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Fuel pump won't stop priming?

Old 09-11-2018, 02:41 AM
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Default Fuel pump won't stop priming?

Car is an NB1 with a DW200 which replaced the stock unit when the motor went in over the spring.

Weird thing just started happening. When I put the key to the 'On' position, I hear the fuel pump whine to prime... except it doesn't stop. This seems to mostly happen when the car is cold. Testing after a drive leads to the expected 1-2 second prime noise and then things turning off. If anything, the car seems to be running a bit richer than usual during warmup.

I'm a little unsure how to diagnose this since it happens only when cold. I'm pretty sure it's coming from the tank because I can hear it pretty well if I pop off the gas cap and listen through there. Can't really hear it once the car is on though. The whine just stops then, so it's almost like the priming pulse won't turn itself off when the key is just in the 'on' position and the car isn't running.

I don't think it's MS doing anything because I haven't touched anything on there related to the fuel pump, but I'm attaching the log just in case. Any help figuring this out?

Attached Files
File Type: msq
Storm 9.9.18.msq (272.6 KB, 7 views)
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Old 09-11-2018, 03:03 AM
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Light green wire at the fuel pump relay is the trigger from the ecu. Can also be found at the diagnostic connector.

Measure for continuity to ground on that wire. The pump should only run when that wire shows continuity to ground. If it's running when it's not the relay is sticking.
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Old 09-11-2018, 07:37 PM
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Thanks, that's what I was thinking. I might pull the relay out to see if I can make it click or just check it for continuity with a multimeter first. That should make it easier to figure out what's up.
I'll check the fuse box for continuity as well, which is about the same thing as far as I can tell. Appreciate it!
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Old 09-12-2018, 12:03 AM
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You said it was intermittent. If it is then you can't test it outside of the car because you won't know if it's exhibiting the issue or not.

Don't make this harder than it is. When the pump is running when it shouldn't be (key on engine off) set your meter to continuity and put one lead on ground and the other lead on the fuel pump pin in the diagnostic connector under the hood.
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Old 09-12-2018, 12:26 AM
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Ahh,that makes sense.

So just to test, i pulled out the plug to the relay and put the key to the on position and got no noise. Okay, so I confirmed the fuel pump relay location. I had pulled this (and the injector fuse) out when doing a compression test a few weeks ago. Put it back in and ensured it was tight.

I connected in the diag box with the car off and it reads a high number, no noise.
With the key on engine off, reads a negative number similar to above except negative and it has the noise for continuity. However, the fuel pump has been priming and then stopping when I did this test. I'll report back with what I find when it's acting up, i.e. not turning off. I'll leave the MM in my car for now. Because science.
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Old 09-12-2018, 12:31 AM
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Any meter I've ever used will show resistance when on the continuity setting. You can't have negative resistance......

What meter are you using?
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Old 09-12-2018, 01:18 AM
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Originally Posted by SpartanSV View Post
Any meter I've ever used will show resistance when on the continuity setting. You can't have negative resistance......

What meter are you using?
Its just a basic MM. I confirmed that it's on continuity setting. Connecting fuel pump and ground when the key is on but engine is off leads to the beeping you'd expect from a completed circuit. It doesn't make the noise with the key out. I'll see if it's any different if / when the problem returns.

Polarity shouldn't matter right because it's just testing for a complete circuit? It reads at one when the leads aren't touching anything and beeps when they're contacting one another.
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Old 09-12-2018, 01:57 AM
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Originally Posted by ridethecliche View Post
Polarity shouldn't matter right because it's just testing for a complete circuit?
Correct.

To clarify, what we're testing is whether the relay is running without the trigger from the ecu or not.

If you turn the key on and the pump continues after the initial prime then test for continuity. If you don't have continuity to ground on that wire and the pump continues to run then that would point to the relay contacts sticking in the on position.
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Old 09-12-2018, 02:24 AM
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Okay, so right now I basically confirmed the relay isn't sticking because:
a) the priming noise stops (duh)
b) when the noise isn't happening, there IS continuity using the diagnostic box.

If I start seeing a lack of continuity WITH the noise, then I can pinpoint it to the relay.

I might just order a couple of spare relays for the motor, like the main relay etc. Some necessary ones to keep in the glovebox in case something fails.

Thanks for your help man!
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Old 09-14-2018, 02:24 AM
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So the issue is happening again. When I check continuity with the pump continuously priming, it still shows that there's continuity.

What gives?
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Old 09-14-2018, 03:31 AM
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Intermittent short to ground on that wire or it's the megasquirt. Either the tune or the hardware.

