Need Help on Identifying Misfires
08-03-2008, 12:19 PM
#1
Need Help on Identifying Misfires **UPDATE - Problem Solved! It was a plugged catalytic converter! See my last post.
OK, I'm about ready to shoot this thing! I need some help trying to tackle a massive misfire problem under a load. Here's the rundown: 2001 Trans Am. Original motor exploded due to valve spring failure. Replaced with a 2004 LS6 block, LS6 heads (milled .020), Mahle forged -6cc pistons, SCAT H-Beam rods, SCAT 4" crank, Comp Cam 224/230, .610/.605" 114 LSA cam, stock intake and injectors. G-Force loaded a 383 tune, but didn't fix the problem.
I am getting P0300 and flashing SES light. I know this means a misfire and fuel dumping into cats.
The question is why. Plugs (NGK TR55's) were black on passenger bank, fairly normal on driver's bank. So, I replaced O2 sensor on the passenger bank this morning - no changes. Previously have switched coil banks, put stock wires back on, put new plugs in (NGK TR55 platinum), still no change.
Read about crank relearn. Possible problem with the crank crankshaft? G-Force said that it would have throw a code if the crank needed a relearn. True? Another thread mentioned crank position sensor. Can engine still runs with a bad one? How about the cam position sensor?
Also, did a compression check yesterday. Results: cylinders 1, 3, 5, & 7 all had around 210 pounds. Cylinders 2 &4 - 200lbs, 6 - 195lbs, 8 - 180lbs. Now, would cylinders 6 & 8 be bad enough to cause a misfire?
Please help! Can't figure this out! If anyone local has a Tech II or other scanning tool, I would be greatful for some help! Thanks!
Brian
OK, I'm about ready to shoot this thing! I need some help trying to tackle a massive misfire problem under a load. Here's the rundown: 2001 Trans Am. Original motor exploded due to valve spring failure. Replaced with a 2004 LS6 block, LS6 heads (milled .020), Mahle forged -6cc pistons, SCAT H-Beam rods, SCAT 4" crank, Comp Cam 224/230, .610/.605" 114 LSA cam, stock intake and injectors. G-Force loaded a 383 tune, but didn't fix the problem.
I am getting P0300 and flashing SES light. I know this means a misfire and fuel dumping into cats.
The question is why. Plugs (NGK TR55's) were black on passenger bank, fairly normal on driver's bank. So, I replaced O2 sensor on the passenger bank this morning - no changes. Previously have switched coil banks, put stock wires back on, put new plugs in (NGK TR55 platinum), still no change.
Read about crank relearn. Possible problem with the crank crankshaft? G-Force said that it would have throw a code if the crank needed a relearn. True? Another thread mentioned crank position sensor. Can engine still runs with a bad one? How about the cam position sensor?
Also, did a compression check yesterday. Results: cylinders 1, 3, 5, & 7 all had around 210 pounds. Cylinders 2 &4 - 200lbs, 6 - 195lbs, 8 - 180lbs. Now, would cylinders 6 & 8 be bad enough to cause a misfire?
Please help! Can't figure this out! If anyone local has a Tech II or other scanning tool, I would be greatful for some help! Thanks!
Brian
Last edited by BAD2000TA; 11-29-2008 at 09:40 AM.
08-03-2008, 12:53 PM
#2
Are you using tuning software to read the location of the misfires?? That would be a good first step. Not just know what the SES light means but where the actual misfires are happening. If you dont have EFIlive or HPtuners and are just using a handheld to scan codes you need to go to a shop or buy software to diagnose. Otherwise your just guessing and this isnt an old school sbc where there is only so many things to replace and then you stumble across the part that fixes it.
Lot of guys in Houston on here, try the local texas section for help. Someone might be close with software that can help. OR give Gforce a call, they work with some of our customers down there.
Lot of guys in Houston on here, try the local texas section for help. Someone might be close with software that can help. OR give Gforce a call, they work with some of our customers down there.
08-03-2008, 03:38 PM
#3
it is not dumping raw fuel into the cats, a flashing SES light means its a random misfire and the injectors are shut off to the affected cylinders when it sees a misfire. if it were a certian cylinder, your code would be P030X. X being the number of the misfiring cylinder. ex, P0301 is a misfire on number 1 cylinder. my guess its a fuel or air related issue, or plug wires perhaps. do a fuel pressure test, make sure your not losing fuel pressure. i would say if you changed the entire rotating assembly and top end, you would have eleminated any issues with combustion, unless your short block or heads were installed/built incorrectly.
