LS Engine won't start

[Dave Forster]

Hi guys,

I recently tried to start the engine in my SLC for the first time, but it won't start and I'm looking for ideas.

- New LS7 Crate Engine
- GM Performance Engine Controller Kit
- Fuel pressure is 60 psi verified at the rails
- Oil pressure builds to 60 psi with cranking
- Will crank, but will not fire
- Plugs are sparking when removed and grounded, so coils etc, appear good
- Fuel vapor comes out of the cylinders when cranked with the plugs out, so its getting fuel
- DTC P0016 is sometimes thrown ("Crankshaft Position - Camshaft Position Correlation Bank 1 Sensor A)
- There is 4.9v on the plugs to both crankshaft and camshaft sensors
- There is continuity on the signal wires back to the ECM connector
- I replaced both the crankshaft and Camshaft sensors, but the code is still thrown
- Voltage drops briefly to about 8v when cranking starts, but recovers to 10v as cranking continues. The red LED on the GM fusebox stays lit throughout. I tried swapping the battery from my Corvette Z06 into the SLC and it shows the same voltages and same results.
- I pulled the valve covers off to confirm that the valves are moving (i.e. no broken timing chain) and that the valves are fully up when the associated piston is at TDC. I did notice that even with the valves fully up, I can get a feeler gauge under some of the rockers and not others. Not sure if this is normal with an LS engine or relevant to the not starting problem. . .
- The engine controller ordered was for a 2006+ LS7 engine. I don't know how to confirm that what was ordered was what I received?
- The engine has the grey crankshaft position sensor, indicating a 58x reluctor wheel (i.e. post 2006)

Any suggestions or advice gratefully received.

 

[Will Campbell]

Unless you have connected the harness wrong, it may be the battery. Notwithstanding the battery switch, a drop to 8V will cause ISIS to drop out, and cause the car not to start (I think).

Can you try a brand new battery? And check the battery and ground connections (you do have a ground running from the engine to the chassis, right)? I'm not sure, but I think a drop to 8V is too much. So either a bad battery, loose wires, cables that are too small, or some other reason that is preventing adequate power to get to the engine ECU when cranking.

I saw a similar situation with another SLC. There was a "good" battery on it, but it wouldn't crank or start. The mechanic argued with me, but agreed to change them to humor me. A new battery solved the problem. Yours may be a similar issue (I know yours cranked, but the ISIS issue may still be the cause as it was here).

 

[John]

You definitly have an earthing problem or a crook battery for the voltage to drop that low, the thing will never start with less than 12 volts, i only have a dry cell ride on mower battery in the brabham [LS1[ and we can get 3-4 starts out of that before the voltage drops and its connect the anderson plug.

kaspa

 

[Dave Forster]

Thanks for the advice.

I have tried using two batteries; a brand new LiFePo as well as temporarily swapping the regular, 3 year old battery out of the Corvette (also LS7).

The LiFePo showed a drop to 9 point something. The "regular" battery showed a drop to 8 point something.

The engine block is grounded directly to the chassis with a short, 2AWG wire and then a second short, 2AWG wire connects directly from that point to the negative terminal of the battery. The ground wires from the GM fuse box are connected to the block and the ISIS is grounded to the chassis.

The lowest voltage that I am seeing is a transitory drop at the battery on a digital volt meter when the starter first turns over; as it cranks, the voltage on both batteries recovers to 10+ v while continuing to crank.

I just tested the Corvette battery with a load tester; 300 amps for 15 seconds produces a drop down to 10v, which according to the load tester instructions means the battery is good (battery is rated for 600 CCA)

The transitory drop to 8v that I was seeing on first cranking is as displayed on a digital volt meter. The load tester is an analog meter. It's possible that the digital meter responds more quickly and/or is giving a falsely low reading prior to the load stabilizing?

During one of the tests while cranking with the plugs out, I left one of the plugs connected to an ignition lead and grounded on the engine frame. It sparked throughout the 10 second cranking test. I'm not sure, but I would think this means that the ECM is not dropping out?

I'm a bit reluctant to buy yet another battery, but if you guys still think that is where the problem may be, I'll bite the bullet . . .

 

[Eric McClellan]

Couple things stick out for me.... That Crankshaft code that's being thrown every time is a problem.

Something is up there.

You said you have the correct ECM?

Couple questions I would like to see answered...

- Did you have the ECM flashed? Is the VATS system disabled?
- Do you have the correct reluctor wheel and ECM combo? Kinda important.
- Has the ECM been programmed to work in a car like yours? (VATS, only 2 02 sensors... etc)
- Did you build the engine or who did it? Crate engine?
- Did you dyno it, run it?

Sounds to me like you've got an issue between the ECM being either A) Wrong or B) not programmed to work with your setup. That code that keeps getting thrown for the crank sensor is telling I think.

Good luck.

~Eric

 

[Dave Forster]

Hi Eric,

That is my suspicion also.

It is a crate engine, purchased new and never run (unless the factory ran it before shipping).

