740 Turbo-turbo problems

Is it possible to convert a turbo car to a non- turbo? I think it is going
south and am tired of throwing money at it.
Thanks John

1989 740 Turbo

 

Short answer: no. There are too many issues to deal with (the question has
come up a lot before).

What indications of turbo trouble do you have? If it smokes badly at idle,
and especially if it clears up after a minute cruising, my guess is the oil
separator and/or hoses for the crankcase ventilation are plugging up.

Mike
1985 760 Turbo.

 

Possible to convert the car; impractical to convert the engine.
--

TSH


For email, replace 'SpamOnlyToHere' with my initials

 

As a practical matter, no. Sell the car to someone who doesn't mind fussing
with the turbo and buy one that came without it.

 

And why would you want to? The turbo cars are much more desirable.

 

Thanks for the input. I figured the answer would be no. It's my daughters
car and I am her personal mech. She reported what sounded like to me to be
turbo noise, ie bearing noise? I told her to change the oil immediately.
Time will tell.

 

Good approach. Mine has been whining for a couple of years, and it's still
okay. (I've been whining for more than 50 years....)

Mike

 

Ok, I got the car today and found the small hose leading down to the
wastegate valve snapped off. Great! Reconnect and off we go, right? Nope.
No change. It sounds like it is dumping all pressure as the turbo gauge
does not respond as it should and turbo sounds like it is free wheeling.
New wastegate actuator? Also, observed rod from wastegate as the wife
revved and saw no movement. What should occur??

Thanks for any help. John

 

The hose has popped off the back of the boost guage, good thing the engine
didn't blow up when it overboosted from the wastegate hose coming off,
sounds like you were lucky.

 

You should get no movement of the wastegate actuator until you're
approaching maximum boost. So revving the engine in neutral will tell
you nothing. Look under the car up at that rod, and see if it's
connected. Also, report the exact symptoms, whether the car seems
sluggish or has lots of power. Let us know everything that is out of
the ordinary and maybe we can help you better.

--
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.)

 

If it's an automatic you can observe the wastegate actuator by setting the
parking brake fully, standing firmly on the brake, place it in drive and
give it gas until the boost needle climbs. Doing this regularly is not
adviseable but it won't hurt anything for a quick test.

Of course there's little reason to test this in the first place, just get
out on the road, stomp it, and watch how high the boost guage goes (after
you put the hose back on it)

 

Ok. I checked the gauge hose, it was attached. The symptoms are as follows:
idles great, no hint of trouble. Car will run fine until load is placed on
it. Then turbo starts howling like high revs. Gauge shows lack of boost and
car is sluggish. I t is almost as if turbo has no load and is free wheeling.
John

 

wheeling.


Ok if that hose is still on there then you have a hole somewhere else, check
the rubber hose couplings right at the intercooler, take them off and check
with your fingers to see if a flap will open. Also check the rubber elbow at
the throttle body, though any of that should cause lots of black smoke when
you accelerate. It's also possible that the hose to the guage has popped off
the tee at the overboost switch down on the pedal bracket or that the hose
itself has split. If you hear air hissing then the turbo is producing boost
but it's going somewhere. If the turbo was rubbing you'd know it, they make
an awful metallic shriek like cutting metal pipe with a chainsaw.

 

It's worth pointing out that if there is a hole in any of the turbo hoses on
the pressurized side, the engine power will exhibit a "fold-back" behavior -
the power will drop suddenly when the turbo starts spinning and will stay
very low (just more than idle) until you let off on the throttle enough to
spin the turbo down, then everything will be fairly normal until the turbo
spins again.

There is a valve mounted to the turbo that shunts the turbo output back to
the input, allowing the turbo to freewheel. I understand it is to prevent
overpressure in the ducts if you lift throttle suddenly when the turbo is
spun up. Maybe it is staying open?

Mike

 

Also, low boost accompanied by hissing can be caused by an almost
completely clogged exhaust, usually the catalytic convertor. However,
if you have the black smoke problem as outlined above, then clogged
exhaust is not the problem. However, continued driving with the above
problem will overheat the cat, melting the substrate, giving you 2
problems.

--
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.)

 

Thanks for all the input. I really appreciate it!! Could the wastegate
itself be blown out? Will continue the quest... John

 

If this is a Garrett turbo, they have a dump valve mounted on the front of
the engine block right hand side. It has about a 1'' hose going to it.
This valve can become loose and you will dump turbo pressure and not feed
it to the engine intake. its worth taking a look at.


Harold

 

I'm not sure how, it's pretty simple mechanically, it's just a flap on a rod
that covers a hole. The actuator pushes against it's internal spring and
pulls the flap away from the hole.

One other thing to check, if this car has a compressor bypass valve is to
see if it's somehow stuck open, the older Garrett turbochargers had a
separate CBV mounted to the left of the timing belt cover, the Mitsubishi
turbos have it on the turbo compressor housing itself.

 

That's a good point, I'd forgotten that valve. The bolts holding the
flanges on the valve that the hoses are attached to loosen, allowing all
the boost to leak out. One of the connections isn't obvious unless you
look right at it.

--
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.)