Prelude SHO M90 roots running, need help w/ tuning

grey500se

Registered User
I finally had some time and I got this project running on saturday but need some advice from the tuning experts only, the issue is its lean on idle and rich in the RPM range, which is totally bizzare, here are my tweecer settings

94/95 ported blower w/ a SC drive ratio=2.62
Lincoln Mark VIII MAF
86mm SVO trottlebody
water-to-air intercooled

KAM=off, meaning it is always 1.000
Inj offset=85% from stock calibration
cranking PW, stock settings
WOT timing max =25 degrees
lincoln Mark VIII MAF curve
high slope= 48
low slope= 48

@idle lambda, commanded 13.0-13.5
2-4k rpm, commanded lamda= 17.5-18.300

although this may not be Tbird, its still a M90 and far as I know the M90 puts out too much air at low rpm's and thats how it gets good gas mileage this is why its so lean on idle and pig rich once I gas it. Is this normal, tuners? I'm using tweecer RT
 
you are bypassing the SC during idle and cruise correct?

Yes, I am using the remote eaton bypass, overall the setup is the same as a tbird SC setup, TB before the SC and bypass routed back, I'll work on some pictures.

Forgot to mention, on the calibration file

I'm using Accel 48 lb/hr injectors
FP=39 psi relative controlled by a Mallory 0-100psi FPR

-injector breakpoint is stock which I believe is 2.000ms
-idle the pulsewidth is 1.1-1.2, so technically still using low slope.

see if the file uploaded if you want the log and view the calibration
 

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Looks like the MAF function is off a little bit. Try adjusting the values in the curve by the trim amount. Also, once you get the curve dialed in you'll have to adjust the neutral and drive idle air functions to match your MAF curve. Just looks like the low slope is a little lean and the mid range of the curve is fat.

As a side note, I find that setting the low injector slope to a higher value, something like 56 may help idle conditions.
 
Looks like the MAF function is off a little bit. Try adjusting the values in the curve by the trim amount. Also, once you get the curve dialed in you'll have to adjust the neutral and drive idle air functions to match your MAF curve. Just looks like the low slope is a little lean and the mid range of the curve is fat.

As a side note, I find that setting the low injector slope to a higher value, something like 56 may help idle conditions.

I don't know if its such a good idea to start tinkering with the MAF from shoforum member advice without getting the slope values close but I think I have no choice. I should just adjust the idle voltages, can't recall the, somewhere around .7-.9 volts, right?

As for trim, I have it turned off, meaning its always 1.000, never trimming or adding fuel, I am simply using the commanded lambda values to adjust slope.

In most cases it should be rich on idle but its exactly the opposite here. I'll look at it more tonight, all the people familiar with tuning I contacted haven't replied yet. Thanks.
 
Look at your load calculations at idle. I'm not sure off the top of my head what load should be at idle but I'm thinking 15% or there about. If load is low, then increase the MAF. If load at idle is ok, then decrease injector size to richen.

This is only if you are fairly sure about your MAF function of course.

You don't always want to adjust the MAF function to cure a fueling issue, particularly when you don't know the actual injector slopes. For more standard injectors (stock Ford, or lucas 42's, etc.) we have known correct slopes but I don't have the slopes for the 48's. This is a bit of an issue when working with aftermarket injectors because they generally don't publish slope values.

The M90 has nothing to do with your tuning. It doesn't substantially affect anything until you get into boost.
 
Look at your load calculations at idle. I'm not sure off the top of my head what load should be at idle but I'm thinking 15% or there about. If load is low, then increase the MAF. If load at idle is ok, then decrease injector size to richen.

This is only if you are fairly sure about your MAF function of course.

You don't always want to adjust the MAF function to cure a fueling issue, particularly when you don't know the actual injector slopes. For more standard injectors (stock Ford, or lucas 42's, etc.) we have known correct slopes but I don't have the slopes for the 48's. This is a bit of an issue when working with aftermarket injectors because they generally don't publish slope values.

The M90 has nothing to do with your tuning. It doesn't substantially affect anything until you get into boost.


I made an adjustment to the MAF curve between .7-.8999 volts, richened it about 15%, set the slopes to

high=48
low=75

its slightly lean but thats all the time I had today
 

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  • mar_31.zip
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I made an adjustment to the MAF curve between .7-.8999 volts, richened it about 15%, set the slopes to

high=48
low=75

its slightly lean but thats all the time I had today

Why would you set the low slope so high? That' is half your problem (if not all of it) right there. To richen up idle the low slope should be smaller than the high.
 
Why would you set the low slope so high? That' is half your problem (if not all of it) right there. To richen up idle the low slope should be smaller than the high.

Its opposite of what one might think, I know it sounds weird but thats the way it is, usually low slope is 1.2 times high slope, its noted in the tweecer manual, most supercharged SHOforum members have low=85 and high=50 running the Accel 48's, its a good starting point, it may be different on the tbird computers.
 
Its opposite of what one might think, I know it sounds weird but thats the way it is, usually low slope is 1.2 times high slope, its noted in the tweecer manual, most supercharged SHOforum members have low=85 and high=50 running the Accel 48's, its a good starting point, it may be different on the tbird computers.

It's the same thing with our cars, but as Dave is suggesting, you can use the injector slopes much like a mixture screw on a carb. If you're getting a lean idle, you can richen up the ratio by setting a slope lower than 48.
 
It's the same thing with our cars, but as Dave is suggesting, you can use the injector slopes much like a mixture screw on a carb. If you're getting a lean idle, you can richen up the ratio by setting a slope lower than 48.

Yes, you all are correct.
 
The injectors were made for GM, I set the fuel pressure set at 46-47...a world of difference....now the tuning begins.

I little vid at 2500 rpm and TPS=1v, don't make fun of all the clatter.


 
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