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THIS TRICK COULD SAVE YOU $400.00; FUEL PUMP PROBLEM
Topic Started: Mar 19 2013, 08:10 PM (1,834 Views)
guldens
Member
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I RECENTLY BOUGHT A 1992 METRO, THREE CYLINGER, 5 SPEED, THAT I WAS TOLD, "IT JUST NEEDS A FUEL PUMP". THE PUMP WAS ALREADY REMOVED, SO I COULD NOT VERIFY IT WAS BAD. I PUT IN A PUMP AND THE CAR STARTED RIGHT UP. A DAY LATER THE CAR DIED; NO POWER TO THE PUMP. I STARTED TRACING. TO MAKE A LONG STORY SHORT, IT WAS MY BRAIN BOX (ECU). ONCE THE BOX HEATED UP, I LOST POWER. AS SOON AS IT COOLED DOWN, I HAD POWER AGAIN. THE COST FOR A NEW ECU, AT ADVANCE OR AUTO ZONE, OVER $400.00. DURING MY TESTING, I HAD USED MY TEST LIGHT TO TEST THE FUEL PUMP RELAY. WHEN I TOUCHED THE PINK AND WHITE WIRE, (WHERE IT ENTERS THE RELAY), THE RELAY CLICKED ON AND THE FUEL PUMP WENT ON. WHAT GIVES? SO I WENT BACK TO THE WIRING DIAGRAM AND NOTICED THAT THE PINK AND WHITE GOES FROM THE RELAY INTO THE BRAIN BOX, AND INSIDE THE BOX THERE IS JUST ANOTHER RELAY. THAT CIRCUIT THEN JUST GOES TO GROUND. SO, I JUST CUT THE PINK AND WHITE WIRE, ABOUT TWO INCHES AFTER IT EXITS THE FUEL PUMP RELAY AND SPLICED IN A GROUND WIRE, WHICH I RAN OVER TO THE NEGATIVE BATTERY CLAMP. CARS RUNS FINE AGAIN AND HASN'T DIED. I'LL BE ON THE LOOK OUT FOR A GOOD USED ECU, TO KEEP AS A SPARE, BUT FOR THE MOMENT, I'M GOOD TO GO.
I DON'T KNOW WHY THEY HAVE TWO RELAYS TO OPERATE THE PUMP? IF ANYONE HAS THE ANSWER, PLEASE LET ME KNOW. THANKS.
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Reista
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Clutzy Shadetree

Computers at junk yards are pretty cheap, i wouldnt have gone for a new one because a used one should do the same job, they rarely fail
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jkeney


crafty
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Vkhelldog
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I've seen others who had over heating ecu put a computer fan on it.
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nixmixin
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so, in a nut shell, the ECM wasn't bad, the fuel pump relay was? Right? Or, do you think that the relay inside the ECM was bad and you "bypassed" that one?
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Rhinoman
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There was a relay inside the ECU? do you have a picture of that? The ECUs control of the fuel pump relay is for safety, the ECU turns on the fuel pump for a few seconds at key on and then only when the engine is cranking or running. Usually there is a transistor in the ECU that turns on the fuel pump relay, its done that way to reduce the power in the ECU.
Edited by Rhinoman, Mar 21 2013, 05:06 PM.
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t3ragtop
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Turbo3 and Twincam Tweaker

even though your internet ettiquette is bad - CAPS - i'll give you a response.

there is no "relay" in the ecu. there is a driver fet which sinks the circuit to ground and that's what controls the fuel pump relay.

the ecu has certain control modes for the fuel pump for starting and stopping the fuel pump. one in particular shuts down the fuel pump when the ecu doesn't see an ignition event. key on, the fuel pump runs for 3 seconds to prime the fuel rail and shuts down until it sees a signal generated by the distributor's module during cranking. when you crank the engine, the fuel pump runs continuously. if the engine stalls, the fuel pump shuts down again.

if you crash that car with the fuel pump wired like you have it, even if the engine stops running you will still have the pump running non-stop. if the fuel line ruptures and the engine stalls from fuel starvation you could pump gas onto a hot engine component and potentially cause a serious fire and/ or explosion.

your "fix" is neither safe nor smart and i do not recommend this as a suitable repair practice.
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Rhinoman
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t3ragtop
Mar 21 2013, 05:22 PM
there is a driver fet which sinks the circuit to ground and that's what controls the fuel pump relay.
No FETs in a 92, the transistors are either plain BJTs or darlington pairs.
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nixmixin
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Well, I have mixed feelings about this...

I have been chasing this same issue for nearly a year now. I have several threads about it on this site, as well as others. I just got my ECM back from a company that rebuilds ECMs. They checked out mine and put it through a bunch of tests and concluded that my ECM was in perfect running order. So, while my ECM was away being tested, I saw this thread. I re-installed my ECM today and did a couple other easy quick tests including checking the Fuel Injector Resistor's Ohms. I then did a "T" in to the Pink with a white stripe wire and put it into a fresh ground. I also "freshened" up the main ground next to the battery. My car is an '89, not a '92, but has most of the same bits.

Test drive...Ran soooo smooth! had more power than normal and the idle dropped back down to around 700. Drove it for around 20 miles with lots of stopping at lights. No issues....until... :( I pulled into a parking lot and stopped. I then started to "go" again and started to die the same as before. I feathered the gas pedal and kept it alive. The idle then hopped back up to 1100 rpm and has stayed there. So...WHY did the trick work brilliantly only for a while? When I turned the car off and restarted it, the idle is where it is supposed to be, then when I rev the motor, the idle goes back to 1100 now. :(
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t3ragtop
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Turbo3 and Twincam Tweaker

Rhinoman
Mar 21 2013, 05:25 PM
t3ragtop
Mar 21 2013, 05:22 PM
there is a driver fet which sinks the circuit to ground and that's what controls the fuel pump relay.
No FETs in a 92, the transistors are either plain BJTs or darlington pairs.
you got me, rhino. :D

transistor was too long to type. fet, field effect transistor, is more common modern technology and since that's what i currently use for any driver design, i tend to shorten everything up to fet.

the number of guys who would or could get that specific in one of these discussions is fairly small.

it's still my opinion that what is outlined as a cheap fix is actually a disastrous catastrophe waiting to happen so y'all be forewarned.

a replacement ecu does not cost $400 but even if it did, i'd rather see people pay the $400 to fix their problem correctly instead of taking the chance of perishing in a fiery beer can of a car by following the example above. :shake
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DesmondGhostRider
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Quit yelling at us plz
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guldens
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WELL, THAT IS WHAT I NEEDED TO KNOW, SO I WILL BE INSTALLING A FUEL INERTIA CUT OUT SWITCH, UNTIL I CAN LOCATE THE CORRECT ECM. THIS IS WHY FORUMS ARE SO GREAT. THE PASSING ALONG OF INFORMATION. THANKS, GULDENS
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Bill CNC
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Dump the caps, ...
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nixmixin
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Hello? Anyone read my post? I have the exact same problem. Did the same "fix". And had the ECM checked out. It was fine. So, in theory, replacing the ECM wouldnt fix it.
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mikeallen2112


nix have you done a fuel pressure test? I had a very similar problem with it dying and having to feather the gas and mine looks to be a bad fuel pressure regulator.

Do a fuel pressure test. Mine was really high and would dump to 0 with the key off
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