James c Posted February 19, 2019 Report Share Posted February 19, 2019 When starting my engine if I turn the key to acc and allow the fuel pump to prime, at the same time the Tacho will go to the set rpm shift point (7000rpm for example) then drop to zero. Shortly after this it will then return to the shift point (7000rpm) then I will start the car. It seems to crank for longer than expected before starting. However as I stumbled across the other day. If I let the fuel pump prime and then start as soon as it stops priming it will start nice and quick. What I would like to know is could there be a setting which is disabling the spark or injectors momentarily after the start procedure (fuel pump prime and tacho) Thanks Quote Link to comment Share on other sites More sharing options...
jigga009 Posted February 19, 2019 Report Share Posted February 19, 2019 Your fuel pressure might be dropping as soon as your fuel pumps stop priming. Do you have one-way valves in the plumbing of your fuel pumps? Quote Link to comment Share on other sites More sharing options...
James c Posted February 19, 2019 Author Report Share Posted February 19, 2019 I have a gauge fitted to the regulator so I will take a look if its dropping tonight. I don't have any one way vavles currently fitted but have one from a previous system I could try. Quote Link to comment Share on other sites More sharing options...
jigga009 Posted February 19, 2019 Report Share Posted February 19, 2019 If you don't have one way valves in your plumbing, you will run into what you are experiencing; extended cranking before starting since the pumps have to build pressure again following the pressure drop off when the pumps stop priming. With the valve in there, the system maintains system pressure for longer following priming, allowing for more instant injection of fuel into the cylinders when you go to crank the engine over. Quote Link to comment Share on other sites More sharing options...
James c Posted February 19, 2019 Author Report Share Posted February 19, 2019 Thanks for your help I will fit a valve and see what happens. Any suggestions on the best place in the system to fit? Right after the pump or up at the rail? I was under the impression the pump has a non return valve fitted as standard. Its a deatschwerks pump. Quote Link to comment Share on other sites More sharing options...
Adamw Posted February 20, 2019 Report Share Posted February 20, 2019 Yeah, I dont think that is your problem. The DW pump will have an internal check valve. I would suggest you do a couple of PC logs, one with a quick start and one with a long start, then we might be able to see if there are any differences. Quote Link to comment Share on other sites More sharing options...
James c Posted February 20, 2019 Author Report Share Posted February 20, 2019 Can I do a log with the Atom? Quote Link to comment Share on other sites More sharing options...
Adamw Posted February 20, 2019 Report Share Posted February 20, 2019 15 minutes ago, James c said: Can I do a log with the Atom? Yes. https://www.youtube.com/watch?v=_P1LRANeO4A Quote Link to comment Share on other sites More sharing options...
cj Posted February 20, 2019 Report Share Posted February 20, 2019 If you're tacho is doing the startup sweep thing a second time when you crank, it suggests your ECU is being power cycled. Possibly because the current drawn by the starter motor is so high that the ECU resets due to low voltage. Starter current drawn is highest at zero RPM and drops slightly once the engine is turning which is why it then powers back up and starts eventually. Looking at a log might show some very low but still usable voltage and some disconnects, but by the very nature of this problem, the ECU cant log the voltage if the ECU is powered down. Depending on your multimeter and how long it holds down the voltage you may not be able to catch it with this either but it would be worth trying. Where have you run your power and ground wires to/from? If its to the engine block, how big is the ground from engine -> chassis/battery. If your starter motor "uses up" the available ground current in this wire when its cranking, the ECU will die. To check this put your meter on volts, put one end on the battery negative and the other on the engine block and have a friend crank it. If you see much voltage [differential], then your engine ground needs improving. Other possiblity which I have seen before is a worn ignition key switch where the IGN1 signal drops for a split second when you turn the key to crank pos. You can rule this out by bypassing the key when cranking. Get a *thick* wire, turn the key to IGN, then jumper from battery in to the crank wire at the back of the key barrel or the big plug under the dash where the key wiring connects. This makes the engine crank without physically moving the key. You could put a switch in the middle of this wire if you are concerned about it arcing. Quote Link to comment Share on other sites More sharing options...
James c Posted February 20, 2019 Author Report Share Posted February 20, 2019 The second startup sweep all takes place before I even start cranking so I don't think its related to the starter drawing all the current. There is two large earth straps front the engine to chassis with good connections. Starter has no problem spinning the engine over. When you turn the key to ign the pump primes and the tacho goes up to 7, its sits there until the pump stops priming then drops to zero, few seconds later just the tach needle goes back to 7, then I crank the engine. With the laptop plugged in it appears that the ecu stays online the entire time this is happening. Yesterday I primed the fuel system and watched the pressure gauge. It sits on around 45psi while priming but I noticed as soon as the pump stopped priming it was dropping to 30psi. I fitted a one way valve near the pump and this has fixed that issue. Now after priming its holding around 40psi instead of 25 to 30psi. This has definitely had a positive effect on how it starts and reduced cranking time. I will record a log when I get a chance for you guys to take a look at and see if you can see any areas that need attention. Quote Link to comment Share on other sites More sharing options...
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