Head Install - P0300 Misfire Error
Thread Starter
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
Head Install - P0300 Misfire Error
Just finished installing a set of Dart 205's. Car has a VHP cam which is 216/224 .551/.551 115LSA which is not too radical but is a little lumpy on idle. Had no codes prior to the heads, but now it is throwing the P0300 and when I look at which cylinder, it is all of them not limited to just one. I can't detect a misfire and the car absolutely runs fantastic from cold start to running hard. I have not yet had it tuned from the head installation, is this a normal thing to have happen?
Le Mans Master
Joined: Dec 2003
Posts: 5,561
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From: Atlanta metro Ga.
Wow..
I agree, that cam doesn't look that radical at all.
I'm sure you know that the PCM is sampling the crank sensor, measuring the time between each sensor pulse to determine engine mis-fire.
If it is loping as you suggest, then that might be enough to trigger it. I'll add if the mixture is fairly lean it may increase severity of the lope.
I agree, that cam doesn't look that radical at all.
I'm sure you know that the PCM is sampling the crank sensor, measuring the time between each sensor pulse to determine engine mis-fire.
If it is loping as you suggest, then that might be enough to trigger it. I'll add if the mixture is fairly lean it may increase severity of the lope.
Le Mans Master
Joined: Dec 2003
Posts: 5,561
Likes: 448
From: Atlanta metro Ga.
I don't have any pratical experience to share, other than understanding how the mis-fire detection operates. (BTW, manufactures struggled to develop mis-fire detection, causing a delay in releasing OBDII-compliant cars).
All it can do is sample the duration between crank sensor pulses; it has no knowledge of static or dynamic compression ratios, VE changes, etc.
So if it's loping as you say (and knowing you you've already checked the plugs, wires, manifold sealing, etc.), then I guess you'll need to edit the PCM to adjust / prevent triggering the code.
All it can do is sample the duration between crank sensor pulses; it has no knowledge of static or dynamic compression ratios, VE changes, etc.
So if it's loping as you say (and knowing you you've already checked the plugs, wires, manifold sealing, etc.), then I guess you'll need to edit the PCM to adjust / prevent triggering the code.
Thread Starter
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
Just went over everything again, can't find anything wrong. Only thing I can come up with is the new compression ratio has changed the dynamics slightly or I am running last years gas since the car just came out of storage.
Drifting
Joined: Oct 2004
Posts: 1,384
Likes: 8
From: Southwest Virginia
My car is not on the road yet so it is not tuned yet, but after installing a much more radical cam than yours it will set the P0300 code when started cold. Not because of rough idle but surging. When hot it never sets the code and has a pretty rough idle. But cold it starts to surge like the idle control is just a tad behind and it causes the engine to surge up and down about 400 RPM then it will trip the P0300 code. Does yours set the code after the engine has run for 5 minutes or more? Have you had it tuned yet? If not tuning will probably fix that code.
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Safety Car
Joined: Sep 2003
Posts: 3,558
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From: Cape Coral FL
Originally Posted by vettenuts
Not tuned yet, my tuner is telling me something is wrong. I have gone over everything and can't a single thing wrong. My idle doesn't hunt too much at all.
Thread Starter
Team Owner
Joined: Mar 1999
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From: At the beach in little Rhody
My idle is set to stock, around 750-800 from what I can tell.
I did an idle relearn on it, including turning on the A/C and haven't had the code come up since. Not sure if the PCM just needed some learn time or what. Knock on wood, hopefully that was it.
As for you rich one bank, lean on the other. Someone just went through this and the O2's were crossed from where they should be. Have you done anything with the O2's recently?
Also, valve springs?
I did an idle relearn on it, including turning on the A/C and haven't had the code come up since. Not sure if the PCM just needed some learn time or what. Knock on wood, hopefully that was it.
As for you rich one bank, lean on the other. Someone just went through this and the O2's were crossed from where they should be. Have you done anything with the O2's recently?
Also, valve springs?
Safety Car
Joined: Sep 2003
Posts: 3,558
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From: Cape Coral FL
Unfortunately, the O2's are not reversed. I was under there this weekend and replaced the 2 fronts due to them getting lazy from running so rich. It didn't fix the problem so my LTFT's are still way off at idle.
It's not a valve spring either. I checked them out, they only have about 3500 miles on them and still look fine, no breaks.
It's not a valve spring either. I checked them out, they only have about 3500 miles on them and still look fine, no breaks.
Race Director
Joined: Apr 2004
Posts: 16,135
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From: Newberry FL
Cruise-In VIII Veteran
St. Jude Donor '07
Maybe you should just take it to the tuner and have him check it out on the tuning equipment, maybe he can further determine what this is from? Sounds like you are playing a guessing game that may never end.
I could be wrong, but I would call him back up and ask if he is willing to try that.
Micah
I could be wrong, but I would call him back up and ask if he is willing to try that.
Micah
Advanced
Joined: Jan 2004
Posts: 94
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From: McAllen/Cedar Park Texas
When I installed my GX3 the idle surging was an on going problem that my tuner finally figured out how to fix along with the constant misfire code. I have had over a 100 different variations of tunes flashed to get it right. My tuner uses HP Tuners, and the most benificial thing we do is record all of runs at the track and some on the road, which allows you to further tune to perfection. If you are using HP Tuners you can call him.
Ruben
Sanoli's Performance
(956) 424-0600
My C5 has been their guiny pig for three years now. 11.39 @ 121 NA on drag radials on stock bottom end. Of course every different component changes the varitions in the tune.
Last edited by South Tex Vette; Apr 18, 2006 at 10:36 PM. Reason: edit
Pro
Joined: Jun 2005
Posts: 734
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From: Austin TX
If you get it tuned they should be able to take care of that problem. At least....my tuner did. And I had the exact same problem.......it drove me nuts because I checked and rechecked.
Go get it dyno tuned by someone who has a lot of experience with C5's and your problem will be history.
Go get it dyno tuned by someone who has a lot of experience with C5's and your problem will be history.
Thread Starter
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
Yep, three hot starts later and a check with Autotap, no error in memory. I think its a tuning issue and hopefully I will be on the dyno by the end of the week