Predator may be causing misfires on truck

[tarpon4me]

Just what is in the title. I have a predator for my 2001 silverado with a 5.3 V8 (Pacesetter long tubes, ORY, Powerbond 25% underdrive, MSD 8.5's, TR55 plugs, K&N Filter w/ stock airbox). For starters, I pasted a link to a website where I have been tracking my repair efforts and requests for suggestions:

http://www.silveradosierra.com/vortec-5 ... 15674.html

My first mistake was not simply restoring the factory backup and leaving it. I restored the back up, and immediately reloaded the canned 87 octane tune. So, what's the short?

Symptoms: random misfires on cylinders 1,2, and 7

What has been done(note that, not only did I check these items, but so did a mechanic about 2 hours ago to confirm): Complete fuel system check, everythign is fine. (fuel pressure, pump, filter changed, injectors, regulator, TPS, both cam and crank sensors)

Compression is perfect in all cylinders, and there are no vacum or intake manifold leaks. There are no exhaust leaks, and MAF is fine.

Coil packs, plugs, and plug wires perfect. All pulled, inspected, OMD'd where applicable.

Guess what that leaves? Either the predator or the computer is crap. I restored the original back up 15 miles ago. after 15 more i'll view live data with the tool, and i'll know for sure then. I am 90% sure it's the predator. I'm open for suggestion, however. [/url]

[mikel]

tunes cant cause misfires....

[tarpon4me]

That's not entirely accurate. Though, I understand your support for your product, The more popular and reputable websites like silveradosierra.com or performancetrucks.net have documented instances where the tune did infact cause similar/identical symptoms. Of course, not just with a predator, but with multiple different tools and also known custom tuning companies like Nelson. So, i understand it may not be a common problem, but it's most certainly a viable candidate. I am, however, open to suggestion.

[mikel]

Well, I wasnt sticking up for the product, but rather stating what I know to be fact...

What exactly was changed in these tunes that were documented to cause misfires??

[mikel]

bad O2 sensors or O2 harnesses would be my first guess here....especially since you have headers.

[tarpon4me]

The bank 2 O2 sensor is a week old. And agreed, long tubes have a tendacy to fry cheap O2 sensors. Funny thing, I have the bosch (cheapo) sensors installed. I got home this afternoon, checked my codes, and guess what is there? A p1133 code. BUT!!! I'm also still getting random misfires on bank two, not just bank one. It's very possible I have a sluggish O2 sensor, but since iit's bank one, it shouldn't be causing randoms on both banks. P1133 is for bank 1 only. sticky EGR maybe?

[mikel]

Id almost bet your O2 harnesses are burnt on the headers somewhere...

[tarpon4me]

The wires are well away from the headers though. Both sides run directly from the installation point to the back side of the frame. I checked the wiring for burns and crimps, but didn't find anything. If I had a picture i'd show you, sorry about that. But, the upstream O2 mount at an angle (very easy to get to) and the harness runs directly over the frame and attaches on the back side out of harms way. Never had an issue after header installation, and nothing has changed. To my knowledge and best I can tell, the front side of the harness is no where near the headers either. But even then, I've gone through O2's before and never had an O2 cause misfires. I am going to check the cylinders again here in a few, and see if the misfires have cleared up. I'll report back either tonight or tomorrow morning.

[tarpon4me]

The cylinders are still misfiring, not sure what to do from here.

[06MonteSS]

MSD is known for causing misfires man - have seen it over and over and over...

get rid of the MSD stuff and use stock/AC Delco, will be better off...

[tarpon4me]

You're not the first to tell me that about the MSD's. Disappointing if you ask me. Problem is, the main reason I got MDS wires is because this particular model allows me to bend the boot away from the headers. With Long tubes, I can't install heat sheilds on the boot, and I am scared that the stock plug wires may not be able to hold up to the heat. I could potentially heat wrap them, but i'm not sure how that would work. Thing is, we swapped #1 with another standard wire yesterday when I was at the mechanic's shop. It cleared up cylinder 1 for short spell, then the misfires came back. I also noticed today that, the misfires are less often when the motor warms up. What is a good aftermarket wire, that I can bend out of the way of the headers?

[mikel]

the more you remove and reinstall ANY LS style plug wires, the more chance there is for an issue, trust me

[tarpon4me]

I'm going to swap the TR55 plugs for factory Iridium plugs probably today, and see what happens.

[mikel]

I been running TRs since the day I got my Z28, never had an issue....

[tarpon4me]

Yeah, well I swapped the plugs, and though the motor seems to be running a bit smoother, the misfires are still there. Just doesn't make any sense. Once the motor warms up and gets down the road, seems like the misfires are slim to none.