LH2.4 Fuel injection computer

Okay, my cousin's friend came over today and asked me to take a look at his
240 which he purchased only a month ago and been having some engine
troubles. It sometimes refuse to start (cranks but won't ignite), other
times it starts up fine. And when it's running, sometimes it stalls out for
no apparent reason, and the lambdasond light often stays on.

Both his 240 and my 740 were '90 models, both with B230F engine and LH2.4
injection system. First thing I tried to do is to recall any diagnostic
codes from the OBD. I could only recall the codes from the ignition system
(via socket 6) but nothing from the injection system (via socket 2). I tried
running functional test and self-test with the injection system (test modes
2 and 3, pressing the button twice and 3 times respectively) and again no
response, not even the flashing lights.

Next thing I thought of doing was swapping computers, as they're the same
year with same engine and injection system, I thought they should be
interchangeable. When I plugged my computer to his 240, it started fine and
I could also get the OBD test modes for the injection system to respond.
When I plugged his computer to my 740, the OBD test modes for the injection
system failed to respond again.

Then I tried to start my car, with his computer. The car started, ran for
about 2 seconds before the idle speed dropped WAY low and stalled, and I
couldn't get my car to start again, despite numerous cranking. He told me
this is exactly what happens to his 240 from time to time. At this stage I
am fairly certain that whatever engine problem his 240 has, the injection
computer is the main culprit. One thing I noticed is that his car is still
on the old FI computer, with pink sticker, Bosch code 0 280 000 561 and Made
in Germany. My car also came with that computer and I had idle problems
about a year ago, although not as bad as his. My mechanic told me that the
old computer is prone to failing with age and there's a new updated version
with white sticker, Bosch code 0 280 000 951 and Made in Spain, and that's
the one I got when I replaced my FI computer.

Anyway, the reason I'm posting all these is because I want to ask you guys
if (1) I'm making the right assumption that given both cars are '90 models
with B230F and LH2.4, the computers are interchangeable, (2) with the
symptoms and diagnostic steps I've taken, is it safe to assume his
computer's the main culprit, and (3) if any of you guys also aware of the
difference between the old "pink sticker" computer and new "white sticker"
computer.

Lastly, the fuel tank pre-pump on my 740 comes on when the ignition is moved
to position II (the Bzzzzz sound), but cuts out after 2-3 seconds (assuming
engine isn't started), which is normal for my car I believe. On his 240
however the pre-pump stays on as long as his key is left in position II. Is
it normal for a 240? Are they designed to stay on or supposed to cut out
after 2-3 seconds like my 740? I tried to find the fuel injection relay on
the 240 (and made an earlier post enquiring about its location) but still
couldn't find it.
_________________
Will
'90 Volvo 744 GLT (B230F) - daily driver
'73 Volvo 164E - Looking for buyer (restore or wrecking)

 

All your assumptions are correct. Every time I've seen a computer not
give codes at all, it's needed replacement. Your substitution pretty
well proves it. The computer updates have to do with the cold start and
running programs. And the pump should run just like on your 740. On
our LHD cars, the fuel pump relay is mounted on a bracket on the
firewall, directly over the passenger's feet, above the felt pad.

 

In general any part with the same part number is the same part.

Whenever you change a computer you should change the associated relay.
And no the prepump shouldn't run constantly in his car, it should behave
exactly the same as yours.

Bob