760T

I have a problem with my `89 760 turbo,can any one tell me why it will not
run more than about 1800 rpms? The turbo seems to be working fine, we
replaced the fuel filter,& the TBS. At lower speeds it runs great. If you
are driving on flat land, you can get your speed up, but when come to a
hill it will not speed up. It does not make any noises, it just cuts out &
won`t go any faster. It has 191,000 miles on it.

 

My first thought is a hole in one of the rubber ducts between the turbo and
the throttle body. Even a hole that your finger fits tightly in will release
a lot of air when the turbo spins up (whether or not the throttle is open
far enough to send boost to the manifold), and that air has already been
measured by the AMM so enough fuel is being injected to use it. The result
is that the mixture is way too rich when the turbo spins. Often it creates a
weird "foldback" sort of response, where everything goes fine even at full
throttle until the engine should start generating power - then the engine
stumbles right down to an idle. If you back off completely on the throttle
it will soon regain its balance until you ask it to put out power again.

Feel along each of those large hoses at each side of the intercooler (you
will probably want to use a paper towel or rag to keep the goo off your
fingers) or remove each hose for a visual inspection. The hole will usually
be surrounded by a soft spot. The hoses are expensive - about $50 to $100
S - but you would be wise to replace all of them if you find a hole. I did
mine one at a time, but they all failed within less than a 2 year span. I
didn't replace that short blue silicone piece on the turbo, though. In the
meantime it is possible to patch the hose with a cut up aluminum can and
duct tape, provided the hole isn't in a sharp bend.

You will probably also find a hole dissolved through the underside of the
turbo intake duct where it joins the turbo. That duct isn't pressurized, so
it doesn't cause the radical symptoms of the others. Good thing, too - I
paid $150 US for a replacement about five years ago. I understand there are
aftermarket sources with more reasonable prices.

Mike

 

Do you get heavy smoke from the exhaust when it bogs down?

 

No, it doesn`t smoke any time. Also I checked the turbo hoses & didn`t find
any holes or soft spots.

 

Now I forget exactly what the symptoms are, is the turbo developing any
boost at all? IE is the guage going into the yellow?

 

The original text: "I have a problem with my `89 760 turbo,can any one tell
me why it will not run more than about 1800 rpms? The turbo seems to be
working fine, we replaced the fuel filter,& the TBS. At lower speeds it runs
great. If you are driving on flat land, you can get your speed up, but when
come to a hill it will not speed up. It does not make any noises, it just
cuts out & won`t go any faster. It has 191,000 miles on it."

It was the 1800 rpm that got my attention because that is the region where
the symptoms of bad turbo hoses appear. The turbo hoses affect the mixture
even if the guage never goes into boost - boost only has to appear in the
hoses. There is some relation to the throttle setting because more throttle
means more gasses driving the turbo. In the end, trying to exceed about 40
mph on level ground with a hole in a turbo hose (except the inlet hose) is a
lost cause - Lord knows I've tried! Come to think of it, the hose on the
non-manifold side of the idle air control valve will do that. I replaced
both those on our car when the one on the manifold side cracked. Sorry if I
sound like a broken record on this, but the symptoms sound so much like a
big leak in the induction system between the turbo and the throttle body
it's hard to focus elsewhere.

It would also be a good clue to know when this happened - one day it started
okay and wouldn't drive away, or it suddenly did that when using the turbo
or when just driving.

Mike

 

Well first thing to check is that the turbo isn't siezed, but if the guage
is going into the yellow then it's not. Next, I would suspect the timing
belt has jumped a tooth, it's really amazing how much of an affect this will
make on the engine, my dad's 240T did it once and suddenly the car would
barely go 5 mph, then after the literally 10 seconds or so it took to
develop boost it would suddenly spin the tires and take off like a rocket.

 

A blocked fuel filter will give the same results, either main one or in-tank
pump pick-up filter.


All the best, Peter.

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

 

The turbo gauge shows that its working.I will check the timing, but
everything works fine at lower speeds. I put a new fuel filter (main) on &
a new fuel pressure regulator, I don`t know what the fuel pressure is, but
when the line is loosend, it has a strong spray. Could it be an electrical
problem? Thanks for all the help, I really need it!