My 92 F150 4x4 5L auto runs pretty well. I went through some work with EGR codes and replaced some sensors, fixed some vacuum leaks etc. I am still left with one nagging problem.

When towing or hauling a heavy load, the truck has a bad engine knock, which I believe to be the valves rattling. This occurrs, usually on uphill grades. When the truck is empty, there is an occasional ping or two, but nothing major. Last week I pulled a trailer load of hay and the knock was really bad on some steep hills. As the speed went down the noise was worse and it began to overheat. I use it as a work/farm truck and only drive it once or twice a week(not my daily ride). So, it is not something I deal with every day. I have noticed that the truck seems to have a slight miss when idling, but nothing when accelerating or driving. The only other symptom that might be related is that the truck is slow to fire. When I start it, it grinds a while before it fires up. This is better if I make sure to let the fuel pump stop running before I turn it over. It seems to do better if I turn the key off and then let the pump run a second time.

I have tried, premium gas, oil additives, adjusting the timing and no significant change. The guy who had the truck before me did a lot to it, new wires, egr and some sensors. I don't want to start throwing parts at it without an idea of where I am headed. My first thought was plugs, wires, cap and rotor, and maybe knock sensor and coil. It has super stock wires that appear to be 2-3yrs old. Those parts add up quickly.

Any ideas on where to start? I want to start with the least expensive, and most likely problems first.

 

Check your fuel pressure, if it takes turning the key twice to prime the pump may be getting weak, or the fuel pressure regulator may be bad. Also pull the EGR off and clean out the passage on the intake.

 

ive actually seen it where the torque convertor on the tranny can knock when there are loads put on them when they go bad. if the motor isnt knocking at idle or without a load then i can't see it being an engine problem. and as for the ping just try to use a higher grade fuel. and like 89lariet said it may be a fuel pump problem and you should remove the fuel filter to see what kind of garbage is in it. are there any kinds of fuel mileage changes or any other issues?

 

Sounds like you guys do not see this as an ignition/spark/timing type problem. I have cleaned the EGR, it is nearly new. The fuel pump sounds to be a concern on the priming.

What is the probability that this is related to the knock?

As for the torque converter, it sounds like a possibility, but I should hear the sound more to the floorboard or firewall, right?

I do get the ping, an occasional click, on hills w/o a load. Under load, it starts out that way and as the truck strains to maintain speed it quickly gets worse. I tried high octane fuel and saw minimal to no improvement.

The mileage on the truck is bad in general. I just use it as a work truck and live in the mountains, so it is difficult to get a true mileage. Most of the time when I use it, it is loaded, towing or doing a short trip with the trash. I almost never drive it on the hwy empty.

I'll check on the fuel pump. What about another vacuum leak? Would a small leak cause this kind of problem?

Thanks for the help.

 

My old 351 did the same thing, despite all efforts. I was told by a local shop that would require a rebuild to fix it, but it might last a long time before it actually needs a rebuild. If I recall correctly, his reasoning had something to do with carbon buildup on the tops of the pistons, causing increased compression causing predetonation. High octane fuel did help mine though. So I lived with it until I sold it to a landscaper, who still uses the truck to tow his trailer, and has yet to rebuilt it. It had 141k on it when I sold it 3 years ago...

 

You could try a can of seafoam to clean out carbon buildup. No guarantees but it could help.

When the pump on the Cougar started to go out it ran like crap under load. First step would be to check the fuel pressure at the rail and go from there.

 

Either your timing is too far advanced or its running too lean. If the timing has been verified as being on spec, start looking at fuel starvation or vacuum leaks.

 

at your next oil changed, change the filter and not the oil just yet, poor a oil flush in it and run it for about 15-20 minutes and then change the filter and oil to get all the junk out of the engine and it could straighten out the knock. i did this to a truck today because it was knocking slightly and it straightened it right out.

 

Thanks,
I have several things to look at now. The fuel regulator has been recently changed, but I will look at it and the fuel pump. The previous owner may have been working on this problem.

I do not have a lot of experience working with internal engine issues, other than to remove parts for someone else to work on. Would it be acceptable to remove the plugs to pour Sea Foam directly into the cylinders? I am concerned that this may seep around the rings and get into the pan or do some other damage. It may be a terrible idea, but seems logical.

