Significant HP loss

[macoulombe]

I posted before about a 96 Mustang Cobra I recently purchased with a high idle issue among others. After having my car serviced, I found out that my cats are complete toast. I also had to replace my SC belt and tensioner. After the belt/tensioner replacement, my car dynoed at ~255 rwhp. This is with the 10lb pulley and Anderson powerpipe. I ordered a Magnaflow catted x-pipe (emissions) but am wondering if that would be the cause for a high idle and significant power loss? Here is the dyno sheet.

This is a great way to learn how to perform auto maintenance but I feel as though I might have gotten myself in too deep

As always, I welcome suggestions from the wealth of information you all have. I may not have responded much but I have read many forum threads and gained what I feel like is a lot of knowledge.
Here is a pic. Still a good looking car with a powerful sound...just not a whole lot of go

Thanks for your help!!

 

[COBRA90GT]

The catted Magnaflow X-pipe is among the best flowing X pipes out there - it certainly isn't restricting power output.

Are you only making 255rwhp WITH a supercharger?

I would run a compression and leakdown test. What kind of chip/tune?

Have you tried contacting the previous owner to see what kind of issues it was having (or any dynosheets)?

 

[SVT98Snake]

wow....255 is a stock number...and I mean stock.

sounds like you have bad blowby. how s your oil consumption? And what kind of dyno was that? Mustang dyno or a dynojet????

Also...you should be around 400-430 rwhp

 

[macoulombe]

The X-pipe should arrive by this weekend so the toasted cats are one the Cobra now.

YES....the 255 rwhp is with the Vortech V2 supercharger installed

The oil consumption has been very minimal. I just had the oil changed and put in Mobil1 synthetic. Nothing bad was noted with the removed oil (contaminants, color).

I do not know if the dyno was, dyno vs dynojet. The performance shop said the tune was pretty good and they did not note any blowby issues, assuming it should be somewhat obvious if it occurred.

Is a compression and leakdown test something I can do or does it involve a dyno and technical expertise?

I have a can of SeaFoam and an instruction PDF to clean the IMRC. That should help my idle issue and perhaps regain some performance.

I do recall the performance shop saying that when they dynoed the car, my exhaust had separated due to the back pressure. I only hope it is a simple as replacing my x-pipe.

Thanks Cobra90GT and SVT98Snake for your response. I am going to communicate with the prior owner and see what he will offer up on issues with car.

 

[SVT98Snake]

no prob.

leakdown tests are easy, but time consuming. You will need a compression tester, which you may be able to rent.

That kind of back pressure sounds dangerous. I am not sure what is causing it.

Seafom works good, I have read up about it, just don't get your hopes up and expect it to give you 50 hp.

Good luck!

 

[cobrachu]

Try cleaning out the iac for your high idle prob. I recently cleaned mine out with intake cleaner. My car was idling at about 2000 rpm. I took off the iac and I could see the gunk in it. I read that k&n filters attribute to the problem because they are coated with oil. Try it it wont hurt anything. I only have 30k miles on my cobra and the valve was full of crap.

 

[macoulombe]

I am going to install the new Magnaflow x-pipe this Sunday. I will let you know if that made a big difference or not on my HP loss.

After reading this thread http://forums.stangnet.com/showthread.php?t=421991 on AIC cleaning, I will likely just replace mine as well. $60 seems reasonable if it helps my idle. I hate using the gears to keep my idle down.

The excitement never ends with the maintenance of Mustangs. This is my 3rd Mustang and I have put enough into them to make a decent down payment on a home

 

[macoulombe]

The X-pipe quieted the car a little and improved driveability some but still have issues. The IAC install did not fix my idle issue. I treated the gas then the crankcase with SeaFoam and I did not see any smoke like someone did in a video post.
I am going to rebuild the engine but I have to know for curiosity reasons about my idle. When I was in stop and go traffic today, every time I accelerated, my RPMs went up to 2000 and would stay there until the car came to a complete stop. Even when rolling in nuetral. Once at a complete stop, it would take 3-5 seconds for the idle to come down to 1100 RPM. I am going to get a retune performed but I don't understand why it is doing this? I would think that while not in a gear and rolling, that there would be no demand on the engine and it would idle again.
I don't care if I get any recommendations for cams in my shortblock buildup post if I can get this figured out. Thanks for the help!!

Edit: I also noted that when turning on the dash air vents (cool air, heat or AC), my idle goes up to 2300-2500 RPM.

