[white93gt]

When I have a better measuring tool I'll try to grab the wire that runs to the fuel pump. That controls another relay for my fuel pump hotwire so I don't think it would cause much of a draw.

Wait..... your using MFI pin 1 (Black/blue) wire as a control for the pump relay like OEM, instead of the normal bypass of removing pump relay and jumping harness sockets (pin 3 or 5) to (pin 2)?

Also did you see my Edit to post #31?

 

[fastfalcon94]

This? Do you know exactly what his fuse problem was? I'm not blowing fuses or anything.

"After reading this post again, maybe you should monitor voltage at end of this bypass connection. I remember OhioSpyderman having an explainable fuse problem because of this bypass connection. "



So originally I had the fuel pump control relay that is below the engine bay fuse box in tact. If you look at the 2nd picture on the first page in this thread you'll see that ECU pin 31 controls when the relay is triggered or not. When its active it would use the built in resistor box, when its not active it wouldn't. Pin 31 is not used by AEM so the underhood resistor box is never used. I had it this way for 10 years. After this issue started I decided to remove the relay (bypass it by connecting pin 2 to pin 5). I also unplugged the resistor box and removed it.

So pin 1 of the MFI relay goes out to the engine bay, through the bypass, all the way to the back of the car where it triggers a relay for my fuel pump hotwire kit. I did test that relay and also tried a new relay before I really started digging into the wiring diagrams.

Also looks like oscilloscope will be here on Friday.

 

[OhioSpyderman]

My fuse problem was with fuse #12.
I did the relay bypass and after several years (for whatever reason) there was intermittent arcing between two terminals.
I bought an auto-reset fuse that allowed me to troubleshoot without going through dozens of fuses.
I solved the problem by generously applying di-electric grease to all the terminals in that relay holder.
Damnedest thing I ever saw....

Bob.

EDIT: When I saw you post about fuse #12, I realized I put the wrong fuse number here.
In fact, there is NO fuse #15.
I need a vacation....

 

[fastfalcon94]

Interesting. My next test will be to pull pin 1 from he MFI relay and jumper my hotwire relay in the hatch so the fuel pump runs constantly. That should eliminate all the wiring that goes in/out of the engine bay including the factory fuel pump resistor bypass relay socket. We'll see if that helps. None of my fuses have blown. Tested with multimeter and I've swapped them out too as a precaution.

 

[fastfalcon94]

So during my lunch break I looked stuff over. I did find the ground wire running to my hotwire relay in the hatch was pinched. It was caught under the leg of my custom made floor panel. I checked continuity on it and it was fine. I cut it open and all the wire was still connected. Just to be safe I ran a new wire. Same problem.

Then I did the test I described in my last post. I removed pin 1 from the MFI relay. Then on my fuel pump hotwire relay in the trunk I ran an alligator wire from the +12v battery pin and the trigger pin. Basically my fuel pump was on 100% of the time. I started it, after about a minute the car died. Tried it again, died again. So I think that rules out anything downstream of pin 1 on the MFI relay.

Then I removed my rear seat and followed my 12v fuel pump hotwire cable the length of the car just to make sure it wasn't pinched or cut everywhere. It's fine.

I think something is causing a voltage drop on the MFI circuit. The only real change I made was my COP kit. I'm powering the coils with the same power wire that went to the stock coils. Chris said lots of customers do that. Alternatively I could hotwire that and see if it makes a difference. I would think with wasted spark eliminated and only 1 plug firing at a time it wouldn't be as big of a draw as the stock coils would have.

 

[white93gt]

So pin 1 of the MFI relay goes out to the engine bay, through the bypass, all the way to the back of the car where it triggers a relay for my fuel pump hotwire kit.

That’s what I originally thought when I read your first post and looked at diagram. What thru me off was in your post #35 where you said, “When I have a better measuring tool I'll try to grab the wire that runs to the fuel pump. That controls another relay for my fuel pump hotwire so I don't think it would cause much of a draw.” by saying controls another relay lead me to think the fuel pump relay was still in place.

I understand now that was as I expected to look like, just thrown off by wording.

