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Discussion Starter #1
I've been having driveability issues with my 1999 Mustang GT since I purchased it in 2005, and over 2 engines. It regularly bogs down, and runs flat, with a lack of torque. It has never misfired. Some days it will run decent, but not great. When the engine warms up it will get worse. I have checked just about everything, including having the cats cut off and looking for a clog.

When the engine is idling, if I hit the throttle quickly, any more than about half throttle, there is a 1 to 1.5 second delay before the throttle does anything. During this delay, I hear a brief sucking sound through the air filter before the revs increase.
It's been doing this since the beginning, and I'm convinced it is the cause of most of my issues. I have not seen any other mustangs act like this, and I'm fairly certain, once I solve it, the car will drive like new. FWIW, the current engine is out of a 2002. The PCM is the original 1999.

Any Ideas?
 

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Start with the simple things.

Clean the throttle body. Clean the MAF. The fact that it seems intermittent have you changed plug wires and have a newer cap and rotor? Make sure there are no cracks in the distributor cap and base.

You didn't mention any codes but has the check engine light ever come on?
 

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Discussion Starter #3
Intermittent isn't really the best description. It always happens eventually, once it warms up. Occasionally it's better for the first 10 miles or so. Sometimes it starts right out of the parking lot. It seems to continually get worse the longer the engine runs. I haven't taken any long trips in a while, so I can't say what it would do after an hour or so.

I'm running relatively new NGK Iridium plugs. This is a 99 GT, so it has Coil-On-Plugs, and no Wires/Cap/Rotor, etc....

MAF has been cleaned recently. I've been afraid to clean the TB because so many products can strip the anti-stick coating on it. Removing the intake hose, I don't see any excess carbon through the throttle plate.

The only engine code I've ever received is "Catalyst Efficiency Below Threshold".
The car came with rear o2 simulators on it. They quickly failed, and the original dealer replaced them with o2's. It was shortly after this that the car slowly began to run worse. From time to time the above code would display, and I would quickly erase it. After installing Hooker MaxFlows, it hasn't come back. FWIW I have a high flow catted X-Pipe. Unsure of the brand. I finally gave in and ordered a pair of o2 simulators. Will see if they do the trick.
 

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You're referring to MIL eliminators. They aren't the source of your problem, though. The rear O2 sensors only monitor the catalytic converters to ensure they are working properly.

If you've already cleaned the MAF and checked plugs, and you're not getting a miss, then you might want to start looking for a vaccuum leak somewhere.
 

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Also, I'm not a total car-guru, but I'm throwing some ideas out there...
Do you think it could be a fuel issue?
Depress the schrader valve on the fuel rails. Fuel should come out of there. If it doesn't then you're not getting enough fuel pressure.
 

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probably a pcm issue if the same problem crosses from engine to engine and you have the same pcm, not a pro by any means but this seams a logical place to start the trouble shooting,:winks
 

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Basically you have a fuel or fire problem. You say it doesn't miss fire just sluggish performance. So to start w/ easy things:

1. Remove throttle body, get all gaskets needed, clean using CRC throttle body cleaner. Remove the IAC, and TPS, remove all carbon from them, a pipe cleaner will help get into those small holes. Don't be afraid-take a pic first, draw a diagram, whatever first-label it for replacement.

2. Check the gap on your plugs and look at the color for problems w/air-fuel-fowling. Perform Ohms test on coils and insulators-they are a large source of these problems.

3. Check using a light mist of soapy water on your vacuum lines for a leak. Rev. throttle for different rpm ranges because you have an under load, while driving-and static, while idling. Also check to see if you apply or take away any accesories,a/c,defrost,if things change.

4. Install fuel pressure gage, you have to different pressures,startup(cranking) and while driving(under load)

5. If your O2's failed, they usuallly fail in a closed loop(always talking to the computer). This is done so the computer see a lean condition and dumps extra fuel. If not, you would have a lean condition and major detonation problem.

6. As previously posted, make sure the right PCM came w/ that engine. You can't cross "brains". If the engine is a different year model, the pcm associated will be different. If yours is OEM then and eng came out of different optioned vehicle or year, this may be the cause-it won't re-learn through key or rpm cycles.
 

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Check the TBP sensor make sure it has the correct volatge and sweeps correctly. I know you said the same problem spans a few engines, have you used the same TBP sensor from engine to engine.
 

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Discussion Starter #10
Thanks for the replies. Somehow I stopped being notified of responses.

Also, I'm not a total car-guru, but I'm throwing some ideas out there...
Do you think it could be a fuel issue?
Depress the schrader valve on the fuel rails. Fuel should come out of there. If it doesn't then you're not getting enough fuel pressure.
Fuel should be good. A friend has a snap-on scanner. He checked fuel pressure during a 30 minute drive and it seemed ok.

probably a pcm issue if the same problem crosses from engine to engine and you have the same pcm, not a pro by any means but this seams a logical place to start the trouble shooting,:winks
I have always suspected this. If it comes down to it I'll just buy a Bama tuner. I've been emailing them and it seems I can disable the PATS system immediately after hooking up the 2002 computer. If I don't have to pay the outrageous dealer fees to swap the PCM out that makes the tuner worth it.

