vehicle - 1987 W100, 318, 4 pin connector electronic ignition system,
edelbrock 600cfm carb with performer intake and cam.
I just put a new carb, intake maniford, timing gears, and cam in my
truck and checked the timing which was 8 BTDC as list on the label. I
increased the throttle gradually up to 4500rpm and the timing never
advanced to more the 18 BTDC. There is no vacuum or mechanical
advance on the distributor and as far as I can tell there are no
sensors connected to the computer, just the ballast resistor. Reading
the Haynes repair section on this system gave me no answers. Can
someone tell me how the computer adjusts the timing and if the
computer might be faulty? I did not check the advance before
installing the new carb so it may have always been like that. Truck
has always been sluggish but I thought that was from the gearing and 4
Would changing the distributor to one with weights and a vacuum
advance give me better economy or performance? I know the vendors
selling them say it will but what else would the say.
Trucks with the 318 had electronic ignition with mechanical and
vacuum advance distributors.
Trucks with 360 and slant 6 engines had a spark control computer.
You mention a computer, is there one attached to the side of the
air cleaner or possibly on an inner fender? (you can't miss it,
big as a cigar box)
You mention a 4 pin ECU, that is NOT a computer, just an
If you measured 18* timing advance, there has to be an advance
coming from somewhere. The mechanical advance is below the base
plate in the distributor, if you can twist the rotor clockwise an
appreciable amount, there is a mechanical advance lurking in the
distributor. Vacuum advance should be obvious.
Note; of the two advance springs typically installed in the
mechanical advance, the lighter ones can and do break, if this
happens and the fly weights aren't pulled back fully, you'll see
It's entirely possible that someone put the wrong distributor in
the truck, an SCC type distributor from a 360 would certainly fit.
Are you sure the engine is a 318?
Was a 318 swapped in in leu of a 360?
You're sure of the ignition system? Standard Mopar ECU? Is the
distributor hall effect or does it have a pick up coil?
So you do have a computer? That computer will have what looks like a
vacuum advance mounted to it, because that's where it is on the computer
controlled trucks. Is the computer mounted beside / behind the battery?
If you do have a computer, you should NOT have a Mopar ECU, someone's been
fooling with it.
It sounds like you can remove the ECU and use it as is or complete what
seems to be a conversion that wasn't finished. It'll run MUCH better with
the standard Mopar distributor and ECU. BTDT.
This is the complete kit you need, it comes with complete instructions for
your truck, including eliminating the computer from the ignition system.
and I found some instructions, I don't think these are complete?
Use the part number to shop for the best price if you decide to go that
way. It sounds like all you really need to complete the conversion is a
distributor, ballast resistor and wiring harness though? Check junkyards
for the distributor, parts store for the ballast. The harness used to be
available as a separate part number or you can cobble something up from the
junkyard if you're on a tight budget.
Thanks for the responses. Let me try to answer your questions and
correct something I said.
The truck does not have a computer I was referring to the ignition
module or ECU. The distributor has a pickup coil.
It is a 318, does not have any advances on the distributor, I double
checked under the plate and there is no mechanical advance. It is the
original setup, I got the truck from a coworker who was the original
owner and he said everything is stock.
I did not degree the camshaft, I just followed the instructions from
Edelbrock and doublechecked everything I did.
Any and all responses are much appreciated.
The ECU has no timing advance capability.
Sounds like somehow somewhere, the wrong distributor got
installed in that truck.
The path of least resistance might be to just get a
remanufactured distributor for the correct application, install
it, set the timing and go.
The later model engines have a crank sensor as the ignition sensor. The
sensor is a hall effect sensor which is mounted at the rear top of the
passenger side of the block over the flywheel. There are notches on the
flywheel that create the trigger pulses. The pulses occur at maximum advance
and are delayed depending on the engine speed and vacuum. Rotating the
distributor will of course have no effect, as its only job is just to
distributed the spark to the appropriate cylinder. There are different
flywheels and flexplates depending if the engine is internally balenced or
externally balenced. It is possible that the placement of the trigger
notches are also different, but I doubt that myself. The placement of the
sensor is fixed and also not adjustable. From experience, max advance
should be about 37 degrees before TDC. (above 4000 rpm and 0 vacuum)
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