08-03-2008, 05:48 PM
#4
Sounds reasonable. Here's the latest: I pulled the valve covers and noticed that all the valves are in the closed position. Only a few look like that have any pressure from the cam/lifters/rocker arm. When cranking over, they seem to pump up, but immediately collapse - like within 2-4 seconds to the closed valve. Should the lifters bleed down that quickly? Could this be my problem? Does it sound feasible that the valves just aren't opening enough and this is causing the misfire? I'm about ready to pull the heads and replace the lifters. Please advise!! Thanks!!
08-11-2008, 01:12 PM
#5
OK, I replaced the plugs three times - no change. I've replaced the crank position sensor - no change. I went to G-Force this morning. Mike did the crank re-learn - no change. Swapped a coil pack on the passenger side - no change. The passenger bank is clearly the side that's having a problem. All the plugs are showing black on the passenger side, normal on the driver's side. So, I tried changing the O2 sensor - still no change. So, what else can it be? I'm down to:
Bad PCM?
Bad Lifters?
Dead cylinder?
PCM: Anyway to test if it's bad?
Lifters: I can change, but would they be bad enough to cause the problems?
Dead cylinder: Did a compression check on all cylinders. Driver's bank - all 210 pounds. Passenger bank: 2 &4: 200 pounds, 6: 195 pounds, 8: 180 pounds. OK, 6 & 8 are low, but are they low enough to cause a massive misfire? How can I test??
Need help!!!!
Bad PCM?
Bad Lifters?
Dead cylinder?
PCM: Anyway to test if it's bad?
Lifters: I can change, but would they be bad enough to cause the problems?
Dead cylinder: Did a compression check on all cylinders. Driver's bank - all 210 pounds. Passenger bank: 2 &4: 200 pounds, 6: 195 pounds, 8: 180 pounds. OK, 6 & 8 are low, but are they low enough to cause a massive misfire? How can I test??
Need help!!!!
08-13-2008, 01:08 PM
#7
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if stock stroke why load a stroker tune? Also any parts reused like the cam? Since you milled the heads was the PR leanth checked? But the fuel being dumped into one side, You think a bad injector? mabey cracked not holding press? and just sticking open? Oh wait- you said all on that side fuel washed. Mabey the other side not working right and that side trying to compensate?
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08-13-2008, 01:11 PM
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If you're able to scan, find out what the difference (either 02 voltage, or LTFT's) is between bank one and two. Since there's no bank to bank control in the actual program, the only think that can make one bank richer than the other is an 02 sensor. A few things that might cause that would be:
1) leak in the exhaust, causing the 02 sensor to read lean.
2) bad 02 extension wire, or bad wiring all together to one of the 02 Sensors. I'd Ohm test the wires to be sure.
I think you need to find out why one bank is running rich before you can find out the cause of the misfire.
The other thing to consider is based on what you mentioned about the valves not opening. If and exhaust valved wasn't opening properly this would definitely be considered a misfire. If the intake valve wasn't opening, then there's now way that the cylinder could fire.
1) leak in the exhaust, causing the 02 sensor to read lean.
2) bad 02 extension wire, or bad wiring all together to one of the 02 Sensors. I'd Ohm test the wires to be sure.
I think you need to find out why one bank is running rich before you can find out the cause of the misfire.
The other thing to consider is based on what you mentioned about the valves not opening. If and exhaust valved wasn't opening properly this would definitely be considered a misfire. If the intake valve wasn't opening, then there's now way that the cylinder could fire.
Last edited by Tuner@Straightline; 08-13-2008 at 09:07 PM. Reason: Correction
08-13-2008, 01:17 PM
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That is what I was thinking about a valve not opening. A cam profile worn-or lifter not pumping up. But wouldnt the ls lifters make a noise if they have failed? like the other chevy engines?
08-13-2008, 01:27 PM
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You said your car has been doing this pretty much since you got a new engine? After the old self detonated? I guess my point is cam/crank timing off-coils not wired in correct positions-
08-13-2008, 04:19 PM
#11
if stock stroke why load a stroker tune? Also any parts reused like the cam? Since you milled the heads was the PR leanth checked? But the fuel being dumped into one side, You think a bad injector? mabey cracked not holding press? and just sticking open? Oh wait- you said all on that side fuel washed. Mabey the other side not working right and that side trying to compensate?
