Bought a used Mustang and I don't feel good about it, I need opinions and expert insights

[Gaz142]

Greetings,

Few months ago I bought a used Mustang 2018 GT premium with 85,000KM on it. Took the car into three different mechanics for checking and one "before sale 180 points and computer checks" service since I don't have mechanical experiences.

All results came positive that the car is well maintained and there is no signs of anything concerning. Computer checks came clear with no issues at all. Body is legit without any incidents, engine is 100% fine and transmission is 100% fine. So I bought it.

Since I bought it and I'm in and out mechanics for diagnoses however, this is my first ever "sports" car and I always drove SUV before mainly explorers. The first thing I noticed after buying it, which I also posted here about it is the following:
- RPM unstable
- Big "clunk" and jump when shifting gears
- Bad transmission shifting with bad jerks between 4th and 5th gear.

(same visit I noticed that the rear left AXL was in a very bad shape, so i changed it with OEM part bought from dealership)

I searched for solutions and visited many garages for a fix and no one seem to be knowledgeable about the car and usually hesitant to even try to fix it. I gave up, took it to the dealership (prices are extremely high in my country when utilizing a dealership service). Anyway, dealership changed the battery and performed 'transmission calibration" and all issues are gone.

I got finally happy that now I can enjoy the car, then the car started to develop a slight vibration? when idle. RPM is fixed between 610 to 650. Few guys told me "this is how sport cars feel" but I seriously doubt that, since its either I just noticed it or its a new issue. After a while engine light went off, so I did a computer check and got P0420 and P0430 codes, which is issues with Catalytic converter. I took it to mechanic and I was surprised that the car doesn't have either... Seems like the original owner has replaced the whole exhaust system with aftermarket X-Pipe once with NO catalyst converter and now I can not remove the engine light.
The car also have a really bad smell from exhaust. Now I have no idea how to fix this... it's missing two catalyst converter which is super expansive to buy and the exhaust smell bad and engine light is on.

Also lately, after a cold start like 2-3mins after car is on, there is a vert bad grind between 3rd and 4th gear. like the car is holding back to shift the gear with a power that feels like brakes are applied. This ONLY happens after cold start and never happen once car is within normal temperature. Sometimes when breaking the RPM go slight higher with exhaust sound getting louder as its shift down (not always) I also checked transmission oil and it is way above normal range (more fluid than required).

Keep in mind, the car has aftermarket grille and diffusers. Engine cover and strut towers are missing, it came with one key only and no user manuals. I'm really afraid that I bought a badly maintained one or that the previous owner did modify it badly ? I need some insight on how to fix it, or what to do. Should I just sell it and buy a normal once ? should I fix it and use it or is it normal what's going on? I really need insight or help because I really started to dislike this nightmare I bought...

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[Rapid Red]

Shifting 3 & 4 good after operating temp reached. Could try upgrading the transmission oil first, get things slipperier . Would suggest the BG lubricant. It will cost a hundred bucks for the oil, 85km could use it,

Cold drive train will operate differently from start up (on) to operationing temp. Most drivers never pay attention to that.

Every car that's not a DD gets a warm up, folks treat the car like a lawn morrow .


"Keep in mind, the car has aftermarket grille and diffusers. Engine cover and strut towers are missing" < usless mean nothing

"no user manuals." < PDF format is very easy to find suggest you look .

 

[DemonGT]

So there was no code for cats before you bought it and no gas smell?

 

[Dfeeds]

I think it's time to get ahold of the original owner and get a list of aftermarket mods done to the car and ask if it was tuned. If it was tuned for the cat delete and the dealership flashed the OEM tune then you're going to have some issues.

 

[Gaz142]

Shifting 3 & 4 good after operating temp reached. Could try upgrading the transmission oil first, get things slipperier . Would suggest the BG lubricant. It will cost a hundred bucks for the oil, 85km could use it,

Cold drive train will operate differently from start up (on) to operationing temp. Most drivers never pay attention to that.

Every car that's not a DD gets a warm up, folks treat the car like a lawn morrow .


