Intermittent GND in ECM Circut ???

[benjaminjr]

I'm reading from a 96 eng. control wiring schematic(don't have the 97 ) dealing with a no start problem that ocurred suddenly last week--no fuel pump operation = replaced pump, started and ran 2 minutes,died & pump w/o power so no start again. TOM (SVX FILES) ANSWERED MY PHONE Questions on location of FP RELAY & i verified both the fuel pump relay andthe multipurpose relay next to it(sends power to oxy sensors and other solenoids and also powers the fuel pump selonoid) were good--but the MP RELAY was "buzzing " like an electric razor! with the relay out of socket a voltage ck found the brn/blk (relay coil input) had 12 volts and the blk/wht(grnd side) had 2.4 volts with a 100 or more "hertz"--the schematic indicates this blk/wht wire is connected /spliced to somewhere but not "where"--i cut the wire to the relay and ran a chasis grnd to relay--pump activated >CAR STARTED >DRIVES & RUNS SMOOTH>EXCEPT for wild idle speed swings(300-800 rpm but no stalling) when approaching a stop--QUESTIONS: is the blk/wht an above chassis ground(IN THE ecm?) AND why the HERTZ???--will removing relay from circut create more problems?--has anyone else had this happen?? HELP???? SUGGESTIONS --REAL FIX????--THANKS ebp0342@yahoo.com PS: when i grnded the circuit to chassis before cutting loose,it started,ran rough & set misfire codes oncyl 2,4 & 6. setting no codes now with wire seperated .

[superru]

1.) the thing i can see causing the misfire codes the first time would be, when the car was running and the pump failed it no longer sends fuel to the engine and then it begins running like crap!! some times firing on a cylinder and sometimes not right before it dies out. so that's probly where your misfire code came from.

2.) for your "pulsed dc" creating a buzzing relay.. i don't have the schematic in front of me so i don't know where it goes. but mostly ( someone correct me if wrong) ECU's Sink the current> meaning they switch the ground circuit instead of sourcing it, where you Switch the positive side. doing this through Solid state parts. ( SCR's Triacs Mosfets ETC..) possibly a broken solder joint in the ECU? or loose pin? just kind of shooting in the dark here.

[TomsSVX]

A buzzing relay is typically a loose gnd. I have had it happen a couple times. Check the gnd wires on the back pass side of the intake manifold for cleanliness and tightness. I usually pull it and clean it anyway just to mark it off. This is the central grounding point for the ECU and most of the sensors and where I would start

Tom

[svxfiles]

Originally Posted by benjaminjr

I'm reading from a 96 engine control wiring schematic(don't have the 97 ) dealing with a no start problem that ocurred suddenly last week.
There was no fuel pump operation so I replaced the pump.
It started and ran 2 minutes,died & the pump was w/o power so no start again.
I verified both the fuel pump relay and the multipurpose relay next to it
(sends power to oxy sensors and other solenoids and also powers the fuel pump selonoid)
were good--but the MP RELAY was "buzzing " like an electric razor!
With the relay out of socket, a voltage check found the brn/blk (relay coil input) had 12 volts and the blk/wht(grnd side) had 2.4 volts with a 100 or more "hertz"--
The schematic indicates this blk/wht wire is connected /spliced to somewhere but not "where"--
I cut the wire to the relay and ran a chasis grnd to relay--pump activated >CAR STARTED >DRIVES & RUNS SMOOTH>EXCEPT for wild idle speed swings
(300-800 rpm but no stalling)
when approaching a stop.


QUESTIONS:
1)Is the blk/wht an above chassis ground(IN THE ecm?)
AND why the HERTZ???--
2)Will removing relay from circut create more problems?--
3)Has anyone else had this happen??
HELP???? SUGGESTIONS --REAL FIX????--THANKS ebp0342@yahoo.com

PS: when i grnded the circuit to chassis before cutting loose,it started,ran rough & set misfire codes oncyl 2,4 & 6. setting no codes now with wire seperated .

Translation;

Hi Everybody!
I have a 97SVX with a weird problem and I wonder if any of you can help me out?
Why is my multipurpose relay buzzing?
Thank you one and all.

[oab_au]

Sometimes a relay will buzz, because when the relay closes to turn a circuit on, that circuit will short out the power that was there to turn the relay on, so it turns off, the short is removed, so it turns back on.
On, off, buzz buzz.

Can also happen with the ground circuit, when the circuit is turned on, the ground supply to the relay, becomes positive, turning it off again.

Harvey.

[trophy956]

hi the main or ignition relays in subarus are a known cause for many things ,since they are single throw double pole relay ,they can turn on only one side and run the cars very badly ,did you try just jumping around the relay ? i dont have a obd 2 wiring diag in front of me but will check,the 92 book shows this wire to splice B to ground GE,this ground is on the engine above #5 cyl on the intake
i hope this is some help

[Trevor]

From what I gather from your rather confusing post, You have actually measured 2.4 volts at approximately 100 hertz between the negative multi purpose relay connection and ground, with the relay out of circuit. If this is so, the fault must be within the negative circuit to ground.

The 2.4 volts with no load applied by the relay, indicates a second load probably exists, and as you refer to a splice, there may well be some other component in parallel. Resistance within the circuit to ground, as might occur in a solid state switch, indicates possible ECU control and a fault possible therein. Alternatively, a parallel circuit may be presenting an intermittent load.

The fact that isolating the original ground circuit and connecting a direct ground, stops the chattering relay, is further evidence in relation to the above diagnosis. Wild idle speed makes one again wonder about a possible parallel intermittent load.

You must trace and identify all of this circuit. I can find no reference to the multi purpose relay, in any of the manuals or data I have. Please advise where you found a wiring diagram, and try to establish where the unidentified connection may be shown on an associated page.

[benjaminjr]

Originally Posted by TomsSVX

A buzzing relay is typically a loose gnd. I have had it happen a couple times. Check the gnd wires on the back pass side of the intake manifold for cleanliness and tightness. I usually pull it and clean it anyway just to mark it off. This is the central grounding point for the ECU and most of the sensors and where I would start

Tom

: i secured the grnd,replaced the ign switch & both relays and the fuelsystem modulator/resister(w/your help)--now the grnd side of fp relay does not "switch" to gnd(pin32,grn/blk of ecm)-so i probably fried ecm when i injected chassis grnd into both the main relay and the fp relay-grnding the fp relay allows it to start & run on 3 or 4 cyl snd sets misfire codes for 2,4,6 and 1--so if you have another miracle tip--great, but i believe i need an 87 SVX LSi ecm(obdll)--please email me with details @ ebp0342@yahoo.com--thanks--benjaminjr