Breaking up/misfiring under boost
Of course don't jump to conclusions. I've had maybe one buddy crack an intake was in back by the MAP sensor I think.
I'd do plugs, check the turbo system for a crack, then check intake.
I'd do plugs, check the turbo system for a crack, then check intake.
If the intake was cracked you would definitely know it, it would be idling high and/or be very slow to return to idle because of the additional airflow getting in past the TB. I've seen plenty of cracked FAST intakes over the years.
Thread Starter
Joined: Apr 2006
Posts: 3,890
Likes: 1,137
From: Grand Rapids, Michigan
That's good to know, I figured it would show driveability issues other than a miss if the intake was cracked. I'd thought about the smoke machine actually, you can buy a well reviewed one on Amazon for like $45. I'll try the plugs and wires first and see if that's my issue and do some more inspection if it doesn't fix it. My only problem is my entire hot side is wrapped, so it may be difficult to look for cracks. I feel like a crack forming would be pretty unlikely, as I only have about 3000 miles on this build.
I'm not of the opinion the intake is cracked or even the hotside, I've seen videos of guys putting 20+ psi to those Fast intakes without issue.
When I got my car the passenger side v-band was loose at the header and the flanges were offset causing a large exhaust leak, car still made boost and ran normally.
I'd start with what's been suggested, plugs and wires.
Check your grounds, make sure you aren't dropping voltage at high rpm, confirm your AFR, wiggle check the injector plugs and maybe just give everything a good look over where you were working, you might have moved or knocked something loose and not known it.
When I got my car the passenger side v-band was loose at the header and the flanges were offset causing a large exhaust leak, car still made boost and ran normally.
I'd start with what's been suggested, plugs and wires.
Check your grounds, make sure you aren't dropping voltage at high rpm, confirm your AFR, wiggle check the injector plugs and maybe just give everything a good look over where you were working, you might have moved or knocked something loose and not known it.
Teching In
Joined: Dec 2017
Posts: 42
Likes: 86
I have had similar issues once I started hitting boost over 20psi. I had to swap coils, plugs, wires, increase dwell, change gap. Turns out it was the coils all along, they wore out prematurely from increasing dwell. I was running a brand new set of LS3 coils from "AC Delco" only to find out that they were just Chinese knock offs. Even came in ACdelco boxes from a reputable company. Switched over to 2008 corvette LS3 take offs and problem completely went away. I am over 30 psi of boost now, but I am around 4.8ish dwell on those coils without issue. I would def make sure you gap down on your plugs. I would run 15 thou on them. There is no downside for going smaller on the gap.
Thread Starter
Joined: Apr 2006
Posts: 3,890
Likes: 1,137
From: Grand Rapids, Michigan
I have 2 sets of the LS3 style coils, and I swapped them all and it didn't fix the issue, so the problem lies elsewhere. Or maybe it doesn't, it wouldn't be the first time I've had two of the same part fail at the same time. I believe Holley sets the coil dwell at 4.5ms and I've been adding .2ms over 7.5PSI, so I don't think I'm in the danger zone. I could be wrong, however.
I have 2 sets of the LS3 style coils, and I swapped them all and it didn't fix the issue, so the problem lies elsewhere. Or maybe it doesn't, it wouldn't be the first time I've had two of the same part fail at the same time. I believe Holley sets the coil dwell at 4.5ms and I've been adding .2ms over 7.5PSI, so I don't think I'm in the danger zone. I could be wrong, however.
Should have asked but when you swapped coils did you swap as an assembly with a different harness by chance? IF original harness wasn't swapped look at the harness wires closely just for ***** an giggles.
When you start getting frustrated you can easily oversee something. Take a five. If plugs don't do it stop take a 5 you will start chasing you tail and will miss the simple thing staring right at you. That's an easy way to marry a car especially on flat rate...
This is where a stock ecu comes in handy with a misfire counter etc. or it can ruin your day just the same.
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Verdad Gallardo Thread Starter
Joined: Apr 2006
Posts: 3,890
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From: Grand Rapids, Michigan
It's running a Terminator X, so no misfire detection unfortunately. The coil harness is the original off of the donor engine, which was an '06 5.3. I suppose there's a chance there could be a bad wire, but I feel like it would misfire all the time, not just under boost. I'm not going to be able to get to it until Wednesday anyway, so I'll swap the plugs and wires then.
