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My v8 5.7 commodore wont idle. My v8 5.7 commodore wont

Customer Question
My v8 5.7 commodore...

My v8 5.7 commodore wont idle

Mechanic's Assistant: How many miles are on the car? What size is the engine?

My v8 5.7 commodore wont idle

Mechanic's Assistant: What year is your Commodore?

2004

Mechanic's Assistant: Are you fixing your Commodore yourself? What have you tried so far?

Yes i tried checking fuel pump relay and theres power there

Submitted: 2 months ago.Category: Australia Car
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Answered in 21 minutes by:
3/30/2018
AU Auto Mechanic: Matt, Engineer replied 2 months ago
Matt
Matt, Engineer
Category: Australia Car
Satisfied Customers: 23,193
Experience: Automotive Engineer for 20 years, BEng hons degree,
Verified

Hello and welcome to Just Answer

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion will make a leak worse) so leaks can be better or 1 vacuum leak path that you won't find with the above test is if the brake servo is leaking
so try clamping off servo hose to see if this has any effect

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth cleaning out the throttle body as these get clogged up with carbon and some brake cleaner washed through helps free things off.

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter or the connection to it is faulty

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading
Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

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AU Auto Mechanic: Matt, Engineer replied 2 months ago

My goal is to give you the best advice that I can and I hope that I've helped today. Please remember to rate my service by selecting from the 5 stars at the top of the screen before you leave. If you need more help, use the reply box to let me know.
If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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Customer reply replied 2 months ago
It only idles for about four seconds
AU Auto Mechanic: Matt, Engineer replied 2 months ago

hello

can you keep it running if you step on the accelerator?

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Customer reply replied 2 months ago
Hiya sorry for the wait
Nah it doesnt we can rev it abit but it will cut out pretty quick
AU Auto Mechanic: Matt, Engineer replied 2 months ago

Ok then I'd next check fuel pressure, as even though you have 12v at the relay its possible the filter is clogged or the pump is faulty

as this is sounding like not enough fuel pressure

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AU Auto Mechanic: Matt, Engineer replied 2 months ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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