'83 Volvo no start, but AMM checks okay

Hi All!

I've got a '83 240DL with few miles (around 90k) with a sudden and
unexpected case of no-start. The symptom is a typical AMM failure. I can
start wonderfully, but it stalls 1 or 2 seconds later. Disconecting the AMM
lets it run, but very roughly (limp home mode).

Here is what I have tried so far:

1. Checked the resistance of AMM leads according to Haynes manual. No
problems here (~4ohms and ~600ohms, and changes properly when I turn the
pot).

2. Swapped the AMM and plastic intake baffle (between AMM and throtle body)
for a used loaner. No luck, same symptoms.

3. Checked all the tubes for leaks: vacuum lines, baffles, intake, TB, idle
control valve, etc. Nothing found, although I (and 2 witnesses) hear what
sounds like a sucking noise or whining somewhere around the idle control
lines and valve. Unfortunately, I checked with a stethoscope (ok, well, a
tube to my ear) and the sound is just kind of everywhere, not in any
particular place.

4. Checked the air filter. Seems okay, a little dirty. Removing it doesn't
help.

5. Removed and inspected idle control valve (checked resistance, too).
Looks
like new, rotates fine, resistance right on target.

6. Checked resistance of AMM, coolant temp sensor, idle control valve, etc,
from the passenger side compartment, at the LH control computer connection.
Everything seems fine here, too.

7. Checked as many wires as I could for continuity at the LH computer
connector, and checked every pair for possible shorting, and checked for
possible ground faults, and bad ground connections, etc. No problems found.
Since this is one of the biodegradable-wiring cars, there are some badly
deteriorated wires, but they seem unrelated, and have been completely
stripped of insulation for years. In particular, the lead wire for the
console coolant temperature sensor (this one connects only to the
dashboard,
I think, and is positioned just above the knock sensor), the oil pressure
sensor (again just for the dashboard, I think), and the little wire coming
off the alternator near the oil pressure sensor. All these are totally
bare,
and doused in oil.

8. Tried to check the fuel pressure regulator, but having no vacuum pump
thing, the best I could do was detach the vacuum hose and look for dripping
gas. I did smell a little gas, but the whole thing is running so rich that
my whole yard seems to smell like gas.

So obviously I am a bit out of ideas. And I am running out of favors at my
favorite garages -- the first loaned the AMM, to no avial, the second
hunted
for a vacuum leak without success, and the third tried adjusting my
throttle
position and fiddling which only made the car sound better but still in
limp-home mode.

It is a bit chilly here (5-deg F). But if anyone has any ideas whatsoever,
I
would love to hear them. Perhaps my loaned AMM is also bad (it also checks
out with an ohmmeter)? Perhaps those bare wires are the culprit? Or my huge
oil leak in one of the gaskets? The fuel pressure regulator (is there any
way to test this more thoroughly?). Bad injectors? Bad LH computer?

Hopeful in Ithaca,
-kev

 

Are you sure the used loaner has the correct part number on it?

 

Things that cause richness:

1. O2 sensor shorted to ground.
2. Holes in bellows tube (corrugated tube between the MAF (AMM) and the
throttle housing)
3. Shorted orange wire on the throttle switch (grounding gives full load
signal to the Chrysler box which relays the signal to the LH box and
causes the injection to go full rich.)
4. Restricted exhaust. (Cat may be packing up from rich running, catch-22
DO loop).
5. Leaking fuel pressure regulator (when the regulator fails, gas streams
from the vacuum fitting and fills the manifold.)

Things to consider:

1. Usually the car will not run at all if the mass meter is good and it
is unplugged while the engine is running, but if the mass meter is bad
and the car won't even start, disconnecting the the plug sends the car
into limp home mode and the car will idle and may be moved once the
engine is warm with great difficulty.

2. After the car has reached 1500 RPM for a few seconds and then shut
off, after about ten seconds the computer sends 12v to the hot wire in
the mass meter. At 12v the nichrome wire glows near yellow/white to burn
off any deposits on the wire. The only draw back is that a short in the
LH harness can allow the computer to commit suicide by inhaling 12v on an
unprotected port.

3. There is a wax pellet thermostat in the base of the air filter housing
that regulates the fresh air/preheated air control flap. As the sensor
heats up on the preheated air stream it gradually closes to permit only
fresh air into the filter housing. After a year or two the thermostat
fails to the default position of preheat (hot) air only. This kills mass
meters in the summer when it tries to keep the hot wire temperature high
enough to match the thermistor reading of 130-200 degrees F.

The short diagnosis is what you've already. The mass meter has gone away.

Bob