misfire under load
09-05-2017, 10:36 AM
#1
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misfire under load
I have a 94 Camaro lt1 383 stroker with the 6 speed manual and I can't get this misfire figured out. My TPS is set at .59v at idle. It idles great. But when taking of at a stop sign, it will backfire through the intake. It also does it when the rpms are under 2000 and under a load. I can't use 6 gear because of this. It has all new plugs and wires and a new cap and rotor for the opti. Also if I'm idling and snap the throttle quick, it will pop through the intake. I have checked for vacuum leaks and bad plug wires. Everything looks good. It's driving me nuts! I've done some data logging and that shows me everything is good. So confused
09-05-2017, 02:41 PM
#2
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Re: misfire under load
Can you share a .csv file of your data log? Glad to take a look at it for you. Second set of eyes might be a help. What data logging software are you using?
Would seem you can't have a backfire through the intake unless there is an intake valve open when a spark plug fires on that cylinder. Plug wires and new distributor cap would seem to have limited the possibility of cross-firing, carbon tracking, etc. How about a mechanical problem, valves adjusted too tight, sticky valve, etc.?
Would seem you can't have a backfire through the intake unless there is an intake valve open when a spark plug fires on that cylinder. Plug wires and new distributor cap would seem to have limited the possibility of cross-firing, carbon tracking, etc. How about a mechanical problem, valves adjusted too tight, sticky valve, etc.?
09-05-2017, 04:49 PM
#3
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Re: misfire under load
Can you share a .csv file of your data log? Glad to take a look at it for you. Second set of eyes might be a help. What data logging software are you using?
Would seem you can't have a backfire through the intake unless there is an intake valve open when a spark plug fires on that cylinder. Plug wires and new distributor cap would seem to have limited the possibility of cross-firing, carbon tracking, etc. How about a mechanical problem, valves adjusted too tight, sticky valve, etc.?
Would seem you can't have a backfire through the intake unless there is an intake valve open when a spark plug fires on that cylinder. Plug wires and new distributor cap would seem to have limited the possibility of cross-firing, carbon tracking, etc. How about a mechanical problem, valves adjusted too tight, sticky valve, etc.?
09-05-2017, 08:57 PM
#4
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Re: misfire under load
To upload a file (.csv) or photo from your PC, click on "Go Advanced" under the message box. When the new screen opens, scroll down to "Manage Attachments". Click on that and follow instructions.
If you are not averse to trying another free data logging program, try Scan9495. I prefer it to others.
https://www.camaroz28.com/forums/com...95-lt1-874306/
If you are not averse to trying another free data logging program, try Scan9495. I prefer it to others.
https://www.camaroz28.com/forums/com...95-lt1-874306/
Last edited by Injuneer; 09-06-2017 at 08:17 AM.
09-05-2017, 11:49 PM
#5
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Join Date: Sep 2017
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Re: misfire under load
To upload a file (.csv) or photo from your PC, click on "Go Advanced) under the message box. When the new screen opens, scroll down to "Manage Attachments". Click on that and follow instructions.
If you are not averse to trying another free data logging program, try Scan9495. I prefer it to others.
https://www.camaroz28.com/forums/com...95-lt1-874306/
If you are not averse to trying another free data logging program, try Scan9495. I prefer it to others.
https://www.camaroz28.com/forums/com...95-lt1-874306/
09-07-2017, 03:10 PM
#7
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Re: misfire under load
Downloaded the file, converted to Excel. It's on the large side (30 minutes, 10,000+ lines of data) and will take a day or so.
A quick review indicates it took a bit longer than usual to go into closed loop. Typically that happens at 206 seconds, which is set by a timer. Yours did not go into closed loop at 206 seconds because the coolant temp was only 127*F. The system waited until ~250 seconds until the coolant temp reached 140*F. Eventually it warmed up to 185*F, but seems a bit slow to warm up.
How big is the cam? Programmed idle speed is 1,050 RPM. Stock M6 programming is 800 RPM fully warmed up, and I had no problem keeping that with a 230/242 114 LSA. I suspect you have something larger than that, with a narrower LSA (mine is a "nitrous" cam, and was selected to pass NJ tailpipe emissions, hence the 114* LSA). With that idle speed, MAF flow is 17 to 18 grams/second, about 2X to 3X what we would see with a stock idle speed. MAP is in the low 60 kPa range, consistent with a healthy (but not radical) cam. Do you have cam specs?
Idle advance is 28-30*, again, something typical of tuning for a larger cam (vs 19-22* for a stock cam).
The long term fuel corrections are all over the place, but not too bad. Ranges from a split of 134 left/120 right in Cell 14 to 121 left/121 right in Cell 6. I haven't found all the cells yet. Idle at the very end in Cell 16 is 126 left/128 right, which is excellent.
As noted, just a preliminary scroll through the file.
A quick review indicates it took a bit longer than usual to go into closed loop. Typically that happens at 206 seconds, which is set by a timer. Yours did not go into closed loop at 206 seconds because the coolant temp was only 127*F. The system waited until ~250 seconds until the coolant temp reached 140*F. Eventually it warmed up to 185*F, but seems a bit slow to warm up.
