1G 1990 GSX ECU exploded, replaced, Now car won't start

[PangguloCrew]

Car: 1990 GSX M/T
Problem: ECU exploded (Blew a Capacitor), was replace with a known working 90 M/T ECU and Car won't start.

The topic sorta says it all. Basically my car was idling, I stepped inside my house, came outside the car wasn't running. I opened the door and smoke came billowing out.

After the smoke cleared I pulled the ECU opened it up and it was charbroiled. .

Had a known working ECU and plugged it in and the car would crank but it won't start.

Is there anything else that could have been cause when the ECU blew? Is it possible it could have jumped timing? I checked all the fuses under the dash and under the hood. Am I missing a fuse some where?

Thanks for any help.

 

[huafist]

How did the ECU "blow"? Did a capacitor explode or something else? You should've found the reason for the ECU's failure before plugging another one in - chances are you fried another one.

 

[PangguloCrew]

How did the ECU "blow"? Did a capacitor explode or something else? You should've found the reason for the ECU's failure before plugging another one in - chances are you fried another one.

Capacitor blew. I know I didn't mess up the other one because we put it back in the donor car and it still runs.

 

[talon1987]

i would check for fuel and spark


-Pat

 

[steve]

I'd check to make sure the new ECU powers up in the car before I'd go chasing anything else.
The car will crank with a dead ECU but it's not going to start.

If the ECU is powering up and running it will turn the CEL on for 5 seconds when you turn the ignition on and the factory boost gauge will go to zero. If that doesn't happen then you start checking the wiring and fuses back to the battery until you find why it's not working.
That means you'll need the wiring diagram for your car.

Steve

 

[PangguloCrew]

I'd check to make sure the new ECU powers up in the car before I'd go chasing anything else.
The car will crank with a dead ECU but it's not going to start.

If the ECU is powering up and running it will turn the CEL on for 5 seconds when you turn the ignition on and the factory boost gauge will go to zero. If that doesn't happen then you start checking the wiring and fuses back to the battery until you find why it's not working.
That means you'll need the wiring diagram for your car.

Steve

I checked to see if the ECU was getting power and it isn't the CEL doesn't come on at all.

One of the techs at work said I could have blown a Main fuse. Where is the main fuse in our cars?

Also, where can I find a good wiring diagram of the car? Would a Haynes manual have it?

 

[steve]

The main MPI and Ignition fuses are on the positive battery terminal. Since the car cranks that means the Ignition fuse is good so you should check the MPI fuse.

I wouldn't touch a Haynes or Chiltons.

I buy a Factory Service Manual when I get a car. Alot of what you'll need is in the Manual CD but '90s are unique DSMs and the Manual CD doesn't cover that uniqueness so you may need to find a paper copy of the 1990 FSM.

Steve

 

[PangguloCrew]

Well I checked the MPI fuse and it looks pretty good.

Is there a positive way I can check if the fuse is actually blown? Other than a visual check?

Would a short somewhere in the wiring harness cause an ECU capacitor to blow?

Thanks for all the help.

 

[steve]

Visual checks don't count.
You need to use a multimeter and check either by measuring the voltage after the fuse or by pulling the fuse and measuring the resistance of the fuse itself. A good fuse would read 0 ohms.

The next thing you need to check is fuse 19 in the drivers footwell and then that you have battery voltage all the time at pin 10 on the MPI relay and at pin 103 on the ECU
http://www.vfaq.com/mods/ecu-harness-1G.html

No a fuse won't cause the capacitor to blow. That happened because you waited too long before having the capacitors replaced and the cap shorted, blowing up.

Steve

 

[PangguloCrew]

What is fuse 11? Is it labeled Fuse 11 on the fuse box cover?

 

[steve]

It might be labeled "room" on the cover. I don't have the cover in front of me. Just the manuals.

Steve

 

[PangguloCrew]

Visual checks don't count.
You need to use a multimeter and check either by measuring the voltage after the fuse or by pulling the fuse and measuring the resistance of the fuse itself. A good fuse would read 0 ohms.

