VT V6 Starts every few hours then no spark

[2O4TS]

Mixed feelings about posting this as my expectation of anyone having had the same issue is extremely low. I have found some slightly similar issues but none identical in hours of scouring forums.

VT V6. Has been throwing a CEL. Has been occasionally missing but often runs perfectly fine. Bridging pins 5 & 6 doesn't work on my vehicle. Was intending to take the car to my local auto sparky to diagnose with Tech2 on Wednesday when on Tuesday the car decided it didn't want to go to the sparky and started digging it's heels.

Basically, I left home, drove about 500 metres. It bogged and stalled at 60km/h. I rolled in to the next side street.

It wouldn't start. Sent a text saying I'd broken down. Had to wait. So after a few minutes, I couldn't help but try it again. It started and promptly stalled. Again, it would not start. Cranks great but won't fire. So again I sat and waited. Ten minutes later I tried again. It cranked, started, ran for about 5 seconds and stalled. I tried to start it again, it cranked fine but it wouldn't fire again.

Hmmm... first thing that came to mind was something immobiliser related. I removed the key, locked the car, waited 30 seconds and reversed that procedure and it started, ran for about 5 seconds, started to falter and stalled again. Would not fire immediately but went through the key out, lock. wait, unlock, try to start again and again it started. I fluttered the throttle, it revved and died down and revved and died down (between about 1800 and 1200 rpm) and stalled again.

I repeated the process a 3rd time and it started again. This time I revved the crap out of it. 3000 RPM and bursts of higher revs, all the while ensuring it stayed over 3000 RPM. Slammed it into drive and limped the 500 odd metres back home, left foot on the brake, right foot on the accelerator to keep it running, dodging traffic as much as I possibly could to avoid completely stopping.

As I turned the final corner with about 50 metres to go it started to 'feel' different. I pulled up in the drive and it idled as smooth as silk. I noticed it had just reached operating temperature. That very second as I looked at the temp gauge, on came the CEL.

I switched it off and attempted to start it again and it started and idled perfectly. I did still have to go out though and my car would have sat for a few hours and gotten cold again so I borrowed a car for the evening rather than risking it not starting, miles from home.

Hoping to go to the auto sparky Wednesday morning I jumped in the car, went through the previous nights' start routine and it cranked fine but wouldn't start again. I left it a few hours and the next time it started but quickly stalled again. I tried again about an hour after that to no avail at all. I had to leave it.

Twice today, after leaving it at least 3 hours in between it starts but immediately stalls. My neighbours will freak if I'm out revving my car at 3000 RPM so I've avoided that but it seems from what I can determine so far, that it will start (spark) if left several hours when cold but has spark and therefore no issue starting anytime when warm.

So I have determined it has no spark when attempting a second or subsequent start when cold. I have replaced the BCM and ECU (& key fob obviously) with known working replacements from another vehicle of mine. I have swapped the DFI and coils. I replaced the CAS as a service item before it caused issues about 2 years ago now and furthermore it is doing exactly the opposite to CASs I've replaced on other cars where the issue arises when the car is hot. I have checked the contact ring on the ignition switch and checked for continuity from the contact ring to the loom and it is fine. The immobiliser light goes off when unlocking the vehicle remotely with the key fob and/or making contact between the key and contact ring.

All fuses are fine (but I don't even know why I bothered because a blown fuse isn't repairing itself when the engine is warm and blowing again when it's cold) and I have swapped the ignition relay for another known, working relay. I cannot see any wiring issues. Everything looks good. Nothing loose. Nothing broken. I've had the vehicle nearly 18 years and it's been regularly serviced and maintained. Until now it's been incredibly reliable considering its' age and mileage.

I'm out of ideas.

*Reminder: when it won't start it has no spark. It seems it sparks for one cranking cycle when cold then not again until left for several hours.

Furthermore the fuel pump is working fine and the filter was replaced (and the old filter was flowing fine) about 10,000km ago. Even if it had no fuel pump as far as I'm aware it should still spark when cranking.

If it was a no spark when hot issue I would've already replaced the CAS.

Anybody?? Anyone ever seen a CAS that faulted badly when cold but worked fine when hot? Know of any similar issues of no spark when cold but all good when warm? I don't really want to continue blindly replacing sensors etc without some logical explanation as to what might cause the issues I'm having.

 

[devilly]

sounds like a blocked fuel filter to me. change it over and see how it goes cheapest idea and a 5 min job if you have the special tool to remove it.

 

[lout]

wont be fuel filter as op has confirmed no spark
what happens when you bridge pin 5 and 6?????
do you have serv error on dash or x if triple window dash
when you first start engine, the ecu sends a signal to the dfi to lock the timing
when it starts it then uses crank angle to synchronise the timing
i would think you have a faulty crank angle sensor

 

[SavVYute]

10% chance its a dud CAS.

90% its the wiring loom connection where it bolts to the bottom of the DFI.
If someone's ever wiggled it a bit when disconnecting that's where the problem will be.
Tighten those connections with a fine pick or probe.... even if you reckon they look tight.

 

[lout]

actually had a bit of time last night to think
as a crank angle is normally better cold than hot i have changed my bet to the efi relay under the hood
the bit about keeping the revs up to get home throws me as that sounds more fuel/vacuum related
as for your fuse idea i had a job about 20 years ago that nobody could diagnose, luckily the sun was shining on the fuse panel, old holden from memory with the glass cylinder fuses, the fuse had cracked and was acting like a thermal switch
we really need fault code or what happens at 5 and 6

 

[2O4TS]

actually had a bit of time last night to think
as a crank angle is normally better cold than hot i have changed my bet to the efi relay under the hood
the bit about keeping the revs up to get home throws me as that sounds more fuel/vacuum related
as for your fuse idea i had a job about 20 years ago that nobody could diagnose, luckily the sun was shining on the fuse panel, old holden from memory with the glass cylinder fuses, the fuse had cracked and was acting like a thermal switch
we really need fault code or what happens at 5 and 6

Cheers Lout. I value your input.

