Tim C

I have a 78 F150 with a stock rebuilt 351M I use offroad (rockcrawling). I originally swapped the stock two barrel carb to the 7747 setup from a 89 C1500 with a 5.7. A few years ago I did a 7427 swap and converted it to a MAF setup using Dimented24x7s code and instructions from this site. I got the MAF tuned in easily I also disabled the MAF and tuned the VE tables in speed density mode. The truck runs really good except for one thing. If it is below 50*F and the truck has been sitting at least 8-10 hours when I crank it it sounds like an old tractor chugging when it idles immediately after you release the key for the first 30-60 seconds. After that it smooths out and idles fine. If the engine has been run in the last few hours, or its above 50*F, it starts just fine and idles normally. It fires up immediately hot or cold, just sounds like its laboring if its below 50*F.

It sounds like when the distributor is off and the timing is low when you crank something after the dizzy has been pulled, but I dont think its timing related. Ive verified with my MAC timing light on cold start its at 30* of timing. It labors then and if the EST wire is unplugged and the timing light shows 10*. However when I first started trying to tune the cold start my WB O2 gauge (innovate motorsports) showed AFR immediately after the cold starts were in the 8.xx-10.5 range. Open loop AFR table is all around 14.2-14.7 across the whole table. Crank to run transition didnt seem to make any change when I adjusted it up or down, but Choke AFR did. Choke AFR was ranging from 9.x to 0.9 I've been lowering it finally down to 0.6 at -40 and .2 at 152 on the table. That has helped the cold start and it now reads 10.5-12.0 on cold startup when its chugging but its still there some. After 30-60 sec it starts climbing up to the 13:1 afr range and leaner then the idle returns to normal sound. Occasionally it will lope a little for the first few seconds too but not always. If you open the throttle some it will smooth out too, chugging and lope.

Ive had a hard time finding info on how to tune the cold start especially on the $0d mask, plus its been a warm winter here in NC so I can only make changes once a day or every few days. This is part of the reason why Ive just been putting this off for the last couple of years.

If someone whos familiar with the MAF hack or $0d masks in particular could just give me some pointers on where to look to try to figure this out I'd really appreciate it.

RBob

iTrader: (1)

Sounds like you are on the right track by working with the choke AFR. Those rich WB readings are too rich for a cold start. I would continue to lean out the choke AFR. To add, go by how the engine runs, not by a WB AFR reading.

RBob.