MSD Atomic EFI lean on acceleration problem fixed!

System would go to about 19:1 AFR on light accel and stumble from stops. After a week of trying different settings, I told the computer the engine was bigger than it was and so far have had no issues. (PS, I forgot to mention in the video that I checked fuel pressure and it was normal under all driving conditions)
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gasketcasegara...

[@caseyhunt1]

Great info. i'm going to look at mine this afternoon. thanks!!!

[@rickyroof806]

Thanks! I get tired of waiting 30 minutes to talk to a msd tech! And then they don’t know what you’re talking about! There is nothing on wiring different things in, I still don’t have a speedometer!

[@marshallbarry958]

Thank You very much for that info. I am currently adding the same system to my beaumont. I am installing rotor phasing to help with timing. If you have more videos I will check them out. Thank You

[@RodBeauvex]

From Wikipedia, about the emissions system: *In addition, there were difficulties adapting the M-block to the second generation of emissions controls. Unlike previous Ford engines, Thermactor and exhaust gas recirculation features had already been built into the 351M and 400 engine, rendering adaptation to electronic feedback fuel/air systems difficult.[31] One requirement of the second-generation equipment was an oxygen (O2) sensor in the exhaust, which had to be placed before the Thermactor air was added. Since Thermactor air was injected right into the block's exhaust ports in the M-block, there was nowhere for the O2 sensor to go.* This is as opposed to this extra air getting injected a little further down the line, closer to the cat, like in most other engines. My theory, and this could be totally wrong, is that because of the 400's unusual implementation of the thermactor system that injects air BEFORE the O2 sensor , there is a mismatch in what the sensor reads and what it actually is (which is why some of your other ratios may seem a bit off). Increasing your displacement is what compensates for this mismatch in the AFR. What strikes me is that this problem should has made itself known from the very start, instead of only appearing later.

[@GasketCase2024]

I agree, it worked for three years with no problem it should have shown up sooner. The air pump has been gone for years and it has been plugged. The forums I was on most people had chevy engines, and the problem they described was identical. So unless they have a similar egr/ air pump set up (I'm not as familiar with the chevy stuff) I'm still drawing a blank. I also know I don't have any exhaust leaks causing a false reading. I'm also considering this more of a hack than a fix, but hey it works.

[@RodBeauvex]

@@GasketCase2024 Ah, so the smog stuff was already gone. Interesting to know. Guess that kills that theory.

[@GasketCase2024]

@@RodBeauvex I appreciate your input though. It can be very easy to over look things like that.

[@erikturner5073]

The Cleveland and modified 400 have a much higher big block like breathing capacity than other 400 cid engines from other manufacturers. Those cylinder heads can move a lot of air. Make sense that the fuel map doesn't compensate for that since those engines are in a league of their own.