Hey guys, i've been having some issues lately with the truck. # 8 piston failed on me. somewhere around the 5k rpm mark before the shift it went into a miss. limped it home. Pulled the plug, 8's electrode was bent closed, boroscoped it. The crown chipped out on top.. Pulled the heads, cylinder was ok, head and piston top looked about the same as the rest for carbon. Pulled the pan and replaced the piston, had the rod checked and re-pistoned at the machine shop. New gm rings, rod bolts and bearings as well, Even though the stock rod bearings looked great, checked rod endplay as well, was good. Rebrushed up the cylinder and Closed it all back up, ran it for 2 more days and it does it again, haven't pulled the head off again, but it looks like the same chunk out of the same area of piston, towards the center of the v and to the front.

i have been beating on this little 4.8 with boost for 20k. 8lbs for probably the last 10k I went up to 11lbs a couple weeks ago, still all stock engine internals and i've smacked this piston similarly twice. So what i'm wondering is, am i floating the intake valve a little into the piston with the extra manifold pressure? Valve springs are stock, so i know they arent that great, was just gonna do them with a cam this winter anyway..

What do you guys think? seen this before? I 've got a couple pictures but bear with me on the quality, as they are pretty shitty.

 

That's from detonation dude. You need to have your tune done for the increase in boost. It's to lean and/or to much timing.

 

That is caused from detonation. Did you re-tune after the pulley change? The most likely culprit is not enough fuel or too much timing with the new boost. The rear cyls always run more lean on a boosted gen3 due to the air pressure being slightly higher in the back of the manifold from the forced air hitting the back wall. At least that is my take on it. Being the same one there is always a chance of trash in the #8 injector but if you didn't re-tune for the boost then that is where i'd start.
Also, you are very likely to be maxing out your injectors with 11psi on a 4.8. That is if the MAF sensor is correcting the fueling enough anyhow.

 

Thanks for the replys!

I probably do need a tune. I have just kinda modified my custom tune from the original 7psi kit as i went up in boost, but seeing as it is not a dyno tune, or wide band monitored tune its probably quite wild. I have 43lb injectors installed from the kit. Is that insufficient? I found increasing my fuel delivery at all in the past via the tuner resulted in an over fueling situation, and i had to run them in the leanest setting. So once again, i probably can't tune very accurate.. or pretty weak for mapping.

What kinda timing should a guy run with that much FI? I usually run under 100F boosted intake temps in summer. When i watched the scanner in real time, the computer never retarded the timing for detonation, and i could never hear it.

I had detonation problems in the past, when i went up in boost, (i could hear an odd ping under full load on a hot day) so then i went aftercooled, and got rid of the cats and i never had an issue. I could even go down to reg. unleaded without a problem.

Does anyone know any good tuners in alberta? Davenport Racing maybe?

 

stick a wideband in that thing! Have you checked out EFI or HPTuners yet?

 

Here are some Alberta tuning options for u depepnding on your location.

Calgary:
Davenport Racing. I would recommend them Shannon does an excellent job.

Dynomotive. Toma Has been tuning for many years and is one of the most respected tuners in Alberta

Edmonton:
Horsepower Solutions. (I am the tuner there)
Campbell Automotive: Nolan Is an excellent tuner and has many years of experiance.

Hope that will help you out dude!

 

Thanks black x,

Sounds like Davenport might be my choice as Calgary is far closer for me (Med. Hat), and i've heard good things of them before. Anyways probably looking at next spring for it all.. In the mean time,

Making a whole bunch of decisions, stay with the little lr4 fix her and cam it, or go deeper?
Go to an '05 lq4 and transfer fi setup and build up, then my tranny will probably out smart itself again and won't hold up so i'd have to spend more.. but i'd have the buildup to go alot further.. ahh decisions, decisions, and spent paychecks... haha

anyways, thanks again for the info, i'll keep ya in mind.

 

Westers Garage in Tilley is right on your doorstep dude. Lynden there is also very capable of giving you the help you need.