Issue with LS3 swap - starts then dies

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07-31-2015
brandonconner

1 Attachment(s)

Issue with LS3 swap - starts then dies

We're having an issue with an LS3 we've swapped into a 72 Chevelle. Using modified stock harness, stock ECU (from 2010 GMC Truck/6.2). I've turned off both VATS1 and VATS2, disabled starter checks. Car will start, run for maybe 1-2 seconds and dies. I'm also not seeing any RPM signal when using VCM scanner (along with a speed of 158mph). I've attached the tune, it's completely stock other than the vats/starter mods. Car has long tubes and a holley EFI intake. I originally thought the intake could be causing it, but the lack of RPM in scanner makes me think something else is going on. Ideas? Tune attached....
07-31-2015
brandonconner

As an update, I do see an RPM signal in scanner on occasion and I've verified the crank sensor is plugged in.
07-31-2015
10_SS

you can log crank sensor counts, and do you have oil pressure sensor connected? It needs to be working or it will cut fuel. If not 0 the Oil Pressure Min table.

Also try shutting down and restarting scanner and pull batt on ECU when you see no RPM on scanner... I was getting this on my bench simulator.. pulling batt power and restart scanner seemed to fix it. ECU doesnt seem to like some inputs that are way out of what it thinks are normal. Injectors will fire during crank and 1-2 secs later will stop after most of these situations, excluding a security problem, they wont fire at all, but may show pulse on the scanner. If you have a fueling tune problem or other, then your injectors will still show to be pulsing... so post a log.
07-31-2015
Howes

start stall is classic security issue. try scanning codes i believe like a p1629 or p1632. make sure it doean't have any security codes.
07-31-2015
PDYoung

try adding more airflow to the start up airflow table
08-04-2015
brandonconner

2 Attachment(s)

ok, so I played with the car a little more today. I've attached a log of several start attempts. At one point, with the mass air unplugged, the car started and actually idled for a couple minutes. After I shut it off - back to the same start and die. I've attached the latest tune and the log file, any help is appreciated. The car actually ran really good for what time it ran....
08-04-2015
brandonconner

also, car only has codes for fuel sender, evap and rear o2s.....no security codes.
08-04-2015
brandonconner

I should also say, from the original questions...the oil pressure sender is NOT hooked up and I zeroed out the oil pressure min/rpm table. Another irritation is that almost without fail every time I flash the car I have to disconnect the battery to get it to cycle the fuel pump when I power up the ECU.
08-04-2015
10_SS

you say it's a stock LS3, with a truck ECU. Your truck ECU injector flow rates dont match that of an LS3.

Also the MAF sensor settings are about 400% off compared to an LS3, which makes sense why it runs longer with it unplugged, since the crank/start mode doesnt seem to use the VE table or MAF sensor..

So, if you have LS3 hardware, and a truck ECU, then copy as much fuel and air stuff from a stock LS3 tune, then it might fire right up. this includes most everything.. VE coefficients, spark, injector, MAF, etc... none of it is anywhere near that of an LS3.

Then, depending what Throttle body you have... LS3 with drive by wire? Then you may want to copy those tables too... but be careful when copying that stuff over.. couild cause problems. If you notice a strange problem with no Throttle, or REP... then go back to the stock truck settings, no guarentee that will work either.

Then you still have Variable Cam enabled... set that to "None".

There's 604 differences from your truck ECU file and my stock 2010 Camaro LS3 file. I'd say just use the Compare/View Comparison Log and just copy over all your spark/Fuel/Airflow, etc... then try again, Just make sure whatever you disabled to get it to fire up is still disabled.

You probably dont have a fuel pressure sensor installed and wired? You may have to play with the Injector Flow Rate vs. Pressure table, make it a steady value across the board. ... but probably not until after you do all the above stuff.

Regarding the Fuel pump not running till you reset the batt... that's probably something to do with the ECU not getting a certain signal correctly, or getting one WAY out of normal... it will shut down in these cases, like your speed showing 150mph at startup. But try the above settings first since they are easiest, and are obviously wrong. Then if it continues not to keep running then investigate why the Speedo or other are not reading right (check the pins in the ECU... something may have been connected to the wrong pin). And when the ECU shuts down like this I usualyl have to restart the Scanner or it wont read RPM. Pretty similar to what you described.

In the future, just choose "Save Data As" when your done scanning... then attach the .hpl, dont create an excel file.
08-05-2015
brandonconner

Update - it's running! Turns out there are some pretty major differences between the truck ECU calibration and the camaro. I ended up pulling down a stock 2010 camaro tune from the repository, running a compare and copying as many differences as I could. After adding about 25% on the base airflow minimum table car starts and idles like a champ. Thanks for the info, now on to seeing what we can do power wise!

Quote:

Originally Posted by 10_SS

you say it's a stock LS3, with a truck ECU. Your truck ECU injector flow rates dont match that of an LS3.

Also the MAF sensor settings are about 400% off compared to an LS3, which makes sense why it runs longer with it unplugged, since the crank/start mode doesnt seem to use the VE table or MAF sensor..

So, if you have LS3 hardware, and a truck ECU, then copy as much fuel and air stuff from a stock LS3 tune, then it might fire right up. this includes most everything.. VE coefficients, spark, injector, MAF, etc... none of it is anywhere near that of an LS3.

Then, depending what Throttle body you have... LS3 with drive by wire? Then you may want to copy those tables too... but be careful when copying that stuff over.. couild cause problems. If you notice a strange problem with no Throttle, or REP... then go back to the stock truck settings, no guarentee that will work either.

Then you still have Variable Cam enabled... set that to "None".

There's 604 differences from your truck ECU file and my stock 2010 Camaro LS3 file. I'd say just use the Compare/View Comparison Log and just copy over all your spark/Fuel/Airflow, etc... then try again, Just make sure whatever you disabled to get it to fire up is still disabled.

You probably dont have a fuel pressure sensor installed and wired? You may have to play with the Injector Flow Rate vs. Pressure table, make it a steady value across the board. ... but probably not until after you do all the above stuff.

Regarding the Fuel pump not running till you reset the batt... that's probably something to do with the ECU not getting a certain signal correctly, or getting one WAY out of normal... it will shut down in these cases, like your speed showing 150mph at startup. But try the above settings first since they are easiest, and are obviously wrong. Then if it continues not to keep running then investigate why the Speedo or other are not reading right (check the pins in the ECU... something may have been connected to the wrong pin). And when the ECU shuts down like this I usualyl have to restart the Scanner or it wont read RPM. Pretty similar to what you described.

In the future, just choose "Save Data As" when your done scanning... then attach the .hpl, dont create an excel file.
03-25-2024
Corvette Chris 39

I’m having the same issue sir . Is there anyway you can help me
03-25-2024
gtstorey

Quote:

Originally Posted by Corvette Chris 39

I’m having the same issue sir . Is there anyway you can help me

Starting to fill like you are spamming. You need to start your own post with a lot more details given, as was answered the other times you have tagged onto other old post.