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New engine, no fuel pump, blowing ignition fuse

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Street9s

Proven Member
64
15
Apr 26, 2017
Pasco, Washington
Recently finished by 6 bolt 2.4 swap in a 91 talon. Fresh motor. Ecmlink v3 speed density, walboro 255(not rewired) for electrically related mods. Wideband and boost gauge wires ran, grounds hooked up but no power to them yet.

The issue is when I went to crank it, fuel pump didn't prime or turn on when cranking. Previously i tried to turn it on in Link with no luck. Then after a few attempts at cranking, it popped the ignition fuse. Pulled the fuel pump to make sure everything was square, it was. And I ran power straight to it and it turned on. I jumpered the blown fuse to test some things and the mpi relay seems to be good, even swapped it out for a known working unit. Playing with some settings in Link I randomly turned off an injector, and the fuel pump kicked on. Very strange to me.

Further testing reveals excessive current when the key is in the on position, not acc or off. It maxes out my multimeter and it gets very hot very quickly. I'm getting 12v at the connector at the fuel pump.

Seems to me there's a short somewhere, what are some common things that could be shorted? Previous experience with this weird issue? Strategic approach to diagnosing this? Any help would be greatly appreciated, and pm's might be in order due to the nature of this beast.
 
check all of your grounds since you just did the swap. also, imho any time a pump upgrade from stock is done a rewire is a good idea to do.
 
check all of your grounds since you just did the swap. also, imho any time a pump upgrade from stock is done a rewire is a good idea to do.

I did check the grounds. Pass side to trans, starter ground to trans, batt to firewall, and intake mani to firewall. Cleaned and sanded.

I have the rewire kit, just didn't do it yet to get it running and one less thing to worry about.
 
A good way to eliminate ground fault, is to make a secondary ground source you know is good. Use it to supplement each circuit one at a time. Test with each, if it cures it, that's the bad ground. There's a lot of shared grounds. But you can also use a ohm meter with some long leads to test each wire of a circuit. For example, from the ECU to any sensor. Just Google the pin assignment on your car. Start there, and with a long section of wire, find where it ends on whatever sensor you are testing. If there is any resistance in line, you have a wire with an issue. So long as it's a straight shot from the ECU to sensor. Also watch jafro's you tube channel. He has a ton of diagnostics for wiring harness issues. It's a must for any dsm'er. He's genius.
 
How are you testing current with your multimeter and where are you placing the leads inline? Dont understand what you mean by "maxes out your multimeter" as you cannot test current draw using your multimeter in parallel. You arent placing your multimeter leads across battery terminals in ammeter mode are you?
 
How are you testing current with your multimeter and where are you placing the leads inline? Dont understand what you mean by "maxes out your multimeter" as you cannot test current draw using your multimeter in parallel. You arent placing your multimeter leads across battery terminals in ammeter mode are you?

Ooh no LOL. I was putting it on the fuse pin and a ground.
 
I'd try a new ground back at the pump. And it doesn't take much time to do a pump rewire, About an hour or so on mine. That would eliminate that as the source. U can get all the supplies from your local auto parts store for about $30.
 
Ooh no LOL. I was putting it on the fuse pin and a ground.

You cannot test current in parallel; you are essentially creating a short-to-ground by doing so and its no wonder why any part of the multimeter gets hot. It must not have a good internal fuse setup and using a multimeter like this can result in melted components or fire (not as likely) if it does not have adequate internal protections.
To test current you must place the multimeter inline with whatever circuit you wish to test.
Voltage can be tested parallel.
 
You cannot test current in parallel; you are essentially creating a short-to-ground by doing so and its no wonder why any part of the multimeter gets hot. It must not have a good internal fuse setup and using a multimeter like this can result in melted components or fire (not as likely) if it does not have adequate internal protections.
To test current you must place the multimeter inline with whatever circuit you wish to test.
Voltage can be tested parallel.
You know, I brought up the same thing but my buddy insisted. He's an electrician, so he's gonna need a new career.
 
Just FYI, there are expensive meters that can test amps in parallel. A clip style meter is the easiest way to test current. Keep in mind current is flow. If there's no load (pump, starter, etc) running. There will be current draw. So really most people, me included don't use current/amps to troubleshoot a circuit. Better off looking for excessive amount of ohms on a circuit. Looking for voltage drops. Testing for ground faults. Always process of elimination. Hopefully this helps.
 