How big is the cam? Programmed idle speed is 1,050 RPM. Stock M6 programming is 800 RPM fully warmed up, and I had no problem keeping that with a 230/242 114 LSA. I suspect you have something larger than that, with a narrower LSA (mine is a "nitrous" cam, and was selected to pass NJ tailpipe emissions, hence the 114* LSA). With that idle speed, MAF flow is 17 to 18 grams/second, about 2X to 3X what we would see with a stock idle speed. MAP is in the low 60 kPa range, consistent with a healthy (but not radical) cam. Do you have cam specs?
Idle advance is 28-30*, again, something typical of tuning for a larger cam (vs 19-22* for a stock cam).
The long term fuel corrections are all over the place, but not too bad. Ranges from a split of 134 left/120 right in Cell 14 to 121 left/121 right in Cell 6. I haven't found all the cells yet. Idle at the very end in Cell 16 is 126 left/128 right, which is excellent.
As noted, just a preliminary scroll through the file.
Last edited by Injuneer; 09-07-2017 at 03:12 PM.
09-07-2017, 09:06 PM
#8
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Re: misfire under load
Downloaded the file, converted to Excel. It's on the large side (30 minutes, 10,000+ lines of data) and will take a day or so.
A quick review indicates it took a bit longer than usual to go into closed loop. Typically that happens at 206 seconds, which is set by a timer. Yours did not go into closed loop at 206 seconds because the coolant temp was only 127*F. The system waited until ~250 seconds until the coolant temp reached 140*F. Eventually it warmed up to 185*F, but seems a bit slow to warm up.
How big is the cam? Programmed idle speed is 1,050 RPM. Stock M6 programming is 800 RPM fully warmed up, and I had no problem keeping that with a 230/242 114 LSA. I suspect you have something larger than that, with a narrower LSA (mine is a "nitrous" cam, and was selected to pass NJ tailpipe emissions, hence the 114* LSA). With that idle speed, MAF flow is 17 to 18 grams/second, about 2X to 3X what we would see with a stock idle speed. MAP is in the low 60 kPa range, consistent with a healthy (but not radical) cam. Do you have cam specs?
Idle advance is 28-30*, again, something typical of tuning for a larger cam (vs 19-22* for a stock cam).
The long term fuel corrections are all over the place, but not too bad. Ranges from a split of 134 left/120 right in Cell 14 to 121 left/121 right in Cell 6. I haven't found all the cells yet. Idle at the very end in Cell 16 is 126 left/128 right, which is excellent.
As noted, just a preliminary scroll through the file.
A quick review indicates it took a bit longer than usual to go into closed loop. Typically that happens at 206 seconds, which is set by a timer. Yours did not go into closed loop at 206 seconds because the coolant temp was only 127*F. The system waited until ~250 seconds until the coolant temp reached 140*F. Eventually it warmed up to 185*F, but seems a bit slow to warm up.
How big is the cam? Programmed idle speed is 1,050 RPM. Stock M6 programming is 800 RPM fully warmed up, and I had no problem keeping that with a 230/242 114 LSA. I suspect you have something larger than that, with a narrower LSA (mine is a "nitrous" cam, and was selected to pass NJ tailpipe emissions, hence the 114* LSA). With that idle speed, MAF flow is 17 to 18 grams/second, about 2X to 3X what we would see with a stock idle speed. MAP is in the low 60 kPa range, consistent with a healthy (but not radical) cam. Do you have cam specs?
Idle advance is 28-30*, again, something typical of tuning for a larger cam (vs 19-22* for a stock cam).
The long term fuel corrections are all over the place, but not too bad. Ranges from a split of 134 left/120 right in Cell 14 to 121 left/121 right in Cell 6. I haven't found all the cells yet. Idle at the very end in Cell 16 is 126 left/128 right, which is excellent.
As noted, just a preliminary scroll through the file.
Duration: 238/246
Lift: .365
Intake center line: 112
09-08-2017, 12:21 AM
#9
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Re: misfire under load
Sounds like the Erson 298/306.
Duration at 0.050" 238°/246°
Lobe lift 0.365" = 0.548" valve lift w/1.5X rockers; 0.584" w/ 1.6X rockers.
Except Erson quotes that as "108° Lobe Center" which they appear to use as lobe separation angle. If it was ground w/ a 112° LSA, that would explain the smooth idle and the moderate MAP at idle.
Other than the specs on their website, I'm not familiar with their cams. That appears to be a fairly aggressive cam, and would take a dyno tune to optimize. Who did the tune?
What rear axle are you running? Are EGR and EVAP deleted?
Duration at 0.050" 238°/246°
Lobe lift 0.365" = 0.548" valve lift w/1.5X rockers; 0.584" w/ 1.6X rockers.
Except Erson quotes that as "108° Lobe Center" which they appear to use as lobe separation angle. If it was ground w/ a 112° LSA, that would explain the smooth idle and the moderate MAP at idle.
