SES light flashing like a misfire at high speed?? Please help
12-16-2007, 03:04 PM
#1
SES light flashing like a misfire at high speed?? Please help Ok, here is the scoop. 2 weekends ago I changed the driver side spark plugs and wires on my 99 Z28. I drove the car for en entire week and the highway and around town and no problems. Last weekend I changed the passenger side spark plugs and wires with the same friend. He lives a few miles away and on the drive home I got on the interstate and punched it and ran it up to 85 mph or so. About 10 secs after I did this the SES light started flashing indicating a misfire but the car ran fine. Still had plenty of power and no missing, hesitation or anything. I figured we had done something when we installed the plugs so I pulled the coilpack and plug wires back off of the passenger side when I got home. This time when I pulled the coilpack off of the passenger side I happend to notice that the back coil pack had all kinds of gunk and goo that was orange colored all over the little post that sticks out of the coilpack. I cleaned it up as much as I could with some electrical cleaner and threw it all back together. I have been driving the car now for like 4 days with no trouble and no flashing SES light.
Yesterday same scenario I get on the freeway kinda quickly and run it up to 75 or so and SES light starts flashing again but again the car runs fine and seems to have lost no power. I just bought a code scanner thinking that it would tell me what cylinder is misfiring but it just tells me that a misfire is present. Is there anyway to tell which cylinder is misfiring? I am thinking it is because of that one coil pack that is all gunked up but I don't really want to just buy a new coilpack unless I am very very sure.
After some messing around with it today too I noticed that it only does it on the freeway at speeds like 70 mph or above when I am accelerating. If I let off the accelerator or drop down below 65 mph it stops flashing. The whole time though the car never runs bad and never seems to lose power. What is going on here? Should I replace that coilpack or is there a way to tell for sure which cylinder is misfiring? Any help here is appreciated. Thanks!!
Yesterday same scenario I get on the freeway kinda quickly and run it up to 75 or so and SES light starts flashing again but again the car runs fine and seems to have lost no power. I just bought a code scanner thinking that it would tell me what cylinder is misfiring but it just tells me that a misfire is present. Is there anyway to tell which cylinder is misfiring? I am thinking it is because of that one coil pack that is all gunked up but I don't really want to just buy a new coilpack unless I am very very sure.
After some messing around with it today too I noticed that it only does it on the freeway at speeds like 70 mph or above when I am accelerating. If I let off the accelerator or drop down below 65 mph it stops flashing. The whole time though the car never runs bad and never seems to lose power. What is going on here? Should I replace that coilpack or is there a way to tell for sure which cylinder is misfiring? Any help here is appreciated. Thanks!!
12-17-2007, 12:57 AM
#2
What DTC is it? A code scanner is only going to give you DTCs, but a good scan tool will actually allow you to monitor individual sensors in real time. AutoTap does 24 at a time. Is it P0300? That's most common. Check spark plug wires. Are they touching ground? Are the plug wires well seated at the plug and at the coil pack. Watch the engine in your garage at nite with the lites off for signs of arcing and listen for ticking which will also happen if you have a short to ground.
12-17-2007, 05:28 AM
#4
Tech2 costs $2,500 and isn't widely available, except maybe on some place like Ebay. Tech2 has a 1"X3" black and white LCD display. My laptop has a 15" full color display. My AutoTap does ALL domestic brands in Generic and Enhanced as well as foreign Generic. Tech2 only does GM. My Flashscan has bi-directional controls like Tech2. I think I'll stick with AutoTap and Flashscan. Tech2 can't even monitor 24 pids as a time let alone display them side by side. Vetronics has a lot of work to do.
12-17-2007, 09:38 AM
#5
What DTC is it? A code scanner is only going to give you DTCs, but a good scan tool will actually allow you to monitor individual sensors in real time. AutoTap does 24 at a time. Is it P0300? That's most common. Check spark plug wires. Are they touching ground? Are the plug wires well seated at the plug and at the coil pack. Watch the engine in your garage at nite with the lites off for signs of arcing and listen for ticking which will also happen if you have a short to ground.
12-17-2007, 04:38 PM
#6
P0300 is random, while P0301,2,3,4,etc. are cylinder specific. Cam swaps cause P0300 and cold weather(it is Dec.) can do it too when your engine idles rough until it warms up if you're running a big aftermarket cam. DTCs due to aftermarket cams will soon reset themselves once it gets warmer. The engine can shiver just like people do when they are cold and the ECM interpreprets that as random misfires. Other things can cause P0300 too. Your DTC is random not cylinder specific. That another way of saying it's COMMON to all 8 cylinders. Look for something common to ALL 8, not orange gunk on one cylinder. What is in common? Bank 1 is not in common to Bank 2. From the air intake to where the intake manifold enters the heads is common. Once they split they are no longer in common. Autotap.com, OBDii.com, OBD2.com. If you have a laptop this is the way to go. 15" color screen instead of a tiny black and white LCD on a handheld like a Tech2 which costs nearly $3,000.00.
12-17-2007, 05:22 PM
#7
The thing I guess I am having trouble with is why does speed seem to be involved. Like I said it only does it at 70 mph on the freeway while cruising. I can drop down to 30 mph and go that speed all day long and it never comes on. The car is turning the same rpm's at 30 mph in 2nd gear as it does in 4th gear at 70 mph so why does it not flash unless I am going 70 mph.
I dont think its cold related. The day I drove the car home from my friends house 1 week ago it was 76 degrees outside here in virginia and it was flashing on the freeway at 70 mph.
I dont think its cold related. The day I drove the car home from my friends house 1 week ago it was 76 degrees outside here in virginia and it was flashing on the freeway at 70 mph.
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12-17-2007, 05:47 PM
#8
"Flashing" SES is different from the "ON" SES. When it flashes your over the 1.5 times the FTP and you are about to do catalytic converter damage according to the EPA. You need to be able to watch you LTFTS and STFTs as well as Bank 1 and 2 pre-cat O2s while driving at 70mph. You need a good scan tool for that not a code reader.
12-17-2007, 07:40 PM
#9
"Flashing" SES is different from the "ON" SES. When it flashes your over the 1.5 times the FTP and you are about to do catalytic converter damage according to the EPA. You need to be able to watch you LTFTS and STFTs as well as Bank 1 and 2 pre-cat O2s while driving at 70mph. You need a good scan tool for that not a code reader.
12-18-2007, 06:00 AM
#10
No, it doesn't necessarily mean a misfire altho it could. FTP is Federal Tail Pipe standard. Another EPA term. EPA says if your emissions get so bad that you could damage your catalytic converters the SES must "Flash". Before you reach the point of damage it just turns "ON" and stays "ON". "Flash" means go to the dearler right now. "ON" means you can wait a while.
01-15-2008, 11:54 AM
#11
Finally got this problem solved. This is just for people who may have a simliar issue in the future. The problem ended up being that my buddy who did the changes for me in the computer did not do a CASE relearn after he flashed the tune. I guess on the A4 cars this is more vital because of the extra weight of the converter being on the flywheel while it is turning can cause the diagnostic system to think there is a misfire when there really is not. Hopefully this helps more people in the future.
01-15-2008, 12:46 PM
#12
No, it doesn't necessarily mean a misfire altho it could. FTP is Federal Tail Pipe standard. Another EPA term. EPA says if your emissions get so bad that you could damage your catalytic converters the SES must "Flash". Before you reach the point of damage it just turns "ON" and stays "ON". "Flash" means go to the dearler right now. "ON" means you can wait a while.
not saying you're wrong.. it's just odd =p
