Yes, I've searched..

I have an 04 GT with around 70k. coils, plugs and wires changed and CAT gutted at 60k and starter changed at 65k.

Recently, when taking off in first (6-speed) it will spudder real fast until it gets to about 10mph. It wont do this in any other gears and only does this when starting off from zero.

I know the fuel is good. Never idles bad, dies, etc.

Im thinking maybe the fuel pump but it only wants to act up when taking off..
What do you guys think?

 

How does it start when hot? vs when cold?

 

Starts fine on both. I havent trying running it cold yet since it just started a couple days ago.

 

Do you have a vacuum leak? (you can check it with OBD2 live data, if you have a bluetooth adapter)

 

yes, Ive torque for android too. Should this work? its not throwing any lights?

 

yes to the bluetooth. I know nothing about a leak

 

Most problems will never throw a CEL. Too many people rely on the CEL to tell them if something is wrong, when the most critical and expensive failures have no CEL code associated with them, and plenty more common ones aren't even something the ECU is monitoring.

You can identify a vacuum leak by letting the engine get up to operating temp and looking at the MAF values and fuel trims. If the combined long term + short term is +5% or more, and the MAF is under 5g/s, then you have a vacuum leak.

If the fuel trims are all over the place, reset them and then check again.

If those are all fine, then watch actual and commanded AFRs when you are accelerating and experiencing the stumble. See if your AFRs are going crazy.

 

So, now i am having some trouble on starts. It wants to have a hard time starting when the engine is cold. Also when its cold it spudders much harder into much higher RPS. I included the logs (these are while the engine was warm). Seems the AFR is pretty steady while the MAF is all over the place. I went and got some carborator cleaner to see if I can find a vacuum leak, spraying around the filter box, accordion tube, etc. but I'm not entirely sure where all the vacuum lines are.

 

judging by the logs, you guys think this is a vacuum leak?

 

Taking the potato out of the tailpipe might stop the "spud"ering.

Try logging these parameters .....

 

Okay I attached the log, it's in .csv file that can open in excel. As you can see its idling below 1k and it's gotten worse i believe. Today i tried red-lining it and it stoped around 7k and the check engine light started flashing, throwing P0301: Cylinder 1 misfire.

 

can you post something we can see on here please

 

The problem consists. I believe its much worse when the engine is still cold. I found that if I rev past 2k before i let off the clutch it's much less likely to sputter.

He's a video of the rough start it's doing:

And here's a video of it sputtering at high RPMs

*sorry for the video quality, its hard to shift and hold a camera.

I also attached pictures of the logs.
Any help would be insanely appreciated.

 

A few comments:
- Your logs tell us nothing about a vacuum leak, because they aren't showing an extended period of idling. You keep playing with the throttle and it makes it very hard to read. Let the car idle warm and sit there for a good minute after a fan cycles, and then log at least 4 seconds of idling without you touching anything. MAF, RPM, short term fuel trim, and long term fuel trim are needed to determine a vacuum leak, and you can't be playing with the throttle when it happens.

- In your first video, you neutral reved and the coolant light turned on briefly. I would suspect that you have something wrong with your cooling system, since that can happen with a blockage or pressure leak. One of the possible failure points is a coolant seal failure in the engine, which can easily manifest as difficulty starting when cold followed by stumbling at idle.

- A vacuum leak will NEVER cause any problem starting. Because a vacuum leak by definition means air that is getting to the engine that isn't being accounted for by the MAF. The MAF isn't in use until the engine is already started, so a vacuum leak can stall an engine immediately after starting, but can't lengthen the start to begin with.

- Your 2nd video started stumbling at the same time you started misfiring. I could see that from the flashing CEL, which is ALWAYS a misfire. When was the last time that you pulled and inspected your spark plugs? Have you tested your coils / wires with a coil tester?


So far, I strongly suspect that you have a coolant seal failure that is draining coolant into the engine when the engine is off, creating a hostile combustion environment until the coolant is swept out, as well as fouling the spark plugs. This in turn is causing further idle problems, further stumbling. At high RPM, the combustion pressure into the cooling system could be forcing coolant into the engine, disrupting spark, causing misfires.

Let the car sit overnight, then with the gas pedal to the floor to cut fuel, crank the engine for 2 seconds. Then pull the spark plugs and inspect them. If you find coolant on them, it confirms my theory. If the plugs are bone dry, then it disproves it (for now), but it will still give you an idea if you have failing ignition instead.

 

I didnt realize a CEL was always a misfire. I'll check the plugs tomorrow.

I attached a log of it just idling. As you can see, it's over over the place, at 34 it almost dies.

 

as for the coolant light, it's been sporadically coming on well before this problem started so I figured it was just a bad sensor.

 

Correction to your statement: a FLASHING CEL is always a misfire. A solid CEL could be one or more of 118 different codes. Only misfires will make it flash though.



That log looks horrific. MAF at idle, even a high idle, should NEVER top 10g/s. Have you cleaned the MAF? If you did, what chemical did you use? With that log, I'm starting to lean toward a filthy MAF or a failing MAF. It's recording a whole lot more air entering the engine than the engine will use at idle, which the AFRs are showing understandably lean as a result, with a huge positive fuel trim trying to keep it in check.

Go buy a can of MAF cleaner at the local auto parts store.

Then disconnect the negative of your battery. Leaving it off, remove the MAF and hose it down carefully with the MAF cleaner, let it dry, hose it down again thoroughly. Let it dry.

Reinstall the MAF

Reconnect the negative of your battery.

Let the car idle warm, and idle for at least 5 minutes

Then pull another idle log and see where you are at.

 

never been cleaned. I'll grab some cleaner tomorrow and report back. Thanks man.

 

I have at least 1 more alternate theory, depending on how it responds to the MAF cleaning, but i'll get into that once we know what happens.

 

I grabbed some MAF cleaner and sprayed it down pretty well. I got off work pretty late today so I didnt get to pull the plugs today. Still idling low but it seems like it was a little more steady. Still misfiring bad. Check out the log

 

I just noticed your MAF values are in cfm, not g/s.

Ok, you have a vacuum leak.

Converted to g/s, you have 4.11g/s (33cfm) to 4.61g/s (37cfm) at a hot idle with positive fuel trims. That is classic vacuum leak. Basically, the engine uses about 5.5g/s of airflow at a hot idle, period. It doesn't care where it gets the air from. If some of that air is getting to the engine and NOT passing the MAF, then the MAF will read lower, as yours is, and only fuel for that lower MAF rate. So in this case it's only fueling for 4.1-4.6g/s, but the engine is still pulling ~5.5g/s. The O2 sensor will see this extra ~1.2g/s of airflow as a lean condition however, so it will be adding fuel in the fuel trimming to try to get the AFRs to where they should be.

Find that vacuum leak, reset the fuel trims again, and then see where you are at.

Check both ends of every vacuum line, check the service port nipple caps on the lower intake manifold, check the clamps on the accordion. If you can't find it visually, it may be worth taking the car to a shop to have the intake smoke tested, which will leak out smoke from where the leak is to pinpoint it.

 

Also : check the SSV shaft for wear (by grabbing it and moving it up and down)...........