Fried ECU

[el_freddo]

Check the cam timing. Both cams could be aligned exactly the same which means one is 180 degrees out of synch. 

The other thing to consider is open valves. Rust/grud build up could be holding several valves open enough not to let them create the required seal for the bang to make any kinetic energy in the form of engine power. Or rings are clogged up, not producing compression. 

Cheers 

Bennie

[john in KY]

Just from memory the injectors are "paired".  1 and 2 fire at the same time and ditto for 3 and 4.  The wiring for 3 and 4 heading back to the ECU are spliced together some where in the cabin under the carpet.  If 3 is firing and 4 isn't, the problem has to be somewhere between the splice and the injector. 

[davepak]

5 hours ago, el_freddo said:

Check the cam timing. Both cams could be aligned exactly the same which means one is 180 degrees out of synch. 

The other thing to consider is open valves. Rust/grud build up could be holding several valves open enough not to let them create the required seal for the bang to make any kinetic energy in the form of engine power. Or rings are clogged up, not producing compression. 

Cheers 

Bennie

I thought about that, but the car had a recent over haul. I t wasnt driven much, as I live abroad and come back once or twice a year to **try to** use it.

[davepak]

I have the FSM and I've been reviewing all I can think through them @idosubaru. 

[davepak]

3 hours ago, john in KY said:

Just from memory the injectors are "paired".  1 and 2 fire at the same time and ditto for 3 and 4.  The wiring for 3 and 4 heading back to the ECU are spliced together some where in the cabin under the carpet.  If 3 is firing and 4 isn't, the problem has to be somewhere between the splice and the injector. 

As a means of a test @john in KY could I connect a wire from injectorr #3 to #4 (The ECU signal) to test whether both injectors would work then? This considering both fire at the same time? Im guessing if this would work, it will tell me that indeed there is a wiring/splicing issue from the ECU to the injector harnesses and it is not reaching cylinder #4. Alternatively, could I attach a wire all the way from the ECU to the injector harness to try to get the same result? Once again, to test if there is a broken path from the ECU to the injector harness? .

But here is the very odd thing!! Injector harness #3 had 12v on the battery pin side and 0v on the ECU side, however when measured together, these pins read 12v! On the other side, on injector harness #4 I had 12v from the battery pin side and 12v From the ECU side, which is what I expected, as the ECU would actuate the injector by sending a ground pulse. HOWEVER, I can start the car with injector #3 attached  and I must disconnect injector #4. Is the ECU going nuts?

 

But another note is this: the car does not really have any custom wirings or odd splicings. I have found most of the connectors and harnesses in mint condition as close they were from the factoy. 

Just to be clear: The issue is on injector for CYL#4 that needs to be disconnected otherwise the car would not start:

                                                     

                                                    FAN /Front of Engine

                                                          //////--+--///////                                  

                                                          CYL 2     CYL 1

                                                      ** CYL 4     CYL3

                                               --------------------------------------------       

                                            Windshield /Passenger Cabin

 

 

 

[idosubaru]

10 minutes ago, davepak said:

HOWEVER, I can start the car with injector #3 attached  and I must disconnect injector #4. Is the ECU going nuts?

But another note is this: the car does not really have any custom wirings or odd splicings. I have found most of the connectors and harnesses in mint condition as close they were from the factoy. 

Just to be clear: The issue is on injector for CYL#4 that needs to be disconnected otherwise the car would not start:

 

 

Injectors seem to be problematic - What happens if you test for continuity and resistance from each injector pin to the ECU? 

[davepak]

11 minutes ago, idosubaru said:

Injectors seem to be problematic - What happens if you test for continuity and resistance from each injector pin to the ECU? 

I replaced 3 injectors , as they were leaking any time the fuel pump would prime, or when cranking. Here I'm a bit in the shadows..what reading should I get on the injectors? In Ohms? To ensure they are fine? I know i checked for short circuit and there was none.  I changed the last injector yesterday, this was injector #3 that would leak out of its housing and it is now dry and clicking too. I had the car running (on 3 cyl) for a good 5 min and i used a long screwdriver to confirm they were clicking and  the engine running..This tells me the injectors are now fine, is the signal they need the problem

How can I test the ECU's pin for the injectors? To verify signal coming out from the ECU? There might be -as mentioned before- a problem from the ECU to the injector harnesses where its signal does not reach the injectors . When I had the car running on 3 cylinders, as soon as I plugged harness #4, the car died immediately.

