davepak

I've found this more detailed wiring diagram and I see that all injectors share a live B(+) feed from the fusible link also shared with the Fast idle control device FICCD. Thinking that there could be something here. But again, it's only ECU signals for injectors #3 and #4 that are giving me trouble

Oh that's a pro tip yes. I've seen it mentioned before. I checked it and I can't say with certainty that it is fuel laden, but an oil change is in the to do list. To be on the safe side. That and a coolant flush..

Oh dear. I don't know about such ballast thing. I can check tomorrow but as far as I remember I've never seen that near the MAF

*** update *** So I decided to check what was the damage. It seems it's recoverable. I removed spark plug and injector #4 and turn the crankshaft pulley by hand. Expectedly there was a lot of fuel flooding the cylinder. After a few turns, I removed the fuel hoses, the ECU (although it's dead) and cranked the car with the ignition. The engine turned and it seems it cleaned all remaining fuel. Second finding and most mysterious : the wires for injectors #3 and #4 are not "touching each other / or peeled along the way to the injector harnesses. They are fine. But instead, they are showing continuity right from the ECU. The ECU is "shorting" them. I couldn't see this as I had no way to test through the plug (nor I thought this could be the case) but now that I have 2 t-taps attached to these wires I can test and see this. Curiously it is something happening with both fried ECUs and even the third GL-10 MPFI ECU I sourced 1 day ago. All three ECUs are taking injector #3 and #4 signal and putting them together. I have just now traced injectors #1 and #2 and there is no conductivity in between them, I get no Ohms. Now that's really a strange thing! I will try to get another ECU though, as the latest one doesn't work with this car. It seems way "newer" and when I plug it in now it runs the fuel pump right away. It's clearly newer, it's for an 87 GL-10 and my car is an 86 XT. Picture 1 shows cylinder #4 after purging the flooded fuel. Picture 2 shows no continuity between ECU signals for injectors #3 and #4 so long the ECU is not plugged in. This happens with the dedicated wires and the stock wires for those injectors. Picture 3 shows the same wires, but this time the ECU is plugged in. Once again, all 3 ECUs were plugged in and the same results came out. Injectors #1 and #2 did not show these results. I'm in the dark here.. Scratching my head!

Oh well. I'm not sure now what would be the next step. I'm guessing I'd remove the spark plug and injector #4 (the offending one) and say, try to turn the engine over and see if there is /fuel/gas/oil mixture coming out that might have been trapped. I had swapped the injector for a working one. But I'm afraid there must have been something that went wrong on the test. I had isolated the wires that fire injectors #3 and #4 which were known to be "touching" each other. In attempting this, I realized I had cut the original wire #3 (isolating it) but did not cut wire #4 (not isolating it) this meant the bypassing of this 2 wires was not totally effective. Additionally I used a different ECU sourced from a junkyard. This ECU is for an 87 GL turbo MPFI. It has the same plug connectors and an ADDITIONAL plug connector. I opened it and it is really different from the stock ECU for my 86 XT. Still, I tried it and the car ran. Here, the collection of errors appeared : The car actually ran and it sounded smooth At one point it was rough and it died. Injector #4 was full of smoke which then I saw it had to do with a lot of heat on the injector harness and leaking a lot of fuel. What a hazard gosh.. Then I disconnected injector #4 as I have done before and tried to start the car. At this point 2 things happened: The fuel pump runs continuously when ignition is offand it stops priming when key is in ON position. The engine turned a few times then emitted a loud clank and it wouldn't turn over. This is where I am at the moment. Thinking that all these attempts might have ruined the engine. An interesting thing : I plugged in the old ECU that I repaired with soldering (put some components from the other ECU as an attempt to salvage it). This ECU does not work properly but the LED for trouble codes worked. And I saw a long pulse and 2 short pulses. I believe this is Trouble Code 12. I have attached images of both ECU. I'm wondering whether this different ECU might have something to do with the car not firing up properly somehow now? This is turning out to be beyond what I expected with this car :-(

** Sad update ** After trying the result wasn't good. The car started for some time but then Harness on Injector #4 SMOKED. Injector #4 is now leaking the pressure of the fuel pump. The car died. I tried again and then I heard an awful clank from the engine. I tried a few times and now it won't start, actually, it won't turn. Maybe a valve? Maybe I'm actually not sure. I might be declaring this project a totally fried XT.

