A Bosch Hall-Effect electronic ignition, single coil, distributor, fuel injected, etc., 4 cylinder vehicle (Saab 900) w/bucking problems @ same mid-range RPM, retarded ignition timing @ same RPM range, quickly burning distributor cap inner contacts. The root cause has been elusive (long list of normal tests, other than 2 items above, by both Saab mechs & myself)
A recurrent 5 VDC spike, that synchs with the secondary ignition's 6 KV
- 9 KV spark firing line (initial spark plug firing voltage peak), is present in the - Ignition Control Module, Hall-Sensor from the ICM, the Ignition Amplifier, and the positive terminal of the ignition coil - power supply (all four are share the same ~14 VDC feed)*. Scope test leads have been routed, as best as possible, and in various ways, to avoid car's other electrical components and wiring, and HF reject has been used, w/o change to the 5 VDC spike
Spark plug wires are well-regarded OEM, and have been tested for leakage (none found)
Alternator has steady VDC output, with normal 3 VDC spikes that substantially & normally diminish as electrical load is increased, with nominal AC ripple current.
All grounds have been cleaned, secured, and V-dropped w/both scope and DMM.
What little I've read wrt potentially problem/damage causing ignition system spikes, seem to imply much larger voltages(?). Is the 5 VDC spike within an acceptable level (comparable to a low-leve alt spike)?
Can a diode, MOSFET, capacitor, etc (out of my experience here) be placed between the battery's (+) terminal, and the ignition system circuit, to eliminate the spike? If so, what specifically should be used?
Thank you, Lance
- http://216.78.172.20/electrical_system_folder/ezkwir.htm
345 = Hall Sensor | red wire, backprobed at ICM
146 = Ignition Amplifier | terminal #45 = ignition coil | 15 (+) terminal