Resolved 2G No power to PTU

[v8s_are_slow]

Replaced engine and then was only running on 2 cylinders on first start. Trying to diagnose and now for some reason, no power to the PTU at all. PTU has been tested and is good. Just no power going to it. Checked fuses under the hood. Fuel goes to the rail though so assuming MPI isn't the issue.

Where does the power wire go to on the other side of the harness so I can check for continuity? Thanks!

 

[luv2rallye]

For 2g turbo: https://www.dsmtuners.com/threads/ptu.340317/#post-151903320

 

[steve]

Are you back to stock now?

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You have had all sorts of ignition related problems in the past.

https://www.dsmtuners.com/threads/removing-stock-ignition-module-ignitor.75456/#post-153879534

https://www.dsmtuners.com/threads/wiring-in-ptu-pigtail.543188/

https://www.dsmtuners.com/threads/m-w-pro-12-wiring.533148/#post-153847401

https://www.dsmtuners.com/threads/2g-diagnosing-no-rpm-signal.536714/

 

[v8s_are_slow]

Back to stock ignition at the moment, but this has been an intermittent, REALLY annoying issue. Thinking I have a short somewhere. I have power at the ptu now, but no fire on 1&4. I've replaced the one coil. I've tried multiple ptu's. Tested the cas and crank sensors. Tested for signal at 10 & 23 at the ecu and all is well there. I had spark at 1 & 4, and then put the manifold and injectors back on, then no fire.

I've done this 3 times now thinking it was fixed and it wasn't. Gonna maybe replace some of the wires I guess (because I don't know what else to do) and try again I suppose. I HATE electrical issues.

 

[luv2rallye]

Remember 10 and 23 have a very short duration positive pulse (+0v to 5v) that you might not see w/o an analog meter or oscilloscope. However at idle they average 0.34vdc (0.70vac). However at cranking it's so short you probably won't even see it w/o an oscilloscope. You can unplug the PTU and with key on, briefly touch PTU pin 1 (blue/black) to ground for 1 second. Then remove the wire and plugs 2,3 should fire (this is what the PTU does). Then do same with pin 8 (black/white) for plugs 1,4.

Just thought of something. Pin 8 (black/white) turns into a blue/red at the engine speed detection connector (A-59) on the firewall (both on the same side of the connector half on same pin). Perhaps it's disconnected or intermittent. This wire controls plugs 1,4.

 

[v8s_are_slow]

I used a test light and it flashes.

 

[luv2rallye]

It flashed with it on what pin?

 

[v8s_are_slow]

10 and 23 at the ecu

 

[luv2rallye]

Ok put the test light on PTU pins 1 and then 8 (with them still connected to the coil) to see if it dims slightly while cranking. Do pin 1 first to see how the light should dim, then compare to pin 8. They each get +12v through the coil primarys but the PTU should bring them to 0v briefly to fire the plugs.

After further thought, this won't tell you where the problem is. You probably don't even have +12v on pin 8. If you do not, you'll have to test for continuity from there to the coil's pin 2 (blue/red). Wiggle the wires as you test and examine that A-59 connector plug (remember those 2 wires go into the same side of the connector half on same pin just to change wire colors - the other half of the connector won't even be there).

If have solid continuity, you may have a bad coil.

 

[v8s_are_slow]

Can't remember what exactly I tested at the wires and how. A bit sleepy. Needed a break today though before I decided to light it on fire. I'll report back though.

 

[luv2rallye]

Ok. I'm going on vacation and won't be back for a week. Tomorrow re-read my posts 5 and 9 and look at Steve's diagram in post 3. Steve will help you as he's also an electrical guru - so continue with him.

 

[v8s_are_slow]

I'm so annoyed. I ran a wire from the ptu plug to the coil plug to bypass the original wiring for the coil that fires 1&4, and it FINALLY fired up for the first time with this new engine on all 4 cylinders. Great, now let me pull the bypass wire off, pull the intake manifold and injectors off and cut out that portion of wire and replace it. I do that and get it back together. I still have fire on 1&4 finally, but now none on 2&3. !?!?!?!?!

So I pull the manifold and replace the other wire just for the heck of it and put it back together. Now I have NO fire on ANY cylinder. I have 12+ volts to all points on the back of the coils. I have 12+ volts at the #6 pin at the plug on the ptu. But I also have 6+ volts on the tach wire from the ptu plug which is pin #4. Is that normal? Is there a way to test the MPI relay??? Omg this car will be the death of me.

 

[19Eclipse90]

The test procedure is at the bottom of @steve Steve’s article: 2G basic MFI/MPI relay circuit function

 

[v8s_are_slow]

Thank you. I'll check that.

 

[v8s_are_slow]

Thinking about it, would the MPI relay even be bad if the fuel pump is turning on when starting? And is it normal for Pin #4 (tach wire) at the PTU plug to have 6 volts with the PTU disconnected and just testing for voltage at the plug? Just trying to think of all possibilities to check for later, when I'm not so tired.

