ken4228 Posted March 5 Report Share Posted March 5 After getting dyno tuned, I encountered much difficulty in starting the car on every cold starts after being parked overnight. It will crank and catch sometimes but will stall almost immediately. This will go on for many times before it finally starts and will stumble to an extremely low rpm for a couple of seconds before it stabilise. Battery and starter are all good. I tried to increase the fuel pump prime time from 1 second to 2 seconds, waited for priming to complete before turning key but it doesn't make any difference. I'm at a tropical country with summer ambient temp all year round. During cold starts in the morning, oil temp is about 25 - 30 celsius after being parked overnight. Relevant setup is as follow: 1) GSC Stage 2 cams with ported & polished heads, +1mm intake & exhaust valves 2) Dual Walbro 450 fuel pumps staged at 1 bar 3) ID1300 injectors 4) -8AN fuel feed hose / -6AN fuel return hose 5) GFB FX-R fuel regulator 6) 2 steps colder spark plugs (2 months old) 7) Base fuel regulator pressure is set at 3bar Can someone help take a look and see what's wrong? Car is making good power, running smooth and perfect after the dyno tune except for this cold start issue. Logs and tune are attached. Failed Starts PC Datalog - 2024-03-5 4;19;05 pm.llgx stumble start PC Datalog - 2024-03-5 4;23;02 pm.llgx 050324 Cold Start Issue.pclx Quote Link to comment Share on other sites More sharing options...
koracing Posted March 5 Report Share Posted March 5 Best thing to do to determine if you're too rich, or too lean, or not enough idle position is to try cranking in this situation with a few percent throttle opening and see if a small amount of throttle position improves starting. If that makes no difference, try very large throttle inputs and see if that makes any difference. If that does nothing, try spraying a bit of carb cleaner or starting fluid into the throttle body before cranking (just a couple spurts) and see if that improves anything. Knowing how these things affect how it starts cold will help guide what you need to do. Once the car is warmed up is there any issues starting, or restarting? What if you let it sit for 30 minutes then try a hot restart? Quote Link to comment Share on other sites More sharing options...
ken4228 Posted March 5 Author Report Share Posted March 5 Once it's warmed up, there's no issues at all. Even when parked for a couple of hours after some driving, as long as the engine isnt overnight cold, everything seems to be normal and restarting the car is effortless. Quote Link to comment Share on other sites More sharing options...
castillaricardo Posted March 5 Report Share Posted March 5 You should try a few of the things koracing mentioned to find which is the cause. In your tune, the commanded throttle opening while cranking and idling at cold temperatures is higher than the max clamp of your idle control. You could try increasing the max clamp to 10% and see if it improves some. More than likely it is a combination of things. Quote Link to comment Share on other sites More sharing options...
Adamw Posted March 5 Report Share Posted March 5 If you have removed the TGV's the 4D fuel table should be turned off, this removes significant fuel when cold. You are probably going to need to retune a lot of the cold start stuff after tuning this off. 8 hours ago, ken4228 said: Dual Walbro 450 fuel pumps staged at 1 bar Your map still has the fuel pump function setup for the standard 3 speed subaru controller and there are no other outputs set up for staged pumps? That needs investigating as the subaru controller def wont drive 2 x 450's for long - or if that's been bypassed then the pumps wont be priming because it uses inverted logic and I dont think the relay will be happy when its in 33 or 66% duty mode either. Also, do the pumps have check valves fitted so there is full pressure for the pre-crank prime? Quote Link to comment Share on other sites More sharing options...
ken4228 Posted March 6 Author Report Share Posted March 6 5 hours ago, Adamw said: Your map still has the fuel pump function setup for the standard 3 speed subaru controller and there are no other outputs set up for staged pumps? That needs investigating as the subaru controller def wont drive 2 x 450's for long - or if that's been bypassed then the pumps wont be priming because it uses inverted logic and I dont think the relay will be happy when its in 33 or 66% duty mode either. I forgot to mention that the pumps are wired up using iWire's kit which the primary pump will still be controlled by the controller while drawing power directly from the battery. https://iwireusa.com/products/fuel-pump-controller-hardwire-kit-for-radium-hangers-double-pump?variant=41189188894873 Secondary pump is activated via a pressure switch set at 1 bar boost pressure. 5 hours ago, Adamw said: Also, do the pumps have check valves fitted so there is full pressure for the pre-crank prime? The Walbro F90000274 pumps have in-built check valves and were purchased from reliable source. I observed the fuel pressure is at 2.0 bar after priming in between crank attempts. Is this not enough for cold starts? Quote Link to comment Share on other sites More sharing options...
koracing Posted March 6 Report Share Posted March 6 The pump should also be running while cranking as well so that should not be an issue, or at least not much of an issue. Quote Link to comment Share on other sites More sharing options...
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