Ok, so I should say that I'm not saying this will be the issue but it only takes a few minutes to check and rule out the possibility. Crawl under your truck and look for the wiring harness that runs down the front of the engine. It should curve under and head back along the side of your oil pan. It is between your oil filter and the oil pan. Sometimes that harness rubs clean through the harness on that edge of the block and shorts out. Mine did that and never tripped a check engine light. I hit a bump and my truck shut off. It took 2 tries and it fired back up but immediately after getting to work I hit a dip in the parking lot and it died again. From what I understand those wires go to the knock sensor and the crank sensor.

I rigged mine up by wrapping it with thick rubber until I can replace that chunk of wires.

Hopefully that is your issue and it's something simple.

Now that I think about it I haven't had any issues with it doing the long crank since I did that.

 

Thanks, will check that for sure!
At the moment I'm measuring around and found out that the voltage at the injector connector is quite low.
Ignition on, connector disconnected from injector #1, shouldn't I measure 12V there?!

 

Yes, it should.

 

Got only 3,5 volts there engine off. Same on the ASD relais output. Input ist 12V though. With engine running it reads 14.5 volts.
Also ASD sense pin on the PCM reads 0,3 Volts only when engine is off. Reads 14.3 when running though.
Looks like it is touching ground or something?
Very odd.
Will have to do more checks I think.
I measured injector #1 and 2, also ignition coil #1. All same low voltage with connector off.

 

I still don't understand what is going on there.
I suspect the wiring of the aftermarket LPG system hasn't been done correctly.
I am thinking of replacing the wiring for the power supply of the coil packs and injectors.
I checked all the wiring diagrams and from what I can see that the ASD relay is really just powering the coil packs and injectors.
Is that correct?
I'm really hoping that I can get rid of the problems with that.
Really don't know what else to test or do...

 

Yep, that's pretty much it.

You just have one cylinder that misfires on gasoline though, right?

 

Well, I really don't know. When it comes up, then it is either P0300 or P0307 though.
I already re-wired #7, but only the ground/signal wire that goes to the engine controller/ECU. So maybe you think I should try and wire just #7 new?
Maybe I will try that first, yeah.

 

P0300 is random cylinder misfire... 307 is cylinder specific though.

How old/what brand are your O2 sensors?? What spark plugs are in there?

 

Spark plugs are normal NGK copper ones, changed about 8000miles ago.
I haven't changed the O2 sensors yet so I assume these are the original ones.
But I can't see any relation to the P0307? Wouldn't then all cylinders on one bank give problems? I really suspect the wiring. Because the problems are intermittend, one day it is running fine, next day giving the problems again.
I also think it might be temperature related, but I'm not sure though.

 

The P0300 might be O2 sensor related.... easy test would be to disconnect them, see if it runs any better.