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Fragmented piston

Rugger187

Rugger187

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I got some vortec heads and manifold for my TBI 383 awhile back and was getting ready to install them this past week.
But.... A few weeks ago I was hauling up Eisenhower pass in CO with a load and it overheated a bit. All the way home she was pouring oil out the valve cover on the pass side.
I was gonna do a leak down and compression test but figured since I had the new heads I would just tear into it.
The dang thing runs great but my #3 piston is destroyed. Top lands broke off, first ring is busted. It killed a valve as well which was causing my excessive crank case pressure. Heck, I had oil leaking around my intake bolts it was so bad.
The cylinder walls still show the fresh cross hatch marks on it. I have less than 5k on the motor.
So this next week I will begin the rebuild hoping that the cylinders are good and HOPING I can get it together sooner than later without too much more money involved.
 
That my friend was caused by detonation. You will do it again if you don't either repair the issue (timing too far off, EGR not working, or pull down a gear when the engine starts to lug).
 
Could've been the EGR. It was a little bit clogged awhile back and I swapped in a junkyard one I had laying around.
 
dyeager535 said:
What was done to the PROM?

383/TBI/Vortec heads?
Click to expand...


Nothing yet. It ran great with all the stock parts in conjunction with the 383. I have been running a very mild cam which helps. I've never has my check engine light come on.
I've ran it with the 383 for about 10k miles so far.
As for the vortec swap; I'll post on this thread what I have to do. But as far as it looks, I'll just have to move the EGR, extend some wires and hoses, and other various stuff.
 
Nothing? I don't think I'm out of line saying you shouldn't be driving that thing without getting a wideband O2 sensor on it. Obviously you won't be right now, even after its fixed though.

That combo is WAY WAY wrong for a stock PROM, at this point I'd say your problem wasn't EGR, it was/is running way too lean because fueling is so far off. Timing being way off isn't going to help, but you SHOULD have been bouncing off the knock sensor the whole time, which I certainly would have expected you would have noticed? Then again, even at max retard probably still too little fuel and too little pulled timing.
 
Well maybe I'll have to upgrade some things then. Is the stock O2 sensor not a wideband? It never knocked though.
I was also planning on doing all the TBI mods which I figure would help. But the plugs always looked good so I never thought it was lean. But maybe it was. I wonder if TBI chips or someone has a custom chip for a 383?
Thanks for the input.
 
You will want to check out the injection forum here, EagleMark knows what he is doing with these systems. TBIchips doesn't seem to get the same rating for customer service as it did quite awhile in the past.

Expect that fuel pressure may be an issue, injectors may be too small, timing and fueling within the PROM are definitely going to be wrong.

Engines can sound/feel fine lean, but feeling is not knowing. The stock system can't compensate for fuel under heavy throttle...if you are pushing the truck hard (I dunno, like climbing a mountain pass maybe? lol) it's lean at the worst time. The stock O2's are "narrowband" thus are only accurate at 14.7:1 AFR, which isn't correct for heavy load, and isn't right with modern fuel (ethanol) either.

I am surprised you didn't hear some sort of pinging, although with stock injectors (lean) I didn't get any knocking/pinging with lots of advance, it even felt strong, butafter replacing the injectors it pinged, and dialing in timing/fueling fixed that.
 
5K and just one piston failed due to detonation, thats a lot of detonation to only affect one cylinder. detonation sure but probably more than just that, maybe a cracked ring during installation and when overheated let go. Just a thought.
 
I've built thousands of engines and from what he described detonation caused his issue.
 
I wouldn't be surprised if it was simply due to being under prolonged "open loop" operation under heavy load for just that climb.

You'd easily get away with running around "lean" while cruising and what not, if fueling isn't too far off, as with enough fuel the system will compensate in closed loop operation, which is most driving. But climbing a mountain pass in a full size truck? You are likely to be in open loop for a prolonged period (heavy throttle), and if you are lean in open loop, the pistons are going to get hot, and the longer it runs like that, the worse it gets.

Coupled with too much timing in the first place, and recipe for disaster...can't recall what the max timing retard is with most '747 programming, but IIRC 10* is common on other ECM's. If the TBI system with the swirl heads has a max advance of 46*, under max retard (from knock) it could be 36*...that's what Vortec's accept as max normally, so really not retarding timing at all for the Vortec heads. This would be the same idea at every RPM. Programmed advance with full retard might be more along the lines of what the Vortecs actually want, so no detriment to performance based on timing. I can certainly see that the truck would appear to run fine, even under heavy load, with the ECM was retarding timing as much as it could.

You'd get no CEL because under heavy throttle conditions, the exhaust stream *should* be too rich for the O2 to read accurately, so the ECM isn't programmed to use the O2 input.
 
Interesting. Good info. Gives me a bit take think about and to plan for. Thanks!
 
Normally, if timing is "dialed in" for normal operation, when you start hitting the knock sensor, you know it. The engine pretty much falls on its face. What I suspect is about the only explanation I can come up with based on your setup, and the fact you didn't hear/feel it.

On an interesting note about running lean, saw a camper van driving up a hill on the freeway pulling a large trailer. I could tell it was a 454 as I passed them, because I could see the shape of the manifold through the wheel well, because it was glowing red. I actually slowed down to show my passenger, as I've never seen it that bad.
 
Got all the TBI upgrades ordered from RV Morse.
And since I am short on time, my father asked if he could rebuild the motor for me. He teaches automotive at Dixie College in St George, UT.
So I dropped both sets of heads, both intakes, the engine, and assorted parts off at the college. He will CC the heads and order me up new pistons as well as any machine work that needs doing.
 
The cylinder doesn't look too bad where the piston grenaded. Let's hope the machine shop agrees.
Also ordered up a new computer controlled cam and lifters. Also putting in roller rockers, new push rods, and other stuff.
 
What type of piston, hyper-craptic? They don't tolerate pre-ignition very well.
Also report back what your rod bearings look like...
 
I'm not entirely sure it was detonation. All the other pistons look perfect. It is just my #3 piston. Maybe something fell in somehow? But the valve isn't bent and the valve seat is good. Maybe just a bad piston?
But regardless, I got the TBI mods, I will get a chip, and I will get dished forged pistons.
 
TBD. I'll be CC ing the heads this week. Based on other comps it was around 9.5. I should've done it when I built it before but didn't. Now I'm paying for it.
Could've been a tad higher and I got bad gas.
 
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