1986 bronco ii with a constant miss

[Broncoman1532]

New to the forum and like the site (ton of helpful stuff) ihave an 86 bronco 2 with the 2.9 and it has a constant miss I have done plugs wires cap rotor. A friend said to replace inigtion control module (tfi) would it cause the constant miss. I have checked for spark at every plug. Another friend said a fuel injector. I also have another ? I have a fuel pump from a 90 bronco ii is it okay to replace it with the one in my bronco. My float does not work and wanted to switch it to a plastic float. Thanks for the help

 

[kuivinenj]

sounds like an injector to me i got a b2 for free that way it was skipping a cylinder so the guy told me to get it out of his yard when i got it home i pulled the fuel rail and injectors off, one was full of sand and rust so i replaced it runs smooth now so try that. also if u do take it apart oil the injector o rings it goes back together way easier that way

 

[sjr53]

The 86 has 2 fuel pumps, a low pressure pump in the tank and a high pressure pump on the frame. The 90 will have just 1 high pressure pump in the tank, or so I have been told.

 

[big red 138]

do you know which cylinder is missing? if you dont do a power balance test. once you locate the cylinder with that is missing, runn a compression test, cranking and running

power balance test: with engine running, pull one ignition wire at a time. each one pulled should cause an drop in RPM. the one that does NOT lower engine RPM ( or has smallest drop) is the weak cylinder.

Compression testing: once you locate the weak cylinder, run a cranking compression test ( disable the ignition by either removing the ign. wire at the coill)( watch for 4 "puffs") should be somewhere between 125-160psi. (thats industry standard, however all mine were around 170-180) compare it to 1 or 2 other cylnders to make sure theyre all close. if that all checks out, or it is slightly lower, remove the valve core from the compression tester ( so you can watch compression and loss of compression as it goes through the stroke) hook the compression tester up to weak cylinder ( hook the ign. wire back up) and let he motor run. compression while running should be around 60-90psi. but get the readings and shut it off. it IS possible to hydrolock a motor with gas, not easy but why risk it.

good luck man, let us know what works!

 

[shadow88]

The 90 b2 dose have one fuel pump, in the tank only

 

[joenorthcarolina]

I just bought a 90 BII.
I had the same problem. I pulled the plugs and discovered which injector was bad. #4 was the problem on mine.
Runs like a champ now.
I recommend running some fuel additive to clean that cylinder/piston rings and valves. I bought a large bottle of Lucas for $12 at Autozone. Its enough for 100 gallons of gas.