Fuel Injectors and Computer Reset

[WhyNot]

i'm going to be upgrading my fuel injectors.
i think my 91 325i has a memory of some fuel trim adjustments [DME].
Should i reset the system [disconnect battery overnight] or should i leave it alone?
thanks
whynot

[E30-325iS]

If by upgrade you mean going to higher flow,e.g. 19# then it either won't work or be of little benefit unless you also change the chip in the DME with one designed for the injector flow rate.
If you are just replacing them with rebuilt ones of the same capacity then a reset wouldn't hurt, just disconnect the battery while you change them over and it will be reset by the time you are finished installing the new ones. Let it idle for several minutes after the reset and then take it for a drive.

[dnguyen1963]

19# + stock chip = problem. Don't do it.

[nando]

i'm going to be upgrading my fuel injectors.
i think my 91 325i has a memory of some fuel trim adjustments [DME].
Should i reset the system [disconnect battery overnight] or should i leave it alone?
thanks
whynot

yes, it has a long term fuel trim memory. reset it.

be sure your AFM is working, your O2 sensor is new, you don't have any vac leaks, and your TPS is working/adjusted properly. it'll work fine. although, there's not much benefit.

[WhyNot]

thanks for the replies, i appreciate them.
my e30 didnt feel as smooth as fuel injection should.
power delivery, idling, and all around driving just didnt feel right.
it almost felt like a carb car that was running rich and would run better as it cleaned it self out. i used lucas fuel injector cleaner which helped the idle a little bit.
after getting a little edumacation of injectors and seeing the videos here on #6 http://www.r3vlimited.com/board/show...14#post3282114 i figured 20+ year old technology isnt ok anymore.
on the same thread TurboJake suggested these;
The 1998-2000 mercury Mystique/Ford Contour 2.5l Non-SVT injectors are Bosch Design III 4 hole pintleless design, that is 17 lbs/hr @3bar (slightly less flow than the M50 injectors, and 4 hole)
Bosch part number 0280155771
http://www.ebay.com/itm/280929104544...84.m1423.l2649
this link is the current version of the ebay fuel injectors i got.
i did a little more info stuff and then ordered them after they answered all the questions to make sure they are rebuilt and tested correctly and they took quite a lot of time to help me get my mini degree in fi. i figured if they are this helpful and i havent bought anything they are good people.
so i put them in last night. no big problems on the install.
started it up and the idle settled down after a few minutes.
did a 3k max rpm drive for 40 miles then 4k for 15 the 5k for 10 then drove it like normal, bouncing off the rev limiter.
the short story here is ...wow , what a huge difference everywhere.
it start up better, idles smoother without any lumps, has more bottom end and i can lug in 2nd where before it would stall, the power is right there with no delay, the overall power is much more linear.
overall it has more power but not like a new cam type of power.
its quite a bit faster and although i dont track mpg, the instant mpg guage is a few higher for how ever accurate that is.
im planning on doing a good write up on the entire removal & installation process on my m20. it wasnt hard to do and the worst part was the gas smell. maybe 3 hours including a 'beverage' break or two.
just my

whynot

[BMWManiac]

I just installed some m50 17 lbs injectors, and my car sounds like its constantly misfiring....or I drive what sounds like a wrx....no CEL, but I can hear through the exhaust what sounds like a pulsing noise...kind of like misfires....

Do you have to remove the intake manifold to swap out the injectors? Or is it possible to pull the rail? I hate removing, but I think I'm going to go back to the stock injectors.

[nando]

you can change injectors by only removing the fuel rail. it makes it a little easier if you remove the valve cover first.

[WhyNot]

^^+1
Take off valve cover, don't take clips off injectors,
I'm typing on phone, more later.

[jlevie]

...wow , what a huge difference everywhere.
it start up better, idles smoother without any lumps, has more bottom end and i can lug in 2nd where before it would stall, the power is right there with no delay, the overall power is much more linear.
overall it has more power but not like a new cam type of power.
its quite a bit faster and although i dont track mpg, the instant mpg guage is a few higher for how ever accurate that is.
im planning on doing a good write up on the entire removal & installation process on my m20. it wasnt hard to do and the worst part was the gas smell. maybe 3 hours including a 'beverage' break or two.
just my

You'd have probably gotten the same result, or close to it, from having the injectors cleaned and rebuilt. The adaptation in the DME will compensate for the higher flow rate of those injectors by reducing pulse width. That means that mpg gauge will indicate slightly better mileage.

[WhyNot]

You'd have probably gotten the same result, or close to it, from having the injectors cleaned and rebuilt.

maybe, maybe not. i dont know enough to say how much the atomization of the fuel plays but the two videos say that the newer designs are better. and if i had to pay for the rebuild anyways, and these are flow matched, i figured why not get the newer design.

The adaptation in the DME will compensate for the higher flow rate of those injectors by reducing pulse width. That means that mpg gauge will indicate slightly better mileage.

ahhh. i always wondered how it was doing that instant mpg. i guess the average mpg will be off also, which is ok since it is being replaced by a euro clock.

I didnt put in a new oxygen sensor. i've heard that you can clean them with carb cleaner that lists that it is safe for o2 sensors.
i dont know if cleaning is worth it though.
how important is it to use an oem o2 sensor and/or what are good brands?

thanks

[nando]

the stock O2 sensor will come with the right plug. you can use basically any 4-wire narrowband sensor, but you'd have to wire in it yourself.

[jlevie]

Cleaning an O2 sensor doesn't do any good. That can't get the contaminates out of the sensor material.

With the injectors firing as two banks of three I really doubt that a minor change in spray pattern is going have much affect. It has bigger effect on engines that have per-cylinder timed injection

[Quinthirty]

19# + stock chip = problem. Don't do it.

What about: stock chip+ 17lb (M50 stock injectors) @3.5 bar? Is it a problem?

[jlevie]

What about: stock chip+ 17lb (M50 stock injectors) @3.5 bar? Is it a problem?

I would think that would be a problem. I suspect the DME would run of fuel trim in trying to get back to stoich. The engine would probably be okay at high rpm, but would have a poor idle.

If you are thinking of this as a "more fuel equals more performance" it doesn't work that way. Using O2 sensor data the DME will learn to use more or less injector on time as necessary to obtain stoich conditions. The only way to change that is by changing the targets in the DME, i.e., a chip. The stock injectors have more than enough capacity for a tuner to get everything that a stock engine (or one with bolt ons) can deliver. Larger injectors are only needed when going to forced induction or if serious work has been done inside the engine.

[nando]

are you going to try and run them at 3 bar or do you mean they're rated 17# at 3.5 bar?

I'm 110% certain you won't run out of injector trim with a 17# injector anyway.