Sputtering/loss of power
 

My 99 m6 SS is having an ongoing sputtering problem.. So far I have replaced MAP sensor, MAF sensor, checked for any vacuum leaks and found small one coming from intake manifold and fixed that.. replaced 3 out of 4 02 sensors because they were throwing codes and looked shot. the only thing that has helped was replacing the 02 sensors. it sputters less and regained some power but still isn't at its full potential.. The car ran absolutely perfect all until I did an oil change. I used full synthetic 5-30 so I don't know what could have gone wrong. the car has 2.5 pic heads, ms4 cam, headers , fast 92mm 44lb. injectors and 320l fuel pump. PLEASE ANY ADVICE HELPS I'm all out of advice and really want to get this thing running good again.

I don't see how the oil change had anything to do with it, unless you touched/disturbed something else in the process - maybe even by accident.

Which O2 sensor did you still not replace? If it's a front one, I'd go ahead and just replace it too. The rear ones can be completely disregarded, they only monitor the cats and won't have any effect on this condition. And are you still getting any O2 codes since having replaced the sensors? Might be worth taking a look at the wires for these as well.

Have you checked fuel pressure? Have you checked the injectors for resistance (ohms) to see if one is particularly different? Have you looked at fuel trims via a scanner to see if any cells are highly elevated (of course, since you have internal engine work, readings here may or may not indicate a problem depending on the quality of your tune - i.e. the numbers might be high due to a poor tune rather than a broken component). Have you looked at misfires via a scanner? All of this various data might help.

Also, you mentioned a vacuum leak that you found and fixed. Is there any chance that this vacuum leak was present when the car was tuned? If so, then the tune may no longer be ideal now that the leak is fixed (hence the continued issues, even though you replaced the O2 sensors that were throwing codes and may have been the initial cause.) It's also possible that certain DTCs were turned off during the tune, so there may be something wrong that isn't tripping a code due to this.

Is it throwing any more codes?

I did have a vacuum leak when I got the tune .. but once the car was tuned it ran good, then all of a sudden it didn't. the front driver side 02 sensor I didn't replace because the mechanic said it "wasn't needed". I currently have a flashing check engine code, it sometimes reads TP sensor and then doesn't read anything at all but TP sensor is brand new (just replaced). Is it possible a leaking injector could cause a sputter?

I did have a vacuum leak when I got the tune .. but once the car was tuned it ran good, then all of a sudden it didn't. the front driver side 02 sensor I didn't replace because the mechanic said it "wasn't needed". I currently have a flashing check engine code, it sometimes reads TP sensor and then doesn't read anything at all but TP sensor is brand new (just replaced). Is it possible a leaking injector could cause a sputter?

Good place to start is to have someone test the fuel pressures. What codes(the numbers) are you getting? Even though you replaced the TPS<if that what you mean by TP you could still have issues with that circuit or even the new sensor. Best to test it driving and see what the data is.

The flashing SES means you have a significant misfire, which could be due to any number of causes. But, there should be at least one cylinder specific misfire code if the light is flashing (meaning, a P0300 + a P030x, x = cylinder in question). So I'd scan for that.

And you have the TPS code happening, so something could be up there. If the sensor is new, then I image that the old one was doing the same thing (or did you replace it for some other reason?) Have you checked the wiring and connection for the sensor?

Still would be a good idea to look at fuel pressure and LTFTs, as mentioned above. But I'd also focus on that cylinder specific misfire code(s) (which should be present with a flashing SES) to narrow this down to a specific bank or possibly the cylinder itself. Look for elevated LTFTs on that bank, etc., plus see if it's on the same side that still has the old O2 sensor. Could be due to the injector on that cylinder, or a plug/plug wire or coil, or could be a fueling issue on that bank. That TPS issue also needs to be sorted out. You might be dealing with more than one issue here.

If the car was tuned with the vacuum leak, then a retune with everything buttoned up might net you some gains. But obviously that alone isn't the current issue if the problem was happening with and without the leak fixed.

Thank you for the help. I will start with checking the connection to the TPS as well as checking for cylinder misfire/ injectors. I will get back ASAP to let you know if the problems is fixed or continues. THANKS AGAIN!

flashing check engine light means there is a specific cylinder misfiring. You need to get it on a scanner and check the real time data to see what cylinder is misfiring then start moving components like the plug wire/coil/plug/injector one at a time and re scan to see if the misfire moves to a different cylinder.

Might want to check Knock Sensors too. Early LS1's are famous for getting water in them...

thank you all!!

I also have an exhaust leak.. could this be causing the sputter ??

Is the exhaust leak near or before a front O2 sensor (like at the collector or a header gasket)? This might cause LTFTs to be off, but would have to be a pretty profound leak to cause such skewed fuel trims that serious misfires would be the result.

I'm still trying to find the exact leak spot but it sounds like its coming from either the Riverside header gasket or somewhere on the dribverside header/ y pipe connecrtion,.. ill get more info for you in a bit

and a bad knock sensor would create a sputter? they are quite pricy to replace.

flashing check engine light
 

I know a flashing check engine light refers to a cylinder misfire, however when I scanned it, no codes popped up. I also checked each cylinder 1 by 1 and it seems all cylinders are good. if anyone has any idea what this could be please give me some suggestions, Thanks in advance.

One of the knock sensors failed on my '00 car, and it didn't cause any driveability issues at all - just an SES light. But, I guess there could be more than one failure mode for this.

I don't see how that light could be flashing without a code present for misfires, unless the scanner is bad, or you somehow cleared the MIL prior to reading the codes, or some sort of modification was performed to misfire reports in the tune. When the SES light isn't flashing, does it just stay on solid or does it not show up at all?

Checked each cylinder 1 by 1 means what? Did you look at each plug to see if one was wet with gas or oil and maybe not firing? Cracked plug? How are your wires? All good, new or old, pull one at a time to see if the engine changes and gets worse or doesn't change?

Because to me the flashing SES light still points to a cylinder not firing. Plug, wire, coil. Are all of the electrical connections to the coils plugged it right.

I have no explanation for why a flashing SES light does not set a code pointing to one or more cylinders.

I told you above where to start. I'm going to look into my crystal ball and bet you have some type of fuel system problem. Maybe rust or water in the injector screens or worse. Have it scanned while driving and watch the fuel trims and o2s while its sputtering. Data is your friend.