I'm just about to start working on it . And I will clean up that ground point. Even though my car has no power windows. Well it has the wiring but no motors. Just regular cranking

Hahaha can't tell how excited, but I've got a bunch of other stuff for the day. Including getting new wires and the actual ECU. I want to do this job good from start to finish! Thanks as always. More updates coming

We've tested both. From ECU to engine harness and from there to the injectors. The fault was found from ECU to engine harness. Meaning the cut /torn wires are in between these 2 points. I just measured and checked so I can buy a proper length of wire to fabricate this bypass. I'll use insulated "T-Taps" to do this job. Attaching the new wires as a bypass they'll be labeled and protected against rubbing and vibrations.. I'm learning enough with this issue! I'll cut the offending wires, effectively isolating them. They'll be there, but they'll be dead.

Oh thanks @idosubaru! Yes it's a great feeling indeed. I tried to fix the ECU but it's beyond my repair capabilities. I will source another one hopefully today. We've narrowed down the problem from the ECU to the engine bay. I suspect somewhere under the carpet. Or maybe under the rear passenger seat. This Weekend I'll work on that. I would most likely place 2 brand new wires all the way from ECU to engine bay bypassing the now known issue. And attaching them to injectors #3 and #4. In my experience as well, I've seen attempts of fixing the original arrangement - wiring in this case- only for a new issue to develop. It is not preferred but it will have to do. As I'm not looking to dismantle the whole wiring loom for this darn wires. It might be a future project though I'll post updates over the weekend. Thanks as always!

It's a flapper MAF and distributor with vacuum. 86 XT. As of now we've found wires for injectors #3 and #4 to be "touching each other" and this must be the reason why there is a short in the wiring affecting the ECU and forbidding the car to start on 4 cylinders.

We have just had an Eureka moment. 2 fried ECUs and countless hours after: We managed to pinpoint the wires for injectors 1,2,3 and 4 that come out of the ECU. In doing that we tested using a long wire for continuity as @naru2 suggested on all wires. We found all wires were continuous from ECU to each injector. HOWEVER, what we also found was that wires #3 and #4 are touching each other, there is a resistance of 0.26 Ohms between them! We tested this at the beginning right out of the ECU and the main engine harness therefore identifying the issue in between these points. This suggests the following : The ECU controls 2 injectors at a time with one driver, 1 and 2 are fine and working. Injectors 3 and 4 are working and their harnesses are fine BUT only by disconnecting injector #4 the ECU is prevented from shorting between injectors 3 and 4. Originally the stock ECU was fried exactly on the driver /transistor/diode where injectors 3 and 4 operate. Wires 3 and 4 are touching each other at one point. The car would either start with 3 cylinders or not start at all with all 4 as of now. The next action is: Source a new ECU or try to fix one of them. Either identify the torn/broken wires and fix them or fabricate a separate wiring that takes ECU signals from ECU to injectors 3 and 4 and bypass the now known troublesome wires. By confirming continuity among 3 and 4 wires we can confirm that this nullifies operation for these cylinders. I had uploaded a picture showing a wire labeled as ECU injector #3 but this was wrong, that wire was for something else, hence me frying the ECU. "You also learn by breaking things" The image below shows our Eureka moment, there should not be any reading between these prongs. We found a reading both at the beginning of the ECU and at the ending of the engine wire loom. Here are our culprits. I will work on this over the weekend and onwards with more updates. Thanks to @idosubaru @john in KY @el_freddo @naru2 @DaveT and all of you guys for the constant help. I think I'm nearly there

Actually, the first ECU fried on the heat sink, this new one fried right there at the base of the connector. And it happened when I attached a wire to split injector #3 into two to feed both injectors #3 and #4. On this test the car actually ran on 4 cylinders, but soon enough burning smell came and the ECU is toasted I'm considering fabricating the darn wires all the way to the ECU

Actually, the first ECU fried on the heat sink, this new one fried right there at the base of the connector. And it happened when I attached a wire to split injector #3 into two to feed both injectors #3 and #4. On this test the car actually ran on 4 cylinders, but soon enough burning smell came and the ECU is toasted I'm considering fabricating the darn wires all the way to the ECU

Well, I'm pronouncing dead the new ECU, despite soldering attempts. Im on the passenger's side checking the wires. Can't seem to notice anything bad, torn or cut. Just some dampness and a badly corroded ground point. I'll clean that now and I will do as @idosubarumentions@idosubarumentions: To test continuity with very long probe cables. Ah, and trying to get a pulled ECU from a junkyard nearby..

Yes. That's the next call of action. I'm currently trying to make 1 ECU out 2 fried ones :/ I'll remove carpets and check both under the passenger and drivers side. Wiring has to be the issue. That and maybe another ECU if I can't salvage this one

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

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

***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?

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!

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

@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

@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

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

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.