Okay, so yesterday I started hearing some uneasy noises from the engine. It sounds like an exhuast manifold leak but its come from the top of the motor and sounds deeper, also I have a low wine almost buzing noise that starts when I first start the motor the stops after about 10 seconds, also never heard it before. I dont know if that description helps but I cant seem to figure it out. It was pouring pretty hard for the last couple days so I dont know if that has anything to do with it..Thanks for any help.

 

Is the truck in your avatar the one in question? I can't remember what year Bronco you are dealing with.

 

yes, its a 90 bronco

 

and its a 351 motor, sorry, didnt include the details!

 

Ok, lets see, the "whine/buzz" (sounds like what I expereinced after dinner last night) could well be the Thermactor fresh air (smog) pump. They can produce a low noise such as you described if the ruber vanes inside are beginning to vitrify (dry out and get hard). The exhaust leak may well be another part of the Thermactor system leaking. The check valve in the crossover tube at the back of the engine is prone to snapping in half and when it does it allows exhaust to travel back up and out the valve which can produce the kind of sound you are hearing and it would be very near the top of the engine and very close to the firewall. Check for this situation early since that broken check valve leaking up between the back of the motor and the firewall sends the exhaust straight up at the main engine wiring harness that runs across the top of the firewall there. This isn't a definitive answer but its where I'd look first if there is nothing obvious whe you pop the hood.

 

okay, so I checked and it definitly sounds like its coming from that area, now, I looked in the manual I have an most of the diagrams are for a carburated engine, so how hould I go about fixing the problem, just climb in and try and find the broken piece or is there a place where I can find a diagram of that for a 90 351 EFI motor?