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Unread 09-12-2010   #1 (permalink)
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Default 4.6 SOHC symptoms of a bent valve

Has anyone ever bent a valve on one of these? If so, what kind of symptoms did it have?

I have a 2002 PI engine I dropped in my 97'. After firing it up I found I was off a tooth. So I took it apart got the timing set and and fired it back up. Now it acts like I have a vacuum leak. It has a slightly rough idle...but has no power. I did a vacuum check...it is 18psi at idle then drops under acceleration. There is no engine noise and no smoke out the tail pipe.

I do not have a way to test the compression....is there any other way other than taking apart the engine?
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Unread 09-12-2010   #2 (permalink)
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A bent valve will show up in a compression test. A tester can be rented from your local autoparts store. Or go to Harborfreight.

There would almost certain to have increased top end noise.

Explain how it ran before and after the timing was corrected.
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Unread 09-12-2010   #3 (permalink)
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It ran a lot worse the first time I fired it up with it being one tooth off. It absolutely had no power, sputtered when I tired to drive it.
Now, when I start it up..it idles a little rough like it has bad spark plugs, but I can drive it..and it is hesitant and bogs down a little when I accelerate. The more I accelerate, the more it bogs down.

At first it threw a PO203 code....but I pulled the #2 plug and replaced it...checked the wire and found no problems....cleared the code and so far it has not come back. The timing was right on the money this time...I made sure to highlight all the marks and rotate the engine twice....it all lined up perfectly.
This engine was a salvage yard pull. It only had 67k on it...Are these PI intakes prone to crack? and if so...where do I look?
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Unread 09-12-2010   #4 (permalink)
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Go to amazon.com and look for a propane based leak detector

Amazon.com: Vacuum Leak Detector: Automotive

It is not possible to work on these cars if even a tiny vacuum leak. I personally do not agree with those that would spray carb/choke cleaner to find leaks. The solvents could damage the gaskets thus trading one problem for another.

If this motor has a defect in the ignition system, you are wasting your time until the ignition is perfect. How old are the spark plug wires? Are they routed the way it came from the factory?

Try this racer's trick. Run the motor in a totally dark location. Look for evidence of blue spark. Inspect the wires for any white spots as these indicate arching. If the wires are not perfect, replace them. The routing is important as well.

I have a feeling of deja vu.
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Unread 09-12-2010   #5 (permalink)
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You would be correct about the de ja vu. I post in both forums for multiple suggestions. Since I have limited time and finances to work on the car I try and do as many tests as possible in one session.

I can makeshift something...I have several small propane tanks...like the ones used in portable stoves. I will see what I can do....

Good call

btw....the spark plug wires are used. They very well could be a problem...I never removed them from the factory clips...I just left them all attached when I pulled and installed them.

Could the wires/plugs/coil packs give these kind of problems without throwing a code?
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Unread 09-12-2010   #6 (permalink)
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In short, Yes. The coil packs produce a very stong spark. The spark plugs are gapped to take advantage of this. But because of the stong spark, it is easy for it to leak out if the wires are old. The PCM will not throw a DTC until the misfires exceed a level that will damage the cats.

Poor performance could also be from an EGR valve stuck open.

Don't you have an ODB2 scanner? Graph the LTFT1/2 and RPM's. Looking for LTFT's that switch from idle to load. Also looking for differences between bank 1/2.

For example, one prime symptom of MAF contamination is an AF ration that is rich at idle and lean under load. The PCM respond by taking away fuel at idle and adding fuel under load.

One symptom of a vacuum leak is a LTFT that goes from very big postive values at idle to not as big positive values under load. Therefore, if your LTFT are -17, this is not normally associated with a vacuum leak.

So... just stating that the LTFT is -17% with no other details really short cuts process.

IMO, you are silly to drive this car if you actually suspect a bent valve. Expect to have a new pile of metal scrap should the value keepers give way and the value drop into the cylinder.