 

[white93gt]

So during my lunch break I looked stuff over. I did find the ground wire running to my hotwire relay in the hatch was pinched.

What!!!!..... There you said it again..... another RELAY in the trunk.... So basically you just moved original pump relay from the engine bay to trunk and added a bunch of extra wiring. Maybe just me but modifying, re-engineering and complicating original wiring just adds places for problems to occur. Even though you just bypassed that relocated relay and confirmed your problem is not there, from our stand point these unknown modification makes it difficult for us to offer good troubleshooting advice. It also seems to make it harder for even you to trouble shoot.

I see you’ve also modified stock coils to COP. Is there any other modifications to stock wiring system we should know about?

 

[fastfalcon94]

That is how 99% of people add a hotwire kit for the fuel pump. They cut the original power wire to the fuel pump on top of the fuel pump assembly and use that to trigger an aftermarket relay that has a power source directly to the battery. Most people aren't aware about the relay under the hood (unless its failed for them) which was not used as a hotwire by the factory, but rather to determine if the fuel pump resistor should be used. It basically varies fuel pump speed with a high/low setting. Regardless of what speed its trying to run, the wire works fine to trigger a hotwire relay.

The AEM ECU doesn't output anything to the underhood relay. It remains in its naturally open state which means the resistor isn't used. Its essentially bypassed without doing anything as the 5 pin relay in its naturally open state acts just like a jumper wire. I could also bypass the underhood wiring by running my own trigger wire from the hotwire relay directly to pin 1 of the MFI relay. I could even bypass that half of the MFI relay entirely and let AEM use a low side output to trigger my hotwire relay. That's how my Supra is setup. But regardless what I do, I just ruled that part of the circuit with my test.

Tonight I'm going to temporarily power all my coils directly to the battery. Chris assures me it is not the issue, but I'm running out of tests to perform.

 

[white93gt]

That is how 99% of people add a hotwire kit for the fuel pump. They cut the original power wire to the fuel pump on top of the fuel pump assembly and use that to trigger an aftermarket relay that has a power source directly to the battery. Most people aren't aware about the relay under the hood (unless its failed for them) which was not used as a hotwire by the factory, but rather to determine if the fuel pump resistor should be used. It basically varies fuel pump speed with a high/low setting. Regardless of what speed its trying to run, the wire works fine to trigger a hotwire relay.

The AEM ECU doesn't output anything to the underhood relay. It remains in its naturally open state which means the resistor isn't used. Its essentially bypassed without doing anything as the 5 pin relay in its naturally open state acts just like a jumper wire. I could also bypass the underhood wiring by running my own trigger wire from the hotwire relay directly to pin 1 of the MFI relay. I could even bypass that half of the MFI relay entirely and let AEM use a low side output to trigger my hotwire relay. That's how my Supra is setup.

When you unplugged the original pump relay from harness plug and jumped pin 2 to pin 5 of harness connector, that alone did every thing you just explained without anything needing to be added or removed and no need for AEM output was then required. Simple and uncomplicated.

Just for curiosity where did you pickup power for wire you ran back to the hatch area? Not questioning because of the hatch relay, but wondering if the new wire attached at fuse box might be affecting power delivery from fuse box to MFI.

 

[fastfalcon94]

When you unplugged the original pump relay from harness plug and jumped pin 2 to pin 5 of harness connector, that alone did every thing you just explained without anything needing to be added or removed and no need for AEM output was then required. Simple and uncomplicated.

Right. The jumper wire is the simplest way to bypass the resistor if using stock ECU. If using AEM simplest way is to do nothing. I was still utilizing that underhood relay in its natually open state for 10 years without issue on AEM. I only made the 2-5 connector bypass as part of a recent troubleshooting step.

Just for curiosity where did you pickup power for wire you ran back to the hatch area? Not questioning because of the hatch relay, but wondering if the new wire attached at fuse box might be affecting power delivery from fuse box to MFI.

The power wire for the fuel pump hotwire relay goes directly to the postivie battery terminal. There is an inline fuse near the battery.

