hey guys. this problem all started when my fuel pump went out. i replaced it, a few days after that i wasnt able to draw of my front tank.( dont know if this is related to anything, just wanted to mention all the symptoms). then gradually strarted running a little rougher every day. eventually it was running so rich that it would flood out as soon as i hit the key to start it. chugging and running very rough. i have a 86 van with a 300, so i pulled the carb and put it on the truck, hit the key and it started right up. ran really good for a 20 year old carb without adjusting anything. then the only problem i had was i use to get 13.5 mpg, that dropped to about 10mpg. so i replaced the plugs thinking i fooled them out with the old carb. that didnt help. actually the truck started running worse. replaced the wires, and the cap and rotor. now it runs worse that it did with the old carb. really rough, burning rich, black smoke. the only thing i can think of is maybe the new pump has stronger suction and sucked some sh$t off the bottom of the tank that the old one didnt. replaced the fuel filter but maybe something is getting by the filter and screwing up the carb some how. or is there something electrical that can be causing this with both carbs? any help would be great. im about to snap.

 

is the pump electric? it sounds like you have an efi pump if it is... if so than the carb is getting wayyy too much fuel pressure

 

That frickin feed back carb has wires hanging off it you can add some juice and fire it off to kinkdomcome. It's also conected to a computer to be use for target pratice. All the sensor that are connected to it, well use your imagination. That was the last year for the carb on the 300I6 and it's the test mule for the EFI system. Dang good motor, crap for sparkey stuff. Try to hook up all missing sensor wires, about 6? Look at your wires to the sensors. Mine were sooo baddd it freaked me out that I drove it home that way after buying it. Did get a good deal tho. If you wires/sensors are about to make you kick the dog, just get in there and yank the computor/sensors with the wiring harness. It does come out in one huge bird nest. Get a old school dizzy with vacumn advance and a old carb with out the feed back electrical crap. Hang tough, man.

 

thanks for the responces guys. i still havent got it figured out yet. i dont have the time or money to do the carb and distributer thing but probably will in the near future if i dont get it running right soon. i did go to autozone and put the scan tool on it and it said the map sensor, o2 sensor, egr, and throttle positioning sensor were all putting out codes. took the map off my van and swaped and that did nothing. im about to pull the erg and replace the o2 sensor. the guy at autozone said the o2 sensor if bad could make the other 3 put out codes. i really doubt all 4 went bad at the same time. anybody had this problem with a bad o2? thanks again guys, and when i get it running right i will let you all know. maybe it will help somebody else out.

 

On my 85 Itried the o2 sen. It did not work. I agree with Van85 just rip it out and start again. The motor is strong and trust worthy. Like Van said, hang in there. You have a great truck.

 

ok. i tried the o2. guess what. it didnt work. i pulled the egr of the van and my truck, and the one from my truck seems in better shape than the one on the van which seemed to be running right. i give up. i got a carb, and as soon as i can afford one and find one, i will be buying the points distributer. i will need some guidence and advice. is the computer on this thing on the back of the engine to the left of the valve cover, or is that more sensors? besides the carb and distributer what else will i need to change? thanks guys.

 

Mine's in an aluminum box under the dash, for others it's on the driver's inner fender near the firewall. All the stuff on the rear of the motor are the solenoids and controls or sensors.

Mine was half-converted. Most all of the smog and sensor stuff was removed but it still had a computer control carb and dist. Without the input from the sensors, the computer has no tuning info, so it switches over to "limp-home mode." That is, fuel and timing is set to some make-it-run position. There's no spark advance or fuel mixture control. If you manually adjust the timing to some in-between spot, it'll run halfway decent, but either idle or high-speed will be off. Mine runs surprisingly well for being crippled up like this.

Swapping to an older carb and going to a vacuum distributor is what I also plan to do. Got the parts, but I need to rebuild the carb before sticking them on. I bought a rebuilt late 70's distributor, I forget the exact year, I just made sure it had points and vacuum advance. It was 70-odd bucks. I think all you need to do is provide the coil and ground wires to the dizzy and add a vacuum line off the carb for the advance.

Not sure how to deal with the EGR, if I should block it off or try to keep it working through a constricted vacuum line in a sort of home-brew "analog" mode.

Plug all the abandoned sensor vacuum lines and that oughta do it! There's plenty of posts on this subject here, do a search on distributor or carb swaps.

-Ed

 

hey guys, just wanted to give an update. well, for the heck of it i took the truck to a local ford guys shop. everybody said if anybody can fix it he can. dropped it of at 8 am on a wednesday, didnt hear from the guy till friday night when he called me to come pick it up because he couldnt figure it out. soooo, i bought a carb for an 84 off ebay, bolted it on just the way i got it and it runs alot better. im back to about 11 or 12 mpg. not quite the 13 or 14 i was getting but better than the 4. i was also wondering if i change out the distributer to the older kind if that will help my mpg? im guessing since the computer is not getting any signals from the carb that maybe the distributer aint working right, advancing ect. i see the new distributers arent to expencive, but i will still need the box right? can those be bought new or do i need to hit up the junk yard? thanks again guys.

 

You can go the wrecking yard route or you can do what I did and get a complete update kit that will take you about 3 hours to install from start to finish for about $170. Mine came with a rebuilt dissy with vacumn advance, new GM HEI module and coil. That is all you need. Phone Buck at 503.931.5978, Oregon Ignition Supply.