LS Engine won't start

You have verified that you have spark, but not injector pulse. Use an injector noid light to check if the injectors are firing. Google injector noid light tester.
make sure all ECM ground wires are connected tightly. I think there are 3 different ground terminals coming out of harness at different points.
Thanks for all the tips.

Further to your advice, I have connected all three GM harness grounds to one of the heads, with another dedicated wire from the same point all the way to the battery. I also ran another wire from the same point to the other head, so both heads are now grounded to each other and directly to the battery.

According to Chevrolet Performance, the MAP sensor should cause rough running, but not failure to start.

The main 4 AWG ground is from the block to the frame and from the same point on the frame to the negative terminal of the battery. About 12" for each cable.

The LiFePo battery has previously shown a lesser voltage drop than the "regular" Corvette battery and the Corvette battery is back in the Corvette, so using the LiFePo battery, the lowest transitory voltages with ignition leads disconnected (occurring immediately as the starter engages) measure as follows:

At battery, normal wiring: 7.x volts
Starter post to ground: 7.x v
At battery, w/jumper cables parallel to normal wiring: 8.x volts
Across starter posts when cranking: 0.03v
Battery jumped directly to starter, completely bypassing all car electrics: 10.8v, BUT the starter just spun at this point and did not turn the engine over. I assume it must have some kind of clutch or shear pin internally, which has just failed. This voltage result is interesting; I would have thought that with no load on the starter and the battery connected directly to the starter, the voltage drop should be negligible.

The above voltages are transitory bottoms; as the engine cranks, it immediately recovers to 10.x. It's a bit hard to read the transitory bottoms because they happen so fast and the numbers are not terribly repeatable within a 1 v range (so I have listed them as ".x")

Considering the voltage drops I am getting and the fact that it just broke, anyway, I have a new starter on order. Will report back once it is installed and testing can resume. In the meantime, I am googling Noid lights . . .
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It might be informative to run the engine management from a different battery (negative terminals connected between both batteries) - i.e. one for the ECU and one that only supplies the starter motor and solenoid. That would rule-out the voltage drop as the cause of the non-start, assuming that the starter motor turns the engine over fast enough.

Howard Jones

The reason the starter just spins is the solenoid isn't powered at the same time and does not pull in the bendix drive. Nothing is wrong so far. Now try the same thing from the top solenoid connection. This will pull bendix drive in at the same time. Measure voltage at the starter post at the same time and again at the top solenoid post. They should be the same voltage.


I actually powered both. I connected the battery directly to the regular post on the starter and then I used a dedicated wire to run from the battery to the terminal on the solenoid.

Just to make sure there wasn't something funky happening, I then connected the starter to the car exactly as it was before and used the starter button in the car and the same thing happened - the starter spun but the engine didn't turn over.

I'm assuming this means something internal in the starter is hosed. I didn't realize they have a bendix, but if so, it looks like it is not being powered anymore.
P106 code. MAP sensor PN 12615801 $50.00 from Lingenfelter. If you have another GM car check to see if it uses the same sensor and remove and try it before you buy one.
If you have any question your battery is the problem barrow a jump box with as many amps a possible and try that. Make sure all electric connections are tight.
Good luck
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I don't know if this helps, but several years ago I was trying to flash new ECU software into my mini. Charged the battery and bought a big charger to charge the battery as the flash was occurring. Didn't work, as the voltage needed to be maintained above 13 vdc for the flash to work. So I jumped the mini from another running vehicle, and got the required voltage for the flash. If this is a voltage issue, perhaps you could try to do the same thing I did....jump it from a running vehicle to get a steady 13.8v.

Then when/if it starts quickly disconnect the jumper cables.
I'm not getting a P106 code and re-reading the GM Performance Engine Controller Kit installation manual doesn't say anything about MP sensors, however the Jegs site does have a statement which says that the Engine Controller "Will run all LS7s with MAP Sensor p/n 809-12615801". As far as I can tell, there is no such sensor, but there is a sensor with the part no. 12615801 (i.e. no "809"). The sensor on my engine is 12644569. The sensor on the Corvette is 16212460, which doesn't match either of the above.

Although its not throwing the P106 code, I'm going to order the 12615801 sensor, anyway.

A few posts back, Howard mentioned needing to reset the CPU. I assume that disconnecting and re-connecting power will reset it? Is there something more that needs to be done?


Just a quick and probably stupid question, but if it has fuel and a spark, why no BanG? I mean what prevents the BanG, a very weak spark? Would it fire on a squirt of ether? (You can tell I'm totally old school)
Just a quick and probably stupid question, but if it has fuel and a spark, why no BanG? I mean what prevents the BanG, a very weak spark? Would it fire on a squirt of ether? (You can tell I'm totally old school)

I've gotten bad fuel before and holding the throttle wide open (DBW pedal) and cranking it over sometimes breaks through that crap gas situation.

Howard Jones

What had happened in the case I cite is the engine in question had several things that needed to be addressed. While this was going on the throttle position sensor and/or the peddle assemble itself had been removed and replaced and or disconnected.

This caused the ECU to believe that the throttle position signal had been lost while the car was running. In such a case GM wants the car brought into the dealer and checked out before the ECU is reset. This is safely concern for GM in that loss of peddle position would be very dangerous on a running car as you can imagine so the ECU will not allow the car to run until this issue is resolved.