 

[edbo]

The X-pipe quieted the car a little and improved driveability some but still have issues. The IAC install did not fix my idle issue. I treated the gas then the crankcase with SeaFoam and I did not see any smoke like someone did in a video post.
I am going to rebuild the engine but I have to know for curiosity reasons about my idle. When I was in stop and go traffic today, every time I accelerated, my RPMs went up to 2000 and would stay there until the car came to a complete stop. Even when rolling in nuetral. Once at a complete stop, it would take 3-5 seconds for the idle to come down to 1100 RPM. I am going to get a retune performed but I don't understand why it is doing this? I would think that while not in a gear and rolling, that there would be no demand on the engine and it would idle again.
I don't care if I get any recommendations for cams in my shortblock buildup post if I can get this figured out. Thanks for the help!!

Edit: I also noted that when turning on the dash air vents (cool air, heat or AC), my idle goes up to 2300-2500 RPM.

When you ran the SeaFoam, did you suck it into motor and kill it, let it stand about 15-20 minutes or so then restart? I did this to my '98 last week, although there was no noticeable smoke when the stuff was going in (through PCV hose), it sure smoked like a chimney after I got it started some 20 minutes later!

I had a problem with my IMRC's on my Cobra. I would be cruising and all of a sudden the car would like fall off a cliff on power. I could barely climb a hill despite running a Vortech V-trim when it was 'acting up'. Then, all of a sudden, the problem would disappear and I'd be back up on power.

I ran the SeaFoam and it didn't immediately cure the problem, although the problem seems to happening less often. I took my car to Tim at Modular Powerhouse for a trim and had mentioned the problem I was encountering. On the dyno, the problem resurfaced during one of the runs and Tim determined it was the IMRCs. He said that they tend to get pretty dirty and the best way to clean them is to totally remove the manifold and clean them directly. If they continue to cause a problem, acquire a "Delete Kit" for them. I hear they're about $500 which is cheaper than trying to replace the faulty IMRC controller/etc.

I had originally thought the problem was with my MAF sensor as it cleared once after cleaning my MAF sensor out. I would at least try to clean it really good, especially if you're running a K&N or oil-based, cotton filter. You should be getting much more power than that. I'm pushing 15lbs boost, but on 30lb injectors and an inadequate fuel pump and still way over 400HP. I would think you should be in the 350-400 neighborhood at the least. Good luck in getting that beast to wake up!

 

[hotpony]

Sounds like a pretty good vaccum leak to me, check all vaccum lines, sometimes you can spray a little carb cleaner on them if you suspect one is leaking, if the idle raises when you spray, then it's a leak. Listening for the vaccum leak is probably going to be your best bet, but sometimes you can't hear them as they may be covered by a plastic casing. What's your vaccum look like on your boost gauge at idle? How much boost is it peaking at? The IMRC's are a pain in the arse, and with a blower you will be safe with an IMRC delete kit.. You can make one yourself if you have the willingness to pull them apart and make it work, it can save you a pretty penny as Edbo stated above, I don't think they're quite that much but you can find them on Corral.net or Stangnet.com Classified sections a lot of the time....

Looking at your dyno sheet I'd suspect that there is some issues with the IMRC's because there is a huge dip 3500-4200RPM which is right where they are supposed to open anyways.. And like Edbo also stated, taking the intake off and cleaning them directly is the only way to get them working flawlessly, but even still, for how long? Even though the IMRC's are an issue, I don't think it's your only one, and without a fuel/air ratio graph it's hard to say what it is.. If your cats were toast that usually means you were running pretty darn rich, which would definitely toss fuel into the Cats, and since they stay super hot (that's their purpose), the fuel would catalyze on them and burn them up. I'd be willing to bet your fuel mixture is too rich, which could also be the cause of your high idle (excessive fuel in the combustion chambers)..

The compression check would be a good idea, however I don't think your Cobra is due for a rebuild.. Start with the tuning and go from there.. We'll get ya up and running!!! Supercharged Cobras do cost a bunch to get tuned right but once they're good, they're a blast.. Let me know if you need more advice, I'm here to help

 

[macoulombe]

Hotpony,
I had researched what I could from the net and a vague Hanes manual but could not find anything on troubleshooting the IMRC's. I had sprayed ether all around the upper intake, hoses, ect without any change of idle. I also paid a local ford garage to troubleshoot/fix this problem and drove away after having narrowed it down to a likely vaccum leak unresolved. The idle did change significantly (~900 rpm) when I disconnected the air vent line from the base of the IAC. As mentioned earlier, the IAC is new. All hose fittings are on securely.
My boost gauge usually sits at -20 psi and on hard acceleration, goes up to 5-7 psi. As for the tuning, I wanted to get a pretuned hand held tuner (Excalibrator II) however, I was told that tunes can not be made for supercharged Cobra applications. I have otherwise had some trouble finding a tuning shop in CT and time.
I appreciate your suggestions and I will look at the tuning again and those damn IMRC's. Thanks.