Edited December 15, 2020 by davepak
content

[john in KY]

As a means of a test @john in KY could I connect a wire from injectorr #3 to #4

I can't see why not.

Appears that somehow injector 4 is not allowing the other 3 injectors not to fire by "taking away the ground".  

Use a test light probe and see if 4 fires when cranking the engine.  

 

When I had the car running on 3 cylinders, as soon as I plugged harness #4, the car died immediately.

Sounds to me somehow injector 4 is somehow back feeding 12 volts in the wiring harness.  

Edited December 15, 2020 by john in KY

[idosubaru]

2 minutes ago, davepak said:

should I get on the injectors? In Ohms? 

How can I test the ECU's pin for the injectors? To verify signal coming out from the ECU? There might be -as mentioned before- a problem from the ECU to the injector harnesses where its signal does not reach the injectors . When I had the car running on 3 cylinders, as soon as I plugged harness #4, the car died immediately.

What we want to test is the wire between the injector *plugs* and ECU *plugs*.  

I'm weak on electrical but on a very basic level here are two simple tests: 

1. place one probe of a multimeter on an injector plug pin and place the other probe at the ECU plug pin for that same wire - and set the multimeter to "Continuity".  Most meters simply make an audible beeping noise (if the wire is good) or no noise (if the wire is bad). 

This means the wire is not completely shorted but doesn't tell us if there's excessive resistance, so the next step is to measure resistance - yes Ohms. 

2.  with the pins still in the same place - switch the multimeter to "Ohms" and check resistance of the wire. 

repeat that process for both injector pins of each problematic injector and write down your ohms for each one. 

The FSM has a detailed sections on which pins to check. 

[john in KY]

Been 30 years but just thinking the early XTs had some sort of "resistor" over on the passenger side of the engine bay that was part of the injector wiring.

I would as a test determine which wire at 4 is the ground side and wire it to ground.   

[davepak]

2 minutes ago, john in KY said:

Been 30 years but just thinking the early XTs had some sort of "resistor" over on the passenger side of the engine bay that was part of the injector wiring.

I would as a test determine which wire at 4 is the ground side and wire it to ground.   

Oh dear ! A "resistor" there , I had a regular GL-10 before, it always ran. But this one, I feel I'm dealing with an Apolo Space Module 

[idosubaru]

On 9/17/2013 at 2:25 PM, naru said:

If the injector(s) fire w/cranking,disty is OK.

If injector works and coil negative has power,but still no spark,ignitor is likely fried.

Here it's suggested that the distributor and injector firing are related - which is why I would be tempted to swap a distributor - but i've also got spares so it's easy for me. 

I would think testing the wires from the injector to the ECU as described above, or the distributor is important for injector operation. 

 

I think if the igniter (or 'resistor') was bad you wouldn't have any spark.  I thought that igniter was just for the ECU to fire the coil and spark?  

On 12/13/2006 at 12:08 AM, GeneralDisorder said:

The "ignitor" is used on fuel injected engines so the ECU can control the coil.... The external ignitor is neccesary for FI as the ECU does all the timing adjustments and needs to trigger the coil when it chooses.

 

GD

Edited December 15, 2020 by idosubaru

[Rampage]

17 hours ago, davepak said:

When I had the car running on 3 cylinders, as soon as I plugged harness #4, the car died immediately.

Try this for S&G.

When you have the engine running on 1, 2 and 3, wiggle and twist a little bit the #4 connector. If it is still running plug one of the old injectors into the #4 injector connector. Does it die?

[davepak]

6 hours ago, Rampage said:

Try this for S&G.

When you have the engine running on 1, 2 and 3, wiggle and twist a little bit the #4 connector. If it is still running plug one of the old injectors into the #4 injector connector. Does it die?