I'd unplug the megasquirt when you're seeing the issue then check for continuity.
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Old 09-14-2018, 08:55 AM
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Originally Posted by SpartanSV View Post
Intermittent short to ground on that wire or it's the megasquirt. Either the tune or the hardware.

I'd unplug the megasquirt when you're seeing the issue then check for continuity.
This. Either the MS is faulty and is grounding out the fuel pump wire constantly, or you have a chassis wiring issue that is allowing the wire to ground out (frayed wire rubbing the chassis or relay has failed closed). I’d actually kind of lean towards the relay being bad if you haven’t recently done any work near the wiring for the relay.
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Old 09-14-2018, 10:52 AM
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I drove the car around for a few minutes and it was back to normal when I got home. I didn't get a chance to check continuity again, but I thought I was supposed to see continuity when i wasn't hearing continuous priming?

I can order a new relay and try that. Ill also follow up and disconnect the megasquirt to test if, err when, it happens again. Other than that is there anything else I should try? I'll put the new relay in as well when I get it Any reason to pull the pump? I don't think that's where it would be having issues.

I can look up some wiring diagrams, but where's the ground for the pump? I haven't done anything with wiring lately, but couldn't hurt to try. It feels that the issue only happens when things are cold if that makes sense




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Old 09-14-2018, 12:36 PM
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Originally Posted by ridethecliche View Post
I didn't get a chance to check continuity again, but I thought I was supposed to see continuity when i wasn't hearing continuous priming?
Alright I'll take another crack at explaining this cause you still don't understand it.

The lt green wire at the fuel pump relay we're talking about is the wiring coming from the fuel pump output on the megasquirt. When the megasquirt grounds that wire the relay is triggered and power is provided to the fuel pump. If that wire is grounded for any other reason the same thing will happen. We are trying to determine if the megasquirt is grounding that wire of if the wire is shorting to the chassis somewhere.


You should ONLY have continuity to ground on the lt green wire when the pump is running. If the pump is running when the lt green wire shows no continuity to ground see post #2.
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Old 09-14-2018, 02:27 PM
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Also pro-tip - if you need to drain year old gas from your Exocet, you put a jumper between the terminal w that wire and ground to keep the pump running longer than the prime cycle. I did that Weds night.
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Old 09-14-2018, 10:25 PM
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Originally Posted by SpartanSV View Post
Alright I'll take another crack at explaining this cause you still don't understand it.

The lt green wire at the fuel pump relay we're talking about is the wiring coming from the fuel pump output on the megasquirt. When the megasquirt grounds that wire the relay is triggered and power is provided to the fuel pump. If that wire is grounded for any other reason the same thing will happen. We are trying to determine if the megasquirt is grounding that wire of if the wire is shorting to the chassis somewhere.


You should ONLY have continuity to ground on the lt green wire when the pump is running. If the pump is running when the lt green wire shows no continuity to ground see post #2.
Oh good, you noticed that I'm a TOTAL noob at wiring haha.

I only checked continuity in the diagnostic box! Where would you ground the lt green wire? Can I pull the wire off the relay and use the MM on the prongs of the relay itself?
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Old 09-15-2018, 01:58 AM
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Sorry if this is vague as I'm operating off memory but I had a similar issue. My brain-built ms3xwas shipped with many issues and it was either Q16, Q2 or D4 in the fuel driver circuit that had failed causing this. If you already checked everything else, that's where I'd start, or figure a way to put a switch to stop the fuel pump for safety purposes.
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Old 09-15-2018, 04:36 AM
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Originally Posted by ridethecliche View Post
Oh good, you noticed that I'm a TOTAL noob at wiring haha.

I only checked continuity in the diagnostic box! Where would you ground the lt green wire? Can I pull the wire off the relay and use the MM on the prongs of the relay itself?
The wire at the relay is spliced to the one at the diagnostic connector so they're electrically the same.

You need pictures and I can't make one until Wednesday. Hang tight or hope someone else has more time than I do.

I still would like to know the model of the meter you're using. It makes the spooning easier.
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Old 09-15-2018, 07:35 AM
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Old 09-15-2018, 11:21 AM
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If the FP wire in the diag box has constant continuity to ground, the relay, and therefore the fuel pump, is going to stay constantly on. This is either because the MS for some reason is commanding the FP stay on, or there is a short to your chassis somewhere.

If the FP wire in the diag box has continuity to ground for only 3 seconds when you KOEO, then your relay is most likely sticking.

If you want to check at the relay socket, you won't hear the fuel pump obviously, but yes, you can stick your MM probe in the ground side of the relay's coil (light green) and test to see if it's staying grounded or not.
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