BLM numbers.. question

[NC87GN]

By changing injector constant I can get my BLM's up to 120 from 102. Are there any adverse affects in raising injector constant? Will I have to take some fuel out from my PE trim vs. RPM table? Wonder if I have to mess with another table to compensate for the change? TIA



Mike Banas
87GN
mbanas@triad.rr.com

 

[wilkinshc]

Assuming all is in tune (good Maf, good O2). Getting the blm close to 128 is good. I change the injector constant till I get the first two blms close to 128 then adjust the PE vs Rpm table to get the rest as close.

Chuck

 

[Brooks]

Hi Mike, I'm no guru but I've been going through this exact scenario over the last week or two so I'll toss my two cents in!

The explanation a friend has given me is...

Short: If you raise the injector constant you'll have to raise the amount of fuel given in the PE-RPM table.

Longer: The ECM sees the higher injector constant and believes that the injector really is that size. The ECM shortens the pulsewidth at higher RPM's because the injectors are supposed to be larger (according to the injector constant). To offset this you have to add more fuel to the top end. The larger the difference between the injector constant and the actual rating of the injector, the larger the difference in the PE-RPM table has to
be.

In my case, I'm running 009's (42.5Lb/hr) with an injector constant of 47.25 at a fuel pressure of 42-43PSI (My gauge is tiny, and hard to read). At 20psi of boost, my PE-RPM table looks like...

RPM Percent fuel added

5600 67.19
4800 63.28
4000 43.75
3200 8.59
2400 9.38

My WOT O2's are around 800-820, BLM's at idle are around 114, BLM's at cruise hover around 130 which is close enough for government work, eh?

I'm still wet behind the ears when it comes to chip burning and tuning TR's but I'm having a blast doing it


Charles Brooks

 

[NC87GN]

Hey charles,
Thanks for the post.. Explained very well. I'm not to concerned about WOT BLM because I run BLM lock patch in my chips. However, I am tweaking the injector constant to increase BLM's at idle. However something must be compensated for the inj constant change, as you explained, which I expected. Just wasn't sure what.. Tanx again!

Mike Banas
87 GN

 

[TurboJim]

You SHOULD be concerned with cell 15 despite using a BLM patch. Heres my opinion why:

Cell 15 learns 140. The ECM has learned to add 12% fuel. Now you lock it to 128. Now you have to raise the fuel pressure to regain that 12%. Now what happens to the rest of the grid? whoops, all the work you did and the grid is back down to where you started.

If you ask me, and you didnt, I would tune the car so there is minimal corection being made across the board. The deal with 009's is pretty much this. Below 7mS PW's they act almost 70% larger than stock. Over I think it was 12mS they start copming back down and act like the 46% or whatever larger than stock they are. I personally use a 2Eh as my constant (I think ~44.1) which is kinda in between where you are. When needed I will trim some fuel out of low op MAF, but so far most of the cars I've set up fall in around 120 on the idle BLM and 130-135 max as you get into the higher blocks.

As for PE trims, I'm a little leaner than you. I go like -15, -8, -4, 0, 6, 18, 30, 55 or something to that effect (I max the injectors at 6400 so when the ECM interpolates the values I should have plenty of fuel). This seems to help with the "fattness" of the 009's and gets them to spool quite well. I also like to use WG ramp and timing to aid in spooling.

I guess there are many ways to catch a chicken. I have my own which seem to work well.

 

[Brooks]

Hiya Jim, one of the vendor chips I have for the 009's is setup similar to what you decribed. I had to set the FP around 36 or so to get semi-reasonable BLM's but at that FP the pulswidth would max out somewhere around 17PSI of boost at 4400 RPM or so (102% PW according to Direct Scan). I double checked that my regulator was increasing with boost and it does so I'm not sure why the car would go lean.

I've been trying to find more info on the tweaking chips for 009's but haven't had much luck. Even posted here in Chips 101 a week or so ago.

I ended up just doing what the car seemed to want and it's working out all right but I'm at a loss as to why my fueling tables look so different from the other 009 chips I have. Now my BLM's are much better and the injector PW has come down to 90% from 102%. I would very much like to compare with somebody that's experienced in tweaking for 009's.

Charles Brooks

 

[TurboJim]

Charles:

There is no WAY a stock turbo will need 42# of fuel at 17#. Something isnt right there dude. Those injectors should have been somewhere around 50% at 17# unless you got a car runs 11.5 at 17#. Changing FP will ONLY affect PW if the BLM is outa whack. I believe what you say, it just sounds like something aint right.

See, there was a thread a few weeks ago about displayed PW and how accurate it is. This goes with my thoery. Theres no way a basically stock car, needs 42# of fuel. Nowif you're using a 47# constant I can see a higher PW because the ECM pulses shorter just cuz the injectors are larger, so you gotta open em up more. Se despite displaying 102%, the injectors might have only been 70-80%. (Which BTW STILL sounds like a lot to me)

 

[wilkinshc]

Just a thought, are you sure they are 42# and not 30# green strip? We had a few problems we guys get msd 36lbs when they were suppose to be 50lb and 009 that ended up being 30lbs green strips. Also they might need cleaning and to be flowed. I have the 42# lime green tops (flow curve is different) on a stock motor, stock turbo, stock intercooler. At 17lbs of boost I am hit 80% on the PW. Dynoed the car last year at 311 rearwheel hp. No track anymore to get a real time. If you would like a bin from my thumbwheel I could send you one. It probably be a little different unless your run the lime green tops.

Brooks Also you state
Longer: The ECM sees the higher injector constant and believes that the injector really is that size. The ECM shortens the pulsewidth at higher RPM's because the injectors are supposed to be larger (according to the injector constant). To offset this you have to add more fuel to the top end.

this is true if you were not really rich on the top before, if you were really rich because of an inaccurate injector constant you might have just corrected the problem, so in short you need to see what has happen with the change and adjust the PE Vs Rpm table as need.

Chuck