My buddy has a 1993 F250. We just put a 351 480hp crate engine in it. He bought a MAF conversion for it because the factory speed density system wouldn't work with the setup. The told him to use 46 pound injectors so he did. The engine has Trick Flow heads,Edelbrock intake,and a decent cam and headers with roller rockers. Well it runs so rich it makes it run like crap. I kinda thought it is because of the 46lb injectors but the company that built the engine says it should work fine. I think the stock injectors are a 15 or 30 lb. So I thought that 46lb was an overkill. Anyway it is so rich that it bucks going down the road. The only way it will run is wide open. We also took the plugs out and looked and they were black as hell. I know that running rich is what is making the plugs turn black but why is it so rich? Hope somebody can help. Thanks in advance.

 

I've been looking at the MAF conversion process myself and I'll throw out a few random guesses:
1. You must take the vac hose off the MAP sensor so it measures ambient air pressure, did he do this?
2. 46 lb injectors sound excessive and very suspicious. Did he change to a higher pressure regulator? Can you check what pressure the reg is actually making (use an tire gauge)? Is the vac hose for the reg hooked up? Did he keep the stock injectors so he could just put them back in there again to see if that's the problem?
3. How did he solve the oxygen sensor issue? Ford SD initially had one sensor where they meet, but MAF uses one per side. I've seen web pages that talked about just adding one O2 sensor onto one pipe and leaving the other at the "Y", this sounds like a terrible idea.

 

The hose is still hooked up to the map sensor. We didn't do anything with the o2 sensor. The kit he bought is a ford motorsport and it came with a new computer. I also thought the injectors are way too big. We still have the stock injectors. We can unplug the map sensor and see what it does.

 

the maf sensor has to be calibrated to run that size injector as well. sounds like you guys need to find a dyno shop and have the ecu tuned. that is to much motor for the stock mass air ecu to handle. the combo sounds ok , the injectors might be a little big but if tuned properly will be fine. I would not drive it anymore because if to much fuel is being dumped into the motor it could wash the bearings and seize that motor in a hurry. you must unhook the vac line to the map sensor as well.

 

Yea he said the MAF is calibrated for those injectors. We will unhooh the map sensor and try that.

 

And be sure to plug the vac hose coming from the intake (obviously). I would have thought leaving the MAP plugged into the intake vac would run it leaner since it sensed lower air pressure, but really there's no telling what it would do.

You want to pull the codes too, in case there's something blatantly obvious like it can't read the MAF sensor.

 

We figured it out. The Maf was bad. We put another one on and it works good. Thanks for all the help.

 

Great, you might still think about a custom tune on that motor to really get all its potential out not to mention make sure its running perfect. dont want it running lean at wot for instance.

 

Yea he is going to put his supercharger on as soon as it gets broke in.

 

whats the compression ratio on that motor.

 

I think it is 9 to 1. It was built so he could run normal gas.

 

Check your temperature sending unit for the electronics not the gage. I had a similar problem with a stock rebuilt 351W, I put a cheap aftermarket unit in and did not work correctly. Went to Ford dealer and got a motorcraft part, runs good now, before almost choking out and really spitting out black rich smoke.
Hope this helps.

Justin