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1G No power to ECU

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knochgoon24

DSM Wiseman
6,135
92
Jan 29, 2008
Troy, Michigan
I guess my question is, what can cause the ECU to not have power, or to not turn on when starting the car? Can those with experience check my plan below? As long as we don't get too much rain tomorrow, I plan to run through this list to troubleshoot.

It's been a while, but I'm starting to get back into the DSM game.

Picked up a 91 Talon 2.0 NT (absolute base model) last night with a no-start issue.

I've traced it back to the ECU not getting power... and then it got too dark out to work further. The MPI relay checks out all right. I also have power on fuse #19. Pulling that fuse kills the interior lights.

This is what I have so far:
Step 1:
-Check for 12v on ECU pin 103 at all times. This is ECU backup power from fuse 19.
(If there is no power here, it's a broken wire between fuse 19 and the ECU.)

Step 2:
- Check for 12v on ECU pin 110 when Ignition Switch turned to RUN.
(Power come from Ignition Switch pin 4. Can check for this power by checking for power to fuses 11, 12, and/or 18.)

Step 3:
- At this point, ECU pin 63 should get pulled low, pulling MPI pin 8 to ground, closing that circuit.
(If not, check ECU grounds. ECU pins 101, 104 (MT), 106, are to ground. If those have ground and still no go, then ECU is bad. -- Try grounding MPI pin 8 to see if ECU boots. --> Confirms ECU bad.)

Step 4:
- Now there should be 12v on ECU pin 107 from MPI pin 4, and ECU pin 102 from MPI pin 5.
(MPI relay bench tested fine, so this shouldn't be an issue.)

Step 5:
-When ECU boots, CEL should light for 4 seconds, or stay on if CEL is present.


Other notes:
-When ignition switch is turned to START, ECU pin 108 should see 12v from ignition switch.
- ECU pin 56 controls MPI pin 7.
- ECU pin 64 is the "check engine light" output, in case the bulb is just blown out. This pin gets pulled to ground.
- Pins 17 and 24 are sensor grounds.
 
I did! Thanks for that awesome post.

I opened the ECU and only saw the tiniest sign of what may be a cap leak. I struggled to get a good photo. It only looked to possibly affect these 3 solder joints (mainly the middle pin of that green MOFSET(?).
If I have power coming to the ECU, and it leaves this as the only culprit, I'll replace the cap. I'll probably still replace all of them eventually, but it really didn't look that bad.
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Change all three out. You'll need to clean and inspect the circuit traces since that cap usually leaks under the heatsink and eats the traces where the orange EMI filters are.

There is also a ISC circuit trace that runs under that capacitor that is usually damaged when the cap leaks.

The green transistor is the pass transistor for the +5v voltage regulator.

The white board to the lower center controls switching the MPI relay on. Either a trace is open or the driver transistor for the MPI relay coil on it is blown.
 
Oh fun. Here's a better photo of the damage that can be seen.
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Now for a recap of the results.
Step 1:
-Check for 12v on ECU pin 103 at all times. This is ECU backup power from fuse 19.
(If there is no power here, it's a broken wire between fuse 19 and the ECU.)
Got power.

Step 2:
- Check for 12v on ECU pin 110 when Ignition Switch turned to RUN.
(Power come from Ignition Switch pin 4. Can check for this power by checking for power to fuses 11, 12, and/or 18.)
Yep. Check.

Step 3:
- At this point, ECU pin 63 should get pulled low, pulling MPI pin 8 to ground, closing that circuit.
(If not, check ECU grounds. ECU pins 101, 104 (MT), 106, are to ground. If those have ground and still no go, then ECU is bad. -- Try grounding MPI pin 8 to see if ECU boots. --> Confirms ECU bad.)
MPI pin 8 does NOT get pulled low. Shorting MPI pin 8 to ground makes it so the car starts and runs. However, the seized alternator and very hard to turn water pump forced me to shut down quickly as the belt turned into a billowing cloud of smoke. I cut the belts and it ran fine long enough for me to figure that's the problem.


Step 4:
- Now there should be 12v on ECU pin 107 from MPI pin 4, and ECU pin 102 from MPI pin 5.
(MPI relay bench tested fine, so this shouldn't be an issue.)
Since the MPI jumper worked, I didn't even check this.

Step 5:
-When ECU boots, CEL should light for 4 seconds, or stay on if CEL is present.
The CEL stayed on.


I guess my next task is to track down some new caps. I'll have to check the stash I have on hand. I'll check at work as well. Otherwise, I guess I have an order to place with Digikey.


Thanks for the help Steve. I tried to decipher the TSM, but those wiring diagrams aren't always the most clear.
 
