Runs like garbage....

mixedupcat

Registered User
I'm new here and really know nothing about Ford products. I'm here on my buddies behalf as he has a '87 XR7 that was a 5.0 auto. The motor on that one ran extremely rich and wound up blowing a hole in the #3 piston. So, he put in a HO 5.0 from a '91 'Stang, but still runs rich, intermittently doesn't want to idle, no power down low, etc. It does have new O2 that are in the range, TPS is also new and adjustable, well within specs. MAF is working properly, and all other sensors are replaced. We know the 5.0 and the HO have different firing orders, and the fuel rail has been adjusted. The computer has tried to go to the shortest setting for pulse length, and still runs rich. Do we have a computer problem ( bad main ground) or should we go back to the 14 lb injectors, what? I'm afraid if we go to the 14 lb, we may run lean for that cam and head flow. Can some one help with an answer and maybe some specifics about pins if the computer does need changed?
 
Are the stock 19 lb injectors on the motor. Also does the engine run on all 8. Are you sure that your running rich and not lean. Are you only using the engine block from the 91 stang. Because your 87 xr7 should be a speed density motor and not use a maf sensor. Theres only a couple sensors that can cause your engine to run really rich; maf, o2, map, coolent temp(Comp Sensor). Those are the 4 that i would start with. Make sure that there working properly. Also is your check engine light on??
 
Your rifght about it being speed density. Like I said, I'm no Merc man. We have checked in those sensors on open and closed, everything is within specs. The "check engine" light does not come on. We've searched a few times in search of a vacuum leak, but no results. The 19 lb units are stock for the HO. We're going nuckin futz over here.....
 
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