04 Merc in need of help

[04merc]

Having a problem with the car, it bucks or jerks, like its not getting enough fuel. But heres the kicker, its only after the car has shifted and when you apply light/ to mid throttle, but not enough to cause the car to downshift, it jerks...

But when I floor it, no problems at all! Nor are there an CEL's...

Again, feels like its related to fuel.

Car has the following mods,
JLT RAI
SCT Tune
373 Gears.
and 81k on the clock

not an aggressive tune. Just to correct speedo and to adjust shift points and torque converter lock up..

I removed the tune today, car ran worse than with the tune installed. Without it , car actually bucks at idle....

[stangracr]

Just a guess here, but are you sure it isnt torque convertor shudder? Lots of fords have this problem. It usually happens at light throttle after the car has shifted. I would suggest have the trans fluid flushed at your local ford dealer. It happens just as the convertor is going to lock up. I will just about bet ya it will be fixed with a fluid flush. I work at a local ford dealer.



ed

[ctrlraven]

Check your transmission fluid to start with lol. If it's any other car besides a nice cherry red I would have it flushed especially if you've never had one done since owning the car.

[4drpower]

AHHHHHH THE FAMOUS "TPS" SENSOR same thing happened to me before, well if you car sometimes runs out 1st gear longer or when your on the highway it randomly downshifts or something to that effect then thats what it is..

[Darrin]

I am going to suggest that it has a misfire under certain load conditions. I would start with the plugs and coil packs.

Darrin

[RF Overlord]

From your description of the problem, I initially thought that it sounds like torque converter clutch shudder.

Until I read this:
I removed the tune today...Without it , car actually bucks at idle....That's bizarre, or as we say up here in Boston: "bzah".

If you haven't changed the ATF in the last 30,000 miles, start by doing a complete fluid exchange...it needs it anyway even if that isn't the immediate problem.

[MitchB]

Start with the basics. Are there any stored DTCs in your computer?

Mitch

[Vortech347]

I agree with Mitch, use the SCT to check for codes. Then start with basic's.

Spark plugs, fuel filter, clean the MAF replace/check the TPS voltage, check the IAC make sure its working. You can do all of this for under 30$

I'm wondering if you got water down under the coil covers. You'll find out when you pull the plugs.

[Bradley G]

This was my experience with my 2002 GMQ LSE, there were tiny cracks in the spark insulators.
A couple of the coils were marginal but new plugs corrected the misfire under slight load.

I am going to suggest that it has a misfire under certain load conditions. I would start with the plugs and coil packs.

Darrin

[Marauderjack]

Also consider the solid connectors from Granatelli.....fixed mine!!:beer:

[Vortech347]

Who sells them now? I can't find them anywhere...

[4drpower]

run to a local auto parts store have the hook it up to the scanner.. dont know if there is an autozone near by they do it for free.. i had the same EXACT problems as yours and mine was the TPS sensor

[justbob]

My Escort does this exact same thing but only in fourth gear at smallest amount of throttle, also i've had two f-150's that did the exact same thing, sometimes shake you out of your seat. All three vehicles were/are stick. I never bothered to track this down but had a couple resources tell me the tps switch's can get flat spots and make the signal all screwy. Hope this helps. I will continue to just switch gears because i have no interest in putting a single cent into my work vehicles.

[BigCars4Ever]

Sounds like coils/boots to me too. Easy check. remove coil covers and look for water intrusion/rust/staining in the plug holes. You may even be able to see some arcing in the dark with the car idling in park.

[04merc]

Start with the basics. Are there any stored DTCs in your computer?

Mitch


Already did this with both the sct and a snap on Modis.
Nothing. Everything checks out. Was planning on moving on to the plugs/ coils, wanted to see what you guys thought.

[04merc]

no water in coils, spark plugs are perfect.
coils all checked out good.

cleaned the maf sensor, iac. car is alot more responsive, but still does the studdering at idle when given gas to move foward.

[mdskiing]

I am experiencing the same symptoms.....

Will start the hunt for the same cause!

[lucenti]

had a similar problem, light throttle =jerking full throttle ran fine. problem was caused by 2 weak coils. I don't recomend this testing procedure, but what I did was pull coil started car then watched spark as it grounded to an engine bolt, blue spark = good coil
orangish color or other than blue = weak coil. narrowed it to 2 coils, had extra coils, replaced 2 and problem solved. hopes this helps

[04merc]

AHHHHHH THE FAMOUS "TPS" SENSOR same thing happened to me before, well if you car sometimes runs out 1st gear longer or when your on the highway it randomly downshifts or something to that effect then thats what it is..


It's definately not the tps. Because I gave in the other day and just bought a new 1 and threw it on the car. Made no difference what so ever.
I just gonna throw a new set of platinum plugs, (gapped correctly of course) and keep switching around an extra set of coil packs I have left around from my long time sold 04 cobra