I have a 93 F150 4.9L with 140,000 miles. Lately when I start it up, it has a "Diesel" sound in the front of the block, like one of the front two rods has a bearing going south. I had just noticed the sound several days after changing my oil (Every 3000 miles like clock work). I rushed to the store and purchased some engine flush (Assuming maybe low oil pressure) and after pooring it into the block, the sound went away with in seconds. Changed the oil, and presto, it is back. But the only thing is, it will go away after 20 minutes of driving. It will come back once the block is cooled off and started again.

Now, assuming that the bearing or rod in the front is failing, I want to head this off before major problems occure. I went to my local "Salvage" yard to get a long block to run down to the machine shop. He had several from the early 80's, but nothing from the 90's. I called Northern Auto Parts and they have engine rebuilds kits for the 4.9L engine, but they too wanted to know the year of the block, seems the 87-94 kits are different that the early 80's.. WHY? Are the blocks identical, just internal parts different (Cam)? I don't want to grab a block and spend $$$$$ getting it ready to find it won't work in my 93.


PLEASE HELP....


Justin

 

The only difference I am aware of is in the intake/fuel system. The block itself went pretty much unchanged for 30+ years.

What grade oil do you use? My 4.9 makes a "diesel" sound the first second or two, but it always has since new. When I tried using 5-30, instead of the usual 10-30, it was worse.

Take care,
-Chris

 

PKRWUD,

I am running 5-30, was told that was what I need to run in it. AS for the block, did some calling, looks as if there is a difference in Cam and Bearing OD size. Not much more info than that so far. Up to 84 has the origional size, then mid 85 thru mid 86 version two was used and then in 87 to 94 a 3rd version was used, but this does not tell me if the blocks are the same.

So, should I use 10-30? My new (not any more) Windstar calls for the 5-30, I think.....


Thanks,
Justin

 

Interesting info! I'll look into the block issue a little later, when time permits, but it sounds like you found your answers. As far as the oil, use 10-30. The 4.9 is a very different engine than the one in your windstar. It will help.

Take care,
-Chris

 

Hey PKRWUD,

I noticed on the way to work today, that the oil pressure guage moves around. It starts its day between the N and the O in NORMAL, it moves between the O and the R on the highway, after getting back on city streets, it will drop back to the N then slowly creep back to the space between the N and the O.

I still have not changed the 5-30 for the 10-30, been toooooo busy at work and the rain when I get home doen not help either. My Funny car project is in the garage, so I am religated to the driveway.

Any insight into the cam differences of the 4.9L block? If the later blocks had larger bearing OD sizes, would that imply that the bearing bore on the block is larger?

Be good, be well, behave.

Justin

 

Well, i can't find anything anywhere that says there is any difference. All my manuals call for the same measurements and clearances from 1980 on (I haven't looked for pre- 1980).

Take care,
-Chris

 

PKRWUD you disapointed me..you forgot to suggest Justin93F150 the best engine knock remover ever invented!!!!
Justin93F150 change your oil the 10-30 and add a bottle of Slick50...it works wonders on these engines.



BTW- PKRWUD I'm not forgetting the 22nd.

 

PKRWUD,

Well, changing the oil did not stop the problem. I did add the Slick 50 and yada, yada, yada.. The knock is still there until the engine comes up to temp, maybe 5 minutes. Yesterday I had to drive several hours to Indianapolis, IN. Heading up the highway and the oil gauge is pointed between the "O" and "R" in NORMAL. Then slowly it slid to where it was barley touching the "N" and stayed there the rest of the trip at 70 MPH. On the way home, it never left the front of the "N" until I got a cell call and I rolled up the window and turned on the AC. The Oil needle rose to the "R" or a little after while the AC was on. Turned the AC off and the needle slid back to the "N". I played the game for a little while, but the gas milage with the AC running is BAD.

So, could it be a bad oil pump causing the knock until oil is properly pumped thru the block?

If I replace it, should I go with a stock or High Pressure? I have heard some not so good stories about flooding the top of the engine with oil and starving the bottom end with the high pressure pumps, any truth to these types of stories?

Thanks.

Justin

 

Okay, first, I don't recommend Slick 50 for bottom end knocking. That is usually a cause for rebuilding.

Second, don't buy a high pressure pump.

Third, the oil pressure gauge in your truck is supposed to be an on/off switch type gauge, and shouldn't represent changes in oil pressure, other than yes or no, you have 7 psi.

Fourth, Excessive clearance is the top cause of low oil pressure readings.

