Ok so here goes...
The background of my problem is as follows, '86 302 EFI that was burning a quart of oil every 60 miles. In preparation for pulling the heads..I found out that the oil burning was not caused by bad valves/seals but instead the pcv. After fixing the problem, the oil burning went away. Fast forward a few weeks later...


I was driving down the road and hit the gas to go up an overpass, the truck started pinging once I did this. By the time I slowed down to turn onto my street, I noticed the second symptom, studdering/rough running. The truck runs so rough in the lower rpm's that it feels like the whole thing is going to fall apart.


Here is the list of what I've inspected/replaced.

• Checked Codes, code came up for o2 senses lean condition

• Checked Fuel Pressure, 34 psi at idle in park, 38 psi idle in gear, 40+ psi when revving

• Checked manifold vacuum, behaves as a healthy engine with steady 18in. Hg at idle

• Checked compression, all cylinders are close in compression

• Checked egr valve operation, valve holds vacuum – when vacuum is applied engine runs rough as expected – no vacuum present at the valve until throttle is goosed

• Tested TPS sensor – works fine

• Checked TFI module – tests out ok

• Checked coil, cap/rotor – tests ok

• Fuel leakage test – no pressure drop after 10 minutes

In addition to these tests, I have done:

• Replace spark plugs due to suspected fouling from carbon (Autolite copper)

• Ran Seafoam due to suspected carbon in engine

• New upper intake manifold and throttle body gasket due to suspected vacuum leak

• Retarded timing to 5 degrees BTC - truck still pings though not quite as bad

• Suspected MAP sensor problem, replaced

• Visually inspected all vacuum lines

• New fuel filter

In regards to the lean code, I don't see how it could be running lean, its gone through 12 gallons in 88 miles and starts as if it were flooded. (have to floor it to start it)


I have new ford racing spark plug wires coming tomorrow, if they don't solve the problem then I have no clue as to what the problem could be. Any insight would be greatly appreciated, as this problem has me, my dad, and his coworkers (know lots about cars) all stumped.


Thank you!!
(Sorry for the long post)

 

check that new pcv valve, make sure it didnt fail causing a big vacuum leak. While its idleing you can spray a little carb cleaner down the throttle body and see if it smooths out. Also, you can pull plug wires while its running to see if you have a couple dead cylinders (you can still have compression even and have valves not opening) When you pull the wires off the plug make sure you can hear spark jumping to the spark plug for a good .25-.5"

 

The pcv valve itself was not replaced (it still rattled), the problem there was sucking oil into the intake due to a lack of valve cover baffles.

My dad did the wire pulling method the other night..I'll have to ask him what the results were 'cause I don't remember.

 

clean IAC or replace.

 

I thought that the IAC has no effect on part-throttle or full-throttle performance?

 

Just wanted to post up on the conclusion to this issue. After finally convincing my dad (I'm at school now and don't have time to help him) to do a compression check, (the one we did previously was before the problem occured) cylinders 2 and 3 only had 30psi each. After my dad got around to pulling the head, the headgasket was blown between those 2 cylinders. Should be up and running in a week.

 

This is a good case study for how a simple tool can help you confirm or not confirm a problem before all kinds of efforts are undertaken....get a $10 vacuum gauge. It would have shown a serious blip in the needle when those cylinders came around. $10!!!

 

I know its not that likely; but, You might have a small hole in your Fuel Preasure Regulator, Mine had a hole in it and fuel made its way into my air intake and flooded my engine that way, smelled really bad too. But that could be your problem, If you try that, Go to Ford and get it, I went through one from Advance Auto Zone, NAPA, and the blew with in like 2 miles down a farm path when testing it. (Fowled Spark Plugs Each Time), So use MotorCraft from FORD, you can't go wrong. (Check your return line on the fuel, If you have dual tanks, your return valve may have got stuck between ports, thats what I think happened to me.

 

Running on 6 cylinders would definitely cause a problem.

 

srercrcr, funny thing is that the vaccuum gauge showed that everything was perfectly fine!!