Ephinshise

Hi community,

I'm new here and would like to see if anyone is able to help diagnose my check engine code?

I have been having issues with my engine for a while now. The engine runs poor, it shakes at idle, it has little power and when I accelerate hard it chokes up. Originally my code said, "low compression in cylinder 8." I replaced all my spark plugs, all my injectors and all my coils. It was still running poorly, so I replaced my crankshaft position sensor. Also, nothing changed.

Recently, I had my check engine light come on and the code signaled my engine is running lean.

At this point, I am shooting in the dark because I don't want to continue to waste more money trying to figure out what is wrong. I am starting to think it is a MAF sensor or there is some issue with the throttle body. However, my guesses have only turned up dirt.

Does anyone have any insight or ideas on what other possibilities it may be?

My truck is a 2004 F150 with 200,000 miles. It is the Tritan 5.4, V8.

Thank you.

RLXXI

If you have low compression there's nothing you can throw at it short of a rebuild or good used engine. www.lkq.com best price around with delivery and a warranty.
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Ephinshise

So the code for low compression never came back on once I replaced everything. It just came back on with the lean code.

What does low compression indicate? Do I have a groove in the cylinder?

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RLXXI

Worn out engine.
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chimmike

Where did he say he had low compression? Just the code? I'd rather OP actually run a compression test. couldn't he just pull the plug wire for cylinder 8 and the engine otherwise run OK if cyl 8 compression is crap/leaking? If the whole engine shakes/shudders, makes me wonder if MAF leak is an issue...

OP: Have you checked for vacuum leaks? Cars with MAFs HATE metered air leaking out. Also check exhaust manifold gaskets? Leaky?

RLXXI

He stated code for cylinder 8 low compression, the onboard diagnostics can sample relative compression in all cylinders, there's an actual test that can be run using IDS to verify it but yeah an actual compression test would be in order.

Judging by his statement of symptoms, self diagnostics and the 200,000 miles on the engine it sort of leans toward being worn out.
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Ephinshise

After replacing everything, I ran a compression test and it did actually pass. So I was wondering if I might have some sort of groove in the cylinder and that code would come back. But then the code came back suggesting"running lean."

I took it onto a mechanic who also suggested it may be a MAF leak. He said the intake manifold may have a leak. I was wondering about a vaccum leak. I didn't want to spend the money to replace anything again without getting a second opinion.

I have not checked for any leaks in the manifolds. I will have to check those out over the weekend.

I truly appreciate the advice and I will keep you updated.

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chimmike

I had a car years ago with a MAF system, a 2001 model. I swapped on headers, and there was an exhaust leak at the manifold/head flange, and the car ran like absolute garbage and I couldn't figure out why until I saw the soot marks from the leak. Once I got a replacement gasket in there, all was well.

MAF systems can be a real PITA sometimes. One leak of metered air can throw the whole system wild. Which could be why it's triggering the lean code...who knows

Eric Kleven

Not sure if 'metered air leaking out' is the right verbage... I think the MAF systems hate UN-metered air leaking in.

chimmike

yeah, you've probably got the verbage right...important thing is you understood my intent!