Fifth, how does turning on the A/C change the job the oil pump does? It add's a load to the engine, but a load won't affect the speed at which the pump is turned, or the bearing clearance in the engine, and shouldn't alter the gauge reading. Because of this, I am suspicious of the gauge and/or sending unit. Probably has a bad ground connection where the sending unit screws into the block.

I would install a mechanical gauge temporarily just to verify the condition. The knocking needs to be isolated.

If it's a rod bearing, you can tell by killing one cylinder at a time while the engine is running, and watching for the noise to lessen. If/when it does, you have found the cylinder with the rod bearing going out.

To determine if it's piston slap, pour several ounces of 40 weight gear oil into every cylinder, replace the plugs, crank the engine over a few times, and start it. If the knocking goes away, it's piston slap. If the noise remains, it's something else.

Take care,
-Chris

 

As for the Slick 50, it was a try . I will obtain a mechanical gauge today.

As for why I thought the pump was affected by the AC, if the engine loads, it causes the engine to work harder, does it not? If load increases, it would cause things to work harder to compensate for the increased load on the engine, causing the pump to word harder to maintain speed with the engine RPM...

Any way, that is one of the causes of a dropped cylinder in T.F. dragracing, engine losses load thru tire spin and dropped cylinders are a result. Keep engine load up, things run better.. Just over thinking I guess.

I did pull the front two plugs on the engine to see if the sound goes away. It does not, just causes the engine to stumble.

The only time I got the sound to go away without waiting for the engine to build heat, was when I added the engine flush to the block while it was running. It went away in seconds, which lead me to believe it was a rod bearing. If it were piston slap, I would not believe it would cure it that fast. My idea of piston slap is worn rings causing the piston to move in the cylinder wall. Are we talking about the same thing?

If it is a bearing, and since the knock goes away after the thing warms up, would it require me to pull the block, or do you think replacing the bearings from the bottom will help? I don't know if it has cause any damage to the journal of the crank or the big end of the rod yet, but again, I am just looking for what if's.

I don't mind pulling the oil pan to look around, what should I look for?

Since it does go away, why would it do it when it is cold? It is not a loud knock, and the truck responds to the throttle, no engine vibration, nothing. The higher the RPM's when cold, the less I hear the noise.

I don't want to spend $$$$$$ rebuilding a short block if I can avoid it.

Thanks CHRIS for your help...... It is much appreciated!

Justin

 

I love Slick 50, I just wanted you to know that I didn't recommend it for this.

The oil pump is driven off the camshaft, and the camshaft is driven at half speed off of the crank. It is always pumping in a direct proportion to the engine rpm, not load. Load is the resistance against which the engine turns, and is felt the stongest in the pistons and the crank. While the cam is driven off the crank, it doesn't experience any of the load that the crank does, thus neither does the oil pump. With a mechanical gauge, the oil pressure will vary with different engine speed (rpm's), but load has no effect. Your gauge shouldn't move at all, other than on/off.

Try pouring gear oil, like I suggested before, into the #1 and #2 cyklinders at cold start up, and see if the noise goes away.

Take care,
-Chris

 

I placed a mechanical oil pressure gauge on the truck. At idle it is about 25 and at cruising speed it is about 55. So I cleaned the OEM sensor and placed it back in the truck. It now reads on the "A" in NORMAL. So that issue is solved, but the knock on startup is still there. I pulled the plug wires again (Now have VERY Curley Hair). The sound did not diminish. It stayed a faint knock. I will try the 40WT oil in the cylinders.

Can you or anyone recommend a place to buy a rebuild kit? Northen Auto has a complete Master KIT for 300 bucks. Is this a good price? Anyone have a book on the 4.9L rebuild?

Thanks,

Justin

 

That sounds like a fair price to me. I don't have any manuals that are exclusively for rebuilding the 4.9, but I do know the specs and the basics. Let me know how the piston slap test.

Take care,
-Chris

 

The 40 WT oil in the cylinders did not make a large difference in the sound other than to make it (Truck) a smoke machine for a little while. I went on and got a short block and it is off to the machine shop. The sound did diminish more once I added oil to the engine. Could it be something in the head? Is there a compression check I can do?

Thanks,

Justin

 

PKRWUD as was scanning over this post and at first I read "pour 40 weight oil into each cylinder" and i could just picture someone filling the cylinder right to the top and hydralicing the motor....I guess it pays to read slowly.

I had a water pump that was going south and it sounded like a bottom end knock...just a thought.....