The only time it stops buzzing, is when I short circuit the relay at the diagnostic block (check connector)... through +B and Fp. I checked the relay for continuity and it is still good. Weird. Van:1zhelp:
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What would cause the fuel pump relay to buzz, even when the key isn't in the ignition
- Thread starter Van
- Start date
Buzzing relays is normaly poor ground. meaning the relay is buzzing because somthing is grounding through the coil from another circuite poorly grounded or the relay itself is poorly grounded and buzzing because its grounding through the coil to another circuit on its ground wire also.
By connecting +B to FP one is connecting FP to battery positive after it goes through the ignition switch, EFI relay, etc. There is normally no buzzing when that's done. Yet when connecting FP directly to the positive battery post (the same point electrically as in the first case) with the key off the relay buzzes. This is true even when the car's wiring is factory perfect. Once it's understood why that happens the reasons behind your symptom should become obvious...
Let me see if I can get my head around this... The problem is ground related. So, I need to start checking all the ground points in the fuel pump circuit. Right?
Mine does that same thing with the key off when I jump FP in the plug. Its normal. When the car is running it does not do it.
Possibley? when a relay is buzzing it is because it is in series with another circuite that takes a full 12vdc because the relay also uses 12vdc
Relay contact chatter is caused when you supply the coil 6vdc instead of 12vdc for example because the coil is only half way closing the contact.
I know one of the fuel pump relays have 2 coils in it maybe to fully pick it up look at the schematic to be sure it maybe normal.
Relay contact chatter is caused when you supply the coil 6vdc instead of 12vdc for example because the coil is only half way closing the contact.
I know one of the fuel pump relays have 2 coils in it maybe to fully pick it up look at the schematic to be sure it maybe normal.
Today, I'm planning to diagnose the problem(s) with the EFI system. Wish me patience... After today, if the FP Relay persists with the buzzing, the Supra goes to the mechanic. Van
Hi Evilempire1.3JZ-GTE, I received this post via email, it is missing in this forum, so here it is... Van
Originally posted by Evilempire1.3JZ-GTE:
"Did you ever figure this out on your own with some of my hints?
When I look at the schematic I see which coil makes noise and why.
Refer to below:
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=D&P=4
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=D&P=5
Your [Fuel Pump Control Relay] is buzzing because on the normaly 0/ground voltage side of the coil you apply 12VDC at the check connector with B+ If your EFI syststem was on or your ECU sparks will fly possibley even damage you should only apply ground if anything at FP at check connector like your ECU would during normal operation.
Well anyways now you have 12VDC on one side of that coil but remember how i said coils chatter when applying lower voltage due to poor ground or going thr multiple cicuites well it apears your coil gets ground through the 3 volt dropping resister and fuel pump motor or just the fuel pump motor.
Since the coil/windings of the fuel pump and the resister drop the voltage going to your relay it causes it to make a buzzing noise from it partially engauging.
*This is normal!* stop applying B+ to it before you damage the ECU ground output driver or short EFI MAIN to ground."
Originally posted by Evilempire1.3JZ-GTE:
"Did you ever figure this out on your own with some of my hints?
When I look at the schematic I see which coil makes noise and why.
Refer to below:
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=D&P=4
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=D&P=5
Your [Fuel Pump Control Relay] is buzzing because on the normaly 0/ground voltage side of the coil you apply 12VDC at the check connector with B+ If your EFI syststem was on or your ECU sparks will fly possibley even damage you should only apply ground if anything at FP at check connector like your ECU would during normal operation.
Well anyways now you have 12VDC on one side of that coil but remember how i said coils chatter when applying lower voltage due to poor ground or going thr multiple cicuites well it apears your coil gets ground through the 3 volt dropping resister and fuel pump motor or just the fuel pump motor.
Since the coil/windings of the fuel pump and the resister drop the voltage going to your relay it causes it to make a buzzing noise from it partially engauging.
*This is normal!* stop applying B+ to it before you damage the ECU ground output driver or short EFI MAIN to ground."
