Blow injector channel when bouncing off the rev limiter hard

[tom70]

Can I have some advice on desoldering the FET off the board. Me and my mate are having trouble with it. Cheers

[lugnuts]

Is everyone else as concerned as I am about how "fragile" these ECU's are in general? INJ FETs, P259, Flyback, etc.
Why is there such controversy about such a simple hardware issue?
I have installed 10 other brands of ECU and have never had an injector driver failure.
I did a Vi-PEC V44 last month, (old style with saturated drivers) and during diagnosing an unrelated car issue - the car was driven for several hours inadvertently with 2 ohm injectors (big no-no), and since then has been running flawless with Bosch 5 ohn 1600cc injectors.

With the VEMS I have 50+ ECU's that have never had a problem, and 5-10 that have had problems that nobody can pinpoint.  That is simply a completely unacceptale failure rate.

[rob@vems.co.uk]

The P259 problems really irriate me, sure I've never lost one since blowing it up on my first ecu, you then get it clear in your mind not to do it again - trouble is for a DIY ecu that means you've got the potential for a 1:1 failure, the reason for the seperation of grounds is a good one, and you'll find that theres better analog accuracy because of it.

FETs and IGBTs I've never personally had a problem with, and really a fuse should blow before a component like that would - most people think that its easier to "risk it" without a fuse.  Sure there are cases like Tom70's here which I've not come across before.

Flyback is not uncommon on OEM ecus and if you decided to re-wire an existing ECU install and leave the flyback disconnected, you'd find the drivers failing.  The flyback can be internally routed to the main ECU power supply but there were concerns about injecting high flyback voltages in directly to the components inside the case.

But there is something that shows a lack of completeness with these systems which I think is more about the software usability, upgrade path and configuration which makes these systems a nightmare to support, which is fine once you have a fully tested configuration, but it can be painful getting there.  I'm pretty sure that other manufacturers have these issues with configuration (some I know do), but they're able to do the development in-house and send out fully configured and tested units with all the config closed to the user.

[Sprocket]

I know of one perticular manufacturer that boasted about how robust their ECU is and how they have never had a failure. I then had a chance to work on one of their engines, another story in itself, and found no spark. With no interface device, yes, thats right, you needed to spend anther £110 on software and an interface device to connect a PC, additional to an already expensive £550, suposedly robust ECU, that requires a non statdard dedicated connector that you cannot buy seperately so have to buy the complete loom. Only to have both ignition drivers fail. This was one of the manufacturers engines and it was their instalation, so it shouldn't have failed, but it did.

Its a bit like my work. I work for a manufacturer, and see loads of faults and issues with our machines, and if I were to just take that into consideration, I would have to think that the gear we manufacture was shite, when infact, the problems we see is only a tiny percentage of the machines we have in the field that we never ever see because they run perfectly without a problem for years.

One other thing to consider is that OEM ECU failures are not uncommon, and why there are loads Network 500 agents around the UK at least. The actual number of failures to cars on the road is tiny, but thats because of the multi million pound research programs OEMs have.

Ibuilt my own ECU and that is most likely why I had so many problems I did. I smoked the P259 chip trying to resolve the FET blowing by seperating out the grounds. like rob says, you do it once, and you dont do it again.

[GintsK]

It is something wrong with hardware. I am not specialist of electronics. But now I think purpose is spikes on FET gates. And main reason could be too less balancing capatitance on FET drivers chips. There are four. But just two 0.22uF capacitors are used. Datasheet suggest :

Suggested capacitors are
a low inductance 0.1 uF ceramic in parallel with a 4.7 uF
tantalum. Additional bypass capacitors may be required
depending upon Drive Output loading and circuit layout.
Proper printed circuit board layout is extremely
critical and cannot be over emphasized.

For fet drivers manufacturers accent layout and balancing importance because of some inductive phenomena in long gates traces.
Now i use additional 10uF ceramic from rescue kit on each my board.

Gates seems most unprotected part. Some developers suggestion was to change respective FET driver chip for fried FET and then if it does not helps - capacitors. I still can not imagine how driver can be damaged! These small chips are almost capable to drive injectors directly! But capacitors simply can be too small (it has huge tolerances like -20/+80%).
Other point - our local production ECU do not use flyback circuits at all. Many FETs are capable to suppress flyback spikes internally. And this ecu has no problems with FETs - much smaller smd ones with similar characteristics as ours. Also this says to me that most probably something from gate side is blameable.
But it is just my non-pro opinion.

Gints

[MWfire]

Is everyone else as concerned as I am about how "fragile" these ECU's are in general? INJ FETs, P259, Flyback, etc.
Why is there such controversy about such a simple hardware issue?
I have installed 10 other brands of ECU and have never had an injector driver failure.
I did a Vi-PEC V44 last month, (old style with saturated drivers) and during diagnosing an unrelated car issue - the car was driven for several hours inadvertently with 2 ohm injectors (big no-no), and since then has been running flawless with Bosch 5 ohn 1600cc injectors.

