I successfully had a great first start yesterday of my new LS3 with a TSP stage 2 - in a vintage Porsche. I only ran the engine for 20 seconds and then turned it off to check for any leaks. However, when I tried to start it several minutes later, there was no idle-catch, and the cylinders fired like it wanted to start but didn't. I did step on the gas pedal (drive-by-wire) a little and it didn't help any. I think when I was done the voltage was 11 on my voltage gauge. Fuel PSI is at 58, no fuel leaks.

Specific Setup Issues:
-PSI harness (rear engine)
-1 AWG welder's cables between battery and starter (positive) and battery and cylinder head (ground).
-4 AWG cable between Holley 150A high performance generator and positive post on starter.
-1 AWG chassis ground from battery.
-New Odyssey PC680 Battery (always on trickle charger, 1.5A)
-Holley EFI Sniper Fuel Rail, full-return setup with Aeromotive regulator.

HPTuners Scanner results:
During KOEO, the only DTC's were that the tach signal was working. The APP and TP are working because the throttle plate moved when I stepped on the gas pedal. Below is an image of the DTCs and it indicates the engine didn't heat up enough for the O2 sensors to do there thing (600F).


PSI Tech Support:
-Tech support at PSI said that everything in the ECM will work with voltage above 9.5. They also said the gas pedal will work during starts (I did read that e-pedals don't work during starts as they a deadened or locked out).

What I think happened (why engine wouldn't start a second time):
-I think I may have had a voltage "brownout," where the ECM voltage was too low during cranking.
-My understanding is that the throttle motor draws a lot of amperage to fight the spring, and if voltage drops during cranking the ECM will kill the signal to the throttle plate(?)

Question:
-What do you think I should look at while logging that may help if it doesn't start today?

 

Did you log it at all?

 

yes, i made several logs

 

ahh ok cool. can you post the log, tune and full spec's of the build?

My "tuner crystal ball" is in for warranty right now.

****.

 

Edcmat on the HPT forum keeps a crystal ball handy for these situations, lol.

 

Here's the tune file, and two scanner log files. The log with filename "More Channels" shows multiple attempts without holding the throttle at 25-30% when cranking. The other one shows longer 1-2 minute runs with the throttle held to prevent RPM from dropping below e.g. 1200. It won't maintain idle and go near 1000-1100 RPM by itself if I let off the e-pedal.

 

Please also note, that sometimes the MAF was locked at zero, and during another run it wasn't, so I think the ECM was using speed-density. Overall, you need to look at the tune file in the context of a stage 2 cam. FYI - the build also involved getting the new heads CNC'd, double valve springs, titanium retainers, and Comp trunnion kit. TSP did the CNC and valve springs/retainers, I did the stage 2 and Comp trunnion. The exhaust is also only 2 feet long, since the car is a rear engine chassis -- so probably little back-pressure.

Something to note in the log file called "More-Channels" is that the voltage gets down near 10.4-10.6. But PSI (harness) tech support said that all internals in the ECM work when voltage>9.5, so I don't think it's a brownout.

 

If it started first time okay & then idled okay for the 20 seconds from cold, it might be worth trying that again by unplugging the body connector, which resets the E38 as if it had never been started. Fueling & airflow is different in that state & any fuel trims are reset. Throttle min learn also resets. Best not to touch the throttle for at least 30 seconds after key on from the E38 reset so the throttle learn completes.

O2's should start cycling after 15-20 sec depending on ambient. Maybe longer if colder.

 

Do you mean disconnect then reconnect the 2 large multipin connectors that have locking arms on them?

 

[RESOLVED] I tried the trick to remove the vacuum cap on the manifold near the small tube close to the throttle body (driver side), and it started right up and idled on its own near 850. I did have to start it using a little gas on the e-pedal, then gradually let RPM down near 900 and it rans itself. I was making a scan/log, which I sent to the tuner for tweaking.

 

Only the 73 pin connector which is plugged to the black socket. It has the full time as well as run start power.

 

Cool 😎. A sign of needing more start & idle airflow 👌.

Hopefully your tuner can make the changes so you don't need to touch the pedal cold or hot starting.

 

Thanks, and yes, creating the vacuum helped the tuner know what was needed.