Part Throttle Misfire Help
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From: Skippack, PA
Part Throttle Misfire Help Been plagued with this damn part throttle misfire for years now. I should have addressed it a long time ago but I lost interest in the car awhile back and haven't touched it since. I finally got the car out today, my buddy was driving it while I was taking a video and of course the car started breaking up as soon as he pulled out onto the road (the car was already wrmed up, sat for 5 minutes before he fired it up to drive it - see first video). If I remember right this misfire/breaking up has only ever occurred during part throttle shortly after the car has been started up. It breaks up for a couple seconds then it's all good and won't do it again. Doesn't matter if it's a cold start or warm start but the key seems to be that it only occurs shortly after being started up. It does not occur every time and it runs good otherwise. No issues at WOT.
Pertinent details: Car is a '97, mileage somewhere in the low 20,000 range, replaced the ICM a couple years back with a new ACDelco one, has Delphi opti with maybe 10,000 miles on it, Autolite 104 plugs at a .040" ish gap. I bought a new ACDelco coil for it a couple years ago but I forget if I installed it or not. No codes and I do not have any LT1 software.
I'm wondering if it's an open to closed loop transition thing? (if the car is warm and turned off then started back up, is it in open loop?)
I appreciate any thoughts you may have, I'm going to make a list of things to look into and I will make some time to dive into it.
Video of misfire (edit: it breaks up between the :27 - :29 second marks):
Video of WOT (because why not
):
Pertinent details: Car is a '97, mileage somewhere in the low 20,000 range, replaced the ICM a couple years back with a new ACDelco one, has Delphi opti with maybe 10,000 miles on it, Autolite 104 plugs at a .040" ish gap. I bought a new ACDelco coil for it a couple years ago but I forget if I installed it or not. No codes and I do not have any LT1 software.
I'm wondering if it's an open to closed loop transition thing? (if the car is warm and turned off then started back up, is it in open loop?)
I appreciate any thoughts you may have, I'm going to make a list of things to look into and I will make some time to dive into it.
Video of misfire (edit: it breaks up between the :27 - :29 second marks):
Video of WOT (because why not
):Last edited by StealthFormula; Sep 3, 2018 at 06:31 AM.
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From: Kernersville, NC
That didn't sound like a misfire to me(unless it was just after he got on the road maybe...hard to tell with the exhaust). Looks like it may have nosed over on throttle tip in when he was pulling onto the main highway....possibly a VE tuning issue.
What has been done to it? Doesn't sound like a stock cam.
I have an off idle, light throttle, tip in bucking issue that I have not been able to fix since installing my CC503. Most certainly is worse just after startup when either warm or cold. However, I didn't see that in your video......just seemed to nose over pulling on the road for a second or two.
What has been done to it? Doesn't sound like a stock cam.
I have an off idle, light throttle, tip in bucking issue that I have not been able to fix since installing my CC503. Most certainly is worse just after startup when either warm or cold. However, I didn't see that in your video......just seemed to nose over pulling on the road for a second or two.
Last edited by ACE1252; Sep 3, 2018 at 02:46 AM.
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- I listened to the video again, seems too occur at the 27 second mark and sort itself out by the 29 second mark. It has a cam, head work, true duals, converter, etc. I had it dyno tuned about 9-10 years with Bryan Herter. I don't remember if it was an issue back then or not, I wish I cold remember that way I could potentially rule the tuning out but since I can't the tuning could be a possibility.
That didn't sound like a misfire to me(unless it was just after he got on the road maybe...hard to tell with the exhaust). Looks like it may have nosed over on throttle tip in when he was pulling onto the main highway....possibly a VE tuning issue.
What has been done to it? Doesn't sound like a stock cam.
I have an off idle, light throttle, tip in bucking issue that I have not been able to fix since installing my CC503. Most certainly is worse just after startup when either warm or cold. However, I didn't see that in your video......just seemed to nose over pulling on the road for a second or two.
What has been done to it? Doesn't sound like a stock cam.
I have an off idle, light throttle, tip in bucking issue that I have not been able to fix since installing my CC503. Most certainly is worse just after startup when either warm or cold. However, I didn't see that in your video......just seemed to nose over pulling on the road for a second or two.
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From: $oCal Goodne$$
You can definitely hear something bogging it down, then going away, my vote is Knock Retard.
