Ingnition switch, cause of power loss
Discussion
Hi,
I thought I would recount a recent problem and simple fix in case anyone is suffering with the same issue.
I had been having long term problems with variable engine performance, there have been a list of symptoms but basically my SBC seemed to be down on power / torque and felt like it was being "pushed" to rev over about 4.5k rpm. The most frustrating thing was that the performance of the engine could change by large amount between outings in the car.
After trying lots of stuff a link was established with spark energy produced by the ignition coils. Engine’s performance was much more dependent than it should be on ignition coil charging time (set using the engines ECU). So focus moved to the health of the 12v feed to the coils. The first step in fixing the problems was to replace a couple of relays that are specific to the set up of my ECU. These relays switch power to the engine’s ignition coils and injectors. They were replaced with higher current (70 amp) items which bought a significant improvement in power and the engine’s general behaviour. After a while however engine performance deteriorated again.
This time the wiring was traced back right back to the Battery. It seems that the standard Ultima wiring loom has the ignition coils and fuel pumps (and on my car the ECU, injectors and high pressure fuel pump) switched directly by the car’s ignition switch. These components together have a significant current draw and some are inductive loads that are hard on ignition switch contacts. To test for poor contact quality the ignition switch was operated 20 or 30 times with the battery disconnected to try to clean the ignition switch contacts. The engine’s performance was significantly stronger after this with noticeably stronger power delivery, smoother running and happy right to the redline.
A couple more 70amp relays were fitted, operated by the ignition switch, that now switch power to the ignition coils, fuel pumps and injectors etc. The engine is now feels very strong and is 100% consistent each time the car is driven.
I know the fault is simple one but I thought I would mention as I guess it develops slowly over time and could have developed on other older / high use Ultimas.
All told it cost about £20 to put the relays in the ignition switch relays, what a difference to the car !
Nick.
I thought I would recount a recent problem and simple fix in case anyone is suffering with the same issue.
I had been having long term problems with variable engine performance, there have been a list of symptoms but basically my SBC seemed to be down on power / torque and felt like it was being "pushed" to rev over about 4.5k rpm. The most frustrating thing was that the performance of the engine could change by large amount between outings in the car.
After trying lots of stuff a link was established with spark energy produced by the ignition coils. Engine’s performance was much more dependent than it should be on ignition coil charging time (set using the engines ECU). So focus moved to the health of the 12v feed to the coils. The first step in fixing the problems was to replace a couple of relays that are specific to the set up of my ECU. These relays switch power to the engine’s ignition coils and injectors. They were replaced with higher current (70 amp) items which bought a significant improvement in power and the engine’s general behaviour. After a while however engine performance deteriorated again.
This time the wiring was traced back right back to the Battery. It seems that the standard Ultima wiring loom has the ignition coils and fuel pumps (and on my car the ECU, injectors and high pressure fuel pump) switched directly by the car’s ignition switch. These components together have a significant current draw and some are inductive loads that are hard on ignition switch contacts. To test for poor contact quality the ignition switch was operated 20 or 30 times with the battery disconnected to try to clean the ignition switch contacts. The engine’s performance was significantly stronger after this with noticeably stronger power delivery, smoother running and happy right to the redline.
A couple more 70amp relays were fitted, operated by the ignition switch, that now switch power to the ignition coils, fuel pumps and injectors etc. The engine is now feels very strong and is 100% consistent each time the car is driven.
I know the fault is simple one but I thought I would mention as I guess it develops slowly over time and could have developed on other older / high use Ultimas.
All told it cost about £20 to put the relays in the ignition switch relays, what a difference to the car !
Nick.
Paul,
I wish really I had searched :-)
One more symptom was that oil pressure on the dash gauge had dropped to just over 1 bar at idle. When the ignition switch relays went in the pressure displayed on the gauge jumped back by more than a bar at idle so all good again. I was actually planning a rebuild because of the oil pressure drop.
Nick.
I wish really I had searched :-)
One more symptom was that oil pressure on the dash gauge had dropped to just over 1 bar at idle. When the ignition switch relays went in the pressure displayed on the gauge jumped back by more than a bar at idle so all good again. I was actually planning a rebuild because of the oil pressure drop.
Nick.
it doesnt help i
f you have a sbc and turn off the ignition while driving, pump the accelerator pedal a few times and turn back on...
this is usually followed by lots and lots of flames and bang from the exhaust, but also burns the ignition switch as it gets hot after a couple of goes...
f you have a sbc and turn off the ignition while driving, pump the accelerator pedal a few times and turn back on...this is usually followed by lots and lots of flames and bang from the exhaust, but also burns the ignition switch as it gets hot after a couple of goes...
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