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What tells the fuel pump to run/ dumb cold start drama

turbofonz

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Sep 27, 2006
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Granby, MA
Alright, I haven't looked deeply into this, but my car overnight will sometimes not want to start. Or will start, and stumble. Pull spark plugs, clean the wet fuel off them, then start again and it'll be fine. Rest of the day it's fine.

When the key is, the fuel pump is on no matter what. The car is 100% stock, there is no hack ass wiring anywhere, or fuel pump rewires etc.

I replaced the coolant temp sensor already
Unplug the CAS, the pump still runs.
Both times I've unplugged the MPI relay resulted in a blown MPI fuse.
Down by the ECU/ MPI relay, is a green/white wire connector that's unplugged/ normal? test plug?

Whether this is the problem with flooding the plugs or not, I know it's not right.

My 1g is under 2 feet of snow otherwise I'd grab dsmlink out of that and at least have a few things to look at.
 

G

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Wait what? You're saying the fp runs when you turn on your ignition? That's not stock. The fp just running won't flood your injectors the fuel will just get dumped back in to the tank. If the injectors are energized and spraying then you can flood.
 

GSTwithPSI

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Yup, G is right. The fuel pump should not run unless the car is cranking or started and running. The key in the on position should not activate the fuel pump.

The connector you're describing is probably the O2 test connector:
img.php



What spark plugs are you running?
 

turbofonz

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Granby, MA
I know it's not supposed to do that, that's why I made this thread.

That's the connector .yes, noted.

Plugs are br7es.
 

G

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If your fp is running with just the ignition on then this is not true > "The car is 100% stock, there is no hack ass wiring anywhere, or fuel pump rewires etc." More than likely someone bypassed the relay or some other hackery in order to get the fp to run with out blowing fuses instead of fixing the actual problem.
 

turbofonz

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Granby, MA
Everything I've checked so far has nothing altered looking. I'm not sure why someone would want it this way on purpose.

If were gonna list a stuck relay or jumped wire as "modded" , then I better change my signature.
 

GSTwithPSI

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Either you have a short to power (unlikely) or someone messed with the harness. I'd start by trying to trace the harness and see if anything obvious sticks out. Maybe someone did a pump rewire gone wrong?

What's more curious is the MPI fuse blowing when you pull the MPI relay. Usually it's the other way around...
 
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CutlassJim

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Jul 17, 2006
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Manchester, NH
Is the fuel pump running when the key is in the ignition at all or only when in the "on" position?
 

turbofonz

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Messages
475
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Granby, MA
Fuel pump wiring is stock.

Only when the key is at ' on'

I bought the car off a 73 year old eye doctor who was the original owner that dealer maintained the car. I think we can rule out any mods.
 
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CutlassJim

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Is this the RHD one that you sent me a picture of?
 

turbofonz

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Granby, MA
haha. yes, but that was me using the front camera on my phone , reversing my LHD car and looking RHD;)
 

tektic

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ronkonkoma, ny
Do you have another mpi relay to swap in? What's the board surface of your ecu look like?
 

GSTwithPSI

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Basically, the MPI relay consists of two relays. We'll call them relays 1 and 2.

Relay 1 would be powered by the starter circuit (during cranking) or the ECU after the car is running. This relay can provide power to the fuel pump in either of these conditions.

Relay 2 would be powered once certain conditions are seen by the ECU. This relay provides the main power source to the ECU and peripherals.

I your case, you're mostly concerned with relay 1, which provides power to the fuel pump.

Power supplied in:


Key in the START position. The green box indicates the relay 1 side of the circuit. This is the circuit you'll be most concerned with:


Engine running. In this diagram, the green box indicates the relay 2 side of the circuit:


My advice would be to trace the harness in various places of the circuit. I'd start by checking for power at the MPI relay, and work my way back toward the fuel pump until I found something funny. I'd also do my tests tests with the key in the ON position, and see where there is power where there shouldn't be. If the fuel pump is running with the ignition in the ON position (engine off and not cranking), it's getting power from somewhere it shouldn't be. That could be the ECU, a short to power, a stuck relay, etc. It's going to take some prodding around on your part to find out what that is. Bottom line, there has to be a place where the pump is receiving power when it shouldn't be.

Keep in mind, there's a lot more going on in the circuits above than I have traced out. I just tried to give you a quick overview without going too in depth. What I've drawn out doesn't give a clear picture of the order of operations, so try not to interpret it that way. Just concentrate on what could be powering the fuel pump when it's not supposed to receive power. I feel like It's hard to convey logical electrical troubleshooting advice over the internet, so, I hope this makes sense to you. Good luck.
 

turbofonz

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Granby, MA
Swapped MPI relay did the same thing.

I just noticed 2 black/white wires cut and spliced together going to the MPI relay. I put them back to factory, pump doesn't run when keys off. Car will start, run for like 3-5 seconds then shuts off like the pump shuts off.

Oh, and the fuse popping stopped.
 
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G

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Yes! that's the problem, some independant shop performed that band aid fix. Could have even been a mits dealer. I know your car is stock and not modded. By modded I meant some incorrect repair was performed. Do you hear the relay click right before the car shuts off?
 

turbofonz

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Sep 27, 2006
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Granby, MA
Yes. With my hand on the relay, I feel it click on when started, a few seconds later , clicks off, a second later the car stalls.
 

turbofonz

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Granby, MA
The 2 black /white wires that go to the MPI relay were cut and tied together so they bypassed that part of the relay. All the wiring looks fine down there now. now it just won't stay on.

So the Bw at the c15 plug
 

turbofonz

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Sep 27, 2006
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Granby, MA
I just pulled the ECU out to check it. It's been rebuilt. Hard to read what it says, but it says something about circuit 107, which according to VFAQ is Power supply (to MPI Control Relay and ??). So I'm going say there's an ECU issue and they jumped the MPI relay. I was going to send it to ECMlink anyways and have them upgrade my v2 chip that I've had laying around.
 

GSTwithPSI

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Go find the fuel pump test connector on your firewall and apply 12v to it. That will bypass all the ECU controls. If it stays running, it's likely there's an issue with the ECU or associated relays and/or wiring.

fuelpumptestconn.jpg
 
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