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Stock 1993 940T = 16mpg. combined highway/street driving with a light foot .OMG Don't stop I'm almost there!

240 240

240 240

Millennium Falcon BIG BLOCK CHEVY SWAPPED
Joined
Mar 3, 2022
Location
under the car
Shouldn't I be like 20-22 mpg combined?
light driving, 13c turbo spools super easy. last tank was 15mpg but driving harder to sort out issues and check new intercooler hoses.
When I was driving it daily in 2019-2021 it was about 19-20mpg which is closer to what it should be.

Basically did stage 000.
hoses etc etc. tires are stock hydras on whatever 205/55 tires. Car is slightly lifted. New hoses the whole thing.
15-40w diesel oil. trans fluid new 3 gallon flush. and 80-90 diff oil fresh.
new belts

plugs are light-medium brown. lighter than they should be but not terrible. never did distributor cap but looks good. fresh 8mm ipd plug wires.

compression is good. don't remember numbers but all cylinders even and no smoke under full throttle.

did seafoam 2x and it ran way smoother afterward

I haven't cleaned the tailpipe to see if soot is coming out.

O2 sensor works, but unknown age.

passed smog with flying colors after new cat. Car was super high Nox before the cat.

*********

known negatives.

turbo has small exhaust leaks.

has a thule bars on it, so -1mpg?
lifted -.5 to 1mpg?

California Catalytic converters do a number on old cars. Maybe -1mpg?

california gas is garbage-1 or -2 mpg?

old cat was clogged after 10k miles. not terrible but enough to not pass smog.

*******
My concensus Overview:

I need to really put a wideband on this to see what is happening.
Car shows slightly running lean but is it really? Or are there huge leaks and the fuel dumping is still slightly lean. There's really no or little pinging under load.

swap turbo for one that isn't leaking. This is obvious.

I think the cat is working too well. swap out for high flow outlaw cat and delete stupid rusty resonator for 1 muffler only to help with flow.

I ordered RBP stage 1 chips that brag slightly better mpg and a better map.







TLDR
Car runs super smooth, and plenty of power, but garbage MPG. Am I overlooking anything?
 
That's interesting. If traffic is really bad (construction or lots of bumper to bumper due to an accident) my economy drops to like 16-18 mpg in the city at worst. On weeks when I do a lot more highway and backroads driving I can get it up to 26. Real average between those is about 20-22 mpg in usual driving conditions.

My meager drastically improved after I got a new (used) MAF (cleaned), returned to the factory airbox with a new filter, put an exhaust on it (resonator and a tailpipe vs just a catback side pipe) and ran some fuel system cleaner through it.

My old average when I'd just gotten the car was like 12/18 mpg city/highway.

Take all that with a grain of salt, though - Canadian road speeds are generally a lot slower so I'm very rarely driving it above 3000 rpm and am almost never in boost unless I need to pass someone. Mine's also a stick, so there's that.
 
My Holset swapped 940 does 24MPG (albeit with manual transmission).

Knock sensor OK, temp sensor too?

The cars and engines might be utter shit in every aspect but 16 MPG is way out.
 
JW240 said:
My Holset swapped 940 does 24MPG (albeit with manual transmission).

Knock sensor OK, temp sensor too?

The cars and engines might be utter shit in every aspect but 16 MPG is way out.
Click to expand...
I do run a 171* Tstat, but in summer efan is hitting a lot.

temp sensor should be fine even with varience from tstat.
I doubt is suspect with near perfect emissions and plugs looking lean.
bad temp sensor should be a cold start fuel dump but all the time.
 
fatcatbestcat said:
That's interesting. If traffic is really bad (construction or lots of bumper to bumper due to an accident) my economy drops to like 16-18 mpg in the city at worst. On weeks when I do a lot more highway and backroads driving I can get it up to 26. Real average between those is about 20-22 mpg in usual driving conditions.

My meager drastically improved after I got a new (used) MAF (cleaned), returned to the factory airbox with a new filter, put an exhaust on it (resonator and a tailpipe vs just a catback side pipe) and ran some fuel system cleaner through it.

My old average when I'd just gotten the car was like 12/18 mpg city/highway.

Take all that with a grain of salt, though - Canadian road speeds are generally a lot slower so I'm very rarely driving it above 3000 rpm and am almost never in boost unless I need to pass someone. Mine's also a stick, so there's that.
Click to expand...
plenty of traffic, but I had that when I used to drive this car before and was doing 19mpg on the worst fillup.

3mpg loss, something is wrong.

did you do the exhaust at the same time as amm?

Freeing up exhaust would help mpg.
 
