J. Sweet: 740 rpms cruising?

Well, I finally drove the 92 740 turbo wagon enough to get a MPG
figure. Not good....16 mpg, mostly highway speed. The kickdown cable
has been adjusted to where the tranny does shift into high gear (at
first it wouldn't). THe turbo is working perfect, the engine runs
really smooth! But I am thinking it may still be turning more revs
than its supposed to, making it eat gas. At 60 mph, it is turning
2500 rpm. That is an awful lot more revs than my 88 Camry turns! I
know the O/D has kicked in, as when I hit the button on stick, it revs
up to 3500. A spare tranny came with the car, but no telling if it is
REALLY a good tranny, as the motorheads (not good ones as it turns
out--- since they assembled engine without crank pulley key) claim it
is. Replacing a tranny is beyond what I would want to tacke myself,
and probably too expensive to have done, so if it is a tranny issue
making the MPG bad, then I need to buy a replacement car that gets
near double that. On the other hand there is possibility the car is
running too rich....but it seems that if the control system was
out-of-wack, then I would get a check engine light. How could I test
for a rich condition without one of those sensors you stick up the
tailpipe? I recently had the fuel rail up to check each injector, and
all are fine, none are stuck open, and none leak. Should I maybe
change O2 sensor and PCV valve and see if that helps MPG? I hope it is
an engine issue---- not tranny, as I can do something about that, and
possibly not cost much. thanks, Geronimo

 

As you accelerate, do you hear and see the shifts from first to second, and
from second to third? You may have to disable OD to verify that.

Mike

 

Mine runs about 2200 RPMs as I recall crusing at 60 MPH, it has an M46
manual gearbox and gets 25-26 MPG on the highway and about 18 around town.
Something is still screwy if you're only getting 16, I've gotten that low
once but I was really thrashing it and mostly around town. With the slushbox
you should be getting 22 or so highway and around 17 in town.

 

Well, it definitely shifts into third. 1st to second is perfect, and
automatic....however, you have to let the car wind up to abt 3400 RPM
in second, then you have to let off the gas a little to get it to
shift into third. If you don't let off the gas a little when it should
shift, it never will shift into third. You can make it shift into
third at a lower RPM, but because of the load on the engine, it won't
want to stay in third as you are getting up to hwy cruise speed.
Since my 740 turbo wagon doesn't have the manual gearbox, it
probably has a different RPM for hwy speeds. (Man, I wish it did have
manual shift!) Hopefully I can figure out some way to determine if its
running rich, as I need to rule that out as a factor.
I have tried putting more slack in the kick-down cable, but it did
not help with the third gear shifting.

Thanks, Geronimo

 

Well you could convert it to manual, I've done that to a couple Volvos and
it's pretty straightforward so long as you can find a donor car at a wrecker
with all the parts you need.

 

I'd guess that the torque converter isn't going into lockup. That is of
course if a 92 740 has a lockup torque converter?

Shawn

 

Even so, it should still do better than 16 mpg, that's pretty bad.

 

Hi all,

I've been watching this thread so, out of curiosity, when I went on the
the freeway today I kept an eye on my mph/rpm on my 1990 740 GLE (B234F
non-turbo) with auto trans and I got about 2500 RPM at 65 and about
2800/2900 at 70.

My average MPG has consistently been just a little bit below 24, perhaps
23.8 overall.

All the best,

Perk >)

 

Gee, thats not all that different.....at 65, mine (its turbo model) is
doing about 2700rpm, only around 200 rpm faster.

I don't have a clue whether the tranny is lock-up type or not, and
whether there is some external circuit/relay that could be at fault.
I don't think I have seen any electrical control circuits for tranny
in either the Haynes or Chiltons manuals. Anyone know?

Wonder if there are automotive shops that have those exhaust gas
analyzers? I think those anayzers can show percent O2 and thus
indication of rich or lean mixture. In Texas they are scarce I think,
as you don't have to have an emissions test....or at least not where I
am in Texas. I can at leaast see that there is not a puddle of fuel
below the exhaust piple after it runs a while, and it doesn't smell of
fuel, either. The exhaust is normal/ clear.

At such a poor mileage figure, with gas price very high, it just
doesn't pay to keep the car, it would actually *save* money to pick up
payments on a mid-90s manual toyota or Camry. But I have invested so
much time and money (like brand new set of tires) into it already.

thanks, Geronimo

 

This
http://store.summitracing.com/partdetail.asp?autofilter=1&part=ATM-2244&N=700+115&autoview=sku

plus this

http://store.summitracing.com/partdetail.asp?autofilter=1&part=ATM-3375&N=700+115&autoview=sku

will give you real time indication of your air/fuel mixture. If you can
determine which is the signal wire from your O2 sensor, you would just need
the gage.

Shawn

 

Could always do the shotgun approach. Replace the O2 sensor, rear coolant
temp sensor, remove the injectors and have them tested/cleaned and if fuel
consumption is still high try swapping the AMM with a good used one.

Don't forget also the possibility of a fuel leak.

 

Well, that is an expensive means to find out mixture. Not $$$ for that
now. Seems to me if I just tapped into the signal wire from the
existing O2 sensor, and read it with a D.M.M., I could see what the
mixture is. The problem is tht I would have to have a chart to
interpret the voltage reading, and I don't know if such a chart is
available on internet. I think it is millivolts?


Hey James: I was thinking that the sensor connector under the intake
manifold toward the FRONT was the one feeding signal to the ECU, and
the conn. behind it, towards the REAR, was for the gauge in inst.
cluster. Have I got it backwards? I am finding some bad connectors,
as the rubber insulation that holds the pins in place inside the
connectors has hardened and crumbled from age/heat.

 

James:

(see earlier post first) Well, I pulled both temp sensor
connectors off one at a time, and you are right----the one driving the
gauge is in front. But something strange. Eiiither one, when
disconnected, sets the CHECK ENGINE light on! This could not be
unless both temp sensors tie in to the ECM. But why would the sensor
for the gauge be tied in also? And it seems to be bad. THe temp
gauge NEVER goes above mid-scale, no matter how overheated the engine
becomes. (There were a couple of steaming overheats before we realized
there was this problem with it). When I swapped in a whole new inst.
cluster trying to fix the speedometer problem, the temp gauge still
did not go above mid-scale, so that is why I think the sensor is bad.
When I saw that a new sensor would cost around $40, I just got me a
whole new temp gauge and sensor for $15.00, and rely on that now.
But since it sets the check engine light also, maybe it could have an
adverse effect on performance/gas mileage?

It seems a little odd for a thermistor to fail like this....increasing
or decreasing its resistance to a certain point, and then not an ohm
further. If it is a negative coefficient thermistor, then maybe
there is an abnormal external resistance, and it cannot go lower than
that?

 

Usually when the sensor fails, it goes open circuit. You should be able to
find one at a junkyard, I've never paid more than $2 for one. IIRC they're
about $20 online brand new.