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91 Engine problems, knocking, rattling

devhawes

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I just bought a 91 XLT. It has about 85000 miles. Ran great when I bought it but after a 2000 miles it has developed a knock/rattle. Sometimes on start up it sounds like a diesel for a few seconds then it becomes less noticable at idle. I can hear it in neutral or in drive. At 2000 rpm it seems to have a fairly continous rattle. Seems to be coming from the passenger side. Plugs look good. Hooked a vacum gage and its steady at 20 inches. Pulled the plug wires one at a time and it still rattles. The previous owner had the heads rebuilt about 12,000 miles ago because of a burnt valve. The only code in the computer is 22 for map sensor out of range (this is on the engine off test) Any ideas? Thanks.
 
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Gary Steeber

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devhawes


Knowing the recent tpye of work performed on your Explorer I would suspect something has came apart in the Rocker assembly/valve adjuster on the passenger side.
You might want to remove the valve cover and inspect the assembly.
This is where I would beging checking.
 
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SteveVB

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lifters

Do a search of the site for lifter problems. The lifters have a trendency to give up between 75 and 100k, could be helped along in your case by some debris from the head change.

Also since the heads were just worked on check to make sure that the rocker shaft pedestal bolts are torqued correctly, and that the pedestals themselves are sitting flat on each of the 3 stands. Check that the shaft is true. Also check the pushrods and rocker arms, if they are the originals they may not have been reinstalled in the position they came from and have worn quicker with different contact points.

Good luck.
 
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Ira

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See if this helps...Cleaning MAF article

Dead Link Removed
 
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devhawes

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I cleand the mass air sensor but no luck. I also replaced the sensor with another one. Did nothing. Checked the timing it is bang on at 10 degrees with the spout connector disconected.
 
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Ira

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After doing that, did you disconnect the battery for about 5-10 minutes to reset the computer? If not, try that first.

Another possibility...pre-ignition. This could be caused by the spark plugs. Pull your plugs and check them. You may find that you have one that looks totally different from the others. Be sure you have the correct heat range and gap.

One last alternative is to change the plugs and use some that are one heat range colder. This would help to eliminate the possibility of pre-ignition. I have seen many vehicles that give 2 different plug numbers. One is for combined driving, and the other is for highway alone. The highway plug is generally a colder plug by one step and this is because the engine is operated at a higher speed and warms up faster and more complete. I have also heard similar stories with other car brands and the colder plugs seem to remedy the problem.

Keep us informed.
 
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devhawes

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I reset the computer with no luck. This morning I noticed that is was not as bad when cold (I still could here it but not nearly as loud. I drove for 10 minutes it was a lot worse. All of the plugs look good, nice light tan color. I am thinking it may be the egr valve or something related to the egr. Can anybody tell be where the EGR VALVE is? Been looking for 1/2 hour. Thanks.
 
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SteveVB

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No EGR on the 91's,
not until 93 or 94 as far as I know.

Im still going with lifters/valve train.
 
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niceguy

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Could also be a knocking rod, but my money's with SteveVB and Gary - valve-train. (And EGR is on the driver's side of the intake anyway...)

Get about a 4 foot piece of old garden hose and use it as a stethoscope to listen to different places under the hood while the engine is running. This will help you locate the problem for sure. I had an old Chevy with what I thought was noisy lifers. Running my "stethoscope" along the valve covers allowed me to hear it clear as day - even which cylinders were worst. If that's where you find the noise, pulling the cover and doing a visual inspection is going to be your best shot at really finding the problem.

Michael
 
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devhawes

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I have a stethascope but have not been able to pin point the noise. It is loud enough that you can here it from almost any point on the motor. Looking on the old bill I noticed that all new rocker arms and pushrods were change with the head job. I re torqued the lower intake with no luck. Looks like I am going to have to pull the motor apart to find the problem.
 
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lucas

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I have the same problem with my 91XLT Explorer,it has 113k it started @ around 95k. I was told by a mechanic that the lifters were the problem. Have decided to run it till it smokes. He told me that it can be fixed for around $600-900.
He has worked on many explorers with the same problem.
 
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devhawes

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I had for take a look at it this morning. They say it is a piston slapping or a rock knock. They say it is too slow for a lifter. I don't buy it for a couple of reasons. 1.) The sound gets worse when the engine is warm. I would think as the piston expaned it would get slighty better. 2.) When I pull the plugs one at a time it makes no difference.

Is there any way to confirm it is a lifter?
 
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niceguy

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huh?

You say the Ford mechanic says that is too SLOW for lifters? That's odd, 'cause if memory serves me correctly, the lifters actuate at HALF the speed of your crankshaft, so a bad lifter would only "tap" every other engine revolution. Knocking rod or piston slap would be twice as fast (not slower) as a bum lifter (unless there was more than one of 'em). Someone correct me if I'm wrong here...

However (bad part), I'd think that a bad lifter would provide a more localized noise source than a knocking rod. If the sound is coming from everywhere under the hood (as you indicate), then might be a rod :-( .