Very silly considering the relatively low price of a Harborfreight compression tester. Even more silly if the tool is rented.
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Unread 09-12-2010   #7 (permalink)
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I am going to purchase new coil packs, plugs and wires this coming week.

If this does not eliminate the problem I am going to bite the bullet and have it towed to a Ford Dealership. Since this is a used engine....its hard to say what could be causing these issues......

BTW I snagged up a compression tool from a neighbor....I start on it tomorrow. Any special way to do the cylinder order?
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Unread 09-12-2010   #8 (permalink)
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Yea the plugs and wires will definetely help i just replaced a set on my 98 cobra. I upgraded to 9mm wires as well. stay simple with the spark plugs autolites or motorcraft work just as well as the others. Im looking into replaceing my coil packs later on but not sure if that would make a difference or not. if it bogs down under acceleration did you ever check your fuel system at all? could be a faulty fuel pump. my camaro did the same thing. It would be hard to start and bog for a little bit but once it got going it was fine. also a salvaged motor could have alot of problems with it. Do you know how long the motor was sitting? If it was sitting for more then a year and you just went and turned it over then it could have alot of problems with it.
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Unread 09-12-2010   #9 (permalink)
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if its a bent valve your exhaust would be throwing white smoke a bunch of it. it happened to me not so long ago.
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Unread 09-12-2010   #10 (permalink)
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It had only been sitting about two weeks. I happen to stumble on it when I went looking for a T45. The engine only had 67k on it........I actually pulled it apart and replaced the head gaskets myself. (IE, is why the timing was off....lol). It appeared to be in really good shape. I also cut the old oil filter in half to see if there was any metal or debris...and nothing that stood out. I think if anything was wrong with it, it might be the intake. I do not see any signs of abuse..but that does not mean it does not have a fine crack some where. It came complete all the way up to the throttlebody/injectors/flywheel.......according to the salvage yard compression was 200# across the board....which I am not so sure about. This whole thing started out as a tranny swap..and now look.... Its a damn thing I don't gamble

BTW...for anyone reading this....if you do get a whole engine, use your own upper plenum with your original IAC and EGR valve.
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Unread 09-13-2010   #11 (permalink)
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I did a compression test on all but two back cylinders.....the average was 180.
I also found a frayed wire on the passenger side coil plug. I will try and pick up a new pigtail to replace that. I think I may have a small vacuum leak, but the larger problem is my ignition some where.
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Unread 09-13-2010   #12 (permalink)
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Wtf....has one purchased one of those 3 wire coil pack pigtails lately? If so, where did you get it? Napa is saying the part number is obsolete. OReilly autoparts wants 36.99 for it....!@#%#%@
Wow...who would have guessed it would be that hard to find one?!?!
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Unread 09-13-2010   #13 (permalink)
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You don't seam to think that the frayed coil pack wire has anything to the ignition problem?

Let's recap. Reasonable compression. No unusual valve noises.

I'd be throwing a party! :kooky:
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Unread 09-19-2010   #14 (permalink)
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Ok so get this......The timing was right on the money, nothing wrong with anything I did....except...the dumba$$ at OReilly auto parts gave me the spark plugs for a 3.8...not the 4.6. I swapped those out with some new plug wires runs like a champ.....

If it was not for bad luck, I would not have any luck at all
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Unread 09-19-2010   #15 (permalink)
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That's great news. Must be like a great weight has been lifted from your shoulders.

One of the possible causes called out was an ignition problem. I certainly would not have thought about wrong spark plugs as it is a new build.

Were the plugs too short? How did you find it?

Consider updating the other threads you have opened so that others can learn.

With regards to your luck, I guess that depends on your view point. Yes, the project took a lot more re-work due to wasted effort. But no damage was done and it works now.

There is an oppertunity for learning here. It has to do with understanding the job and checking your work. At the risk of stating the obvious or starting a flame, if the timing procedures had been completely followed and more pictures taken during the work, then you would have known beyond all doubt the motor was correctly timed. No wasted effort going back to re-check the timing.

I think you should pat yourself on the back as you have accomplished something that many talk/dream about but few actually do.

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