Can't push gas pedal more than half way...

[Shiroelex]

So, I'm driving my car a few days ago and everything was fine, until out of nowhere, everytime I would push the gas more than about halfway down, it sounds like I have a stutter box. The exhaust seems to get louder right under me, and it's an even, consistent loud GRRRRRRR noise. Not like an uneven backfire or anything goofy, just almost sounds like I'm sitting on a 2 step at the light waiting to go. It stops when I let off the gas. If I drive the car without going more than half pedal, it runs and drives fine. If I free-rev the car, it's definitely apparent if I mash the pedal down. If I slowly bring the RPM up, it all sounds normal, even past half pedal. It really seems to be bad under load.


I've replaced the injectors, plugs, MAF, checked and cleaned all of my Accel COPs, put octane booster and topped off my 1/4 tank that was left with fresh 93 octane, unloaded my tune and tried it, and even reset the ECU. I did the octane booster and gas mostly because that last tank was from BP, and who knows how much ocean water is in my tank now, although the car should have been acting up as soon as I filled it up. That tank of gas ran fine all the way until just above a quarter tank left.


I'm stumped on this one. Could it be the fuel pump going? It seems to run and drive just fine if I don't really push it. There's no CEL or anything. Any ideas?

 

[trombonedemon]

So, I'm driving my car a few days ago and everything was fine, until out of nowhere, everytime I would push the gas more than about halfway down, it sounds like I have a stutter box. The exhaust seems to get louder right under me, and it's an even, consistent loud GRRRRRRR noise. Not like an uneven backfire or anything goofy, just almost sounds like I'm sitting on a 2 step at the light waiting to go. It stops when I let off the gas. If I drive the car without going more than half pedal, it runs and drives fine. If I free-rev the car, it's definitely apparent if I mash the pedal down. If I slowly bring the RPM up, it all sounds normal, even past half pedal. It really seems to be bad under load.


I've replaced the injectors, plugs, MAF, checked and cleaned all of my Accel COPs, put octane booster and topped off my 1/4 tank that was left with fresh 93 octane, unloaded my tune and tried it, and even reset the ECU. I did the octane booster and gas mostly because that last tank was from BP, and who knows how much ocean water is in my tank now, although the car should have been acting up as soon as I filled it up. That tank of gas ran fine all the way until just above a quarter tank left.


I'm stumped on this one. Could it be the fuel pump going? It seems to run and drive just fine if I don't really push it. There's no CEL or anything. Any ideas?

Fuel Pump, had a class mate whom of which had a Ford Probe and when it got down to a 1/4 of tank it started to shutter underload. Change your Fuel Pump and Fuel Filter.

 

[sneaky98gt]

I don't really have anything technical to say, but the fuel pump very easily could be the culprit. It certainly makes sense: it can support the fuel needed so long as the car isn't under a load, but when it's under a load (i.e. needs more fuel), it starts giving you trouble. Makes sense. Especially since you have already replaced everything else that could cause this problem (injectors, MAF, COPs, etc).

If you replace the pump, go ahead and get a SVT Focus pump. It is a direct drop in, and will support plenty of future horsepower. You can find them pretty cheap, too (<$100).

 

[Shiroelex]

I was afraid someone would suggest the pump, after I JUST filled it up.
I suppose the good news to this is that I work as a mechanic at an auto parts warehouse and can get a Focus pump for really cheap. Does it matter what year pump I get? 02-04 is the only year range we have listed.

 

[trombonedemon]

I was afraid someone would suggest the pump, after I JUST filled it up.
I suppose the good news to this is that I work as a mechanic at an auto parts warehouse and can get a Focus pump for really cheap. Does it matter what year pump I get? 02-04 is the only year range we have listed.

Those should be fine. But to make sure, see if a cheap brand you have is only for a specific year between the 99-04, if the brand can be used for all of those years, then you have your answer.

 

[Shiroelex]

Ok, an update. I just got done putting in my new SVT Focus pump, as well as both new fuel socks, and a new Motorcraft fuel filter. I filled up again with 93, and even added some octane booster. It's STILL doing the same thing. Very smooth off idle and when not under a load, but as soon as you give it any pedal if it's under load, it makes that loud exhaust GRRRRRRRR and doesn't really go much faster. Any more ideas? Here's what's been done.

