Looking to get better mileage 940se M90 swap

Has the mileage suddenly dropped? Was it always that bad? Did you do all those mods at once? What is your driving style? Way back when I first dialed up the boost on my 240 I got 12.5mpg out of a tank, stock everything at the time, just increased boost and that added power was so much fun I used it frequently and paid the price at the pump. Driving style has a huge effect on economy, exceeding about 60mpg causes fuel consumption to increase rapidly, hard acceleration uses a lot of fuel, getting on the boost causes it to go rich and use a lot of fuel. If you are driving gently and still getting 14mpg then something is wrong with the car. Tweaks and aero mods might get you an extra 0.5-1mpg but it's not going to bring 14mpg up to something sensible.

I should state I'm currently using volvo 960 16" alloys at the moment. so there is no current 17x10 wheel drag currently. I will reset the ecu and then try again and see if I can get better mileage.

@k-jets on a plane the reason it has an M cam is because that was what the 240 motor I received came with. The goal was to get the car running and running properly with the engine swap and +T to the motor and afterwards add the cam to it. I do have a t cam laying around and I do know there is a ton of power and torque that i'm missing out on because of the m cam.

Restore to stock

That is remarkably bad if it's aligned and on original wheels/tire sizes.

I'd try to find what's broken and experiment with driving style and remember rough terrain/traffic/weather conditions as you record your fuel economy or lack thereof

To be fair I had a 1991 945T and in mixed city/highway/traffic that thing always got 18-20ish. Often closer to 18 to maybe 19 once in a while most of the time rain or shine. Which wasn't dismal, but just seemed 1-2mpg low. They're heavy tho and have to be tip top in an auto 940t to do all that well. I had it at the same time as the 1 owner M46 744T, which in stark contrast returned 22 no fuss average city/mixed with freezing a/c and 28-30 most all highway with no drama whatever.

Often I had a fair bit of weight and tools in it, but certainly not always.

Cliffs note History of said miserable 1991 945T:
Bought it with a horribly blown head gasket (melted head).
Did a "redneck leskdown test" and let carb cleaner/atf mic sit in the cylinders over night to roughktndefermine if the pistons had survived and if the bottom end had minimal/at least even leak down and was viable. All indications said "yes" before installing a fresh minty head (barely leaked down from being filled to the top with the pistons all at the exact same height), had good cross hatch and no horrible ring ridge at the top.

Did an extensive stage 0 and measured s ton of things, swapped out anything questionable that could be found, didn't hurry, planned to keep and drive that car a while.

Installed a healthy n/a head carefully installed turbo exhaust valves and shimmed T cam.

Installed minty radiator, fresh hoses, heater valve delete and topical fan clutch along with new tstst and Bosch Germany coolant temp sensor.
Cleaned/resealed injectors with correct Bosch pintle caps.
New Bosch reman amm for testing purposes.
Wheel bearings/brakes all checked out, suspension tight (had pretty new decent shocks / struts on it when I got it).
At some point alignment was checked and little camber mod done.

Engine seemed pretty tight and glass smooth and didn't really seem to use oil, but it probably had some wear though compression and leskdown #s looked good and quite even and it ran beautifully once it was up on its feet, but it wasn't pulled apart and scientifically dissected either, just compression, leskdown and the fact they volume of blowby/oil out the crankcase vent seemed acceptsble/minimal and I'd see a whole lot worse on N/A engines from experience that returned ok economy

I didn't take it on a lot of highway trips but it got about 22mpg with no traffic most all highway iirc not doing anything special to improve or wreck fuel economy.

All I can think is the trans was maybe a little tired, but I don't think that is *all* it was.

Point is it always used s bit more fuel and there was/were probably some niggling little variable(s) (probably not just the transmission) I missed thet was/were marginal due to the car's condition/upkeep mostly and/ or it was buried deep in the AW trans, which mostly seemed to work and shift ok, so there was no apparent justification to swap Ot or rebuild it to try to get the 1-2mpg better thet car might or I felt "should" get. Who knows, maybe that one was built on a bad day?
I wasn't with it from building inception knowing every detail to the 20 years it was driven and accumulated some wear/issues/neglect/hack repairs (which I didn't find any evidence of).

