Drop in voltage from fuse panel to main relay with stalling

[mellow65]

So driving around the last few times I noticed that every once in a while I would get a small hiccup like the car stopped running just for second then came back to life. Didn't really think much of it until the first time it happened at a stop light and it was enough to kill the motor. It would fire right back up but it still is starting to drive me nuts.

So in all of my checking and poking and testing I found what was happening was the main relay was clickin off then back on, momentarily killing power to the car. So this made me start to look at the circuit for the main relay. I tested the voltage at the fuse panel, it's battery voltage, I tested the plug at the main relay, I have the same voltage. But after the car is started the power at the relay is no longer charging voltage like I'm getting at the fuse panel, it's about a volt-ish lower.

So my thought was maybe I'm getting a draw down stream of the main relay causing some flux in the voltage and possibly making my relay click off and on. but not sure where to start. And because The ecu pulls power from the main relay I'm wondering if the ecu is having the same flux in power. Because that might lead into the odd part of the whole thing is when the cooling fan turns off it makes the main relay click off then back on but it's enough to kill it at an idle, which make zero sense to me considering they are on two completely different circuits.

I have checked grounds anywhere and everywhere I can. All are solid and show good connections. I have tested the battery voltage at ecu and it's solid battery voltage.

I'm just kind of stumped on what to try. I have spares of most everything, so I can try to swap out stuff if needed.

Any thoughts would be much apreciated.

Also this is on a 94 Lego wagon 5 speed

Thanks

[oldscoobyturbo]

is your wagon originally a 5spd? I've had this happen a few times not sure it was the fan but was idling every time so far since my swap. I'll have time to investigate this further in 2 weeks as Wicked Big Meet is around the corner and a need to do a few tests on the RS-RA

[mellow65]

Yeah it used to be an auto, but I pinned the ecu to be a manual and added the nutral switch.

But that's an interesting idea though. I wonder if swapping made some issue I cant foresee.

Whenever you get a chance I would like to hear what you find. I'm going to keep playing around and see what I can figure out.

I wonder if it would help anything to swap to a 5 speed ecu

[oldscoobyturbo]

I can try the ecu swap I have a spare manual one. It runs and drives perfectly fine I just find it odd that it stalls out from time to time. Again this has only happened a few times and I blamed it on the new clutch/wrx pedal box etc.. before reading this
I have a fully rebuilt engine, delta cams with low miles, jdm sti trans with lots of new parts
PS: Today the sunroof leaked for the first time but on the passenger side only!

[mellow65]

Have you measured voltage at your main relay? Im curious if you have the same thing I do.

Or I wonder if a voltage drop is something normal.

[oldscoobyturbo]

i did a few tests on the main power distribution
i found a small drop from the main fuse link to the inside fuse box nothing more than .5V
i also checked 2 relays,
the power going to the relay for the starter interlock which i installed with the swap was good
the power going to the main relay had the same .5V drop that shows at the fuse link

i also had the car stall again when i was going up my driveway to park it shut down just like i had turned off the ignition. i did the tests right after this happened. i suspect that the voltage drop is from resistance in the old wiring. i will try this test on my other 2 Legacy's just to see if i get the same results. The other cars have never stalled out during my ownership.

[mellow65]

Yeah mine is well over .5v drop. I'm also wondering if the old wiring is the culprit. My next thing I'm going to try is to run a good gauged wire from the battery to the input side of the main relay wiring. That way I know that for sure it's getting solid battery voltage. and then do my voltage testing again.

Let me know what you find on your other cars. This is the first time I have a legacy do this too.

[Legacy777]

I would suggest maybe added an additional lead from the fuse box to the relay. That wire may be bad and when you start pulling higher current through it, it heats up and causes a higher voltage drop.

You could also try disconnecting the power and checking the resistance of the wire from the fuse box to the relay.

[mellow65]

That's my plan, but as a temporary check I was just going to run something from the battery first to check I out.

And I did check the wire from the relay to the fuse panel, it checked out just fine.

[oldscoobyturbo]

I too have had intermittent issues with stalling even after doing many tests it still does this.
I also think I found a possible issue with the ignition wiring setup from the swap. I'm going to try testing the ignition 'on' circuit as I think this is culprit.

