My PMO ITB Project

[Trog]

Originally Posted by brads911sc

I verified this AM that I have full time 12V when needed and 12V only when in Run/Crank Position when needed. Both at fuse area and on relay board.
So my EFI is overriding the ignition switch? Any thoughts?
After I start the vehicle, I get power at both "on" all the time and "switched" as expected.
When I turn off the ignition, I get 11 volts at switched power. Enough to run the ECU. For some reason the act of turning on the car wrecks havoc on the switched power.
Merely turning the key into the Run position, does NOT do this.
Thoughts?

I experienced a similar electrical problem with this ITB upgrade. Although the engine starts up easily, it won’t stop. There are many Pelican threads on this subject, with different solutions. In my case, when I turned off the ignition, the “BATT” warning light illuminates and the TECgt and its associated fuel relay remained powered. Seems the alternator was back-feeding through the “BATT” warning light.

The Bentley manual shows a diode in the circuit to prevent this backflow. The Haynes wiring diagram states that in 1984, only the Turbo model has the diode. I searched for it, but couldn’t find it.

In any case, I installed a #1N5820 diode as shown below, now the engine shuts off without any hesitation. If you’ve experienced a problem similar to mine, this may be your solution.

[brads911sc]

Yes. I saw that in your post. In mine, the charge light is not on.

Is there a way to test?

Originally Posted by Trog

I experienced a similar electrical problem with this ITB upgrade. Although the engine starts up easily, it won’t stop. There are many Pelican threads on this subject, with different solutions. In my case, when I turned off the ignition, the “BATT” warning light illuminates and the TECgt and its associated fuel relay remained powered. Seems the alternator was back-feeding through the “BATT” warning light.

The Bentley manual shows a diode in the circuit to prevent this backflow. The Haynes wiring diagram states that in 1984, only the Turbo model has the diode. I searched for it, but couldn’t find it.

In any case, I installed a #1N5820 diode as shown below, now the engine shuts off without any hesitation. If you’ve experienced a problem similar to mine, this may be your solution.

[Trog]

Originally Posted by brads911sc

Yes. I saw that in your post. In mine, the charge light is not on.

Is there a way to test?

Remove the charge light when the engine is running. If the engine dies, you need a diode.

[brads911sc]

Great Trog. Ill check that and report back. Thanks.

Originally Posted by Trog

Remove the charge light when the engine is running. If the engine dies, you need a diode.

[brads911sc]

Its not backflow. Disconnecting the light in the guage had no impact. Other ideas?

[DUK]

I'm going to throw my .02 in here. I have an MS3 running extra. I had some initial problems and it was a simple wiring error. I'm sure that with JN's help you have covered all of this but just make for certain all the relays and grounds are right. Maybe show a diagram of your setup to help us help you.

[Trog]

Originally Posted by brads911sc

Its not backflow. Disconnecting the light in the guage had no impact. Other ideas?

A schematic would be helpful.

[Jeff Alton]

Why don't you just wire and switch, maybe hidden for theft protection, on the main power to your ECU. Hit the switch, and the motor will stop, right now. I assume your ECU triggers your fuel pump relay as well so this will take care of it. Plus, you have some extra built in theft protection.....

Knowing I was not going to use my key to start my car, I have a master toggle for ECU and a second toggle that can take just the fuel pump out of play (for fiddling with the ECU when the engine is not running) and a push button starter.

Cheers

[dfink]

Depends on how your relays are wired and if you are switching the ground or the power. Some relays are self holding. Meaning that if you switch the power to pull in coil for the relay then when it turns on it holds itself in the on position even after the power to pullin coil is switched off. This is not the main power to the relay but the pullin line. If you switch the ground when you turn off the switch the relay has no choice but to release. I don't recall the numbers on the relay now but just make sure you are breaking the ground and not trying to break the line to the pull in coil.

[brads911sc]

Ok. Now throughout this "run on" fiasco... i noticed that after i turned the key on to run the fuel pump, and then off (without running car) that my fuel pump would run-on a few seconds. I also had a scenario where the fuel pump would not shut off even though wired through the relay board and ECU to shut off if the car didnt start. The switched wire I was using was the switched fuel pump wire that tied into the CIS over at the wiring harness.. so i suspected something in the fuel power circuit. I also tested all the switched power connections (fused fan /defog in engine bay, test wire at o2 control module) and all of them had the continued but reduced power (about 11 volts) with the ignition shut off. Also for the car to keep running, I needed power at ECU, Spark (MSD), and Fuel. Highly unlikely that everything in the car i tested was bleeding through my relayboard/ECU. This would be especially true of power to the fuel pump since it would need to go through the relay to get power to the fuel pump. It was also unlikely it was relay wiring, mis-wiring, fuse-wiring, because everything ran through a prefabricated relay board that was pretty idiot proof. I swaped out the red fuel pump relay with a plain old black one and my problem is solved. Dont ask me how I thought to check that except that I knew my electrical issue seemed to be in the fuel power circuit. Ill order a new red one... thanks for the help problem solving. you guys are great!

[dfink]

If I remember correctly one color is the self hold type and the other is not. It is a simple of matter of a small loop-back wire inside the relay. It is still a good idea to switch the ground side of the relay insead of the power side.

[brads911sc]

I think switching the power vs ground is a function of the relay board. It has 4 fuses, 3 relays all built into the prefab'd board. All you do is solder on ground, power, and switched power and screw in the wires to the sensors and injectors and youre done. not sure you could or need to do your own thing on this setup. i dont have a switch on power or ground. its all in the board...

Originally Posted by dfink

If I remember correctly one color is the self hold type and the other is not. It is a simple of matter of a small loop-back wire inside the relay. It is still a good idea to switch the ground side of the relay insead of the power side.

