LS376-480 start problem

[Glenn Martin]

I am having problems with starting the LS-3 in my SLC. Engine turns over fine. Fuel pressure is 58 psi. I have ignition spark and signal to the injectors. No codes in the PCM. The engine turns over but will not start. After spraying a little bit of starter fluid into the intake, it starts and runs rough at first and then evens out. It continues to run as it should. If I turn off the engine and immediately try to restart the engine, it will not start. Anyone have any ideas as to what the problem may be?

 

[Ken Roberts]

What are you using for a fuel pump? Have you checked your fuel pressure at the rails during cranking? After it shuts down is the fuel pressure maintaining or does it bleed down quickly?

My thoughts are that there might not be a check valve at the fuel pump or it's defective. When you start the engine the fuel pump is told to turn on momentarily. This is enough fuel to temporarily charge the fuel rails. Then the ecm watches to see pulses at the crank sensor. Once this is detected the ecm then commands the fuel pump to run continually.

If you have HP Tuners you can actually increase the time the fuel pump runs during cranking before shutting off and waiting. This is to compensate for fuel pumps that have a poor ability to hold pressure.

 

[Ken Roberts]

Another scenario is that you having an injector hanging open. Dirt or a small bit of debris could have accidently been deposited in the rails or after the fuel filter location during assembly.

You could remove the fuel rails leaving the injectors still in them and hold the assembly over a large bucket and then jumper the fuel pump relay for a second or two. See if one is spraying. Have a fire extinguisher handy though. Do at your own risk mind you.....I didn't tell you to do this....lol

 

[PeteB]

Ok, maybe a dumb question, but since you said you were spraying starter fluid into the intake, I'll ask - do you have the MAF sensor installed and connected?

 

[Glenn Martin]

There is a MAF sensor installed and is working. The fuel pressure does leak down fairly quickly after turning off the pumps.

 

[Ian Anderson]

2 things immediately spring to mind
1) During cranking you are getting a voltage drop to the coils, which in turn are not generating a good enough spark. The Ethanol stuff being easier to burn will fire up and then the engine is turning fast enough to continue.

2) Poor earth on one or more components - Possibly coils - do you have a good strap from chassis to engine block?

Ian

 

[Roger]

After spraying a little bit of starter fluid into the intake, it starts and runs rough at first and then evens out. It continues to run as it should.

Given that it runs fine once assisted to start, is the temperature sensor working?
Have you run it up to temperature before stopping and attempting to restart?

 

[Bill]

This could be an ignition wiring problem.

When the key is in the Start position, it is clear that 12V is getting to the starter.

When the key is in the Run position, it is clear that 12v is getting to the ECU's ignition signal.

Check to ensure that you also have 12v to the ECU's ignition signal when the key is in the Start position. If not, this type of wiring problem would be consistent with you having no OBDII trouble codes.

From your post, I wasn't sure if you checked "ignition spark and signal to the injectors" in Run or Start mode.

 

[Glenn Martin]

I have two ground straps from the block to the chassis. Grounds to the PCM are good. I have checked the voltage to the injectors and all the voltages that I have checked are good. I ordered a check valve so I should know by the weekend if that is the problem. I will update the forum then. I will be on business travel until then.

 

[Shane]

My vote is with Bill. If it was a fuel related problem, the engine would not run.

 

[Howard Jones]

I think Mesa had a issue with his setup that went something like this. If you unplug the throttle body from the system and then reconnect it the ECU needs to be reset. Otherwise the computer will not allow the engine to run beyond the start mode. This is to prevent the car from running if the ECU looses the throttle position signal until the car is serviced and the throttle body is confirmed to be OK. Makes sense.

I may have got this a little bit wrong but it might lead you to an answer that you haven't considered up to now. Then again the symptoms are different in that his car started and then didn't want to run. Your issue is more or less the opposite. It may be another reset the ECU thing however.

 

[Terry Oxandale]

I had the exact same problem...running battery down in some cases trying to start it, but once started, ran fine...UNTIL I found out about a feature in which if the pedal is pushed once prior to start, after the ignition is hot, signals an extra rich start-up mixture that very quickly settles out (within seconds) to a normal idle mixture. Once I turned that EFI feature "on" in the software, I never had a start problem again.