Will try to inspect the injectors on the passenger bank.
08-13-2008, 08:21 PM
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Sorry bout that. I saw elsewhere that you did have a stroker. Not going into changing any sensors without a test on them with a multimeter. But you finding a loose injector connector is good in a way, Wish I could help look with a second set of eyes/ears to find your gremlins.
08-13-2008, 08:42 PM
#14
If you're able to scan, find out what the difference (either 02 voltage, or LTFT's) is between bank one and two. Since there's no bank to bank control in the actual program, the only think that can make one bank richer than the other is an 02 sensor. A few things that might cause that would be:
1) leak in the exhaust, causing the 02 sensor to read lean.
2) bad 02 extension wire, or bad wiring all together to one of the 02 Sensors. I'd Ohm test the wires to be sure.
I think you need to find out why one bank is running rich before you can find out the cause of the misfire.
The way the car caluclates misfires is by the 02 sensor. They VCM knows when a given cylinder is firing, and it expects a voltage increase from the 02 sensor within a certain amount of time of the event. If the voltage doesn't increase, it figures that the cylinder didn't fire.
The other thing to consider is based on what you mentioned about the valves not opening. If and exhaust valved wasn't opening properly this would definitely be considered a misfire. If the intake valve wasn't opening, then there's now way that the cylinder could fire.
1) leak in the exhaust, causing the 02 sensor to read lean.
2) bad 02 extension wire, or bad wiring all together to one of the 02 Sensors. I'd Ohm test the wires to be sure.
I think you need to find out why one bank is running rich before you can find out the cause of the misfire.
The way the car caluclates misfires is by the 02 sensor. They VCM knows when a given cylinder is firing, and it expects a voltage increase from the 02 sensor within a certain amount of time of the event. If the voltage doesn't increase, it figures that the cylinder didn't fire.
The other thing to consider is based on what you mentioned about the valves not opening. If and exhaust valved wasn't opening properly this would definitely be considered a misfire. If the intake valve wasn't opening, then there's now way that the cylinder could fire.
Yeah, I'm going to have to disagree with you on that one. Misfires are counted through the CKP, but thats neither here nor there. The missing cylinder has to be identified and diagnostics pursued from there. If it is an entire bank missing, it should be pursued as such. Bottom line: identify the faulty cylinder through scan tool data by whatever means possible.
08-13-2008, 09:07 PM
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Yeah, I'm going to have to disagree with you on that one. Misfires are counted through the CKP, but thats neither here nor there. The missing cylinder has to be identified and diagnostics pursued from there. If it is an entire bank missing, it should be pursued as such. Bottom line: identify the faulty cylinder through scan tool data by whatever means possible.
08-14-2008, 12:17 PM
#16
Yeah, I'm going to have to disagree with you on that one. Misfires are counted through the CKP, but thats neither here nor there. The missing cylinder has to be identified and diagnostics pursued from there. If it is an entire bank missing, it should be pursued as such. Bottom line: identify the faulty cylinder through scan tool data by whatever means possible.
08-14-2008, 12:58 PM
#17
No, it will not. Use a loaded spark tester like an ST-125 on it and make sure you have hot spark. If that isn't an issue try doing an injector balance test which can be done through the tech 2. It almost sounds to me like you are not fueling on 6, and the ECM of course sees that as lean and is overcompensating. Can you take a snapshot and email it?
09-04-2008, 12:48 PM
#18
No, it will not. Use a loaded spark tester like an ST-125 on it and make sure you have hot spark. If that isn't an issue try doing an injector balance test which can be done through the tech 2. It almost sounds to me like you are not fueling on 6, and the ECM of course sees that as lean and is overcompensating. Can you take a snapshot and email it?
Also, what scanner besides a Tech II can do an injector balance test?
11-29-2008, 09:34 AM
#19
**UPDATE - Problem Solved!! Well, I finally found out what the problem was: plugged catalytic converter on the passenger side. I pulled the Y-pipe off, fired the car up and there was no flow at all. Remove the cat, gutted the interior, re-installed and fired it up again. Success!!
This was without-a-doubt, the most frustrating problem I've ever had with a car!! I'm just glad I finally could figure it out!!
This was without-a-doubt, the most frustrating problem I've ever had with a car!! I'm just glad I finally could figure it out!!