[brads911sc]

[Jeff Alton]

If that is the case it must get its 12V+ from a single source right? Put a switch, of correct amperage, in that circuit.....

Cheers

[dfink]

I understand that you are using the relay board but you also must still an original fuel pump relay. The old round type as you indicated that is what you changed to make the system work. Here is what I see as happening I will use points 30, 86, 87 that relate to the connections on the relay. (30) is the main power to the relay. The relay board for the ECU would put power to the pull in coil to the fuel pump (86) when the car started. This would apply power to (87) the output of the relay to the fuel pump. Because the relay was self hold as soon as it made contact an internal wire then connected (86) back to (30) because (30) always had power this held the coil in even when the outside power to (86) was removed. The reason the voltage was lower was because the ECU was only seeing the power that could go through the small wire on the relay From (30) to (87) back through the relay and small wire to (86). In this case I assume (86) to be the wire from the CIS control box that would have originally controlled the fuel pump.
There are other placed to get switched power. But you have to keep in mind the switch has several outputs. One has power at switch position 1 & 2 but not during crank. One has power at position 1 & 2 plus crank. And one has power at only position 2 & crank. Then of course the yellow one only has power during crank. The line you really want to find to feed the ECU is the one that provides power only at position 2 and crank. Get this power right after the switch not from some line that comes from someplace that happens to have power. You don't know where that power has been
I would move the power connection from where you have it and connect directly to the switch.

[brads911sc]

Thanks for the explanation. That makes sense. So I probably do not have a bad relay, I just have it all wired together which allows the ECU to draw power through the hold wire... The standard black relay doesnt have the small black hold wire so its why it worked.

Question, Why cant I just use the black round relay without the internal wire and call it a day? Is there a reason you wouldnt want all these wired together? I have them on a circuit breaker so not worried about the current load.

I had originally used the old CIS fuel pump power/cut-off because its where TBitz tapped in for his kit as well, so I figured I wouldnt reinvent the wheel. At this point I have the Hot Switched Power, the MSD, the ECU and the fuel pump relay wire all together. This is obviously not going to be a long term solution if I want to keep stock wiring and have my key work.

i was reluctant to tap directly into the ignition switch. Is that is what you are proposing? what about from the front fuse panel? would that be better?
In looking at the bentley it appears that 15 off the ignition (red/black) is hot at the right time. It goes to Fuse 12 and runs the Fresh Air Blower and Rear Window Defogger Switch. Would this be an ok wire to tap into? Could I also tap into the fuel circuit power pre-relay at the fuse panel (Fuse 11)? Appears that Fuse 11 and 12 both share power from the Red/Black (15). Fuse 16 and 22 also have the right power, however 12, 16, 22 are all pulling power from Fuse 11 entry wire.

Thanks in advance for all the advice.

Brad

Originally Posted by dfink

I understand that you are using the relay board but you also must still an original fuel pump relay. The old round type as you indicated that is what you changed to make the system work. Here is what I see as happening I will use points 30, 86, 87 that relate to the connections on the relay. (30) is the main power to the relay. The relay board for the ECU would put power to the pull in coil to the fuel pump (86) when the car started. This would apply power to (87) the output of the relay to the fuel pump. Because the relay was self hold as soon as it made contact an internal wire then connected (86) back to (30) because (30) always had power this held the coil in even when the outside power to (86) was removed. The reason the voltage was lower was because the ECU was only seeing the power that could go through the small wire on the relay From (30) to (87) back through the relay and small wire to (86). In this case I assume (86) to be the wire from the CIS control box that would have originally controlled the fuel pump.
There are other placed to get switched power. But you have to keep in mind the switch has several outputs. One has power at switch position 1 & 2 but not during crank. One has power at position 1 & 2 plus crank. And one has power at only position 2 & crank. Then of course the yellow one only has power during crank. The line you really want to find to feed the ECU is the one that provides power only at position 2 and crank. Get this power right after the switch not from some line that comes from someplace that happens to have power. You don't know where that power has been
I would move the power connection from where you have it and connect directly to the switch.

[brads911sc]

I know this seems like a weird situation, but I decided to clean the contacts for the red relay. Sprayed it with electrical contact cleaner, pluged in the red relay... and it works fine... with the red relay... not sure that I need to go about rewiring all of this now...

[jpnovak]

Brad, The fuel pump run-on should last 3 seconds. This is the typical prime pulse for MS systems. It sounds like your relay had some trouble releasing the contact. I see no reason to change the wiring now that the relay board is working properly.

Now GO TUNE THE CAR! Its a nice day for a drive here in Austin.

[brads911sc]

Thanks Jaime.

Think I am still off on idle. Are poeple really getting AFR's in the 13.5-14.5 range at idle? Couldnt initially get AFR past 10.5... very rich... Realized i had synchronization problems. I closed each screw, then opened each screw on the base of the throat two turns, then synch'd each bank to the others on the bank and synch'd the two banks together at 900 RPM's. AFR went up to 11.4-11.6. Im getting about 4 on each throat with the synchometer. sound right?

Tomorrow Ill take it to 3k RPM and make sure my linkage is right. I did it early and i got some serious hestitation at accel... youre right weather is perfect. 63 degrees and sunny.

Originally Posted by jpnovak

Brad, The fuel pump run-on should last 3 seconds. This is the typical prime pulse for MS systems. It sounds like your relay had some trouble releasing the contact. I see no reason to change the wiring now that the relay board is working properly.

Now GO TUNE THE CAR! Its a nice day for a drive here in Austin.

[gsmith660]

My idle AFR is around 13.2 this summer I want to get it to 14. But I am not using ITB's.