I've been driving my truck around and putting some miles on it before I go back to Nelson's on Friday for the final dyno tune and have noticed something interesting. I have an AEM UEGO A/F gauge and it doesn't always read the same when I'm in boost. The tune I have now is a safe mail order tune from Allen Nelson. Here is an example:

Sometimes:
I floor it and as it is going through the RPM the gauge will begin by reading about 10.5 then it will creep up to 11.5 at which point I let off to avoid trouble. It seems to still be climing when I let out.

or

Sometimes:
I floor it and as it is going through the RPM the gauge will begin by reading 10.0 and stay there for as long as I keep it floored (running it through the gears).

Why would a custom tune vary like this. I would think it should do the same thing everytime. EXPLANATIONS???

 

10 and 10.5 are really rich. Most widebands can't read richer than 10 AFR, so 10 just equals omgrich (mine actually reads 'rich' for anything 10 or lower). You want to be at 11.5:1 (ish).

It's being inconsistent because there is something throwing off the tune in certain conditions -- or it may be mechanical. You need to log it and capture a run that causes the AFR to climb and get a run where it doesn't.

 

I don't have any software to do any logging so I'll probably have to wait till I go to Allen's on Friday. I just wanted to see if I could learn anything on here before I went.

Could an inadequate fuel pump cause this problem only sometimes. I only have 1 255 intank pump.

 

It's possible, but then you'd have something else going on - your truck would be requiring more fuel during those times (maybe a colder shot of air)

 

how much boost