[mellow65]

Well let us know what you find. I haven't had any time to get under the dash of the car. This summer school is kicking my ever living ass.

[oldscoobyturbo]

so far nothing new but it seems to be related to the ignition power supply and turning off the engine even in gear. I had a stall today pulling into the parts store. I'm doing some more work sunday i'll try a few more tests on the ignition circuit as its been modified

[mellow65]

Alright so I got a chance to play around today in the garage.

And here is what I found and did. So i was measuring voltage at the two places I was thinking I had any issues, at the ecu and at the main relay. When the car was off, the voltage at the constant power at the ecu, the main relay, the battery was all constant. Then when I turned on the key I had a drop in voltage at the switched power on the ecu and at the main relay. Both of these voltages were the same so I started only keeping track at the ecu and put a test light on the main relay that would turn off if the main relay lost power.

So what did I find

At the ecu with the car running this was my voltage.



Now yeah it's in the 13s but it seemed to hunt around and never be very constant.


I then ran a good gauged wire strait from the battery to the main relay and rechecked my voltage at the ecu.



This voltage was rock solid, maybe flexed .02 voltage either way.

So I let it run for a while this way and the voltage dropped a little over time as the battery charged (been a month or so since I started it). But regardless of what the voltage was it was only .1 of a volt lower then it was at the battery.

So i let it warm up and waited for the fan to kick on, because at least for me, when the fan would switch off is when it was stalling.

So watching the voltage at the ecu and with a test light on the main relay I waited.

When the fan switched on the voltage flexed a little bit, but that would be expected, but recovered back where it was immediately I waited and waited and the fan switched off and, nothing. No movement in voltage, no flicker of the test light, nothing but a running car.

Soooooo, did this fix it? Idk really. As of right now the only time I knew it would stall it didn't, so clearly I have something that needs to be explored more.

So my next plan of action is to run extra wires to the main relay so I will know for certain that I will be getting the same results as I did today. I still am going to replace the relay, I mean it is 20 years old and definitely not helping anything by being old.

Later down the line I am going to swap to the newer style alternator for two reason, one they have more amperage and two because they are a two wire hook up rather then a three wire. That third wire is also attached to this same circut and to have the least amount of stuff on the circut the better.

[Legacy777]

Good testing!

When I pull my dash, I'm planning to replace all the primary relays there....just due to their age. I'll probably do some similar testing to check if I have any wiring issues, or if it's just relays.

[oldscoobyturbo]

I have the newer alternator it helps with the delta cams at idle too

[mellow65]

so i just wanted to give some updates because I got a chance to get out the garage and put my car back together.

What I did was run a pretty hefty wire, 8 gauge (it was all I had), from the battery to the location of the main relay. Once I got to the area of the main relay I spilt to the 8 gauge to two smaller wires, but staying with same gauge as both the wires going into the main relay, and soldered one new power wire into each power wire going into the main relay.

I did do a fuse on this wire but only a 10 amp. The factory fuse for this system is 30 amps, and I didn't want to add a huge fuse to the new system because really all it is, is a supplementary power source, not the main power.

Also as an added thing, I ran a 8 gauge wire directly from the alternator post to the battery. So rather then the juice from the alternator having to go to the main fuse pannel (which is no where near my battery now because this isn't in a lego anymore) then back to my battery, it's just a straight shot to the battery.

And I replaced both my main relay and fuel pump relay.

with all that I fired it up, and checked my voltage in different locations. I had the same results as I did with my earlier testing. I had solid battery (-0.1v) voltage at the main relay and at the ecu.

So all is well, I let the car warm up and let the cooling fan cycle on and off with no stalling (because this is where I had my relay clicking off).

Now mind you, this is all just sitting in my garage and not out driving it yet. But i have a feeling this was the correct path to go down. I'll give you an update when I get the car on it's wheels again and driving. I'm hoping that is going to be over the winter break from school here starting next week.

[Legacy777]

Thanks for the update.

I'm planning on replacing my ignition and fuel pump relay when I pull the dash to help eliminate any voltage drop that might be a result of old relay contacts.