mntnresq

Hi all,
I have been pouring over every post I can find for the last week or two, trying to find some poss solution to my very weird issue, and no luck so far.

A little backstory-
I just finally finished a new stroker build after a broken piston about a year and a half ago. Everything worked and was fine when I pulled it. Got the motor in, everything hooked up, and was excited to finally get 'er going again. Turn the key and....

Nothing. No gauges, no turn over, no fuel pump prime, nothing. Eventually get a No Bus error on the cluster, occasional CEL, and airbag light. Also have strange issue of backup lights receiving about 5 volts all the time.

So, I start researching No Bus issues. Lots and lots of threads about bad connections at the cluster, the PDC, grounds, ASD circuit, etc. Run through all of the probable solutions. Eventually find a note buried somewhere about the TCM. Unplug the TCM, and voila, no bus is gone, gauges work, fuel pump primes, no CEL (initially), backup light issue is gone, and she will crank. Still no start. Seems obvious bad TCM, but nothing I can find indicates that it is necessary to run, nor should it cause my issue.

Of course I see 1000 posts about bad crank sensors being primary culprit. Run through every diagnostic I can find described, and it checks out.
What I have checked/done:

• Crank sensor checks good. No resistance through the leads, it is getting the 5 volt CCD bus signal. PCM seems to be reading it, no change in gauge behavior when disconnected. I can connect to the PCM through DTC and pull codes. I replace it anyway, still no spark.
• Disconnected, cleaned, and reseated every ground I can find.
• pulled every fuse and relay, tested, cleaned contacts and replaced
• All others sensors on the CCD bus have appropriate voltage
• Verified Injectors are firing
• Fuel pump does prime, and I have 12v at the coil during the inital key ON.
• pulled the coil, and tested for spark by inserting all the plugs and grounding them, no spark visible. Tried replacing the coil just in case, no change.
• Am getting proper bias voltage through the DTC to PCM (2.4-2.5 volts)
• Pulled, cleaned, and reinstalled NSS. No change, though do still have wierd backup light issue, and No Bus if TCM is reconnected.
• only codes listed are 1698 (no tcm communication, because it is disconnected), and P1800, which I find several different explanations of, but mostly related to TCM issues as well. I cannot connect to PCM if the TCM is plugged in.
• PCM is new, was replaced becuase of previous error indicating bad memory block. Behavior is the same when I swap the old ECM in.
• No apparent problems with wiring, though I haven't completely stripped the harness apart, obviously hoping not to.

So, here is where I am. I have narrowed it down to no spark. Acts as if the ASD circuit is engaging, and shutting down spark, but everything seems to check out, and it should work. That usually points to the ECM not receiving a timing signal from the CKPs to fire, but it seems like it is.

At this point, I'm about ready to take a gas can and match to it.
Is there another means of verifying that the PCM is actually receiving a signal from the CKPs? Not having the TCM connected should not affect any of this, correct?

The only other thing that I haven't mentioned is the RKE (keyless entry module) is currently disconnected. I did try to plug it back in earlier, with no change in behavior. That also should not affect this, correct?

Any thoughts would be appreciated.

mntnresq

Well, the plot thickens.

Tested most of of the sensor circuits from the PCM connectors to the individual sensor connectors, as well as the ASD relay, all checked out good. Didn't get to the O2's yet.

Voltage from the batt to the starter and pdc are also good, not more than a couple tenths of a volt difference.

PCM grounds are good.

As far as I can tell, this thing should be working. But it doesn't.

What I'm not 100% sure on is if the TCM and RKE being disconnected will activate the ASD circuit to disable spark. From what I can find so far, that answer should be no.

I haven't been able yet to chase or check the wiring between the TCM and the trans, or wherever it goes, so unsure what the problem with that is.

Nobody has any better ideas? Getting closer to getting the torch out...

fb97xj1

You can drive with the TCM and RKE disconnected, but you will have to shift manually without the TCM. Thats actually one way to rule out mechanical or electrical issues with the transmission during a roadtest, by disconnecting the TCM. The PCM couldnt care less about the RKE.