Been there and still experiencing some of that. Thankfully I didn't have to guess what it was thanks to the Scanmaster showing 7 - 13 degrees at the time of the incident, and seconds later when it works itself out and goes back to 0.0 it's like a electronic gas pedal delay on these new vehicles and scoots right out on its way.
Now as to why it happens... we've all been down that road.
Happy Labor Day!
Been there and still experiencing some of that. Thankfully I didn't have to guess what it was thanks to the Scanmaster showing 7 - 13 degrees at the time of the incident, and seconds later when it works itself out and goes back to 0.0 it's like a electronic gas pedal delay on these new vehicles and scoots right out on its way.
Now as to why it happens... we've all been down that road.
Happy Labor Day!
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Thanks guys, sounds like I ought to be invest in some scanning software then. I’m not up on what my options are or what’s recommended, anyone have any suggestions?
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I think if it was knock it would run low on power throughout WOT vs just a temporary "stumble" as it appears. The one WOT video shows it pulling pretty hard.
I suspect it is more within the tune....might be cheaper to have another tuner other than Herter do a mail order
This assumes the motor/car does not have some issue as simple as a sensor like pcm temp, TPS or something like that. Just a guess.
There are OBD2 scan tools like Actron that will show knock and several other PID's. Not familiar with SanMaster. IIRC it doesn't show codes for OBD2 but maybe someone who has it for a 97 (OBD2) car can comment
I suspect it is more within the tune....might be cheaper to have another tuner other than Herter do a mail order
This assumes the motor/car does not have some issue as simple as a sensor like pcm temp, TPS or something like that. Just a guess.
There are OBD2 scan tools like Actron that will show knock and several other PID's. Not familiar with SanMaster. IIRC it doesn't show codes for OBD2 but maybe someone who has it for a 97 (OBD2) car can comment
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From: Skippack, PA
I think if it was knock it would run low on power throughout WOT vs just a temporary "stumble" as it appears. The one WOT video shows it pulling pretty hard.
I suspect it is more within the tune....might be cheaper to have another tuner other than Herter do a mail order
This assumes the motor/car does not have some issue as simple as a sensor like pcm temp, TPS or something like that. Just a guess.
There are OBD2 scan tools like Actron that will show knock and several other PID's. Not familiar with SanMaster. IIRC it doesn't show codes for OBD2 but maybe someone who has it for a 97 (OBD2) car can comment
I suspect it is more within the tune....might be cheaper to have another tuner other than Herter do a mail order
This assumes the motor/car does not have some issue as simple as a sensor like pcm temp, TPS or something like that. Just a guess.
There are OBD2 scan tools like Actron that will show knock and several other PID's. Not familiar with SanMaster. IIRC it doesn't show codes for OBD2 but maybe someone who has it for a 97 (OBD2) car can comment
From a tuning perspective I don't even know who tunes these things anymore lol. I definitely don't have the time or desire to learn so I need to rely on someone else for sure. May be time to upgrade to the LS1 computer setup.
My bad earlier, meant to ask for what people are using these days to datalog the OBD2 LT1s?
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From: Kernersville, NC
For the data logger I have Autotap and Scan XL Pro. Autotap is no longer for sale and my Scan XL Pro setup was not cheap. Just over $400. Looks like Scantool.net may not offer it anymore, so you'd have to get it off Palmer's website.
My thoughts on it here...
https://www.camaroz28.com/forums/com...-770192/page2/
Autotap was decent, but they don't sell it anymore. One of the gotchas on it was one of the long term fuel trims was not logging correctly.
There may be better choices for OBDII data logging, but I have not run across them yet. Seems like the scanners with HP tuners and EFI live are the end all and be all of data logging....but of course....they are LS based.
My thoughts on it here...
https://www.camaroz28.com/forums/com...-770192/page2/
Autotap was decent, but they don't sell it anymore. One of the gotchas on it was one of the long term fuel trims was not logging correctly.
There may be better choices for OBDII data logging, but I have not run across them yet. Seems like the scanners with HP tuners and EFI live are the end all and be all of data logging....but of course....they are LS based.
Last edited by ACE1252; Sep 5, 2018 at 11:12 PM.
Initially I was thinking you had a spark plug wire that had built up a ton of resistance, but since this only happens after start up and only intermittently... I think data logging is the next step.
