MSefi.com read only forum (Jan.15,2018)

MS-II, V3 board, V2.88 code, MT V2.25
Ford 4.6L V-8 naturally aspirated
EDIS-8
42 lbs. injectors
Innovate LC-1 WB O2


This afternoon I went out and did a short datalogging run. While reviewing the log I noticed something that always seems to be there. During steady state cruising with very light throttle loads the O2 levels are all over the place. There is no corresponding change in PW so I am not sure why the AFR is jumping around like it is. Notice between about 345.900 to 352.370 the jumpiness while the throttle position isn't varying much. In particular though from 360.570 to 375.200 was just loafing along and look at that AFR. I would expect it to be nice and smooth just like the PW. Am I wrong in that assumption? With the throttle closed and just coasting in gear the AFR is nice and smooth as can be seen from 382.158 to 402.800.

I have a theory though. I built the exhaust from scratch and am wondering if I might have a leak. I can't hear one, and the truck is not loud so I would think I would hear a signifigant leak if one was present. Would a pinhole leak in a weld cause these kind of swings?

Thanks in advance for any help.

did you happen to buy the "summit" 42# injectors, if so they are very touchy to voltage for opening times. i did some semi-accurate testing on them which helped me alot for stabilizing afr. by semi i mean a 60cc syringe for capturing fuel and a battery charger and headlights for varying voltage with some formula i can't remember where i found. if i can get my head out of my arse ill try to post up the results for ya

i took a closer look at your msq and log. accell enrich is all wrong for that size injector. try settings something like this
tpsdot threshhold of about 25-30
turn off map dot completely for initial dial in and ve tuning. (slider all the way to the right)
make a tps chart that looks something like this.

rate value
200 7 ms
150 5.5ms
80 2.7ms
25 1ms

i see your running 2 squirts, im not sure if the standard code considers this into the accel enrich or not if its too lean double the ms value.

ashford wrote:i took a closer look at your msq and log. accell enrich is all wrong for that size injector. try settings something like this
tpsdot threshhold of about 25-30
turn off map dot completely for initial dial in and ve tuning. (slider all the way to the right)
make a tps chart that looks something like this.

If you are not having problems with accel, then you should probably not change it. If accel is kicking in during cruise, you should see the accel light come on and the PW would increase, which contradicts your initial post.

PJF wrote:This afternoon I went out and did a short datalogging run.

How short? Was it long enough for everything to warm up completely?

PJF wrote:Would a pinhole leak in a weld cause these kind of swings?

It could. There are other considerations though. Exhaust temp, exhaust pipe length, muffler, cat converter, etc. All of these can cause exhaust flow changes that can "fool" your WBO2 for a split second.
Also be sure your ground for the LC-1 is not loose or attached to a surface that gets really hot. Ultimately, it should be grounded to the same place as MS.

PJF wrote:There is no corresponding change in PW so I am not sure why the AFR is jumping around like it is.

Is your advance moving up or down at all? Is it causing your engine to surge or stall for a second?
A WBO2 is awesome for tuning and evaluation, but, (like most things), is not perfect.

Thanks for the input guys!

I think I have put this mystery to bed though. I did more datalogging and got the same results, but I found a trend.

I have noticed that PW times above 4.0 MS give a relatively stable AFR.

Here is my theory, the rather large injectors (42 lbs/hr) are not able to meter fuel very precisely below 4.0 MS. As soon as PW's go above 4.0 MS the AFR begins to steady out. Most of the time that I am complaining about my AFR's bouncing around my PW times are in the low 2 MS range. 2 MS is really a pretty short amount of time!

I wish I had some stock 24 lbs/hr injectors to swap out and see what happens to the AFR. For right now though the 42 lbers are what I have to work with!

I tested the exhaust this afternoon for leaks and it is definitely tight, no leaks that I could find. So at this point I am just going to drive it and see what happens.