Vx - Does knock detection cause spark misfire?

Holden/Delco Tuning. ALDL, OBD 1.5. Circa 1989 to 2004.
Charlescrown
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Re: Vx - Does knock detection cause spark misfire?

Post by Charlescrown »

From what I know a missfire actually shows as a lean mixture sending the o2 sensor low. I have seen a DFI module cause a single cylinder missfire which is not a common occurence. -30 is a big number in the fuel trims. Have you checked the fuel pressure and also the vacuum hose going to the pressure regulator. It may have high fuel pressure or a hole in the regulators diaphragm.
yoda69
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Re: Vx - Does knock detection cause spark misfire?

Post by yoda69 »

I’ve seen a leaking diaphragm on the fuel regulator do this. Excessively rich at idle as fuel was being sucked in the vacuum hose into the engine. Try pulling the hose off and check for any fuel in the hose or leaking out of the regulator.
JohnDee68
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Re: Vx - Does knock detection cause spark misfire?

Post by JohnDee68 »

Thanks guys for taking the time to work with me on this issue. I do appreciate all the help. I am also determined to resolve and find the actual cause of it all. If not just for me, but for others who also love their commodore.

I am hoping tomorrow doesn't rain so I can get to spend some time on the car issue. I will try to check the fuel pressure regulator is ok with the limited tools I have access to here.

I ordered a new set of coil packs and plugs last night. Not sure if we are allowed to say where I have ordered them from, but they aren't from a "china" shop online. (I hope they will arrive from Victoria before next weekend, but I wont hold my breath yet as they'll be coming via AusPost. They may fix the issues, if I am lucky enough.

I realised there is also small rubber seals on the DFI modules which seal the coil pack connectors from weather. Knowing my luck with stranger than common types of failings with most things. I was wondering if these may be deteriorated or soiled in a way to actually cause some electrical leakage (at times) resulting in spark failings. I saw that some of the more expensive coil packs in the USA, come with replacement seals for the coil packs. I would presume the ones i have ordered wont have the seals.

I know a while ago (2017) I couldn't actually get the pressure regulator apart, as I was hoping to service it when I rebuilt the motor in 2017. I will try again tomorrow if weather and tools permits.

I went back over my cars running history. Some of you might recall me trying to resolve the fuel consumption issues since I have had this engine in the car. Anyway, I think a lot of that could have been early signs as to the major issue now. I can only hope, that if we can fix this issue, my economy might also go back to what I would expect. :)

It would also save me doing a Trans swap if this also fixes the vibrations which I thought are trans or Torque at this point.

Thanks,
John.
Charlescrown
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Re: Vx - Does knock detection cause spark misfire?

Post by Charlescrown »

You must have an aftermarket fuel regulator if you can pull it apart. It's easy to check if theres a hole in the diaphragm. Just disconnect the vacuum hose and see if theres any sign of petrol int there. If you game connect a rubber hose to the regulator vacuum fitting and start it up. If you see fuel coming out it's got a hole in it.
immortality
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Re: Vx - Does knock detection cause spark misfire?

Post by immortality »

Charlescrown wrote:You must have an aftermarket fuel regulator if you can pull it apart. It's easy to check if theres a hole in the diaphragm. Just disconnect the vacuum hose and see if theres any sign of petrol int there. If you game connect a rubber hose to the regulator vacuum fitting and start it up. If you see fuel coming out it's got a hole in it.
VT - VY V6 have a slightly different design (to VS V6) where the regulator comes out of the pressed steel body which is attached to the pressed steel fuel rails.
Charlescrown
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Re: Vx - Does knock detection cause spark misfire?

Post by Charlescrown »

Yea but you still can't pull it apart but only replace a couple of O rings and checking for a diaphragm leak would be the same as any regulator I would think.
JohnDee68
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Re: Vx - Does knock detection cause spark misfire?

Post by JohnDee68 »

I don't think there is any diaphram in the pressure regulator on the Vx. Its just a simple pressure release system much like a radiator cap (without the return). I did do a pressure test the other day and it is within specs (43psi) on both idle and hi throttle. 1-2psi variant.

I am about to look in to what the Dual Bank O2's setting actually does in the Tunerpro software. As I am wondering if it has anything to do with my issues other that coil packs, plugs and DFi module. (awaiting some of the parts to arrive still).

As the car really doesn't feel like it is misfiring (to me anyway). Though it is a very strong (almost throat burning ) smell coming out the exhaust.
Charlescrown
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Re: Vx - Does knock detection cause spark misfire?

Post by Charlescrown »

I'v never cut one open but going by the pics it will have a diaphragm inside it.
immortality
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Re: Vx - Does knock detection cause spark misfire?

Post by immortality »

Definitely diaphragm type FPR. See,
FPR General info V6 Engine.pdf
(74.69 KiB) Downloaded 65 times
This should help with removing the FPR from the fuel rail.
FPR Service Operations - V6 Engine - 6c13.pdf
(127.37 KiB) Downloaded 65 times
JohnDee68
Posts: 249
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cars: L36 Vx Series 2 8/2002 Acclaim Wagon 3.8L ECOTEC II.
Location: South Australia

Re: Vx - Does knock detection cause spark misfire?

Post by JohnDee68 »

Thanks guys.

I am going on your and others advice with the fuel pressure regulator potentially at the heart of my issue. It does seem to be an exact match to the symptoms i am experiencing.
large negative fuel trims, both ST and LT (in the -20's and even -30's), smelly (rich) exhaust, poor performance and poor fuel economy.
Something also to keep in mind as a helpful diagnosis though I am yet to check, but someone mentioned also that if fuel has been going in to the plenum chamber via the vacuum line, there will likely be a cleaner spot inside the plenum near the vacuum line input. I might check that tonight as well.

I am waiting on part to arrive before I am able to confirm it as a fix. I will keep you guys posted to the verdict. (Should be within the next 7 days).

Though I will check this evening for fuel evidence in the vacuum line. I have never been so happy to actually wanting to have fuel in a vacuum line. ( i have a boring life obviously :D )

Thanks again guys. I was really at a loss this time with this one.
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