rickdew

Help!! I have a 2005 Mustang GT with a manual tranny. Recently, I'm having issues with hard, WOT acceleration. It feels like it's being starved for either air or fuel, but it is totally random and not repeatable. There was no clear event that started the problem, no major work on the car, etc.

I have the 4.6L 3V and have modified it with a C&L cold air intake, a throttle body spacer and a custom BamaChips ECM torque tune for 91 octane. I made all these modifications last July (2008), and it has been running like a scared rabbit for over a year. It pulled hard from about 2500 rpm all the way to redline in every gear, all the time. No change if it was 50 degrees or 95 degrees. Then, out of the blue, it started to stumble. Now, it randomly loses power under hard acceleration. It revs really hard and loud but doesn't make any power. There is no problem with backfiring, and it idles perfectly and smooth as silk. I've tried the following to address the issue:

Replaced air filter with new one
Replaced fuel filter with new one
Added one can Seafoam injector cleaner to one tank of fuel
Added one can of Techron to another tank of fuel
Checked for vacuum leaks, none discovered
Removed and cleaned MAF sensor and re-installed

It does seem to happen more frequently during straight line acceleration from a dead stop, and not as much when I accelerate hard coming out of a corner. Because of this, I'm thinking it's probably fuel related and not airflow issues, but it could also be spark related. I'm wondering about the following possible problems:

Sediment in fuel tank
Bad fuel pump
Bad fuel pressure relay
Bad spark plugs
Bad coils
Fuel rail blockage
Bad injector (one or multiple)
Bad O2 sensor
Bad EGR valve
Bad PCV valve
Bad MAF sensor
Others???

I have the capability to do data logging and capture on my SCT Flash Tuner, but I don't even know what to look for, and if I find something then how to determine if it's OK or way out of whack. I really don't want to spend $100 to put it on the diagnostic machine at the Ford dealer, but if I have to then I guess that's the next step. I'm trying all the inexpensive fixes first. I thought maybe some of the forum members that have experience with later model Mustangs might have some suggestions. Please respond to let me know you if you've experienced this, and pass on any wisdom you can offer, or forward it to another friend, member or other technical resource that might have some insight. Does anyone have any friends in the service sector that I could speak to and pick their brains? Thanks for your help. I look forward to your replies.

brunobluto

Your clutch could be worn out and slipping under hard acceleration. How many miles does it have?

modaddict

It is 90% either a fouled/burnt plug(s) or an 02 sensor going out. My guess is the plugs first. Change your spark plugs.

Nuke

Ignition or fuel delivery. Someone else just posted about what sounds like fuel starvation under load at high speeds. Anything unusual if you go WOT from 50 or 60?

Check plugs and COPS. If those are fine, check the injectors and fuel pump.

rickdew

The car has about 58K miles on it. I thought about a clutch issue, but no smell of burnt clutch, and I'm still getting good solid shifts. When this problem occurs, it almost feels like it's trying to downshift, as if it were an automatic transmission. The hesitation is sudden, and the revs get louder. But, it is completely random and not repeatable. It also happens when accelerating hard at speed, if I downshift or not. But when I'm driving at a constant speed, any speed, it's smooth as glass. And my mileage hasn't changed either. Still averaging about 20-21 mpg every tankful. Thanks for the advice so far. Would still like to talk to an automotive mechanic with experience on the 281 CID Mustang 3V engine as well, if anyone knows someone. If I change plugs, what does everyone recommend? Is it expensive to change the COP's? What does one cost? Thanx again.

Rick Dew

hammeron

this sounds like a slipping clutch as brunobluto
suspected.


if your plugs, ignition, cops, fuel, etc, check out fine......you
may need to consider the clutch.

2007VistaBlueGT

If the plugs, COP's where causing that it would throw a MIL. I'm leaning towards clutch too.

brunobluto

Yes, that is strange, but it feels like its trying to downshift and the revs get louder? I dont know but that sounds like a slipping clutch to me. Even if its random , it could be the early stage of wearing out and only slipping under extreme acceleration. As far as plugs, i dont know, i have'nt changed mine yet. It can be expensive to change out COPs. If you upgrade like i did and get the 60,000 volt COPs , a set will cost around 500.00. But you can find oem sets on ebay all day long for around a 100.00 or less.

Kurupt Kustoms

i say plugs....my car is notorious for this and it has always been the plugs...car has 22000 miles on it and 5 sets of plugs

graygt07

my car also had a problem that was about the same. some hesitation at WOP. I did have backfire but i am supercharged so more fuel it. I did not throw any codes and i changed the plugs. Runs like a champ now. my vote is the plugs