I'm now the "new" mechanic for a good friend's 87 f150 4.9L, so I may be spending alot of time with you folks.

Our situation: Engine stalls once or twice during startup and sounds like there is a miss during idle (putt......putt.....putt out of the exhaust). The throttle response is also sluggish. The exhaust also smells horrible and burns my eyes. I forget if this is an unburnt fuel condition or what.

We are getting a code 12 & code 46 using our scanner during the KEOR test. I've read what they are....but that's not much help. There were ALOT more codes but I had corrected those issues.
So far I have:
Cleaned EGR valve and tested
Replaced EGR vacuum solenoid
Replaced fuel filter & tested fuel pressure (40-45lbs)
Replaced plugs & inspected wires, cap, etc (replaced sometime in the past year??)
Cleaned IAC valve (and even swapped with another for verification that it was still good)
Installed new O2 sensor

I'm not sure which way to go from here. I'm thinking about checking the base timing (SPOUT plug off). Is the timing numbers stamped on the timing bracket? All I see are a serious of small notches and one large notch. Specifications says 10 degrees BTDC. Is the large notch 0 degrees? Is each notch 2 degrees?

How about the fuel pressure regulator? Isn't 40-45lbs a little high from what I've read? I removed the vacuum to the regulator and the truck sounds the same. I may do a leak down test when I get some time.

Thats all I have right now. I hope we can do some brainstorming and get this thing figured out. I think I have all my signature info....let me know if there's something else I"m missing. Thanks!

 

Disconnect the battery for 5 minutes minimum (as you should every time you replace a sensor).

Then put some miles on it.

Then rescan. Start w/ KOEO (Key on/ engine off) codes first. KOER's aren't reliable w/ active KOEO's present.

I would do a "Seafoam" treatment. Skip adding to oil, unless your planning on an oil change in the next few hundred miles.
See link: https://www.f150forum.com/f33/how-se...-1991-a-31505/

If you disconnect the Vac hose on the fuel pressure regulator & find gas at the hose, or pressure does not increase, then replace the regulator.

I would have it checked for Cat converter back pressure condition. Most muffler shop's will do it for free.

 

ymeski56,
Thanks for the advice. We had plans to cut the cat out (the entire exhaust system had rusted out and fell apart anyway). I will also try the seafoam too. I will let you know how it works out. Thanks again.

 

What???? In what vicinity in relationship to where the O2 sensor is located?

If outside air can mix w/ the exhaust flow being read by the o2, the ECU will max out your fuel trim, assuming you're running too lean, based of what the 02 is reading!

 

What indeed! The exhaust was rusted from after the cat back to the tailpipe. Also the smog pump pipe to the cat was rusted off......oh wait, it gets better. Not more than 5 minutes before I wrote this message did I find the exhaust manifold had a large crack where the outlets from the upper exhaust manifold meet. It's large enough for me to shake the pipe and watch it move away from the rest of the manifold. Ugh. As soon as I saw that I knew it wasn't good for o2 sensor readings. I need to fix that first before I continue with any other tests.
I tried the seafoam too....what an awesome smoke show. Anyway, throttle response seems to be better.
I know the right thing to do is remove the lower exhaust manifold and repair or replace it. I have welded the steel pipe type manifolds before and with great results. I just hope I don't break any bolts in the process. I'll keep you posted.

 

Well, it does explain an over rich air/fuel ratio.

Start soaking w/ penitent every time you think about it...and then some!

 

Finally removed the Y pipe to weld up the crack. Took a bit of work (a regiment of muriatic acid to dissolve rust, then some WD-40). I was able to remove 3 of the 4 bolts/nuts holding it on. We had to torch the last bolt head off to remove the exhaust pipe. After heating the manifold cherry red and using a good vice grip, the remaining bolt came out.

After all is said and done, the pipe is back in, no leaks but still idles like crap. When I hit the throttle it doesn't want to rev easily. I checked the TPS with a meter and all seems well. I'm not sure where to go from here, still getting code 12 and 46.

 

Are they "Continuous Memory" codes?

 

This truck is 25 years old so I would check the integrity of the internals before spending a lot of time with the externals. Do a compression test and leak down to see if maybe you have a burnt exhaust valve or cracked ring. The 3.0 are notorious for wristpin chatter and piston slap, so a quick rebuild might not bad idea if you have some internal issues. I used to have an 86 F-250 with the 300 six and 5 out of 6 piston skirts were cracked. It sounded like a marching band playing the spoons going down the road.

 

X2

To see if you have who know's what, or if you're good to go!

My 87' 302 has lead a sheltered life. Only 84K on her. I enjoy 183 PSI +- 3 PSI between cylinders. You didn't give us a mileage on your's but regardless, a compression check should be darn near the first thing you do to an older vehicle new to you before filling up a shopping cart at the part's store, or investing a lot of time in other types of diagnosis.

New dentures ain't gonna do anything for a patient with a bad ticker, other than make him a little better looking for the funeral. Start with the Ticker!