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Discussion Starter · #1 ·
Hi community.

I decided to rescue an old worn out girl. A 163000 mile '14 Focus ST still recovering from a broken engine from her last owner. Blown head gasket repaired and the coolant isn't leaking anymore. I checked the repair record and no sign of a cracked block or resurfaced head.

Anyway, so I've had a little misfire at idle since I got her. At first I thought it was the petrol, so I put premium. Then I put octane booster after that didn't fix it. Then the CEL came on, misfire on #4. Fixed that with a new coil, CEL gone. Didn't fix it completely. Replaced the spark plugs with Motorcraft OEM iridiums (.29 measured). Didn't fix it. Replaced all the coils with Standard ones from OReilly's. Didn't fix it.

Basically at idle it just rumbles every few seconds and maybe once a drive it'll dip the RPM down to about 500 or so and return momentarily. Same cool/hot. Doesn't get any worse the longer I drive. Only happens at idle.

I haven't touched the injectors. At $95/ea. obviously I don't want to also replace the injectors. Could it be the injectors? This girl has seen some use. I put just a little bit of Seafoam- we'll see if this improves it.

What else could cause this problem on these engines? Has anyone had a similar issue that wasn't resolved with plugs/coils?
 

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compression test first, if that is okay you could start with checking if the intake valves are gummed up. why waste money throwing parts at it
 

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Discussion Starter · #4 ·
compression test first, if that is okay you could start with checking if the intake valves are gummed up. why waste money throwing parts at it
Time to add a compression tester to my kit. Will update tomorrow when it arrives. Thanks.

If the compression is good, I heard you can take it to somebody who services GDI and have them blast the valves out. Shouldn't be too expensive...

Also I scraped down the chassis ground. No change.
 

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Discussion Starter · #5 ·
OK so I took my $18 Amazon Basics compression test kit and measured 150-160 on each cylinder after 10 seconds of cranking. Idk how accurate this gauge is, but the same reading across the board seems good to me.

Still no CEL after continued driving.

I'm going to install the suggested secondary chassis ground mod tomorrow- will update.

If that doesn't fix it it's going to have its valves blasted.
 

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Hi community.

I decided to rescue an old worn out girl. A 163000 mile '14 Focus ST still recovering from a broken engine from her last owner. Blown head gasket repaired and the coolant isn't leaking anymore. I checked the repair record and no sign of a cracked block or resurfaced head.

Anyway, so I've had a little misfire at idle since I got her. At first I thought it was the petrol, so I put premium. Then I put octane booster after that didn't fix it. Then the CEL came on, misfire on #4. Fixed that with a new coil, CEL gone. Didn't fix it completely. Replaced the spark plugs with Motorcraft OEM iridiums (.29 measured). Didn't fix it. Replaced all the coils with Standard ones from OReilly's. Didn't fix it.

Basically at idle it just rumbles every few seconds and maybe once a drive it'll dip the RPM down to about 500 or so and return momentarily. Same cool/hot. Doesn't get any worse the longer I drive. Only happens at idle.

I haven't touched the injectors. At $95/ea. obviously I don't want to also replace the injectors. Could it be the injectors? This girl has seen some use. I put just a little bit of Seafoam- we'll see if this improves it.

What else could cause this problem on these engines? Has anyone had a similar issue that wasn't resolved with plugs/coils?
Just had this kind of issue. And it was the purge valve. Bought coils plugs. No change. Code for purge popped up. Amd it all went away
 

