My 89 740 GL saga: J Sweet

Well, this is a continuation of the post from yesterday, it wasn't
a fuse problem or loss of power to ECU at all.
It has the B230 (or 2330?) 4-cylinder FI engine, BTW.
To describe a little better what the car is doing, it seems to be
getting around 2 miles to the gallon. Even before the acelleration
problem developed, it had started to eat gas. it will run fine when
in park or neutral,has normal acceleration. When you drive the car, it
will take off with normal pwer from a stop, but right after it shifts
into third, the engine just shuts itself down to idle speed, even
though you continue pressing the gas pedal. You kind of get thrown
forward in teh seat! To get going again, you have to let off the gas
completely, then you have control of the engine speed again.
I was told it was a bad AMM sensor. However, it doesn't look like
that is the problem. HOwever, like I said, the check engine light is
NOT on...and when I read the codes for both 2 and 6 (its the Bosch
LH2.4 system) I got 1-1-1 on both. No codes are being set, even though
it has this severe drivability problem. To test if the ECU was
picking up faults from the AMM sensor, I disconnected it. Sure
enough I then got a 1-2-1 code. SO the ECU is telling me that the
sensors are good.
I noticed that the big flex duct between the air intake and the
AMM has gotten almost kinked off....I thought Aha! Its getting starved
for air! but when I shortened up the duct and repositioned it so it is
not kinked anymore, I still have same problem. I checked the air
filter, it looks fine.
So what could it be.... fuel pressure? fuel pump? The oil and
tranny fluid are fine.

 

Unplug the AMM and see if it runs any better.

 

I had an 89 740 that exhibited similar behavior and it was the wiring
harness. The wiring was shorting out right at the connector by the
passenger side headlight. I forget what it is called but there is a
big square connector over by the passenger headlight. I know that
electrical problems usually cause the car to buck and fuel problems
casue the car to die slowly. Mine was electrical that was shutting off
the gas flow and starving the engine of fuel.

Regards
Russ

 

Fuel pressure regulators have been known to go bad - a quick (and not
positive) test is to pull the vacuum hose off the regulator and see if there
is gas inside the hose. If so, you can be sure the regulator is bad. If not,
you still don't know for sure.

Mike

 

No.....it runs MUCH worse. With AMM connected, it will idle perfect,
and does not run rough/erratic. Disconnected, it will not idle at
all, and at lower RPMs it runs rough. Looking through the grate, the
filament is intact. Thanks, Jim

 

That makes me really wonder about the fuel pressure. The O2 sensor can't put
the mixture off that much, and the limp-home setting isn't right either.
There isn't much left besides fuel pressure being too high. Time to get
serious about measuring that.

I assume *all* the plugs are sooted up?

Mike

 

Well, I will go get a fuel pressure gauge. It doesn't sound easy to
tee into the fuel rail somewhere...and then I have to run the gauge
line through the firewall somewhere so I can watch the gauge while
driving. What a pain!
I don't quite understand why an extremely rich mixture isn't
turning the chk engine lite on, as it seems like the o2 sensor would
trip an "o2 level out of range situation" for the ECU.

BTW, I am not sure my Haynes gives the normal fuel rail pressure. Do
you know what it is? Is the regulator suposed to keep it the same
whether driving or in park?
thanks for the help.

 

Is there a junkyard near you? I've always just kept a spare around to swap
in if there's a problem, it's easier than trying to test the pressure.

 

I cut the fuel supply hose about 1 1/2 inches from the fuel rail fitting and
inserted the tee there, then removed the short piece and connected the hose
back to the fitting when I was through. With the vacuum hose removed from
the fuel pressure regulator (and the hose plugged) the corect reading is 36
psi, or 42 psi for the turbo model. Reconnecting the hose should drop the
reading by the amount of manifold "vacuum" - about 10 psi less fuel pressure
at idle. What you are looking for is a big deviation, like double the fuel
pressure.

In the '89 I don't know if the check engine light would come on with the
rich mixture, but it would make sense that it would. Just a wild thought -
when the battery failed in my Nissan 300ZX the mixture went way rich (so the
top speed was about 40 mph and there was a black cloud following me) because
the ECU was constantly being reset by the noise from the alternator; no
check engine light. Oddly, the engine still cranked okay but replacing the
battery fixed the problem. If you have a DVM around a check for AC voltage
across the battery terminals would ward off a few evil spirits - it should
be below 0.1 VAC. In addition, there should be less than 0.1 volt DC between
the engine block and the chassis - more than that means the engine ground
strap is bad.

Mike

 

Autozone doesn't have a fuel pressure tester, so I am shopping for
one on eBay. This one is available (at a very good price),

http://cgi.ebay.com/ebaymotors/ws/e...ry=43989&item=4557331361&rd=1&ssPageName=WDVW

it has an adapter which actually is made to fit GM, but it is
metric. F itting size: M16 x 1.5 I don't have a clue what the fuel
rail fitting size is on my 740, so can't tell whether this one will
work. Then I have the problem of extending the gauge hose, as 3 ft
isn't going to get the gauge located inside the car to be read while
driving. I think it is best to buy a guage rather than shotogun a new
fuel press regulator, as my brother has a 740 GL also, and I am
probably going to buy another one myself. I haven't had good
experiences with parts from salvage yards, so I would have to pay $52
for a new regulator, posibly only to find it wasn't needed.

I gather that since fuel consumption has gone way up, then the fuel
rail presure might be too high at low speed or idle, and then way too
low when punching the accelerator? I checked the oil for signs of gas
in it...it is okay. I pulled the vacuum line off of the fuel press.
regulalor while running (immediately closing off the open end of
hose), and there did seem to be a slight difference in the sound of
the engine (possibly indicationg a change in fuel rail pressure/fuel
delivery)....but it was very slight.

I checked the spark plugs, and they have a light coating of
blackish stuff, but not jet-black soot...and there is not any smoke
coming from the tailpipe. They all looked identical.

Thanks, Jim

 

Since it's got a malfunction of that magnitude but no codes are being
set, I'd suspect the ECU itself. I had a similar problem with no codes
and it was the computer itself, hence no codes.
I would, however, test the fuel pressure/fuel system.

 

I figured it out!!! That 3 in. black plastic duct running between the
AMM and dthe intake manifold was the problem. It has gotten very weak,
flexible, and so even though the air filter didn't look very dirty at
all, there was enough of a vacuum in the duct when you punched the
accelerator that the duct was collapsing right near the intake end.
And it was collapsing on the BOTTOM side so couldn't be seen readily.
The duct finally "popped" inward and stayed that way after shutdown,
so I spotted it. Now the problem is getting a replacement. Autozone
doesn't have one, and there isn't a Volvo dealer where I am. A generic
duct won't work because the AMM end is about 3 in., and the intake end
is about 3.5 in. ID. So all I could do for now is wrap it with metal
mending tape to help it hold a circular shape. Regards, Jim

 

Isn't there a junkyard nearby you could get one from? The tape should hold
up for now, you might also be able to mail order one.