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The thing I said is true at least for my '91. And "right" side means starboard, passenger side. No guarantees about other model years.
So that's what I have on the right side. There's nothing in the trunk (although the '94 I recently pulled parts from had a Fuel Pump Controller in the passenger side of the trunk), nothing under the MAF, and the relay box has been moved to the other side of the engine bay, next to the coolant reservoir. My car doesn't have air suspension, so that box presumably does nothing, as do the six or so empty relay spots in the relay box. As far as I know, the fuel pump relay is called the EFI relay in this car. I have no idea what those metal boxes next to the "air pump" box do, I assume they're resistors for other stuff.
Things did get changed after 1992, I don't know what all the changes are, some like a stepper motor egr is one of them.
So when it does this dying thing, check the voltage at the pump with it dying or running or what ever it does. It could be a corroded ground or terminal / connector. Corroded fusible link connections. If it really is dying something is causing low voltage I think. Or even the opposite its powered on high speed all the time?? Maybe if there is a controller in the trunk that has something to do with it.
Without reading the whole thread and knowing who gave you what suggestions. Just from reading your thread headline. I can tell that it is clogged fuel filter. If your fuel filter is clogged it will put more strain on the fuel pump and will most definitely kill your car's fuel pump.
If you haven't checked your fuel filter I would recommend replacing fuel filter. Beside that also clean your car's injectors. If injectors are clogged those can also damage fuel pump.
Without reading the whole thread and knowing who gave you what suggestions. Just from reading your thread headline. I can tell that it is clogged fuel filter. If your fuel filter is clogged it will put more strain on the fuel pump and will most definitely kill your car's fuel pump.
If you haven't checked your fuel filter I would recommend replacing fuel filter. Beside that also clean your car's injectors. If injectors are clogged those can also damage fuel pump.
You're right, you didn't read the thread. It's not the fuel filter.
Another note; when I started the car for the first time today, the fuel pump came on for a second, and was really slow. Then it stopped, came back at a higher pitch, stopped again, and finally came on at the regular pitch and stayed there. I'd think it was locking up but it hadn't been running in over twenty hours so I have no idea why it'd do that.
I'd check the resistance first. It should be 0.73±0.3Ω. If it's OK, I'll check the fuel pressure next.
One thing I have experienced is that the resistor tends to increase the resistance as it ages. This is a common problem among resistors that dissipate big heat. The increased resistance can't supply enough current to the motor and it can't work well.
So that's what I have on the right side. There's nothing in the trunk (although the '94 I recently pulled parts from had a Fuel Pump Controller in the passenger side of the trunk), nothing under the MAF, and the relay box has been moved to the other side of the engine bay, next to the coolant reservoir. My car doesn't have air suspension, so that box presumably does nothing, as do the six or so empty relay spots in the relay box. As far as I know, the fuel pump relay is called the EFI relay in this car. I have no idea what those metal boxes next to the "air pump" box do, I assume they're resistors for other stuff.
That photo is different from my '91. Here's what I can tell you:
- Those two "metal boxes" are the igniters, they are identical and each one feeds one of the ignition coils, each of which feed one distributor.
- That "air pump" box has another cover over it, which you have removed for the photo, right? In my car, I don't have air suspension, and don't have that "air pump" label. On my car, the fuel pump relay is in that box.
- On my car, the resistor is exposed without removing anything, you can just look down and see it. It is slightly below and inboard (toward the left, port) of the igniters. As I mentioned above it is cast Aluminum, with cooling fins, about 3x as big as a normal relay.
So bottom line, from looking at that photo, your fuel pump resistor is somewhere else. Maybe nearby, maybe not. I have no idea.
As far as I know, the fuel pump relay is called the EFI relay in this car.
That may be true on many cars, but it is NOT true on my '91.
Sorry to keep making the disclaimer about what I say only applying to my '91, but I know all of that 100%, and most LS400 things are pretty similar if not identical, but no guarantees, as you found with the resistor location.
But anyway, for my '91 the true "Fuel Pump Relay" (different from the "EFI Main Relay" and the "Circuit Opening Relay") connects directly to the resistor. So if you find the relay, the resistor might be nearby.
In there, I refer to a circuit diagram (again for my '91, no guarantees, probably similar or identical) and explain how everything works and how I used it while troubleshooting my fuel pump problem. It will probably help if you confirm if that is valid for your car, then understand it, find the individual components, and take careful measurements with your multimeter to see what is working and what is not.