I have some days off coming and will plan to get into this. I would lot rather spend a day off trying to find an answer than beside the road overheated.

I'll let you know what I come up with.

 

I believe in doing a cleanup gradually - put the Seafoam in the gas tank if you think you have deposits.

 

Best way to start, but I would keep an extra fuel filter with you. When I had my old Grand Marquis it had been sitting for a long time so I ran a can of fuel system cleaner through the gas tank, clogged the hell outta the filter.

You can also pour it gradually into the intake directly through a vacuum line, brake booster line is usually the best.

 

A little info on bottom end engine noises:


Main Bearing Knock:
Main bearing knock is usually apparent when the engine is pulling hard, when an engine is started, during acceleration, or at speeds above 35 mph.

Loose Flywheel or Broken Flexplate:
A loose flywheel or broken flexplate can usually be detected by this procedure:
1) Advance engine idle to 2000 rpm.
2) Turn off the ignition switch.
3) When the engine has almost stopped, turn the switch on again.
4) Repeat this procedure several times.
5) If the flywheel is loose or the flexplate is broken, a distinct knock will be heard every time the ignition switch is turned back on.

Harmonic Balancer:
A separated harmonic balancer will generally produce a heavy rattling noise that can be heard at low speed.

Rod Knock:
Excessive connecting rod bearing clearance noises are usually a light rap or clatter much less in intensity than main bearing knocks and the loudest when the engine is "floating" or running with a light load at from 25 to 35 mph. The noise will become louder as engine speed is increased. By grounding out each of the spark plugs, one at a time, you can determine from which cylinder the noise is coming. The noise may not be eliminated entirely by grounding, but it will be reduced considerably in intensity. The easiest way to ground out the cylinders is by inserting a 1.5" piece of 5/32" vacuum hose on each terminal on the distributor cap, and then placing the spark plug wires over the vacuum hose. With the alligator clip end of a non-powered 12 volt test lamp attached to ground, touch the test light tip to the vacuum hose to ground out that cylinder.

Piston Slap:
Piston slap is loudest when the engine is cold, and lessens or disappears after the engine is warm. When driving the vehicle (at from 25 to 30 mph) the noise will increase in intensity as the throttle is opened and additional load is applied. To detect piston slap, try the following procedure:
1) Pour several ounces of 40 weight engine oil into the suspected cylinder(s).
2) Crank the engine for several revolutions with the ignition turned off. This will allow for the oil to work itself down past the rings and act as a cushion.
3) Install the spark plug(s).
4) Start the engine.
5) If the noise is eliminated, the engine has a piston slap condition.

Piston Pin Noises:
Piston pin noise is usually the result of excessive piston pin clearance. This will cause a sharp, metallic, double-knock sound most noticable when the engine is idling. Sometimes the noise is more audible at car speeds of from 25 to 35 mph. To test for excessive piston pin clearance noise, use this procedure:
1) Run the engine at idle speed.
2) Retard the spark to reduce the intensity of the knock.
3) Return the spark timing to the normal setting.
4) Short out each spark plug, one at a time. The double-knock sound will become more audible at the cylinder with the loose pin.

Other possibilities to consider include:
1) Loose timing chain hitting the inside of the front cover.
2) Connecting rod bolts hitting the inside of a dented oil pan.

I'm not saying your noise is coming from the bottom end, but at least now you have the info necessary to determine for sure.

 

Thanks. This is some great info. A main bearing knock sounds the closest here. I was afraid that might be the case. I am going to pick up Sea Foam today and go through some things the next couple of days.

Does a main bearing issue usually come with oil pressure issues or any other symptoms?

 

I had a spun main on my old Capri, it will cause the oil presure to fluctuate with engine speed. On mine the guage red 0 at idle and would go to normal while driving. Ran just fine for a long time like that.

In your case though it does sound like a fuel problem.

 

My oil pressure gauge has consistently read in the low-mid normal range. No fluctuations. That's good news. I am using seafoam this morning and see what happens. I also plan to recheck timing and look at the plugs. I may get to the crankcase flush. The bottle said that for engines over 100k I should plan to remove the oil pan and clean the screen. Is this necessary? As far as I know this truck has been serviced regularly.

I noticed that the plug wires are one size fits all and there are some loops bunched up under the throttle body. I am a little concerned about this. Anyone else seen this causing a problem.