Hey guys. I have a problem and it's about to be the end of me!!! I have a 1992 F-150 4x4 302, E4OD tranny. We rebuilt a 302 from a 1984 E150 and put all the efi stuff on it off the truck. Used a comp cams 31-255-5 cam. The truck will backfire thru the exaust when you rap it up and it seems like it does not want to take its throttle when you tramp it. If you get in the throttle easy and only give it about 1/4 to 1/2 throttle it runs ok. but then when you give it over half throttle its like you jerked the E-brake and it will backfire thru the exhaust and sometimes thru the intake. We used a rebuilt set of E7TE heads when we built the motor and machine shop where i live said motor should be around 9:1 compression. It has no valvetrain noise and timing is dead on, but when its ideling it seems like it has a dead miss or is kinda rough. we pulled codes. KOEO codes there were none. KOER codes there were 2. 1 about no knock detected when the dynamic response test was done so we chaged the knock sensor and that code went away and the other one had something to do with the transmission could not turn on and off the overdrive swith. We have changed every sensor in the motor and tried a new computer also with no luck. changed all the injectors and no luck again. now the weird part is i put a computer on it off a 1995 F150 with a 4.9 MAF 5 speed and the motor will not backfire and seems to run better but it loads up real bad and blows black smoke. Thats to be expected, and the trans will not work..... also to be expected. also with the code scanner plugged in and running the key on, engine running test you can mash the gas and it will not backfire anymore and seems to take its gas better. It also has new plugs wires and cap and rotor. HELP!!!! Im about to go crazy. Is there any way i can convert engine to carb and duraspark or points and still make the tranny shift properly with out taking out a 2nd mortgage on my house? Any and all help will be greatly appriceated. Thanks Guys!!

 

check your firing order. sounds like you crossed 2 or more wires.

 

i agree, that cam is going to use the 351w or 302ho firing order. so you must change the order on the dizzy. your haynes or chilton manual should show the order of the wires on the dizzy cap. also put the original ecu back in. you might have to pull plugs and replace them because im sure some are fouled pretty good. also check for vacum leaks. your not using platinum plugs are you?

 

No, I am not using platinum plugs. I'm using Autolite 25's. Checked vaccum leaks and there are none. Put new plugs in today and same old stuff. The comp cams that i am running is #31-255-5. This cam is meant for the 302. The windsor version of this cam that i think you are refering to is #35-255-5. You have to watch the first 2 numbers. They are different. The 1 i got was meant for the 302 firing order. I suppose anything is possible, but if i were running a 302 firing order on a 351W cam i would think it would not even start and if it did it would run worse than it is now, but i will try the windsor order and let you know what happens. Also today we changed distributors and that did nothing and when i took it out for the last test drive of the day if you pump the gas pedal rapidly when you take off and thru the gear changes it will run like a scalded dog, but if you get in to it easy at about half throttle it will start popping and backfiring thru the intake. I am almost ready to call it quits!!! this thing has cost me more to fix than what i paid for the damn truck!!! Thanks for the advice guys. I will let you know what happens next.

 

whats your fuel pressure at the rail?

 

Well Good news guys!!! We finallyt figured out the problem. When we checked the fuel pressure on it, it was well within specs and appeared to be operating correctly. We did the key on engine off and the engine running with and without the vaccum line pluged into the regulator and everything seemed normal. We took a reading of the exhaust ports individually with a digital temp prob and found that 3 cylinders were running 85 to 110 degrees cooler than the other 5 so we knew we had a lean condition, But Why???? Well here it is. Anyone familiar with the early 90's ford trucks mine being a 1992 knows that ford used what is called a FDM ( fuel delivery module) instead of a regular old fuel pump. This FDM takes the place of several previously seperate components in the fuel system including the 2 way resivor tank on the early EFI's. We pluged the pressure guage in and took off in the truck and run it under extreme load and the pressure instead of rising when you gave it throttle droped or stayed the same but did not raise under demand. by the time we got back to the shop i was carrying only 23LBS. at an idle. YIKES!!!!! Not good! Put a new extremely overpriced FDM in front tank and..... Problem Solved!!!! Hurray. Hope this helps anyone else who may have a similar problem. Check fuel pressure underload and i mean when driving. By the way the comp cams that i put in this RULES!!!! Very torquey and loves the 1500 to 3000 RPM range. great for towing. Thanks everyone who replied!! I'm GONE!!!!

 

righton. good find. so it was the second pump on the frame rail back by the tank huh. jive pumps lol