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Discussion in 'SN95 4.6L Mustang Tech' started by evolucion311, Aug 18, 2011.
Do a leakdown test on the low cylinder and one of the good cylinders...bad or bent valve
Gotta be a spark issue. The car symptoms were identical to my car when my lower intake-manifold started to leak coolant in the spark plug wells, steam cooked the heck of the coil boots.
At low idle the car stuttered, but when the throttle was pressed the stuttering went away.
Question for Sir Burns, does the voltage change with RPM's with the Coil on Plugs.
To me I'm thinkng its not a sensor problem, but fuel and fire.
Is it possible that a compression test would not show a stuck valve or better yet an improperly seated valve?
Is it possible that the valve only improperly seats while the car is idleing.
What about my original idea about the high fuel pressure and slow O2 sensors?
As I said early on this could be more than one problem.
Is there ANY change in symptom?
+1 on the leak down test. That's a great idea! It will help narrow down what's different about the misfiring cylinder.
I haven't replaced the O2 sensors yet. After all of this nonsense I've been doing on the car I've accumulated $40 of reward credit at AutoZone. I'll go pick up some oxygen sensors shortly.
Meanwhile, I'm going to get deeper into the wiring and keep checking for issues like ground faults, etc.
Burns, you seem to be the wiring gangster on StangNet. Can you point me in the right direction for the test procedure for testing that will conclusively say if a fault exists in the wiring?
I'll replace the PCM before I pull the cylinder head off. Of course, I'll do a leak down test before pulling a cylinder head.
Problem.... I don't have a leak down tester but do have an air compressor.
Anyone have any creative ideas on how to procure a tester? I'll only need it once or twice and don't want to buy the damn thing.
Most autoparts stores will rent a leak down tester. Harbor Freight also sells a very affordable unit.
Also, did you ever do any of the "noid" tests to confirm a firing pulse on the COP's and injectors? Noid test lights can be rented as well.
You sir are going to need to put the service manual and wiring diagrams to work. PM if you have any troubles with the service manual. I maybe able to help.
Well, I put a screwdriver up to the #2 fuel injector and heard it tapping just like the rest of them. I've verified spark. I've verified compression.
Now it sounds like all that is left is a bad exhaust valve on this cylinder.
Here's a video of what the car sounds like. There is a distinct tapping that can be heard, particularly under the car.
TAPPING SOUND VIDEO
Is that an Accel coil? Those COP's are crap. Get a new one or swap it and see if the code follows it. Also, check the spark plug torque on that cylinder too just in case the plug has backed out.
I know you have dug much deeper, but if your back to the drawing board just check these real quick.
Josh, I have swapped coils from here to the moon. My problem is not COP or spark related.
OK guys so I ran a leak down test, sorta.... I don't have access to a proper leak down tester and the reviews I've read about the Harbor Freight unit are making me not wanting to waste my time or money on it.
I used EricTheCarGuy's YouTube channel's video on performing a leak down test as a starting point for how I ran the test. His video is located here: ERICTHECARGUY
I got a compression tester from AutoZone and removed the schrader valve from it, allowing air to pass straight through it. I then attempted to get my cylinder #2 at TDC. Please watch the 1st of 2 videos I made here to see: AM I AT TDC? STEEDA CRANK PULLEY MARKS
Assuming that I'm at TDC for #2 cylinder, the results of the leak down test can be observed here: EXHAUST VALVE BAD CONFIRMED???
Here is the condition of the TIMING COMPONENTS VIDEO
If you can here air in the exhaust something is going on, carboned up valves, bent valve or possibly a seat issue.
Do another cylinder, this will test out "your procedure"
So I got the cylinder head off but am not sure of what I'm looking at as far as a bad valve would go.
The good news is that the cylinders don't appear to be damaged nor do the valves show any obvious sign of distress. The cylinder walls still show a cross-thached machining pattern from when the motor was manufactured..... is this a ridiculously low amount of wear or something to be expected?
Maybe you guys can school me.
Here's a video of the cylinder head pulled off the engine: EFFING FINALLY GOT IT OFF
Pics below in order.... cylinders 1 & 2, top of the valve train, combustion chamber 1 & 2, combustion chamber 3 & 4.
putting vacuum to the head is best but a quick and easy test to see leaks is this...
Grab some rubbing alcohol add a drop or two of red food color or use winsheild washer fluid and some in the port and see if you have leak out around the valve.
Its been burning some oil, that could be valve seal related. Do you see any pitting in the chamber or piston crown? Did the plug look normal?
Rick, could you please point me in the direction of how to put vacuum on the head? I have a little hand vacuum pump that I rented from the parts house.
Vacuum Table for Testing Cylinderheads and more - YouTube
Heres the best I can do Im out grabbing dinner for my wifes birthday. Here's a link to a youtube video it will give you an idea of what the fixture or pad that you need to fab. The guy has it on when the video starts.
Basically what you do id put the pad over the port, and make sure it holds vaccum, it ir doesn't you have a leak. I dabbed mine from a alum block that I put a soft durometer foam over to seal it up tight.
The fluid test I mentioned earlier will work as well.
I did the fluid test through the exhaust ports using gasoline and a leak on cylinder 2 was immediately apparent. The same gasoline test on the intake side revealed no leaks.
Test may be observed here: Yep, it was a bad exhaust valve (video)
Sucks, but Im glad you were able to track that down!
Nice! I can't imagine it would be crazy money to have the cylinder heads rebuilt. I've not priced it in forever though.
Glad you got it tracked down though.
New Romeo PI heads from Summit are $395 each.
Ford Racing M-6049-P46 - Ford Racing 4.6L Performance Improvement Cylinder Heads - Overview - SummitRacing.com
Another option is to get a whole salvage yard motor for say $500-800. Take the heads off of the salvage motor and use them. This has the advantage that should the original bottom end give out, the replacement is right in the garage.
Rick91GT, can you explain why all the cylinders have similar compression but the leaky #2 exhaust causes a misfire whereas the low compression in the other cylinders does not?
Or is it a case of dynamic compression? IE, more exhaust gas would leak out of #2 than the other cylinders. Therefore #2 is affected more (looses more power through the exhaust valve).
Did I just answer my own question?
Dog gone you Burns you've got me thinking about rebuilding the whole motor now.
The car will never, ever be for sale, except possibly to my oldest niece who will be of driving age in a few years.
I bought the car after coming back from deployment and will never, ever sell it.
I'd like to rebuild my own engine simply because I know how the engine was run and taken care of. A junkyard motor would be alright but I wouldn't trust anything with more than 60k miles, especially if it came out of a Mustang. Not everyone takes care of what they have. Too many stangs have been ragged on and beat up.
If rebuilding I would do all of the disassembly and reassembly as I could, using a machine shop to bore the cylinders, machine the bottom end, balance the crank, etc.
I'm not looking to put a supercharger on the car so I don't need any crazy forged internals. If anything, I'd go for N/A with more aggressive cams, ported heads, and a tune. The car is a DD and needs to stay reliable above anything else. My budget is flexible depending on what is necessary and desirable but I'm not going to throw money at it for no apparent reason.
Can anyone recommend an ethical and reliable machine shop here in the Atlanta area? I used Will's Automotive Machine Shop in Chamblee, GA to resurface my flywheel when I did the clutch job. Their reviews and ratings online are all five star... which could be good service or shill reviewers. Caveat emptor.