Hi everyone,

Last night I finished up the install of a set of 42# bosch injectors. (Had stock 22# installed) I installed them because my current injectors have unknown miles on them and also because I'm planning on adding a power adder this summer. I have a few questions of how the engine runs after the install. In a nut shell, it's running unusually lean, usually holding the BLM at 160 for at least the bottom third of the powerband.

Originally I set the injector constant for both single and dual fire injector size at 42 and the BLMs were pretty much a steady 160. I see in tunerpro the injector constant is to be sized at 40 psi and not 43.5. According to the flow sheet I have for the injectors, at 40 psi the injectors flow 40#. Adjusting the constant to 40 did help a little bit, but I'm still riding 160 BLM quite often. Especially at low throttle. I guess now it's time to start adjusting the MAF tables. Is it normal to have to adjust the calibration this much after an injector swap?

My next question is unrelated to the injectors, but has to do with the min air and IAC settings. At idle my counts are in the 75-80 range and I know this is too high. I'm afraid to adjust the idle any more because I'm starting to run out of TPS range. Right now my TPS maxes at 4.18V. If I adjust the throttle blades to bring the IAC counts down, I'm afraid I'll lose the 4.00V needed for WOT. Is there an easy solution for this? Drilling small holes in the throttle blades perhaps?

I'm running '165 MAF with a ARAP as base calibration. It was tuned fairly close for the 22# injectors. My engine mods include ported and polished base/runners/plenum, trick flow aluminum heads, headers, 280/280 adv. duration .480/.480 lift cam.

That's it for now, but I'm sure I'll have many more questions as my calibration continues. Thanks for the help.

-Howdy

 

changing the idle position of the throttle blades will have no effect on the TPS reading at WOT. Visualize the throttle body being held at WOT, and now turn the set screw which controls the idle position - it isn't moving the throttle blades, it's not even touching them, it only affects how far _closed_ the blades can go. In your case, you're going to be opening them up a bit so that the IAC steps will go down. The only way this change would affect WOT TPS is if you also adjust the TPS to maintain the same idle (closed throttle) TPS reading, but you should have enough leeway to make it all work.

Can you give some more details on your new injectors? if they are standard saturation injectors they could just be slower to open/close than your old ones. Going from 22# to 42# will really shorten up your pulsewidths, especially around idle and low load to the point that the injector may not even be fully open before the pulse is over and done with, which would lead to a lean condition. Do things tend to straighten out at higher rpm/higher load?

I'm not ultra familiar with ARAP / 165 / MAF stuff, but certainly on SD/ $8D there is a table which attempts to linearize the injector pulsewidths (i.e. with short calculated pulsewidths, the pulsewidth is extended by a lookup value to linearize the pulsewidths). in tunercat it's called "low pulse width injector offset vs. BPW". On a stock AUJP, if the calculated PW is 0.488 msec, then 0.274msec are added - over 50%! - in order to linearize it. Odds are your big injectors need even more compensation especially at the short pulsewidths you're probably running at/near idle.

 

"The only way this change would affect WOT TPS is if you also adjust the TPS to maintain the same idle (closed throttle) TPS reading, but you should have enough leeway to make it all work."

This is exactly what I'm doing. I'm trying to keep the TPS idle voltage at .54. What is the acceptable limit for idle TPS voltage? .65?

What your describing with the injector behavior is exactly what I'm experiencing. The lower MAF tables appear to be very lean while mid throttle and WOT seems to not be effected at all. I'll keep adding to the values in the lower MAF tables to compensate. I've been trying a new tune everyday on the way to work and I think I'm almost there. Thanks for shining some light on the injector behavior.

 

I never got 42# to run right. Whats your idle msec ??

-- Joe

 

Note that modifying the MAF tables to counteract an injector linearity problem is probably not really the best way to do this. in $8D, there is a table dedicated to linearizing the injector PW, I would imagine there has to be something similiar in $6E. I took a quick look at an old tunerpro install I have and I don't notice anything, so perhaps someone with a HAC or experience with $6E can jump in.

 

I didn't see anything in $6E having to do with injector linearization either. I've got the tune down pretty close right now, but will probably re-pin one of these days to run MAP. In the mean time, it runs ok. I ended up dropping the injector constant down to 39lbs and adding 20% to the MAF tables, diminishing 5% per table. My idle msec is about 1.5 +- .2

Thanks for the help.