In that thread, he had been making guesses, asking for and getting advice, swapping in 3 different ECU's, etc., with lots of confusion and no real progress. I think once he looked at the diagram and started tracing and measuring carefully, the problem was quickly isolated, turning out to be the 7.5 Amp IGN fuse between the ignition switch and the EFI Main Relay. Probably would have been tough to find with random checks and part swaps, but was pretty quick and easy with the directed search that the circuit diagram allowed.
That photo is different from my '91. Here's what I can tell you:
- Those two "metal boxes" are the igniters, they are identical and each one feeds one of the ignition coils, each of which feed one distributor.
- That "air pump" box has another cover over it, which you have removed for the photo, right? In my car, I don't have air suspension, and don't have that "air pump" label. On my car, the fuel pump relay is in that box.
- On my car, the resistor is exposed without removing anything, you can just look down and see it. It is slightly below and inboard (toward the left, port) of the igniters. As I mentioned above it is cast Aluminum, with cooling fins, about 3x as big as a normal relay.
So bottom line, from looking at that photo, your fuel pump resistor is somewhere else. Maybe nearby, maybe not. I have no idea.
That may be true on many cars, but it is NOT true on my '91.
Sorry to keep making the disclaimer about what I say only applying to my '91, but I know all of that 100%, and most LS400 things are pretty similar if not identical, but no guarantees, as you found with the resistor location.
But anyway, for my '91 the true "Fuel Pump Relay" (different from the "EFI Main Relay" and the "Circuit Opening Relay") connects directly to the resistor. So if you find the relay, the resistor might be nearby.
In there, I refer to a circuit diagram (again for my '91, no guarantees, probably similar or identical) and explain how everything works and how I used it while troubleshooting my fuel pump problem. It will probably help if you confirm if that is valid for your car, then understand it, find the individual components, and take careful measurements with your multimeter to see what is working and what is not.
In that thread, he had been making guesses, asking for and getting advice, swapping in 3 different ECU's, etc., with lots of confusion and no real progress. I think once he looked at the diagram and started tracing and measuring carefully, the problem was quickly isolated, turning out to be the 7.5 Amp IGN fuse between the ignition switch and the EFI Main Relay. Probably would have been tough to find with random checks and part swaps, but was pretty quick and easy with the directed search that the circuit diagram allowed.
Alright, I'm beginning to think someone seriously screwed with the wiring on this car at some point. When I bought it, it had a Sony 6 CD changer in the trunk that never worked, not the stock one, but I thought that was the extent of it. Looking at the fuel pump wires and where they go, I'm pretty sure this car used to have a fuel pump control module - I pulled one off a '94 a few weeks ago, and thinking back on it, the wiring wrap was a completely different color on that car. I can't find an FP resistor anywhere on the car, and no diagram of the '93 seems to have it included.
As for the electrical tests, I have a multimeter but no idea how to use it. I can't get to the terminals on the pump when it's still in the car and running, and for the voltage drop I've been told I have to stick one lead of the multimeter on the negative terminal of the battery, and the other on the negative terminal on the pump itself. The wires on the multimeter aren't long enough for this so I have no idea how I'd even do that. Turns out the circuit opening relay is next to the ECU, and I have to dismantle part of the passenger side of the dashboard for that - I'd rather not use a crowbar like I have on the junkyard LS400s, and I see no obvious way of getting to it.
Here's a picture of the wiring in the trunk. As you can see, there's no secondary wire coming out of it to go to a fuel pump control module. It just goes into the trunk roof, and given how the shrink-wrap on some of the wires hasn't even been shrunk, I don't think this is the way it was originally set up.
I don't even know where the ground for this is. If I did I'd check it, but it just disappears into the trunk roof.
Edit: Apparently the shrink wrap is stock. Who knew. Got another sacrifice fuel pump in today as the old one is just about to crap out completely. I should buy stock in Denso.
Its a process to get to the ecu with out messing stuff up. First is to remove the glove compartment. At least on 90 to 92.
Yeah, it's just that I can't see any obvious way to remove it and I'm working six days a week for the next two weeks, so I don't really have the time to screw with it.
You don't specify what model year you're working on.
1998; under hood fuse box on the left side. The fuse box cover should have a location diagram:
He did mention it in the title of the post, not the post itself. 93.
But the relay is in the fuse box mentioned, under the hood, black rectangular cover with two screws next to the coolant tank. It's one of the round silver relays but I'm not sure which one. It will say on the bottom side of the cover. To see if it's bad you can change it with one of the other relays, such as the AC relay, as long as you know that one is good.
08-06-18, 02:34 PM
