1998 Engine Knock

[PinkFloydEffect]

I've been chasing an engine knock at highway speeds that goes away when OD is disabled and/or running 89+ octane gas. It has 175k miles and I have always ran 87 in it. In the 7 years I've owned it I have not spent a lot of time on the highway but my job has me traveling so maybe I am only noticing it now, or something is failing.

Ive checked the plugs to make sure I am not down on any cylinders as I read some people found a bad side of their coil pack causing engine knock. I ran Seafoam in my fuel tank to potentially clean the injectors and also fed half the bottle into my brake booster vac line but got no smoke, neither did I several years ago so I think my intake is clean as nothing is burning off.

Could my timing chain be stretching? Does the knock sensor actively stop knocking in real-time by altering the timing or does it only report when knocking to trigger a CEL?

The truck has always struggled with acceleration so not sure if that is something related as well, every once and a while on a cool morning it will have an enormous amount of acceleration.

Any suggestions? Thanks!

 

[franklin2]

The knock sensor actively stops the knocking. The computer advances the timing a little bit at a time, inching it more and more advanced till the knock sensor hears a knock. That tells the computer stop advancing and retard a little bit. It then starts the cycle over again, slowly advancing till it hears a knock, and then retards again.

This keeps the timing as high as it can be with the type of fuel you are running. This gives the best power and fuel economy.

You might want to double check your initial static timing. If it's like the older trucks, you get it warmed up fully, hook the timing light up, and then unplug the spout connector to take timing control away from the computer, and then set it, usually 10 degrees BTDC. Then plug the spout back in.

Do you think there could be carbon built up in the combustion chambers? Some people rev the engine while slowly pouring water down in the engine and claim this will knock the carbon loose.

 

[4.0blue98]

My 4.0 pings and knocks like an MFer when I accelerate while cruising on the highway. Is yours a 4.0? Mine is carbon related. There's a tsb out there about cleaning it out. I use Motorcraft PM3 but it's gotten expensive. I'm sure Berrymans B12 would be a good substitute but I have never been a fan of seafoam. Never did anything for me whether in the tank, crankcase or sucked into the intake. Berrymans always works. Mines done this for the past 20 years and I just live with it. I'm pretty sure the 4.0 OHV doesn't have knock sensors.

 

[PinkFloydEffect]

The knock sensor actively stops the knocking. The computer advances the timing a little bit at a time, inching it more and more advanced till the knock sensor hears a knock. That tells the computer stop advancing and retard a little bit. It then starts the cycle over again, slowly advancing till it hears a knock, and then retards again.

This keeps the timing as high as it can be with the type of fuel you are running. This gives the best power and fuel economy.

You might want to double check your initial static timing. If it's like the older trucks, you get it warmed up fully, hook the timing light up, and then unplug the spout connector to take timing control away from the computer, and then set it, usually 10 degrees BTDC. Then plug the spout back in.

Do you think there could be carbon built up in the combustion chambers? Some people rev the engine while slowly pouring water down in the engine and claim this will knock the carbon loose.

Thanks for your response. I do not own a timing gun and have not playing with engine timing before but I will ask around to borrow one. I believe I read the knock sensor is not easy to replace and is located under the intake?

I do not think there is carbon as I mentioned running half a bottle of Seafoam through it already via brake booster vac line while revving engine. Got no smoke at all.

Did you say run water through the engine?! Was that a typo? That will kill an engine real fast like mud bogging without a snorkel.

My 4.0 pings and knocks like an MFer when I accelerate while cruising on the highway. Is yours a 4.0? Mine is carbon related. There's a tsb out there about cleaning it out. I use Motorcraft PM3 but it's gotten expensive. I'm sure Berrymans B12 would be a good substitute but I have never been a fan of seafoam. Never did anything for me whether in the tank, crankcase or sucked into the intake. Berrymans always works. Mines done this for the past 20 years and I just live with it. I'm pretty sure the 4.0 OHV doesn't have knock sensors.

This is the 3.0L sub-forum so no it is not a 4.0L

I misspoke, I did run Berryman B12 not Seafoam and got no smoke even from half a bottle fed into the intake vac so I assume it washed the intake and cylinders down.

20 years?! Engine knock is known to blow engines up or at least cook your pistons I thought?

From what I understand people favor the 3.0L over the 4.0L because the gain is minimal for the risk you take on with the 4.0L since its vulnerable to catastrophic timing failures?

 

[Shran]

Did you say run water through the engine?! Was that a typo? That will kill an engine real fast like mud bogging without a snorkel.

He doesn't mean drown it, just a little water won't hurt it. Spritz it with a spray bottle.

From what I understand people favor the 3.0L over the 4.0L because the gain is minimal for the risk you take on with the 4.0L since its vulnerable to catastrophic timing failures?

They all have their own set of problems but the 4.0 OHV does not have multiple timing chains, guides and tensioners to fail like the 4.0 SOHC engine does.

 

[PinkFloydEffect]

He doesn't mean drown it, just a little water won't hurt it. Spritz it with a spray bottle.

Ohh I guess that makes sense it could moisten up the carbon buildup making it more pliable but you would think the solvent the engine is running on would do that haha this is new to me.

They all have their own set of problems but the 4.0 OHV does not have multiple timing chains, guides and tensioners to fail like the 4.0 SOHC engine does.

So the rumors I hear are half true it comes down to OHV vs SOHC! The 3.0L always kept the cam down low in the block like atraditional V8 right?

On a side note I have seen some interesting suggestions with the 3.0L such as using a lightly modified plastic intake off a Taurus. Mine has some serious acceleration problems even with the stretched throttle cable zip tie spacer hack. I feel as if the automatic transmission poorly manages the power. The gears are too long and I think its 2nd gear I noticed is much shorter than all the others.