65 fi

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.

65silververt

check the crank sensor

Ironcross

if it cranks and NO start, then the plugs could be fuel fowled.....then replace the plugs or at least dry them out

Land Shark 64

+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.

John McGraw

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

65 fi

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.

Poorhousenext

If you are getting fuel to cylinders and spark to coils the cam sensor is working.

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.

mikey

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?

65 fi

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. ???

Land Shark 64

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.

mikey

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.

65 fi

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.