To determine lifters for sure, gotta tear it apart (could be other valvetrain bugaboos). Pull the valve cover and see if any of the pushrods are noticibly loose. Probably ought to turn the engine over by hand (BIG wrench) through a couple of crank rotations to see if there's significant slack in the valve train at any given point in the cycle. You should find NO free play (end-to-end) in your pushrods. If you find one, then pull the intake manifolds and have a look-see at the offending lifter. Hope that's your problem.

I don't know how to diagnose a knocking rod or piston slap. Maybe someone else with more busted knuckles than me can chime in here...

You say that pulling plugs makes no difference. You mean it doesn't even run WORSE (miss) when you pull a plug? Or do you mean that all cylinders run equally bad when their respective plug is pulled? Please clarify for me...

Michael
 
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devhawes

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I think when you pull the plug wires one at a time the noise should lessen or stop on the cylinder with the bad rod or piston slapping cylinder (Sound usually is worse on the power stroke). The ford mechanic thinks the sound is coming from the passenger side. After listening carefully I believe he is correct.
 
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devhawes

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Also I noticed my fuel mileage has went way down. On 3/4 of a tank I have went only 150km (90 miles).
 
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devhawes

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Pulled off the intake manifold and valve covers. Everything is very clean with no sludge at all. I was hoping to look at the lifters for a problem but I it looks like the heads have to come off to get the lifters out. I have the feeling I am going to have to pull the motor to find the problem. Sure wish I new the problem before forking out the cash for a full gasket kit etc. When a lifter is making a knocking sound what kind of damage will you see on the lifter?
 
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Gary Steeber

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devhawes

A lifter can either collapse or stick, it's actually hard to a sight a bad lifter.
Before you go tearing everything apart you need to better analize the problem. I agree with niceguy, double check all of the rocker arms and push rods. You should have no play in them, make sure you rotate the engine to raise each rocker arm as you check.
Did the Ford mechanic say the sound was too slow or did he say the sound was too LOW. A lifter knock is normally high pitched tick kind of sound. Piston slap, piston rod knock is a medium pitch sound and a main bearing is a low knocking noise. I believe if the problem is a bad piston rod or piston the sound may dissapate if you disconnect the plug wire. Main bearing and lifter noises will not change when you remove the plug wire.
You should get a second mechanics opinion of the noise before you start tearing down any further.
A qualified mechanic should be able to analize this sound in a few seconds.

Good luck
 
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niceguy

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You shouldn't have to pull the heads to get the lifters out. However, you WILL have to loosen or remove the rocker arm support shaft assemblies. If you do this, make sure that you keep track of what push-rods go where, and which head which rocker assembly goes on (I'm pretty sure they're interchangeable). You want to make sure you put everything back where it came from.

Do you notice any "play" in any of the valvetrain? You'll probably have to rotate the crankshaft by hand through a couple of revolutions, and check for loose parts every 15-20 degrees of rotation. If you don't find anything this way, then pull off the rocker arm assemblies and check the rocker arms, valve stem ends, both ends of the pushrods, etc., for visible wear-and-tear.

The lifters in my '94 are roller lifters. I assume the '91 has got 'em too. Check the roller on the bottom to make sure it's OK, then have a close look at the pushrod "cup". If the lifter is not "pumping up" properly (which would cause valvetrain slack and noise), then this cup may be depressed into the lifter. You might try pushing down on each pushrod (into the lifters) before you remove everything, to see if one of them is noticibly easier to depress. I think I've read on some other threads that Ford has had some lifter problems with some model years, but I don't recall any of the details. Might be worth a search, though...

The full top-end gasket kit is expensive!! ($120-170 - yikes!) Intake and valve cover gaskets will hopefully be cheaper. Having just had the heads off of my motor, I can honestly say that you don't really want to go there just for the fun of it...
 
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devhawes

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I cant see any way to get all the lifters out with out taking the heads off. The head overhangs and blocks some of them. I will try removing and inspecting the rockers and pushrods tonight (Both the pushrods and the rocker arms were replace 12,000 miles ago). Also will check the lifters that I can get out. I noticed 2 of the lifters don't have the funnel at the top. I am assuming this is for better oiling. They are both on the opposite side that the noise was coming from. Also when the truck was running, pulling a plug wire did not make the sound go away. So my guess is its a lifter or a main bearing. I have never heard a lifter make a Knocking sound have you?
 
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niceguy

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Hmmm. I just had my heads off a couple of weeks ago, and al of the lifters had the plastic "funnels" on them, so I'm curious why a couple of yours are missing. Don't know what function they serve... I only pulled a couple of lifters out, and did this while the heads were off, so I could be wrong about being able to get them out - I didn't consider that there might be an interference problem witht the heads. Sorry about that.

Gary's description above was right on - the lifter noise will generally sound like valve tappet clatter, while rod knock, etc. will be lower in pitch and more of a "knock" than a "clatter".

Keep us posted...
 
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