Engine not running well, need help - Ford Mustang Forum
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post #1 of 12 (permalink) Old 12-09-2019 Thread Starter
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Engine not running well, need help

Hello all, I have a 2005 GT and I’ve been having a problem with it running badly occasionally as of late. I’m a delivery driver so my car is constantly being started and turned off, and whenever it has been warmed up and then sits for 10-15 minutes and I start it back up, the engine runs rough and I’m not sure what would cause that. I’ve cleaned out the throttle body which seemed to help for a few days but then the issue came back, I cleaned the MAF at the same time as the throttle body, and I also changed the fuel filter which helped for a few days before it returned to its shuddering. It never happens on a cold start and the misfire or rough run stops once I give it some gas, even if I just rev to 2.5k or so in neutral and doesn’t start again until it sits for a few minutes and the I start it back up. I’ve heard it may be a vacuum leak but have no idea how to check for that or where all the vacuum lines are to check them all. It could be the electronic IAC but I would think that would also affect it when idling at stoplights and stuff but it never runs bad except for on the start up. It also hasn’t thrown any codes. Spark plugs are only about 8 months old and I haven’t checked them to see if they’re blackened or anything yet but I would imagine it wouldn’t be them and my coils seem to be in good shape though they’re old. Does anyone have any ideas on what I can look for/fix and also how to look for it if it’s a more complicated process? Thanks in advance for any help and sorry for the novel lol

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post #2 of 12 (permalink) Old 12-10-2019
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The 05-09 wasn't designed to be a delivery car. Get a Toyota for that!!
I can't even begin to tell you how much my stomach churns to read crap like this.
It's equivalent to animal abuse!!!

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post #3 of 12 (permalink) Old 12-10-2019
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It's pretty simple. Your 4.6 V8 is not comfortable with your delivery schedule. Your motor is acting reasonably compared to your expectations.

08 GT 5spd
Spectra CAI, Comp Cam Detroit Rockers, Kooks headers w/catted H-pipe, Revolution Automotive dyno tuned, FB430 race mufflers, 3.55s, JLT catch can, BMR Lca's and relo brackets. Prothane motor mounts and sway bar bushings.
20% tint, smoked markers and tail lights w/sequentials. Clear front signal covers, series 3 chin spoiler.
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post #4 of 12 (permalink) Old 12-10-2019
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Lol. On a serious note, I have been chasing a similar issue after installing my long tubes. The O2 sensors just don't want to fully "wake up" on a hot engine restart after a 5~10 minute off period sending fuel trims through the roof (+65!) for the first minute or 2+. The O2 voltages hover around 0~2 millivolts and then will pop up to 450~500 millivolts before they begin switching normally. This will sometimes pan out faster if I give it a bit of throttle or just start driving. Its as if the heater circuit doesn't work once the engine is hot. So far I've installed 2 new sets of O2's (first pair were aftermarket NTK and 2nd set are Motorcraft(NTK). Only a few times has it ever set a "slow response" code. I use the Torque Pro app with a bluetooth OBD2 transmitter to monitor live data. I've also sent data logs to the tuners capturing this behavior. So if you have access or know someone with access to a scanner that will display live data, try to see if your O2 sensors are "waking up" properly on a hot engine restart.

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post #5 of 12 (permalink) Old 12-10-2019
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You dodn't say how many miles are on it,,, but I assume well over 100,000 if you recently changed the spark plugs. My thought is that the fuel injectors may be dirty? and not sealing properly, allowing fuel to leak into the cylinders. Something you may try the next time you have to restart the car like you described, before you turn the key, put the gas pedal to the floor. then try to start. Doing that prevents the fuel pump from operating, and would allow the engine to clear out a flooded condition.

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post #6 of 12 (permalink) Old 12-10-2019 Thread Starter
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It’s currently at about 124,5xx miles and I replaced the old spark plugs at around 115,000. Also yes I know it’s not the ideal delivery car lmao but it’s my only car for at least a few more weeks. I didn’t plan on delivering in it when I bought it a little over a year ago but my old job sucked and I make more as a driver so I took the chance when I had it. Someone mentioned clogged injectors, I did run some injector cleaner through but didn’t notice any difference with that. I’m not sure really how else to check them, I am a backyard mechanic and am learning to fix these things as they continue to break and I’ve never dealt with those so any advice on how to check them would be great. Thanks for all of your help already.
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post #7 of 12 (permalink) Old 12-10-2019 Thread Starter
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One more thing I forgot to mention, I did try to turn the key to the run position a few times before actually starting the car when I knew I would have this issue as to let the fuel pump prime and it seems like when I do that the issue isn’t happening, is it possible that the pump wouldn’t be pressurizing the fuel system enough that it’s causing this issue? I can test the fuel pressure sometime soon, my brother in law said he knows how to do that but neither of us were sure if that was a possible cause so we haven’t gone and done it yet.
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post #8 of 12 (permalink) Old 12-11-2019
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It could be poor fuel pressure.
You have an 05 GT.
Ford had a lot of kinks to work out since they debuted the 4.6 mustang in 05.
Lousy pressure may be one of them but I've never heard that hear.
My wife works for the local school district and doesn't travel far. She uses our V8 pickup. It doesn't even begin to warm up by the time she gets to work. We've had fuel delivery problems with it.
My point is, take it out and blow the carbon out of it!! Run a V8 like it's meant to be run.
Maybe that's all it takes.
Good luck, keep us posted.