@Rampage Oh this is a great idea, I will do so later on for sure.  And as asked before, yes I have a new knock sensor in place

[naru2]

On 12/15/2020 at 4:50 AM, davepak said:

 

But here is the very odd thing!! Injector harness #3 had 12v on the battery pin side and 0v on the ECU side, however when measured together, these pins read 12v! On the other side, on injector harness #4 I had 12v from the battery pin side and 12v From the ECU side, which is what I expected, as the ECU would actuate the injector by sending a ground pulse. HOWEVER, I can start the car with injector #3 attached  and I must disconnect injector #4. Is the ECU going nuts?

 

 

 

 

Are these measurements taken w/both injectors unplugged or both plugged in?

[davepak]

17 hours ago, Rampage said:

Try this for S&G.

When you have the engine running on 1, 2 and 3, wiggle and twist a little bit the #4 connector. If it is still running plug one of the old injectors into the #4 injector connector. Does it die?

@Rampage, @idosubaru, @john in KY, @naru2 I have made the following the test, with a mystifying result:

-I started the car on the 3 working cylinders: 1, 2 and 3. It starts immediately.

-Harness for injector #4 was unplugged while the car was running. I attached an old injector, and IT WORKED on  harness #4. I could see and feel that injector opening and closing, and the car is still running. I even attached a wire to the injector housing and touched the negative terminal of the battery and the car was still working. HOWEVER, if I disconnect the loose injector and place that harness back on injector #4, the car dies immediately. 

Speculations: 

The ECU has to be working fine, and sending the correct pulses/signals to all 4 injectors, since I managed to see it doing so even to a loose test injector held by hand.

The ECU gets "confused" once the harness goes back to injector #4 for some reason that I cannot explain, does not like it and kills the car.

The ECU does not like this injector #4 even though is a working / non leaking injector. 

The car is possesed by an unkown force that prefers running on 3 injectors attached to the block, and one "loose in the air".

I gotta make some jokes here instead of abusing as this is such  a strange situation.

Awaiting your wise comments, inputs and guidance 

Dave

 

[davepak]

5 hours ago, naru2 said:

Are these measurements taken w/both injectors unplugged or both plugged in?

The injectors are plugged on the engine block, I took the harness out and measured them. I read voltage on the harness, ignition switch was on OFF position. So it meant the fusible link is sending direct power to the injector harnesses and so is the ECU sending it via its pin

[idosubaru]

What happens if you just swap those injectors - pull #4 out and install the one that worked in your hand?

Sounds like the injector or wiring is bad?

Check continuity and Resistance from injector connector to ECU connector 

 

[davepak]

1 minute ago, idosubaru said:

What happens if you just swap those injectors - pull #4 out and install the one that worked in your hand?

Sounds like the injector or wiring is bad?

Check continuity and Resistance from injector connector to ECU connector 

 

Tomorrow I will run several tests and report back. 

I will swap injectors and see if there is a change.

@idosubaruthis is most strange as it tells me that the injector harness and its wirings are coming in fine from the ECU, since it made the injector work in my hand without issues, no stalling, no dying. But then again, as soon as I place that harness back on injector #4 on the block, the car dies. Following suit, this should point at a bad injector... Which is this one known to be fine and that it does not leak like the one I had in my hand! Sure I can be very unlucky getting this sourced injector as of being faulty. Odds against me. So I'll swap them tomorrow 

I'm planning to back trace all 4 wires that come out of the ECU to the injectors and check for continuity and resistance. I will write down the values I get from the Multimeter for comparison 

Thanks again, a lot actually! 

[Rampage]

Cool, it ran with an external injector plugged in. That is what I wanted to hear.

It sounds like the #4 injector coil has some shorted turns or is shorted to the housing of the injector.

If you have an OHM meter, see if you get a reading between the two pins on #4 injector and the body of the injector. It should read open. No resistance at all even at a high setting. Measuring OHMS on the two pins only tells you half the story with a coil, unless the reading is very low compared with the other injectors.

You could change the o - rings on the one that leaked externally with o - rings from the other old ones and replace #4 with it.

[davepak]

5 hours ago, Rampage said:

Cool, it ran with an external injector plugged in. That is what I wanted to hear.

It sounds like the #4 injector coil has some shorted turns or is shorted to the housing of the injector.