Just FYI, there are expensive meters that can test amps in parallel. A clip style meter is the easiest way to test current. Keep in mind current is flow. If there's no load (pump, starter, etc) running. There will be current draw. So really most people, me included don't use current/amps to troubleshoot a circuit. Better off looking for excessive amount of ohms on a circuit. Looking for voltage drops. Testing for ground faults. Always process of elimination. Hopefully this helps.

Wouldn't it be a lack of ohms? Because it's a short?
 
first of all ohms is a measurement of resistance, a short is a unintended path from the battery to ground before a load so a short will not have much resistance true. if there is no load on a circuit there will be no current draw if circuit is in tact, that doesn't mean there is not voltage to the load as long as ignition is on. so from what i see everything worked and you swapped up to link what if there isn't actually a problem with your car and more of a problem with the ECU upgrade? speed density can also take a while to get good at tuning but i don't see how it could affect the fuel pump although the ignition switch turns both on. i know on the second gens ECM needs to see signal from the crank sensor to turn on the fuel pump but you should be able to do that in link. my next step would be get a pin out of the ignition switch and resistance / volt drop test it and all its circuits. very well could have a pinched wire somewhere crossing 2 circuits, bad fuel pump relay or bad ignition switch. if you have a short literally the easiest way to fix is turn on the circuit that is shorted and it will physically get hot. then follow that wire till it is no longer hot might have to turn on a couple times but heat will stop at short. i think that Sbgriffin was saying that most mechanics use volt drop tests and resistance tests to do most of our testing and if you don't have a short that is what your up against.
 
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Yes all of the above is true, and solid advice. I'm really suspect of the pump relay. I'm about a year away from being a journeyman electrician, so I'm hoping this the one area I can be of some help here. And one of the 1st things that we're taught in the program, and most used equations for electrical theory. Called ohms law, basics is E=I/R. E=voltage, I=amps, R=ohms. So with basic math you can figure any missing variable. All u need is 2 of the 3. So you can easily get the amp draw from knowing the volts and resistance of any circuit. There's more to it when solving for P=power or watts, but u can google that. This the most valuable tool when diagnosing a electrical gremlin. And to answer your question, all circuit will have some resistance, even just a length of wire. For example, 20 feet of 10 awg wire might have .5 ohm, where 18 awg wire might have 1.5 ohm. U must be sure there nothing inline or parallel on a circuit to add any resistance. Then test the ohms of the circuit, from start to the end of the length. If there's excessive resistance, then u might have a wire pinched, or mangled somewhere in the middle. But connections are much more likely to be at fault. My car has connections all over failing, from years of heat and use. Always attack by process of elimination. From simply to worst case scenario. Sorry from being so wordy, hope this was of some worth. And keep us updated.
 
Just FYI, there are expensive meters that can test amps in parallel. A clip style meter is the easiest way to test current. Keep in mind current is flow. If there's no load (pump, starter, etc) running. There will be current draw. So really most people, me included don't use current/amps to troubleshoot a circuit. Better off looking for excessive amount of ohms on a circuit. Looking for voltage drops. Testing for ground faults. Always process of elimination. Hopefully this helps.

Well, yes, there are but the assumption was a consumer grade (potentially even an auto store special) multimeter was in use, hence inline.


If you are going to perform continuity testing, disconnect the battery first to avoid an accidental short.

If you cannot turn the pump on via link manually, there is another issue altogether besides simple ignition or cas signaling. Did you perform a 2g ecu swap by any chance LOL
 
Ive tuned speed density on a few other cars. Way easier than maf imo.

I've swapped out the mpi relay which is the only relay I was aware of having anything to do with the fuel pump. I did get the fuel pump to turn on briefly when I turned off an injector by accident in the link software.

I'm also having some small compatibility issues with the ecu.. You mentioned I might have a 2g ecu. It was saying something along the lines of "some of the data is not compatible, try saving one tab at a time". I've never seen that error on my other 1g. I'll have to check that out, I didn't think the connectors were the same.

I assume a 2g ecu would cause the fuel pump issue, but what about the short?
 
Got it. Fuel pump power wire was pinched between the tank and the hangar. Now to find another TPS to use since mine seems to be broken. Thanks for all your input. Should have the motor broken in this weekend!
 
Got it running smooth already! Glad to see my work come together after a short month to tear down, wait for parts, and assemble. Believe my timing belt is too tight though. Live and learn.
 
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