I recently noticed that my AFRs are unstable (spike) while under boost. Here's what I did to test this:

I changed the requirements to go into PE mode so that I would hit PE well before boost kicks in.

Going into PE under light load and no boost (2nd gear, 35MPH, 2500+ RPM) resulted in a pretty smooth AFR.

Hitting PE under heavy load and full boost (4th gear, 40MPH, 1500 RPM, WOT) resulted in the AFR spikes.

Because of the low engine RPM, I'm pretty sure I'm not fuel deficient. Any ideas of what would happen under boost (4PSI) and high compression (10.5:1) that could cause the AFRs to be unstable?

BTW, I changed my NGK TR6's out yesterday for a new set and ohm'ed the plug wires..
Here's a screen shot of my log (click to enlarge, then click image again to make full-size and readable)

 

Iam not sure if this would help, but my car did the same when the O2 sensor got hot.

 

how are you on injectors? usually when AFR flutters like that on high load is a sign of maxed out injectors.

 

The injectors should be fine. They are 42#'ers and held rock solid on the dyno a few months back. I also checked fuel pressure this weekend. I'm running 58PSI at idle and spike to a tad over 60 under boost with the KB BAP.

 

umm... svo 42s are _really_ easy to overpower on boost, even on the most basic of FI setups. i've tuned a t67 sts setup that ran out of 42s by ~5000rpm without even going full 5psi. i'd seriously watch it, you don't wanna blow it with something that silly.

 

My 42 SVO injectors pissed out on the dyno at 479@4700rpm with my old cog/ATI set up. Glad the Cog set up didn't hold a belt for one solid track pass or I would have probably toasted the motor from going lean....use to turn the engine to 7100 with the procharger.

Just didn't have enough injector with the ol procharger being such a parasitic beast. So I went to the 60's and upgraded the rest of the fuel system and its been all good since.
J

 

I read your post on the CF site, I have a non-IC mag with 2.9" pulley
I did the same thing to mine with the 243 head and used a 0.40 gasket.

I replaced the 42# ford injector with Dephi's and there is no comparison, they burn cleaner at closed loop (no soot on the tips, nothing! still shiny after 2 months 1,500miles).

The IAT should not be in the manifold just move it out. don't worry about timing, use the stock table, 15 degrees max is lots on these engines.

I run 50/50 water alky, through 8 nozzles looking down the runners, 20 amp MAF controller 150psi shurflo pump, seen a couple of 100 degree days with no problems to report (2 months now).

My fuel pump is trapped at 15 VDC, (all the time), I personally think 15 volts continuously is easies on the pump then letting the voltage float from 11 to 14.5 through the charging system, and then have the computer try to compensate for the variation in other dependant devices. (15,000 miles now)

When I changed the onset of Open loop I did this;

I set my throttle position at about 30%, this is about what cruise control needs at 80 MPH to handle a 2% grade (hill).

There is a Wide Open Throttle table, The Hot Temp onset is set at 142 Degrees Celsius. This means that the onset is disable by the factory as this temperature is never reached.

The WOT COLD table controls the onset of Power Enrichment which is set at 64% (for <3200rpm) by the factory

If you want the Hot table to rule the Hot Temp needs to be set at say 60 degrees Celsius. I have been like this for 25,000miles, 3 years.

 

Thanks for the input BillC5. I agree with your comment on the injectors. I've run both the SVOs and the Delphis. Seems the Delphis run smoother overall and have less varience from commanded AFR at idle/low speeds.

Your water/alky injection sounds interesting. PM me when you have a chance, I'd like to hear more about how you have this setup.

As for the IAT, until I can relocate it, I'm thinking of just zero-ing out the timing retard in that table.