2008 GT Bogging Intermittently

[Weisguy05]

I have a good tune, done in-house by fastlane motorsports on a dyno. And I haven’t changed the tune since the time I bought the car 2 years ago, so this issue isn’t related to that. Spark plugs were replaced back in December with OEM Motorcraft plugs along with the entire timing chain system and a new melling oil pump. One of the vct solenoids are was replaced at that time as well. In-line fuel filter was done 20k miles ago. No codes pop up and I have been fighting with forscan so haven’t gotten any big data yet

 

[Weisguy05]

Throttle body position sensor and MAF sensor both replaced with Motorcraft parts as well

 

[StockishS197]

Throttle body position sensor and MAF sensor both replaced with Motorcraft parts as well

If it were me, I would pull the intake manifold and inspect the CMCVs.

The IM on these cars is fairly easy to remove and would give you a look at how easily the CMCVs actuate. I would also at that point just install CMDPs and a tune

 

[Weisguy05]

Great idea, thought of that too. but I have the Ford Performance intake so the CMCVs are already gone anyhow.

 

[Weisguy05]

Thinking about plugging the scanner in again and watching the short term fuel trims when it bogs since I don’t have a wideband. The confusing part is that it runs great up top all the way to redline, and if you whack the throttle at low rpm it doesn’t bog. It’s when you roll into it that it does. Like 0-100% throttle is fine, but going from 20-100% it bogs. Also, only happens at operating temp and more often when it’s been sitting in the sun all day. In the mornings when it’s sat all night it usually runs great.

 

[StockishS197]

Thinking about plugging the scanner in again and watching the short term fuel trims when it bogs since I don’t have a wideband. The confusing part is that it runs great up top all the way to redline, and if you whack the throttle at low rpm it doesn’t bog. It’s when you roll into it that it does. Like 0-100% throttle is fine, but going from 20-100% it bogs. Also, only happens at operating temp and more often when it’s been sitting in the sun all day. In the mornings when it’s sat all night it usually runs great.

Even after resetting the KAM, issue persists?

If you are able to log, I would do that. If nothing there, probably tune related.

WOT tuning is the easy part. Part throttle transitions and MAF tables can be tricky.

 

[Weisguy05]

Yes, have had the battery disconnected many times, once for multiple days in a row.

Yeah, I plan to log once I get an adapter for my computer that works, bought a cheap ELM327 for forscan but it worked intermittently. The tuner that came with the car is a SCT X2 so it’s really outdated and I can’t log with it.

It very well might be a tune thing, but the cars had the same tune on it for 10 years and didn’t do this until this year. I did “reprogram” it again with the same tune file just in case but no change there.

 

[StockishS197]

Yes, have had the battery disconnected many times, once for multiple days in a row.

Yeah, I plan to log once I get an adapter for my computer that works, bought a cheap ELM327 for forscan but it worked intermittently. The tuner that came with the car is a SCT X2 so it’s really outdated and I can’t log with it.

It very well might be a tune thing, but the cars had the same tune on it for 10 years and didn’t do this until this year. I did “reprogram” it again with the same tune file just in case but no change there.

TB clean?

 

[Weisguy05]

Yep, cleaned it 10k miles ago and hasn’t thrown any codes for improper throttle body blade angle, which it used to do. Also is the 62mm Ford performance throttle body and only has 40k miles put on it since replacing

 

[DieHarder]

You said you changed the plugs. It's often the case that the pigtails for the coils will retreat into the boots so far that they don't make good contact and when you give it partial throttle the engine will bog down due to the spark having to jump a gap. If this is the case you should be able to see it on a scanner. New OEM COPs are relatively inexpensive on feebay ($60 - 100 for all eight) depending on if you have gray or black boots.

 

[Weisguy05]

You said you changed the plugs. It's often the case that the pigtails for the coils will retreat into the boots so far that they don't make good contact and when you give it partial throttle the engine will bog down due to the spark having to jump a gap. If this is the case you should be able to see it on a scanner. New OEM COPs are relatively inexpensive on feebay ($60 - 100 for all eight) depending on if you have gray or black boots.

I’ll have to investigate that then. Yeah I haven’t changed the coils and have no idea how old they are. However it’s not throwing any codes when I scan it.

 

[StockishS197]

One other thing I would look at is where you bought your MC plugs from…very common to get counterfeits unless you bought from a known good source (basically anything but eBay and Amazon).

I also had better luck with the Autolite HT1s than the MC SP547Xs in my car. The Autolites have a smaller gap and overall make my car run cleaner….though YMMV.

I will second DieHarder above…the secondary electrode (spring) should protrude out of the boot. If it’s recessed, it could cause intermittent spark.

 

[whitmanink]

One other thing I would look at is where you bought your MC plugs from…very common to get counterfeits unless you bought from a known good source (basically anything but eBay and Amazon).

I also had better luck with the Autolite HT1s than the MC SP547Xs in my car. The Autolites have a smaller gap and overall make my car run cleaner….though YMMV.

