Afterfiring around 3k

Amazedz said:

Actually I take that back, dad just dropped two. So I doubt they're any good now

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If the porcelain isn't cracked I'll still take'em. For the price of shipping I don't have much to lose.

It's tune related (y) I had the same issue with K&N filter
No tune *random misfire due to colder air*
With tune. WOT ALL DAY

I have a buddy who has a spare set of aftermarket coil packs I may give a shot if I can't figure it out. And like I said I would ship em to ya for shipping cost but dad dropped two of em right after I typed that and the ceramics broke (he has ms, so it's really not his fault). I wouldn't recommend them anyways, as I didn't like them at all on my kenne bell car. They might work really well on nitrous car, but not so much on an fi car.

People have had problems with aftermarket coils. OEM is best if you can get them.

I just re-read the original post and saw the car ran fine before the tune. Even if the coils are good it won't hurt to replace the coil boots as they're only $5 a piece. But since you've done your part by following the tuner's recommendation on plugs, I'd go back to them since the problem still persists.

Amazedz said:

Yea I've already thrown the autolites in the car, and went from 35 thou to 30 thou and it really helped. The afterfire is much less now than it was, but it's still there. If you want those brisk plugs they have maybe 100 miles on em, just dyno time. You can have em price of shipping if you'd like.

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The tuner had me gap the plugs on my 2005 to .028 with 10psi boost running a Custom Blower Grind NSR Comp cam and LT's running 93 Octane on stock compression. Not quite as aggressive as your setup, so you may wish to close that gap a little bit more. May wish to bounce it off the tuner first.

I'll give him a call in the morning and see what he says. You can tell by the dyno sheet it had a spark issue. I have a felling that's why he wanted me to pull the old plugs and put autolites back in it.

Is the tuner aware of which cams you are using?
Sounds a lot like the injector timing hasn't been adjusted and it is still spraying fuel when the intake valve is open.

Yea he is fully aware of the cams. Out of curiousity, if the injectors were spraying while the intake valve was open wouldn't that cause a back fire through the intake instead of the exhaust?

Amazedz said:

I'll give him a call in the morning and see what he says. You can tell by the dyno sheet it had a spark issue. I have a felling that's why he wanted me to pull the old plugs and put autolites back in it.

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Were there disruptions in the curve? Just wondering what spark issue looks like through a dyno sheet.

Amazedz said:

Yea he is fully aware of the cams. Out of curiousity, if the injectors were spraying while the intake valve was open wouldn't that cause a back fire through the intake instead of the exhaust?

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That would depend on valve overlap I think. When all three valves are open simultaneously, fuel could spray right through the cylinder if the timing was off just right.

Someone tell me how to post pics? I have pictures of the dyno sheet right here on my phone. I discovered a very slight vacuum leak today that was causing me to only get 6.5 lbs of boost instead of 8 like it's getting now. I almost feel stupid after I found it. It's still popping though, so I still have work to do.

I use imgur, and use the link for the image here in the img tags

Imgur is great.

www.imgur.com
1. Create account
2. Login in and then click "new post" button
3. select "upload images" from drop down
4. Click "BROWSE"
5. Locate photo on device.
6. When upload is complete click on your login name in the upper right hand corner.
7. Select "images" from the drop down screen
8. Single click on the image you wish to share.
9. Copy the BBCODE hyperlink which will post the full photo.
10. Paste into your reply.
11. Watch others enjoy. Delete when tired of looking at it.

Back on topic...

Amazedz said:

Yea he is fully aware of the cams. Out of curiousity, if the injectors were spraying while the intake valve was open wouldn't that cause a back fire through the intake instead of the exhaust?

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Those cams have a lot of overlap so if fuel was spraying while the intake valve is open, some of it would get sucked right out the exhaust valve and pop in the exhaust, which sounds like what is happening here.

Oh I didn't know I could use Imgur, I've been a loyal imgurian for 2 years now. Anyways, I got to thinking about overlap earlier actually, and that makes sense that raw fuel being sprayed into the cylinder and running right out the exhaust then igniting in the headers/exhaust, but wouldn't it be doing it from idle all the way to redline instead of just between 2600 and 3k? Also right before the afterfire it almost seems like it's busting back like it's on a 2 step at 3k or something. it's difficult to describe, but it for sure wasn't there before the kenne bell went on. I talked to Dan @ prodyno today and he said he would look into it so I'll see if he can come up with something.

Here's the dyno sheet for those interested (lets hope this works)

Amazedz said:

Oh I didn't know I could use Imgur, I've been a loyal imgurian for 2 years now. Anyways, I got to thinking about overlap earlier actually, and that makes sense that raw fuel being sprayed into the cylinder and running right out the exhaust then igniting in the headers/exhaust, but wouldn't it be doing it from idle all the way to redline instead of just between 2600 and 3k? Also right before the afterfire it almost seems like it's busting back like it's on a 2 step at 3k or something. it's difficult to describe, but it for sure wasn't there before the kenne bell went on. I talked to Dan @ prodyno today and he said he would look into it so I'll see if he can come up with something.

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I am guessing you retained your stock VCT, and with the way cam phasers work, it's not that cut and dry. If you had the same cams before the blower went on and the car drove fine before, I still think this can be fixed through a tune adjustment.

I agree, I'm starting to think it might be tune related. I've since placed a gopro under the hood filming the bypass valve during a drive to make sure it opens and closes like it should since I don't have a low vacuum bypass because the car was holding 15 in hg at idle according to my boost/vac gauge. Dans bringing the dyno to VIR here in a few weeks so I'm taking it to him to have him adjust on it alittle bit more and see what happens. Until then I just have to drive the car differently. Pulling the car out of overdrive to climb hills or pass cars on the highway seems to keep it out of the dangerous throttle position/rpm range, thus keeping it from afterfiring and doing the 2 step like misfire.

Kind of off topic but did anyone comment on your power numbers? It seems low for your setup. Maybe you'll get some power back once you address this afterfire.

Yea, i found a small vac leak after it came off the dyno and it was about 1psi of boost low. Afr's are still in the 11s I'm just worried about the 18* of timing being set on 7.5lbs vs the 8.5 it's making now. Even Dan said it should've been around 470 and that he thought it should have made more. Also the torque converter has 90 miles on it, so that may have a bit to do with it not making so much. It would've made a lot more power with a blower cam though. Those cams are killing that car, but they sound sooooo good.

I had the same exact problems..A small vacuum leak at the boost gauge and spark plugs that have loosened themselves. It only made 429whp on a 93 degree day and I am planning to do another dyno pull now that it's all fixed. The hot rod cams I have create more valve overlap than blower cams do so my setup isn't ideal either.