• Sign Up! To view all forums and unlock additional cool features

    Welcome to the #1 Fiesta ST Forum and Fiesta ST community dedicated to Fiesta ST owners and enthusiasts. Register for an account, it's free and it's easy, so don't hesitate to join the Fiesta ST Forum today!


Engine stutter , failed spark plug

B

Bg99

Member
#1
Messages
13
Likes
8
Location
Ireland
#1
So yesterday out of nowhere I noticed a slight hesitation on full load when revs were between 2500/3000 revs. Ran codes on forscan with no sign of anything unusual. Went for a drive logging data such as timing and maf sensor. The blips are shown clearly on the red line below. Today I took it out and the stutter has developed into a huge misfire sounding like 3 cylinders. Nursed it home and removed the plugs. Removing the coil packs individually I could hear a noticeable change in engine tone across all 4 cylinders. However further inspection shows Cylinder 3 has a failed spark plug shown below and the earth electrode is no where to be found. I am hoping a bore scope and a magnet will find the missing piece and that it dropped whilst taking the plug out. Worst case scenario it has been flung throw the turbo or up into a valve. These plugs were changed when I bought the car just under a year ago. I have never come across a failure like this and I am trying to figure out what would possibly cause it. Cylinder 1,2 and 4 are perfect. I have always monitored data on the torque app , boost intake temps and coolant temps showed no change leading up to this failure so it has me stumped. If anyone has experienced anything similar, any advice would be greatly appreciated


 


S

SteveS

1000 Post Club
#2
Messages
1,401
Likes
1,670
Location
Osage Beach, MO, USA
#2
Most common cause is running lean. This results in overheating of the spark plug, ergo melting. Other causes of high cylinder temperature will do this as well. I once had it on a 1978 Fiesta when a big valve Formula Ford head developed a crack between valve seats.

There have also been problems with counterfeit spark plugs which don't do what the original does.
 


OP
B

Bg99

Member
Thread Starter #3
Messages
13
Likes
8
Location
Ireland
Thread Starter #3
With no indication on fueling to lean or high engine temps , would there be any other way to diagnose an issue like that ? No fault codes , no warning lights or any other symptoms.
 


S

SteveS

1000 Post Club
#4
Messages
1,401
Likes
1,670
Location
Osage Beach, MO, USA
#4
When it's due to something like the cracked head I mentioned, the engine coolant did not overheat. It was only that cylinder's temperature which got hot. I diagnosed it by taking the cylinder head off just to look at the valves and cylinder (It melted 4 spark plugs in a couple of weeks).

Since you apparently are using an accessport you should be able to watch it coming by looking at misfires. But that really won't help you with the cause.
 


OP
B

Bg99

Member
Thread Starter #5
Messages
13
Likes
8
Location
Ireland
Thread Starter #5
Prior to the larger “misfire” there were not any logged misfires if that makes sense. The original stutter on high load didn’t sound or feel like a misfire more like a power cut. However I was not logging it whilst limping home. I’ll put plugs in after a bore scope and compression test at the weekend and see what happens. If compression is good and no sign of damage, next area to diagnose will be fueling
 


Nitelife

Nitelife

Member
#6
Messages
389
Likes
391
Location
SE, PA
#6
I had this happen on my cylinder 3 plug right after returning from my trip to Tail of the Dragon. I eventually threw the P0303 (cylinder 3 misfire). Same as you the earth electrode was completely gone. I replaced that plug and drove the car which began to have the stutter misfire within a few days. This lead me to believe #3 coil was on the way out. I replaced all coils and no further issue.
 


OP
B

Bg99

Member
Thread Starter #7
Messages
13
Likes
8
Location
Ireland
Thread Starter #7
Nitelife said:
I had this happen on my cylinder 3 plug right after returning from my trip to Tail of the Dragon. I eventually threw the P0303 (cylinder 3 misfire). Same as you the earth electrode was completely gone. I replaced that plug and drove the car which began to have the stutter misfire within a few days. This lead me to believe #3 coil was on the way out. I replaced all coils and no further issue.
Click to expand...
Did you search for the electrode ? Any damage to the cylinder or turbo ? Hopefully that’s all I have to deal with. Appreciate the response
 