If you have an OHM meter, see if you get a reading between the two pins on #4 injector and the body of the injector. It should read open. No resistance at all even at a high setting. Measuring OHMS on the two pins only tells you half the story with a coil, unless the reading is very low compared with the other injectors.

You could change the o - rings on the one that leaked externally with o - rings from the other old ones and replace #4 with it.

***UPDATE***

 

@idosubaru, @naru2   I have tested injector #4, there is NO reading for continuity between the injector pins and the body of the injector. I get very similar resistance reading in Ohms when compared to injector #1 which is working fine:

Injector #4: 08.7 Ohms between pins at 200 Ohms and 008 Ohms at 2000 Ohms. 

Injector #1: 10.1 Ohms between pins  at 200 Ohms and 008 Ohms st 2000 Ohms. 

 

I did the following test, a bridge taking ECU pulse from injector #3 and splicing it to feed both injector #3 AND #4 since both fire simultaneously. The car started and it sounded very smooth, I hit the gas and again it sounded "normal" BUT BUT on checking the ECU... There was burnt smell and a bit of smoke  I stopped the test right away and disconnected that wiring /splicing test. I tried and the car started (on 3 cylinders). 

 

 *EDIT* Using that spliced cable from injector #3 I held an injector test on my hand and it did NOT make it work. When I attach the harness #4 to the test injector, it worked. 

 

What could be killing the ECU? The injector checks out in its readings. The ECU sends the signal to the Harness and this provides the pulse to the injector as I tested another injector in my hand. But car won't work on 4 cylinders, when forced to do so via that splicing, stealing the signal from injector #3 it starts killing the ECU!? 

 

This seems to be the same event that lead to burning the first ECU. The car would somehow run, but killing the ECU meanwhile. 

Any thoughts? 

Edited December 17, 2020 by davepak
content added

[DaveT]

It sounds like you paralleled 2 injectors. ...  this would almost certainly burn out the driver for the number they were wired to.  Injectors are not trivial loads, and the drivers need to be robust, but they are not likely to be designed with double the headroom required to run one injector. 

[davepak]

I opened the newly acquired ECU and found a burnt piece. It's labeled D1320. 

 

[davepak]

22 minutes ago, DaveT said:

It sounds like you paralleled 2 injectors. ...  this would almost certainly burn out the driver for the number they were wired to.  Injectors are not trivial loads, and the drivers need to be robust, but they are not likely to be designed with double the headroom required to run one injector. 

Yeap, it looks like I did.. . I will try to solder a new D1320 salvaged from the old ECU. 

[idosubaru]

I think the wiring needs tested.  Honestly I've been humoring the other suggestions to a degree and just keep repeating the wiring issue thinking it's obvious there's a short and eventually you're going to have to test it - except maybe swapping in another injector - but it seems like we need to know for sure the wiring is good.  And if you're having problems this bad, all the time, it shouldn't be intermittent and should test bad somewhere. 

I would test all the pins from ECU plug to injector plug.  Disconnect them and test. 

I have heard of old XT's having running issues due to the wiring where it runs under the passengers side seat being damaged.  I haven't seen it myself so I'm not sure where exactly or what causes it, but I've heard of it a couple of times over the decades on XT's. 

On 12/15/2020 at 8:24 AM, idosubaru said:

What we want to test is the wire between the injector *plugs* and ECU *plugs*.  

I'm weak on electrical but on a very basic level here are two simple tests: 

1. place one probe of a multimeter on an injector plug pin and place the other probe at the ECU plug pin for that same wire - and set the multimeter to "Continuity".  Most meters simply make an audible beeping noise (if the wire is good) or no noise (if the wire is bad). 

This means the wire is not completely shorted but doesn't tell us if there's excessive resistance, so the next step is to measure resistance - yes Ohms. 

2.  with the pins still in the same place - switch the multimeter to "Ohms" and check resistance of the wire. 

repeat that process for both injector pins of each problematic injector and write down your ohms for each one. 

The FSM has a detailed sections on which pins to check. 

 

On 12/15/2020 at 11:02 AM, idosubaru said:

I would think testing the wires from the injector to the ECU as described above, or the distributor is important for injector operation. 

 

14 hours ago, idosubaru said:

Check continuity and Resistance from injector connector to ECU connector