Engine Management Units

It can take some time for an ECU to "learn" your engine. You'll probably find it runs just as well as the old one after a tank or two of gas.

Hi guys,

I have an EMU from a Land Rover which just suddenly failed one day without warning as I was driving down the road. I was wondering if there's any possibility of fixing it, given that schematics are AFAIK unavailable due to commercial confidentiality. Of course there are some basic checks that can be done without a diagram, but take a look at this thing and tell me what I could try doing with it. I've carefully inspected it close up but can find *nothing* at all visibly wrong with it:

BTW, the whole board has been thickly sprayed with clear varnish which accounts for all the bright dots which appear on some of the parts - they're not indicative of any failure.

Any suggestions?

A:try to get a replacement from a car wreckers shop. B:Or get a magnifier glass and start searching for damage/discoloration. And check big caps and big transistors. If no success, try solution A. Or let repair shop handle it.

It's up and running again with an exchange unit, but it ran smoother, quieter and started up quicker with the old unit that failed, so I'd like to get the old one working again if at all possible.

I have fixed a couple of ECM's and in both cases the Xstal failed due to mechanical vibration. Power it up using basic shop electrical prints to the unit and find that the Xstal not operating.

Another one I did was intermitting in some function and popping up codes randomly. I replaced a couple of caps, fixed.. The coating is tricky to get off without damage.

Jamie

That will fix itself.

The same is true if you disconnected the battery for a while with the other one.

I wish. It's been replaced for over 9 months now and it's still the same as the day it was fitted. But this is really about trying to rescue the old one. They don't come cheap!

Try this:

Re-install the new unit. Power up the electrical system, but DO NOT start t he engine.

Here is the tricky part and be exceedingly careful: While powered up, disco nnect the battery, NEGATIVE FIRST. Make sure when that clamp comes off the battery it does so cleanly and quickly. SHORT the positive clamp to the neg ative clamp immediately and hold for a minimum of 30 seconds. This is the f unctional equivalent of rebooting the ECU. Shut off the electrical system. Reinstall the battery. Attempt to start. Does this help?

Note: If you have any coded devices such as so-called 'infotainment' system s and such, you will have to re-code them. If you have a chip-based navigat ion system, remove the chip for this process. But, 3 times in 10, it works. Not bad odds if the alternative is landfill.

If you have a Bosch unit, this is far more likely to work than if you have a British-made unit.... getting back to that old joke: why do the British d rink warm beer?

Peter Wieck Melrose Park, PA

We're getting completely off topic in being distracted by the new EMU, but I'll just answer this point. Every time I leave that vehicle for a few days, I'll isolate the battery, anyway. So it has been repeatedly "rebooted" dozens of times since the old one was replaced.

BUT my question is NOT about the new one; it's about how easily the old ONE can be fixed without schematics (M. Philbrook, many thanks I'll try your suggestion re xtal).

Wrong! The question *solely* concerns the *old* unit that failed.

The issue is with the new part, not the old one.

Have you mentioned this to the technicians who made the change?

RL

Whooops! Meant "OLD" unit. Isolating the battery does not constitute a rebo ot. Shorting the battery leads while the unit capacitors are charged DOES d o a reboot. Mere isolation does not. Hence the need to disconnect the batte ry and short the leads (on the car, not the battery) while the system is en ergized but the engine not running.

Peter Wieck Melrose Park, PA

On 15 Mar 2016, Cursitor Doom wrote (in article ):

Welcome to USENET. There is no ?on-topic?!

Under conformal coating it is difficult to examine anything.

Check any large transistors.

I?d also look for broken solder joints on the large devices (caps, transformer, choke, I/O connectors). Also look closely at the cap ?north? of the big choke. Has it leaked and damaged a trace?

Also check ESR of all the electro caps.

And as was mentioned earlier, be sure the xtal is working. A success story:

Good luck!

If all else looks good, a winding in that transformer might be open. Remove and ?ring? it.

The issue is your dissatisfaction with the repaired automobile.

You're not in a position to resurrect the old ECU.

RL

The new ECU in all probability just requires a software tweak. My question was about the OLD one (at the risk of repeating myself).

Well, are there any symptoms that can be figured out? Do dash indicators do something like what they used to do? If it appeas totally dead, there's a possibility that a voltage regulator or other power switching circuit has failed. Looks like it has a switching power supply, that will make things a little harder. Yeah, the conformal coating is really necessary in automotive gear, but makes rework tough.

Also, check all connectors and other large parts soldered to the board, breaks in the solder joints are supposed to be a very common cause of failure.

Jon

Any chance of posting a super-high resolution image?

If I can figure out how to get the back off and photograph both sides, I'll do it. The blurring issue I am having is with the autofocus which is being hijacked by the two big electrolytics. I'll have to read the camera's FM and find out how to switch it to manual. These damn things are so complicated nowadays. :(