Some searching has led me to this thread.

Helping a buddy that just picked up a 90 AWD talon. The car will not start. Test the MPI, seems to operate fine. No 12 volts to the CAS. If we jump the red CAS wire, everything seems fine and the car will start. (although we didn't let it idle since the car was sitting for 10 years and needs other work.) Without jumping the red wire, there is no power to the ECU and other corresponding items that the MPI sends power to. After testing a few of the pins, the only issue we are having is getting 12 volts to pin 110. This is supposed to "activate" the MPI and turn everything on, including the ECU. However, we are getting nothing to pin 110 with the key turned. Pin 103 does have voltage, always. Fuse 19 is fine. Battery terminal fuses are good. Kinda stumped here. Why did everything run fine when the CAS was jumped, but nothing otherwise? We are thinking the wire at pin 110 is shorted. Thoughts?
 
If the wire to pin 110 was shorted you would blow a fuse or melt a wire in the ignition circuit.

Go back to the ignition switch and check there (black/White) making sure when the switch is in run or start that your seeing 12v. This switch contact also feeds junction box fuses 11, 12, and 18. You can also check that you get 12v at the coil back (pin 4 on a 90 Black/White wire) and pin 3 of the MPI relay (Black/White)
 
If the wire to pin 110 was shorted you would blow a fuse or melt a wire in the ignition circuit.

Go back to the ignition switch and check there (black/White) making sure when the switch is in run or start that your seeing 12v. This switch contact also feeds junction box fuses 11, 12, and 18. You can also check that you get 12v at the coil back (pin 4 on a 90 Black/White wire) and pin 3 of the MPI relay (Black/White)


Thanks for the tips. I talked to my buddy yesterday and after he described the issue to the guys over at ECMlink, they are claiming the circuits for pin 63 (pulls down voltage when 110 is high) is damaged and the ecu needs to be repaired. Sounds about right I guess. I'll update this thread when we get the ECU back.


Fuses 11, 12, & 18 all checked out fine. We tested so many damn pins and wires (many ideas coming from your posts) including testing the MPI relay on a bench and the only thing we found out of wack was no voltage at pin 110 when the key is turned. Hopefully ECMlink guys are right. (I would think so.)
 
Yes, ECU looked fine to our untrained eyes. However, Ecmlink claims the ecu was more damaged than they anticipated. Anyway, ecu is back and motor runs. :) Now back to fixing everything else on a car that sat 10 years. Lol
 
Yes, ECU looked fine to our untrained eyes. However, Ecmlink claims the ecu was more damaged than they anticipated.

I'm not surprised, not having seen the ECU. If it was pulling pin 110 low there was more going on than typical.
 
Looks like the trace from IC110 that goes to pin 63 to pull the MPI coil down might be corroded away where I circled.

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WE HAVE A WINNER, FOLKS!!!

Got the area cleaned up, and this is what I found.
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Otherwise, the other 2 caps werent leaking... yet.
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I'm guessing that running a jumper wire from the pin where IC110 connects to the main board to pin 63 is a reasonable way to fix this.
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Yep, If it hadn't corroded so close to C38 I would have scratched off the solder mask and fixed the trace with wire wrap wire but running on the bottom will work.

Make sure you check the ground trace between C106 and C37 and the ISC via between the + and ground that under C106. You can see where it was shorted to ground from the leakage.
 
Well, it runs. Steve, I'm so glad I had your help. If you're ever in Detroit, let me know... I owe you a few beers.

This is what I went for as a fix to the first issue. I now get power to the MPI relay.
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This was the next issue. When I scraped off the solder mask, it became clear that there was a gap in the trace. I had some trouble trying to bridge it with just solder, so I used a piece of lead clipped from one of the caps. I also double checked that it there wasn't still a short under C106. I get >1M ohm resistance now.
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She runs. the alternator is seized, so there's no belt (hence the light). I still get a warning light for coolant level. I need to see what that's about, since the bottle is full. Probably just a fouled sensor.
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I had enough time to give it a wash as well. Previous owner said that the headlight motors were both toast. Turns out, they were adjusted incorrectly. Both work fine.
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And it doesn't even look too bad inside. I'm getting some dampness in the driver's foot well. I'm not sure if it's from power washing the engine bay, or if it's from somewhere else. TBD.
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So all is not well in ECU-land. I've been chasing idle issues since the fix, but for most of the time, I've been able to live with a high idle when cold, and a slightly low idle when hot. When I autox'd it, I'd just turn the BISS to set a high idle (cheap dino oil didn't like autox, and pressure was low at idle).