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The intermittent idle misfire is kind of a wandering ghoul on these motors. Valve cleaning may help it, but I don't know if you'll ever get rid of it, I bought my 2018 with 62 miles on it and by 5k I was having lil intermittent misfires usually only while cold starting. I never get CELs only once and I had the cold start misfire tsb done and it didn't do anything. I find the best way to keep them to a minimum is run as high octane as possible, I change my plugs every 12 to 15k miles because I notice when it starts to pull a tad more ignition timing then usual or a knock here or there more then usual I know it needs new plugs. This is where I stand on the misfire issue. The RS pistons were redesigned from the 2.0 piston as they gave the ringlands steel support and more important to fuel combustion, the bowl area was redesigned for better atomization and combustion to help with ignition, efficiency and to prevent fuel wash down the sides of the pistons and get hot spots which cause detonation and broken ringlands, all of this is why I suspect you don't hear really much about the RSs having misfires like the 2.0s, just a thought. As far as your compression, for a 163k that comppression sounds pretty darn good. Was this a cold comp test or did you let it warm up to full temp give it like 15 mins and then test? Because they say operating temp comp test are the most accurate. Either I think your pretty good, id say work out any other issues, look into cleaning valves, clean your map sensors in intake hose and intercooler and start getting everything else kosher, I believe your ok.
 

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I will say I put in the new NGK ruthenium spark plugs I have no misfires at all on idle or on a cold start up. I'm just getting the misfires while cruising with light throttle modulations.
 

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Discussion Starter · #9 · (Edited)
Okay so I don't have any codes from the purge valve, and I'd rather not continue easter-egging this thing as it's getting expensive. I'll keep that in mind though.

I have been putting only Chevron 91 in the tank, and I've also put octane-boosting fuel additives (Lucas, Seafoam, and O'Reillys octane booster at different times). I don't think it's that as I've had little to no change from the tank of 89 I put in at first.

So I actually gave it to a very trustworthy shop and paid their diagnostic fee. They got stumped and are calling in a specialist. I have good feelings about this shop because they haven't tried throwing parts at it yet.

We'll see about these spark plugs if they can't figure out what's wrong with it. The good thing is they ran some tests and verified the head gasket and ignition system is working as intended, and reverified the cylinder compression. For the record I ran it warm.

Thanks for the information. I will update when we figure this out.

Edit: And the shop stuck a scope in the intake and the valves were clean.
 

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Okay so I don't have any codes from the purge valve, and I'd rather not continue easter-egging this thing as it's getting expensive. I'll keep that in mind though.

I have been putting only Chevron 91 in the tank, and I've also put octane-boosting fuel additives (Lucas, Seafoam, and O'Reillys octane booster at different times). I don't think it's that as I've had little to no change from the tank of 89 I put in at first.

So I actually gave it to a very trustworthy shop and paid their diagnostic fee. They got stumped and are calling in a specialist. I have good feelings about this shop because they haven't tried throwing parts at it yet.

We'll see about these spark plugs if they can't figure out what's wrong with it. The good thing is they ran some tests and verified the head gasket and ignition system is working as intended, and reverified the cylinder compression. For the record I ran it warm.

Thanks for the information. I will update when we figure this out.

Edit: And the shop stuck a scope in the intake and the valves were clean.
Did you ever figure out what the issue was?
 

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Okay so I don't have any codes from the purge valve, and I'd rather not continue easter-egging this thing as it's getting expensive. I'll keep that in mind though.

I have been putting only Chevron 91 in the tank, and I've also put octane-boosting fuel additives (Lucas, Seafoam, and O'Reillys octane booster at different times). I don't think it's that as I've had little to no change from the tank of 89 I put in at first.

So I actually gave it to a very trustworthy shop and paid their diagnostic fee. They got stumped and are calling in a specialist. I have good feelings about this shop because they haven't tried throwing parts at it yet.

We'll see about these spark plugs if they can't figure out what's wrong with it. The good thing is they ran some tests and verified the head gasket and ignition system is working as intended, and reverified the cylinder compression. For the record I ran it warm.

Thanks for the information. I will update when we figure this out.

Edit: And the shop stuck a scope in the intake and the valves were clean.
Hey did you ever figure out what it was?
 

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Discussion Starter · #12 ·
Hey did you ever figure out what it was?
Not entirely. Shop said one of the valves wasn't seating right, so I brought it to the shop that had done the head job and they presumably popped off the valve cover and tightened something, though they wouldn't tell me what because the guy who did it wasn't there when I picked the car.
 
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