Sudden Missfire VS V6

[JoshSvc]

Working on a VS V6 at the moment that has developed a sudden engine problem, initially it was missing under hard acceleration, then it had problems starting and would missfire badly, when it starts it idles fine but if u touch the pedal it will bog down, if u push through that it will rev.

Disconnecting the MAF did make it run better, but it wont even start now.

The fuel filter is fine i was thinking maybe fuel pump as i cant hear it priming, the spark plugs are new.

No logged codes

Any ideas?...

[soop]

Try another MAF?
Replace the spark plugs, leads and coils.

If that doesn't work check the cat is intact and change the o2 sensor.

[Brett_jjj]

Replace the sparkplugs and plug leads if they are old,and if theres still no difference,it might be 1 of the 3 ignition coils thats faulty.These coils will sometimes idle and run ok,but break down when the engine is put under load,which then causes it to misfire and splutter etc.If all the coils are a couple of years or more old, then its best to replace all 3 coils at the same time if 1 is found to be buggered.

[JoshSvc]

Spark plugs are brand new, i'll try and test the coils. Would the coils cause the car not to start though?

[soop]

Age, they just give up eventually.

[Brett_jjj]

The CAS (Crank Angle Sensor) will also cause a similar problem with misfiring and not starting,and its very common for it to stuff up too.

[soop]

Will generally cause an issue all the way through the range though. Not just under load.
My money is on coils.

[JoshSvc]

I'll try and borrow a coil tomorrow, are the coils the same as VR?

[Brett_jjj]

Yeah,you would think it should still attempt to start though,unless more than one coil has gone at the same time, or the DFI module under the coils is stuffed.Id try some other coils, and then if theres no difference,then look at the CAS,also a faulty CAS will sometimes not log an error code either,so it can be hard to track it down if its causing problems.Most people just replace the CAS anyway if they are having problems of this nature and cant find the cause..

[JoshSvc]

Ok i swapped the coils around and the car started instantly, but still with a big miss, it has started to give an oily smell and some slight smoke is coming from the back of the inlet manifold, so i'm tipping that the inlet manifold gasket has shat itself, letting water into the fuel system causing the problems

[soop]

Good diagnosis.
Whip it off and replace it.

[JoshSvc]

Fingers Crossed.......

[soop]

Bah, she be right.

[JoshSvc]

ok it wasnt the inlet manifold gasket, its not the Maf either, i eliminated that today. No logged codes... i'm abit lost. Next step maybe fuel regulator? Is there a way to test them or clean them?

[justbad4you]

try leads champ>i had the same prob in my old vs v6 ute(was a doddgy lead) more than likely it will be the shortest or the longest lead that goes 1st( it did in my case it was the smallest 1)

ok it wasnt the inlet manifold gasket, its not the Maf either, i eliminated that today. No logged codes... i'm abit lost. Next step maybe fuel regulator? Is there a way to test them or clean them?

[JoshSvc]

ok i have read that the fuel pump should flow 1.25 litres in 30 seconds, i'm not if that is while cranking or while running. Ours is flowing roughly 750ml in 30 seconds while cranking.

Can anyone confirm the flow rate?

[bpefi]

ok i have read that the fuel pump should flow 1.25 litres in 30 seconds, i'm not if that is while cranking or while running. Ours is flowing roughly 750ml in 30 seconds while cranking.

Can anyone confirm the flow rate?

If thats what it says it would be about right - with key on - though I wouldnt have thought it would cause a miss - pull each injecter connecter off & see if you can find which cylinder it is & check the plug or lead & do a compression test.

[JoshSvc]

The injectors are fine, they have been tested, cleaned and new o rings fitted

[FstStig]

Tps? Iacv?

[JoshSvc]

iacv is working fine, throttle sensor is lubbed up and rotating fine with spring pressure

[bpefi]

The injectors are fine, they have been tested, cleaned and new o rings fitted

I understand that the injectors may be ok - what you need to do is find out which cylinder is missfireing & then you can go from there - pulling injector leads is infinately safer than pulling ignition leads off to find a missing cylinder & sometimes the injector lead can be only partially on causing a miss in itself

[JoshSvc]

I have pulled the leads off and the injector leads as well and all cylinders give an equal miss. I tested what voltage is going through the fuel pump fuse, 11.9 with ignition off and 10.6-10.9 with ignition on, and 14.2v with the car running.

[Brett_jjj]

Id be taking another look at the coils,try to get a "known" working set of coils to try on your car.Id also try another DFI module,its the electronic module that the 3 coils sit on.Theres a wiring connector on the side of it,theres a small bolt that has to be unscrewed before this wiring connector can be unplugged.The contacts in this connector can also get corroded and cause problems so Id check them whilst its unplugged too.

[JoshSvc]

Done all that with a known working set of leads, coils, and the dfi module and the contacts in the connector are clean, i'm trying to find a fuel pressure tester to borrow but not having any luck!

[FstStig]

If its not your Fuel pump, Check your Cam Angle sensor. I have one here if you need to test it with a working one.