525hp GM crate engine start but no run
02-16-2019, 01:22 PM
#1
525hp GM crate engine start but no run As the title says. It will fire but only for a couple seconds and then dies. Here's the set set up, new 525hp LS3 6L80e E38 and psi harness. Using HP tuners. Original tune was for a 2010 camaro 6.2 with auto trans. Matched all the start and idle parameters to a 525 GM performance tune from the HP repository. Deleted vats and went through the whole immobilizer list in the DTC's. All physical basics checked. Switched and unswitched power to pcm. 58 psi of fuel pressure. Drained gas and added fresh fuel. Power at coils with key on, power at injectors with key on. Fuel pump comes on and stays on for 5 sec as configured in pcm. Turn the key and it barks to life for a second, maybe two and then dies. It will continue to do that. Went into the tune an re enabled Vats and starter fault checks. It does the exact same thing with vats enabled as it does with vats disabled. Fires, coughs, dies. Tune attached for somebody smarter than me. I'm about 10 hours into this. Any help greatly appreciated.
02-16-2019, 01:29 PM
#2
TECH Senior Member
Weird. Starts then dies. ACTING like VATS is on. Are you positive VATS is tuned out? Not to bug you, just gotta make sure...
02-16-2019, 01:43 PM
#4
TECH Senior Member
Look for a fuel restriction. The time between starts is allowing enough fuel to get in the system and start, but not run. Only thing I can think of right now.
02-16-2019, 01:46 PM
#5
What vehicle and are you sure the ignition switch is wires correctly with good fuses? I agree it sounds like VATS but since that’s been ruled out I’m wondering if the ign switch is receiving 12v in START but then losing 12v once the key or button toggles back to ON
02-16-2019, 02:24 PM
#6
TECH Senior Member
Good call! I forgot this is a new install where wiring gremlins may be undiscovered!
02-16-2019, 04:17 PM
#7
This is going into a 2008 Miata. Its about the 6th one I've done so I have the wiring pretty buttoned down. I check both switched and unswitched power for pcm and also confirm I have what I need in key on, run and crank. Not loosing any voltage at the coils or injectors and fuel stays at a constant 58 psi. I have a gauge on the rail and I also purged the system. The thing that leads me back to the pcm is it does the exact same thing with vats enabled and disabled. Not something I've run into before. Most my wiring utilizes stock Mazda configuration. So the switched and unswitched feeds that went to the Mazda computer now go to the GM pcm. The ground triggers for the fans go right to the mazda fan relays. That makes it really easy if the owner has a problem down the road. I keep all the wire colors constant as well.
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02-16-2019, 05:12 PM
#8
TECH Senior Member
I suspect a bad PCM if it acts like VATS is on no matter what.
02-17-2019, 12:37 PM
#11
There are two vats switches and a starter disable. Disabled all and did a write entire. No love. Also removed fuel pump and inspected and put in fresh fuel. Pump voltage stays constant and gauge on the fuel line sits at 58 psi. My pressure gauge has a purge set up so I can make sure there is no air in the system. Data log is showing no dtcs at all.
02-17-2019, 12:57 PM
#12
TECH Senior Member
OK you have sufficient fuel pressure to the injectors. Do the injectors keep "firing" during start and subsequent shutdown? Same for ignition system? Just thinking out loud here...
02-17-2019, 01:25 PM
#13
Sounds like you’re checking all the right areas. Did the car run before the swap? Is it possible there’s a broken 12v ign wire on the Mazda side of things? Also check the crank sensor and wiring as that can cause similar symptoms. If you have a spare crank sensor I would swap them just to rule that out
02-18-2019, 05:39 AM
#14
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Will it start and catch with some throttle pedal? Might just need more air. If it will run with pedal, bump the startup air and also check BRAF ETC multiplier table. It probably filled with really low numbers like 0.4. Raise those multipliers
02-18-2019, 07:17 PM
#16
Agree on needs fuel. I put volt meter on #1 injector and it never looses voltage so i'm kind of ruling out vats. I'll try maf table in the am. I'm going to compare my file with stock GMPP 525 map and see how close I am. Pedal has no effect of staying running. I have pulse width set up in logger and as i recall they weren't shutting off. Thanks for all the suggestions. Keep them coming! Oh, swapped maf and map sensors. No change. Will try crank sensor tomorrow as well. Fortunately have a few crate engines in the shop at the moment.
02-18-2019, 08:54 PM
#17
You need to verify if it is a fuel or ignition problem, a set of noid lights will tell you if the injectors are firing, the injectors should have positive voltage when the key is in the run position, then the ECM sends the negative voltage signal at the proper time to each individual injector which completes the circuit and allows the injector to actually fire. If the noid lights tell you that they are firing then possibly the engine has been sitting awhile and the injectors are gummed up and stuck shut, you can test by spraying staring fluid in the throttle body to see if it will stay running.
You sound certain the VATS is off then check to make sure your ECM is getting the proper voltages in the start and run position of your key switch, only takes three things for the engine to start; fuel, air, ignition.
With those tests you can eliminate two of the three and the third one (air) is the easiest to eliminate.
You sound certain the VATS is off then check to make sure your ECM is getting the proper voltages in the start and run position of your key switch, only takes three things for the engine to start; fuel, air, ignition.
With those tests you can eliminate two of the three and the third one (air) is the easiest to eliminate.
02-18-2019, 09:00 PM
#18
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Is this speed density by any chance? If so, set the lowest cell in your maf curve to 20 g/sec so it gets fuel until the maf fails out
02-19-2019, 07:44 PM
#20
G atsma gets the chicken dinner! Swapped in another e38. Fired right off and settled into a lumpy idle on a stock 2008 Corvette 6.2 tune. Thanks for all the input. At least I confirmed my wiring blueprint for LS3 into Miatas is correct. Shout out if you need a schematic!!
Last edited by sbwrench; 02-19-2019 at 07:45 PM. Reason: spelling