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Running Lean with Headers?

anupaum

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I had a blower on my 4 cylinder Ranger for more than 10 years before buying the 4 liter Sport Trac that I own right now. About 18 months ago, I put on a set of Doug Thorley headers, thinking that they'd help somewhat with the engine's rather tepid performance.

Now I've got a burnt valve in my #5 cylinder, and the mechanic is blaming my headers. Personally, I don't see how a shorty header on a fuel injected engine is going to cause a lean condition. He thinks I should dump the headers and go back to stock exhaust manifolds.

Does anyone here have any experience in this kind of situation?
 


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I don't see it either. Seems that if it were the headers, it would be an issue across the board, but I still don't see how headers would cause a lean issue. I'd suspect a fuel injector if its isolated to one cylinder.
 

anupaum

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I don't see it either. Seems that if it were the headers, it would be an issue across the board, but I still don't see how headers would cause a lean issue. I'd suspect a fuel injector if its isolated to one cylinder.
Yeah, it seems odd to me . . .

I just got a phone call from the shop. They said, "We can't even find a replacement engine for this thing. We recommend you take it to a dealer and trade it in on something new."

I think they're nuts. Are there BETTER heads out there than the factory ones?
 

RonD

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You would have noticed Lean condition on 4.0l SOHC because it has a knock sensor.
It would have a noticeable power drop during Lean condition.

Running cylinder hot enough to burn a good valve would cause knocking so timing would be retarded and power would drop.

I too do not see headers causing that, or a Lean mix specific to 1 cylinder.

I would chalk it up to a bad or misaligned seat from the factory, or maybe previous owner had a spark plug break in #5, debris damaged seat.................
 

anupaum

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You would have noticed Lean condition on 4.0l SOHC because it has a knock sensor.
It would have a noticeable power drop during Lean condition.

Running cylinder hot enough to burn a good valve would cause knocking so timing would be retarded and power would drop.

I too do not see headers causing that, or a Lean mix specific to 1 cylinder.

I would chalk it up to a bad or misaligned seat from the factory, or maybe previous owner had a spark plug break in #5, debris damaged seat.................
It's not given me a code for a lean condition, which I believe one of the O2 sensors should have picked up. (The codes were for general misfires, a misfire in the first 1 000 cycles, and a misfire in #5.) I asked if he'd done a wet compression check, but he told me that the spark plug looked pretty good (no fouling) and given the dry compression check readings, he believed the valve was the most likely culprit.

The wires and the coil pack all checked out. That leaves us with fuel -- which brings us back to the O2 sensor -- and possibly an EGR malfunction.

Now . . . The headers I bought had no provision for EGR. I had a local shop fabricate an EGR bung for me. It's been less than perfect, to be honest, and that might be a contributing factor.

The trouble is, if I buy a new set of heads and install them, I don't want to have the same problem down the road. I drive over two mountain passes every time I come home and go back to work, so I need my machine to be rock solid reliable.

I don't think the headers contributed here. That diagnosis makes no sense to me.
 

RonD

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Lean code would only come up if fuel trims got up in the +20's for any length of time, and lean or rich code is just the computer letting the driver know that the MAF data and computer's 14:1 mix ratio is not in line with the O2 sensors oxygen content in exhaust, so computer is having to add more fuel than expected to the air that the MAF sensor says has come in.
The computer adds the extra fuel past the +20 so engine is not actually running lean, this is why even when you get the CEL and Lean code engine is still running fine. Computer adjusts the mix to keep O2 sensor voltage close to the .45volts for a correct burn oxygen content.
So Lean or Rich codes don't mean cylinders are actually running lean or rich, it means the MAF sensor, air temp sensor, engine temp sensor, and O2 sensor data do not add up correctly for the computer.
Computer ultimately defaults to O2 data(voltage) to keep the air:fuel at 14:1.

For there to be an actual Lean condition in a cylinder and associated misfires you would most likely get a flashing CEL not a steady CEL on, the flashing denotes possible engine damage if conditions don't change.
An incorrect O2 sensor could cause that, since computer relies on those as the final word, BUT you would/should get the lean/rich codes at that point and well before any engine damage.
 
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anupaum

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Lean code would only come up if fuel trims got up in the +20's for any length of time, and lean or rich code is just the computer letting the driver know that the MAF data and computer's 14:1 mix ratio is not in line with the O2 sensors oxygen content in exhaust, so computer is having to add more fuel than expected to the air that the MAF sensor says has come in.
So, therefore, it's unlikely that a lean condition has caused this problem?

