VS V6 Ecotec Starts for 5 seconds then stalls

[The Big O]

Pulled up in my VS V6 Ecotec (Nov 98 Series 3 Ute) and was idling fine then in a split second started running very rough and could not get off idle. Now it will start no problems everytime and run for 5 seconds and then start running rough and coughing and stall.
If i put aerostart up the aircleaner it will start and run fine and rev and no missing but as soon as i drop the aerostart it start running rough again and stalls.
So far i have done the below.

1. Replace Fuel Filter
2. Clean MAF sensor
3. Clean IAC valve and try another IAC valve
4. Try another MAF sensor and Air intake sensor
5. Block the brake booster hose
6. Check for Vacuum leaks
7. On key turned to on i can hear the fuel pump prime
8. Swapped fuel pump relays and check fuses
9. Bridge the fuel pump relay and pump runs fine
10. Do a diagnostic and only get code 12 so no errors

Feels like fuel or air but any suggestions and testing?

 

[Lex]

Feels like fuel

Bad fuel?
When was the last time you refuelled?

 

[The Big O]

Bad fuel?
When was the last time you refuelled?

Yeah have been thinking that also. Any suggestions on adding something to the fuel or draining the tank?

If i had to drain it as there is no drain plug do i drop the fuel filter line into a drain pan and bridge the fuel pump relay and try and pump it out?

 

[Lex]

Yeah have been thinking that also. Any suggestions on adding something to the fuel or draining the tank?

If i had to drain it as there is no drain plug do i drop the fuel filter line into a drain pan and bridge the fuel pump relay and try and pump it out?

Methylated spirits? Will displace any water. Amount, not sure, half a cup?
Another member may have a better suggestion?

 

[_R_J_K_]

Metho you'd out like a litre bottle or two in.

I'd start looking at ignition though, starting with pulling plugs and seeing if it's the same across all cylinders or one. I had a similar problem with a car I used to own and it turned out to be an issue with old leads.

 

[Trevor loves holden.]

Could be fuel rail pressure.
Injector pulse.

 

[The Big O]

OK just as an update to all i swapped the fuel pump and problem solved.

 

[Phillbert]

OK just as an update to all i swapped the fuel pump and problem solved.

Thanks for the reply with solution.
It makes it easier for the next person with same issue

 

[The Big O]

OK just as an update to all i swapped the fuel pump and problem solved.

I should also mention that prior to changing the fuel pump i did the below

1. Swapped fuel pump relay
2. Turn key to pre crank and the fuel pump could be heard priming for 2 seconds
3. Bridge relay terminals and make fuel pump continously
4. Each time it would start but start running rough within 5 seconds so clearly the pump was not maintaining pressure.

On a side note not easy to test without special tools and not the nicest job but as soon as it was swapped it started first time and ran faultless since.

 

[vs-lover]

I've only just seen this new thread and as I started reading my thoughts instantly went to fuel pressure which would correlate straight to the pump and have nothing to do with plugs or a general EFI electrics. The fact that it would run on SYB instantly says it's a fuel issue and the main component that fails in these cars is the high pressure in tank pump.

Anyway great to have an positive outcome as suggested above, thus it makes it much better for future reference to others.