Hello

We have been told that the above unit has failed in great numbers. I am not sure if the #561 is specific to 89 740's or if other applications were affected. A repair shop familiar with the problem has explained the emergency fix is grounding the fuel pump relay lead going to the fuse box. Has anyone ever attempted opening up the #561 unit to understand what the fault is and why so many units were affected. Weird enough we also had a different 89 740 with unit #557 which failed within the same month. Thanks in advance. See ya Bill

Why don't you open up said defective unit. Examine the solder connections at the main connector with a powerful light and a magnifying glass. Look for defective solder joints, which would show up as dark circles around the pins. Check all other solder joints too.

If there are bad solder joints, resolder them and reinstall the ECU. Worth a try and it might work.

BTW, various relays suffer this fate, the fuel punp relay being the most prone, so why not the ECU.

Hey Steve

Thanx for the help.

Bill

I've experienced the same failure. The only visible sign of problems was baked solder points on the bank of Darlington transistors. The transistors seemingly aren't rated for very high currents and easily overheat under increased fuel pump load such as when the fuel pumps begin to wear/fail. The re-built units come with all new transistors, capacitors and diodes. Unfortunately most of these components have Bosch private part numbers and are virtually impossible to cross reference. Others have mentioned that there may be a circuit board design flaw such as traces too close together or too close to a solder point.

Re-soldering these components before a failure occurs might help extend the life of the unit, but you'd have to be careful to use appropriate heat sinking so you don't fry the transistors and diodes.

I'm a little confused. My 1986 740T wiring diagram shows the fuel pump relay being operated by the ECU, not the pumps. I could see the transistors having problems if the injectors had problems, perhaps. As for soldering, I have never had any problems with soldering components, afterall, these things are passed over a wave soldering machine. I would still like to know if anyone has pulled an inoperative ECU apart and checked the solder joints.

Just my $0.02, or if adjusted for inflation, $2.00 worth.

> I'm a little confused.

Not half as much as I usually am.

> My 1986 740T wiring diagram shows the fuel pump relay being operated

> by the ECU, not the pumps.

Yes, the ECU provides a switched ground for the pump relay, which operates the pumps indirectly. I supposedly knew that, just wasn't thinking clearly. Now that I'm awake and actually have a schematic in front of me, I'm thinking that a general voltage surge would be about the only thing that could kill the pump relay part of the ECU.

All I really know is that on my failed unit some of the transistor and diode solder points showed signs of overheating and that some ECU failures reportedly just affect fuel pump operation. In my case it was a more extensive failure. Tracing these hot points back through the circuitry to their source was a bit beyond my skill level.

> I could see the transistors having problems if the injectors had

> problems, perhaps.

Yes, that's a much better theory. The injectors are pulsed to ground directly through the ECU transistors which have to carry more amps than those for the fuel pump relay. An internally shorted injector might overload the ECU, but I don't think that's a likely failure mode. The injector gets it's power from the radio noise supression (injector) relay. On LH 2.2 systems (but not LH 2.4) there's also a ballast resistor between these. If a surge or short started at or went through one of these then you could have problems. One such possibility would be a worn injector relay where the internal contacts are starting to arc. If I'm right then replacing that relay may be a preventive measure. Another would be an old ballast resistor that is crumbling and partially shorting internally.

> As for soldering, I have never had any problems with soldering

> components, afterall, these things are passed over a wave soldering

> machine.

Yes, but that's hot and fast so it doesn't get a chance to build up excessive heat in the component. If you use a wimpy soldering iron and have to linger with the heat to get a melt or if you're trying to remove a component and have to repeatedly apply heat (especially if you don't have a de-soldering tool) then more heat gets a chance to conduct into and build up in the component risking frying. I suppose it's more of a precaution for us neophytes -experienced types with a proper iron that can get the job done fast have less to worry about, at least that's the rule of thumb I was taught.

> I would still like to know if anyone has pulled an

> inoperative ECU apart and checked the solder joints.

Yep, first thing after checking for a dirty edge connector was to inspect for dirty/cold/cooked solder joints. These are fairly high quality boards so apart from the odd hot spot there was nothing. Anyway, I re-soldered 50 or so points just on spec -didn't help. On a second attempt to actually pull a few suspicious components out of circuit for testing I noticed a couple of the traces at the hottest looking solder points separated easily from the substrate. A solder bridge or jumper wire would repair that -still nothing.

I was able to get a Bosch re-furbished unit without having to do a core exchange. So, being the inquisitive type, I cracked the new one open and compared it side by side with the old one. As I recall, the board itself had a different number, but looked the same to me. Almost all transistors, diodes and major caps were new and, if anything, looked beefier. A few that I checked had different Bosch house part number from the originals. As I recall, I was able to cross reference one new transistor and it had a slightly higher rated amperage than the generic cross reference of the original one.

The old one has been sitting in my parts bin for over a year waiting for the day I've got nothing better to do than attempt a re-build.

It would sure be interesting to hear the story from the techs that actually re-build these things. Probably something like, "Re-build 'em? Heck, we just chuck the board and re-use the case."

Hey Dave

Thank you for your reply. Do you remember whether the Fuel Injection Control Unit's Number on your car actually ended with 561. Additionally what did you pay for the refurbished unit.

When our 561 failed a friend pulled the fuse tray out. He turned the tray over and cut a single wire which ran from the fuel pump relay (seated in the fuse tray) to the 561 Fuel Injector Control Unit. Once the wire was cut, he grounded the end of the wire which lead to the fuel pump relay. The part of the wire that to the 561 was just taped and not used.

The car started then. Have you ever heard of this repair.

I noticed that this wire which connects the 561 to the fuel pump relay had

been kinked. Do you think a kinked wire could have contributed to a failure in the 561.

Lots of questions

Thanx in advance for any thoughts.

Mine was a 571 (used for the '89 B234F). This would be a very, very close cousin to the 561 (used for the '89 B230FT) likely using an identical board layout with only firmware differences.

I paid the equivalent of about U$850 for the refurb unit through a Bosch distributor. Getting one through Volvo would have been about $75 more. Originally, new (non-refurb) units through Volvo were about $1150. Note that units with the same Bosch number may have different Volvo p/n's to reflect things like re-furb vs. new and special PROM's for specific market areas or for specific problems (like cold start).

Cutting the fuel pump relay ground wire and making a direct connection would certainly get the pumps running. You might even have a semi-normal operating engine provided there is nothing else wrong with the LH control unit and it doesn't care about seeing current on the relay ground pin (from your experience, it would appear this is so). However, there is obviously some reason they put fuel pump control in the LH unit. Most likely it's done for safety reasons so that gas isn't pumped unless the engine is running or cranking. Just don't leave your ignition in the KPII position unnecesarily (like to run power windows) or you'll be wearing out your pumps for no reason and, in case of a major accident, remember to shut off the ignition before you crawl out and dial 911.

A kinked wire would only cause a problem if the conductor was severed or the insulation exposed the conductor to a short circuit. With a broken conductor you would notice a weak flex point at the kink. Did you actually check for continuity through that kink to the LH connector? I suppose it's possible that wire was your entire problem. You should be so lucky.

Hey Dave

Thank you for your time. Your response answered all my questions.

At the time of the repair I was watching so I did not question whether the wire was the problem itself. I actually have been learning as people show me things.

Since then, the reputation for the 561 has kept me thinking about it instead of the wire. But you bring up an excellent point.

Thanks again for all your "most excellent" advice.

See ya later