No idea why it would fire on 2&3, replace one stupid wire and then fire on 1&4 but not 2&3. Replace the other wire and no fire on any, and my brain is too tired to think of this garbage. Electrical kills me and yes, it's been an ongoing issue that's driving me insane. It takes me a good while to wrap my head around how all this electrical stuff works.

 

[v8s_are_slow]

No fire at pin 10 at the ecu now for some reason. This ecu recently came back from Ecmlink but anything else aside from the ecu that y'all can think of that would be causing the issue? Maybe that's why I'm pulling my hair out.

 

[steve]

I'm very uncomfortable using test lights on ECU circuits. Any incandescent bulb draws more current than many transistor circuits are designed for. But that's me.

Lets take the ignition circuit apart.

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A large part of these diagrams is information on the wiring, what color, how big, from where to where. But much of the magic here depends on the 4 NPN transistors, two the the ECU and the two in the PTU that switch the current going through the coils to charge and fire them.

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An NPN transistor works by making the Base (B) more positive in voltage than the Emitter (E) and once you do so, current flows from the Collector (C) to the Emitter possibly causing a voltage drop at the Collector. So when using a NPN transistor as a switch a positive voltage at the Base causes a drop in voltage at the Collector.

Looking at the ECU transistors you see that the Base is connected to somewhere else in the ECU circuits, the Emitter is connected to ground and the collector is connected to a resistor and to the Base of the PTU transistor. The resistor is connected to a power supply (likely battery voltage since they don't specify) this causes the collector to be at that voltage when nothing is present at the transistors Base. When a signal is present at the Base the Collector switches on and pulls the voltage from the resistor to ground. That resistor limits the current and keeps the transistor from releasing it's magic smoke.

Looking at the PTU transistors you see that the Base is connected to the ECU, the Collector to the coil and the Emitter to ground via pin 3. When the ECU provides battery voltage to the Base of the PTU transistor in the it provides a path for current to flow from through the coil through the Collector to the Emitter to ground charging the coil. When the ECU turns on it's transistor the PTU transistor not longer has a voltage at it's Base and current via the Collector is cut off causing the coil to fire due to the magnetic field in the coil collapsing.

The transistors on the ECU are much smaller than those in the PTU because they only have to pass the current from the resistors on the collector, (until you stick a light bulb in there) where the transistors in the PTU have to pass the large currents needed to charge the coil.

Based on thinking that through I would expect to see battery voltage at ECU pins 10 and 23 when it's charging the Coil (dwell) and 0v the rest of the time. If you look at the PTU Collector connection to the coil you would see battery voltage most of the time, a short drop to ground while the coil charges and a huge voltage spike after when the coil fires.

Only on my second cup of coffee this morning so there's a higher chance than average for mental errors. Question anything you don't understand or don't agree with.

 

[v8s_are_slow]

Well, currently my thinking is that my ecu is just being funky and working when it wants to and pin 10 not firing at the moment.

Pin 4 at the ptu has me scratching my head as well because I thought the voltage would vary and be sent TO the ecu. Not showing 6 volts from the ecu on that pin. Can anyone confirm?

Key on last night and not running, my isc on the throttle body was very warm which seems very odd as well.

 

[v8s_are_slow]

Just an update but I've sent the ecu in today to get checked out.

 

[v8s_are_slow]

ECU tested good. So back to the drawing board while I wait for its return.

 

[v8s_are_slow]

Had an engine fire a few years ago. After digging and digging, I found a wire that I missed for the power to the CAS that was pretty beat up looking. Gonna replace that portion and then hopefully be good to go. Crossing fingers.

 

[chrisman287]

Had an engine fire a few years ago. After digging and digging, I found a wire that I missed for the power to the CAS that was pretty beat up looking. Gonna replace that portion and then hopefully be good to go. Crossing fingers.

I had a bad wire also on my CAS adapter harness (I’m 6 bolt swapped). Got me going after fixing it.

 

[v8s_are_slow]

I finally fixed that wire, but when I rotate the cas by hand, no flash of the noid light I have in the #4 injector plug.

I checked voltage and that's at 12 volts at the cas. But have 5 or 6 volts at the signal wire that goes to pin 88. With it unplugged from the cas. Can ANYONE tell me if this is normal or why I might have voltage at that wire for pin 88?

 

[steve]

Are you using a 1G CAS or a 2G Cam and Crank Sensors?

In either case the sensors get 12v from the MPI circuit (1.25 Red wire) and a ground (1.25 Black wire). The other two wires (either together from a 1G CAS or from each sensor on a 2G) are signal wires that the ECU pulls up to 5v using a resistor inside the ECU. The sensor(s) pull the voltage to ground to signal to the ECU. So with the ECU turned on you should see 12v on the red wire, like you are, and 5v at pins 88 and 89. Those pins should toggle between 5v and 0v as the engine turns over.

With the sensors unplugged what your seeing sounds normal as long as the ECU is turned on to provide both the 12v MPI power and the 5v pull-up power.

 

[v8s_are_slow]

Thank you! Been struggling to get that answer from anyone and didn't wanna put this sucker back together until I was sure.

Oh, and 98 sensor with Kiggly 2 tooth trigger plate on the crank with 98 cas sensor there as well.