i have a '94 4 liter v6 ranger with 167k miles. about 3 months ago it started spark knocking pretty bad. in the 11.5 yrs that i have had the truck it has never done this. i changed the plugs and there was no unusual wear.

i hooked up an autoxray computer to see if there were any memory codes, there were not any stored. i ran koeo and koer tests, again no codes (except 111~system passes). i ran the dlc scan and got o2 sensor readings that fluctuate wildly between .09 and .80 @ 2000rpms. i have read that they are supposed to be between 0 and 5 volts. are my readings low and are they suppose to fluctuate that much?

fuel mileage has fallen off slightly.

thanks in advance for any help given!

 

forgot to mention, the spark knock occurs after the engine gets hot.

 

A vacuum leak maybe, so check all your vacuum lines, including the PCV system & all the vacuum using accessories, including the brake booster.
Also the 4.0L is known to have lower intake manfold gasket leaks from loose fastners, so be sure to look there too.

Or maybe this condition is exacerbated by a dirty MAF sensor, although it would seem the scan tool should have spotted a problem with it's response if it were dirty & seems to me a dirty MAF would more likely cause a lean mxture, but then maybe not.
But, seeing the vintage of your ride, maybe it wouldn't hurt to clean that puppy anyway!!!!

With the occurence of the knock only with the engine warmed up, kinda points to a A/F ratio problem.

The O2 will normaly like to average around 0.5 volts. A 0.45 volt reading=14.7:1 stochiometric & with 0.1=lean & 0.9=rich, your numbers say your on the rich side, not lean, which one would normally assocate with ping, if a lean mixture were the root cause.

Other causes could be combustion chamber deposits, maybe from a rich fuel mixture, you seem to have detected.

If that is found to be so & considering you said your fuel mileage has dropped off some too & seeing as how this ping problem seems to come about AFTER the engine gets warmed up & the system is supposed to go into closed loop operation & the fuel mixture lean out from it's cold start trim, but doesn't seem to be doing so, maybe the ping problem, is carbon deposit related.

I might test the COMPUTERS engine coolant temperature sensor & see if it's telling the computer the truth about true engine temperature. If it's untruthful & the computer thinks the engine is still cold, it'll keep the fuel mixture too rich!!!

I suppose bad fuel should be considered too, as it can cause ping, BUT it shouldn't affect the O2 readings like you've seen & cause them to be on the rich side of normal.

Just some thoughts from the sidelines, let us know what you find.

 

great post pawpaw....thanks!

i replaced the maf about a year and a half ago. i will check it though to see if it is dirty. i have run several gas treatments (i think gumout) through so i am not sure there would be much chamber deposits (though that's not to say there isn't). also, like i said when i changed my plugs they looked very clean. no deposits.

the thing that got me thinking was the point about the engine coolant temp. i replaced the radiator last year (the water pump and thermostat the year before that.) since then, there are wide swings in the water temp as i drive. i don't have the specific temps (i will read them tomorrow), but it goes half way up the guage, drops back the low end of the acceptable range indicated on the gauge and then just repeats this process throughout the trip. may need to replace the thermostat.

thanks again for the help.

 

OK, good feedback about the wild swings in indicated engine temperature.

Could be a faulty temperature gauge sending unit, or intemittetly sticking thermostat, thats what I found was wrong with my 99 4.0L temp swings, new thermostat fixed her up.

If the thermostat is acting up, such that it lowers the engines temp, to the point the computer thinks it's cold, I suppose it could confuse the computer, such that it could effect fuel trim.

I think it's still a good idea to check the computers engine temp sensor though, just to cover all your bases, although it does sound like you may have a thermostat problem.

Let us know what you find & how it goes.

 

I have been running premium (93) and the pinging stopped completely during the first tank of premium. It seems weird that for 11 1/2 years 87 octane worked just fine.


i've heard that this could be because of carbon buildup. Is there a way to remove the carbon buildup? i've used gas additives, but i think i'm passed that point.

 

Well in my 99 4.0L I use Chevron, Chevron/Texaco, or Shell/Texaco as a last resort, to help keep my combustion chamber deposits in check, as mine will suffer start up "marble noise clatter"from (CCDI)Combustion Chamber Deposit Interference, from the slightest dposit build up, until it warms up some & things expand enough for it to hush.

So my 4.0L is danged persnickety about the brand of fuel it gets.

Chevron Techron Concentrate is a good carbon remover too & expensive, but I just noticed this past weekend that AutoZone has the 12oz size, buy one, get one, so thats 50% off, not a bad deal, if your of a mind to give it a try.

Also in the "Technical Information" thread, loacted atop this forum, you'll find among other interesting things, a link to a thread dealing with a Ford 4.0L TSB de-carb proceedure, using three cans of Motorcraft PM-3, slowly fed in through a vacuum line & some spirited driving, to clean her out, if you think carbon deposits are the root cause!!!!

In recapping previous post's, what did you determine the root cause of the wild engine temp swings to be.

Ever find the root cause of the wild swings in the O2 sensor readings????

 

i've put a bottle of Chevron Techron Concentrate plus in the truck. i will run another bottle through with my next fill-up and then drop the octane back to see how it sounds. i also plan on checking out the article about the Ford 4.0L TSB de-carb proceedure.

i replaced the thermostat and the swings don't go as far down to the cool side as they used to. it now swings from the "N" to between the "R" and "M", but i can live with that. at least its not bottoming out like it was.

i haven't checked into the O2 sensor swings anymore, because i got looking in different directions. i was thinking about a possible vacuum leak until the knock went away with the higher octane fuel.

i will update as i find out more info and for kicks and giggles, i will be replacing my clutch slave this fall. that ought to be fun.

 

If your still using premium fuel, in an engine timed for regular, it's like retarding the timing.

Premium has a slower flame front, thus it combusts slightly slower & in lower compression engines timed closer to the mark, it can exacerbate any deposit problems your trying to remove.

Because the premium is still burning when the exhaust valve opens, things are exposed to the combustion flame a little longer, run a little hotter, get cooked a little more & tend to build more deposits a little faster,because of it!!!!!

Vicious circle it is.

Thats right, premium fuel can cause combustion chamber deposits. Our owners manual cautions against using it for these reasons.

I don't think a tank or two is a problem, but extended use may be.

It may also mask a lean A/F problem too, so don't give up on looking for a intake side vacuum leak yet.

If you have a vacuum gauge, hook it up & see what it tattles on!!!!

Just some more thoughts to ponder.

Keep us posted on what you find.

 

A couple things come to mine with a 4.0L of your vintage. The lower intake is known to loosed up, causing a vacuum leak, which will cause pinging. Another
thing that will cause it is a dirty MAF sensor. So, check your lower intake bolts, and clean your MAF sensor with an electrical cleaner, that does not leave a residue. If your intake bolts were loose, you may want to check to see if there is still a leak after tightening them by spraying carb cleaner along the intake / head interface while your engine is idling. If you get a change in idle speed, then you still have a leak, and the gaskets need changing.

Sorry pawpaw, just noticed you have already suggested these!!!

 

hey, thanks to both of you. this gives me a few things to play with. I will update as I continue to try the different remedies.

 

Ok, well it has taken awhile, but I think the problem is solved and I wanted to share.

I did replace the MAF sensor way back and it got a little better, but not much. I just had a coolant leak and took it in to have an intake gasket kit put on. Low and behold, the knock is gone. Its nice having my quiet engine back.

 

OK, good feedback & good to hear you finally ran the ping problem down.

The feedback could help others with like problems, troubleshoot their rides.

Thanks for taking the time to close this thread out.