The bottom line is IF this is the issue then you need to check with GM or another qualified tech to ask how to do this. I am not that person. My intent is to give you a lead.

My concern about battery voltage during cranking is that 6 volts is very low and it is possible that a lot of the electronics will not like that or 6 volts is very near the point that they won't work. MSD systems say that 6 Volts is minimum running voltage before things get weak or intermittent.

From now on if it was me I would conduct future testing with two battery's connected in parallel so as to eliminate the low voltage condition. It is very possible that you have two or more things going on here.

Tight new motor putting a lot of load on starter.

Possible bad contacts on solenoid causing a voltage drop across them and adding to the high load on the starter thus dropping voltage to 6 volts.

Bad crimp on a lug.

Small gauge wire.

Bad big master switch contacts if you have one.

Then once you can maintain the voltage to 10 volts or more during starting and IF it still won't start it appears that you have a software/hardware interface mismatch. That could be a bad part, mismatched parts, correct parts not connected properly, everything connected properly and correct parts and software mis installed, or missing sensor inputs, wrong sensor input/output values, bad connections in a plug or even wrong software.

Get the voltage up, then get a correct fault code reader for your ECU, aftermarket pieces, and engine and troubleshoot one thing at a time until it works. Chevy LS engine hotrod forums might be of some help also. I'm sorry but there isn't another way except take to a good Tech write check.

Ken Roberts

Disconnecting and then reconnecting the battery is correct to reset the ECM. Make sure you have connected all the engine grounds for the GMPP engine wiring harness (3 ground eyelets).

Here is the run down on the MAP sensor part numbers:

12644569 was installed on 2012 and up LS7

12615801 was installed on 2009 to 2011 LS7

16212460 was installed on 2006 to 2008 LS7. (It is now discontinued and replaced with 12614970)

A bad battery will produce all kinds of odd behaviour with the ECM.

The DTC P0016 will be set due to the fact the ECM is watching the crank sensor and cam sensor correlation as the engine cranks. Check that both sensors are pinned correctly at the ECM. I have read in the past of two pins being installed incorrectly. Both are 5volt sensors and you verified their output during cranking. You changed out both sensors. Seems like if they are pinned correctly then the only remaining issue could be the fact the cam sprocket was incorrectly timed with the crank sprocket (dots were not aligned). You mentioned that you visually confirmed this.

Dave please describe what the "ignition leads" are connected to.
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Thanks for the input, guys.

The sensors each show +4.9v with the correct polarity, which persists while cranking. The signal wires have continuity back to the correct pin on the ECU plug.

I confirmed that the valves are fully closed when the related piston is at TDC, but have not confirmed that the index marks on the crankshaft and camshaft line up.

When I say "ignition leads", I mean the leads from the coils to the spark plugs. For much of the testing, I have left them disconnected so as to avoid the occasional firing of a piston at the wrong time (it doesn't fire often, but out of every 10 seconds of cranking or so, it might fire once, and stop the engine).

I don't have a master switch.

As a sidenote, I have called 4 different local shops who are experienced with LS engines. Two of them are not interested in troubleshooting a crate engine installation; they just want to tune already running engines. Starting about 4 weeks ago, each of the other two have promised several times to come "sometime next week". Probably they're very busy and a house call for a custom installation is pretty far down their priority list.

I am currently waiting for a new MAP sensor and 2/0 wire to arrive. Once these are installed, I will try starting again with a second battery jumped directly to the starter, in line with the installed battery. If that doesn't work, I will probably buy HP Tuners or something similar, so I can see what the engine is seeing. I was hoping to hire someone locally who already had the experience and equipment to connect to the ECU, but given the above, it looks like I will just need to learn how to do this myself.

Thanks for everyone's help - I'll keep you posted after the next start attempt.
The new Manifold Pressure sensor finally arrived, so I installed it along with the new 2/0 battery cables and then connected the Corvette battery directly to the starter with the old 4AWG cables, leaving the Shorai LiFePo connected in its usual place on the SLC.

The Corvette battery starts the Corvette without a problem and the Shorai has been showing a lower voltage drop than the Corvette battery when cranking the SLC, so between the two of them, there was plenty of power to turn the starter over.

However, the result was the same as before; the car would occasionally fire, but when it fired, most times the cranking would stop and I would have to release the starter and press again to recommence cranking. It seemed like it was trying to fire at the wrong time.

I think this leaves only a few possibilities for what is wrong:

1) The Computer is hosed or;
2) There is an internal problem in the engine or
3) Some other thing that I’m completely missing

From what I understand, GM Performance runs each new crate engine on the test stand before shipping, so hopefully #2 is not the case.

GM Performance wants me to hook up to the computer so that we can see what it is seeing for rpm, etc. while cranking. To do this, I will need HP Tuners or something similar.

Next step: I will ask a couple of the local LS experts again if they would be willing to come out with their equipment. If there's no response there, I'll order a copy of HP Tuners myself.

To date, troubleshooting the engine start has consumed 17 hours in the shop, 5 weeks on the calendar (waiting for parts and local experts who said they would come "next week") and about $250 in parts that didn't need to be replaced to start an engine with all new components, which theoretically should "just run". This is getting pretty discouraging . . .