12 volts on the reference circuit? (99 Astro)

Hi!  Wrestling with a 99 Astro that periodically stalls and will generally restart after a short break.  When it stalls its a result of sudden no spark.  Trying to check reference circuit.  Any idea why I would have 12 volts on the reference circuit?

Thanks in advance for any assistance.

Jim

Edit:  Sorry...I'm new to all this and was checking coil battery voltage.

Exactly what reference circuit ? and measured where ?

Thanks for the response Steveturbo.  I'm pretty new to this stuff and was mistakenly measuring battery voltage at the coil.  I just checked my MAF sensor and the reference voltage was 5 so I don't think that is my problem.  Going to post a summary in the hopes of getting some thoughts from folks as to what to do next as I am at my wits end.

Situation:  99 Chevy Astro van that runs well except for a habit of random stall and difficulty restarting (until you wait 5 minutes). When it won't start I have confirmed it has no spark as measured from the coil wire to distributor.  Fuel pressure seems good.  60 plus pounds with key on no start.  Runs with between 55 and 60 psi.  It is not giving me any fault codes.

So far I have replaced ICM (twice) and coil, CKP and swapped in a VCM from a 2000 Blazer and problem persists.  I have checked and redone grounds on the engine block by the knock sensor, and the thermostat housing (which I understand are the grounds for ignition system).  Checked the wiring harness as best I could given that it is a van and difficult to see everything.  I am thinking that I have a random break or ground in the power supply to the ignition system and will be checking that out this morning.  One random probably unrelated issue is that the gas gauge sometimes goes to zero even though the tank is full.  I have diagnosed this a being the sending unit in the tank based on resistance check and because I can get the gauge to read by rocking the van. 

Thanks for reading this far.  Any ideas from you folks would be greatly appreciated.
 

 

firstly, stop changing parts without testing.

Are you getting a crank signal ? test with a scope
Are you getting an rpm reading on your scan tool ?

Are you getting a trigger from the ecu to the ignition system, whether that's a coil directly, or via an amplifier. Test

Are you getting a trigger from ecu to injectors ? Test

You've already said the fuel pressure is good, so assuming the pump circuit is ecu controlled this would suggest the ecu is alive and somewhat well. Throwing multiple ecu's in is just silly.

Thanks for the feedback Steve!  Good advice re: swapping parts for sure.  Old habits die hard I suppose.  I don't have a scope so am somewhat limited to what I can do with just multimeter and test light.  My biggest problem is trying to recreate the fault so I can do more troubleshooting.  I was just was out there and the van started right up.  I ran it for 20 minutes yesterday no problem.  I suspect however if I go far from home it will die on me again.  If I can get it to act up again I will try to perform the tests you suggest to the best of my ability.  I am also going to cast around to see if I can find somebody with an engine scope that can lend me a hand.  I am reluctant to go to the dealer.  I was talking to them the other day and they said they had a vehicle with similar symptoms that they had 40 hours (at a shop rate of $120 per hour) into trying to diagnose!  I love my van but can't justify that kind of expense.  Thanks again.   

If it is intermittent, then yes it will be much more difficult.

It will be easier if it breaks full time, not that either is ideal

OK...another piece of the puzzle.  I disconnected the harnesses the ECM, Coil, CKP, and injection system, in short everything that is supposed to be supplied by power from the ECM-1 fuse.  Power off I have continuity between this power circuit and ground.  With key on voltage in the system is 12.1 volts while battery voltage is 12.27?    Does this mean I have a short in the power supply to this line or am I missing something?

Thanks in advance.

No, it proves nothing.

You're just measuring a slight difference in voltage due to volt drop within the wiring.

known to fuse box problems . when does run then stalls check your fuel gauge did it drop again as you mentioned . i had to do some wiring in my friens fuse box , on his . you can try taping fuse box when won't start. good luck

Thanks Lupe!  I had the fuse box apart this morning and didn't see corrosion or anything else suspicious but I will check that out next time it stalls.

 

So...I thought I would close the loop on this as "fingers crossed" I think I have solved this one.  I'm thinking the issue all along was coil or coil wire periodically/randomly shorting to ground.  After reading in manual that these systems were extreme high voltage and that steps should be taken to avoid the ignition grounding out I took steps to orient the coil wire cap 45 degrees to the coil (as per the manual), wrapping the coil wire in a layer of electrical tape and electrical conduit, and after having put several hundred kilometers on the vehicle,  I have not had a recurrence of the problem. 

While it is somewhat embarrassing to discover this was the problem in my defense I had checked for ground early on, but it must have been hidden and intermittent.  Anyway, just posting in hopes of potentially helping someone else out.

Thanks for the help with this.

the only high voltage is from the coil to the spark plug.

All other regular copper wires are 12v systems

At least it seems to be resolved.