Spark Knock in 4th and 5th gear. - Ranger-Forums - The Ultimate Ford Ranger Resource


SOHC - 2.3L & 2.5L Lima Engines Discussions and Topics specific to the Lima 4 cylinder engines

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Old 02-16-2016
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Icon5 Spark Knock in 4th and 5th gear.

Hi, I am new here to this forum. A little background about the truck.I have a 2001 ranger with the 2.5l engine. The guy I purchased this from was going blind and he was not allowed to drive anymore. His wife could not drive a stick so she could not drive it either. He has let it sit for the past year or more while going out to start it every once in a while.. He has kept up on the oil changes and other maintenance but While driving I have noticed spark knock at higher speeds 65-70mph or on hills. It occurs sometimes if I am in 4th gear and strain the engine going up a hill or more frequently in 5th gear if I do the same thing. It also will occur if I'm in 5th going 65-70mph on the highway and try to go faster by applying more throttle. It definitely sounds like spark knock. I figured it was just bad gas as the thing has sat for quite some time. I have already ran two treatments of total fuel system treatment through the truck. My next thought is to fill up with a higher grade gasoline, say the middle grade of 89 octane and see if this prevents it from happening due to deposit build up. After that if its not fixed the only things I can think of are to change the spark plugs (maybe he has the wrong plugs or gap?) and wires because it does have a small miss that is very noticeable at idle. As well as clean the MAF sensor. Any other ideas would be greatly appreciated. Has anyone had this problem? I would like to get it resolved soon because I know it is not good for the truck at all.
Thank you for the help!
Brandon
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Old 02-16-2016
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Yes, it is pre-detonation, pinging/knocking.
Yes, higher octane fuel will most likely prevent it.

Octane is a heat rating, lower number means fuel will self ignite(pre-detonation) at a lower temp.

You have a Lima 2.5l engine, last year of that engine, just FYI.
It is a good engine.

When you put a load on any engine, i.e. going up hill, accelerating, trying to accelerate in OD(5th), the cylinders will start to heat up, if they get hot enough 87 octane fuel will start to self-ignite before spark plugs fire, and that causes the noise you hear.

Another thing happens when cylinders heat up, NOx level spike very high, so EGR valves were added to keep cylinder temps lower when engine is under a load.
Adding exhaust gases to intake air slows down explosive detonation enough to keep cylinder temps down.
Added side effect is that it also helps to prevent pre-detonation with 87 octane.

You may want to check that the EGR Valve and tube are clear, if flow is reduced then NOx will go up and so will pinging/knocking.

Another thing can be carbon build up in the cylinders, this comes from engine running slightly rich for long periods, pull out a few spark plugs and have a look at the tips, if you see a blackish build up then that will be the problem.
Spark plug tips should be a very light brown color, if fuel mix is good.
If carbon build up is seen replace the O2 sensor nearest the engine, that will either be the problem or it will be damaged by the carbon so needs to be replaced in any case

Because the vehicle seems to only have been driven on short trips, driving it daily for at least 15-20mins trips will help clean it out, the injector cleaner you are adding will also help.

Last edited by RonD; 02-16-2016 at 03:20 PM.
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Old 02-17-2016
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Hey Ron,
Thank you for the quick reply!
It's been pretty cold here in Ohio lately. Its supposed to be warmer friday and saturday. I am going to be resealing my rear window with Urethane adhesive. I have been having trouble with it leaking. After I get that done I will check out the EGR and see if the tube is cleared. I know he did replace the EGR because he mentioned it and it looks new. The tube on the other hand he did not replace so I will see if that has any gunk built up inside it. I will also pull out a couple spark plugs since it's going to be nice out. The spark plugs under the intake manifold look interesting. I might have to pick up some universal extensions before getting those out if they end up needing replaced. I also should mention there are no DTC on the truck including no CEL. I drive the truck almost everyday in town to work only about a 5 mile drive tho.
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Old 02-17-2016
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Sounds good.

If you get a length of vacuum hose you can put that on the EGR valve and suck on the other end, create a vacuum.
If engine is idling and you do this, it should start to run rough and if you open it enough engine should stall, that should tell you if exhaust flow is good.

The vacuum hose removed from the EGR valve doesn't need to be plugged, there should be no vacuum there unless engine is under a load, vacuum to EGR is control by a solenoid that computer opens and closes.

The computer can tell how much flow of exhaust there is into the intake by the DPFE(Differential pressure feedback) sensor.
It has two hoses connected to exhaust, one is close to or on EGR tube, other is on main exhaust manifold.
When EGR valve opens the pressure on the closer hose goes down a bit more than at the farther hose, this difference in pressure tells computer flow.

Normally you would have codes if flow was low, but DPFE sensor hoses often get moisture inside which can foul up the readings.
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Old 05-06-2016
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Please let me know your findings. I am having this same problem.
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Old 05-08-2016
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If you get spark knock or pinging when you are 'cruising', but it goes away when you give the engine a bit more gas, i.e., push a bit on the gas pedal, then I would suggest you need to give the engine an 'Italian tune-up'. Rev the beans out of it, run it up some in the lower gears. Put some carb cleaner into the intake and wash down the inside walls of the intake manifold(use CAT SAFE cleaner). Let it sit for a while. Some will get into the cylinders and work a bit on the piston crown and loosen the deposits.
As an old man, most of us don't drive aggressively enough to keep the pistons clear of carbon deposits. The above should remove carbon, and lower the compression ration a smidge.
A while ago, I could make the engine ping and then quit by moving the gas pedal. Back off and be at steady cruise, and the slightest hill would cause ping. Press a bit on the gas pedal, and it would go away. I think the timing would be diddled with as the manifold vacuum changed, being advanced at higher vacuum, and lowering when the throttle was opened. Did the cleanout and it got a lot better.
tom
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Old 05-11-2016
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I actually have not done anything yet since the two tanks of fuel treatment as well as a mid grade fill up (did not seem to help the problem at all), mostly the truck gets driven around in the city so I don't really notice it. I did pull a spark plug and noticed they looked a little brown. They were not motorcraft brand. I have some extra cash now and its warm in Ohio so I am going to purchase 8 motorcraft fine wire plugs today as well as new wires. Do you think these plugs would be best for the 2.5, or would the motorcraft double platinums be better? I think maybe the plugs are the wrong heat range and contributing or all of the problem, its worth a shot anyways. Im really ready to get this fixed lol.
any info is always appreciated
Thanks,
Brandon
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Old 05-14-2016
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Go to the Ford site and download an owners manual for your truck:

Fleet Homepage | fleet.ford.com
(I had a direct listing to the owners manual link, but they moved it)

The spark plug recommended is listed inside.

I would not spend extra on 'special' plugs. Regular $2 plugs will work fine. The drivers side plugs are NOT used to run the engine, just for specific emissions control under specific circumstances, and will not affect startup, idle, and normal operation.

tom
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