Other than the specs on their website, I'm not familiar with their cams. That appears to be a fairly aggressive cam, and would take a dyno tune to optimize. Who did the tune?
What rear axle are you running? Are EGR and EVAP deleted?
Last edited by Injuneer; 09-08-2017 at 12:24 AM.
09-08-2017, 03:25 AM
#10
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Join Date: Sep 2017
Posts: 12
Re: misfire under load
Sounds like the Erson 298/306.
Duration at 0.050" 238°/246°
Lobe lift 0.365" = 0.548" valve lift w/1.5X rockers; 0.584" w/ 1.6X rockers.
Except Erson quotes that as "108° Lobe Center" which they appear to use as lobe separation angle. If it was ground w/ a 112° LSA, that would explain the smooth idle and the moderate MAP at idle.
Other than the specs on their website, I'm not familiar with their cams. That appears to be a fairly aggressive cam, and would take a dyno tune to optimize. Who did the tune?
What rear axle are you running? Are EGR and EVAP deleted?
Duration at 0.050" 238°/246°
Lobe lift 0.365" = 0.548" valve lift w/1.5X rockers; 0.584" w/ 1.6X rockers.
Except Erson quotes that as "108° Lobe Center" which they appear to use as lobe separation angle. If it was ground w/ a 112° LSA, that would explain the smooth idle and the moderate MAP at idle.
Other than the specs on their website, I'm not familiar with their cams. That appears to be a fairly aggressive cam, and would take a dyno tune to optimize. Who did the tune?
What rear axle are you running? Are EGR and EVAP deleted?
09-08-2017, 10:11 AM
#11
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Re: misfire under load
What kind of dyno results? Depending on the heads, I would think you would be over 500 HP at the flywheel (close to 450 at the rear wheels).
As a reference point, build as tested after the stroker was initially built - M6/steel Street Twin/3" chrome moly DS/12-bolt/3.73 gears/street tire's I had dyno figures for flywheel (490) and rear wheel (427), showing a 13% drivetrain loss. That was using 93 octane pump fuel. When it was baselined w/ C16 for the nitrous tune, made 496 flywheel.
As noted cam (NJ emissions friendly) 230/242 114°LSA 0.590"/0.590" w/ a shade over 10.8:1 static CR. HP does suffer with heavy crown nitrous pistons, dropped ring pack. Lighter, more stable pistons would have netted a bit more. And in 2000 there was a more limited head selection. I got the GM LT4's from CNC Cylinder Heads in Pinellas, FL. Flowed a bit under 300 CFM w/ ported GM LT4 intake in place. Much better heads available now.
As a reference point, build as tested after the stroker was initially built - M6/steel Street Twin/3" chrome moly DS/12-bolt/3.73 gears/street tire's I had dyno figures for flywheel (490) and rear wheel (427), showing a 13% drivetrain loss. That was using 93 octane pump fuel. When it was baselined w/ C16 for the nitrous tune, made 496 flywheel.
As noted cam (NJ emissions friendly) 230/242 114°LSA 0.590"/0.590" w/ a shade over 10.8:1 static CR. HP does suffer with heavy crown nitrous pistons, dropped ring pack. Lighter, more stable pistons would have netted a bit more. And in 2000 there was a more limited head selection. I got the GM LT4's from CNC Cylinder Heads in Pinellas, FL. Flowed a bit under 300 CFM w/ ported GM LT4 intake in place. Much better heads available now.
Last edited by Injuneer; 09-08-2017 at 10:14 AM.
09-08-2017, 07:15 PM
#13
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Re: misfire under load
Nothing wrong with ported stock heads. Done correctly they can support 500 HP at the flywheel. The benchmark for reasonably priced stock ported heads is Elliott Port Works:
http://elliottsportworks.com/
Advanced Induction is a bit more expensive, and can produce a bit more HP.
Advanced Induction - LTx Performance Parts
http://elliottsportworks.com/
Advanced Induction is a bit more expensive, and can produce a bit more HP.
Advanced Induction - LTx Performance Parts
09-11-2017, 05:36 PM
#15
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Re: misfire under load
There's only one portion of the data log that I found where you actually got it into power enrichment mode (2,439 RPM/53% TPP). Everything looked very good. O2 sensors on both sides were a bit leaner (850 mV) than the stock tune, and that's good. It was in Cell 15 and LTFT's L/R were 129/131. No sign of misfires, very little variation in the O2 sensor readings, no blips in the MAP readings indicating a backfire.
I did find periods when it was just idling, vehicle not moving, and one or both sides of the engine would go lean for several seconds, almost like an injector was sticking closed, or the fuel pressure was low.
Still need to look at the places where you were blipping the throttle at idle.
I did find periods when it was just idling, vehicle not moving, and one or both sides of the engine would go lean for several seconds, almost like an injector was sticking closed, or the fuel pressure was low.
Still need to look at the places where you were blipping the throttle at idle.