Car ECU think I found the fault?

[Donny121]

I am working on a car and it has a fault which occurs when it gets to temprature.

Anyway, I got the ECU stripped and found a spot that looks overheated or maybe just prolonged heat has created a spot that I am concerned about?

I first scraped back all the raised area thinking it was the copper tracks that had blown but they all seem intact. The Diode to the area looks to be the culprit.

Does this mean the diode is faulty? I have a good multimeter and it reads the same ohms in both directions does this mean it is faulty? I know its a different type of diode so not sure quite how to test them.

I am no expert just learning, I used a Mac tools EM710 to test in ohms position.

If faulty how can I get an identical part?

Many thanks

 

[Bluejets]

Symbol is for a zener diode but either way, difficult to test in circuit as there could be other components giving a false reading.

 

[Donny121]

OK, thanks

So if I desolder one leg and test I can use the Ohm meter?

Would this type of heat be typical to find but not be a problem?

The tracks that I have cleaned up seem fine but have no coating could this be an issue? and could there be a problem with the tracks?

 

[dave9]

My initial suspicion is that you're going about this the wrong way, or at least have not mentioned troubleshooting up to this point. The ECM is not usually the culprit for a problem that occurs once an engine reaches full operating temperature.

First what is this "fault" when it gets to temperature? Exactly what happens? Engine just dies? What vehicle year, make, model, and engine?

Does it have OBD1 or OBD2? Have you hooked up a scan tool capable of showing live data and looked at things like the temperature sensor(s), MAF reading, and long term fuel trims? Before even that, does a scan tool show any set or pending OBD diagnostic codes?

When it stops running and you try to start it, does it start, and then run or stall? If it does not start, is the fuel rail at the right pressure, are all spark plugs firing, and does the problem start the moment the ECM switches from open loop to closed loop operation? Depending on how the engine is behaving, one of the most common faults would be a vacuum leak, making it too lean once the ECM sensing high enough engine temperature to switch it to a leaner fuel ratio for emissions and fuel economy purposes.

Maybe you're already well beyond the issues mentioned above and have somehow determined that the ECM itself is not operating properly based on it not outputting the needed injector pulse or spark firing signal?

The first thing I would do is get some lacquer and coat those exposed copper tracks before there's not anything left of them due to oxidation on top of the abrasion.

 

[(*steve*)]

The first thing I would do is get some lacquer and coat those exposed copper tracks before there's not anything left of them due to oxidation on top of the abrasion.

Yeah, and check that the leftmost trace hasn't been cut.

 

[Donny121]

Dave9 thanks for such an in-depth and considerate reply.

It's a Lexus soarer 300 n/a engine
It starts up perfect cold and sounds perfect and revs spot on.

After a minute or so it will die as if fuel has been cut.
Will turn over and not start, the fuel pump is working and I have bypassed the fuel ecu to check.

It does at some points start again and behave ok for a moment but dies quickly. its been an increasing problem that has got worst.

There complicated engines and doesn't have any codes from a paper clip test or any warning lights. I have a good diagnostic machine but no obd port present.

There are known problems with the caps blowing in the ECU which prompted me to open it up but visually everything but the affected area seems fine.

Just looks suspicious to me and thought the diode may be the problem?

 

[Donny121]

Yeah, and check that the leftmost trace hasn't been cut.

The track seems fine.
What lacquer would i use to coat with?

 

[Bluejets]

This is RS Components Aus, should be similar at Mouser or whatever.

Another one I normally use,......... on Ebay
https://www.ebay.com.au/itm/Circuit...OSwpnhbe2o8:sc:AU_StandardDelivery!4670!AU!-1

 

[kellys_eye]

Do you have a full wiring diagram for the engine?

Can you show a more complete picture of the ECU?

Cut one lead of the diode (leave enough to remake the joint using a soldering iron) and test the diode again - if you feel you must. As above there are usually many other reasons for the engine cutting out and your decision making process regarding the diode isn't exactly.... 'professional'??? Not that it's 'wrong' (it would be a great stroke of luck if you found the diode was dud!) but the diode would also fail FOR A REASON - which may be unrelated to the original issue and just repeat itself if the 'real' fault wasn't found and fixed.

 

[Donny121]

Do you have a full wiring diagram for the engine?

Can you show a more complete picture of the ECU?

Cut one lead of the diode (leave enough to remake the joint using a soldering iron) and test the diode again - if you feel you must. As above there are usually many other reasons for the engine cutting out and your decision making process regarding the diode isn't exactly.... 'professional'??? Not that it's 'wrong' (it would be a great stroke of luck if you found the diode was dud!) but the diode would also fail FOR A REASON - which may be unrelated to the original issue and just repeat itself if the 'real' fault wasn't found and fixed.

I agree that is would be lucky, as stated the reason I checked ECU is they are a known problem on this car which displays the problem that I have had, it has had three garages look at the car and near on 600 quid spent with no joy.

It's the Capacitors that normally break down in the ECU that causes the car to have random cut outs. But the Caps seem fine but I did find this suspicious looking area that has got obvious heat burn.

One of my main questions really is would this be a normal thing to find on a circuit i.e a diode getting so hot that it burns the lacquer or should I investigate.

 

[kellys_eye]

But the Caps seem fine

How do you know? The only true test of their reliability is a measurement of ESR, something you can't do in-circuit.

Standard practice would be to replace all electrolytics in this case.

You are right to investigate any suspect heat source and diodes don't normally dissipate enough heat to cause 'singeing' (some under-rated zeners will do this though) but without access to a schematic we can't determine if this is a genuine problem or simply as a result of external influences.

 

[Donny121]

I agree i need to check further on the caps especially knowing they are a common fault. I will look into that ESR check you mention it will be a new thing to learn.

I've tested all traces and they all test good. Was a pain as have no working diagram and have trauled the net and cannot find one.

Good job i enjoy fault finding as i have spent hours on this now.

So would this type of heat desrtroy the diode?

 

[debe]

When the engine dies the first things I check when trying to start it, is there Spark & are there pulses at the injectors when cranking. Also ive had faulty intermittent relay that feeds power to the ECU, that took awhile to find as it was intermittent.

 

[kellys_eye]

So would this type of heat destroy the diode?

I have no idea what the picture you posted is supposed to show....?????

Yes, heat can destroy components but some components handle heat better than others whilst others are MEANT to dissipate heat - there are many variables.

Show a wider picture of the whole ECU circuit board.