Nitelife

Nitelife

Member
#8
Messages
389
Likes
391
Location
SE, PA
#8
Bg99 said:
Did you search for the electrode ? Any damage to the cylinder or turbo ? Hopefully that’s all I have to deal with. Appreciate the response
Click to expand...
I did not. I was going to take an extension magnet and fish around through the spark plug hole but could not find it in my collection of tools. I replace the coils back in February and have since put ~2700 miles on the car. No issues to report since (knock on wood).
 


scooter123

scooter123

Member
#9
Messages
467
Likes
543
Location
Metro Detroit
#9
There is a LOT of carbon on that spark plug. Enough for me to ask if this plug may have worked loose. If you have a loose plug it will result in a very lean condition in that cylinder due to the vacuum generated during the intake stroke. It will also result in exhaust gases depositing carbon on the spark plug. I will also note that it also sounds just like an exhaust leak from a blown out exhaust gasket. Just something to consider.

One thing that you will want to do is use a borescope to give the top of the piston a very good looking over. After that do a compression test and perhaps a leakdown test. As for the parts that came off the spark plug, if they aren't on top of the piston it's a near certainty they went out the exhaust and probably thru the turbo. How much damage was done by that event only time will tell.
 


OP
B

Bg99

Member
Thread Starter #10
Messages
13
Likes
8
Location
Ireland
Thread Starter #10
T
scooter123 said:
There is a LOT of carbon on that spark plug. Enough for me to ask if this plug may have worked loose. If you have a loose plug it will result in a very lean condition in that cylinder due to the vacuum generated during the intake stroke. It will also result in exhaust gases depositing carbon on the spark plug. I will also note that it also sounds just like an exhaust leak from a blown out exhaust gasket. Just something to consider.

One thing that you will want to do is use a borescope to give the top of the piston a very good looking over. After that do a compression test and perhaps a leakdown test. As for the parts that came off the spark plug, if they aren't on top of the piston it's a near certainty they went out the exhaust and probably thru the turbo. How much damage was done by that event only time will tell.
Click to expand...
Thanks for that insight , I have seen these cylinder heads can develop cracks along the spark plug threads overtime from heat. The spark plug was definitely loose when taking it out and really hoping it hasn’t developed a crack in the threads. Something a bore scope might not pick up and would probably need the head off for confirmation. Bore scope and compression test to do this weekend and if they are all clear hopefully it can just be put down to plugs and coils.
 


Dpro

Dpro

6000 Post Club
#11
Messages
6,359
Likes
5,974
Location
Los Feliz (In the City of Angels) aka Los Angeles
#11
Bg99 said:
T

Thanks for that insight , I have seen these cylinder heads can develop cracks along the spark plug threads overtime from heat. The spark plug was definitely loose when taking it out and really hoping it hasn’t developed a crack in the threads. Something a bore scope might not pick up and would probably need the head off for confirmation. Bore scope and compression test to do this weekend and if they are all clear hopefully it can just be put down to plugs and coils.
Click to expand...
I have seen these engines lose their spark plug threads and drop a plug. End rresult without damage helicoil the head and replace plug. Though ya it can happen if you beat on it a lot and don’t take care of it.
 


OP
B

Bg99

Member
Thread Starter #12
Messages
13
Likes
8
Location
Ireland
Thread Starter #12
Dpro said:
I have seen these engines lose their spark plug threads and drop a plug. End rresult without damage helicoil the head and replace plug. Though ya it can happen if you beat on it a lot and don’t take care of it.
Click to expand...
Hasn’t been beat on too hard to be honest and it is serviced regularly so really hoping that this isn’t the case
 


Dpro

Dpro

6000 Post Club
#13
Messages
6,359
Likes
5,974
Location
Los Feliz (In the City of Angels) aka Los Angeles
#13
Bg99 said:
Hasn’t been beat on too hard to be honest and it is serviced regularly so really hoping that this isn’t the case
Click to expand...
It quite often happens in two scenarios one is undertighten they work themselves loose and get combustion blow by that cracks or breaks threads. Other is overtighten which literally strips threads off. Either way Aluminum head aluminum threads be careful when threading in sparkplugs not to loose not to tight.
 