A ton of factors go into fuel economy, more details would help but a +T hodge podge of used largely untested parts is all guesswork to me or the factory service books/guys in white lab coats who came up with this stuff. You have to look at the whole picture/condition of the car.

What I can say is I did have the misfortune of Trying to diagnose anything lol on a hacked up 940T with a B230F+T in it and one complaint was poor fuel Econ. It pinged so easily at light throttle thwt the knock sensor was always being triggered and retarding the timing. It was difficult to verify that.

Timing, air fuel ratio, health if engine, all stock or modified?...and so on. What exactly has been done and what's been verified and how?

okoye said:

I should state I'm currently using volvo 960 16" alloys at the moment. so there is no current 17x10 wheel drag currently. I will reset the ecu and then try again and see if I can get better mileage.

@k-jets on a plane the reason it has an M cam is because that was what the 240 motor I received came with. The goal was to get the car running and running properly with the engine swap and +T to the motor and afterwards add the cam to it. I do have a t cam laying around and I do know there is a ton of power and torque that i'm missing out on because of the m cam.

Click to expand...

Something is definitely not right. What does your sample size for fuel economy look like?

My Evo gets better mileage at the track than this.

Idk what to say I'm running some bpr7es plugs block mount dizzy, boost gauge reads at 19hg at idle. I'm not sure what else could be the problem. I'll change the temp sender at the back of the head and throw a spare amm in as well as an O2 sensor. But obviously each at different times. I need to put my wideband in as well.

Why fire the parts cannon at all?
The coolant temp sensor was only replaced because the original was melted/obviously broken.

Why was a +T engine and the original LH EFI paired together?
Why was that decision made?
What has been tested and using what methods?

So far this thread Title might as well say:
"I swapped in an m90, why isn't my fuel economy teh awesome?!?!"

"It's anyone's guess still, M90 or not."

Kjets On a Plane said:

Why fire the parts cannon at all?
The coolant temp sensor was only replaced because the original was melted/obviously broken.

Why was a +T engine and the original LH EFI paired together?
Why was that decision made?
What has been tested and using what methods?

So far this thread Title might as well say:
"I swapped in an m90, why isn't my fuel economy teh awesome?!?!"

"It's anyone's guess still, M90 or not."

Click to expand...

Yes, we haven't even addressed what MIGHT be causing this issue... why swap parts? It's not magic man... it's internal combustion.

Kjets On a Plane said:

Why fire the parts cannon at all?
The coolant temp sensor was only replaced because the original was melted/obviously broken.

Why was a +T engine and the original LH EFI paired together?
Why was that decision made?
What has been tested and using what methods?

So far this thread Title might as well say:
"I swapped in an m90, why isn't my fuel economy teh awesome?!?!"

"It's anyone's guess still, M90 or not."

Click to expand...

so the car has had 3 motors since I've owned it. The first was the original 220k mile motor that the previous owner over heated and put stop leak in to fix a headgasket issue. The motor ended up killing 3 or 4 turbos so I took it out and swapped the 2nd motor from my high mileage 312k 940se that I'd done a manual swap to and wrecked. That motor blew because it ate a bearing and had a loose conrod cap.

3rd motor is from a 1991 240 that a friend had kicking around and got that for 80 bucks. Buddy and I drilled and tapped it for the drain and I slapped it together to go into the car.

The temp sensors on the motor are the originals and I don't trust either of them. So I'm replacing them.

Car is originally LH 2.4 so I'm not understanding why you are asking why the LH EFI and motor were put together?

But you should still TEST the sensors before you swap them out. It's just a resistance test to find out if it's whack or not. Parts cannons just blow cars up...

What ECU's are you running? NA or Turbo? What AMM #? What injectors?

Car is a factory turbo car so it's running turbo ecu and ezk. Again blue injectors and stock AMM for LH 2.4

I managed to get 350 miles out of the tank, Half of which I was carrying a b230ft in the back.