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Old 01-30-14, 06:08 PM   #1
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MFI relay

Hey guys. I'm having issues with my fuel pump not kicking in. I posted the issue on 3si but got derailed by another member have issues.

Basically my fuel pump wont run. But if I use the jumper in the engine bay it runs and builds pressure fine. I am trying to narrow down the causes, I am under the impression its the MFI relay.

Any thoughts? (I recently replaced the ECU and it ran for a while until I sprung a leak and replaced my fuel hat, so I know that's not the issue)
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Old 02-03-14, 11:52 AM   #2
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Your ECU can turn the fuel pump on / off, so there's a small chance it could be that too.
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Old 02-04-14, 10:03 AM   #3
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if you bypassed the relay and it worked then just leave the "jumper wire" in the plug and run it like that

Kyle
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Old 02-04-14, 05:49 PM   #4
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It would start up but the tac would go wonky and it would die.
I tried putting a new MFI in and it didnt work. I'm starting to think the new chrome ECU I got it not working, although it had no issues a few weeks ago. In addition I have no way of verifying it unless I can slip in another ECU to test (which I don't have).

I've just about had it with this.
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Old 02-04-14, 07:38 PM   #5
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I doubt it's the ECU......

eliminate the relay in the engine bay and try doing the fuel pump hotwire, to avoid doing a lot of work just run the wire on the outside of the car to the fuel hat to see if it fixes your problem
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Old 02-04-14, 07:39 PM   #6
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or get a buddy and check the voltage at the pump while the car is cranking
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Old 02-05-14, 08:47 AM   #7
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Someone discovered they had a 24volt relay instead of a 12volt relay causing fuel pump issues. Another person discovered they had a damaged stock fuel pump wire. Just some ideas for you to look for.

http://www.3si.org/forum/f1/odd-no-s...engine-633009/
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Old 02-05-14, 09:49 PM   #8
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I'm going to re-check my ground (the wonky tac when I got it to run makes me suspect a problem with that). I'm also going to grab an inline fuse and try running a cable straight to the pump, then a hotwire with relay if that works.

Thanks for the ideas. I will let you know how it turns out Monday when I get some time off work.
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Old 02-15-14, 05:30 PM   #9
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Well I had a go at the problem again and still nothing.

Ran a ground from the hat to the rear strut tower.

Checked the voltage while cranking and read 0.

Ran a wire from the battery with a fuse to the pump, it ran and built proper pressure. Car still would not start (starter cranked no problem).
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Old 02-18-14, 08:41 PM   #10
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if your tach is acting up that's a problem with the PTU, did you check to see if you had spark?
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Old 02-26-14, 03:28 PM   #11
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Hey guys update.
I bit the bullet and got it tower to a shop. Apperently the wiring information with my hat and stealth316 did not match my car so he follow3dthe leads and rewired it.

New issue. Car runs now but idles like shit. I disconnected the MAS sensor and the idle is smooth but power band is rough. Could it be a boost leak?
Based on the way he drove it around the block after I complained about the idle, he drove it around the block like he stole it and said its normal for a car that age. I left before I would have lost it on him.

Edit: I replaced the IAC prior to this while mess, Im going to throw the old one back in and see if that does the trick.
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Old 02-28-14, 02:04 PM   #12
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I tried starting the car today and it would not start.
I checked the following:
-Fuel pressure (Good)
-Boost leaks, none found
-Tried old and new IAC/ISC
-Checked plugs (one had fuel on it the rest were pretty clean)
-Tried new and old MFI relay

I basically paid this guy $400 to be able to drive it home.
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Old 03-11-14, 02:13 PM   #13
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In case anyone was wondering I had a blown fuse that was causing the no start. I just have to track down the boost leak the mechanic caused.
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Old 05-16-14, 08:05 AM   #14
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Well Im back at it. With a new set of problems. I think I've ruled out a few things.

The car starts now BUT I have to crank it first to pressurize the fuel system (if the car sits for a few hours the fuel rail pressure is 0). After it has pressure it starts fine.

I recently replaced the MAF and the car ran pretty good for about 15 minutes then went back to the way it was with the old MAF.

Idle is low with MAF plugged in and car bogs and has almost no power.
MAF unplugged it runs very rich and is stuck in limp mode.

I've replaced the PTU, coils, and plugs which got rid of my misfires BUT I still have a twitchy tac.

I did a ghetto boost leak test (folded garbage bag between MAF and filter) and the system was not holding pressure. I checked all my IC piping and no leak. Could this sort of issue be a leaky BOV? (If so is there any way to check other than trying to feel for the leak? [Its a metal mits evo BOV])

I've posted this on 3si as well but its not getting much traction.
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Old 05-16-14, 08:53 AM   #15
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the lack of fuel pressure could be a few things, sticking injector, bad fuel pressure regulator, bad O ring on the fuel pump or the check valve on the pump is faulty

when you did your leak test did you cap any lines?

I'm going to take a shot in the dark and say you have a vac. leak somewhere or you don't have sufficient fuel pressure

good luck hunting down your problem
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