vx v6 cranks but not starting up

[kirraweeae]

battery changed while charging other battery,still the same. Was told first motor has low compression on three cylinders (should still run badly with low compression). Was told to change engine by local holden dealer. Checked fuel lines they are correct, half a tank showing on gauge. tried another fuel source as well (another fuel pump in drum with fresh fuel), dropped off exhaust incase of blocked exhaust system. All sensors and plugs look like they are on correctly.

 

[kirraweeae]

Its not starter / battery / Key because it cranks over.

I would throw a fuel ressure gauge in line with injector rail and see what sort of fuel pressure you have at the injectors. It's unlikely to be the cause, but it will confirm that fuel is ok. Another way to check is to drop the air hoses off tothe throttle body, open the throttle wide and spray aerostart into the plenum while they try and start. if it fires at all, even poorly, you have a fuel problem. Look at lines, injectors, injector trigger connections and the like.

You probably need to make sure your TPS and CAS are hooked up and look okay.

The most likely culprit is Spark. Pull a plug out, Clamp it to some hard area well away from the plughole, insulate it from earth, then have someone try and start it. Use a long screwdriver or something with an insulated handle to bridge between a known good earth - like a strut tower bolt, and the spark plugs outer electrode. Look for strong spark. If it's hard to see, or non existent, you have problems.

If thats the case, look at your coil packs, connections from coil pack to eart and positive and the like. Remove the coils and check the undersides for split cases.

Can only be one of three things, and one of those is a no brainer.

Fuel, air, spark.

have replace DFI module , coil packs, leads and plugs. no fault codes present. can put fault codes in by disconnecting tps and other sensors

 

[Not_An_Abba_Fan]

If the other engine was doing it then it has to be something on the car.

How is the actual ignition switch? Pull it off the back of the barrel and spray it with contact cleaner.

 

[Tsunamix]

Got to look at things a little more closely. Another fuel source is all well and good but all you have removed fromthe equation is the tank. Could still be fuel lines, rails, poor fuel pressure, frozen injectors, injectors not being triggered, or injectors beingtriggered at the wrng time.

Fuel pressure gauge rules out lines, pressure and rails. Frozen injectors on all 6 is highly unlikely, unless it gott a belly full of filth and every injector is crammed full of crap. Check that each injector has its electrical connection intact to the harness. Check that the harness is connected to the PCM and ECM. If the harness is busted it would be VERY hard to find so cross your fingers that it's something else. If the PCM is functioning - and it would be reporting alarms all over the place if it wasn't, your injectors will probably trigger. It would be pretty hard to make them trigger at the wrong time but it is possible. Again if the PCM and ECM have worked in the past, and remain unchanged, its agood bet that they are ok.

 

[Tsunamix]

I had rulled out the key / key barrel as it cranks over. Am I missing something there ?

 

[neet_wagon]

It has to be spark then if it is 100% definatly getting fuel, like Tsunamix said - try the aerostart. If that doesn't work than you know its not fuel causing the issue.

Did you hook up the DFI and coils properly when you changed them?

 

[Not_An_Abba_Fan]

If the ignition switch wasn't getting a full contact it will crank but one out of the four contacts required to start may not be contacting.

 

[Tsunamix]

Aah thanks abba. Definitley worth looking at.

 

[kirraweeae]

Aah thanks abba. Definitley worth looking at.

tried start you barstard, no different. will look at ignition switch.
fuel pressure is about 260 kpa, with other fuel supply was 330 kpa.
fuel flow from inlet 750 mls after 15 second cranking
fuel flow return about 1 litre after 1 minute cranking.

 

[Tsunamix]

Time to look at the electrics then.

Youve ruled out DFI/ECM, Leads, coils, plugs.

Hmm check earth strap to engine block ? The starter could be piking up negative through the harness. Actually it would throw an undervolt alarm if this was the case, so it's not likeley.

That leaves just DFI harness and contacts, ECM/PCM harness and connections (all of which would throw fault codes). All thats left is your ignition circuitry and the Key barrel.

$10 bucks says Abba is right.