 

[Glenn Martin]

Here is my checklist so far. The fuel system is a low pressure pump to a surge tank to a high pressure pump. I installed a check valve. The fuel pressure is 58 psi at the start attempt and remains at 58 psi. Using starter fluid the engines starts in a stumbly mode and then smooths out and runs normally. I tried depressing the accelerator pedal before and during starting but there was no change. The battery voltage drops to 10.6 volts during canking but it has a strong spark. The engine turns over as one would expect. The MAF sensor is installed and connected. I tried disconnecting it and there was no change. I am getting 12 volts to the PCM, injectors and coils without the engine running. There are 2 ground straps from the engine to the chassis. I ran the engine to 191 degrees before turning it off and it would not immediately restart. I tried disconnecting the temperature sensor to enrichen the mixture but no change. I am getting a signal to the injectors.

Any one have any more ideas?

 

[TSR]

If I understand this thread correctly the engine is a new, so you might try and exorcize the GMPP warranty since it should be free from manufacture defects. It's obvious you have exercised a reasonable standard of troubleshooting and you are running out of options.

 

[Allan]

Here is my checklist so far. The fuel system is a low pressure pump to a surge tank to a high pressure pump. I installed a check valve. The fuel pressure is 58 psi at the start attempt and remains at 58 psi. Using starter fluid the engines starts in a stumbly mode and then smooths out and runs normally. I tried depressing the accelerator pedal before and during starting but there was no change. The battery voltage drops to 10.6 volts during canking but it has a strong spark. The engine turns over as one would expect. The MAF sensor is installed and connected. I tried disconnecting it and there was no change. I am getting 12 volts to the PCM, injectors and coils without the engine running. There are 2 ground straps from the engine to the chassis. I ran the engine to 191 degrees before turning it off and it would not immediately restart. I tried disconnecting the temperature sensor to enrichen the mixture but no change. I am getting a signal to the injectors.

Any one have any more ideas?

Swap out the MAF sensor and make sure it is oriented correctly.

Find someone with a loaner engine computer that you can try. (something may be wrong with the start up parameters)

Swap out the MAP sensor.

Go back and check anything modified in the engine harnass.

 

[Shane]

I am getting 12 volts to the PCM, injectors and coils without the engine running.

What are you getting for voltage to those components when the engine is cranking? Have you tried unplugging one of the fuel injectors and hooking up a test light across and cranking to see if you are even getting a pulse to the fuel injectors while cranking? Obviously you are getting spark or it wouldn't start on starter fluid....but the fact that it does start with starter fluid tells me that you have no fuel during cranking...and the fact that it will run after started with fluid tells you that your injectors and fuel system are fine. That just leaves one possibility.....that you either have zero injector pulse during cranking, or not enough fuel for the engine to start.

Does the throttle move at all? You say you tried depressing the pedal, but you don't say whether depressing the pedal actually opens the throttle plate or not?

 

[Henry Nickless]

Sounds like crank sensor to me. I have had this happen 2 times before on different engines. Both times happened to cars out on the road and both times started with start fluid to get home.

 

[Glenn Martin]

Shane,

I am getting injector pulse. The voltage at the injector is the same as the system voltage. 10.6 volts when cranking. Jumping the battery, the voltage during cranking is 11.0-11.1 volts. Fuel pressure is still 58 psi. Tonight while trying to start it, it would hit once or twice and then no more. I will try the crankshaft position sensor next.

Allen,

The MAF sensor is oriented correctly. The harness has not been modified except pulling the ETC wire out to reach the pedal assembly. I will check the MAP. Still no DTC's.

Thanks for the suggestions. If anyone can think of anything else, I'm open to ideas.

 

[Ted - LS MAN]

Glenn, sounds like the mixture is Lean @ start-up - not enough fuel enrichment when starting cold. Use a scanner to see what the coolant & air temp is, should match ambient temp with engine cold. disconnect coolant temp sensor & check scanner temp reading, should show extreme high or low. try starting with sensor disconnected, see if it sets a code. Try starting with MAF sensor disconnected, see if it sets code. Check that the PCM has constant power on circuit 40F, orange wire (keep alive memory)- check voltage at fuse. Get engine started with starting fluid, let it warm up to operating temp, check temps on scanner. Check that ALL PCM grounds are grounded to engine, If I remember, there are 3-4 ground terminals in harness.

 

[mark b.]

Can't help with the start problem, but be careful with the ether, you can do a lot of damage real quick. You can use an oil can and squirt gasoline into the intake, that should fire it.