4.6 stroker going lean at wot

[rammit11]

Hi, I have a question on my engines air/ fuel ratio. The engine is a 1998 4.6 short rod ,step removed from stock throttle body, comp 231-4 cam, stock exhaust,99 up intake ,9.2 compression. I have about 300 miles on the engine so far and it seems to run fine, 14.4 to 15 at idle ,does seem to fluctuate a lot though. Moving the throttle quickly It goes to around 11.5 momentarily then goes back to 14.7(seems normal). I was thinking that the afr should stay pretty much at one level and not float around as much as it does. I gave it a short burst the other day at very near wot (backed off around 3500rpm) and noticed it settles out at 16.5. I am looking for any ideas as to how to get this lean situation cleared up and get it going to the rich side as I would expect it should be.

[IH 392]

11.5 is RICH!, 16.5 is LEAN! it should cruise between 14.0 and 14.7.

[rammit11]

Thanks , not to sound sarcastic , I understand that and the rich reading is at crack of the throttle which I would say would be normal as it is only for a few seconds till the computer adjusts. What has me concerned is the 16.5 reading (a lot lean) for the throttle position and how to correctly diagnose why it is occurring and how to remedy it. I am running the 703 neon injectors which are supposed to be very near 24# at 49psi fuel pressure.

[Cheromaniac]

I have about 300 miles on the engine so far and it seems to run fine, 14.4 to 15 at idle ,does seem to fluctuate a lot though. Moving the throttle quickly It goes to around 11.5 momentarily then goes back to 14.7(seems normal). I was thinking that the afr should stay pretty much at one level and not float around as much as it does. I gave it a short burst the other day at very near wot (backed off around 3500rpm) and noticed it settles out at 16.5. I am looking for any ideas as to how to get this lean situation cleared up and get it going to the rich side as I would expect it should be.

A fluctuating idle A/F ratio between 14.4-15.0 is normal and indicates that the O2 sensors are working properly.
When you nail the throttle and keep it there, the A/F ratio will fluctuate only slightly. If you keep changing the throttle position, it'll fluctuate more wildly and go full lean when you snap the throttle shut.
It'll be helpful if you can give us an indication of the WOT A/F ratios over a wide rpm range.

[SilverXJ]

What injectors are you running?

[rammit11]

I am running the 4 hole neon 703 injectors.

[rammit11]

cheromaniac , what would you say a good range of rpms to work with would be? I had another strange thing happen today as I started cold when I left work. The engine seemed to start normal was idling at 750 and then it jumped up to 1200 and stayed there till it got warm. Could I have a map sensor that is not working correctly ,not sending a check engine light and causing all the problems?

[Cheromaniac]

Could I have a map sensor that is not working correctly?

No, but you could have either a sticking IAC motor or a vacuum leak. A bad MAP sensor will make the engine either run very poorly or fail to start altogether.

[rammit11]

just a small update, I pulled the iac and cleaned it . There was not a whole lot of change so I went with a new map sensor (the one on was the original at 200,000 miles) I have seen a more stable afr 14.4-14.9 crusing and idle. The weird thing is if I am in overdrive and cruising at 1200 and get on the throttle as in going up a hill the afr immediately goes to 16.5. I tried this at different loads and the same thing happens. The other thing that confuses me is if I hit the throttle hard any rpms or load the afr spikes to off the gauge lean momentarily before it goes to rich.