This one has me stuffed. Unfortunately having swapped the BCM and ECU I no longer have any fault codes. If only I could start it & drive it until the CEL lit up. Bridging pins 5 & 6 has not worked on my car ever AFAIK. That was the reason I was going to go to the local auto sparky, just for the Tech2 fault diagnosis. An ALDL cable is on my shopping list too so I can do the diagnosis myself in future but building an engine at the moment (for which I will need the cable and software) so it's down the list under "have new valve seats ground" and "pay rego".

I agree re the fuel/vac. That was one idea I had floating initially but then got home and of course checking for spark is the quickest & easiest thing to do when it comes to fault finding so as soon as I discovered no spark, fuel became very much secondary. But then of course you would think that issue would stay consistent and by the time I pulled up home it was idling smoothly and quietly. Regardless of whether or not there is a fuel issue (doubts). I did check relays but not sure about the EFI relay. Would that cause a no spark issue?

I have a lot on my plate at the moment besides this. The timing of this issue could've been better. I think I'll have to look into the wiring diagram and check that DFI module loom and see if there's a signal there. It's just that every time I get an idea..."Hmmm, what about...", I find myself instantly thinking of a logical reason for it not to be it. The intermittency only makes it worse. The crank sensor as you mentioned, normally a hot issue and sure, it could fail way prematurely but again, it's barely 20,000k old. I picked up a brand newy someone had bought thinking that was their issue and replaced my still perfectly working unit BEFORE it could become an issue. They're not expensive and it's a simple job so rather than break down, I just do preventative maintenance. Never actually had it break down either prior to this. What about the cam sensor? I have a known working unit I have to locate but if that failed, are you aware if that would cause a no spark issue? Logically I can understand why the ECU might like to know the cam timing before generating a spark.

I'll spend a few more hours on it when I can but if I have no luck it'll get towed to the sparky (a guy I've dealt with for years) and we'll put our heads together and see what we can sort out. I'll post back when I have more to report. Will be a few days I expect.

Currently my greatest fear is that it turns out to be something that I should've sussed myself and I successfully make myself look like a total numpty.

Just as an aside for anyone reading, the fuel filter is pretty new. I only replaced the original recently. When I removed the original at around 300k it still flowed like new. It regularly gets a tank of BP premium through it for maintenance purposes. No idea if that helped but either way, massively doubt there's a fuel flow issue. Pressure maybe, sure. But until I can get a spark any possible fuel issues are secondary.

 

[2O4TS]

10% chance its a dud CAS.

90% its the wiring loom connection where it bolts to the bottom of the DFI.
If someone's ever wiggled it a bit when disconnecting that's where the problem will be.
Tighten those connections with a fine pick or probe.... even if you reckon they look tight.

I'll do this after I determine I have a signal at at the DFI plug. Can't hurt.

 

[delcowizzid]

You should get spark even without an ecu plugged in it's hard wired on ignition dfi module or cas or power to dfi module

 

[2O4TS]

OK, well yesterday (Saturday) I couldn't start it at all. I had to get stuff from my car on several occasions which meant unlocking it. On a couple of occasions I forgot to lock it which all in all meant that it didn't sit locked for several hours at a time and I had no luck starting it and it had no spark when I tried it on the 3 or 4 occasions I attempted to start it.

Today, after having been locked overnight I have just gone outside, turned the key and within two cranks, vrooom, away she goes. Running just as poorly as back on Tuesday (before it reached operating temperature mind you). So I try to warm it up. I hold it at 3000 RPM. Every few seconds it dies off. To explain, it's as if I turn the key off and back on again while holding the revs. That's the 'missing' etc I explained earlier. So it drops from say 3000 RPM to 2600 then almost instantly goes back to 3000 over the course of a second or less and does this randomly. And I mean it cuts instantly. I had to flutter the throttle to keep it running at times, pushing the revs right up to 4500+. It'll run 'fine' for a few seconds then ignition cuts for a fraction of a second or so. After managing to keep it running for about 20 seconds it died off for too long, the revs got down below 1200 and I couldn't keep it running any longer. It stalled. It will not start again and again now has zero spark.

So if I unlock it, it has (random?, as it does seem to cut out) spark for a while then stalls and has no spark. If that pattern continues I expect that again, in about 4 or 5 hours from now I'll be able to unlock it, hit the key and it will start again, albeit with the ignition cutting until operating temperature is able to be reached. This is exactly why I first thought BCM/immobiliser. Lock it a few hours and it'll start. Leave it unlocked, it won't. So I swapped them for spares I had which I know were working fine as I drove the car and stripped it myself. Yet the issue remains unchanged. It is this repeatable pattern of having spark when left locked for several hours then subsequently no spark that makes me think that, as much as I appreciate the genuine efforts to help some people have offered, they just aren't logical. E.G. if it was the DFI connection, either the plug or socket, why is the issue so repeatedly not there when the car has been locked several hours, but is there if the car is left unlocked? It just doesn't add up.

Anyway this is all just food for thought. Out of curiosity I'll have another crack at starting it and keeping it running later today.

 

[2O4TS]

You should get spark even without an ecu plugged in it's hard wired on ignition dfi module or cas or power to dfi module

Cheers mate. Valuable information. You're on pcmhacking hey?

Any ideas? Even if it's just where you might suggest I fault trace based on the information I've provided. Just bear in mind, I'm no electronics wizz myself. With this stuff it's a 'learn as issues arise' thing for me.