Blown injector driver inside Renix ECU

Yes, it is blown. Following minor electrical incident in engine compartment, injector #4 wires got melted and there was short.. Which fried output driver inside ECU.

I've disassembled ECU for visual (and infamous electrical burnout odor!) inspection as per instructions from another thread, but didn't find anything obviously wrong. It looks so nice and clean, as it was assembled yesterday!

Anyway, I've checked injector signals with oscilloscope, and it was obvious from result that #4 doesn't get good signal. It is 98% of cycle time 12V and at correct timing it drops to about 7V for some really, really short time. Quite opposite from readings that I get on good outputs for others (short 12V spike, then some small interference and then 0).

So the question for Renix gurus, which of the big ones from ECU - I mean components that are on heatsinks are output drivers? I'm very good with electronics, my welding skills are good and I have great deal on understanding how things with microcontrollers work.. However if anyone knows, it would be much better than removing every transistor and checking it. There are also few IC-s with heatsinks. Hopefully they are not for outputs.. See, the main problem is that I expected to see at least group of 6 of some big elements.. but failed.

Please help, new ECU would be pricey here, and I don't wanna trash this one coz of what looks like trivial problem.

Thanks!

PS, I do have LPG conversion in my XJ, so I can keep driving it.

May be a simply response, but you didn't mention it. Have you checked that the wire harness is intact. I know a guy who built his own ECU for a different engine from a micro-controller using a 16 bit processor. He went through several transistor sets because the ones that he could get fairly inexpensive for injector drivers kept burning up. He ended up having to get some 5 amp rated FET's to run the injectors. My point is i really don't know what is in the renix ECU as far as injector drivers. But my guess is that they are fairly heavy duty. I could see where maybe a voltage drop test on the wire from the ecu connector and the injector connector would be a valid test.

Just my .02

Jerms

PS. I picked up a replacement ecu after mine died from my local self service junk yard for 30$. Might be worth looking into.

Could you link to the thread with the disassembly instructions, and possibly post any images you have?

I'm also somewhat good with circuits, but my RENIX is working fine so far.

If you end up really screwed and need to replace it, I'm sure someone could ship one to you from the US. Here old XJs are everywhere.

There's also MegaSquirt, which might be more effort than you're looking for.

I checked wires and it seems ok. I don't know how would I get such a signal from bad wiring - it would need to be shorted out to 12V and then to have something pull it down to 7 for short period.

I can get very strong FETs at local store for next to nothing, however I didn't write down the numbers from Renix computer - stupid me. It just seems that it can't be the problem. I wish I had.

Anyway around here we don't have jy with jeeps, they are waay overpriced and for every part that is unique to jeep you have to pay hand and leg..

Now if anyone was willing to find one $30 ecu for me, and ship it here, it would be great!

@Jonathan,

The instructions are easy, suggesting to unbolt top nuts that are holding bracket to chassis. There are only two of them (at least in my '90) not three as suggested. Also, there is no point in trying to unbolt computer from bracket while bracket is still in place. There are some nuts on bracket that look promising at first, but later I've discovered that they are welded to it, and you can access bolts only when you remove complete ECU with bracket.

Top two nuts are pain to get, and you will need to push and bend bracket a bit in order to get your hands inside.

Disassembling ecu case is straight-forward job.

I can take it out tomorrow to write down part numbers, and take some photos. It is too late today.

Well, if you get desperate I can try to find an ECU for you. I'm not sure what the salvage yards would charge for it, but $30 sounds about right, maybe just a touch low. Shipping might be killer, though...

mr_W said:

I checked wires and it seems ok. I don't know how would I get such a signal from bad wiring - it would need to be shorted out to 12V and then to have something pull it down to 7 for short period.

Click to expand...

You're measuring this with an injector attached? Have you tried swapping wires between injectors to make sure it's not a bad injector or wiring to that injector?

The injectors may be controller from a single, large chip as opposed to individual transistors or fets. If that's the case, it's probably impossile to find a replacement for less than a used ECM would cost. If you have a meter, you might be able to trace the wire back to one of the items on the heat sink.

I have managed to remove ECU again (took 10 minutes this time!) and track A4 pin (that is #4 injector output) to transistor Q1, which is glued to Q3. I will have to remove them both, and then scratch some sort of protective coating to actually see the marking. I can see just one letter at the moment.

Also about measuring, I did it with injector disconnected and I've compared this not-working output with three of others that are working indeed.

I'll post photos quickly./

Housing:



PCB:



Drivers:


Driver that controls #4 is the one without visible markings. LM2931A should be common thing, and ones on the left I couldn't find online.

And here is the sucker.. blown alright
I'm trying to identify it but no luck so far.. have posted question on electronics related site, hopefully there will be something. If not I can always try with something that looks and feels similar have nothing to lose in fact..

according to this PDF, quite likely they are just simple NPN, TO-220 transistors. I would just try fast-switching, highest current you can get in that package. There is slight mention of Renix (although a Volvo article),
and it shows 3 different configurations, all NPN drivers...

hope this helps

http://www.volvoclub.org.uk/tech/service/850/Waveforms.pdf

Have you traced back one of the other injectors to see what transistor it's using? The LM2931a is a voltage regulator, so probably not what you're looking for.

Yes I tracked others also, and they are all the same. This protective coating was hiding part numbers, but I used some solvent to remove it and got it.
Now, while nobody can yet find them (or equivalent) by that part number, I did read document that cygnus58 has posted. It is indeed good reading on the subject.

I'm also looking into MegaSquirt at the moment, to see what type of drivers they use. So most probably I will find replacement in same package, with highest specs. At the end, it is only used as switching device.

Probably an internal Motorola part number that can't be easily cross referenced then.

Have you checked the other known good ones with analog meter for junctions?
Assuming NPN, BCE configuration, I always hook black lead to base, and junction should read to C and E from that point. This would at least confirm that they are in fact transistors. SCR or FET check so much more differently.
NTE 379 is high speed, high current TO220.

Impresive, most impresive, you left me in the dust with BCE config? Nice article. Wondering where 5-90 is, he has a renix ECU with one or more blown drivers too just sitting around somewhere, only failed Renix ECU he says he has ever seen.

cygnus58 said:

Have you checked the other known good ones with analog meter for junctions?
Assuming NPN, BCE configuration, I always hook black lead to base, and junction should read to C and E from that point. This would at least confirm that they are in fact transistors. SCR or FET check so much more differently.
NTE 379 is high speed, high current TO220.

Click to expand...

This is how it looks, I jumped too fast and said B C E, but it actually has only B and E printed.



I'm not at home right now, so I can't check the other one in detail.

The other thing that got me into more thinking is if these have protection diode. Should be easy to check, but if they do have, I must choose one with it. It would also be good to measure Hfe also. They could be darlington also.
So much thinking, I can't do my work Have to go home right now!

that pic says much of it.
they are surely transistors, if you try a common NPN in place of Darlington, it just won't work right, shouldn't cause any harm. probably no need for Darlington by design, the circuit really is just a transistorized switch. And yes, this is BCE config which is very encouraging.
excellent job getting them out BTW. even the tiny foil looks good.

paydirt!

at least for what each part is and what is does.....

(scroll down)



http://www.diy-efi.org/efi332/other.htm

Damn - not your part number. On to try to see what is is though..

I may be jumping the gun here.....

sorry, overzealous to find what the critter is.