hi
I have h2 2006 and is dead, it become more and more difficult to start it, sometimes 4-5 cranks, and after summer start running very rough while cold, when warm runs fine. It is dual fuel petrol and LPG-same on both. there is no after market alarm in this car except for remote start Valet model 561R with Audiovox AS-GM4
2 weeks ago I tried to start it and nothing, it is cranking fine but no start. I have check fuel pressure and it is 60psi but going to 0 psi after few second. I replaced fuel pump for new and it is 60psi dropping max to 55 psi. no help still dead.
I pull basic scanner, no codes. all fuses ok, vats on dash is off after few sec.
I crank for 15 sec, still no codes
while cranking no rpm needle move or rpm on the scanner, rpm 0
put new crank position sensor, checked wiring from ECU to CPS, all 3 wires ok. put power and earth to ecu pins and observe signal on voltmeter, while cranking moving from 0-5volts, same test on CMS, same result.
I took sparkplugs out, grounded it to manifold, crank the engine nothing.
I check power and ground to coils-ok, pull ECU out, ground signal from ecu plug to coil and it is sparking
same with injectors, put test led light into injector plug and while cranking no signal to injectors, checked fuse and is ok, power is coming to it, ground injector signal from ecu plug and each injector is working.
I took earth on left side of the engine and clean it. no help
I have tried to remote start and is is cranking but nothing on sparks or injectors.
I though ecu is dead, bought 2nd hand put it in, relearn key with 3x 10min procedure, vats is going off after few sec, cranking ok but no sparks or signal to injectors.
any help?

 

Camshaft position sensor, rear of engine at the back of the valley, under the intake manifold. I've seen these fail with no codes. Usually begins with intermittent starting issues on the first crank. Make sure you only use genuine GM or AC Delco. You will need a bidirectional scanner to do the crank and camshaft relearn procedure. You should do that anyway if you changed the crankshaft sensor.

There's other possibilities for sure, but this is a known failure considering the age of the vehicle, and frequently will not trigger a code. Also not too expensive. I've seen the Walker brand camshaft position sensor sending the correct signals to the ECM.... Yet the engine would fail to start every time on the first turn of the key. It would then start on the second attempt every time. So unfortunately the only reliable way to eliminate the camshaft sensor as the cause is to replace it.

While you have the intake off:
The intake manifold gaskets are reusable, however I always replace them. Check the valley cover bolts. They're notorious for being loose and causing oil leaks. It's a great time to replace that oil pressure sending unit since you'll be looking right at it. Might want to consider that depending how many miles you have. When you remove the intake manifold don't tip it too far. It's probably going to have about a half couple oil in it from the PCV system.

 

Try the Camshaft sensor like stated above first. I am concerned though that there is only 0-5 volts at the ecu while cranking. This is not enough for it to work. There may be a voltage drop issue due to a corroded/loose wire/connection.

 

i beleive he was stating the 5v refreance voltage to the sensors

 

Just reread it and it appears to say 0 to 5 volts while cranking.... But I'm a little unclear on what exactly and where exactly that measurements being done. If it is in fact erratic coming off either the cam or crank sensor, but the power to the sensor is steady, then obviously would be the sensor. Or it could be interpreted that there's less than 5 volts coming off the ECM.... need some clarification.

 

It is signal wire from sensor to ecu 0 to 5 volts, pin with power to sensor supplayed with 12 volt, and last pin earth.

 

but if the CPS is giving signal to ecu while cranking would it give something like single spark or injector signal to operate? According to manual it would start without CMS.

 

If you are getting signal from the crankshaft position sensor, I would go ahead and replace the camshaft position sensor and do a relearn. Make sure both sensors are genuine GM or AC Delco. Holding the disconnected plug for the sensor, I would go about 5 in back and remove and expose all the wires carefully, and look for any cracked wires. Engine movement over 20 years can easily cause that. When done inspecting wrap it up better than factory. As usual, double check the harness plugs are seated all the way in with the rubber molded grommet fully inside.

One very, very important thing to check. You should have a ground strap between the back of the engine and the firewall. I would remove that, clean the ring terminals on it down to shiny metal, as well as the fasteners and the surface it's bolted to. Then lean over the driver side fender and reach way down almost to the oil pan lip, you will find a single bolt where your negative battery cable attaches. There should also be a smaller wire with a ring terminal which carries the ground to the ground point at the very front driver side frame rail. If you look up near the driver side front tow hook, you will see it secured with a 10 mm headed bolt. Clean those connections as well. After cleaning, use any multimeter and check for resistance, voltage drop. (While you're at it, go around the underside looking up at the body supports protruding from the frame rails. You will find several grounding locations that probably need thorough cleaning.)

When reinstalling the intake manifold, also inspect very closely the plug to the coil packs, as well as your injector harness plugs.

Probably the number one issue on most GM vehicles in the past 25 years, ends up being a corroded ground connection. And the symptoms can be almost anything, and frequently very erratic.

Complete that and you should be somewhat confident that your system that triggers your ignition is okay. With the age of the vehicle, it's good maintenance to just do it regardless.... It is not a question of if those connections will fail, but when.

Then you can start verifying the ignition switch, pass lock system, and that the harness is carrying the proper signals to the ECM. In the end you may very well find out the ECM is defective.