Hoping for some troubleshooting help with my 2004 C5 that has a cammed LS3 engine with an A&A supercharger. The engine and system has been in the car for over a year, but over the past month, the car has stalled after start-up and only after I've been driving it. For example, it stalled yesterday after I had stopped for gas. It started fine and idled strong at initial start-up in my garage, but then after driving 10 minutes and stopping for gas, it stalled when I restarted it and tried to move out of park and into drive (A4). It did the same thing last week when I stopped at a hardware store after driving it 20 minutes. However, it doesn't stall at start up or if the car cools down as I drove it on Friday to play golf and the car started and drove fine to and from the course but it was parked for four hours in between.

I checked for codes and the only two that showed were P0l02 and P0103 which are both MAF sensor related, however the performance shop and tuner who helped work the build told me that is common when you add forced induction systems to a stock C5. The check engine light does not come on and the car handles well otherwise. In terms of additional parts, it has a LS2 throttle body, a LS1-LS2 throttle body adapter harness, an OEM Mass Airflow sensor (Part 19220121) with integrated Intake Air Temperature (IAT) sensor, a custom made inline pipe with IAT breakout installed for the Alky Control methanol injection kit although the meth kit only sprays during WOT and was not activated during any of the short drives I took prior to the restart problem,

Hoping someone can walk me through the trouble shooting steps. I've already checked the engine fuse for the starter/ignition, checked hoses for leaks, etc. The car also has an auxiliary oil cooler but the operating temps are all in the target range, especially considering the car was only driven for a few miles before stopping and then stalling at re-restart.

Thanks!

 

I would monitor fuel pressure during a hot start. See if it's spiking or dropping from base 58psi. Do you have a wideband to verify AFR? Anything close to 14.8 or lambda 1 is fine at idle. If overly rich you might have fuel injector issues. If overly lean you might have vacuum leak.

MAF errors can cause stall condition to protect the engine. However tuners often turn off a lot of CEL conditions. Scan tool with live data will help narrow down a lot of issues.

 

Faulty gas cap?

 

Yup, if this is a new condition and or recent problem, your gonna need to start from the beginning with the diagnostic process. Usually stalling at idle is a fueling problem and the easiest way to tell is look at the NBO2's and WBO2's traces.

There are many things that can be an issue that may cause your complaint and I would start with a quick datalog to look for STIT, LTIT, fueling, and so on. Long term trims may point you in a direction to solve your issue.

 

Thanks for the all the replies. Interestingly, The problem has not occurred again over the past week or so which makes me wonder if I simply bought some "bad" gas. I had filled up the last two times at a convenience store and even though I select 93 octane, I may not have gotten what I paid for as there are local news stories about some stations being caught dispensing the wrong octane.

 

Nice build!
Just curious, do you have a stall converter in this setup?
Mine does not, and it should, which is being done in July. Sometimes, it does the same. No check engine lights. Just an occasional stall and restart. Also, small world, I’ve got an LS2 throttle body on mine. It rarely stalls, but I do wonder about the LS2 throttle body possibly having an issue, not sure. Please let us know what it turned out to be.

 

Thanks. It's a lot of fun. No new stall yet as it's an A4 and I'm planning to add one when I swap in a new Level 7 trans from RPM. The rear gears have already been changed from 3.15 to 3.42.

 

Outstanding! That’s a mean transmission. How’d you like the change to 3:42? I’m doing the swap from 2:73 to 3:42 with 245mm Circle D 3,200 stall, trans cooler, etc., in July.
As for the engine stall, I’m wondering if it’s possibly related to the LS2 throttle body? Mine does that on occasion. If it gets more common, I’d want to fix that. Would hate to stall in the wrong spot, traffic all around, etc.,

 

I didn't really notice the change from my 3.15 "performance axle" to the 3.42 gears as I added the SC and headers at the same time with the original LS1 engine. The reason I upgraded to 3.42 was to better manage the increased HP and in preparation of a new trans and stall which is the final phase of the build.

As to the LS2 throttle body, I'm not sure if that's the culprit as it was needed to bridge the gap between the LS1 and LS3 as the LS3 and LS7 throttle bodies operate in reverse and have different TPS scaling. The LS2 throttle body 6-pin connector tricks the LS1 computer by using a harness adapter.

 

No leaks at the alky nozzles dripping into the intake prompting an unmetered oxygen delivery, ecu overcompensation of fuel, followed by an immediate rich flood spike and stall?

That's a far reach. But one to chdck.

 

I'm doing quite a few modifications in July. I'll ask the performance shop doing the work what they think could cause the occasional stall. I've also noticed an increased idle at times, running 1,200, then sooner or later, back down to 800-900 range. I'm wondering if it's tune related, or throttle body related. We'll see. The original build/tune was done in 2016. Hasn't been touched since.