mechanical misfire?
mechanical misfire? I've been chasing what I thought was cam surge for a long time now. After doing 24x and tuning this thing with every combination of variables possible over the last 3 months it's still not as smooth as I would like. Basically it's jerky when I cruise slower than 50mph and below 2000rpm. Someone said it could be a mechanical misfire. I had never heard of that so I searched it and it sounds like they are valve train or fuel injector related. Anyone have any experience with this?
I want to pull my injectors and have them tested. I suspect an injector because there isn't a set consistent pattern to the jerkiness and the exhaust makes faint popping noises when it happens. I've only found 2 local web sites that say they test injectors and they're both diesel shops. What should I look for or ask about when trying to find a place to test them? Is there a name for the service or a special piece of equipment or anything? Thanks.
I want to pull my injectors and have them tested. I suspect an injector because there isn't a set consistent pattern to the jerkiness and the exhaust makes faint popping noises when it happens. I've only found 2 local web sites that say they test injectors and they're both diesel shops. What should I look for or ask about when trying to find a place to test them? Is there a name for the service or a special piece of equipment or anything? Thanks.
Witchhunter performance in Bothell has done a good job for me, fast service too.
Where in WA are you located? I know a guy up North of Seattle that I'm sure could help you with any tuning issues.
Where in WA are you located? I know a guy up North of Seattle that I'm sure could help you with any tuning issues.
TECH Veteran
Joined: Apr 2008
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www.cruzinperformance.com is where I sent my injectors for test/cleaning SVO 30's if you hit the wall on finding a "local" shop
How do you know its still not in the tune? as far as injectors, I would first use a can of BG44K, this is the stuff the dealers use and if you have a clogged injector this will fix it, No other auto part store cleaner will come close to this stuff, You can only get it at usually a Toyota dealership or at a NAPA..
I did the cylinder balance test in HPTuners and every cylinder got 97%. Found a local injector place and took my injectors there anyway. They want $25 per injector, does that sound about right?
I don't know for sure if it's still not in the tune but this will eliminate one more possibility.
I don't know for sure if it's still not in the tune but this will eliminate one more possibility.
Last edited by AdsoYo; Dec 23, 2014 at 05:39 PM.
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Verdad Gallardo Got the injectors back in and the car doesn't drive any different. The guy at the injector place said flow was improved by 10% after they worked on them so I guess that's cool. He also said they all performed identically.
A little side story about my injector install: once they were all in, I cycled the fuel pump twice before attempting to start. There was a strong fuel smell but I didn't think much of it and started the car anyway. It started and ran fine, and I backed it out of the garage. Once I got far enough back to see the garage floor, I saw a huge puddle gas. Turned the car off right away and popped the hood to find the passenger side of the engine soaked. I turned the key on to prime the fuel pump and saw injectors 2 and 4 were leaking like crazy at the fuel rail. After pulling off the injectors they both had pinched o-rings. Didn't even know that was possible. I massaged them back to shape, re-oiled and re-installed. No more leaks! Next time I will be checking for leaks BEFORE starting the engine though
So now I want to make sure the valve train is good to go. Can anyone link me some threads or websites detailing how to check and adjust springs, rockers, etc. Never done it before.
A little side story about my injector install: once they were all in, I cycled the fuel pump twice before attempting to start. There was a strong fuel smell but I didn't think much of it and started the car anyway. It started and ran fine, and I backed it out of the garage. Once I got far enough back to see the garage floor, I saw a huge puddle gas. Turned the car off right away and popped the hood to find the passenger side of the engine soaked. I turned the key on to prime the fuel pump and saw injectors 2 and 4 were leaking like crazy at the fuel rail. After pulling off the injectors they both had pinched o-rings. Didn't even know that was possible. I massaged them back to shape, re-oiled and re-installed. No more leaks! Next time I will be checking for leaks BEFORE starting the engine though
So now I want to make sure the valve train is good to go. Can anyone link me some threads or websites detailing how to check and adjust springs, rockers, etc. Never done it before.
I'm just going off of google. Top search result described a mechanical misfire as worn piston rings, valves, cylinder walls, or lobes on a camshaft; a leaking head gasket or intake manifold gasket; damaged or broken rocker arms; defective fuel injectors (and/or the electronics that control them); and a slipped or incorrectly-installed timing belt or timing chain.
A leak down compression test would be a good start to diagnose a mechanical issue. Who did the tune? If I was you I would look into having a reputable tuner look at some data logs.
The above advise about a dragging clutch or a drive-line issue sounds like something from the Twilight Zone.
The above advise about a dragging clutch or a drive-line issue sounds like something from the Twilight Zone.
I don't think tps because it comes across fine on data logs.
The tune is mine but it behaved the same with pcmforless and a professional dyno tune. Car has been doing this since day 1. I'll probably have a different performance shop look at it at some point but I want to make sure the hardware is good first.
The tune is mine but it behaved the same with pcmforless and a professional dyno tune. Car has been doing this since day 1. I'll probably have a different performance shop look at it at some point but I want to make sure the hardware is good first.
I don't think tps because it comes across fine on data logs.
The tune is mine but it behaved the same with pcmforless and a professional dyno tune. Car has been doing this since day 1. I'll probably have a different performance shop look at it at some point but I want to make sure the hardware is good first.
