04 CV8 crank/no start

[OversizeTigra]

Evening all. A bit of background: I changed my fuel lines then did 500 miles in a week with no issues. I only mention this because when I started it after replacing the lines, I didn't hear the fuel pump prime - but it fired right up so I didn't think much of it.

A week later I replaced a frayed driver's seatbelt. Disconnected the battery just in case, took the back seat and rear quarter trim off, didn't unplug or disturb any wiring, just undid the bolts and chucked the new belt in. Got back in and she cranked over but wouldn't fire.

Here's what I know so far. There is no spark, no fuel pump prime and no fuel pressure when cranking. The fuel pump relay works (I swapped it with an identical one) and the ignition/injection fuses get battery voltage with key on. I unplugged the pigtail under the fuel filter and confirmed no power being sent to it. I also powered up the fuel pump with a spare battery and it works. After that, there was fuel in the rail. In addition to the fuel pump relay click, there's a second click some way down the car, but not as far down as the pigtail, with key on.

To my mind this points to an ECM or wiring issue. Seems odd to suffer loss of spark and fuel right after changing a seatbelt but I can't see how they're connected? Surely even if I was really clumsy the worst I'd do is set an airbag code or muller a pre-tensioner?

I did have a look at engineering mode and it didn't show any fault codes. I don't have a scan tool and may have to call in someone who does, and knows what they're doing, and/or pay for access to GM's wiring diagrams and then try to understand them! But maybe the above sets alarm bells ringing with someone?

[vxr2010]

try your spare key , second option key in ignition push un lock on the fob then try starting it , if that’s no go i would re check wiring near where the seat belt was swapped over , i assume battery has enough charge and volts to run every thing ?

[mfp4073]

A wild guess, I'm wondering if you have somehow triggered the factory immobiliser? To have no spark at the plugs and no fuel pressure sounds to me to point in that direction.
It really is a guess, I'll have to have a think about this one. Hopefully someone with a bit more knowledge will shout up.

[stevieturbo]

First obvious thing to do...is get some communication with the ecu to see if it is alive and has power. No sense fking about with fuel pumps etc when it sounds like the ecu is not powered up.

[OversizeTigra]

Quality ideas, thanks chaps. Battery is new, the old one was clearly near the end of its life. Limited number of cranks and key-ons to check stuff just about toasted it. Does sound like it's time to establish comms and see if anyone's home.

[vxr2010]

i’m still thinking immobiliser issue as pump and spark not on , possibly around battery swap , or key fob is getting old , the above method can sometimes work re the immobiliser

[OversizeTigra]

So ignition on and then press the fob button? I only have one key but it is relatively new, the previous owner had it replaced at a dealer. The one bit of paperwork that came with the car! And it did lock and unlock the car after the problem started.

One thing I haven't done yet is check for 5 volts at a couple of sensor plugs. My theory is if the 5 volt reference is there, that tends to point towards an immobiliser issue because it means the ECM is at least powered up. Only just learned about that and am miles from the garage so I'm trying to make sure i go back there with a decent plan!

[vxr2010]

if the fob battery is going or the arm disarm not working well on the fob , key in the ignition then turn ignition on , push the unlock button and try starting it , the immobiliser has a red lock display come up on the dash , it will stay red and lit if the immobiliser is still on and therefore it won’t start

[vxr2010]

Did it work ? fingers crossed

[OversizeTigra]

Going back to it tomorrow. Found some wiring diagrams in the meantime so I can make the trip count and do more testing if need be.The way I read it, ignition on sends power to the interior fuse box and two terminals from that box send it to the PCM. The PCM then turns on the fuel pump relay and the ignition/injection fuses under the bonnet. Since I'm getting battery voltage at the underbonnet fuses and the relay works, it seems unlikely the PCM is toast. Times like this it would be handy if the garage was a bit closer to the house!

[OversizeTigra]

Well, I had hoped to be able to contribute something worthy to the collective, a diagnosis that would help others in the future. But it turns out my car has an aftermarket fuel pump isolator switch hidden away and I knocked it when changing the seat belt! Should have gone back to where I'd been working straight away but I was convinced it wouldn't be anything easy or obvious, I mean it never is, is it!

[Lincsls1]

That's good news! At least nothing was broken and there is no more cost to come.
Did you swap your belt for a new one or second hand? I believe these belts are known to have a weak recoil mechanisms, I have to help mine retract a little.

[OversizeTigra]

Second hand, off a 42k mile car. Mine was frayed, I shaved off the evidence for the MOT but felt bad so got it sorted!