closed loop gain #'s for big injectors (XFI)

[Blazer406]

What closed loop gain values are you guys running? 160# injectors......I am helping someone with a 231in 109 motor and the AFR is up and down like a yo-yo. It goes from 8.5:1 to 13:1 or so..... 02 correction is up and down as well.... just slower than the actual AFR.

I realize these are some big honking injectors for a 231 in motor..... but it is either these or 72's ......problem is the 74GTQ turbo will suck those dry pretty quick. I figured if I could get it to idle.... the rest would be fairly easy......

Oh... to further complicate the tune.... the car is running alky as well.... My VE table numbers generally get higher until about 200kPa... then taper off above that due to more and more alky progressing in..... so far we have been mainly tuning from 18-20 psi boost.

I am not wanting to go more until we get the yo-yo under control.

 

[Blazer406]

Here is a screenshot of "the yo-yo". If I understand the concept... I can lower the gain % and that will lower the swing. For the most part.... the correction stayes negative.... but it swings wildly.

 

[Blazer406]

Here is the closed loop gain % map prior to being modified. I was thinking about trimming -50% for the entire table and see if that makes the yo-yo travel go way down.

 

[Dusty Bradford]

I turned the WB off to get the 160's to idle on a 235. I believe you must get it right before letting the ecm take over. Data log the car at idle and watch what happens. It's usually the car going from lean to rich in a narrow rpm and map range. I had to adjust the injector opening time to get the VE 's into a reasonable range for some extra resolution. If your trying to use 1.0 and the VE #'s are very small, a change of only 1 number is a large change. I ended up reviewing the data log and making corrections to keep the a/f more stable. Increasing the fuel pressure also helped, going from 43 to 50. I guess it helped atomize the fuel better rather than dribbling the fuel in.

I'm a dealer for the new 120# injectors which may be a great alternative in situations like this. I'll have pricing next week.

 

[Blazer406]

We are running an injector opening time of .7. This allows the idle cell in the bottom left to be in the mid to upper 20's on the VE table. It idles pretty good all things considered..... just want to see a more stable AFR at low boost before going any higher....

What do you think about lowering the closed loop gain?

 

[lazaris]

.7 is the wrong opening/dead time for the 160 injector. Try using 1.2-1.3

 

[Blazer406]

.7 is the wrong opening/dead time for the 160 injector. Try using 1.2-1.3

If you do that...... your idle numbers (on the VE table) will be much lower.... and like Dusty said... you will have a much lower resolution..... Anyway... IMHO... this is not what is causing the yo-yo at 17 psi - 20 psi boost.

 

[Chuck Leeper]

take a look here, if you've not already seen it.
http://www.turbobuick.com/forums/performance-ecm-upgrades/209061-how-streetable-160-inj.html
In the FWIW dept:
I've flowed many sets of 160's. 1 of the last sets was for a 10.5 car. The customer sent me 24 injs, all bought off the shelf. I ended up w/ flows varying over 10%, and had to swap/sort, to get 8 that would flow close enuf to use. That's nearly $2K to get 8, that should of cost approx $600.
Afer having said that, and reading thru the above link, the questions are:
A. Is this a flow matched set?
B. Why not sell the 2 sets, and buy a set that will be closer to what's really needed?
If you want, I can flow test them....

 

[Blazer406]

take a look here, if you've not already seen it.
http://www.turbobuick.com/forums/performance-ecm-upgrades/209061-how-streetable-160-inj.html
In the FWIW dept:
I've flowed many sets of 160's. 1 of the last sets was for a 10.5 car. The customer sent me 24 injs, all bought off the shelf. I ended up w/ flows varying over 10%, and had to swap/sort, to get 8 that would flow close enuf to use. That's nearly $2K to get 8, that should of cost approx $600.
Afer having said that, and reading thru the above link, the questions are:
A. Is this a flow matched set?
B. Why not sell the 2 sets, and buy a set that will be closer to what's really needed?
If you want, I can flow test them....