 

[cold96snake]

I'm betting that a rich A/F burned your cats and O2 sensors and put you in limp mode.

ps I've got a 8lb pulley and a power pipe and see 10lbs, 434hp, 377tq.

 

[blackfang]

Personally with that many issues I would drop some coin and take the car to MPH and get it fixed right!

 

[hotpony]

It's possible that may have sent you into limp mode but I'd think there'd be a check engine light on if that was the case. Among the IMRC's being an issue for you, the A/F is also looking to be a culprit. Are you using an FMU? The IMRC's probably won't be in the Hayne's manual because it's not in my Chilton manual either, however if you just follow the steps of removing your upper/lower intake manifold they just rest under the lower intake. The controller unit is mounted to the bottom of the lower intake manifold so before you go pickup the lower intake make sure you unbolt this, think it's like four 8mm bolts. The ****tiest part about removing the lower intake is that you have to drain some of the cooling system and disconnect the fuel rails. You can take the fuel rails off if you have the tool but I just took the 4 bolts out that hold the rail to the lower intake, lifted the injectors out carefully as not to ruin any of the o-rings and then rotated the entire fuel rail w/ injectors off to the side and out of the way.

Just let me know if you're using an FMU and if you have a fuel pressure gauge, if so, what's it read at idle and WOT?

 

[blackfang]

Limp mode? What is that? I have never heard of that. I have heard of open and closed loop.

 

[macoulombe]

I understand what is implied by limp mode and could not agree more. I do not believe there is an installed FMU. I looked at some graphics online and did not see anything under the hood resembling an FMU. Cold96snake, yes the cats were toasted as were 2 of the O2 sensors. Replacement of both components made the car run a little smoother but solved nothing. I downloaded a PDF with step by step instructions for removing the IMRC's. I do not have a fuel pressure gauge, just boost and oil pressure which does not budge. The engine has eaten its second pulley tensioner and belt. This would have been a great car for some of you "do-it yourselfers" but sucks for the novice. I suppose when all is done I will have accumulated enough maintenance instructions to contribute to an auto maintenance archive perhaps in the distant future for similar circumstances. Thanks for the help.

 

[hotpony]

haha, well that's one way of looking at it! Who installed the supercharger? Shop? Previous owner? If there is no FMU, and that is a possibility, I've run an S-trim at 13lbs of boost on just 42lb injectors with an adjustable fuel pressure regulator at 41psi (idle, vaccum on). Run's super rich but ran good. Did they give you an A/F read out with that dyno sheet? That's probably the best way to cancel that idea out, if not then you might need to get a gauge and see what kinda fuel pressure you're looking at. Who knows if they changed the fuel pump and fpr also? Shoot, there might even be a chip installed in the PCM already causing all this nonsense?! Take a look, it's in the passenger side kick panel.

 

[macoulombe]

The supercharger was installed by the previous owner at Modular Powerhouse Racing in Marietta, GA. I contacted Vortech and they said the Supercharger was sold as a tuner kit (no programming and no fuel management). The kick panel has what looks like a stock chip with LLX4 imprinted on it. Here is my AF read out:

This is what makes this site so awesome. I feel like I am making more progress towards a fix with this forum than bringing my car to the local mechanics!

 

[hotpony]

Car's running really rich, you said it's got a chip in there? There's a slot on the back side of the ECU, should have some ford tape on it or something that says VOID, something like that, if there's a module in there it has a chip, if not then it doesn't. The huge spike makes me think that it could be something to do with the the FMU as it probably has one with a A/F looking like that. You can see first off it's really choppy like the fuel pump is having a hard time supplying the injectors, so check to see what kind of fuel system you got going there, you want a 255lph in-tank and a T-Rex 255lph external at the least, there is some nice Aeromotive ones as well but big bucks! If you got an FMU get rid of that thing and get it tuned the right way!

 

[blackfang]

The supercharger was installed by the previous owner at Modular Powerhouse Racing in Marietta, GA. I contacted Vortech and they said the Supercharger was sold as a tuner kit (no programming and no fuel management). The kick panel has what looks like a stock chip with LLX4 imprinted on it. Here is my AF read out:

This is what makes this site so awesome. I feel like I am making more progress towards a fix with this forum than bringing my car to the local mechanics!

I would contact Tim and see what info he can provide. I bet that was sold as a Mongoose kit that MPH offers and the prior owner messed with it before he sold it. Tim doesnt send out messed up cars. They pride themselves on 600+ 4V's