MREL circuit faulty?

[suprra_girl]

So I'm going to be doing a lil work to the car soon and would like to resolve this issue I have. My mrel drops voltage severly on cranking and I think has lower voltage compared to the rest of the ign wires.

Here is an old thread bout it
http://www.supramania.com/forums/showthread.php?105453-Low-voltage-on-MREL-pin-of-ecu&highlight=mrel

Reading that makes me want to revisit where I have my accessories running and off what, the only reason I noticed in the beginning a problem with mrel is that I was jumped off it to power my relay for my wideband screen and my screen doesn't always power up correctly. My screen still does this, it suggests I still have it on that circuit but I thought I changed it.

I've put up this thread for now and will update it with better information and notes of where my accessories are powered and what voltage I have coming from ign switch etc, I would love to fix this as I really hate things not working like they should lol.

 

[Dirgle]

I know Pi said the the M-Rel is powered by the IGSW but according to the Toyota tech articles the M-Rel is powered by the Batt wire which is powered by the 15A EFI fuse. Hopefully he can pop in here to mention if anything has changed since he started digging deeper into the TCCS. It's a pretty basic circuit so it limits the number of places a problem can be present.

 

[IndigoMKII]

Could be your EFI relay getting hot from cranking. How long do you have to crank before the car normally starts?

On a side note, why not power your wideband screen from the cigarette lighter?

 

[suprra_girl]

Since the new fuel pump I gotta prime the pump up but it technically starts quickly once it has fuel.

As for where I powered it, nfi, probably had some horrible good reason at the time

I'm going to release alot of the load or ensure the loads for the gauges are on good circuits before I test mrel and cranking stuff, a quick squizzie at the diagrams looks like it'll be fine to test with no efi fuse, don't want to be emptying retarded amounts of fuel in the engine heh

 

[Dirgle]

Could be your EFI relay getting hot from cranking. How long do you have to crank before the car normally starts?

On a side note, why not power your wideband screen from the cigarette lighter?

The EFI relay has nothing to do with cranking. It's activated as soon as the ignition is turned on until two seconds after the ignition is turned off to allow the ISCV to home. There is no difference in it during cranking.

Since the new fuel pump I gotta prime the pump up but it technically starts quickly once it has fuel.

As for where I powered it, nfi, probably had some horrible good reason at the time

I'm going to release alot of the load or ensure the loads for the gauges are on good circuits before I test mrel and cranking stuff, a quick squizzie at the diagrams looks like it'll be fine to test with no efi fuse, don't want to be emptying retarded amounts of fuel in the engine heh

The M-Rel gets biased through a transistor so it's current handling is limited. By putting other systems on it you may have overdriven it causing it it overheat and cause problems. Further testing will be necessary to tell.

 

[jetjock]

Need to avoid main relay contact/coil confusion. The ECU powers the main relay while the main relay powers other things. As Dirgle pointed out one does not want to connect anything to the M-Rel output on the ECU. Connect to the main relay contact (B+ circuit) instead although I'm not a fan of doing that without fast acting overcurrent protection.

 

[kotu100]

Good thread, I'm having this same issue with my car and still haven't chased down the issue.

 

[3p141592654]

Well, my comments in the linked thread still stand. Leave MREL, B+ and BAT alone, and use the GAUGE circuit for aftermarket gadgets and gauges. Especially don't load MREL, as it is controlled by a complicated circuit inside the ECU and has low current handling.

 

[suprra_girl]

I finally have time to start testing this

Had another look at my wideband relay and looks like the relay is energised by the battery and +b which is still the efi circuit, least I moved it off mrel, I'm going to jump it off the b/o which is IG2 rather, my resistor pack has been bypassed so that location is rather convenient so I'll do it there, it feeds ignitor, resistor pack, 7.5a ign fuse. Any issues going on this circuit do you think?

Once I've done this bit then I'll head on the checking mrel cranking etc

 

[suprra_girl]

Wideband relay now relocated, and funny, my few tests so far seems my screen works every time now

On to mrel testy test tomorrow, getting dark here and keeps drizzling :/

 

[suprra_girl]

Crap I fukked it up again LOL

Just been going through the old thread and 3p you said to avoid IG2, going to move it again hah

Yay, found a good gauge fuse source, gonna whack it on there

edit: first issue I've found, b/o from efi main relay to engine harness connector which then goes to mrel on the ecu but the plug right at the ignitor area 2.1ohm resistance from the engine bay fuse block :/ That is not cool

dammit >.< its now started pissing down again *sigh*
I'm quite concerned that in 25-30cm of wiring there's 2ohm resistance, gotta pull up the engine bay fuse block and untape the wiring there to see where this problem is.

edit2: that'll teach me, I didn't firmly connect the meter and it appears I was on a dirty part of the pin heh, I'll be checking ig2 - igsw next but I got distracted making my valve covers look pretty again hah

 

[kotu100]

Did you ever have any luck chasing down the cause of these issues?