It's no secret - putting a crossover tube on the fuel rail will help with
the fuel issue - but just better control. The excessive lean condition
claimed has yet to present itself every time I yank the heads on these
things. However, the biggest issue causing head problems is the cooling
system - causing the rear cylinder head cracks (always on #5,7,6,8). Drill,
Tap, and put a crossover tube on the rear cooling passages to help circulate
the coolant instead of building up the "hot spots".
The funny thing in their explanation (while there may be some truth to the
lean condition they're claiming), the injector drivers would pick this
up...along with the misfire monitor. A lean condition (violent explosion)
would cause a unexpected change in crankshaft rotation. Then again...so can
a "el-cheapo" serpentine belt.
- Bernd
-----Original Message-----
From: jon@dakota-truck.net [mailto:jon@dakota-truck.net]
Sent: Monday, August 04, 2008 3:14 PM
To: dakota-truck-moderator@bent.twistedbits.net
Subject: DML: Magnum engine "design flaw"
In the August 2008 issue of Mopar Muscle there's an article on a
'69 Satellite into which the owner transplanted a 318 Magnum from an
'02 Dak. (http://tinyurl.com/5amxf6) In the article, the owner of
the vehicle says that the Magnum engines have a "fundamental flaw"
with the fuel system. He says:
"Chrysler feeds the driver-side bank of injectors from the fuel pump
in the tank, and then they use a very skinny hose to go between the
fuel rail on the driver's side to the one on the passenger side. So
when you fire up the engine, cylinder numbers five and seven fire.
When they fire, the whole pressure in the rail drops momentarily, and
then they want to fire cylinder number two, which is as far away as
you can get from that spot. So the fuel pressure drops over there,
and that cylinder always ends up lean."
He says used a prototype set of fuel rails from Ross Machine
Engineering to cure the "number two cylinder starvation problem".
Something about the above didn't sound right to me, so I thought
I'd run it by you folks and see what you thought. (Plus, there
were a few goofy things about the car that kind've made me question
the guy in general; for example, his intention with the EFI system was
to set up the car for the best fuel economy as opposed to power, and
yet when he installed an aftermarket 5-speed, he chose one with a 1:1
top gear instead of an overdrive...)
I'm certainly no fluid engineer and don't even play one on TV, but
his explanation doesn't make sense to me. The distance between the
fuel feed and a particular injector shouldn't matter because the
entire rail is pressurized and it is the pump which is creating the
pressure. Its not like the injectors are sucking fuel out of the rail
and then the pump has to kick on and make it back up or something.
The injector is just a gate; the only reason fuel comes out when it is
opened is that the pump is pushing fuel up into the rail from the
tank, so as long as the crossover tube outflows any individual
injector, the pressure in the fuel rail should remain the same at all
times. Also, his claim about having #5 and #7 firing together
dropping the fuel pressure a bit doesn't seem right either. Its not
like they are firing at the same time, the firings are spaced out
equally across all 360 degrees of engine revolution. So, if firing
two injectors sequentially was enough to drop the fuel pressure in the
rail slightly, then the next firing would drop it a little more, and
so on until soon you'd have no pressure at all. It is my contention
that if even a single firing is big enough to drop the pressure in the
fuel rail such that it is not back up to its pre-fire pressure by the
time the next injector opens, then your fuel pump is not big enough or
you've got some other restriction prior to the fuel rail.
Anyway, does the above make any sense, or am I just off my game
today? :-) For those of you who have torn into a bunch of these
engines (Bernd?), has it been your experience for the #2 cylinder on
Magnum engines to be running lean?
--
-Jon-
.- Jon Steiger -- jon@dakota-truck.net or jon@jonsteiger.com -.
| '96 Kolb Firefly, '96 Suzuki Intruder, Miscellaneous Mopars |
`-------------------------------- http://www.jonsteiger.com --'
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