The computer adds the extra fuel past the +20 so engine is not actually running lean, this is why even when you get the CEL and Lean code engine is still running fine. Computer adjusts the mix to keep O2 sensor voltage close to the .45volts for a correct burn oxygen content.
So Lean or Rich codes don't mean cylinders are actually running lean or rich, it means the MAF sensor, air temp sensor, engine temp sensor, and O2 sensor data do not add up correctly for the computer.
Computer ultimately defaults to O2 data(voltage) to keep the air:fuel at 14:1.
Yes. This was my understanding of how the system works, which is why I was rather suspicious of the whole, "You've put headers on this thing, which leaned out the mixture and now you've burned a valve" diagnosis.


For there to be an actual Lean condition in a cylinder and associated misfires you would most likely get a flashing CEL not a steady CEL on, the flashing denotes possible engine damage if conditions don't change.
An incorrect O2 sensor could cause that, since computer relies on those as the final word, BUT you would/should get the lean/rich codes at that point and well before any engine damage.
I don't have any lean / rich codes. Only codes for misfire in #5 and "general misfire." I'm pretty sure there was a code for the EGR the first time this happened (about two weeks ago), but that code has not re-emerged.

I did my own compression check this morning. The #5 cylinder showed 73 psi. I left the gauge on for about 10 minutes and the reading didn't change. I squirted a bit of oil in the cylinder and the reading bumped to 120 psi, which still isn't great.

I'm going to take the truck to a different shop on Friday morning to have a proper leakdown test done. Any other suggestions? I'm tempted to pop the valve cover off to see if there's been any damage to the cam and rollers.
 

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My compression gauge holds the highest number until it's reset, check valve opened.

But if yours is open, then I would suspect a problem, with the gauge, if cylinder held 70psi pressure for more then 20 seconds.
Metal rings on metal cylinders and metal valves on metal seats can't hold air pressure for any length of time.
That's what a leak down test is for.
You keep a steady air pressure flowing to the cylinder, say 100psi
Then have a gauge on that line.
If it shows 95psi then you have a leak down of 5%, which is quite good, almost new engine.
Most older engines would 88-92 psi so 10-12%
As soon as you shut off the 100psi pressure it will drop to 0 very fast.

When you added oil to the cylinder the compression jumped up quite a bit, that means a ring issue not valves.
Wet test seals the rings better, so when you do the wet test and compression is still low then valve is the issue.

4.0l SOHC has 9.7:1 compression ratio.
Compression test needs to be done with all spark plugs removed and throttle propped open, this allows crank to build up speed between compression stoke on the one cylinder being tested.
And at least 3 cylinders need to be tested, all is best, compression test is not really about the actual numbers since there are many outside variables, including gauge calibration and battery condition(crankshaft speed).
What is being look at/for is a cylinder that is more than 10-15% above or below the average of the other tested cylinders.


For curiosities sake, the general rule of thumb is 18.3 X ratio = psi at sea level
My '94 4.0l OHV has 9.0:1 so expected test result would be 165psi at sea level, and that is what I get, even after 300k on the engine, love the OHV
For 9.7:1 you should expect 175-180psi at sea level.
 
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anupaum

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Okay, I'm doing the test wrong, then. I don't have access to an air compressor, which is why I suggested the leak down test at a shop. I've arranged for that to happen on Friday.

If the rings are the problem, shouldn't I be getting air blowing through the PCV valve when I put the gauge on that cylinder and crank the engine?
 

RonD

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No, not really, you could listen at the Vent hose but I doubt you would hear much over the engine cranking noise.

And you don't need a gauge for that, simply cranking the engine with spark plug in place would be the same thing.

Putting air pressure in a cylinder can show up at vent hose or PCV valve opening, if rings are bad, but it really isn't definitive since all rings leak air.
 

anupaum

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No, not really, you could listen at the Vent hose but I doubt you would hear much over the engine cranking noise.

And you don't need a gauge for that, simply cranking the engine with spark plug in place would be the same thing.

Putting air pressure in a cylinder can show up at vent hose or PCV valve opening, if rings are bad, but it really isn't definitive since all rings leak air.
I'm not sure that I'd prefer a ring job over a set of rebuilt heads.

Whatever the problem, tracing down the SOURCE is vexing me right now. This engine only has 102 000 km (a little over 60 000 miles) on the odometer. I hope this isn't a harbinger of more woe to come . . .
 

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Well, the 4.0l SOHC hasn't been without it's problems, timing chain issue was the big one, and I think that effected '97 to '05, even though Ford TSB was for '99-'02.
And of course the thermostat housing, lol.

But never read about a ring issue or valve issue for that matter.

I miss what year this engine is?

A 6 cylinder compression test, dry then wet, would tell you alot.
 

anupaum

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Well, the 4.0l SOHC hasn't been without it's problems, timing chain issue was the big one, and I think that effected '97 to '05, even though Ford TSB was for '99-'02.
And of course the thermostat housing, lol.

But never read about a ring issue or valve issue for that matter.

I miss what year this engine is?

A 6 cylinder compression test, dry then wet, would tell you alot.
It's a 2004.
 

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