Hey Guys,

New here but not new to forums. I am also over at FSB forum.



Any suggestions are very much appreciated.

I am trying to figure out whats wrong with this Bronco.. I have been told it needs new valves or just a top end repair/replace by a mechanic that listened to it but I am trying to see if he is indeed correct or if it could be something else as the cost is high and the knowledge is low on my part as far as doing any sort of repair like that. I have had it checked for compression by a mechanic when I first got it and it had good compression on all cylinders, 130-140 PSI or so I was told at least.

The truck is running very rich, smells of gas coming from exhaust and it has a slight surging idle around 750 RPM. It also vibrates and shakes the truck some in idle, not crazy but noticeable. It runs and drives, starts up everytime, doesn't blow any smoke, its just running rough. There is some kind of ticking sound that even the mechanic that looked at it briefly couldn't understand what it was coming from the top of engine area.

It used to have Key on engine off codes for the SPOUT and PIP sensors being either faulty or out of wack but now it shows no codes. It is clear. I was thinking it may be something up with the Ignition Control Module but now since there aren't any codes I don't know. Maybe I should drive it around and then as soon as its off do the test? I did the test multiple times.

But, when it is key on engine on it did run a code for the HEGO (Heated oxygen sensor or its circuit) or I think AKA the O2 sensor. I have no idea what that is or where it would be. What do yall think?

It has new plugs, wires and distributor cap. Original rotor button and distributor. IAC has been cleaned.. just trying to figure out what to do with it.

 

I kind of sounds like it might just have a vacuum leak or a misfire. Do you know if the spark plugs, plug wires, and distributor cap were replaced in an attempt to fix this, or if maybe when they were installed is when this issue started? Also, do you know how old the gas is?

HEGO is the Heated Exhaust Gas Oxygen sensor, which you're correct, is more commonly referred to as a heated oxygen sensor. Nowadays pretty much all oxygen sensors are heated, so now many just refer to an oxygen sensor. Depending on the specific code I wouldn't necessarily replace the HEGO sensor yet since the code may just be indicating the HEGO sensor is getting readings that are unexpected but due to a misfire or a vacuum leak. And if you have a misfire you don't really want to install a new oxygen sensor until you get the misfire fixed. But the sensor will be in the exhaust stream. I'm not so familiar with the 1986, but there will be at least one before the catalytic converter and there may also be one after the converter, but I doubt that.

Does this Bronco have a Mass Air Flow (MAF) sensor? If so, you might try unplugging that to see if it improves the way it's running. Although that would typically be an indication of a vacuum leak, and since you mention it's running rich, that would seem less likely.

-Rod

 

it’s got fresh gas. It’s been running rough since I got it. It was backfiring at first so I replaced/cleaned a couple of the Idle air control valves/sensors around the intake and that fixed that. This ticking seems to be new, as in post distributor cap, wires, and plugs. Is it possible I screwed up on my gapping on the plugs? It’s possible as we were kinda in a rush doing it. Also I am unsure on the MAF sensor I’ll have to do some research.

 

It did tick before but it went away after I added some MMO in the crankcase. This new tick sounds different..

 

That old Bronco has a one wire O2 sensor
And a Map sensor
If it is the original engine
Good on Ford for building a decent one for yours
It will be tired by now (flat cam and loose valve guides) (low compression etc.)
Check the timing chain for loose and rebuild the motor when you can afford it

 

Vacuum gauge diagnosis is a thing of the past but is still a test that needs to be performed on older engines
You put a vacuum gauge on yours and find a old Motors Manual that has a vacuum gauge diagnostics section
That is most likely what your mechanic did when he advised the valve job

 

nah the mechanic that looked at it this week just listened to it didn’t perform any tests. He was pretty confident. I think it just may need some new valve seals. I haven’t pulled off the new plugs and checked but here’s what the old ones looked like. I’m not sure how long they have been in there but I’d say awhile they are all rusty. Couple show some deposits on them

 

Those look fine except for the black ones
Replace them and the cap rotor and wires and retest
Those two real white ones may not be getting enough fuel
The black three are getting too much
I use a spare fuel rail and pressurized injector cleaner to test them

 

That black looks like soot / carbon, not oil to me
I think your base engine may be okay
Do a compression test and write the numbers down for your future reference

 

check the fuel pressure regulator hose to see if its wet or smells like fuel. if it does then it might be leaking.

 

86 bronc , for extra help ,also try posting in 1980-1986 bullnose forum .More participants and the two daves are great help ,not knocking any one here! TR

 

Hi, did you manage to resolve this? I have the same issue

 

it is the original motor. 302. I’m gunna replace the 02 sensor this weekend. I haven’t messed with it in months. Just been sitting. I think this noise I’m hearing is just an exhaust leak by the manifold seal.

where is the MAP sensor for the 86 302 EFI? Feel like it probably needs to be replaced as well. Could be doing all kinds of janky ****

 

haven’t gotten back around to it. Been so busy. I’m gunna take a stab at it this weekend if the weather holds out

 

The MAP sensor is located above the left side of the heater case (in the RH / middle of the truck)
Plastic vacuum line going to it