As the weather gets colder, the idle has been more and more of a pain, so I started trying to fix it. I just rebuild the TB with a kit from Brian (awesome kit, BTW), and that didn't help. Swapped ISC's with a known working spare, didn't help. Checked for vacuum leaks, didn't help. So I finally pulled the ISC out of the TB and watched it during a key-on. It just twitches. Opened up an ISC and screwed it all the way back in, fired up the car, pulled it back out... it didn't move. Did the same with it screwed all the way back out.

So I'm thinking that one of the ISC drivers is dead. Since it twitches, I think at least one is working. REALLY wish I had a 4-ch scope right now. Might do something silly with a breadboard and and Arduinio to see what's up.

I'm guessing one of the ISC drivers was damaged.
 
My ecu is currently on route to ECM Tuning. I could never get the isc to sit still in link at 30 and it was also buzzing when the car was off along with the mpi relay. I tested the resistance in the isc coils and they were good but the thing just lightly twitched when I turned the key on. I then opened up the ecu and some of the ic drivers looked like they had damage. Hopefully ecm tuning can fix it and therefore fix my idle problem. I feel your pain.
 
So I'm thinking that one of the ISC drivers is dead. Since it twitches, I think at least one is working. REALLY wish I had a 4-ch scope right now. Might do something silly with a breadboard and and Arduinio to see what's up.

I'm guessing one of the ISC drivers was damaged.

Either a driver, one of more of the traces from the drivers to connector, or both. I'd start by measuring the traces from the ECU connector back to the driver pins. I can see plenty of corrosion still and suspect that if you removed the metal heatsink there would be more under it where the EMI filtering is. (orange capacitor arrays)

About 25% of the ECU's I saw had damage to the ISC circuits and no visible damage to the drivers. Found both damaged traces and drivers that couldn't pass enough current to activate the ISC.
 
Either a driver, one of more of the traces from the drivers to connector, or both. I'd start by measuring the traces from the ECU connector back to the driver pins. I can see plenty of corrosion still and suspect that if you removed the metal heatsink there would be more under it where the EMI filtering is. (orange capacitor arrays)

About 25% of the ECU's I saw had damage to the ISC circuits and no visible damage to the drivers. Found both damaged traces and drivers that couldn't pass enough current to activate the ISC.

I was going to buy another ECU off eBay to have on hand for parts, and I've now had 2 deals fall through because they opened the case and saw nothing but acid damage. At least both pulled the listings.

I'll pull the ECU and start ohm-ing traces. I suspect you're correct. I didn't check all the traces before. And looking at some of the photos of those traces, I could definitely done a better job at cleaning up around some solder pads. At least I got my other car fixed and back on the road. I can take my time fixing this issue.
 
Step 2:
- Check for 12v on ECU pin 110 when Ignition Switch turned to RUN.
(Power come from Ignition Switch pin 4. Can check for this power by checking for power to fuses 11, 12, and/or 18.)
would you be able to speculate why fuse #18 and #12 would not have 12V on it? I checked my fuse and I got 1V on #18 and 9V on #12... which ultimately gave me 9V going to ECU pin #110.
This question is related to a problem I am trying to solve right now:
no spark, no CEL
 
Either a driver, one of more of the traces from the drivers to connector, or both. I'd start by measuring the traces from the ECU connector back to the driver pins. I can see plenty of corrosion still and suspect that if you removed the metal heatsink there would be more under it where the EMI filtering is. (orange capacitor arrays)

About 25% of the ECU's I saw had damage to the ISC circuits and no visible damage to the drivers. Found both damaged traces and drivers that couldn't pass enough current to activate the ISC.

Sorry to resurrect and hijack an old thread but the photos and content here are hugely useful for me. I have a JDM Galant VR4 (E39A). I replaced the 3 large caps a few years back but I never actually finished getting the car back on the road. there was some damage due to the caps leaking but I thought I had caught it all. Now looking at the pics in this thread I have realised I am missing C37 completely. The pads are gone and the short trace to the via next to the c37 label is damaged too.

Can anyone confirm the rating of C37? I will aim to replace it and connect the via with a little bit of lead much like the repair in the thread (but 180 degrees opposite direction).

What does the circuit C37 is part of actually do?

@steve you also mentioned the via and trace under C106 being ISC related. I am having problems with idle seeking and stalling once in closed loop so will start investigating this connection. Is it just a matter of making sure there is no continuity between the via and the pins of C106?

As I mentioned, this s a JDM ecu so there are a couple of differences to the USDM boards, for example, I don't have a C34 next to C37.

First time posting here but man, there are some really useful threads on this page and the knowledge of these cars that you guys have is phenomenal!

Thanks in advance
 
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