I will second DieHarder above…the secondary electrode (spring) should protrude out of the boot. If it’s recessed, it could cause intermittent spark.

about 2 months ago ,my wifes wrx i put the auto lights in ,,
got missfire about 200 miles later,,,
the one sparkplug the porcelain is loose and will slide up the electrode and back down,,
covering the electrode
like the weridest thing ive ever seen.,

so i went to autozone and exchanged it,,
not even 2 miles later the same thing,,
missfire..
took the new autolight plug out and that one too the porcelain will freely move up and down and cover the electrode ??????
welp went back and get 4 new $20 a piece plugs in and since has been fine...

i still have the one plug and after work i will attempt to upload a video ..
so my autolight experience is quite different from yours,,
even tho it was a wrx and not a 3v,, still the same manufacturer

 

[Weisguy05]

One other thing I would look at is where you bought your MC plugs from…very common to get counterfeits unless you bought from a known good source (basically anything but eBay and Amazon).

I will second DieHarder above…the secondary electrode (spring) should protrude out of the boot. If it’s recessed, it could cause intermittent spark.

I honestly don’t remember where I bought them but they looked legit once I opened the boxes. I’m not getting any misfire codes so not sure of that either.

I’ll pull the coils later and inspect them to see if I find anything.

 

[StockishS197]

about 2 months ago ,my wifes wrx i put the auto lights in ,,
got missfire about 200 miles later,,,
the one sparkplug the porcelain is loose and will slide up the electrode and back down,,
covering the electrode
like the weridest thing ive ever seen.,

so i went to autozone and exchanged it,,
not even 2 miles later the same thing,,
missfire..
took the new autolight plug out and that one too the porcelain will freely move up and down and cover the electrode ??????
welp went back and get 4 new $20 a piece plugs in and since has been fine...

i still have the one plug and after work i will attempt to upload a video ..
so my autolight experience is quite different from yours,,
even tho it was a wrx and not a 3v,, still the same manufacturer

Autolite is the manufacture of the Motorcraft plugs. They are identical aside from the different gaps and heat ranges offered for the Autolite HT series.

One of the few times Autolites are actually a good/recommended plug over OEM lol

 

[Pentalab]

ok ok .,
I'm gonna say it,,
try a real tune .. not the canned sct tunes or bama tunes ..
like a lito tune or another real tune,, id start there,,

also its possible one or more of your cop packs are going out,,,
electronics tend to do funny things when they are going bad and get warm or hot.

and also ,, make sure you don't use cheapo spark plugs from amazon,,

I used Brisk plugs, correctly gapped, and my misfires completely vanished. I had another issue years ago.....and that turned out to be the 'sock filter' that goes on the bottom of the fuel pump itself. It was clogged up. Eng ran fine..... but only if I was out of boost, like 0 psi or less. This was with a small Roush M90 blower.

 

[07 Boss]

about 2 months ago ,my wifes wrx i put the auto lights in ,,
got missfire about 200 miles later,,,
the one sparkplug the porcelain is loose and will slide up the electrode and back down,,
covering the electrode
like the weridest thing ive ever seen.,

I've had that happen a couple of times. It's hard to track down sometimes because every time I pulled that plug it looked normal and good. But as soon as you turn it upside down to install it the insulation would slide down over the electrode. I've used Brisk plugs since then except for this last round I got a set of plugs from Accel.

 

[Jon Hendrix]

I’ve had the car for a couple of months and about 2k miles. The issue is noticeable in all gears (manual transmission) below 3500 rpms. Sometimes the car runs great and at the next stop light it has nearly zero power below 3500 rpms. It has about 135k miles right now. Since I bought the car I’ve changed plugs, air filter, fuel filter, cleaned throttle body and MAF sensor. I installed a canned SCT 87 tune just to check but the issue exists both stock and tuned.

If I clear the KAM or change tunes it runs great for a while but the issue always returns. It seems worse on warm days and when the car is fully up to operating temp. It is not a misfire and feels to me like a fueling issue. The only code I’ve ever got was P0115E which is what led me to cleaning the TB.

I’ve read that bad catalytic converters could cause similar symptoms but how would I diagnose bad cats? Anything else I can look for? Cam position sensor maybe?

The car is completely stock. It idles perfectly smooth and doesn’t make any odd noises? When it’s running good it makes full power at all RPMs. When it’s bad it only makes power at high rpms. It bogs and slowly builds rpms and then feels like a nitrous shot was added if that makes any sense.

Any help or ideas would be greatly appreciated! Thanks.


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Any resolution? I have a similar issue with no codes

 

[Weisguy05]

Any resolution? I have a similar issue with no codes

I know I’m not the guy you asked, but for me it was an issue with my reluctor wheel on the crank snout. The Harmonic balancer hadn’t been seated tightly enough to hold it in place, so the wheel slapped around enough to wallow out the key way. That caused an incorrect reading of engine timing, not enough to throw a code but enough for it to make very little power in certain situations.