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The FP relay is getting voltage when it should not. The ignition is off (ignition key in my pocket), yet the relay is still getting voltage. I will be checking the circuit opening relay, next. Van
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=110
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=110
OK, I want to check the "Circuit opening relay", so I disconnect it from the circuit and to get a baseline reading, I checked the fuel pressure relay plug coming out of the firewall, and it has six volts DC (using multi-meter). I put the circuit opening relay back in, and there is still six volts measured on the fuel pressure relay plug. I checked the continuity of the circuit opening relay and it has 10.20 ohms, at terminals STA and E1, and terminals B and FC. I'll need to check the continuity of terminals B and FP after applying battery voltage as described in the TSRM: http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=110
My question is, what purpose does the curcuit opening relay serve?
Thanks. Van
My question is, what purpose does the curcuit opening relay serve?
Thanks. Van
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Dont worry about my post the FP wire is on the positive but it is supposed to buzz as jet mentioned acutally it drops the voltage through the relay as an parallel circuit the EFI system FP does tie into positive not negative ECU signal.
Either way yes it is supposed to buzz when voltage through the coil is dropped.
Its not supposed to buzz during normal car driving though.
There is 2 relays
One drops the fuel pump voltage to 9 volts or 12 volts.
The other turns on when the ECU says to pump gas to the engine.
Either way yes it is supposed to buzz when voltage through the coil is dropped.
Its not supposed to buzz during normal car driving though.
There is 2 relays
One drops the fuel pump voltage to 9 volts or 12 volts.
The other turns on when the ECU says to pump gas to the engine.
O.K. I give up! :3d_frown: It's off to the mechanic at Auto Electric Specialties, for the Supra. Thank you, to all who have helped me the past week. Van
I discovered that I had unknowingly connected a bundle of wires to battery pos terminal of the starter, that are all ground wires.:3d_frown: This was a costly mistake... I had to purchase a new TPS, fuel relay, ignition coils, and a used TCCS ECU, before the motor started working reliably again.
Please see the thread Where-do-these-attach-to in the General MKIII section, of the forum, for more information on what those wires look like and where they are supposed to be attached. HTH Van
Please see the thread Where-do-these-attach-to in the General MKIII section, of the forum, for more information on what those wires look like and where they are supposed to be attached. HTH Van
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Thanks for the 2-3 year old posting on this. Guess we're #3 to admit it.
Many months ago met a guy with an 89 7MGE NA Auto in my credit union parking lot. I'm in the local Supra scene, but MK II, give him info. Get a panic call about removing the harmonic balancer to fix a BHG (bubbles only, not milkshake) I was WTF, I'll be there in an hour (Looking at Haynes, that is one of the steps, ugh). He'd removed the intake and exhaust, so we pull the head, give him directions on cleaning it. A few days later return to put it back together.
I'm a 5MGE guy, mostly the same but some differences. And being management I'm not about to crawl under a car unless it is my own. So the brown ground wire combo went to the starter just like you. Two sets of ground wires to the same bolt? Never seen that before. He said he had a ground connection on the starter and I didn't think twice.
Connect battery and fuel pump control relay is buzzing,
With some minor timing fiddling (I've never gotten a dizzy in right the first time) we got it running with zero accessories (cooling, alt, etc, but pumpkin puked out some fluid).
Did research and found this thread. Buzzing fuel pump relay.
Many months ago met a guy with an 89 7MGE NA Auto in my credit union parking lot. I'm in the local Supra scene, but MK II, give him info. Get a panic call about removing the harmonic balancer to fix a BHG (bubbles only, not milkshake) I was WTF, I'll be there in an hour (Looking at Haynes, that is one of the steps, ugh). He'd removed the intake and exhaust, so we pull the head, give him directions on cleaning it. A few days later return to put it back together.
I'm a 5MGE guy, mostly the same but some differences. And being management I'm not about to crawl under a car unless it is my own. So the brown ground wire combo went to the starter just like you. Two sets of ground wires to the same bolt? Never seen that before. He said he had a ground connection on the starter and I didn't think twice.
Connect battery and fuel pump control relay is buzzing,
With some minor timing fiddling (I've never gotten a dizzy in right the first time) we got it running with zero accessories (cooling, alt, etc, but pumpkin puked out some fluid).
Did research and found this thread. Buzzing fuel pump relay.