1991 Dakota with the 5

  • 124 MILES
1991 Dakota with the 5.2 V8 TBI. No spark out the coil, there is fuel
though. I tried a new coil just to be sure along with the Hall effect
switch. There is positive coming from the ASD Relay. There is continuity
from the negative post of the coil harness to pin 19 at the SBEC, and
from the 3 wires coming from the Hall effect to pins 4, 7, and 24. And c there is continuity from coil posiive to relay. There
is the 8v reference voltage at the Hall effect. I took a test light and put it to the coil (-) and battery positive and cranked, but the light does blink, but very very dim. So the computer is actually getting a signal from the Hall effect, any suggestions before I try a new computer? Thanks !
Wednesday, April 10th, 2013 AT 1:45 AM

1 Reply

Are you familiar with voltage drop tests? Check the ground wires for the Engine Computer. There will usually be four of them. Two are listed as "signal grounds" and two are "power grounds". They all go to the body but the high-current injectors and ignition coil are on a separate circuit inside the computer. The two power ground wires could have a very little resistance due to corrosion or body rust. That resistance is too low to measure accurately but we can measure the RESULTS of that resistance with voltage measurements just like we do in high-current starter circuits.

We normally think of resistance in the coil circuit as being in the positive side, in this case coming from the automatic shutdown relay, (and that voltage should be measured too, but it can also be in the ground side, and that includes the wire between the negative coil terminal and the computer, and the wire between the computer and the body. When the coil is getting ready to fire current is flowing through it to build the magnetic field. That current is what causes the voltage to appear on the computer's ground wires, and it's that resistance that reduces that current flow which reduces the strength of the coil's magnetic field.

You can typically expect to find perhaps 0.2 volts on the power ground wires but if there's more than that you have excessive resistance. That 0.2 volts, by the way, is why they have separate ground wires for the sensors. That voltage would raise the voltage the computer sees from the 5.0 volt sensors substantially, and if it's pulsing as the coil and injectors fire, the computer is going to really get confused.
Was this
Saturday, April 13th, 2013 AT 2:09 AM

Please login or register to post a reply.

Recommended Guides