I'm at a loss... weird "stutter"...log file attached
Thread Starter
Joined: May 2004
Posts: 654
Likes: 5
From: Fredericksburg, VA
I'm at a loss... weird "stutter"...log file attached Ok, I've developed a weird low idle, part throttle, "stutter" that surfaces just as I put a load on the car. I've replaced the IAC, PCV, new air and fuel filters. MAF, fuel injectors, O2s, and plugs all have under 10k miles. It feels like an intermittent coil, but I'm not getting any no codes. Definitely feels electrical, and I can fairly consistently produce the fault. When it occurs, it feels exactly the same every time, the duration of the event is the only inconsistency. It seems happen between 1200-1800 rpm, in pretty much any gear.
Again, no codes, but when we hooked up HPTuners, it said it had an incomplete testing on the O2s and Evap system. O2s appeared to be working normally from what we could tell though.
Anyway, hoping someone can take a look at the attached log file and come up with a viable theory. My next step is to buy a single coil and just swap it around to each cylinder to see if I can clear it up that way.
Thanks in advance...
Again, no codes, but when we hooked up HPTuners, it said it had an incomplete testing on the O2s and Evap system. O2s appeared to be working normally from what we could tell though.
Anyway, hoping someone can take a look at the attached log file and come up with a viable theory. My next step is to buy a single coil and just swap it around to each cylinder to see if I can clear it up that way.
Thanks in advance...
TECH Fanatic
Joined: Jun 2003
Posts: 1,869
Likes: 99
If it is a coil or injector, the first step is to check the ground on the back of the head and next the coil harness's. Wiring is getting old and brittle after almost 20 years on these cars. Since you have recently removed and replaced the injectors, one might have a loose connection or partially broken wire. After 10 years since last injector change mine were almost impossible to remove from the injector (the old style).
Shooting a temp gun at each exhaust pipe will tell you if it is either a bad plug, bad coil, or injector because the exhaust temp will be lower than the others. So if its firing and not getting fuel it will be cold or vice versa.
Shooting a temp gun at each exhaust pipe will tell you if it is either a bad plug, bad coil, or injector because the exhaust temp will be lower than the others. So if its firing and not getting fuel it will be cold or vice versa.
Thread Starter
Joined: May 2004
Posts: 654
Likes: 5
From: Fredericksburg, VA
If it is a coil or injector, the first step is to check the ground on the back of the head and next the coil harness's. Wiring is getting old and brittle after almost 20 years on these cars. Since you have recently removed and replaced the injectors, one might have a loose connection or partially broken wire. After 10 years since last injector change mine were almost impossible to remove from the injector (the old style).
Shooting a temp gun at each exhaust pipe will tell you if it is either a bad plug, bad coil, or injector because the exhaust temp will be lower than the others. So if its firing and not getting fuel it will be cold or vice versa.
Shooting a temp gun at each exhaust pipe will tell you if it is either a bad plug, bad coil, or injector because the exhaust temp will be lower than the others. So if its firing and not getting fuel it will be cold or vice versa.
TECH Fanatic
Joined: Jun 2003
Posts: 1,869
Likes: 99
The Evap DTC might be the connection on the control valve solenoid driver side. Is it firmly connected snapped in or forgotten while changing injectors? The vacuum hose from it runs right into the throttle body and to the hard line just next to the feed line near the fuse boxes. Other place, but unlikely is near the tank where there is another solenoid. But it shouldn't be loose unless you disconnected it if working on fuel pump.
You can feel each injector as it opens and closes when idling with thumb and index finger. A cheap temp gun is your friend at Harbor Freight.
BTW - apply dielectric grease when you connect back together. Also check both female and male ends on the Delphi connector on each coil as well as the main connector that connects them all to the main harness with the ground that connects to backside of the head - especially the female side or the male side if one is slightly bent. Each wire is color coded for each coil as well as the ground. It's doubtful two are cross attached because of the length of each. That said my car idles pretty good even though a coil is crossed.