The ECM has not been flashed or edited in any way. It is a stock GM Performance Engine Controller kit for 2006+ LS7 engines.

I don't know how to verify that the Engine Controller I received is the one I ordered. I'm hoping GM Performance Tech Support may be able to provide some guidance on that tomorrow.

The Crankshaft Sender on the engine is grey in color, which I understand identifies it as a post 2006 version with the 58x reluctor wheel (pre 2006 should be black in color, with the 24x reluctor wheel). I'm assuming that the wheel installed in the engine matches the color of the sender and is in fact the 58x version. The engine was bought new in 2013, so it should be the post 2006 version. The question (in my mind) is if I might have received a pre-2006 computer by mistake.

Dave

 

[John Ross]

You have spark and you have fuel, but no joy. Sounds like the crank is seriously out of phase with the cam, and I suspect this condition would throw the code you are getting.

The first thing I would do is pull the valve cover and the #1 spark plug, crank the motor over with a wrench, and verify that the piston is approaching TDC with both valves closed when the plug fires.

JR

 

[Fran Hall RCR]

Dave
have the bled the air out of the fuel rail by the Schrader valve?
I know it sounds simple but we have had customers with no start issues before and its something simple every time

 

[Jack]

Try Fran's remedy, if that won't work, try swapping pin positions on the harness plug,
1 for 3 and 3 for 1. I have heard this one before.

 

[Eric McClellan]

What part #'s for each engine and controller kit?

 

[Cam]

A longshot, but is the MAF pointed in the right direction?

 

[Eric McClellan]

A longshot, but is the MAF pointed in the right direction?

It would still fire, but just run like crap.

 

[Dave Forster]

Hi guys,

Thanks for all the good ideas.

- The valve cover was pulled and the valves were fully closed when the associated piston is at TDC.
- The Schrader valve on the fuel rail was pressed while I was hooking up the fuel pressure gauge to the fuel rail, spraying fuel everywhere. I guess this means it has been vented. In any case, the cylinders blow fuel vapor when turning the engine over without the spark plugs installed, so I'm pretty sure any air would have been bled out of the rails.
- The wire color and plug connection locations (A/B/C) on each of the crankshaft sensor and camshaft sensor plugs do match the documentation that came with the engine controller. Also, the correct wire color connects to the correct pin location at the engine controller plug. The correct pins on the sensor plug ends of the harness show +4.9v polarity.
- The MAF is pointed in the right direction.
- I'm not sure what the engine part no. is, as Fran sourced it for me with the kit, but assume it is probably 19244098. The Engine Controller kit is part no. 19258553.

 

[Eric McClellan]

Ya know... just for S&G's... do two things, both easy....

1.) Looks like your able to connect to the OBDII system, see if your scanner can ID pedal control... i.e. How much throttle input it recognizes...

then...

2.) Floor it, hold it and try and start the engine.

See what happens.

 

[Dave Forster]

I just spoke to GM Performance Tech Support. They suggested watching the voltage at the plug end of the cam or crank sensors to see if the voltage is good throughout cranking.

The voltage is a solid 4.9 throughout cranking.

Just for fun, I reconnected everything (including ignition leads) with the Corvette battery and tried starting again while watching the battery voltage. The voltage dropped down to a low of 6.x v and the engine stopped cranking and the LED on the GM fuse box went out until I turned the ignition circuit off and back on again. I tried again, and it cranked OK, but again stopped after a few seconds with a low voltage indication again.

This is a lower transient voltage than I am seeing with the ignition leads disconnected and the engine never stops cranking with the ignition leads disconnected. Maybe something is firing (though it's not sounding much like it) and creating a little more resistance to cranking, which is stopping the engine and causing the starter to stall out, drawing more current?

For comparison, after completing the above test, I swapped the battery back into the Corvette and watched the battery voltage while cranking the Corvette. It dropped down to a transient 10.x v before the engine started.

So, in summary:

1) The battery sags to 8v with the ignition leads disconnected on the SLC, but then recovers to 10v as it continues to crank.
2) The battery sags to 6v and stops cranking with the ignition leads connected on the SLC
3) The same battery sags to only 10v on the Corvette and the engine starts fine.

Clearly there is a significant difference in current draw between the two cars that might be causing the problem or making it worse.

On the other hand, maybe a significant difference in current draw should be expected with a new and tight engine? Or one which is firing at the wrong time, causing more physical resistance to cranking and causing the starter to stall out? Or just the fact that it is a different starter? (The SLC has the Bosch SR0408X starter).

 

[Dave Forster]

My "scanner" doesn't do very much and doesn't ID pedal position. I'm thinking that pulling the ignition leads off, connecting something like HP Tuners and looking at all the outputs is the next logical step . . .

 

[Will Campbell]

I just spoke to GM Performance Tech Support. They suggested watching the voltage at the plug end of the cam or crank sensors to see if the voltage is good throughout cranking.

The voltage is a solid 4.9 throughout cranking.

