|
Diesel engine 'run-away', where the engine runs on other than the injected fuel, is seldom caused by worn rings -
A. Gassers (patooie!) develop ~26"HG vacuum on the intake stroke which can 'suck' crankcase vapors thru the worn rings, which you see as blue smoke
Engine oil burns blue, because combustion temperatures are too low for complete burn - Diesel fuel (a light oil) emits white smoke when combustion temp is too low for complete burn - Diesel fuel emits black smoke when mixtures are too rich for complete burn
Diesels do not develop vacuum on the intake stroke, so the vapors normally* have no path to the combustion chamber
Crankcase vapors result as heated oil vaporizes (avg turbo temp is ~650deg) and thrashed oil vaporizes (the rotating\reciprocating assembly, crank and rods, thrash the heated oil even at idle) - also from the normally slight combustion-pressure leakage thru the piston rings
Combustion leakage past the piston-rings is, guess what? Post-combustion gasses, or..........EGR. Ain't even gonna burn if recirculated thru the intake.
B. Rings worn or overheated to the point of excessive leakage are unable to maintain the pressures required to ignite Diesel fuel - the engine will be easy to crank but very difficult to lite-off, or 'hard-starting', because of the lowered cylinder pressure resulting from the badly-leaking piston-ring seal
C. Medium-duty and heavy-duty Diesel engines normally vented crankcase vapors thru a tube to the draft under the vehicle - crankcase vapors and blow-by had no path to the combustion chamber
D. *Light-duty Diesels became popular in the early '80's, and as such were required to meet emissions standards for passenger vehicles - crankcase vapors were plumbed to the intake manifold to be consumed with the injected fuel
Suddenly, Diesel crankcase vapors and blow-by (high-pressure leakage) had a direct path to the combustion chamber
Even at that, no sudden incidence of engine-runaway was evidenced as those early engines 'matured', or were severely overheated or abused - the only symptom was surging, where the engine was burning the excess vapors, as evidenced by blue smoke in the exhaust, and rpms increased slightly over demand as controlled by the injection pump
Stationary Diesel engines and vehicles in oil-field service can experience uncontrolled runaway, where killing the power to the injection pump does not shut the engine down - this occurs where an external source of gaseous fuel is available, as from pipeline or valve leakage, or intentional blow-down - propane, butane, natural gas, etc.
So - runaway is not a concern - surging can be a symptom of fuel source external to the injection pump - can also be symptomatic of EFI system problems - if killing IGN power does not kill the engine, pop the airbox cover off and stuff a large rag in the intake duct to the MAF - gotsta have air to sustain combustion...........right?
_________________
'05 CRD Limited
Pricol EGT, Boost
GDE Hot '11; EDGE Trail switched
SEGR; Provent; Magnaflow;
Suncoast T\C, Transgo Tow'n'Go switch;
Cummins LP module, Fleetguard filter, Filterminder
2.5" Daystar f, OME r; Ranchos; K80767's, Al's lifted uppers
Rubicons, 2.55 Goodyears
Four in a row really makes it go
Last edited by gmctd on Fri Nov 09, 2007 2:09 pm, edited 2 times in total.
|
Login
Register
FAQ
Search
I was sure it was a gonner by the racket it was making. 
But like any good VW diesel it started right up and lived on till a S10 Blazer ran a stop sign and T boned my wife one morning. It was a $500 car from jersey that was already broken with a few dings and she loved that car 
She even filled her own tank from the dirty pump 