OP
B

Bg99

Member
Thread Starter #14
Messages
13
Likes
8
Location
Ireland
Thread Starter #14
Dpro said:
It quite often happens in two scenarios one is undertighten they work themselves loose and get combustion blow by that cracks or breaks threads. Other is overtighten which literally strips threads off. Either way Aluminum head aluminum threads be careful when threading in sparkplugs not to loose not to tight.
Click to expand...
Cheers , when I replaced them last time out I was pretty cautious with torque and the damaged one doesn’t seem to have any Thread issues , I tried another spark plug in the hole and it tightened up no problem. Here’s hoping it will be okay with new plugs and coils
 


scooter123

scooter123

Member
#15
Messages
467
Likes
543
Location
Metro Detroit
#15
Per the shop manual the Torque Spec for the spark plugs is 12 Newton Meters which is not a lot. Note this is equal to 8.85 foot.lbs or 106.3 inch lbs. Considering the length of thread used I would bump that up a bit to 14 foot lbs. or 170 inch lbs. I would also suggest using a proper inch lbs. torque wrench because this level of torque is light enough that most will over torque this thread by a lot. I just checked and the old Craftsman 1/4 inch drive beam type torque wrenches are no longer available. The least expensive 1/4 drive torque wrench I found is at Harbor Freight a Pittsburg click type at 18.99.
 


OP
B

Bg99

Member
Thread Starter #16
Messages
13
Likes
8
Location
Ireland
Thread Starter #16
Out for a test after an all clear on the borsescope and compression test with 160-170 across all four cylinders. No sign of any electrode. Used a telescopic magnet and removed some of the remains of it and some carbon build up. New plugs in and it seems to drive perfect again. Making boost like it was originally and no strange noises so hoping the turbo came out okay. Coils don’t look in the best condition so they are up for a change with parts ordered.
 


OP
B

Bg99

Member
Thread Starter #17
Messages
13
Likes
8
Location
Ireland
Thread Starter #17
Back where I started …. Another misfire and this time a failed plug on cylinder one. Cracked ceramic so engine temps must be way too high. I’ve been monitoring long term fuel trim and afr and at idle trim is stupidly high, upwards of 35% but drops to 8-10 when driving. Car is eating fuel so I can only presume it’s trying to compensate for lean conditions in the cylinder. It’s parked up now until I get coil packs delivered and more than likely going to have to get injectors too. No other symptoms to note. IMG_3860.jpeg
 


OP
B

Bg99

Member
Thread Starter #18
Messages
13
Likes
8
Location
Ireland
Thread Starter #18
IMG_3914.jpeg Replaced some pretty nasty injectors today as well as the coil packs. The car still runs fine as it did however fuel trims at idle are still way too high between 30-40%. I noticed that when the car is started from cold it seems to read around 20% and as it warms up to temperature the trims at idle rise with it. When accelerating the trims drop but still only to around 10% Fuel economy is poor. Any ideas where to go next ?
 


Attachments

OP
B

Bg99

Member
Thread Starter #20
Messages
13
Likes
8
Location
Ireland
Thread Starter #20
Car is completely standard, switched between an airtec cone filter and silicone hose to factory air box but no tune
 


You must log in or register to reply here.
Thread starter Similar threads Forum Replies Date
B procedure for starting the engine after an accident Maintenance, Warranty Issues & Troubleshooting 2
R How screwed am I? Downpipe to engine bracket. Maintenance, Warranty Issues & Troubleshooting 3
Tim_021 Custom engine build tune suggestions. Performance Tuning 0
FiestaSTdude Blown engine Maintenance, Warranty Issues & Troubleshooting 7
ploobster P1450 Check Engine Light - Common fixes tried, other ideas? Maintenance, Warranty Issues & Troubleshooting 5
XR650R Six stroke engine? General Automotive Discussions 2
M Dealer says new engine Maintenance, Warranty Issues & Troubleshooting 10
S Puzzling engine stop Fiesta ST Discussions 5
V down on power after new turbo/engine. Maintenance, Warranty Issues & Troubleshooting 22
S Engine stutter when aggressively accelerating. Maintenance, Warranty Issues & Troubleshooting 62

Similar threads

Ford Community Posts



Top