Just for fun, I reconnected everything (including ignition leads) with the Corvette battery and tried starting again while watching the battery voltage. The voltage dropped down to a low of 6.x v and the engine stopped cranking and the LED on the GM fuse box went out until I turned the ignition circuit off and back on again. I tried again, and it cranked OK, but again stopped after a few seconds with a low voltage indication again.

This is a lower transient voltage than I am seeing with the ignition leads disconnected and the engine never stops cranking with the ignition leads disconnected. Maybe something is firing (though it's not sounding much like it) and creating a little more resistance to cranking, which is stopping the engine and causing the starter to stall out, drawing more current?

For comparison, after completing the above test, I swapped the battery back into the Corvette and watched the battery voltage while cranking the Corvette. It dropped down to a transient 10.x v before the engine started.

So, in summary:

1) The battery sags to 8v with the ignition leads disconnected on the SLC, but then recovers to 10v as it continues to crank.
2) The battery sags to 6v and stops cranking with the ignition leads connected on the SLC
3) The same battery sags to only 10v on the Corvette and the engine starts fine.

Clearly there is a significant difference in current draw between the two cars that might be causing the problem or making it worse.

On the other hand, maybe a significant difference in current draw should be expected with a new and tight engine? Or one which is firing at the wrong time, causing more physical resistance to cranking and causing the starter to stall out? Or just the fact that it is a different starter? (The SLC has the Bosch SR0408X starter).

Good data on the voltage drop.

I agree that there is probably a difference between the two cars. I'm guessing that one of the differences may be that the cables to/from the battery, alternator and starter probably have too much resistance on them. Did you calculate the correct cable size for the battery location you have?

Also, I've seen cases where the cable sizes were OK, but the connectors were improperly crimped or soldered, causing too much resistance, which if course is what drops voltage.

I mounted my battery up front, and calculated the optimum cable size, then went up a size or two because there were connectors in the mix.

 

[Dave Forster]

The battery is in the rear, about 24" from the starter and the cables are 4AWG with crimped connectors.

Next time I try a start, I'll feel the connectors to see if they are hot. However, with the short runs, fat wire and the heavy duty crimping tool, I'd be surprised if this is causing much voltage loss. Good thought, though . . .

 

[Fran Hall RCR]

Switch to 0 gauge starter/power and ground wire...

Just had this conversation with another builder yesterday and once he changed from 4 to 0 it solved his sluggish starting issue

 

[Howard Jones]

Measure the voltage from the starter solenoid post to ground and then measure it again at the battery + to ground. Do this at the time that max current draw is happening. If the wire between these points is of the correct size and the connections are tight and correct then both voltage readings should be the same. Or at least within a .1 -.2 volts drop max.

If you think this is a problem add another cable between these two points. Use a battery jumper cable for testing. Clamp it onto the battery post and the starter post along side the wire you have made. Easy to do and you don't need to take anything apart.

You could also have a high resistance set of contacts inside the starter solenoid (new, old, used, what?). Measure the voltage drop across these contacts the same way as above. They should not drop voltage at all. I have had bad brand new solenoids before.

Then you could just jumper to the starter + post from the battery and see how it cranks. This takes all of the start circuit out of the process. Key on and complete jumper circuit. If it starts then you have a problem in the big wire battery circuit. Be careful doing this. Try and make the connection very quickly and without sparking. The electronics don't like sparking connections much.

One way or another you must find wherethe 6 volts is going. A 50% loss is far beyond what is normal. When you did the test with both battery's in the circuit the cranking voltage should have held up to right at 12 volts. Two battery's in parallel is a lot of available current capacity.

You have a simple small circuit there. Battery, big wire, starter solenoid, starter, all of the connections, then ground. Must be either a bad connection between two OR MORE of these points or a high resistance part in there somewhere (burnt contacts in the solenoid). By the way, do you have a master switch in the circuit some where? If so that's another piece to jumper out so that you can test it. Even new pieces can be bad. Happens all the time.

By the way. How are you grounding the system? You should run a ground wire from the (-) terminal of the battery to the block of the motor and as near to the starter as a bolt hole is available. Then separate ground wires to the individual systems. ESPECALLY the computers and electronics like MSD systems. Do not rely on chassis grounds for everything. Modern systems like yours want perfect ground planes. That means all the way back to the battery (-) must be zero ohms for all grounds no mater where they are connected.

If you just old school it and attach your grounds to available chassis points around the car you will have nothing but issues. I ran ground wires back to a central ground near the dash and then attached that point to the battery(-) with a nice big wire. My battery ground is attached right on the block next to the starter itself. I used welding ground cable for the starter wire and the ground wire. Really the best stuff you can buy.

On another troubleshooting track, I know of a case of a LS motor that wouldn't run correctly because the computer was seeing that the drive by wire throttle peddle signal had been missing and then reconnected. The ECU must be reset after that or it will not allow the engine to run.

This is to enforce a failsafe condition on the system if throttle peddle signal is lost.