hello,
i'm failing my emissions and i've been narrowing down the problem.

one issue i see, and i don't know if it's related, is my rpm @ 70 mph is about 3k.

my 240s only get to 3k when i'm driving 80 mph.

same engine, b230f, different injection systems bosch vs rex/regina.

is my 940 sensor wrong?

thanks,
byron golden
86 245
92 245
94 944

Our 940 runs that RPM at 70. It's the 4.10 rear axle which causes that relatively high RPM. Later 240 automatics had a 3.73 axle (as did 940 turbos), and their tires were slightly larger in diameter than the 195/60-15 that you find on many 940's, so they would run at lower highway RPM. Against that is the 240's lack of a lockup-type torque converter on their automatics, so the resulting slippage would raise cruising RPM's a bit. In the end - probably little difference. Fortunately, sound insulation in the 940 is much better than the 240, so just ignore the tach!

Both our 1983 240 and 940 will give 30MPUSG with steady 70mph highway driving. The 83 turns about 2600RPM at 70 with the M46/OD transmission and a 3.31 axle, so the higher speeds of the 940 engine are perhaps offset by its more sophisticated (LH2.4 and EZ-116K) engine management systems.

If your car has EGR, that valve and its actuating vacuum solenoid are failure prone, and that will give higher NOX readings.
--
Bob (son's 81-244GL B21F-M46, dtr's 94-940 B230FD, my 83-244DL B23F-M46, 89-745(LT1 V8), 98-S90, 77MGB and four old motorcycles)

Sounds about right. The 95-940 I just traded off came with a 4:10 diff gear. The replacement 780 with 3:73 gear turns around 2K @60 mph.

My 93 945t is at 3k @70mph, Turbo cars had a 3.73 rear axle and a non-locking trans.
If you have a 3.31 rear axle that rpm sounds high, and a locking trans should drop the rpm some as well.
I'm not saying you have a problem, without knowing the specs. of your drivetrain it's hard to know. Are you able to feel the shift between 3rd and OD? If there is a problem the first thing I'd look at is the OD system not working.

hello jonathan,
thanks for your input.

i forgot to check the ratio, but others reported having about the same rpm at that speed.

regards,
byron

Yes, unfortunately 3K for 70-75mph seems to be correct for a NA 940, even with the lockup torque converter. That's what I get with mine, and that's in line with what others get, based on prior threads.

I also find my 240 sounds a bit less stressed on the highway. Major repairs ate my budget before I got around to installing a tach., so I don't know how the actual numbers compare.

john

hello
94 945 turbo is 3,000 rpm @ 75 mph, same on the 95 944 turbo.
your rex/regina car im pretty sure is 4.10 rear and turbo is 3.73 going by memory. your 240 also is geared for lower rpms. i believe they used them gears in your 940 for 0-60 pickup speed.
can you feel your tranny lock-up?
what is your highway gas mileage?
the 94 944 NA we used to have got 27-28 hwy.
i dont see how it would have anything to do with failing emissions, but if you post your emission numbers someone here can probably pinpoint the problem.
good luck
Mike

thanks mike.
this is my first 940. i don't know my gas mileage, yet. just bought the car in may, 2009. i've been working on it since for different things. inspection is one of them.

i'll post the numbers in the next post. failed both times. all that i did didn't put a dent in the high nox numbers. almost the same in both trials.

regards,
byron

High NOx numbers points to an air leak in the intake system, makes the engine run lean, higher temps, more NOx.
Have you checked the output of the O2 sensor?
--
84 242Ti IPD bars&springs, 89 745 16v M46 IPD bars, 89 744 16v M46 IPD bars, 93 945 Turbo AW71, 91 245SE AW70 IPD bars, 93 245 CLassic M47

hello jeff,
thanks for your reply.

no, i haven't checked the o2 sensor, but i did check the obd codes, all 1-1-1.

the o2 sensor is 4-5 years old but with only 30k miles on it.

you think it would go out that fast?

regards,
byron