03 cobra low compression on just one cylinder

[topless03svt]

Alright. Here is the short story. Just picked up an 03 convertible with 87,000 miles. Got it inspected, tag....etc. Had it one week and the service engine light came on. Diagnostics showed #6 cylinder misfire. First I swapped the coil packs around and changed all the plugs, reset code. Few miles later..... #6 cylinder misfire again. Also a rough idle. I performed a comression test and all cylinders were in the 175-180 range except for #6 of course. It was roughly 75 psi. I added a lilttle oil to the cylinder and retested compression. This time she jumped up to 150 psi. From what I have read it sounds like the rings but I have no clue where to go from here. I am mechanically inclined and have the means to pull the head/engine if needed. My question is, do I replace head/piston or pistons. Can the head be salvaged? If so should I pull both heads and have them ported? This is the fifth mustang I have owned but really the first modular motor Ive had to tear down. Any help would be greatly appreciated. :shrug:

 

[racebronco2]

Alright. Here is the short story. Just picked up an 03 convertible with 87,000 miles. Got it inspected, tag....etc. Had it one week and the service engine light came on. Diagnostics showed #6 cylinder misfire. First I swapped the coil packs around and changed all the plugs, reset code. Few miles later..... #6 cylinder misfire again. Also a rough idle. I performed a comression test and all cylinders were in the 175-180 range except for #6 of course. It was roughly 75 psi. I added a lilttle oil to the cylinder and retested compression. This time she jumped up to 150 psi. From what I have read it sounds like the rings but I have no clue where to go from here. I am mechanically inclined and have the means to pull the head/engine if needed. My question is, do I replace head/piston or pistons. Can the head be salvaged? If so should I pull both heads and have them ported? This is the fifth mustang I have owned but really the first modular motor Ive had to tear down. Any help would be greatly appreciated. :shrug:

You need to first see what the problem is. The heads are probably good, porting our heads shows very little increase in hp. Spend your money some where else.

 

[Scotty B]

Sorry to hear. There are a few things that could cause low compression. The main ones are piston/rings, valves/valve seats and head gasket. you could perform a leak down test and try to determine if the leakage is coming thru the intake/exhaust or crankcase. check for coolant in the oil, air bubbles in the coolant. What did the spark plug look like?

 

[topless03svt]

The spark plug looked normal. Actually it wasn't burning any differently than the other plugs. Oil is fine. Thats the first thing I changed when I got it home from the previous owner. So its fresh oil but def no water in it like a head gasket.

 

[333arod333]

I have the same problem topless and many on here have told me to stop driving the car because it may create worse problems. If you gouge the side of the cylinder wall with a faulty piston rings it will mean a rebore and new pistons. Do a leak down test and listen for blow by. intake or exhaust pipes means valves, crankcase noise means piston rings. I have an exhaust valve leak at 30% but I can hear a little noise in crankcase too, so a whole rebuild is what svt guys say. Bummer though!

 

[topless03svt]

Yep. Looks like the money I had set aside for mods will now have to go towards just getting the car back to normal again. Oh well. I guess its the chance you take on anything used. Luckily I picked the car up cheap enough I should still be ahead of the game even after the rebuild. Thanks for the responses and advice.

 

[hotcobra03]

im a winner on cyl 6..

1st time exhaust valve [email protected] 4 thread plugs

2nd time cyl 6 exhaust valve..1st change. 9 thread plugs..had head repaired

3rd time cyl#7 crack in plug threads...replaced head

im on the most upto date head..

piston has 2 huge hash marks from valves...

i only did head..engine has 180psi+ @ 320k

 

[1MeanNonPI2v]

Leak Down Results

I would start by removing the cylinder head and inspect the valves and valve seats. Forced induction engines generate extremely high combustion chamber pressures and temperatures. This can cause damage to the valve seats, dropping of a valve and/or tulip-ing of the valve. A tulipped exhaust valve will give you a misfire and leak cylinder pressure. It is caused by extreme heat and the valve curls downward and will resemble a tulip. It will still hold some cylinder pressure but the valve will no longer seal to the valve seat properly. If that is what has happened to your engine you may be able to get away with just a new valve(s) and a valve job.
Also after removing the head it will give you the opportunity to inspect the engine block and questionable #6 cylinder. Any physical damage should be visible to the naked eye, and try to inspect the cylinder wall for scoring or any signs of abnormal wear. There is also the possibility of failed head gasket being the culprit, but I doubt it.
If you have any questions you can reach me at Granatelli Motor Sports, 805-486-6644, my name is Nick and I will be happy to help.

 

[topless03svt]

Thanks 1 mean and hot cobra also. I had to work late this evening so i didnt get as much done to her tonight as i wanted. Got as far as pulling the valve cover on that side. Took forever because I didn't pull the motor out. I'm still being optimistic and hoping that it is a head/valve issue and not the rings so the motor may not have to come completely out. I'll update tomorrow once the head is off and I diagnose the issue.

