i have a f250 1990 351w. i have done alot of work on this truck and i'm still not able to solve the engine running rich. i do not have any stored codes but with the key on and eng running i do get a code 44 which is secondary air inop. i have run this test many times and the code does not show everytime. would this cause my truck to run rich? when my truck idles it sounds like it my be missing, when i go up hills i really have to put the peddle down to make it upshift. i have taken apart the exhaust and noticed that my cat was gutted, could this cause a back flow and make the eng run poor? i also have a problem with my cruise control and no a/c. i did a compression test today and all the cyl. are about 140 psi. i checked my timing and it is at 10 btc. i have checked and replaced my tps, oxy sensor, pcv, coil, ign control mod, plugs wires ,cap, idle air control, rebuilt transmission, and had to remove the heads due to a broken spark plug. i have checked the eec plug and all the pins look fine. i'm tempted to disconnect my exhaust y pipe at the cat converter and see if this helps. if this does not help i will invest in a vac.pump and t/s the thermactor system components. any suggestion? also, one last thing. for the cruise control, my haines manual does not go into it but where is the cruise control module and how could i check it.

 

You might have a vacuum leak or fuel pressure problem. Check the vacuum and the fuel pressure at fuel rail.

The termactor system isn't functioning correctly, probably doesn't have anything to do with it running rich...

How do you know it's running rich? Usually the o2 sensor will tip that off...

You can test the TAB and TAD solenoids to make sure they're working. Check the vacuum hoses and air pump before starting to throw parts at it...

You checked the timing with the SPOUT connector out right?

 

i did check the timing with the spout disconnected, also my gas milage is 7 ml/gal. i can smell the gas from the exhaust and will not pass emissions. i will t/s the tad and tab solenoids and vac today. should i take the time and remove the cat conv and see how it runs?

 

The non-functioning thermactor system would cause you to fail emissions - and if it hasn't been functioning for some time it can ruin your cat converters. Could be the cause of your stinky exhaust.

I don't see why you wouldn't get an o2 sensor code if your engine was actually running rich.

That system puts air into the exhaust for the cat to function correctly. If it is not working it can ruin it. I'd say it's worth a shot to take out the cat and see how it runs - I ran mine straight exhaust once to try and find a problem.

 

Start by checking the fuel pressure like Justin said. I've replaced quite a few fuel pressure regulators on 351s for the same problems you have.
A bad MAP sensor can also cause it and won't always set a code.

 

checked fuel pressure and regulator everything seems fine with fuel. i checked my map sensor and there might be a problem. my haynes book stated that by back probing the map/bp signal (mid terminal) and ground and vacuum applied the volts should fluctuate, mine is reading 2.59 volts all the time. hate to throw another part at this but it appears that this could be bad. replace ?

 

Do you know someome with a similar truck that you could swap with just to test it?

 

maybe, i'll check back and let you know thanks

 

Yes it should vary in voltage - thats how the computer knows it's changing. Swap it out. I have one that'll work for ya if ya want it...it's off my 89. I don't need it.

 

thanks justin, how can i get a hold of you? if you do not need the map sensor i'll take it. thanks

 

I am bringing up an old thread because I have the same type of problem. I have a 95 Bronco with a 351W mild cam, gasket match heads, MAF confersion, and headers. I reuilt the engine a couple years ago. I installed a cam that was to big for the SD system (did not know at the time). My Bronco has been running rich for some time. I did the MAF conversion because of the cam and thought that was the reason it was running rich. I have not been able to find any reason for the truck to be running rich. I have the vacuum line to the MAP sensor removed like I am supposed to. Can the the MAP sensor still cause me to run rich? I have used propane and choke cleaner method to try to locate a vacuum leak and have not found one. Plugs and wires,cap, rotor, timing, are good. I scanned for codes and none came up.