99 C5 LS1 starts for few seconds then stalls. Intermitant
 

This is driving me crazy. I have a C5 drivetrain in a street rod. LS1 with a TSP 228 cam LS2 TB. Dyno tuned last year. Sometimes the car will start fine, sometimes it starts for 1-2 sec then dies. If I let it sit several hrs and try again, it usually starts. The other day it happened cold. Today I took it out for a ride, came home, shut it down, tried to restart it after about 5 min and it did it again. I'm going to upload a video if its not too big. I searched through the forums and found several things to check but they check out ok. My temp sensor is reading properly through the PCM. I have solid fuel pressure throughout the start attempt. I thought maybe flooding due to a bad IAC, but it didn't help to hold the peddle down while starting. Also pulled a couple plugs and they're brown and dry. I did notice that when the key is put in the on position that the IAC whistles and then there's a click. I don't know if this is normal because I never really sat with the key in the on position and listened before. I'll attach a video of that as well. This happened to me one time early last year and never came back. Now I'm getting the car back out after winter and it's happening more often. Not sure what to try next. Its also had to take it to a garage because some days it wont do it. Frustrating! I have no codes. I'm thinking next to change the crank sensor and cam sensor even though I dont have a code. Could it be injectors? How about low voltage to the coils? Which wire would I probe to check this if I unplug the coil packs? I assume it should just have 12V to the coils when cranking.

Looks like my video clips are too large to load. If someone thinks they can help, I can email or text them.

Thanks all!! Mike

Mike,
An LS1 out of a 99 C5 doesn't have an IAC so I don't know what you were listening to that was "whistling"...post a pic !!...when it doesn't start but only cranks see if the Tach appears to move...no Tach movement "may" lead you to a crank sensor issue. If no Tach movement you probably don't have spark but you can pull off a plug wire off the coil and see if there is spark during cranking. So if no spark you now have to check for injector pulse. Pull any connector off an injector and make sure you have 12v at the pink (power) wire...if good now connect a 12 volt incandescent test light to battery POSITIVE...crank the engine and touch the tip of the test light to the other striped injector wire...if the injector driver is turning on the test light will blink dimly as the engine is being cranked....if no spark AND no injector pulse it's most likely a crank sensor...the engine doesn't need a cam sensor to start. Also if the crank sensor is bad fuel pressure will drop like a rock during cranking...if no "ignition pulse" the fuel pump relay control circuit will not be energized...no energize...no fuel pressure. Now if the Tach DOES move spray some Brake Kleen or Starter fluid into a vacuum line...if it starts or tries to start you HAVE a fuel delivery issue...now it might be an ignition problem if you have good starting fuel pressure and injector pulse...FUEL,AIR, SPARK, COMPRESSION....that's it !!...if it looks like a crank sensor I can show you how to test it just to make sure you don't have any wiring issues.

Thanks for the awesome rely! Next time it does it ill try your methods. I wish the problem was consistant so i could diagnose it. I started it after work today and it started. Ill keep trying it every night. Its bound to do it. Happened several times over the weekend. The whistling sounds like its coming from the tb. I have an ls2 dbw tb. I thought maybe they has an iac built in. I never took notice to this whistle before but i never was by the moter with the key in the run position like now. The wistle lasts maybe 15 sec then a click. Mabe the dbw does that?? Ill keep you posted what i find. If you dont mind sharing how to check the crank sensor wiring that would be great to know too. Thanks again

OK, to check the CKP wiring you will need a multimeter and a 12 volt test light. With the CKP connector removed at the sensor we are looking at a 3 wire Hall Effect Sensor. With the key ON for all 3 wiring checks you should have a 12 volt reference at the light green wire. The yellow/black wire is sensor ground...you should see LESS THAN 100mv's...The signal wire is the dark blue/white one. The signal wire is a "pull up" circuit design....with a multimeter you will see maybe .02-.03 volts on the wire...now with the multimeter leads still connected take a 12 volt test light connected to battery POSITIVE and now touch the tip of the test light to the signal wire...that .02-.03 volts should now read 12 volts...you are "pulling up" the voltage from 0 to 12 volts !!...you will also hear the fuel pump operate for 2 seconds !!...if all is good your CRK sensor is bad...the easiest way to check all this is with a scope...you would connect the signal and ground wires and you will see a 0-12 volt square wave...connections are made at the PCM...now you "can" use a multimeter instead of a scope but the multimeter only averages the voltage...you may see between 4-6 volts...My scope takes 400 million voltage samples per second...I've enclosed a vid I did with my multimeter on my good crank sensor...you will not see 12 volts but you know there is a signal there. BTW if you don't see a good 12 volt reference and ground we will have to do more testing at the PCM !!

Good stuff!

You mentioned you're just getting the car out after winter. It may be tune related, since the weather is still cold this time of year; the tune may not be calibrated for these ambient air temp.

Update
 

The car hasent given me the starting problem now that im ready to diangos it. It did however start sputtering the other day after a hot start. So i just went ahead and changed the crank sensor. Started it back up and it sounded very good. Very crisp and good throttle response. Im thinking that was the issue. Ill keep this thread for future use if needed. Thanks again

Good to hear! The Crank Position sensor can definitely cause starting issues. Another telltale sign that the crank position sensor is going out - the engine sputters or dies while running, and the tach needle begins to act erratically (jumps around and drops to 0).