TSB: Carbon Knock Noise On Acceleration for Ford Vehicles with 4.0L Engines

[x5050160]

Some vehicies equipped with the 4.0L OHV engine may exhibit an engine noise which might be perceived by the customer as a piston/connecting rod bearing knock. This carbon knock is heard only under load during the drive cycle. Carbon knock is a customer drive-duty-cycle phenomenon that cannot be repaired with an engine exchange. This may be caused by carbon build-up within the combustion chamber.

Action
Verify condition. If normal diagnostics fail to correct the condition, de-carbon the combustion chamber to help quiet the carbon knock noise. Refer to the appropriate service manual for details.

Service Procedure for Installers
1. Use Motorcraft carburetor Tune-up cleaner PM-3.
2. Carbon removal:
a. Disconnect canister purge linefrom throttle body.
b. Attach a vacuum line to the canister purge port.
c. At hot engine idle, allow the engine to ingest 1/2 to 2/3 of a can of Motorcraft Carburetor Tune-up Cleaner. Use caution not to ingest too quickly due to potential hydro-lock issues.
d. Shut engine off and allow it to soak for one hour.
e. Start engine, allow engine to ingest the remainder of the Motorcraft Carburetor Tune-up Cleaner.
f. Remove vacuum line and re-install canister purge line.
g. Road test vehicle at 3,500 rpm for 2-3 miles.
h. Repeat above procedure two times for a total of three times.
i. Change oil and filter.

3. Review’ the customers’ driving habits. The recommended drive cycle should include daily periods of engine operation above 3,000 RPM, such as a brisk acceleration from a stop position. This will break/burn the carbon off the piston head.

4. Ford recommends customer use regular unleaded 87 octane fuel. Mid-grade and premium fuels may increase the probability of carbon buildup, leading to a knock noise.

Ford telling you to SeaFoam your 4.0.

 

[Number4]

I believe the real cause is oil leaking via the lower intake gasket. Not enough to see smoke out the tail pipe, but enough to cause pre detonation? Pulled mine apart and you can see on the gasket where oil was seaping past.

 

[x5050160]

Interesting. Never thought over that.

 

[Number4]

I can say, after pulling my heads, there was no abnormal amount of carbon build up, which I was really hoping to find. So this TSB was a nice guess by Ford and they've collected a lot of money doing their upper end soaking I'm sure.
Wether it's due to oil, or extra air I don't know. But I've tried everything prior to tearing down my engine. Once it's back together, I'll see if the pinging is still present.

 

[x5050160]

Yea i did the soak and i think I have fouled the plugs. Im going to do the plugs and intake manifold gaskets.

 

[Wolfie_85]

My ping is nearly absent now, after another Seafoaming using Ford's technique. I didn't foul any plugs or hydro lock it. The manual claims some ping is normal, and I'm not hearing nearly as much as I used to (it's actually quite quiet now), so I'm willing to say it's resolved. Appatently, you have to get on it once in a while to keep it clean.

As for intake gaskets, yeah, I do think it's possible. Especially considering our first gens are aging and getting up there in miles.