Let's see if we can shed some new light on this one, and put it to rest for many people. I too had this problem and tried different gas, gas additives, meticulously inspecting the cooling system to make sure overheating was impossible, found the jumper that allows me to back off timing 2 degrees, checked the computer for error codes, and cleaning the MAF sensor. Nothing really worked.

The solution is to decarbon the engine. It is all described in TSB 01-19-7, dated OCT 01. I did this and END of the problem. Pay attention to the part about not ingesting the PM-3 cleaner too fast to make sure you don't liquid lock your engine. The only important step they forgot was that you will need to replace spark plugs when you're done. You may also want to lay some newspaper under your tailpipe too, as the crud is gonna flow.

The TSB notes that the driver should have "periods of daily operation over 3500RPM to break carbon from cyl heads". They also note that you should NOT use mid-grade or super duper unleaded, as these increase the probability of carbon buildup.

This repair will cost about $30 if you do it yourself; if you can change a flat tire you can do this.

 

Here is a link to the TSB: http://www.alldatapro.com/alldata/PR...93498/87891107

I've also cut and pasted the TSB here; enjoy!

Engine - Carbon Knock On Acceleration


Article No:
01-19-7

10/01/01

^ ENGINE - 4.0L OHV - CARBON KNOCK ON ACCELERATION

^ NOISE - CARBON KNOCK ON ACCELERATION - VEHICLES EQUIPPED WITH 4.0L OHV ENGINE ONLY

FORD:
1990-1997 AEROSTAR
1990-2000 EXPLORER, RANGER

ISSUE
Some vehicles equipped with the 4.0L OHV engine may exhibit an engine noise which may 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 following Service Procedure for details.

SERVICE PROCEDURE

1. Use Motorcraft Carburetor Tune-up Cleaner PM-3.

2. Carbon removal:
a. Disconnect canister purge line from 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 Gleaner.
f. Remove vacuum line and re-install canister purge line.
g. Road test vehicle at 3500 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. Use regular unleaded fuel, 87 Octane. Mid-grade and Premium fuels may increase the probability of carbon buildup, leading to a knock noise.



PARTS BLOCK

OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage

OPERATION DESCRIPTION TIME

011907A Remove Carbon From 1.6 Hrs.
Combustion Chamber
(Includes Time To Perform
Procedure A Total Of
Three Times)

DEALER CODING
CONDITION
BASIC PART NO. CODE
6108 42

OASIS CODES: 497000, 615000, 702000, 702100

 

I appreciate your post. It may not be 'the solution' for everyone's truck, but it's definately worth trying. I'll plan on doing this before I replace my plugs and wires... Thanks,

Brian J Wilson

 

Thank you for validating my driving style .

I got a feeling a lot of people are gonna be trying out the procedure you outlined. It's probably something to keep in mind regardless of whether or not your 4.0 is knocking, especially when the miles start adding up.

Even installing a set of cheap "throw away" plugs just for the procedure might even be worthwhile, particulalry for those of us with a brand new set recently installed.

Is that Motorcraft Carburetor Tune-up Cleaner PM-3 I hear flying off the dealers' shelves?

 

Yuppers, PM-3, Motorcraft Carburetor Tune-Up Cleaner is the stuff. My experience shows that the 3000 RPM thing didn't help me though, I still had the problem. I considered everything EXCEPT carbon build up based on how I drive and the large # of highway miles I've got. It sure would have been nice if Ford released the TSB years ago; I've been hearing about the problem since 1995.

 

When it says to "allow the engine to ingest" the carb cleaner, does that mean to just spray it into the throttle body while the motor is idling? I also assume that motor will cough and run rough for a brief spell until the crud is burned/blown out each time? Just want to know what to expect. Thanks.

 

Good job Billy, and welcome to FTE: Home of hopelessly addicted people like me, who spend WAY too much free time typing!

Actually, something very similar to this idea was just recently posted by a very bright ex-mechanic (TomW), the difference being the medium used to burn off the carbon: plain water. His post is under the topic "2.9 valve-knock" at this address:

https://www.ford-trucks.com/forums/s...highlight=tomw

I’ve seen this done first-hand on a carburetor equipped Toyota about, oh, 17 years ago (this getting old thing sucks). The car had so much carbon you could hear it knocking at idle. The mechanic simply poured small amounts of water right down the throat while revving the engine. Worked immediately and beautifully.

Tom also mentioned that with today’s FI engines, this can be done by spraying water into the throttle body using a spray bottle. I too intend to try this on my '94 3.0L once the weather breaks and will be sure to advise the forum of the results.

I’m not aware of this causing any irreversible spark plug damage, but maybe Tom (or other qualified mechanic) will see this and chime-in.

Mike

 

I have heard of the water trick also.....It is effective in removing
carbon from the combustion chambers. On the negative side, you
can ruin the O2 sensors, and ruin / plug the CAT....

 

About "ingestion", the PM-3 cleaner is a liquid that comes in a 1 quart can. With a hot motor at idle, it is ingested via a rubber tube that you hook onto the throttle body in place of the canister purge line and you dip the tube into the can of PM-3 (no spraying). The motor will run rough when you do this. Due to the large amount of carbon that you will dislodge during the process of doing the TSB, the spark plugs will become coated with carbon, weaking the spark, and the engine will run weak and rough when done. That is where the new spark plugs come into the picture. BTW, I got 150,000 miles on my original plug wires and NP. I have a feeling that many people are buying plug wires longgggg before they really need them. They are much better these days than they were 15 years ago.

BTW, about plug wires, that old "lift the hood in the dark and look for arcing" test does not always apply. I've had plug wires break down internally and not arc. The insulation is pretty thick on them now, so beware. The symptom of this happening was missing/backfire with a cold engine, and the problem gets worse as the miles add up.

 

I have had just the opposite experience on Rangers, the plug
wires will go bad before the spark plugs! There are 2 ways plug
wires can fail, the first, the insulation will break down, in this case,
you will see a "christmas light" effect at night. And second, the
core can break down, in this case, you can measure the wire
resistance, and find this problem....The plug wires should be
8K-12K ohms, depending on the length....

 

Bob,

Noted on the possible O2 and cat damage. In your opinion/experience, is this in extreme cases only, or is the risk high even with light carbon burn off?

Billy,

I had to laugh when you mentioned people buying things long before they need to. Stick around these forums a couple months, you'll see that's pretty much par for EVERYTHING replaceable, from oil (3k is still the standard for many, not me) to filters to spark plugs. The reason is often "cheap insurance", but cheap is a relative term and parts prices are FAR from cheap these days. Oh, well -- it DOES help the economy!

 

Thanks for the great post and going to the trouble of passing on the link......

I'm going to give this a try before I go any further down the replacement road. I do have a rather simple question/s though....did you have this problem, have you done this and did it work....I know it sounds like a stupid question (marmots aint that bright) but I have yet to hear it asked and answered in the affirmative.


The link also led me to another great resource....thanks again

marmot

 

just re read your post and it answered my previous reply regarding did you have this problem and did it work....

apparently marmots can't read that well either


thanks again

 

the one question I have is, Do you absoulutely have to use the PM3 cleaner, or would a different name brand carb cleaner work?

I'm going to give this a try, even though I don't have any problems, as I'm a total engine freak with some extra time, and I'll prolly change out the oil as well.

Do you guys think that this carbon knock issue would cause lower gas mileage?

just a thought...

 

Don't think so.....But I notice you are using Bosch plugs, try
getting rid of them, and go with Motorcraft double platinums,
they shoud help your MPG.....