Thread Starter
Joined: Apr 2006
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From: Grand Rapids, Michigan
Well, I got my new plug wires installed and the misfire is gone. However, I am unsure whether the issue lies with the previous plug wires or my install abilities. Getting the connections on the plug side is easy, but on the coil side it's nearly impossible to tell if you have the terminal in the boot around the post in the coil. There's not a really solid "click" when they're in there. I think it's possible that I had the terminal against the outside of the post in the coil, which still allowed it to fire outside of boost, but once I got into boost it wasn't able to transmit full voltage to the wire. Just a possibility, or the cheap wires I bought just weren't up to the task. Either way, I actually unbolted my coils from the valve cover where it was difficult to attach the terminal and made sure the connections were solid. Easier to do that than pull my hair out chasing a misfire again.
As a side note, why in the hell are BR7EF plugs so damn expensive everywhere but Summit Racing? Every chain auto parts store wanted $6-7.50 each for these plugs, but Summit had them for $3 each so I ordered 16 just so I'd have extras on hand.
As a side note, why in the hell are BR7EF plugs so damn expensive everywhere but Summit Racing? Every chain auto parts store wanted $6-7.50 each for these plugs, but Summit had them for $3 each so I ordered 16 just so I'd have extras on hand.
Well, I got my new plug wires installed and the misfire is gone. However, I am unsure whether the issue lies with the previous plug wires or my install abilities. Getting the connections on the plug side is easy, but on the coil side it's nearly impossible to tell if you have the terminal in the boot around the post in the coil. There's not a really solid "click" when they're in there. I think it's possible that I had the terminal against the outside of the post in the coil, which still allowed it to fire outside of boost, but once I got into boost it wasn't able to transmit full voltage to the wire. Just a possibility, or the cheap wires I bought just weren't up to the task. Either way, I actually unbolted my coils from the valve cover where it was difficult to attach the terminal and made sure the connections were solid. Easier to do that than pull my hair out chasing a misfire again.
As a side note, why in the hell are BR7EF plugs so damn expensive everywhere but Summit Racing? Every chain auto parts store wanted $6-7.50 each for these plugs, but Summit had them for $3 each so I ordered 16 just so I'd have extras on hand.
As a side note, why in the hell are BR7EF plugs so damn expensive everywhere but Summit Racing? Every chain auto parts store wanted $6-7.50 each for these plugs, but Summit had them for $3 each so I ordered 16 just so I'd have extras on hand.
I think with as high powered as our ignitions are and as much as we're asking of them, wires should probably get replaced along with plugs more often.
Thread Starter
Joined: Apr 2006
Posts: 3,890
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From: Grand Rapids, Michigan
Yeah, likely so. These Taylor 10.4MM wires I bought are pretty beefy, definitely high quality. I'll hold onto these other wires for stock replacement purposes down the road. I'm glad I got it fixed too, as my last chance to hit the track is Saturday afternoon. Supposed to be a high of 63 degrees, so if I can manage to get it to hook decently, I should be able to click off a 10 second pass.
Yeah, likely so. These Taylor 10.4MM wires I bought are pretty beefy, definitely high quality. I'll hold onto these other wires for stock replacement purposes down the road. I'm glad I got it fixed too, as my last chance to hit the track is Saturday afternoon. Supposed to be a high of 63 degrees, so if I can manage to get it to hook decently, I should be able to click off a 10 second pass.
They've been on the car since the turbo went on but they don't have a ton of miles on them.
Fingers crossed for a good lick and a 10 second slip!
Thread Starter
Joined: Apr 2006
Posts: 3,890
Likes: 1,137
From: Grand Rapids, Michigan
Thread Starter
Joined: Apr 2006
Posts: 3,890
Likes: 1,137
From: Grand Rapids, Michigan
Yeah, they've been stepping up their track prep game there. Lots of cars running records. Would be awesome to see you at the track with the Camaro! As for me, if I can manage to not fully release my clutch and keep the RPM and boost up on launch, it should absolutely rip. I did it my last trip to the track when I sprung a fuel leak, and was a tenth quicker to the 1/8th mile than my best 1/4 mile pass. It would also keep me from spinning the tires as much.
Some day we'll get out there might be a couple years we'll see but it's planned.
Glad the plug wires worked, maybe one of them is bad, I think if you had the wires on fairly good it would not misfire.
Glad the plug wires worked, maybe one of them is bad, I think if you had the wires on fairly good it would not misfire.