Basically you have a fuel or fire problem. You say it doesn't miss fire just sluggish performance. So to start w/ easy things:

1. Remove throttle body, get all gaskets needed, clean using CRC throttle body cleaner. Remove the IAC, and TPS, remove all carbon from them, a pipe cleaner will help get into those small holes. Don't be afraid-take a pic first, draw a diagram, whatever first-label it for replacement.

2. Check the gap on your plugs and look at the color for problems w/air-fuel-fowling. Perform Ohms test on coils and insulators-they are a large source of these problems.

3. Check using a light mist of soapy water on your vacuum lines for a leak. Rev. throttle for different rpm ranges because you have an under load, while driving-and static, while idling. Also check to see if you apply or take away any accesories,a/c,defrost,if things change.

4. Install fuel pressure gage, you have to different pressures,startup(cranking) and while driving(under load)

5. If your O2's failed, they usuallly fail in a closed loop(always talking to the computer). This is done so the computer see a lean condition and dumps extra fuel. If not, you would have a lean condition and major detonation problem.

6. As previously posted, make sure the right PCM came w/ that engine. You can't cross "brains". If the engine is a different year model, the pcm associated will be different. If yours is OEM then and eng came out of different optioned vehicle or year, this may be the cause-it won't re-learn through key or rpm cycles.
1. It seems I cracked the intake trying to change the temp sensor, so I will clean all of that while swapping it.

2. Plugs are relatively new NGK Iridium. I gapped them properly. Haven't pulled them recently to check color though.

3. I have done the spray test from time to time and never noticed an idle change.

4. As replied to sillyrabbit, fuel should be ok.

5. So it's probably not o2's then. I already bought the MIL eliminators, though, so I might as well throw them on.

6. Back to my original suspect. Before buying the engine, I made sure it was from a similarly optioned vehicle. GT, Manual, etc... It may not have been enough. If I can convince myself to spend $379, I'll probably just order the BAMA tuner, and install and disable PATS on the 2002 PCM.


Check the TBP sensor make sure it has the correct volatge and sweeps correctly. I know you said the same problem spans a few engines, have you used the same TBP sensor from engine to engine.
TBP sensor?

Here is a video (watch in HD!) demonstrating the original problem:
Again I've never seen this delay on another mustang.

http://www.youtube.com/watch?v=ahymj1ejvnA
 

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Check your TPS sensor. The sucking sound you hear...thats air being pulled through (normal).

The lack of performance could be possible because the computer is not advancing the timing and changing the fuel curve...all of this is determined by the TPS sensor. I went through 3 of them before mine was resolved. I changed every sensor on the car. When I did some data logging with my livewire and making a lot of datalogs with different parameters being measured is when I seen that the TPS had a dead spot in it. This would trigger a default setting in the PCU that would make it look at a "back-up" file for timing advanced and fuel map.

A real easy way to help point to this direction is to hook up a wideband A/F meter and see if you are running lean when you are driving and go 1/2 or full throttle.
:bigthumbsup
 

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Discussion Starter #12
Check your TPS sensor. The sucking sound you hear...thats air being pulled through (normal).

The lack of performance could be possible because the computer is not advancing the timing and changing the fuel curve...all of this is determined by the TPS sensor. I went through 3 of them before mine was resolved. I changed every sensor on the car. When I did some data logging with my livewire and making a lot of datalogs with different parameters being measured is when I seen that the TPS had a dead spot in it. This would trigger a default setting in the PCU that would make it look at a "back-up" file for timing advanced and fuel map.

A real easy way to help point to this direction is to hook up a wideband A/F meter and see if you are running lean when you are driving and go 1/2 or full throttle.
:bigthumbsup
The sucking sound doesn't bother me, it's the delay between pressing the pedal (moving the linkage), and the change in RPM. This doesn't seem normal to me. You may have to hook up better speakers/headphones if it's not obvious.

The previous engine ran very similar right up until it started knocking, so I didn't think the TPS would have had anything to do with it. The replacement engine was complete with all top end electronics. I didn't swap anything other than the injectors (while troubleshooting). IMO it would have to be something that stayed on the car between the two engines. That said, I work at an auto parts store, so I will go ahead and try changing it. Is there any trick to replacing it. Any calibration needed, etc..?

I have an ELMScan interface around here somewhere. If I can find it, I'll hook up my laptop and monitor the TPS as well.
 

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if you can get the car over to Tampa I can hook you up with my tuner, he can fix any mod motor issue...PM me if you are interested.
 
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