The next thing you need to check is fuse 11 in the drivers footwell and then that you have battery voltage all the time at pin 10 on the MPI relay and at pin 103 on the ECU
http://www.vfaq.com/mods/ecu-harness-1G.html

No a fuse won't cause the capacitor to blow. That happened because you waited too long before having the capacitors replaced and the cap shorted, blowing up.

Steve

If fuse 11 has power and pin 10 and pin 103 don't what should I do next? What would cause it not to have power?

 

[GSX_RCR]

Car: 1990 GSX M/T
. Basically my car was idling, I stepped inside my house, came outside the car wasn't running. I opened the door and smoke came billowing out.

After the smoke cleared I pulled the ECU opened it up and it was charbroiled. .

How long were you away from the car? When my caps blew, I pulled over and shut down immediately. I saw a small puff of smoke coming from behind the radio, so I knew what happened. I also popped the hood and disconnected the battery, just for good measure. Because I shut it off quickly, I was able to save my eprom ecu and repaired it. I've seen other ecu's that were totally toasted when people try to crank the motor on a blown ecu and blew fuses and relays and even fried some wiring, which I'm assuming is what happened to your car since the ignition was left on for who knows how long.

Good luck chasing it down!

 

[PangguloCrew]

How long were you away from the car? When my caps blew, I pulled over and shut down immediately. I saw a small puff of smoke coming from behind the radio, so I knew what happened. I also popped the hood and disconnected the battery, just for good measure. Because I shut it off quickly, I was able to save my eprom ecu and repaired it. I've seen other ecu's that were totally toasted when people try to crank the motor on a blown ecu and blew fuses and relays and even fried some wiring, which I'm assuming is what happened to your car since the ignition was left on for who knows how long.

Good luck chasing it down!

I was probably inside for about 10 minutes (really bad stomach ache, damn mexican food).

I just don't know where else to look for the problem.

 

[steve]

If fuse 11 has power and pin 10 and pin 103 don't what should I do next? What would cause it not to have power?

First, get a copy of the MPI circuit so you can see where things go.
Second, MPI pin 10 comes from the MPI fuse on the positive battery terminal.
If you don't get power to MPI pin 10 that fuse has to be blown and you never get power to ecu main power pins.

Steve

 

[PangguloCrew]

I just realized I have a CD that I got from ebay awhile back that has a factory service manual.

I found the MPI circuit but i have no idea how to read it.

I checked the fuse at the B+ terminal and its fine so power is going through it is there something else between there and the ECU?

you wouldn't happen to have AIM or something would ya?

Thanks for all the help.

 

[PangguloCrew]

Ok I checked everything with a MultiMeter and I'm getting power to pin 10 and pin 103 and also to fuse 11.

is it possible that I may have jumped timing? or is there something else that I'm missing?

 

[kmartsTsi]

When i got my ecu replaced, the place that fixed it told me that before i put it in i should check it isc, which is the idle speed censor. They said that if i put the ecm back in without checking it, it could fry the ecm again. Just something to try.

 

[AWDPetmitsu]

What he said ^^^. Check your ISC motor before attempting to try another ECU.

The instructions are here: http://dmtalon.v8eaters.com/ISC.html

 

[PangguloCrew]

ISC is within specs.

I checked everything that steve has told me to check and they all have power. But i'm still not getting a CEL to tell me that my ecu is getting power.

Anything else I should check?

Thanks for all the help guys

 

[PangguloCrew]

I checked for spark, and there wasn't any. Now would a bad coil pack cause a ECU to not power up?

Is there any way I can check the coil pack to make sure its working properly?

Thanks again.

 

[steve]

I checked for spark, and there wasn't any. Now would a bad coil pack cause a ECU to not power up?

Nope. If the ECU is getting backup power on ECU pin 103 and power on ECU pins 102 and 107 when the ignition switch is on along with the grounds are good it should power up. If you don't get power on 102 and 107 then the MPI relay, MPI power, or ECU are bad.