08 GT 5spd
Spectra CAI, Comp Cam Detroit Rockers, Kooks headers w/catted H-pipe, Revolution Automotive dyno tuned, FB430 race mufflers, 3.55s, JLT catch can, BMR Lca's and relo brackets. Prothane motor mounts and sway bar bushings.
20% tint, smoked markers and tail lights w/sequentials. Clear front signal covers, series 3 chin spoiler.
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post #9 of 12 (permalink) Old 12-11-2019 Thread Starter
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I have done a few full throttle pulls and I do have my fun with it I just have to do it out of town and off the clock so I’m not tempted to do it while I’m delivering lol. If it is that though I would think the driving I have done would’ve blown the carbon out already. I also noticed yesterday when I went and started it to go to work(cold start) it idled super high until it warmed up, I.e. close to 1500rpm until I started going and it warmed all the way up and went back down to the normal 750ish range. I watched a video online last night saying that could be a big vacuum leak. Are there any very prone areas that you know of I could check to make sure that isn’t an issue? If it’s as simple as replacing a hose or something I can get that done easy but I’m completely unfamiliar with vacuum lines and where to find all of them so I wouldn’t even know where to start.
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Quote:
Originally Posted by Tjcob View Post
Hello all, I have a 2005 GT and I’ve been having a problem with it running badly occasionally as of late. I’m a delivery driver so my car is constantly being started and turned off, and whenever it has been warmed up and then sits for 10-15 minutes and I start it back up, the engine runs rough and I’m not sure what would cause that. I’ve cleaned out the throttle body which seemed to help for a few days but then the issue came back, I cleaned the MAF at the same time as the throttle body, and I also changed the fuel filter which helped for a few days before it returned to its shuddering. It never happens on a cold start and the misfire or rough run stops once I give it some gas, even if I just rev to 2.5k or so in neutral and doesn’t start again until it sits for a few minutes and the I start it back up. I’ve heard it may be a vacuum leak but have no idea how to check for that or where all the vacuum lines are to check them all. It could be the electronic IAC but I would think that would also affect it when idling at stoplights and stuff but it never runs bad except for on the start up. It also hasn’t thrown any codes. Spark plugs are only about 8 months old and I haven’t checked them to see if they’re blackened or anything yet but I would imagine it wouldn’t be them and my coils seem to be in good shape though they’re old. Does anyone have any ideas on what I can look for/fix and also how to look for it if it’s a more complicated process? Thanks in advance for any help and sorry for the novel lol
i have 05 gt i would run rough, stall , stumble, clear up run nice, some time go for week, ect, no codes dealer had it for 3 week never fix anything,i did all the thing you have said, drove the car or my wife did it hers, three month finley the TPS throw code R&R tps, it has run good since, its a lot longer story,
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Quote:
Originally Posted by Tjcob View Post
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It sounds like you have two unrelated problems.
Firstly it seems that you have a faulty fuel pump check valve that's causing a rapid loss of fuel pressure after you switch off the engine. The telltale sign is when the engine starts and runs fine after you've left the ignition key in the ON position for a few seconds before starting, as this allows enough time for the fuel pump to prime the system and build pressure.
Secondly, you may indeed have a vacuum leak. Inspect every hose that comes off the intake manifold plus the hose from the intake pipe to the passenger side valve cover.


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post #12 of 12 (permalink) Old 12-12-2019 Thread Starter
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Thanks for the advice Bullitt, I’ll check out the hoses for a vacuum leak and see what I can find. Is a faulty check valve relatively easy to get to/replace? I.e. a rather inexperienced DIYer like myself could handle or is that something I probably shouldn’t be touching? Or would I even need to replace it? Are there potential fixes to that issue without having to go as far as getting a replacement part?
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