Tommy have you measured your rods? My rods were about ~.010-.015 short, which I guess might create lower compression which might decrease MPG?? Who knows.
What was very wierd is the other patterns taht occured in the last 2 months or so of my stock engine's life:
huge decrease in MPG
and the following issues mentioned below would only happen "sometimes" then go away, maybe 3 times a week, or the truck would act up for 2 days straight, then be fine for 5 days etc:
random sporadic idle surge; sometimes really severe associated with eye-watering raw fuel smell from the exahust and whisps of white smoke even when warmed up, like if I was driving and came down to a stop light. I would check my balance rates when it was doing this and 1 or 2 of the cylinders would be way out of whack (+8 or +9 or so). The others would be at the higher end of the "allowable" spectrum, but still barely within spec. Then the next 2 days the truck would be fine and all balance rates normal. Then it would do a slight surge, then be fine, then do 2 days of the really noticible surge. Then it would go back to running perfectly smooth.
I thought it was an injector going bad. "it cant be an internal problem, because then it would exhibit the condition ALL the time, not just sporadicly, so it MUST be an injector" I told myself.
The day it died, we drove 3 hours to a dyno, beat the crap out of it, insane EGT's, 20 second pulls, basically being REALLY stupid loading the truck in effort to get the turbo to spool to full boost on the dyno. Turned out the exhaust evac system they had was so small that it was probably acting like a big plug in the exhaust pipe.
But the truck didnt die on the dyno, we drove 3 hours back to school, and the truck felt a lot weaker, like I was driving with the fuel pressure releif valve partially opened. We messed around on some back roads and I had no idea what was wrong with it. 10 minutes away from school I went WOT to keep my buddy in his LBZ from passing me, downshifted 5-4, ~3000rpm, EGT's started climbing and I think I was passing through 1200 or so when I heard the muffled pop as she let go.
I wish I could have taken apart the engine 10 seconds before it blew (the period when it was still running fine but way down on power) and seen what it looked like; ie what caused the power to suddenly drop off, if there was a hairline crack leaking just a little bit of pressure into the crankcase, etc...I have no idea.
I beleive its EGT's. MAYBE combined with timing, but I think mostly EGT's. The timing bends the rods, but I think the EGT's do the pistons in. As I said, 2 cracked all the way through, and 3 had huge developing cracks. Some of the developing cracks were NOT parallel or perpendicular to the wrist pins. Some were at 45* to the wrist pin, etc... The two that cracked all the way through were parallel to the wrist pin.
Which leads me to another big question that I dont think anyone has mentioned yet.
Does piston to cylinder wall clearance play a factor in this??? Has anyone taken apart some stock motors and seen if the clearance is consistant between factory motors? Do EGT's make the pistons expand to the point where they "bind" on motors built with tighter clearances etc?? OR maybe as the rods compress/bend slightly it changes dwell at TDC a little bit, or maybe stresses the piston in some other way? I have no idea, just throwing some dumb ideas out there.
ben