With the VEMS I have 50+ ECU's that have never had a problem, and 5-10 that have had problems that nobody can pinpoint.  That is simply a completely unacceptale failure rate.

i allways use irf640n, put connection inside ecu for analog and power ground. So far more than 30ecu sold without any problem.

[lugnuts]

In my case I always use fully assembled ecu, and before that I used full assembled boards.
I have zero interest in re-designing and or repairing ecu's.
I have 100% interest in selling products that just "work".

I have been doing the Grounds and Flyback exactly to the recommended methods.

Nobody, I mean nobody else out there, uses fuses for the individual injector and ignition outputs. 

It is very annoying to have to join analolg and power grounds.

No other ecu I work with has had any problem with "dirty or noisy alanog signals"


I hear "bad injectors, bad grounds" as excuses/reasons for Injector FET damage. 

I never had injector cause ecu damage with other ecu. And if someone were to disconnect the ground, the engine would not run, you re-connect the ground, no issues, the engine simply starts and runs.

P259 - I have seen people recommend to not even bother using it. 
It is also bad that if someone has a problem with the P259 - it can cause the car to not run due to loss of trigger.


Not all ecu companies are perfect. Autronic decided to change the design of their main firmware chip socket, to a surface mount soldering instead of thruhole.
That, and there was a boundry layer insulation problem with the chip itself that drove us nuts.


But I can honestly say, in 11 years of doing this, that no other ecu I work with has had a problem with injector driver that caused fuel to be dumped into a running engine.

I fully agree with Gints. Hardware design issue.
I believe he was the one last year who commented that the Autronic SMC has many many capacitors inside for protection.


<<<i allways use irf640n, put connection inside ecu for analog and power ground. So far more than 30ecu sold without any problem.>>>
- Please clarify this statement. What is the irf640n protecting? And how exactly do you join analog and power grounds?

[MWfire]

IRF640n has 200V breakdown voltage. They don't fail even disconected flyback. Once they were driving high z and low z(1.9ohm) injectors in parallel without resistors and without pwm without problem.
For gnd
http://img155.imageshack.us/i/groundn.jpg/

[GintsK]

Yes, but originally used FETs has built in diode for avalanche suppression at 60V. IMHO it should easily handle  flyback spike from  high imendance injector.

200V robust ones with gate protection: http://www.rohm.com/products/databook/tr/pdf/rdn100n20.pdf

[rob@vems.co.uk]

You dont need individual fuses for the injectors, but if the case with these blowing FETs is due to capacitance issues then theres not going to be any fuse that helps you.
Why are you sticking with VEMS though for nearly 60 installs?

[MWfire]

imho gate-source voltage isn't problem. Problem is bad flyback in some instalation. But if you put 200V mosfet then you have space for error.
And 1-3.3uF plastic(MKP) condesator is good between flyback and gnd.

[rob@vems.co.uk]

The only way we'd know is to scope Tom70's offending channel when its driven hard - and unfortunately no one has the time or resources to do this, so we'll have to keep guessing.

BTW - What's the problem with the FET soldering Tom70?

[GintsK]

BTW Megasquirt use almost same design of FET circuits. Usually on one FET two or more injectors connected.
FET driver chip is balanced with two capacitors as datasheet suggest to do. I do not remember any problems with irfiz34 60V ones.
Again my example of another ECU of our local production - no any flyback clamping circuits except built in MOSFET itself. http://www.irf.ru/pdf/irf7380.pdf VEMS FETs seems to me have much stronger avalanche suppression capabilities:
http://www.fairchildsemi.com/ds/FQ/FQPF20N06L.pdf

Both points above leads me to think that voltage spikes on gate is the cause. Yes spikes could be flyback sourced. And capacitor in this circuit simply makes it less noisy for overall wiring. And less noise means less chance feed it back to gate. You think no?

[Jorgen]

It is obvious that there has been a problem but we have been unable to recreate it.

So far I have never seen a FET failure in any of my test cars with the old FETs.

I have seen a FET failure that could be traced to one SARD injector on a customer car, when the injector was moved to an other cylinder that FET driver would fail shortly. I ended up fitting ignition IGBT's in that ECU to be able to use that set of injectors.

A number of modifications has been done over the years to try to find the problem where one of the last included a pretty big capcitor in the flyback circuit. This seems to have solved the problem. Soon after we also started using a far more robust FET, it should handle any flyback issues better. So far I have not heard of any FET failures since the last changes and the spec has remained the same for some time now.

Over the years we have done quite a few repairs and we have never seen problems with lowZ injectors, only with highZ injectors. So if you have experienced problems with lowZ injectors it is very likely that it has just been a short in the harness.

Jörgen

[Jorgen]

Can I have some advice on desoldering the FET off the board. Me and my mate are having trouble with it. Cheers

Simply cut the legs from the FET near the capsule and then desolder the legs one by one, this is by far the safest way to remove them. The old FET's should be thrown away in any case.

Jörgen