Can anyone help? I have an '88 F-150 2WD with a 5.0 and 5sp trans. The previous owner put in a cam and lifters form a mustang (not sure what year) which changed the firing order and shorty headers.He wanted more low end to pull a large trailer. My problem is at idle the engine surges from around 400 rpm's to about 800 rpm's and it runs really rich. The truck has plenty of power and otherwise runs pretty good for an '88 with 283K miles. I have changed the O2 sensor, did a good tune up changed the fuel filter and pumps, but the problem still exist. I was thinking the cam confused the computer. Could I replace the computer with one from a truck with a 5.8 because it has the same firing order as the mustang cam or would I be better replacing the cam with something closer to stock. Please can someone help me figure this out!!

 

Serial data was not available in those earlier years although a dynamic test(running test) was. It might be a good idea to get some additional info from the O2 sensor to see just how it is performing. That has to be done as an individual test either with a breakout box or at the sensor wire to the computer. Once you know what is happening you can make a better decision to either correct a possible problem or go with a change back. It's a lot of trouble to start changing back especially with all those miles, but if everything is working as designed you may have to change it and possibly get better mileage without needing all that additional power.

 

Thanks for your reply, I did a running test with a code reader and no codes showed up, also I can not find any vaccume leaks anywhere. I was thinking the cam is confusing the computer so maybe a computer from a 5.8 truck, also was going to have a crossover pipe installed between the exhaust and relocate the O2 sensor there to closer match the stock set up. Any thoughts?

 

Way back then,, I used to drop 5.0 HO Mustang engines into late 80's F's. Low mileage 5.0 HO donor power plants were plentiful and a lower cost over Ford/reman LB's. Long block swaps didn't have any other problems then the FO differences..

With that mileage,, compression is?

If someone did a cam change, I'd lean towards what problems an unknown cam might make. was it clocked correctly..

No codes and a very rich condition?