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From: Skippack, PA
For the data logger I have Autotap and Scan XL Pro. Autotap is no longer for sale and my Scan XL Pro setup was not cheap. Just over $400. Looks like Scantool.net may not offer it anymore, so you'd have to get it off Palmer's website.
My thoughts on it here...
https://www.camaroz28.com/forums/com...-770192/page2/
Autotap was decent, but they don't sell it anymore. One of the gotchas on it was one of the long term fuel trims was not logging correctly.
There may be better choices for OBDII data logging, but I have not run across them yet. Seems like the scanners with HP tuners and EFI live are the end all and be all of data logging....but of course....they are LS based.
My thoughts on it here...
https://www.camaroz28.com/forums/com...-770192/page2/
Autotap was decent, but they don't sell it anymore. One of the gotchas on it was one of the long term fuel trims was not logging correctly.
There may be better choices for OBDII data logging, but I have not run across them yet. Seems like the scanners with HP tuners and EFI live are the end all and be all of data logging....but of course....they are LS based.
I think I checked for vacuum leak a couple years ago IIRC. I'm gonna go over everything with a fine tooth comb to rule that out.
I tend to agree, I think that's gonna tell the story. Just sucks the datalog options appear to be limited and expensive.
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So I looked my old emails to my tuner from 9-10 years ago, turns out I mentioned the issue to him back then. In addition, I also mentioned how the car had a slight surge when cruising down the road with very light throttle input and that the exhaust kinda made a popping sound when that occurred. I forgot about that, shows how little I've driven the car lately. That means I've been dealing with this intermittent issue since I went from a cam-only setup to the stock ported heads and cam setup that I now have. I changed a lot at the same time including the manifold, plugs, wires, fuel pump, injectors, TB, etc. and then had it tuned. One of the things I mentioned in my emails was that with a .035" plug gap the issue didn't seem to occur but it did when I ran a wider .040' -.045" gap. That could have been a complete coincidence but I'll go back to a .035" for ***** and giggles. Tuner didn't think the tune had anything to do with the issue, I beginning to think it very well may.
I need to datalog this thing but given the high cost of the software I'm thinking of taking a different approach first, someone tell me if this doesn't make sense. I'm thinking I should start with the free/cheap stuff like pull the plugs and wires for inspection, unplug the MAF and drive it and see if anything changes, unplug the 02s and drive it and see if anything changes, throw race gas in it and drive it and see if anything changes, that kinda thing. See where I get with that then report back.
I need to datalog this thing but given the high cost of the software I'm thinking of taking a different approach first, someone tell me if this doesn't make sense. I'm thinking I should start with the free/cheap stuff like pull the plugs and wires for inspection, unplug the MAF and drive it and see if anything changes, unplug the 02s and drive it and see if anything changes, throw race gas in it and drive it and see if anything changes, that kinda thing. See where I get with that then report back.
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Finished my other projects so I pivoted over to the Firebird. I don’t have a check engine light but my code reader pulled a code for an 02 sensor heater circuit malfunction. Bought some rear heated ACDelco C5 sensors and an adapter harness to run them upfront, hoping that does the trick. I’ll provide an update in the event anyone else runs into a similar issue.
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Update:
Finally got the car out after replacing the front 02s with C5 Vette rear heated 02s, replacing vacuum caps, cleaning sensors, replacing coolant temp sensor etc. etc. last fall. So far the car does not exhibit the misfire/breaking up symptoms so fingers crossed that the issue is resolved. Assuming the issue is 100% fixed, I'm thinking it was 02 related for anyone that may be experiencing something similar.
Trying to get back into the LT1 game after my focuses shifted to my motorcycles and other car for so many years. Finally bought all new tires, put insurance back on it and registered it. Off to the drag strip in a few weeks to hurt some modern day muscle car feelings with this dinosaur
Finally got the car out after replacing the front 02s with C5 Vette rear heated 02s, replacing vacuum caps, cleaning sensors, replacing coolant temp sensor etc. etc. last fall. So far the car does not exhibit the misfire/breaking up symptoms so fingers crossed that the issue is resolved. Assuming the issue is 100% fixed, I'm thinking it was 02 related for anyone that may be experiencing something similar.
Trying to get back into the LT1 game after my focuses shifted to my motorcycles and other car for so many years. Finally bought all new tires, put insurance back on it and registered it. Off to the drag strip in a few weeks to hurt some modern day muscle car feelings with this dinosaur
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From: Skippack, PA