A: No. The injectors are not flow matched.
B: The friend bought these for his Stage II stroker motor with TA heads and an 80mm Thumper BB turbo.... and at the time this was the only option. He might consider buying another set of injectors (maybe some 120's).... not sure if the "budget" will allow him to do that right now....

His "spare" is the girdled 109 in the car now... no stroker.

While making the tuning runs yesterday.... we discovered it had thrown a TPS code (TPS was dead below about 30% throttle)....... this could have caused some of the yo-yo we were seeing yesterday..... He is installing a new AC Delco TPS today.....

I guess I should add since he bought the 160's he has added alky.... so he could theoretically get away with much less injector. I don't think he has anything but 72's or 160's..... I think the 72's would be marginal with his hardware on even the 109..... the 74GTQ is no punk IMHO.....

 

[gnxtc2]

What don't you try a 95lb injector?

Billy T.
gnxtc2@aol.com

 

[callmeebryan]

I honestly think 40 gain is too high. I think i have mine set near 25 at WOT and the fluctuations in AFR are only 0.2 ish. Granted, your injectors at 3x the size of mine, but the general rule applies.

the correction numbers you are seeing are way too much. You want to get the car within 5% positive and negative. If the O2's are swaying back and forth like that, the gain is too high. Basically your computer is ramping the o2s in the opposite direction too fast.

Idle the car in open loop and have closed loop come on around 1500-1600rpms. I found this made for a better, more consitent idle for some reason. I was able to get the exact AFR i was looking for.

 

[Otto J]

As far as the Idle moving arond you can also mess with the TIMING TRIM in hte idle parameter,Ive had cars that needed none for good idle and some that make a 6-8*swing to get a steady idle.

 

[norbs]

I would use a gain about 15 and see if it improves, 30 is just way to much.

 

[Blazer406]

We found one problem. The fuel pump hot wire kit was being smashed during a run by the torque arm..... it had compromised some of the wiring.... and the main fuel pump was intermittantly shutting down and turning back on..... It isn't even that close to it when you slide under there and look at it..... I guess the suspension moves around more than we expected.....We knew something was up when we made a pass... and the o2 corrections went real high all of a sudden........It never would show up until you matted it.... and the double pumper was taking up some of the slack.... the 02 corrections were down around 0 today on a pull to the top of second.... and the yo-yo has calmed down considerably.... it is only swinging some in 1st gear.... once in second... she is real steady.... Maybe we found the culprit.

Going to the track tomorrow for the first time with the new combo on the spare motor...... Hoping for 10 anything on 20 psi with pump gas and alky.....

 

[Chuck Leeper]

Soooo...

"and the main fuel pump was intermittantly shutting down and turning back on....."
Maybe a good time to set up FP logging!!

Glad you found it!!

 

[Blazer406]

"and the main fuel pump was intermittantly shutting down and turning back on....."
Maybe a good time to set up FP logging!!

Glad you found it!!

It's on the list.... maybe we can just start printing money......

Seriously.... we had it on the list since BG last year.... smoked the Stage motor at Reynolds..... kinda put a damper on everything else...little motor is hauling @ss for only 20 psi now.... going to the track tomorrow afternoon.... we will see...

 

[Blazer406]

I would use a gain about 15 and see if it improves, 30 is just way to much.

I think so too.... just don't want to change too much too fast... currently have reduced the gain table above by 25%.... will datalog tomorrow at the track... see how she does.....

 

[Chuck Leeper]

"It's on the list.... maybe we can just start printing money......"
When you do, run a batch for me!!
Good luck on the track time!

 

[1985GN]

I guess I should add since he bought the 160's he has added alky.... so he could theoretically get away with much less injector. I don't think he has anything but 72's or 160's..... I think the 72's would be marginal with his hardware on even the 109..... the 74GTQ is no punk IMHO.....

i have 72's and with alky and about 28psi i trapped just under 138 and the DC of them was at most 80% but most of the run was at 76%...

 

[HighPSI]

I thought this was the problem. I'm glad you guys found it. Please don't hesitate to call again!