Hi All,
I have a basic problem that im sure someone here could very easily help me solve. For a long list of reasons not worth going into I've been having hard start issues on my viper. It's something of a known issue on these, the car (and most cars) have a safety feature that only allows the fuel pump to run for a brief period of time on initial ignition on, then only run if the PCM (computer) detects engine rotation, either cranking to start or running. In my case that is a 1-second prime for fuel pump, and its not long enough to start easily without priming it multiple times (switching key on/off etc).
The PCM triggers the fuel pump by connecting ground to the fuel pump relay. Other than the initial 1-second priming time on initial ignition, it uses the crankshaft position sensor to determine if the engine is rotating and thus provides ground to this circuit. This is a safety feature, so that when you crash the stupid thing into a wall and the engine stops the fuel pump doesn't keep pumping fuel, fireball etc.
I've extended that initial prime time by using an ELK-960 delay timer, works great. However, the PCM is now no longer providing that ground circuit, even when the car is returned to default state (no delay timer etc). I'm certain its a PCM issue and I don't want to buy a new one, as this seems to be the only issue with the car now.
I can make the fuel pump work by just grounding that pin such that the fuel pump is always running with the start/run circuit, however that is now an issue in the case of a crash, and i want that safety feature.
What I want to do is to replicate that safety feature. Crankshaft position sensors put out a waveform output only when the engine is rotating. I want to use that input as a signal to connect the ground to the fuel pump relay, effectively mimicing what the PCM should be doing - supplying the ground to the fuel pump relay as long as there is engine rotation.
I haven't measured mine (just have a voltmeter, dont have an oscilloscope) but I assume the output of the crank position sensor is something like described on this page: https://www.picoauto.com/library/automotive-guided-tests/crankshaft-inductive .
damn, its still a wall of text, sorry. Can I use another ELK-960 to solve this? datasheet for it is here: https://www.elkproducts.com/product-catalog/elk-960-delay-timer-module. I can set it to free run as long as there is a signal on the trigger input.
trigger voltage can be as low as 4.5v and <1mA on the ELK-960. I'm not sure if that will do the trick or if I need something to use that same trigger signal to push out a steady +12v that I can use as a signal, like a basic resistor/cap setup in front of a relay? (yes I know thats more or less what the ELK-960 is).
sorry for the long post, any help appreciated. I'm not an auto electrician, nor an expert in electronics, as you can tell.
I have a basic problem that im sure someone here could very easily help me solve. For a long list of reasons not worth going into I've been having hard start issues on my viper. It's something of a known issue on these, the car (and most cars) have a safety feature that only allows the fuel pump to run for a brief period of time on initial ignition on, then only run if the PCM (computer) detects engine rotation, either cranking to start or running. In my case that is a 1-second prime for fuel pump, and its not long enough to start easily without priming it multiple times (switching key on/off etc).
The PCM triggers the fuel pump by connecting ground to the fuel pump relay. Other than the initial 1-second priming time on initial ignition, it uses the crankshaft position sensor to determine if the engine is rotating and thus provides ground to this circuit. This is a safety feature, so that when you crash the stupid thing into a wall and the engine stops the fuel pump doesn't keep pumping fuel, fireball etc.
I've extended that initial prime time by using an ELK-960 delay timer, works great. However, the PCM is now no longer providing that ground circuit, even when the car is returned to default state (no delay timer etc). I'm certain its a PCM issue and I don't want to buy a new one, as this seems to be the only issue with the car now.
I can make the fuel pump work by just grounding that pin such that the fuel pump is always running with the start/run circuit, however that is now an issue in the case of a crash, and i want that safety feature.
What I want to do is to replicate that safety feature. Crankshaft position sensors put out a waveform output only when the engine is rotating. I want to use that input as a signal to connect the ground to the fuel pump relay, effectively mimicing what the PCM should be doing - supplying the ground to the fuel pump relay as long as there is engine rotation.
I haven't measured mine (just have a voltmeter, dont have an oscilloscope) but I assume the output of the crank position sensor is something like described on this page: https://www.picoauto.com/library/automotive-guided-tests/crankshaft-inductive .
damn, its still a wall of text, sorry. Can I use another ELK-960 to solve this? datasheet for it is here: https://www.elkproducts.com/product-catalog/elk-960-delay-timer-module. I can set it to free run as long as there is a signal on the trigger input.
trigger voltage can be as low as 4.5v and <1mA on the ELK-960. I'm not sure if that will do the trick or if I need something to use that same trigger signal to push out a steady +12v that I can use as a signal, like a basic resistor/cap setup in front of a relay? (yes I know thats more or less what the ELK-960 is).
sorry for the long post, any help appreciated. I'm not an auto electrician, nor an expert in electronics, as you can tell.