 

[fastfalcon94]

So I ran the power wire for my coils directly to the ABS fuse bolt in the engine bay (I have abs deleted) vs using the existing power wire for the coils. I let the car start up cold and it ran for 10 minutes without any issues. The voltage on the multimeter was actually 14.06v and never dipped on its own. Running both wipers, having headlights on, and car in reverse (reverse lights) voltage at the mfi relay dipped to 13.46v. I'm going to do a few more cold starts over the next few days and see if that fixes it. If so I'll need a nice hotwire relay in the engine bay for the coil pack. Chris from Rvenge has his setup this way. He said a lot of people run without it hotwired though. Maybe something else is going on with my mfi wiring as. I'm going to measure the resistance between coil power wire in engine bay and mfi relay.

 

[OhioSpyderman]

So, unless I'm reading this wrong, the problem WAS with the COP setup?
Chris has always been a great source of innovation and info. I would not question that...

Again, are you saying that this is solved?

If so, congrats.

You had the best troubleshooters helping you we presently have....

Bob.

 

[white93gt]

Be sure to remove the temporary ground from pin 5 of MFI (if you haven yet) to allow AEM to control fuel pump. That way you wouldn’t be over priming before start and AEM can shut pump off if engine dies (safety issue).

 

[bboyalan]

That is good to hear. It is a bit strange/unusual, but I suppose that every car is different lol 😅🤷‍♂️

My COP in sequential has been doing very well without a hotwire or amplifier and a good number of auxiliary bits running simultaneously. I also have a Mechman alt though.

Interested to see what else you find to conclude this.

-sent from my Galaxy Note 9

 

[fastfalcon94]

So, unless I'm reading this wrong, the problem WAS with the COP setup?
Chris has always been a great source of innovation and info. I would not question that...

Again, are you saying that this is solved?

Maybe. I'm cautiously optimistic. I still want to do some more tests. My multimeter seemed to indicate that voltage was dropping at the MFI relay. My resistance/continuity tests inside the car were good. The only way it didn't want to stall previously is if I had ignition power running straight to the MFI pin 5. Even then I'd see voltage drop some at the relay. Now with coil power hotwired the voltage at mfi relay seems to be slightly higher and doesn't drop. I still have some more testing to do in regards to where that ignition wire runs throughout the engine bay to the factory coils.

That is good to hear. It is a bit strange/unusual, but I suppose that every car is different lol 😅🤷‍♂️

My COP in sequential has been doing very well without a hotwire or amplifier and a good number of auxiliary bits running simultaneously. I also have a Mechman alt though.

Interested to see what else you find to conclude this.

Chris did say other users had his coil kit without the hotwire. Do you know what your dwell settings are? Do they match what Chris showed on his website? I do have an aftermarket alternator. I forget exactly what it is, maybe an Ace Alternator? I've had it for several years. I run a mono amp powering a jl10w7 and I have a 4 channel amp powering my speakers. Both fuses have been pulled as part of troubleshooting.

 

[bboyalan]

Yeah, they match his recommendation. Initially, I ran modified/increased values from a typical DLI setup, but that was only briefly. I have the Mechman 220A "set" for 14-14.5v-ish via its adjustment dial or whatever heh.

-sent from my Galaxy Note 9

 

[fastfalcon94]

After studying the service manual I believe there is some junction between the passenger dash connector D15 and the MFI Relay connector. That junction sends some wire off into the engine bay where I'm sure it splits more. One of those wires definitely goes to the factory PTU and the Factory Coil pack. I measured the resistance from the factory coil pack power wire to Pin 7 of the MFI Relay and it was slowly jumping between 1.2 and 1.5 ohms. It doesn't sound like a lot but it is definitely higher than any other wire I've measured. I don't know if that is normal or if that could be the problem. I'm going to try the measurement on my red 93 vr4 to compare.