You can feel each injector as it opens and closes when idling with thumb and index finger. A cheap temp gun is your friend at Harbor Freight.
BTW - apply dielectric grease when you connect back together. Also check both female and male ends on the Delphi connector on each coil as well as the main connector that connects them all to the main harness with the ground that connects to backside of the head - especially the female side or the male side if one is slightly bent. Each wire is color coded for each coil as well as the ground. It's doubtful two are cross attached because of the length of each. That said my car idles pretty good even though a coil is crossed.
Last edited by dlandsvZ28; Nov 11, 2018 at 04:23 PM.
Thread Starter
Joined: May 2004
Posts: 654
Likes: 5
From: Fredericksburg, VA
Ok...seems like the ground on the head is good to go...unless, there's supposed to be a ground on both heads. Pass side has no ground attached at all...I think that's right though. Wires all seem pretty good, checked all the connections, the only thing I found was a loose spark wire. It came off the plug side very easily and for minute, I thought I found my problem. I snugged it back down and sadly, I still had the problem. I checked it again later and it still came off too easily. I crimped it down better and it's on there good now, but I still have the issue. Seems like I need a set of wires for sure, but I'm not convinced that's the problem and I hate the idea of buying a new set of MSDs without knowing that's the fix.
Checked the evap, fuel injector, and coil connections, all seems pretty good...I'll have to pick up some dielectric grease and go back through it all just for good measure.
Checked the evap, fuel injector, and coil connections, all seems pretty good...I'll have to pick up some dielectric grease and go back through it all just for good measure.
Thread Starter
Joined: May 2004
Posts: 654
Likes: 5
From: Fredericksburg, VA
Trending Topics
TECH Fanatic
Joined: Jun 2003
Posts: 1,869
Likes: 99
How's your alternator and at that rpm what does it do on the gauge? Do you have an underdrive pulley?
https://www.hotrod.com/articles/0206...ur-alternator/
Don't know how this happened after my engine install - not by me. But my battery connection at the alt was arcing and had actually melted the insulation which I think might have contributed to my coils and injectors acting weird on idle. The nut was just was loose enough to where you could rotate the cable on the alt bolt. It is hard to reach or access so one can think it is tight if a socket swivel adapter was used when they thought it was tight, but was still loose.
https://www.hotrod.com/articles/0206...ur-alternator/
Don't know how this happened after my engine install - not by me. But my battery connection at the alt was arcing and had actually melted the insulation which I think might have contributed to my coils and injectors acting weird on idle. The nut was just was loose enough to where you could rotate the cable on the alt bolt. It is hard to reach or access so one can think it is tight if a socket swivel adapter was used when they thought it was tight, but was still loose.
Last edited by dlandsvZ28; Nov 12, 2018 at 04:58 PM.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo Thread Starter
Joined: May 2004
Posts: 654
Likes: 5
From: Fredericksburg, VA
How's your alternator and at that rpm what does it do on the gauge? Do you have an underdrive pulley?
https://www.hotrod.com/articles/0206...ur-alternator/
Don't know how this happened after my engine install - not by me. But my battery connection at the alt was arcing and had actually melted the insulation which I think might have contributed to my coils and injectors acting weird on idle. The nut was just was loose enough to where you could rotate the cable on the alt bolt. It is hard to reach or access so one can think it is tight if a socket swivel adapter was used when they thought it was tight, but was still loose.
https://www.hotrod.com/articles/0206...ur-alternator/
Don't know how this happened after my engine install - not by me. But my battery connection at the alt was arcing and had actually melted the insulation which I think might have contributed to my coils and injectors acting weird on idle. The nut was just was loose enough to where you could rotate the cable on the alt bolt. It is hard to reach or access so one can think it is tight if a socket swivel adapter was used when they thought it was tight, but was still loose.