"Keep in mind, the car has aftermarket grille and diffusers. Engine cover and strut towers are missing" < usless mean nothing

"no user manuals." < PDF format is very easy to find suggest you look .

Thanks a lot for your input, is it really safe to change the transmission fluid at 85km ? and about cold start, I think ill let the car warm up from now on.

 

[Gaz142]

So there was no code for cats before you bought it and no gas smell?

No, there was no smell nor any codes up

 

[Gaz142]

I think it's time to get ahold of the original owner and get a list of aftermarket mods done to the car and ask if it was tuned. If it was tuned for the cat delete and the dealership flashed the OEM tune then you're going to have some issues.

Damn !!! you are right ! I got the engine light up few days after car was out off dealership which they did "transmission calibration" and who knows if they did OEM flash. What am I expecting now? should I re-tune it for the cat delete ? The original ownership said he changed front grilles, added diffusers and changed the exhaust to an X-Pipe. He didn't say anything about tuning. But I seriously think you caught the missing puzzle here.

 

[Dfeeds]

Damn !!! you are right ! I got the engine light up few days after car was out off dealership which they did "transmission calibration" and who knows if they did OEM flash. What am I expecting now? should I re-tune it for the cat delete ? The original ownership said he changed front grilles, added diffusers and changed the exhaust to an X-Pipe. He didn't say anything about tuning. But I seriously think you caught the missing puzzle here.

If you plan on staying catless then you have to. The original owner may have the tuning device and original tune on hand. It's, frankly, a bit shady on their part for leaving out that it was tuned and the cat delete. I'd try to get the tune and, at a minimum, the name of the tuner/company so you can reach out to them. You could start from scratch but you'd need an exact mod list.

 

[Rapid Red]

Thanks a lot for your input, is it really safe to change the transmission fluid at 85km ? and about cold start, I think ill let the car warm up from now on.

You don't need it totally warmed up. Just wait for the temp to start moving up scale .

The main point is a cold car will act sluggish.. Think about when you get up from a hard sleep. You stretch limber up, yawn a few times, ready to go LOL...

Going to a better grade of transmission oil could help. I say that cause thru the post you had experience with shifting a couple of times, at different shift points.

And it seemed to straighten or smooth out. Failed/failing transmission parts don't heal themselves, especially a manual box, automatics is some what of a crap shoot.

 

[Cobra Jet]

Is this GT equipped with the MT82 or the 10R80, it’s not really clear by your initial post.

In either instance, the trans should never be overfilled beyond the Service Manual required level.

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If it’s the manual MT82 trans, the 2018/19’s had issues with the MT82 shift forks and repairs were covered under the 3/36k new car OR the 5/60k Powertrain. There were also multiple TSB’s about the bad shift forks. See here:
https://www.mustang6g.com/forums/th...sted-1-2-3-4-shift-forks.113062/#post-2692560

—
If the car has the 10R80, harsh or delayed shifts could be the cause of a failing valve body or it’s in need of a software update. As of Sept 2021, Ford released a new TSB for 10R80 harsh/delayed shifts. That can be found here, and this thread contains everything and anything you ever wanted to know about the 10R80. For the newest TSB, go to the TSB link in the thread:
https://www.mustang6g.com/forums/th...tions-to-harsh-or-no-shift-conditions.135463/

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Definitely try to find out if the car has an aftermarket tune, that can affect A LOT if a dealership has reflashed the car back to the ‘As Built’ software configuration.

—

The idle stumble could be a variety of things. The most common causes of idle stumbles or drivability is the IMRC plate failure or VCT issues. Both are rather simple fixes and there’s many threads in here about both issues.

—

Absence of Catalytic converters can cause quite a few issues also… and what you’re smelling is most likely fuel - common occurrence when running any modern Mustang (86-current) without cats and an emissions system not operating as designed. You will need to know if the car is on the As Built tune or aftermarket in order to figure out how to proceed here…. You could opt to buy high flow cats and have a shop install them, or if you’re not required to do emissions testing, leave the off-road pipe and figure out tune.

