CEL flashing, bad idle, severe misfire, P0302 P0316, compression test results

Discussion in 'SN95 4.6L Mustang Tech' started by evolucion311, Aug 18, 2011.

  1. I believe that if the OP was to dig deeper -- remove the keepers and retainer and pull the valve out -- that he might find issues with the valve guide or seat that might explain the tapping he heard. The seal on that valve might have been intermittent; perhaps on some cycles there was no seal at all.

    I hope the OP digs into this and follows up so we have a full picture of what's happened here.
  2. As I indicated in my original post, I will most certainly keep the community updated on what my issues are.

    I find StangNet to be an invaluable resource for technical support on my car... a resource that has allowed me to do almost all of my own work with the exception of front end alignments and body work, something I'll leave to the pros.

    When I bought the car I could do little more than a brake job and oil changes. As time has passed and with the support of this forum I have pulled the tranny out myself and performed a clutch job.

    You guys are great. Thanks! :hail2:
  3. Correct I would bet the issue is deeper, at times cylinder head issues are hard to track down with out a complete tear down and inspection of all components.

    I had a car once that pumped 155-158 on all cylinders but had a very audible noise that would increase with rpm. After a leakdown and compression test were un-conclusive I pulled the head. What I found shocked me, 2 broken pistons and the noise I heard was the top ring smacking the bottom of the head :eek:

    I cant do any better on the stock head $395 is the best I can do, if you want to upgrade to the TFS 2v heads I can save you a little money. If need any other parts let me know if I can help...
  4. Rick, I don't want to over or under think the problem but in my case it seems pretty clear as demonstrated by the decent compression test results, that the car ran fantastic before this, and the leakdown test verified by the gasoline fluid test.
  5. By deeper issues I was talking about the valvetrain, with as much oil as it appears was burning on the pistons I would believe there is a guide and seal issue going on, and the comp numbers are low for a 2V so I would guess the rings are worn, however your numbers arent not horrible by no means.

    The issue with putting a nice fresh head on a worn bottom end is it will slowly increase the other issues....path of least resistance.
  6. I was inclined to disassemble my head and check the seals... Assuming it's a job I could do myself? Surely I'll need some special tools. I'm going to pick up a 4.6 rebuild manual today.
  7. Seals are cheap, if you disassemble the head I always replace them..Viton Seals.

    Vac testing the heads will show if there is a leak, leaky seals are not the easiest to diagnose however. You can dykem the valve and seat area and see if you get a nice pattern. Id recommend taking them to a local reputable machine shop and asking them to inspect them, worth the $50-70. Then once you find out what needs to be done, make a decision to buy a new head or fix what you have. A good valve job will cost you about $80 easy, and personally I would do both heads they other once has wear on it as well.

    So youll spend $175 on a valve job, $30 on seals, plus cleaning and disassembly, $80-160. Make a decision then..
  8. Could you explain what dykeming is; is it like porting?

    O.p. are you gonna try to do the valve job your self?:eyebrow:

    You might wanna get the cylinder head Time Serted while the cylinder head is off, spark plug blowout is the worst:nonono:.
  9. Good point. #2 had worked loose and no doubt those threads are already weakened. If the head is salvageable and the OP plans to fix it I second the recommendation to have the #2 plug hole TimeSerted to save having to deal with the inevitable later...
  10. Dykem is a machinist dye, spray or paste that you put on both mating surfaces, then you can turn the valve and look at the mark it leaves to see any inperfections in the seat..or valve or vise versa. I also use the Dykem when I port...

    ITW Dymon l Dykem® l Layout Fluid l STEEL RED Layout Fluid

    Excellent idea about the TimeSert!
  11. Any update??
  12. The head is at the machine shop, I'll know in a few days when I get it back and put on the engine.
  13. So the machinist called me and said that he put a vacuum on cylinder two and it held vacuum.

    This doesn't make sense considering the results of the leak down test with compressed air and the gasoline fluid leak test.

    He then asked me if I had the camshaft installed in the head during the gasoline test, which I replied that I didn't.

    Is it possible that the valve is leaking under compression only and would hold a vacuum?

    I am not sure what to make of his comment but still stand by my diagnosis that the exhaust valve is obviously bad, which two independent tests of different methods seem to have confirmed.

    He is tearing into the head today and will get back to me with the results. I gave him the go ahead on the valve job anyway, if only for an exploratory option.
  14. It sounds to me like the exhaust seat for #2 has come loose (or loosens when the head is hot.) Or perhaps the guide for this valve is really sloppy or ...

    Anyway, something along these lines.
  15. Well, as I was typing the previous post up I got on the phone with my machinist....

    It seems that we were both right.

    He washed the head in a cleaning solution and THEN did the vacuum test. The carbon that was all over the exhaust valves was knocked loose and then settled on the seal/seat to seal up the valve, allowing it to hold a good vacuum.

    When he took the valves out as I had requested he then saw the amount of carbon accumulation and did his work to correct the problem.

    He said that there didn't appear to be anything mechanically wrong with the seats, springs, etc. It seems that carbon was causing the exhaust valves to stick open.

    Which leads me to my next question..... is this a high mileage condition or would running a too-rich fuel mixture cause it, and/or both?

    I will put new oxygen sensors back into the mid pipes before I start the car up again.

    Additionally, when examining my mid pipe (which is out of the car), will I be able to tell if the cats are clogged by doing a visual inspection?
  16. You usually see carbon deposits on the back of the valves as a result of oil leaking past the valve seals and getting down the guides. It's usually worse on the back of intake valves because exhaust valves run much hotter, hot enough to coke the stuff and burn it away.

    I'd suggest mic'ing the guides and valves and checking the clearance and replacing the stem seals as a matter of course.
  17. Minor update: I have the engine mostly put back together but broke a damn heater hose coming out of the firewall. It will be after the weekend before I can replace the hose and give a final resolution.

    Thanks again!
  18. :fuss::cool:
  19. Alright, well the car is back together. It started up ok and I let it idle until it came up to operating temperature and then I took it for a drive.

    The misfire at idle is gone and the car is kinda drivable except it still stumbles under load. It isn't nearly as bad as it was before the valve work.

    I'm going to put a few miles on it and see if it will throw any codes.

    Something I should mention is that when I pulled the head off, coolant got into the oil. I ran about 9 quarts of oil thru the thing the flush out the water/coolant. I doubt I got everything.

    I put 8 miles on the car tonight and noticed a lovely frothy mixture under the oil fill cap.

    I'm going to put some sea foam in it and change the oil again tomorrow.

    Any suggestions? Would coolant in the oil cause the engine to stumble like it is? It only does it under load / wide open throttle WOT.
    I made sure that the timing chain was put back EXACTLY where it came off of. I replaced the upstream oxygen sensors.
  20. Sounds like progress has been made. You should pause to give yourself a pat on the back.

    IMO, your problems are possibly two fold, the general low overall motor compression and the PCM needing time to re-learn.

    Any change in the high fuel pressure numbers?

    Just wondering, did you drain the coolant before tearing into it?