M30 tune-up update

[zmuff]

I installed a set of 19lb injectors last fall to try and help out my aging 535im a little. Other than smoothing out the engine some, I didn't really notice a difference. OBC average MPG stayed around 16.4. New plugs, wires, cap and rotor, fuel filter, valve adjust, and switch to Mobil1 0W40 in March smoothed things out a little more, OBC average MPG went up to around 16.8. Installed a 3.5 bar fuel pressure regulator several weeks ago and now the OBC average MPG is 19.5, I'm on the 5th tank of gas now so that's a pretty good average. Highway MPG was 23.5 before so I can't wait to do another road trip now and see what it is. The bottom line: the 19lb injectors and 3.5 bar FPR are a very good combination. Thanks Mike Holbrook for the FPR recommendation...it was right on target.

[Derek A.]

I am thinking about doing the same. Any installation tips or hurdles to watch out for ?

Thanks

[zmuff]

The fuel pressure regulator is an easy direct replacement. I used the one from a Porsche 944S P/N 0 280 160 263, seems like it was $49.00 plus shipping. The fuel injectors are a bigger project but not hard, I did mine in about two hours. Use this link to Don Gale's site for play by play action...it's very accurate. http://http://www.nmia.com/~dgnrg/page_17.htm The only trouble I really had was when I was started the car for the first time, it ran like one plug wire was off. I spent alot of time troubleshooting trying to find the miss. I ended up taking it for a drive and it smoothed out perfectly in about five minutes. I am assuming the computer had to readjust itself. For tools, a scribe is handy to help pull and hold the fuel injector clips, a flashlight and mirror to find the one that you dropped anyway, and a magnet to retrieve it from the black hole that it fell into...hehe. Good luck.

[zmuff]

Sorry about the link...here it is http://www.nmia.com/~dgnrg/page_17.htm Mike

[mholbrook]

Glad you had good luck with the FPR change. I noticed the same fuel mileage change basically. I just drove to LA and back last weekend and averaged 25 mpg highway. I'm just a nick under 20mpg average for my all around driving (not including and autocross time). I just finished up doing a valve adjustment, changing plugs, wires, distro cap and rotor. Hope to find a little improvement here since the stuff coming out was in some cases pretty used up.

I painted my valve cover aluminum with clear coat and polished the raised portions as well. I'm very happy with the way it looks.....hope it runs as strong!

[Jeff N.]

Your mileage hasn't really gone up.

When you raised the fuel pressure, you increased the amount of fuel per injector pulse. In response to this, the lamda function of the DME shortened the pulse to keep the a/f ratio within the target spec. You are basically putting in the same amount of fuel to the engine but just using a shorter injector pulse to do it.

The fuel mileage is calculated by duration of the injector pulse. The DME (thinks it) knows how much fuel is used for a specified pulse duration. As the pulse is now shorter (but the fuel shot is the same), the DME is reporting better mileage. But that's not what is really occuring.

Suggest you carefully check your tank inputs vs. road mileage and you'll find this out.

Jeff

[Hector]

installing the 19 lb injectors and the 3.5 bar pressure regulator? I never trust the OBC for calculating mpg... always a back of envelope calculation for me. I was also thinking that if they are getting good fuel economy then something is gotta give, either a slight drop in power output or they are really hitting the optimal a/f peak ratio. It would be good to verify the mpg as you suggest. If these mods really give you good fuel economy, then this is something that many of us would want to jump on.

Your mileage hasn't really gone up.

When you raised the fuel pressure, you increased the amount of fuel per injector pulse. In response to this, the lamda function of the DME shortened the pulse to keep the a/f ratio within the target spec. You are basically putting in the same amount of fuel to the engine but just using a shorter injector pulse to do it.

The fuel mileage is calculated by duration of the injector pulse. The DME (thinks it) knows how much fuel is used for a specified pulse duration. As the pulse is now shorter (but the fuel shot is the same), the DME is reporting better mileage. But that's not what is really occuring.

Suggest you carefully check your tank inputs vs. road mileage and you'll find this out.

Jeff

[mholbrook]

On my car, 1989 535im with 3.5 bar fpr and #19 injectors, the OBC is almost exactly what I'm actually getting dividing miles from the odometer by gallons. After checking this numerous times, the difference is less than 1/2 mpg over a 300+ mile range. That's close enough for me to just use the OBC for my benchmark. The OBC does have some adjustments supposedly but I'm fine with the feedback I'm getting.

[Jeff N.]

That's harder to answer. During WOT, the engine stops using the lamda correction and just goes off the WOT fuel map. With larger injectors and more FP, this will shoot more fuel for the specified injector pulse. Sooo.... if your engine needs more fuel at WOT, then it's a good performance thing. However, my understanding is that most of the aftermarket chips improve WOT performance by adding timing and leaning out the mixture a bit. That would mean upping the F/P & bigger injectors would counter a chip from someone like Mark D. or Jim C.

It's gets really fun when you've modded the engine like I have. Then you get into the whole custom chip world - a very dark and scary place to be!

[zmuff]

I guess I should have mentioned in my original post that I did verify actual fuel consumption versus OBC calculated fuel consumption. OBC function #20 correction factor is dead on to actual fuel used, so I trust my OBC readout.