~85 psi at the Fuel Rail??
05-14-2020, 07:01 PM
#21
Since you have HPtuners you can monitor the fuel trims and see if the computer is compensating for a tune that was mapped for higher fuel pressure. It's possible the car was tuned with normal fuel pressure so I would just check trims first to see where things are at. If it's clear the trims are high (i.e. double digit percentages) that would be a good indication the tune was done for higher pressures.
Are you confident you are getting good voltage for the ECM during cranking? Perhaps the way you are wired and grounded is occasionally not giving enough juice for the ECM to fire the injectors and coils during high amp crank draw.
Are you confident you are getting good voltage for the ECM during cranking? Perhaps the way you are wired and grounded is occasionally not giving enough juice for the ECM to fire the injectors and coils during high amp crank draw.
Some background for the situation. This is my LS1 swapped mazda RX8 i built, so the battery is in the trunk due to engine bay space constraints (i.e. its a pretty long run from the trunk up to the starter). As far as how i have it wired...i have the positive run from the battery up to this pass through post:
Then from this post I have 2 cables. 1 goes to the starter, and 1 goes to the alternator.Then i have another short cable that goes from the back alternator post to the fuse box. Is the problem I need the battery DIRECTLY connected to the started, and not connected how i currently have it maybe?? I dont know...
05-15-2020, 07:46 PM
#22
Anyone else by chance looked/logged to see what there system voltage drops down too when they are cranking/starting. Mine consistently drops from ~12.2 to low/mid 9s. Wondering what a normal range is on a car that isn’t having any hard start issues.
05-18-2020, 01:18 PM
#23
You could use a noid light or a timing light to see if your injectors or coils are firing during cranking. That would be a good indication there's sufficient voltage for the ECM to operate. I think 9.6v is considered the minimum, so mid/low 9s could be marginal. Having a pass through terminal like that should not be a problem as long as the connection is tight and the terminals were installed well on the battery cables. Nothing is wrong with the way you describing running two cables from your firewall pass-through to the starter and alternator.
Usually voltage issues for trunk-mounted batteries are related to grounding. How did you run your ground(s)?
Usually voltage issues for trunk-mounted batteries are related to grounding. How did you run your ground(s)?
Last edited by -TheBandit-; 05-18-2020 at 01:24 PM.
05-19-2020, 07:24 AM
#25
You could use a noid light or a timing light to see if your injectors or coils are firing during cranking. That would be a good indication there's sufficient voltage for the ECM to operate. I think 9.6v is considered the minimum, so mid/low 9s could be marginal. Having a pass through terminal like that should not be a problem as long as the connection is tight and the terminals were installed well on the battery cables. Nothing is wrong with the way you describing running two cables from your firewall pass-through to the starter and alternator.
Usually voltage issues for trunk-mounted batteries are related to grounding. How did you run your ground(s)?
Usually voltage issues for trunk-mounted batteries are related to grounding. How did you run your ground(s)?
One thing I came across in my research on here is that people have had problems if you run the power with the starter cable.
I re-ran a power line last night from the ECM straight to the battery. Going to log today and see if when I crank the voltage doesn’t get pulled down as much. Since it was originally connected with the starter on that post I’m thinking when I crank since that huge 2 awg cable is on there to the starter the voltage is going there (path of least resistance) as opposed to the small 14-16 AWG power wire for the ECM.
For grounds....god I have swapped them and added more so many times hoping it helped and nothing did. Currently I have both the grounds for the LS harness mounted to the heads (front of passenger side head, back of drivers side head). Then I have 2 ground straps that go from each head to the strut towers. Then I have 1 massive ground strap from back of passenger side head to the frame/chassis.
05-19-2020, 07:27 AM
#26
Just need to log and see what the trims say to be sure.
05-19-2020, 07:36 AM
#27
Yes, I’m definitely keeping this in mind! It’s just hard to think it’s the true root cause for the intermittent hard starts since the car did this before and after the tune. However, it makes sense if it was tuned with close to 90psi and now it’s at 58psi that there may be an issue.
Just need to log and see what the trims say to be sure.
Just need to log and see what the trims say to be sure.
05-19-2020, 05:43 PM
#28
Gotcha. Didn't know that, but now that you said it, it makes sense. I just logged and tried to start it and it did the same ****. The voltage drop on the ECM only got down to 10V with the new way its wired though, but still wouldn't start on the first try. Fired right up on the second try like usual.
I compared a log of it firing right up, and today's and the only real difference I could see was the IAC step value when it fired right up was reading 185, but today when it struggled to fire up it was reading 213. What should the IAC step count read for a stock ls1 for cold start/hot start? After it starts the IAC gets down to ~60ish when idling and hot. Also LTFT were 0 in both cases of the car firing right up, and the car struggling to start for what its worth.
I compared a log of it firing right up, and today's and the only real difference I could see was the IAC step value when it fired right up was reading 185, but today when it struggled to fire up it was reading 213. What should the IAC step count read for a stock ls1 for cold start/hot start? After it starts the IAC gets down to ~60ish when idling and hot. Also LTFT were 0 in both cases of the car firing right up, and the car struggling to start for what its worth.
05-19-2020, 06:02 PM
#29
Either of those IACs should fire the car if that was the issue. Does it start quicker if you hold the throttle on crank? Have you put a fuel pressure gauge on the shraeder valve? Maybe the check valve in the pump is bad and letting the feed line drain back into the tank.
05-19-2020, 08:00 PM
#30
Either of those IACs should fire the car if that was the issue. Does it start quicker if you hold the throttle on crank? Have you put a fuel pressure gauge on the shraeder valve? Maybe the check valve in the pump is bad and letting the feed line drain back into the tank.