vettnut

My new, GM Crate LS2 engine with fuel injection, while idling at running temp, will miss and sometimes the engine will shut off. No Codes. The engine will start up immediately.

I purchased this new crate engine from a GM dealer about 3 years ago. I have researched this engine problem on the web, and some people have had a bad crank sensor, head gasket, etc.

While driving this car, I have all kinds of power without any other engine issues. I love this engine.

If you had these same symptoms can you share your findings?
What did you find?
How did you find it?
Thanks

American Heritage

Crank sensor

Obviously diagnostics are in order before R&R (simple to do). You described a cps failure (intermittent)

vettnut

Thanks for the reply.
I siphoned out the fuel today and replenished with fresh premium non -ethanol. The O2S is always flashing, running or not on my Innova 3120scanner. I am not sure if this is telling me one of the oxygen sensors are faulty, or do they always flash on the scanner. I was hoping someone else with this type of scanner could reply. My scanner does not have live data. Again, No Codes.
I pulled #1 plug to see what it looked like. The plug looked clean. I read all the plug wires. They all read the same.
I started her up and detected a miss at idle again and got worse the warmer the engine got. I took it for a spin and the engine has gobs of power. The engine is a new GM crate engine with less than 1 hour of run time, but I did add some time to that today.
I will look into buying a crank sensor. It looks simple enough to do except the starter is in the way.
What does cps mean?
What diagnoatic tool should I be using?
Again I have the Innova 3120, no live data.
Thanks
RG

American Heritage

you need an oscilloscope to see the crank position sensor signal.

you either have a failing crank shaft poisiton senor, camshaft position sensor or pcm.
I don't have any experience with the scanner your using so I cant comment on the flashing 02 thing.
Start with a few basic things. check the wring around the crank position sensor (behind the starter), check the wring going to the cam position sensor. Look for cracks, broken wires, pinched wires, ect... If your good with a multi meter you can break that out and start checking continuity from the senor to the pin at the PCM.
If you don't want to do all that then just start by swapping out the cam sensor then do the crank sensor, then PCM. Its one of those three (or the wiring to/from one of those three). If you want to do the diagnostics correctly (which is what I recommend) then you will need to get yourself a wiring diagram of that circuit.

vettnut

Update:
My LS2 crate engine always takes 2-3 seconds of cranking to start. On the road it has all the power it should have.
I still have a miss.
Last night when the engine was cooled off, I started her up and jumpered the electric radiator fan. Doing this casues the engine to stumble momentarily and then the miss starts to happen. I can drop out the fan and the miss continues.
I can shut off my engine and everything is fine again till I jump out the fan to run. The inrush current to the fan is 40+ amps and it runs 20 amps normally. Sounds very healthy. There is a 1 Volt lower reading at the fan than where the fan's fuse is located. Lower voltage increasing the current.
Yesterday, I changed out the Cam sensor and the MAF sensor. I checked my MAP using vacuum observing 5 volts and lowering 1 volt for every 5 inches of vacuum.
I have already changed the Crank sensor, checked fuel pressure 58 lbs., checked plugs for cracks and plug wires, changed out the fuel, pulled the oxygen sensors and they read the same with or without heat.
I was convinced the MAF was bad because when I unplugged the MAF I did not get a check engine light/code. When I would unplug the MAF the miss would go away, plug it in and no miss, yet no check engine light. I installed a new MAF, now I can get a code when I unplug it.

Is my wiring goofy on the MAF, maybe at the ecm?
Is my MAF sensitive to voltage dips, when the fan starts?
I have an optima red top battery. Not sure if its the culprit.

If I buy a live data scanner, how does one know by watching the data, what is good data or BAD data pointing to a skewed item?
Any experienced suggestions appreciated.
Thanks

c5racr1

Check the ground wires on the back of the heads