Swapped out the injectors on the S50 car...

[Nick M3]

After working down a list of the various possibilities for slightly rough running, I finally got around to switching out the stock tiny 17lbs. injectors for 24lbs. of a modern design (along with a matching tune, of course).

I am honestly kind of shocked by the difference that it made.

I have always known that the stock injectors caused the car to lean out at the top of the rev range. Both on the dyno and in testing with a wideband, the mixture went to about 15:1, which is on the lean side. (For those of you who haven't spent time learning about fuel mixtures, a 14.7 ratio is the "perfect" mix for efficiency and emissions. Theoretically, there is exactly the right amount of O2 to completely burn the fuel, without creating nasty byproducts. Higher ratios are lean, lower ratios are rich.) Ideally, the car wants to be around 12-13:1 in this range for maximum power.

What I did not expect was that the car would be smoother from idle and all the way through the rev range, whether at part throttle or wide open.

I suspect that this was a combination of 18 year old (albeit <70k mile) injectors along with the more modern design of the replacements. '95 M3s have always been lean up top on the stock injectors, but I don't really see any reason why it should run better down low. Either way, I'm thrilled. If any of you still have an OBD I car, new/rebuilt injectors are well worth considering. (I spent a whopping $60 and 30 minutes on this.)

[Nick M3]

(I figured that for once I would actually try to talk about cars...)

[wdc330i]

Originally Posted by Nick M3

(I figured that for once I would actually try to talk about cars...)

Well done.

[John V]

I had a set of 24's in my '95 M3 (with a tune as well) and found that the car ran quite a bit better with them. Of course, I put the 540i intake on the car at the same time, so it's hard to say what helped the drivability more. Best part is the gas mileage didn't appreciably degrade.

[Nick M3]

Originally Posted by John V

I had a set of 24's in my '95 M3 (with a tune as well) and found that the car ran quite a bit better with them. Of course, I put the 540i intake on the car at the same time, so it's hard to say what helped the drivability more. Best part is the gas mileage didn't appreciably degrade.

Well, I switch from the TRM 3.5" MAF/stock injector tune to the TRM 3.5" MAF/24# tune. That's about as direct a comparison as you can get.

I wonder if the injectors get stressed by the demand placed on them?

The E30 OBC is pretty hilarious now. It thinks that I'm getting 54MPG on average. (It's calibrated for 14# injectors on an M20.)