 

[hotcobra03]

Thanks 1 mean and hot cobra also. I had to work late this evening so i didnt get as much done to her tonight as i wanted. Got as far as pulling the valve cover on that side. Took forever because I didn't pull the motor out. I'm still being optimistic and hoping that it is a head/valve issue and not the rings so the motor may not have to come completely out. I'll update tomorrow once the head is off and I diagnose the issue.

did you think your the 1st to open front cover?

google safe mode for 4.6...i didnt know about this when i did mine..just to be safe...

heres a pdf of engine assembly,,,read very close,,read all notes..

engine dis-assemble
https://acrobat.com/#d=M4GT7tGzoGd4FJ3DKqZjiw

engine assembly
https://acrobat.com/#d=*XsRMaPtENGX2sP-TNDyWA

head sub assembly
https://acrobat.com/#d=MOHZyb9sSNojVggvy1aB9w..

tousley sell head for 1100 complete to bolt on...

just realize this will happen again...all mine went on startup...the 1 banged untill follower fell off,,than i drove it 60miles home

 

[topless03svt]

Update.... Got the heads off. Thankfully the piston/cylinder were in perfect shape. No wear or ring play. Close inspection on head revealed valves not seating on the #6 cylinder . Heads are at the machine shop now. Still waitng on a call from them. What was the biggest shocker was the amount of heat showed by this head compared to the passenger side head. Every component associated with the drivers side just showed a ridiculous amount of heat. I know the drivers side head causes more heat due to the way the coolant flows in the head. A cooling mod is def going on after I get the heads back. Other than that. Im gonna throw a 2.8 pulley on it, get it tuned and drive it. Lowering springs and exhaust to come soon. :coolman:

 

[hotcobra03]

cool..has was the wear on timing chain adjuster foot? and the longer rail..is there a small groove?

the plastic pieces

 

[1MeanNonPI2v]

As long as you have the heads off, you might want to upgrade the valves. Ferrea Racing valves or Manley are what i would recommend. If you feel like spending big bucks Del West in Valencia California makes some outstanding valves found in just about every race winning car, truck, motorcycle or boat in every major racing series around the world.

Contact Nick at 805-486-6644, Granatelli Motor Sports Sales Associate.

:rockon:

 

[b_dike]

Not tryn to hijack your thread but would 145psi be too low in just one cylinder?

 

[topless03svt]

Im waiting to hear back from the Machine shop now but im def installing all new valves and springs. Plus whatever else he recommends. I just dont want this trouble again down the road somewhere. Was hoping to have it back together before next weekend so the cobra could make its first beach trip but that looks highly unlikely. But id rather let it sit in the garage until I get back as opposed to rushing it back together then driving 200 miles..... There will be plenty of beach trips later

 

[topless03svt]

b dike, sounds like you may be in the early stages of what i am experiencing now. Not 100% positive on that but it would be my guess. I would install a head cooling mod if your car doesn't already have one. The people I have talked to tell me that had my car already had one i probably wouldnt be in the boat im in now. Our drivers side heads do not cool as well as the passenger which is why they came out with an upgraded head in around 2005 i believe. But the head cooling mod is cheap insurance and well worth the money. As far as diagnosing your low compression. There are a few instructions on this thread, but if it is valves, you may be ok with that # as long as it doesnt get any lower. Im sure someone who knows a little more about this will chime in with some answers.

 

[b_dike]

b dike, sounds like you may be in the early stages of what i am experiencing now. Not 100% positive on that but it would be my guess. I would install a head cooling mod if your car doesn't already have one. The people I have talked to tell me that had my car already had one i probably wouldnt be in the boat im in now. Our drivers side heads do not cool as well as the passenger which is why they came out with an upgraded head in around 2005 i believe. But the head cooling mod is cheap insurance and well worth the money. As far as diagnosing your low compression. There are a few instructions on this thread, but if it is valves, you may be ok with that # as long as it doesnt get any lower. Im sure someone who knows a little more about this will chime in with some answers.

I had a compression check/ leak down test down early this year. These are the results.

Compression Test/ leak down
#1 165/10%
#2 160/5%
#3 170/10%
#4 155/10%
#5 160/10%
#6 160/6%
#7 140/20%
#8 165/10%

Was told #7 was leaking through the ring.

Def looking into the ldc gen2 kit. I've heard it's not difficult to do yourself, but I was just wondering how low is too low when it comes to cylinder compression on these cars.

 

[hotcobra03]

Im waiting to hear back from the Machine shop now but im def installing all new valves and springs. Plus whatever else he recommends. I just dont want this trouble again down the road somewhere. Was hoping to have it back together before next weekend so the cobra could make its first beach trip but that looks highly unlikely. But id rather let it sit in the garage until I get back as opposed to rushing it back together then driving 200 miles..... There will be plenty of beach trips later

this is what i was trying to say on having head fixed...why? its the casting not the parts..

fords new casting complete ready to bolt on 1100..

lets see what you shop says on price..

i got 320k on passenger head with 0 issues...4 thread plug head

 

[333arod333]

I had a compression check/ leak down test down early this year. These are the results.

Compression Test/ leak down
#1 165/10%
#2 160/5%
#3 170/10%
#4 155/10%
#5 160/10%
#6 160/6%
#7 140/20%
#8 165/10%

Was told #7 was leaking through the ring.

Def looking into the ldc gen2 kit. I've heard it's not difficult to do yourself, but I was just wondering how low is too low when it comes to cylinder compression on these cars.

140/170= 18% This is getting close to the rebuild zone. I have the same problem going on now but im pretty sure mine is exhaust valves due to leakdown test results. Even so, SVT Gods are advising me to not drive the car at all. If it is truly your piston ring causing low compression, the piston ring might b marring/scraping the side of the cylinder wall. This may cause excessive damage beyond what the highest allowable overbore is for this engine to correct cylinder damage. Not nice!

HotCobra and Topless are right, everyone recommends a head cooling mod. I can't believe Ford designed it without, but then again on a bulletproof engine they had to do some designed obsolescence to get in ur wallet again. Bastards.

 

[hotcobra03]

Bastards.

i agree..when i was searching in 2005 you could get empty heads for 600 or less...

they are screwing us on more than just this part for or car model