 

[Gaz142]

If you plan on staying catless then you have to. The original owner may have the tuning device and original tune on hand. It's, frankly, a bit shady on their part for leaving out that it was tuned and the cat delete. I'd try to get the tune and, at a minimum, the name of the tuner/company so you can reach out to them. You could start from scratch but you'd need an exact mod list.

I will stay catless because at this point, I will use the car for like 4 to 5 months and sell it. So I'm not gonna invest much in it.

I agree with you that it was a bit wierd the original owner didnt mention removing the cats or applying tunes. However, he said that he installed "X-pipe system".

The thing is, I cant reach original owner. So what are my options here ? I don't think car was heavily modded/tuned since it drives actually good once im past the cold start. Dealership confirmed flashing original system as part of there regular maintenance. I did some research, I think he bypassed CLE using mod to switch off cat ptotection and dumping unwanted fuel there.

I have two options now, find a tuning service and bypass oxygen sensor/cat protrction to switch off CLE or just buy a spacer and add them to the oxygen sensor. However, I dont know if im making the correct decition since I dont have much experince in this field really. Any suggestions ?

 

[Gaz142]

Is this GT equipped with the MT82 or the 10R80, it’s not really clear by your initial post.

In either instance, the trans should never be overfilled beyond the Service Manual required level.

—

If it’s the manual MT82 trans, the 2018/19’s had issues with the MT82 shift forks and repairs were covered under the 3/36k new car OR the 5/60k Powertrain. There were also multiple TSB’s about the bad shift forks. See here:
https://www.mustang6g.com/forums/th...sted-1-2-3-4-shift-forks.113062/#post-2692560

—
If the car has the 10R80, harsh or delayed shifts could be the cause of a failing valve body or it’s in need of a software update. As of Sept 2021, Ford released a new TSB for 10R80 harsh/delayed shifts. That can be found here, and this thread contains everything and anything you ever wanted to know about the 10R80. For the newest TSB, go to the TSB link in the thread:
https://www.mustang6g.com/forums/th...tions-to-harsh-or-no-shift-conditions.135463/

—

Definitely try to find out if the car has an aftermarket tune, that can affect A LOT if a dealership has reflashed the car back to the ‘As Built’ software configuration.

—

The idle stumble could be a variety of things. The most common causes of idle stumbles or drivability is the IMRC plate failure or VCT issues. Both are rather simple fixes and there’s many threads in here about both issues.

—

Absence of Catalytic converters can cause quite a few issues also… and what you’re smelling is most likely fuel - common occurrence when running any modern Mustang (86-current) without cats and an emissions system not operating as designed. You will need to know if the car is on the As Built tune or aftermarket in order to figure out how to proceed here…. You could opt to buy high flow cats and have a shop install them, or if you’re not required to do emissions testing, leave the off-road pipe and figure out tune.

It is quipped with 10R80, dealership fixed the bad shifts with "transmission calibration". Coming Saturday ill drain the excess fluid and make it into range as per manual.

As for the tune, I cant seem to be able to reach out to the original owner. However, he confirmed that the only addition was an "x-pipe system". What am I facing if the car was tuned and dealership flashed it ? Is it bad ? Anything to look out for ? My guess the original owner tuned to disconnected back o2 sensors and turn off cat protection. Since I did online research and this was the most common tune after going catless. I'm planning to use spacers to get rid of CLE. You think its good approach ?

There is no emission tests here so I think ill leave the pipes and right now car has stock tune. I dont wanna invest much since im planning to use it for 4-5 month then sell it. Any suggestions ?

 

[sabtaj1]

I use the Big daddies mil eliminators on my rear O2's. Tuners will not shut off O2's anymore. Also, check the glovebox, theres a yellow slide button inside up top and owners manual may be there.
They have two types, I believe I have the mini cat ones but they have a cheaper version too. One is $14.95 each and other is $49.95 each
http://bigdaddiesgarage.com/mini-cat-cel-fix.html
http://bigdaddiesgarage.com/straight-cel-fix.html

 

[sabtaj1]

added links

 

[#1ford]

Sell the car !!! Hopefully you bought it right! You have a bad taste with this car ! Perhaps you can find one with very little mileage and un altered like your exhaust ? I hope I am not being too harsh but I truly believe you will never be happy with this car

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