Its also worth noting that the Ignition Switch also powers more than Fuse 12 (MFI Circuit). It also powers Fuse 11 (Combination meter, Combination gauge, ETACS unit, Speed sensor, Motor Antenna control unit, turn signal and hazard flasher unit, Auto-curuise control main switch, active aero control unit, SRS diagnosis unit, Auto-cruise relay) and Fuse 18 (back-up light, light automatic shut-off unit, SRS diagnosis unit). I did have both fuse 11 and 18 pulled as part of my earlier troubleshooting efforts and it was still stalling.

The "capacitor" is also interesting. I've always been told it was to help with radio signal. Its funny that it is on the same ignition power wire for the MFI system. One might wonder if its there as some kind of reserve voltage in between sparks. Although it seems too small to be useful. Mine still hooked up but its not seeing ground right now as I've got it dangling so I could gain more slack in testing the COP wiring. Originally it was bolted to the front head when I first experienced the stalling problems so I don't think that would be it... unless I somehow fixed the issue (say it was my fuse box and cleaning it helped) and it dangling now is somehow causing the exact same problem. I read some past threads where people said it made no difference and other people said their car wouldn't start without it.

 

[white93gt]

After studying the service manual I believe there is some junction between the passenger dash connector D15 and the MFI Relay connector. That junction sends some wire off into the engine bay where I'm sure it splits more. One of those wires definitely goes to the factory PTU and the Factory Coil pack. I measured the resistance from the factory coil pack power wire to Pin 7 of the MFI Relay and it was slowly jumping between 1.2 and 1.5 ohms. It doesn't sound like a lot but it is definitely higher than any other wire I've measured. I don't know if that is normal or if that could be the problem. I'm going to try the measurement on my red 93 vr4 to compare.

There is a common splice point #12 between D15 and pin 7 of MFI which is only point I can see where resistance could be increased, which you can see below D15 in your attached diagram. In that case I’d have to assume 1.2 – 1.5 ohms would be high. Since we’re talking about mostly solid wire with only other wires spliced to it, I’d expect to see an ohm reading of near zero, same as you get by touching meter leads together.

The "capacitor" is also interesting. I've always been told it was to help with radio signal. Its funny that it is on the same ignition power wire for the MFI system. One might wonder if its there as some kind of reserve voltage in between sparks. Although it seems too small to be useful. Mine still hooked up but its not seeing ground right now as I've got it dangling so I could gain more slack in testing the COP wiring. Originally it was bolted to the front head when I first experienced the stalling problems so I don't think that would be it... unless I somehow fixed the issue (say it was my fuse box and cleaning it helped) and it dangling now is somehow causing the exact same problem. I read some past threads where people said it made no difference and other people said their car wouldn't start without it.

As I understand it the capacitor is only to smooth spikes in power supplied caused by coils, to minimize ignition electrical interference from being pickup by radio reception. You could think of it a reserve I guess but its not needed for correct coil operation, so I can’t understand how someone determined their engine would start without it.

 

[fastfalcon94]

Thanks. I did some tests during my lunch break.

Multimeter leads touched together = 0.3 ohms
Ignition to MFI Relay = 0.3 ohms
ignition to ECU pin 82 = 0.3 ohms
ignition to coil power wire in engine bay = 1.5 ohms (0.3 ohms measured on 93 red vr4)
ignition to PTU power wire in engine bay = 1.2 ohms

I think I'm going to try and pull the MFI wire backwards through the wire loom to the factory fuse box area under the hood. Then I'll cut it there and check resistance. Hoping its just some corrosion near the end. If not i'll have to run a new wire inside the car. I think I'm going to end up hotwiring a relay under the hood too for piece of mind.

 

[white93gt]

I think I'm going to try and pull the MFI wire backwards through the wire loom to the factory fuse box area under the hood.

I’m little confused by you pulling MFI wire backwards thru wire loom, since you’ve identified area of wire with high resistance as being from D15 to coils & PTU, not from MFI to D15. To me it’s almost certainly at the splice joint of that wire or broken internal wire strands, from coil/ptu end to D15.

Edit: An after thought, just remembered while helping someone with a little different issue about power at coils IIRC. I seem to remember him mentioning finding a spliced joint not far from coils of that Black/white wire, not sure if that’s splice #12 shown in diagram or not but worth a look.