Guys, I am cross posting from the bronco forum hoping for a bit more traffic. I am in a rush to solve this. Should be all the same than your trucks. I appreciate your help and input!!!

144k mile, 95 bronco, 5.0 auto. Fresh plugs, rotor, cap, oil.

I took a 350 mile trip today. Half way through it I noticed slight pinging. Then the engine also lightly stuttered - just slightly, so it almost feels like the road is a bit bumpy. This happened only under load up hill / into the wind at high speed. After a pit stop it would not do it for 5 minutes or so and then it would be back. Also, if there were flat sections in which I was going slower, it would not do it. Seems load / temperature related.

I tried putting more gas in it (medium grade) thinking I got some bum gas. Did not change anything.

I came home and bought the Ford code reader. I ran all the tests, engine off, engine on, cyclinder balance test. All passed flying colors several times.

The truck must be running lean to ping like that. Could it be the O2 sensor (without throwing a code?)

Fuel filter has 25k on it - could it be the problem?

How about the catalytic converter? If it is clogged, would the engine ping?

Please help me out, I need to do another 350 mile trip on monday and I am afraid I may get stranded if this gets worse! I was hoping I'd have some codes and this was going to be easy

Thanks!!!

George

 

Yes it could be an oxygen sensor and not throw a code. If you go to autozone .com it will tell you how to test the sensor with a digital volt meter. If you are worried about the cat a rough and ready test is, with engine cold, start engine and feel the pipe going into the cat and then the one going out. If there is good exhaust flow thru the cat both pipes will be at about the same temperature. Why not replace the fuel filter anyway and eliminate it? A friend recently had a similar problem with his `92 K1500 Chevy (not pinging), it turned out to be a defective oxygen sensor.

 

I started replacing things and testing after each step:

New fuel filter (old one had 20k miles - I checked) - same symptoms.
New O2 sensor - same
New PCV valve - same

One thing I had noticed about 6 weeks ago was that my a/c vent would cut out sporadically. I may have a vacuum leak somewhere. But that did not affect the way the car was driving for about 2k miles. I am trying to chase down that vacuum leak now but have had no success so far.

I have not played with the cat temperature. I have an IR thermometer. I will let the truck cool down now and then fire it up getting readings ahead and behind the cat. If that's not it, I will have to give up and drive it solely around town until symptoms worsen. For long distance (especially long climbs or mountain passes) it is currently useless.

The truck runs cool, cooling system is in good order with a new radiator a couple of years ago. I also tried to pull codes again - clean bill of health from the computer. The 02 sensor I pulled was very white. Could show me that it is running lean ...

Any more ideas???

Thanks!

George

 

vacuum leak is my guess.

 

George, did you ever find out what the problem was? I also have the same type of symptoms with my 95 F150.

 

I have spent some more time on this today. I know, it has been a long time. I only drove it in town and it still does the same thing, but hasn't gotten worse.

- Traced all visible vacuum lines and could not find a leak.
- Sprayed starter fluid everywhere I could imagine vacuum leaks. Idle did not increase / nothing changed.
- Took temp on catalytic converter after a few minutes of idling: Incoming temp 180C, outgoing 150C. That is not much difference, I doubt it is clogged.

What do you want me to try next? Again, there were no codes, everything in fresh in terms of the tune up.

Thanks!

George

 

Check your fuel pressure. If the pump is a little weak, you might only notice issues under load...

 

Partial restriction of air flow through EGR valve From deposit buildup and/or leakage of diaphram. But also the conditions right for Excessive deposit buildup to cause incomplete detonation and alteration of the air/fuel ratio by partial absorption of fuel introduced to combustion chamber. Time for SeaFoam thru the air Intake!

 

I vote the air injection tube at the back of the motor or the valve attached is rusted or cracked. Your symptoms sound similar to what happened to my '89 and the air tube was the cause.

 

when you say air tube is that the tube that runs from the egr

 

What kind of motor oil are you using? I was using a synthetic blend when my 95 351W began rattling during situations you describe. I finally went back to Valvoline 5W30 conventional oil, and they went away. My minor oil leak went away too.

 

rotella t 15 40 with stp oil treatment motorcraft filter for about the last 200,000 miles

 

No, it's the tube connecting the heads at the back of the motor near the firewall.

 

i never noticed that i will look,i have the 460 motor an has been taken care of quite well. last year i hollowed out the cat. new temp sensor, module,complete tune up, batt, alt.this year new radiator,water pump,an checked the timing chain.runs rich,last year was black smoke,what i do notice is on my main tank when i use it it runs somewhat normal,i changed fuel filters an theres rust in the fuel, last year i paid to have the tank cleaned,i will do it myself when i get the time.checked codes,none showing.the truck has almost 300,000 motor has never been apart,just put my first water pump on. 1988 f-250 4x4 460 c6,runs rich,hesitates,pings,park an nuet.will idiol,dr. an rev ,sometime dies.when i drive sounds like a major vacccum leak right at the firewall or even inside the cab,only when you drive.i have looked thinking it has to be EGR or CRUISE CONTROL,ALSO I HAVE ALWAYS CLEANED THE o2 never have replaced it. THANKS CONANSKI

 

Here is the solution (from my thread on the bronco forum). Thanks!

This DID IT. The wires (only 30k miles on a new set of Bosch wires) were tucked neatly together on the valve cover using the factory clip. Took the clip off and tied #8 wire up a little with a zip tie: voila!

Thanks a BUNCH! Truck runs great now. No more pinging, hesitation and much better power / gas mileage. I will replace the wires when I get a chance and run them even further apart. Never would have thought something like this was possible.

George