My '99 5.4L has started knocking under load. It has only 43K miles and has never worked hard. I changed the spark plugs and no effect. Runs fine except on hills, even small ones, then I have to back off substantially to avoid knocks.

Is it likely caused by ethanol? Do I have a knock sensor? Could it be defective?

I hate to pay for 93 octane, and I'm not sure it is recommended for the engine anyway. Any suggestions? Many thanks....

 

Does the knock go away if you do run 93 octane? What about 89?

 

definantly try higher octane

 

Most likely insufficient octane fuel. Try a new gas station.

I would probably fill up with premium next, and see if it goes away. If it does, you know it is fuel related. Your regular gas station may have changed their supplier or fuel, or maybe you got a bad batch of gas.

Rule out fuel first if possible, but there are other things that can contribute to knocking, such as overheating. If your cooling system is not doing the job it used to do, your truck will run hot and knock.

 

Dave, thank you for the overheating tip. I will check on that. I have always purchased my fuel at the military gas stations, but I have no idea where they are getting it. The knocking started abruptly a few weeks ago, which could be because the gas changed or because my truck changed. I will try the higher octane gas, but it's going to peeve me if I have to start paying the difference. I will check the overheating possibility. Thank you all very much for the advice....Tom

 

If it started suddenly, it could have been a bad batch of fuel.

You might also change your fuel filter to see if that helps. If it has gotten restricted over the years, it might not be flowing enough fuel when you are going up the hills. FWIW, if you have not changed the fuel filter on your '99 it is a very easy job, but you do need a special tool to disconnect the lines (the tool is cheap, though).

 

Very few people understand the basics of todays OBDII internal combustion engines.

First off If fuel octane is too low for a given compression ratio, the fuel prematurely and spontaneously ignites too early and the fuel charge EXPLODES rather than burns resulting in incomplete combustion. The net effect is a loss in power, possible engine damage, and an audible "knock" or "ping", referred to as detonation.

The octane number of gasoline is a measure of its resistance to knock. The octane number is determined by comparing the characteristics of a gasoline to isooctane (2,2,4-trimethylpentane) and heptane. Isooctane is assigned an octane number of 100. It is a highly branched compound that burns smoothly, with little knock. On the other hand, heptane, a straight chain, unbranched molecule is given an octane rating of zero because of its bad knocking properties.

Basically if you have a high compression engine you need higher octane rating. The manufacture figures this out for you. You do not get better fuel economy from one or the other, unless your engine is not running correctly.

Several things can cause knocking and pinging or detonation. 1. cylinder head is getting too hot. Causes EGR system, coolant problems, low oil.

You could be using the wrong spark plugs.

If you notice knocking and pinging, buy a service manual and read through the emmission section and check the EGR system. If you are incapable of doing this take it to a good mechanic.

Replace and read the spark plugs. Check the O2 sensor.

I found on my F150 the EGR was sticking and the cylinder head was getting too hot. I was not getting a check engine light just knocking and pinging under load. I cleaned the EGR valve and the EVR vacuume regulator and it is working great.

Do your home work and read the service manual you would be supprised what you may find.

 

How about carbon/ oil build up inside the combustion chambers... oil vapor coming thru the PCV.