Sometimes starts other times it wont. engine cranks but does not start

could be the head gasket has gone take out spark plugs and check there condition and look for water in the piston, water and fuel dont burn well. as you have done an oil change it may have gotten into the oil but its harder to tell with new oil, as water will sit on the top of the oil.

There are a lot of different issues that can cause this. Does it crank over normally just not fire? Is the check engine lamp on?

Sounds like a timeing issue

As with any no start issue, you will have to figure out if it is a spark or fuel problem to proceed.

Ok then, from your description and the
make/model/year of the car you have there,
it appears you've reset the VATS.

The car's security immobilizer
reader at the key switch
does not recognize the coded
chip in the ignition key any longer.

You can try to put the key
in the ignition, turn to the on position &
wait at least 10 min like that.
(Do not turn off the key switch before
10 minutes as elapsed!)

Once done, the key is re-programmed and
should allow the fuel injectors to work again.
The car would start now if corrected.

In some cases, the VATS (GM'S VEHICLE ANTI THEFT SYSTEM)
will re learn the code this way, and will then
allow the restart, however if this does not work,
then you can simply tow it to any GM vehicle dealer
to have the service department re code it.

There is a permanent solution though.
Adding the PLJX Self learning Bypass module (59.95)
will bypass the PASSLOCK system in your vehicle
for good. See this at www.PASSLOCK2.com

Good luck I hope method 1 does the trick!

Here is the 30 min relearn:

Ignition keys relearn takes about 30 min to do. 30-Minute Learn Procedure 1. Turn ON the ignition, with the engine OFF. 2. Attempt to start the engine, then release the key to ON; the vehicle will not start. 3. Observe the SECURITY tell tale light. After approximately 10 minutes, the light will turn OFF. 4. Turn OFF the ignition switch, and wait 5 seconds. 5. Repeat steps 1 through 4 - two more times - for a total of 3 cycles of 10 minutes. 3x10 = 30 minutes. The vehicle is now ready to relearn the Passlock Sensor Data Code and/or passwords on the next ignition switch turn from OFF to CRANK Important: Turn the Ignition Switch OFF. The vehicle learns the Passlock Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle. 6. Start the engine. The vehicle has now learned the Passlock Sensor Data Code and/or password. 7. With a scan tool, clear any DTCs if needed. History DTCs will self clear after 100 ignition cycles. Without a scan tool you may have momentary starter interruptions while history clears itself.

Turn key on & off five times in a row. Wait 30 sec. & try again. If it doesn't start wait ten min. with key on & start car.

I can think of 2 possibles,it could be a bad battery cable or an intermitent short in the starter solenoid, check or have the battery cables and there connections on both ends first not only are they a cheaper fix but the problem you describe sounds like a current flow issue.Test them with or have them tested with an ohmmeter they should show o ohms resistance,and while not attributed to the problem I do not reccomend using Bosch spark plugs of any variety,the best plugs for any Japanese vehicle are NGK's,this comes from my personal experience with them and other techs that I have worked with.

Which engine is this? and also do you have a TACH gauge?

check for spark when it wont start there is a common problem with the loss of crank signal on these cars with 2.8/3.1 engines.

If you have no spark its either a crank sensor or the ignition module going bad, but the problem is you need to verify which one it is. having a tachometer would help diagnois this. if you have a tach signal and no spark most of the time its an ignition module but you would need a lab scope to 100% know which one it is. the modules are very common on these engines.

what happens is the crank signal goes to the igintion module. and then the module loses it most of the time cause the module is supposed to send the crank signal tot he ecu. you would have to make sure the signal makes it out of the module and into the ecu. if you get a signal out of the module then you have more severe problems. that need in depth diagnosis.



Michael
ASE certified
plz rate

Engine temp sensor could be faulty not letting enough fuel be commanded by the ECM .

Replace crank sensor. Next time it cuts off pour or spray water on it, to cool it down and if car starts that is what it is. I did this to get my car home to fix it. Next thing I would look at is the coil module if crank sensor does not fix it.