That seems about right if you were driving it hard. I don’t think I ever saw above 20mph unless I was on a freeway road trip and going the speed limit.
The stock tunes are RICH AF when in boost. You can fiddle with the MAF positioning and filter, or try another one. I seem to remember going a full point leaner (like from 11:1 to 12:1) when swapping to a different MAF. But it’s still rich AF for the given setup.
 
culberro said:
That seems about right if you were driving it hard. I don’t think I ever saw above 20mph unless I was on a freeway road trip and going the speed limit.
The stock tunes are RICH AF when in boost. You can fiddle with the MAF positioning and filter, or try another one. I seem to remember going a full point leaner (like from 11:1 to 12:1) when swapping to a different MAF. But it’s still rich AF for the given setup.
Click to expand...
light driving was 16mpg.

Balls to the walls pedal mashing with kiddos laughing inside because they didn't think I knew how to drift netted 15mpg last month. Also needed italian tuneup after sitting for 3 years

before all this tuneup it was like 13mpg.
 
My kjet turbo was consistently getting 16mpg around town. Whether you mashed the throttle or drove lightly. It seemed to love premium gas. Never goes over 20 unless on the highway and I'm sure it wasn't much better than that.
 
I average around 25-26mpg in my 940 w/ M90, 16T and KL IC.
I've gotten it up to 27.5 on lengthy highway trips, it does love driving a steady 75mph.
What made a big difference was the RBP chips, they improved mpg by like 1-2. I see you get that sorted anyway.

FWIW, I do drive like a grandma most of the time and very little stop and go (I live in a pretty rural area) and just go into boost when it's necessary.
 
240 240 said:
I do run a 171* Tstat, but in summer efan is hitting a lot.

temp sensor should be fine even with varience from tstat.
I doubt is suspect with near perfect emissions and plugs looking lean.
bad temp sensor should be a cold start fuel dump but all the time.
Click to expand...

These things seem to like way hotter thermostats for efficiency, 195° IIRC. The later motors do seem to get really worn out compared to the earlier, less efficient cars. @Kjets On a Plane mentioned this some 5000 years ago.
 
Fa182 said:
I average around 25-26mpg in my 940 w/ M90, 16T and KL IC.
I've gotten it up to 27.5 on lengthy highway trips, it does love driving a steady 75mph.
Click to expand...
Fa182 said:
What made a big difference was the RBP chips, they improved mpg by like 1-2. I see you get that sorted anyway.
Click to expand...
I'm curious to see what the RBP stage 1 chips end up doing for my MPGs - my car is similar in spec to yours, except with the stock T cam and 13c turbo. I have some kind of random mystery eBay chips, no clue if they actually do anything. The PO told me they were some kind of fuel economy chip.
Fa182 said:
FWIW, I do drive like a grandma most of the time and very little stop and go (I live in a pretty rural area) and just go into boost when it's necessary.
Click to expand...
Yes, I drive like this too :lol:
 
All the 740/940 Turbos I have owned, and that is on the order of a100 or more, get/got 24 mpg average. The EPA estimates for a 940 15 years ago were 22 city, 27-28 hwy. My current 940T sedan gets a consistent 24 mpg average. On the highway steady cruise at ~ 70 mph all of the 940s I have owned got 27-28 mpg. My customer that bought the last 1994 940 Turbo wagon from me to replace her 940 Turbo wagon that was totaled by an ignorant driver in his Bro dozer complained to me when I saw her a couple months ago that it got terrible mileage. She drives it in town almost exclusively. I asked her what her fuel mileage was. 19 mpg was her response. She had been driving her husband's 1994 940 NA for the past 8 months waiting for me to finish up the 940 T. It likely got more like 21-22 mpg in town. I told her that her car was doing exactly what it was designed to do. Stop and go driving and never exceeding 35 mp, her car was getting very good mileage for the state of technology when the car was designed and built.
 
My old 92 940T sedan got ~18mpg on premium fuel, average city/hwy. BEST it ever did was a highway trip of 24mpg, and that was without cruise. What I noticed in the rolling low hills of the SE, when running in cruise it was in and out of boost constantly attempting to hold speed.

AW71 with 3.73 final...... boost around 18psi with my original Garrett T3.

Economy champs, these aren't.
 
DET17 said:
My old 92 940T sedan got ~18mpg on premium fuel, average city/hwy. BEST it ever did was a highway trip of 24mpg, and that was without cruise. What I noticed in the rolling low hills of the SE, when running in cruise it was in and out of boost constantly attempting to hold speed.

AW71 with 3.73 final...... boost around 18psi with my original Garrett T3.

Economy champs, these aren't.
Click to expand...
I get it that these got poor mpg.
But this same car getting 16mpg 5 years ago instead of the 19-20mpg I used to get, is a 20% loss.
 
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