New plugs. NGK Iridiums
New COPs
New MAF
New Injectors
New SVT Focus Fuel Pump and fuel socks
New Motorcraft Fuel Filter
Fresh tank of 93
Untuned the car and ran it
Retuned the car and ran it



I'm stumped on this one. It's really driving me crazy.

 

[midnightdriver]

Could be some problem between the fuel pump and the engine like a cracked line allowing air into your system.

Or what about a vacuum leak ?

What about the O2 sensors, dirty of damage the engine will not run right under load.

Hope that gives you some direction

 

[trombonedemon]

You need some gauges, if you don't already have some, vacum gauge and fuel pressure gauge. Also you need to see what stats your car is giving.
I put my intake spacer gasket on the wrong side of the spacer and got the same symptom you have. If I had a vacum gauge I wouldn't have spent an hour trying to figure out what was wrong my car.
Any codes by the way?

 

[Shiroelex]

You need some gauges, if you don't already have some, vacum gauge and fuel pressure gauge. Also you need to see what stats your car is giving.
I put my intake spacer gasket on the wrong side of the spacer and got the same symptom you have. If I had a vacum gauge I wouldn't have spent an hour trying to figure out what was wrong my car.
Any codes by the way?

Nope. I can run a datalog with my X3, I suppose. I do have a few random gauges that I've collected over the years. I think one might be a boost gauge. Here's one thing to consider.... When I was removing one of my COPs, the little copper bushing that the hold down bolt threaded into was just spinning when I tried to remove the bolt. It ended up coming out with the bolt itself. I don't hear any air leaking there, however.

 

[nyuk98gt]

Shiroelex:

TPS? Datalogging will show you a lot. You can log throttle position (relative and absolute) to see the TPS working (or not).

Did you make the tune (SCT's Advantage/Pro Racer software)? You might check the MAF function to confirm that it slopes up at ALL points.

HTH,

Chris

 

[Shiroelex]

Shiroelex:

TPS? Datalogging will show you a lot. You can log throttle position (relative and absolute) to see the TPS working (or not).

Did you make the tune (SCT's Advantage/Pro Racer software)? You might check the MAF function to confirm that it slopes up at ALL points.

HTH,

Chris

I didn't make the tunes myself; I bought the tuner with 3 custom tunes from LaSota Racing in Ohio. They sent me a CD with the tunes on it as well, and I even re-loaded my tuner with them and reuploaded that, and it still didn't work. One weird thing to mention, I always had my TCS button unplugged, since I got tired of seeing the light. I plugged it back in after I tried my stock tune, and the light was on but wouldn't turn off. I've got to reinstall Windows on my laptop before I can do any good datalogging. Will probably do that tomorrow. In the meantime, I will grab a TPS.

 

[Shiroelex]

Well, she's FINALLY all better. After a miserable day at work, I decided to install the new Motorcraft TPS, as well as swap my Accel coils out for the essentially brand new Motorcrafts I had laying around. After dicking around with those stupid TPS screws for two and a half hours, I got the new TPS installed. Still ran like crap. After swapping out the coils, she runs like a million bucks. I can't believe TWO sets of Accel COPs had one half-bad coil. Never got a check engine light or anything, and they ran great when not under load. I guess you get what you pay for. Looks like MSD for me!

 

[flstang65]

I have heard lots of problems about the Accel ones and GMS ones. I would stick with the stock COP's IMHO.

 

[nyuk98gt]

Shiroelex:

Glad to hear you got your car running well. Sorry for steering you towards a TPS when it was not the root cause of the problem (blush, blush).

Chris

 

[mrvax]

TPS?

 

[nyuk98gt]

mrvax:

LOLOL! Yes, I think about "The Office" every time I see "TPS" in a Mustang thread. But, it is supposed to be "throttle position sensor" in this thread.

Have you seen my stapler? I specifically said, "No salt!".

Chris

 

[Shiroelex]

Shiroelex:

Glad to hear you got your car running well. Sorry for steering you towards a TPS when it was not the root cause of the problem (blush, blush).

Chris

Oh, the inside plastic of my TPS where it holds onto the throttle blade pin was all chewed up. I still consider it an improvement, so thanks for the suggestion in the first place