Z95m6

If it is the VAT's the car won't crank at all and your security light will come on and stay on. Its also not the ignition switch, since the car cranks. If it cranks and cranks its either a fuel problem or fire problem. So i would check the plugs to see if you have spark, if you do then i would go out and buy a fuel pressure gauge and check the pressure.

CheshireCat

I checked for spark at the plug wire, and I'm not getting spark. Unfortunately, I ran out of light to work with. Although I didn't have a fuel pressure gauge, I did press the schraeder valve on the fuel rail and no fuel pressure was released. So, I guess my question should be...

What would cause sudden loss of both spark and fuel pressure?

Thanks,
Steve

944v8inDFW

VATS

I would try a bypass you might also check the fuses

med_reject

If the switch is shot completely, it wont crank and you will measure no voltage when u check it. If the contacts are bad but still working, the car will crank, and even start if you push the gas a bit, or fiddle with the position of the key. This is because the pcm cuts fuel to the injectors on startup, intermittently or completely, if the switch has fried but somewhat working contacts.

Regardless, this is only something to check if your fuel injector circuits are working but not receiving electrical input during startup, fuel pressure is good, and spark is good.

CheshireCat

Med Reject, that makes sense... In that case, would it be the contacts that engage the starter or the contacts that the "pellet" on the ignition key would contact when inserted in the ignition switch?

944v8inDFW, VSS? what is it and how would it cause a loss of fuel and or spark?

Thanks again,
Steve

med_reject

not sure that it would be either. PCM needs to detect a circuit when the switch is in the crank position, then run position, to give current to the injectors. It would be the part of the switch with the numerous metal contacts that plug into the blue connector pigtail. However, I dont think thats your problem because fuel pressure does not suffer in this case.

CheshireCat

Thanks, I'll have to check for spark at the coil tomorrow... Not sure what else to check.

944v8inDFW

VATS cuts spark and or fuel. That is what it is designed to do. Some years were different but it for sure cuts one or both. Guess one way to check the fuel theory is pull the intake elbow see if it will run on gas or starting fluid. Be careful in any case.

944v8inDFW

Do a search on VATS there is about 1000 or so posts about it

Z95m6

944v8inDFW you may be right but as far as i've heard is that Vats cuts power to the starter and when you turn the key all you get is a security light and nothing happens. That is how my run in with VATS has been too. When its happened to me i had a security light on only and no cranking or anything.

944v8inDFW

Sorry Cat i realized i posted VSS not VATS. See what happens when you sneak forum time at work?

mr_camaro96z28

Did you remember to cycle the key recently before pushing on the valve? It sounds electrical a cam or crank sensor not working would cause this prob. but you would have a DTC I think it's a little odd for you to not have one at this point so I'm thinking it's in your PCM but not real sure, thats the last place you want to go and replace, I would suggest double checking for DTCs if you haven't already done that and also double checking for spark and fuel. I had problems with my VATS system and my car would't crank so I think your going in the right direction by dropping that one. You might check and make sure the PCM is plugged in good and that all your grounds are in good condition. If you unplug the PCM make sure the key is OFF.

Good Luck

944v8inDFW

FYI there is a fuel pump prime / test wire. that take the ignition switch out of the loop so to speak
http://shbox.com/1/fuel_pump_prime.jpg

CheshireCat

944v8inDFW, Thanks for the info... I've been looking at the VATS schematic on Shoebox's website, and it definately can cut off both fuel and spark. I don't see anything there that would prevent the starter from cranking, so VATS is still looking like a strong possibility. Also I see how the ignition switch fits into the VATS system. It could be as simple as bad contacts in the ignition switch. This gives me some stuff to play with tomorrow. Thanks again.

Z95m6, When you had a problem with VATS you say that you weren't able to crank the motor?? I wonder if the system is different on M6 cars?

mr_camaro96z28, Yes, I had recently cycled the ignition key to pressurize the system. I did double check the PCM for codes. I didn't check the grounds for the PCM though. You also indicate that when you had a problem with VATS, you weren't able to crank the motor... Hmmm??? My gut tells me to keep looking there, but it wouldn't be the first time my gut was wrong...

Thanks again all,
Steve

mr_camaro96z28

Well, it might be a different system since my car is OBDII and yours is OBD1 so there could very well be a difference there. There's also that my car is a 6spd so if thats your gut feeling thats not always the bad choice. Keep us updated
Good Luck