in the trunk there usually isn't any room for any of the other stuff in the trunk and the trunk won't close.

This is why I ditched the spare. It needed new rubber and I have no jack kit. So instead it’s a jump/power box, air compressor, tire plug kit. Plan B is AAA.

[David T]

This is why I ditched the spare. It needed new rubber and I have no jack kit. So instead it’s a jump/power box, air compressor, tire plug kit. Plan B is AAA.


This is exactly the "plan" on many new cars. They save a lot of money by eliminating the spare and give you a compressor with sealant and call it a Mobility Kit! Just a factoid FYI, that spare is part of the crashworthiness testing and by not having it the car may not pass the test. Let us know.

[CFI]

Just a factoid FYI, that spare is part of the crashworthiness testing and by not having it the car may not pass the test. Let us know.

Lol, ok. I’ll let you know the results of my next crashworthiness test.:driving1: