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Car Died, Suspected Fuel pump / MFI relay

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BoredOutaMyMind

15+ Year Contributor
304
0
May 3, 2004
Niceville, Florida
Car is a 96 Eagle Talon AWD TSI mods in profile, battery is Optima Redtop and was/is fully charged.

Ok, Longstory short, I was pulling out of my neighborhood one night and car was running great, however a mile or so down the road the car seemed to lose power off and on (lights/instruments stayed on the whole time) for about 5 seconds or so, then then car just shut off. After that the car wouldnt start, but it would crank just fine.

I popped the hood and it seemed like the battery tie down came loose and the positive terminal shorted out on strut tower brace. I retightened everything and tried starting the car and it still wouldnt run. I then noticed the fuel pump wasnt running so i hooked up DSM-Link to my laptop and tried to turn the fuel pump manually, i could hear the relay click but i could not hear the pump running. I got the car towed to my house.

Took forever to find the fuelpump and mfi relays but i finally found them and tested them both at ~73 ohms, which is close enough to the 70 ohm rating. I then connected a voltmeter to the plugs going to the relays (as a member suggested On post 17 of http://www.dsmtuners.com/forums/newbie-forum/276071-mfi-fuel-pump-relay.html ) The first relay plug tested at 12.0v exactly and the second plug only tested at around 7v I had the key on the ON position but did not try cranking it. Ill post pics later today about which relay i tested at 12v because im not sure which one is which (the first relay is on the bottom when the relays and plugs are bolted into their bracket, and tested at 12v)

The first relay clicks a few seconds after i turn the key to the off positition but the second relay that read ~7v doesnt click at all. I tried using a wire to jump the 2nd relay but my pump wouldnt turn on either.

Also the car sounds really weak when i try to crank the car (battery is fully charged) and im afraid when the battery shorted i melted some wires leading to the starter and the relay.

Where can i find the wires from the relay to the battery? and how would i go about testing them? What would be the first fix/test that you guys would try?

Sorry for all the questions but it seems that all the solutions that many members suggest are very vague about where to connect power sources to what etc. Pictures and/or detailed solutions would be GREATLY appreciated. Thanks
 
alright here are the pics of the relays, the one on the left is the first one that i tested, and it was at 12.0v while the one on the right tested at ~7v . can someone atleast tell me which one is the mfi and which one is the FP relay?
 

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Left is MFI, right is FP. FP relay only activates when engine is cranking or running (not when just key is ON and engine not running). ECU turns FP relay on when it sees CPS sensor pulses.

Then why is it in just about every other car (including my 98 gst) that when you turn the key to ON, you can hear a click come from the rear and the whirrr of the fuel pump priming then hear it click off and stop after a couple seconds? where would i hook a direct 12v source up to, to turn my fp on manually?
 
Then why is it in just about every other car (including my 98 gst) that when you turn the key to ON, you can hear a click come from the rear and the whirrr of the fuel pump priming then hear it click off and stop after a couple seconds?

Because what the CPS does when you apply power is undefined. If it glitches the signal the ECU may think that the engine is turning and activate the fuel pump.
 
Left is MFI, right is FP. FP relay only activates when engine is cranking or running (not when just key is ON and engine not running). ECU turns FP relay on when it sees CPS sensor pulses.

So are you saying that the wires leading to the FP relay cant be tested for voltage when key is on, and that it should only read 12v when im cranking or car is running (assuming that when the relay sees 12v it closes the circuit, telling the fp to turn on)?

Should i be looking to my ecu as my problem source? I'd really hate to send off my ecu for someone to fix it >.<
 
Alright well it seems no one wants to bother with fuel pump related threads anymore :( I was kinda hoping that someone else would reply to this thread atleast telling me how to test the fuel pump (even though there are a lot of threads that touch on that topic it was extremely hard to find a post that didn't simply say, hook 12v up to the fuel pump to see if it turns on).

After searching for what seemed like forever I finally found references to a "fuel pump test connector" (which again included vague directions to exactly where it was or what the plug looked like). For anyone who doesn't know I found a picture of this elusive connector ----> http://members.shaw.ca/dsm.1000q/Engineprimer/2G/fuelpumptestconn.htm

Thanks for all the info on the CPS, but hooking up 12v to this plug should bypass the ecu/CPS and everything else so it's possible to test just the fuel pump right?

As for hooking up 12v to the fuel pump test connector, I'm lost. When I took off the "cap" to the FP test connector, I simply saw one metal clip for a spade connector. How am I supposed to hook up 12v with one wire? I figured the wire would be grounded at the fuel pump so I connected the positive terminal of the battery to the plug and nothing happened, I then tried to turn the key to ON, and even tried cranking it and the FP still didn't turn on. Am I connecting this wrong?

I'm either not hooking 12v up to the FP test connector right, or perhaps there is a short between the battery (and/or ecu) to the FP? I should have tested for voltage at the plug going directly to the fuel pump but I'm not even sure which pins to connect the voltmeter to, or if the CPS would prevent me from seeing any voltage at all.

Also, is it possible that my weak starter issue (Engine cranks but doesn't really sound like it's turning over) is related to my ecu, CAS, CPS, etc etc? I'm pulling the starter tomorrow to check for damage, but it won't do me any good to fix this until I'm atleast getting some fuel.

Could someone please point me in the right direction? :cry: I'm sorry this post is so long but I am getting frustrated and really need some good advice as for what to do next.
 
I've decided that I'm finally going to do my FP rewire that I've been putting off for a while to eliminate the odds that there is a short between the battery and the FP. Took a bit to figure out how to wire a 2g AWD FP (as it has a 5pin connector instead of the 2pin connector everyone else has >.< ) Should have it done in the next day or 2 and will post results, in the mean time any help or advice w/ my previous posts would be awesome :thumb:
 
What voltage does you battery read when you are cranking? It shorting to the strut bar may have killed it. It can show fully charged but when cranking can drop low.

Yes you can run a direct power to the fuel pump. It is the black with a blue striped wire as per Mitchel wiring diagrams. It also states that the connector in the engine bay is a direct link to this wire. I've personally never used it and prefer to go directly to the pump. The pump should be self grounding (as long as it does have a good ground) so just put 12 volts from the battery to that black with blue wire. If the pump doesn't run then it is to suspect. When you put power to it try beating the top of the sending unit with a mallet and see if you can get the pump to turn on. If it does then, then you know you have a bad pump.

You can also check to see that you are getting battery voltage at the black with blue wire when you are cranking. That will tell you if voltage is even getting back there.

Good luck.
 
What voltage does you battery read when you are cranking? It shorting to the strut bar may have killed it. It can show fully charged but when cranking can drop low.

Ah Thanks for the reply, I haven't tested the voltage cranking but those "car experts" at autozone apparently said the battery was good and charged it, after I rewire if I get the FP to kick on but can't crank the engine I'll jump start it or swap with my GS-T for a day :D

When you put power to it try beating the top of the sending unit with a mallet and see if you can get the pump to turn on. If it does then, then you know you have a bad pump.

Something tells me if I try this I will probably need a new pump regardless ROFL

I've been up since 11am yesterday and I'm tired as hell, and I need to do the rewire anyway so we will see how it goes. Who knows maybe I'll write a how-to if it works :sneaky:
 
Needs to be done anyway LOL.

If it seems likes its cranking slower something is up. Whether it be in the battery or cables as a result of the battery grounding out. Ohm out the wire going to the starter and make sure it didn't melt any. If you have spare known good battery swap it in to eliminate it as a possibility.
 
Ok things are starting to point toward a bad fuel pump I think...

I checked for voltage at the plug that connects directly to the fuel pump assembly and it tested at 0v with key ON, and ~11-12v while cranking. This means that the ECU is seeing the CPS pulses correctly and the FP relay clicks during cranking as well.

Is there anything else I should check for before taking out the fuel pump assembly?
 
Short of trying to power the pump directly at the connector with a spare battery I don't know what else you could test. You might still have a high resistance connection somewhere in the circuit that would cause the voltage to drop under the load of the pump but it sounds like you have narrowed the problem down to the pump assembly.
 
Heres a quick update for you guys.

Took out the fuelpump, and noticed it was actually a denso unit (last 4 digits 1020) which turns out to be a FP out of a supra TT which flows about the same as a walbro 255 from what I've read.

Hooked up 12v to the pump directly, turned on instantly. Then I figured there must be a connection problem between the fuel pump assembly and the fuel pump itself, so I checked the ohms from the plug to the wires leading to the pump and the + wire was reading 0.3ohms while the - (ground) wire was reading something like 1200 ohms! I'm thinking this is the problem LOL.

How would i go about fixing this wire from the plug to the fuel pump? seems it would be hard to get a soldering iron in there and I'm not used to wiring to a plug. Does the plug come out from the assembly somehow? I included the plug in this pic circled in red.

Sorry for the delay in getting back to you guys but finals week is comin up and I've been busy studying (cough cough) :)
 

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Alright now I'm lost. The plug actually has tabs on the underside of the FP assembly and has 2 seperate plugs that come out (one plug has 3 wires for fuel level sensor etc, and the other plug simply has the + and - wires that lead to the pump itself) I got the 3wire plug out no problem but i couldnt even get the 2wire plug to move at all after trying pliers, screwdrivers etc.

Also now i tested the ohms again and the + wire is still <1ohm while now the - wire is showing almost infinit resistance (wont even read now even on 2000k ohm setting).

I concluded that if i plugged the assembly (by itself, w/o the fp installed) to the car and used DSMLink to manually turn the FP on, i should get 0v from the 2 wires that connect directly to the fuel pump right?

WRONG, it reads about 10.2-10.5v (battery reads 12v directly). :cry:

Could this still be a wiring issue within the plug on the FP assembly? It doesnt make sense i should have so much resistance but read voltage ok. Does the increased resistance play enough of a factor that my fuel pump wouldn't be recieving enough amps to turn on even though the voltage reads fine?(i understand there isn't really any current draw by simply using a voltmeter)

Any tips on how to get the 2 wire plug out under the FP assembly would be very helpful, i can post pics of it if someone asks. Next step is to hook up the fuel pump to the assembly this time and try turning it on with DSMLink but i'd rather avoid running the pump more than necessary without any fuel in it.
 
I was right, the ground wire was causing my FP to not run correctly. I soldered the plug as best I could and tested the ohms and got .1ohms, but as I put everything back together, I tested the resistance one more time and it fluctuated between 200ohms and 20ohms!

Got pissed and pulled out the FP with the wires still attached and VOILA! The + and - wire plug came right out! (Turns out it was superglued in btw) and i found the problem to be at the main plug of the FP assembly. Cut it open and soldered it and its now fixed! :thumb:
 
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