My 89 740 GL saga.....

I got the car towed back to my place from out of town and so am
able to trouble shoot more extensively. Nope...the air intake hose
between the AMM and intake manifold tends to collapse, restricting air
flow *some*, but it is not ruptured, so there isn't un-metered air
entering.
Like I said in earlier post, it has a code set for missing AMM
signal. I found that the air mass meter on our (running fine) 92 740
(turbo version of B230) is the identical part number (-016), so I
swapped it into the 89 740. Still does not start/ run. Put suspected
bad AMM into the 92 740....it still runs fine, so the code the ECM was
setting for missing AMM signal, at least is not due to a bad AMM! The
connector appears perfect.
Engine seems to have resistance to turning, there is some compression
there. I checked for spark at the coil lead (disconnected from
distributor....I get only ONE spark to the valve cover for each
rotation of engine, instead of four! Also it is very weak, comparing
it with the spark developed by the 92 740. So I subbed in the coil
and coil-to-distributor lead from the 92 740....still had the same bad
spark! Checked the coil ground terminal, its grounded...and the other
terminal for the control pulses from the ignition control computer is
OK.
So now I need to sub in the ignition control computer from the 92
740 and see if that is what is killing the ignition (if it also has
the same part no., that is). But...where is it located? Seem like
when I worked on the brake pedal, there was something that looked like
an ECM module to its right. Is that it?
I know the ECM is what monitors the system and sets failure
codes....could it be bad, making it think that the AMM signal is bad,
and causing the ignition control computer to malfunction? (just trying
to think of a common cause for both the bad ignition and the AMM fault
code). Thanks all.

 

Have you checked the Ignition Amplifier for corrosion on it's mounting
and/or poor heatsink mounting?

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

It should be kinda similar to our 85, but acknowledging the big change in
'88 I could be way off....

The module we have under the dash above the brake pedal is an ignition
controller, but not the "power stage." The controller sets timing, but the
power stage generates the electrical fire. Our power stage is located on the
fender well beside the battery, which is on the left side of the car (as the
driver sees it.)

Some models/years(/locales?) also have a "radio suppression" relay that can
become flaky. I don't have one so I can't help you there.

Mike

 

Ok....I need a little help from someone who is familiar with the '92
model 740 Gl. On the broke-down '89 model 740, I did locate an
electronic module that has a heatsink and a round 5-wire connector.
The Haynes diagram shows a unit with a 5-wire connector identified as
an "ignition control module", not a power amplifier. "Power amplifier"
is not listed! It is located just behind drivers side dash, close to
the the left wall.

In looking at the diagram of this module, there are two wires going to
the distributor, a brown and green one. WHat are these for? Could they
be a crankcase position sensor input? Because the other fault code I
am getting (besides for the AMM) is "crankcase position signal bad or
missing", or something to that effect. Is there maybe a Hall-effect
pickup sensing distributor rotor position? Ha! Maybe the rotor or
distributor cap is bad! But if not.....I need to swap in the
ignition control module from the 92 Volvo 740 and see if that is the
fix. Problem is, I looked in the engine compt. and behind/underneath
LH dash, and couldn't spot it. It's in a different place. I do see a
similar ECM just to the right of the brake pedal....but no ignition
control module. Any clue where they stashed it on the 92 model?

 

Yes there's a hall sensor in the distributor which tells the ignition
box when to fire the coil, if that's missing the car won't run. Also
it's fairly common for the connector to break off the distributor and
that can break the little wires on it, I had that happen on mine once,
now it's epoxied in place.

 

A few points:

I've never seen or heard of that ignition module going bad, so you're
probably barking up the wrong tree there. (Now someone will surely
write and tell me about how theirs went bad.)

The ignition amplifier, aka power stage, aka ..., is located on the
inner fender near the front of the car. Check between the airbox and
fender. This unit switches the high current low voltage that provides
the energy to the coil. This is what Peter was talking about, and is a
common failure.

Your 89 non turbo won't have a hall sender in the distributor, it's the
first year of the crankshaft position sensor. This is also a common
failure part, and is located on the top of the bell housing, just under
the distributor. And since the car won't run without it and you have a
code for this...

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Well, it is fixed!

Could not find an ignition amplifier ANYWHERE on the 92 turbo, so
I decided to forget it and check that crankshaft position sensor out
first. I found that the wires, right where they join the body of the
sensor, had lost their insulation....it had just been dissolved by
some grease that was on it (or maybe some sovlent/grease mixture). It
was just gooey " mush", with 3 bare metal wires within an inch of the
sensor. The wires were shorting, thus killing the signal. I just
cleaned the grease/goo/melted wiring insulation off, and encapsulated
the exposed wires in automovitve "goop" (after detemining that the
stuff is a good insulator), wrapped it all up in fusion wrap, and
reinstalled. On the code readout block, I reset #6 jumper (which had
the two codes set) and then was getting 1-1-1 ...AMM and crank
position sensor codes had cleared. It still didn't want to start, but
I had the timing too far off. Finally got timing close enough, and she
runs again!!
I think I still do not have the timing quite right....power seems
OK, but when you start up from a stop, you hear a clattering sound, I
think it's ping or detonation. Didn't do that before the breakdown.
I can't set timing very accurately as the timing belt cover is gone,
and with it the index. The timing belt cover got torn up by a failed
vibration damper a long time ago. So I noted that on the 92 turbo
740, the engine is at TDC when the mark is at 1 o'clock and set it
there....and on the 89 sedan, the #1 piston does seem to be at TDC
with this position.

Also the car had a very minor miss before this breakdown, and I
just installed a new distributor cap and rotor as they were pretty
worn. Well, it still has the miss...in fact seems a bit worse! All
the plugs are pretty new. Only other thing is the plug wires....could
one of them be causing the miss?
Thanks to all , Jim

 

Just pick up a new timing belt cover from a junkyard, it's a good piece
to have on there.

 

Right, and if you suspect that the timing is not set correctly, there's
no point in searching further for a problem until you verify that your
timing is correct. It sounds like it isn't from your symptoms. Note
that you can't adjust the ignition timing even though you can move the
distributor. Timing is set from that crank position sensor you fixed.
However if the cam timing is off, you can have all kinds of problems.
And also if any work has been done around the flywheel since the car
last ran correctly, then it's possible the pickup wheel on the flywheel
has been physically damaged which can give you all kinds of grief.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Fill a spray bottle with water and sparay the plugs wires while the car
is running. Any insulation fault in the wiring will be obvious.

Bob