Read these exhaust manifolds

**JeepsAndGuns** · 08-04-2013

Not sure if this would be the correct forum or the gm injection forum, as its a question I think might be about my mpfi system. But I figured I would put it here for now.

So I just installed a set of headers on my cherokee (the one in my signature) AMC 401 with a 16197427 MPFI system. Anyways, I was looking at my old stock exhaust manifolds as I carried them to my storage building and noticed not all the ports looked the same. 2 looked white/lean, 2 looked black/rich, and the other 4 looked what I thought was normal. The AMC V8 shares the same cylinder numbering and firing order with the small block chevy. So it appears cylinders 1&2 look normal, 3&4 look lean, 5&6 look normal, and 7&8 look rich. Is this normal with a batch fire MPFI system? If it was only one or two cylinders like this, I would suspect engine, ignition, or injector issues, but with it being identical on both sides make me think otherwise. I removed all the spark plugs when I installed the headders, and all the spark plugs looked ok, they didnt look any different from each other, not like the exhaust ports do.
So is this just a batch fire normality? Or some other issue?

**RobertISaar** · 08-04-2013

likely not a MPFI problem so much as due to the firing order. IIRC, the SBC have issues where one cylinder "steals" the aircharge from another, causing one to go lean and the other rich? if that's happening here, that would explain quite a bit.

the plugs SHOULD look the same as the ports though. perhaps it's manifold design that is causing what you're seeing?

**JeepsAndGuns** · 08-04-2013

http://img.photobucket.com/albums/v6...1-28115032.jpg

Thats my intake.
These manifolds have been on this engine since I built it several years ago. So they have seen a carb, tbi, and now mpfi. I have been running mpfi for a little over a year with this intake. Before that it was a regular edelbrock performer carb intake with tbi on it. I ran tbi for probably closer to 2 years before the mpfi. I'm not sure how long it would take the manifolds to start looking like this. So I have no idea if its been like this for a long time, or just recently with the mpfi.

**ony** · 08-05-2013

as hot as manifolds get probly just before you removed them, it might have been an off day where it was rich on a cylinder or 2 or running slow at idle?