Now my 92 Volvo turbo wagon is not running!

It has the LH Jetronic fuel control system.
THis is very strange. I was running around town when it began to die
when I released the gas pedal....the idle was gone. Then it rapidly
progressed to where the car would sort of start, but very rough, and
then since it seemed to have started, I released the key, and it
immediately died without ever accelerating any. When troubleshooting
it the next day, the leak had temporoarily lessened to the point that
it would start and run, but rough...so then I was able to hear a
leak,locate, and fix it. A rubbber cap I had installed on a tee on a
vacuum line coming off the intake manifold had deteriorated and split,
and so it was sucking a lot of air....you could her it. So
immediately after replacing the bad cap, then the car ran perfect
again. But,,, in the evening of same day, my wife tried to drive it,
and it would not start again! And it was the very same symptom again.
You hear it beginning to catch.... the cylinders are firing, but very
rough.... and so you release the key and a second later it dies,
without being able to accelerate. If you don't give it gas, it dies;
if you DO give it gas, it still dies. Every crank you get the same
thing.
So I put my fuel pressure guage on it, and there is good pressure.
I put my vaccum guage on, and at the point when the cylinders fire for
about a second, maybe two, before releasing key/engine dying, the
guage stayed at ZERO. So....how could it be that it just happens to
spring another massive leak? I had a problem similar to this last
year, and there was a barbed union on the inlet tube to the idle air
valve where one side of the tube had come loose, causing a masive
vaccum leak. I checked that again, the whole length of it on inlet,
and the other side, and it seems OK. I looke at all the vac lines in
the top of the intake manifold, but I found no leak, and now you do
not hear any tell-tale hissing. THe ECU is not setting any codes,
either. SO...what to check next? I am still suspicious that it is a
big vaccum leak, as with the engine firinng/sputtering like that for 1
or 2 seconnds, it sieems like I should see the vacuum guage kick
upscale some.....right? Should it show a little upscale movement even
when just cranking? I ckecked the timing, it has not changed. Any
ideas?

 

First thing I would try is unplugging the air mass meter. Also check all the
plumbing between the airbox, turbo, intercooler, and intake manifold, the
symptoms are what you'd get if any of those pipes were disconnected.

 

vacuum line to the power brake booster? Or perhaps a ruptured diaphraghm
inside the brake booster itself?

 

BINGO!!!!! It's the AMM as you suggested. I never would have thought
to try disconecting it, after all the ECU wasn't setting any codes.
I disconnected it, and then the car started and ran...but the idle is
only at 300 RPM, it just barely keeps running at idle without the
AMM....but this allows the car to run, and when you rev it up, it is
fine. And of course the CHK ENGINE light came on with it disconnected.
Sheesh...that sure is an expensive part though! On the bright side, I
shudder to think how much I would have paid to have this repaired at a
shop....they would probably have put hours into it in labor, and
probably doubled the price of the part.

THe car ever since we got it a couple of years ago, is getting poor
gas mileage. it's only about 17 even on highway. I know that since
its turbo that probably reduces the MPG some, but still shouldn't it
be in low 20s? I am just wondering if that AMM could have gone
off-spec causing poor mileage, before completely failing. Perhaps
not, as it would show up in the mixture being too rich I suppose. I
had a shop check the mixture and timing not long ago, and they are OK.

Many Thanks, Geronimo

 

There's a good chance your mileage will improve with a new one. They often
fail in such a way as to not cause the computer to complain, but one day the
car will simply not start.

I once got better than 31 mpg in my 740 Turbo, that's with a manual
transmission and was mostly highway and driving with a very light foot, but
you should be able to manage 24 mpg highway without too much trouble, and
certainly better than 20.