The tune is mine but it behaved the same with pcmforless and a professional dyno tune. Car has been doing this since day 1. I'll probably have a different performance shop look at it at some point but I want to make sure the hardware is good first.
Banned
Joined: Jan 2013
Posts: 588
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From: Las Vegas
If its the tune the tune uses ignition timing for low rpm/idle management though 2000rpm is a bit higher than idle rpm. But if its done this since problem since before u modded it then it reads like a driveline issue.
All OBD II ECM's can monitor and detect misfire down to the cyl. The DTC for misfire is P030x where x = cyl with misfire. U would need an advanced scan tool with frame to frame data to look at rich/lean and MAP readings during misfire.
Quite possible to have other odd issues causing this like evap control sys vlv not closing creating over rich/stumble. Or a stuck EGR vlv open or closed. Even a clogged cat converter - or just plain restricted exh.
But to me your "faint popping noises" reads more like retarded timing to me.
Jerky below 2000rpm is not the vlvs and unless u have successfully adjusted them before then leave them alone. U could create more problems by incorrectly adjusting the vlvs/lifters.
Misfire is one of most difficult faults to diagnose, but u need to make a list of all possibilities and eliminate them one by one.
All OBD II ECM's can monitor and detect misfire down to the cyl. The DTC for misfire is P030x where x = cyl with misfire. U would need an advanced scan tool with frame to frame data to look at rich/lean and MAP readings during misfire.
Quite possible to have other odd issues causing this like evap control sys vlv not closing creating over rich/stumble. Or a stuck EGR vlv open or closed. Even a clogged cat converter - or just plain restricted exh.
But to me your "faint popping noises" reads more like retarded timing to me.
Jerky below 2000rpm is not the vlvs and unless u have successfully adjusted them before then leave them alone. U could create more problems by incorrectly adjusting the vlvs/lifters.
Misfire is one of most difficult faults to diagnose, but u need to make a list of all possibilities and eliminate them one by one.
Light throttle and light load are exactly where I'm having my jerky problem. I feel like I've adjusted every possible variable though. The only thing that seems to consistently smooth out cruising is running richer.
I've had spark from 28-50* and that didn't make a difference, although lower spark seemed to make it worse. So now I've set spark for maximum vacuum.
I've tried messing with throttle follower/cracker and it feels good for a bit but eventually the computer relearns and IAC counts go back to where they were.
I've got my injectors programmed with the correct data. Changed end-of-injector-timing to match my camshaft.
Base idle airflow is set with Russ K's config file.
VE and MAF tables were set according to the multitude of write-ups around the internet.
Right now I have my O2 switch points set to 809 mV and that feels smooth. I just keep seeing people post about how the CC503 is mild and shouldn't have bucking issues. Any tuning advice would be appreciated.
I've had spark from 28-50* and that didn't make a difference, although lower spark seemed to make it worse. So now I've set spark for maximum vacuum.
I've tried messing with throttle follower/cracker and it feels good for a bit but eventually the computer relearns and IAC counts go back to where they were.
I've got my injectors programmed with the correct data. Changed end-of-injector-timing to match my camshaft.
Base idle airflow is set with Russ K's config file.
VE and MAF tables were set according to the multitude of write-ups around the internet.
Right now I have my O2 switch points set to 809 mV and that feels smooth. I just keep seeing people post about how the CC503 is mild and shouldn't have bucking issues. Any tuning advice would be appreciated.
Banned
Joined: Jan 2013
Posts: 588
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From: Las Vegas
Like i posted before, the idle speed control is done with ign adv not IAC. The computer uses a reference amount of advance (which is a little retarded) and increases adv when items like the AC is turned on or trans placed in park (increased load). This is because IAC is way to slow to respond to load and the eng could stall/quit.
Spark at 28* at idle or near idle speeds sounds huge to me.
Spark at 28* at idle or near idle speeds sounds huge to me.
Right now I have no evap, egr, and a brand new random technology cat so we can rule those out. While cruising I have timing set to 37-39* since that's where MAP is lowest. The faint popping doesn't seem to correlate with drops in timing. The 28* was while cruising, not at idle. Although my idle spark advance is higher than that 
Timing is used to stabilize idle RPM, not control it. There is a High Idle Correction and Low Idle Spark Correction tables to stabilize the idle RPM. It does not control the idle speed. The IAC actually does that. Pull that shifter out of Park or Neutral, the IAC starts to back up to flow more idle air for the load of Reverse or Drive. You can zero those tables out, and the IAC will still control the idle speed. May hunt around some, but will idle at the same RPM. Many stock LT1 calibrations (aka tunes) idle at 26 degrees, unless at lower temps where the PCM backs the timing up to raise EGTs, to make enough heat to bring the Cat(s) on line sooner. Some guys seem annoyed seeing the timing move around on their scan tool at idle, so they zero those two tables. They then back the timing up to stop idle surge. Too far there, and it becomes hard on your header coatings.
28 degrees at idle is not high for a bigger cam.
None of this has anything to do with his drivability problems. Everything I mentioned goes away above 1% throttle angle, unless that throttle angle has been altered. None of the runing software that I have seen, that you guys would have access to has that parameter included anyway.
28 degrees at idle is not high for a bigger cam.
None of this has anything to do with his drivability problems. Everything I mentioned goes away above 1% throttle angle, unless that throttle angle has been altered. None of the runing software that I have seen, that you guys would have access to has that parameter included anyway.