Is there any way I can check the coil pack to make sure its working properly?

There are test in the FSM for the coils, You can also make sure that the coils are getting 12v to the primary. After that you need something like an oscilliscope so you can watch the signals from the ECU to the Power Transistor Module and from there to the coils. You might be able to see the PTM side of the coils primary pulsing between 12 and 0v if it was working but that whon't help much if it isn't.

Steve

 

[PangguloCrew]

Is the MPI relay the thing connected to the battery terminal? If not where is it? and what is the MPI power?

 

[PangguloCrew]

I just checked pins 102 and 107 for power with the key turned to ign and its not recieveing any voltage. So would it be my MPI relay? Is this a part that I can buy from a parts store? LOl

Thanks again for all the help.

 

[steve]

Remember back in post 9 I suggested you check for power at MPI relay pin 10. You said it was good but I wonder how you did that if you don't know where the MPI relay is?

From my ECU powerup sequence document.

The 1G DSM has two main circuits for the engine. The MPI circuit and the Ignition circuit. The ECU is connected to both but powered from the MPI circuit.

Power for the MPI circuit comes from the MPI fusable link on the positive battery terminal to pin 10 on the MPI relay and should be present all the time even with the car off. Power for the Fuel Pump and the rest of the ignition circuit comes from the Ignition fusable link on the positive battery terminal and for the fuel pump winds up on pin 3 on the MPI relay.

The MPI relay has two actual relays inside, one for the MPI power and one for the fuel pump power. The fuel pump relay has two trigger inputs, the MPI relay one. Pin 10 in the input for the MPI power and pin 3 is the input for the FP power. When one of the control lines to either relay is activated the relay switches the power from the input to the outpin pin(s)

The ECU receives backup power on pin 103 from fuse 19 (room) in the drivers footwell fusebox. This is used to maintain the RAM in the ECU's CPU and allow the ECU to power itself up. Like MPI relay pin 10 the backup power on ECU pin 103 should to present all the time even with the car off.

The ECU sits dormant in a powered down state waiting to see pin 110 (IG1 from ignition switch) go high (to battery voltage). When pin 110 goes high the ECU pulls its pin 63 (MPI relay pin 8) low (to ground). This causes the the relay to activate and switches the MPI power from MPI pin 10 to MPI pins 4 and 5 providing power to the ECU on pins 102 and 107 along with various sensors, solenoids, injectors, ISC, and O2 Heater in the engine bay.

Shortly after battery voltage shows up on ECU pins 102 and 107 the reset circuit in the ECU wakes the ECU up and if it boots up you'll get a heartbeat on ECU pin 1, the CEL will come on for about 5 seconds, the boost gauge will display 0 (Stock ECU software on turbo cars) and the ISC on the throttle body will move in and out to rehome.

The next interesting condition is when ECU pin 108 (indirectly START from the ignition switch) goes high (to battery voltage).

The START signal also goes to the Fuel side of the MPI relay to power up the fuel pump, and to the ECU causing the ECU to do the things it needs to do the start the engine. Once the engine is running the ECU pulls it's pin 56 (MPI relay p[in 8) to ground and continues to hold it low until you turn the car off or the engine stops running, to keep the fuel pump powered after you release the ignition.

The first thing you should do if your ECU doesn't power up (CEL on for about 5 seconds, the boost gauge displays 0) is check the two fusable links and the room fuse. Measure the fuses for continuity (0 ohms resistance) rather than look at them. Then check for battery voltage at the ECU and MPI relay pins. Remember that the ECU doesn't get power on pins 102 and 107 until the MPI relay is activated by turning the ignition key to RUN or START. If the MPI relay doesn't activate try grounding its pin 8 and check that power shows up on its pins 4 and 5. If that works then either the ECU isn't seeing the IG1 signal or the ECU is damaged.

If power is present on ECU pins 102 and 107, the ECU grounds are good and the ECU doesn't power up it's damaged.

Steve