LS-3 Starting issues
Thread Starter
Drifting
Joined: May 2006
Posts: 1,864
Likes: 148
From: Santa Barbara California
LS-3 Starting issues
I am hoping for some advice regarding a LSX376 my son is having fits with. The engine was placed into a 1990 Camaro with a 4L60E trans, Strange rear-end, DSC-1 Supercharger, and has had a more radical cam installed. It was at a dyno shop and came home to have the exhaust system installed and was to go back for a final dyno-tune. The engine started without problem about four times. Now, it cranks and is getting gas but will not start. He has replaced the starter relay but nothing.
Any ideas?
Thank you to anyone with insight, in advance.
Any ideas?
Thank you to anyone with insight, in advance.
Instructor
Joined: Aug 2010
Posts: 126
Likes: 0
From: Dallas TX
+1 on checking the crank sensor. You can check this by backprobing the sensor and checking for correct voltage or by looking at the OBD II readouts to see if it registers RPM. After that, I would check to see if electricity is making it to the coil packs.
Safety Car
Joined: Mar 2001
Posts: 4,359
Likes: 116
From: AUSTIN Tx
If you do not have access to a computer with software to see what is going on, then a noid plugged into one of the injector plugs will tell a lot. If the noid does not flash, then the computer does not recognize that the engine is cranking. Could be the cam sensor, crank sensor, or a number of other issues. Just like troubleshooting a conventional engine, verify spark, fuel and compression, and the engine should run. The ECM will not trigger injectors, or coil packs, if it does not see engine rotation. One other little idiosyncrasy of these engines, is that the computer will not turn on if it sees low voltage. You can have sufficient voltage to crank the starter, but not enough to turn on the ECM. Make sure that your battery is up. If you put a set of jumper cables on it, and it starts, then you will know that battery voltage was too low to start the ECM. Unlike old engines, it will not just have a weak spark when the battery is low, it will have no spark at all, and no injector pulse. If memory serves me right, the threshold for computer operation is about 10.5 volts. Also make sure that the grounds are good for the ECM, as it will not work with a bad ground.
Regards, John McGraw
Regards, John McGraw
Thread Starter
Drifting
Joined: May 2006
Posts: 1,864
Likes: 148
From: Santa Barbara California
Thank you all for your responses. Unfortunately, there does not seem to be any readouts that indicate a problem. We tried replacing the Crank Sensor but no luck. I guess the cam sensor.
Interestingly, this problem occurred only after the installation of a new exhaust system.
Interestingly, this problem occurred only after the installation of a new exhaust system.
Melting Slicks
Joined: Nov 2007
Posts: 2,162
Likes: 649
From: Chattanooga TN
Thank you all for your responses. Unfortunately, there does not seem to be any readouts that indicate a problem. We tried replacing the Crank Sensor but no luck. I guess the cam sensor.
Interestingly, this problem occurred only after the installation of a new exhaust system.
Interestingly, this problem occurred only after the installation of a new exhaust system.
Check wiring to make sure it's pluged in if not 1st. I have to check two connectors on my harness since it's one of the 1st 8 HO LS3s and GM had a short connector harness back then to go from LS2 style connector on one end of short harness and LS3 cam sensor style plug on other end.
I had problems 1st time starting due to 2 wires reversed on my main engine harness cam sensor connector. It's connector was wired like LS2 instead of LS3. Had fire to coils but no fuel due to wireing.
Last edited by Poorhousenext; Feb 5, 2013 at 09:58 PM.
Melting Slicks
Joined: Mar 1999
Posts: 3,029
Likes: 137
From: Nashville TN area
as was mentioned, check the cam sensor wiring. the engine actually should fire even if pins a and c are reversed, since after one revolution it can estimate and fire (i know because mine were reversed for 3 years, causing intermittent hard start issues!).. but it could take several tries to fire.
going back to "what's different?" since the last time your car was running properly.. you said just an exhaust change. Did any ground wiring get disconnected or not hooked back up properly?
going back to "what's different?" since the last time your car was running properly.. you said just an exhaust change. Did any ground wiring get disconnected or not hooked back up properly?
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Thread Starter
Drifting
Joined: May 2006
Posts: 1,864
Likes: 148
From: Santa Barbara California
PH and Mikey, The car had been firing up and running prior to the exhaust and immediately after the exhaust. The second time attempting to fire it up after the exhaust was installed is when the problem occured.
The jumper cables yielded nothing, grounds have been checked but there is a Lingenfelter box that has a red and green light. The green light is not coming on now and for some reason the heater fan is now not working. The thought of a burned wire came to mind but none found. In addition there are no error codes. ???
The jumper cables yielded nothing, grounds have been checked but there is a Lingenfelter box that has a red and green light. The green light is not coming on now and for some reason the heater fan is now not working. The thought of a burned wire came to mind but none found. In addition there are no error codes. ???
Instructor
Joined: Aug 2010
Posts: 126
Likes: 0
From: Dallas TX
Hope this isn't the case, but last fall, I had a similar problem. When on a test drive, stopped to get gas and the car wouldn't start. Had to tow it back to the house. Spent the next 2 weeks looking at cam/crank sensor, coil packs using noid lights, wired up a new ignition switch (to make sure I hadn't shorted something there), and more.
As a last resort I sent my LS7 ECU back to Street & Performance for testing. They said it had shorted out (how I don't know). Sent me another unit and car worked fine. Now I have a battery cutoff switch I use everytime I touch anything on the car.
As a last resort I sent my LS7 ECU back to Street & Performance for testing. They said it had shorted out (how I don't know). Sent me another unit and car worked fine. Now I have a battery cutoff switch I use everytime I touch anything on the car.
Melting Slicks
Joined: Mar 1999
Posts: 3,029
Likes: 137
From: Nashville TN area
what does the lingenfelter box do (or what is it supposed to do?)?
land shark provides a good reminder - best to disconnect the battery anytime you're working on the car, even if it is just wrenching on it.
land shark provides a good reminder - best to disconnect the battery anytime you're working on the car, even if it is just wrenching on it.
Thread Starter
Drifting
Joined: May 2006
Posts: 1,864
Likes: 148
From: Santa Barbara California
Well, it turned out to be a bad connection out of the Lingenfelter box. I am surprised some kind of code didn't show but it is now running again.
Thank you all for your ideas and help. All responses are very much appreciated.
Thank you all for your ideas and help. All responses are very much appreciated.