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 My Vr Over Fuelling - Whats going on?  

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J-train
  • J-train
  • Regular User
  • Member No.: 44,868
  • Joined: 4-April 06
  • Posts: 1,405
  • From: North Ipswich
Post #1 post 22nd April 2010 - 02:56 PM
I have a 3.8L buick motor in my VR that I bought for my brother and as of late it is running rough as guts. It has been sitting for a while but I have been turning it over fortnightly.
The motor starts fine but sits there hunting and trying to find an idle and eventually dies.
The exhaust seems to smell very much like unburned fuel and it has backfired (possibly running very rich)

The tank is clean and the fuel pump is giving good pressure, the coils are all throwing a decent spark.
My brother wants to drive his car but it is undrivable at the moment, please help.

--------------------
Too many past rides and not enough current ones.
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tj1097
Post #2

your spark plugs could be corroded up, i would replace them first as they are reasonably cheap

J-train
Post #3

Forgot to mention that I have replaced the spark plugs.

tj1097
Post #4

have you checked the leads are they damaged and earthing out, I had that problem with the stock leads

J-train
Post #5

I have newish 8mm talon leads but number three wasn't throwing as good of a spark as the others so I replacd the coilpack with a new one.

tj1097
Post #6

how's the throttle body and air filter?

J-train
Post #7

Air filter is clean, haven't checked the throttle body but that couldn't be causing it.

iamhappy46
Post #8

I would hazard a guess that one of the injectors is damaged and flowing excess fuel into the engine on one cylinder. I would also strongly suggest replacing the exhaust O2 sensor as well

eurekamad94
Post #9

try doing a self diagnosis on your car, here's a guide with all the codes

http://forums.justcommodores.com.au/holden...vs-revised.html

try the oxygen sensor and MAP sensor at first, if the doesnt work then get you injectors leak tested

Chris!!
Post #10

as above, O2 sensor

also start it up, let it run for a minute or 2 then turn it off and pull the plugs out, 1 or 2 might be covered in fuel so get those injectors done... also fuel pressure reg could be buggered

Claytond
Post #11

if u increas the gap of ur spark plug it will help with how rich u run just dont go over bored 1 or 2 degress larger and it will help heps

49AZM
Post #12

iac motor in the throttle body?

VZ_commo
Post #13

map sensor maybe

iamhappy46
Post #14

QUOTE (Claytond @ Apr 24 2010, 09:20 AM) *
if u increas the gap of ur spark plug it will help with how rich u run just dont go over bored 1 or 2 degress larger and it will help heps


LOL. Please dont take this advice. Opening the spark gap on an engine that is running rich cause misfires = no spark at all = MORE unburnt fuel in the exhaust.

They also measure it millimetres not degrees of gap wink.gif

Claytond
Post #15

if u increas it buy 1 mm it will fix the problem ask a mechanic oh hang on how bout u ask me im a fuking mechanic

iamhappy46
Post #16

QUOTE (Claytond @ Apr 24 2010, 03:00 PM) *
if u increas it buy 1 mm it will fix the problem ask a mechanic oh hang on how bout u ask me im a fuking mechanic


FUCK... GOD HELP US.

How many years more experience do you have over me? wink.gif Based on your past threads, I would say negative 15 years.

Increasing spark plug gap(not degrees) requires the spark plug to increase its time in the capacitive phase(building up charge before it can arc over the gap) which means that there is MORE compression occuring in the cylinder and is more likely to miss. Actually, if an engine is running rich and the engine is not missing then there is excess fuel in the combustion chamber which 'cools' the mixture further so widening the gap actually makes it less likely to fire. REDUCING the spark plug gap makes it easier to arc over in the capacitive phase(resulting in a longer inductive phase) which is more likely to burn all fuel. However, since a qualified mechanic would look at the problem and DIAGNOSE that either the O2 sensor is out of range or a fuel injector is supplying excess fuel(possibly MAP sensor but unlikely as Closed loop would bring the mixture back within stoich mixtures) is the likely culprit, then you fix the problem and not apply a bandaid solution of playing with spark plug gaps.

If this is based off your expreience from your 175Kw Commodore... maybe you should look at my 481rwKw VY SS ute I built and see where a real commodore makes power smile.gif

Please improve your diagnostics skills before you attempt becoming a member of the Technical Members group wink.gif

TwinCam16
Post #17

QUOTE (Claytond @ Apr 24 2010, 03:00 PM) *
if u increas it buy 1 mm it will fix the problem ask a mechanic oh hang on how bout u ask me im a fuking mechanic


At the risk of backing up iamhappyrootingsheep46, he is right.

I mean, how can you claim to know your shit when you post


This...
https://www.boostcruising.com/forums/index....;pid=1285710860

... this....
https://www.boostcruising.com/forums/index....;pid=1285710730

... and THIS?!
https://www.boostcruising.com/forums/index....;pid=1285710479
iamhappy46
Post #18

QUOTE (Claytond @ Apr 21 2010, 02:58 PM) *
But wouldnt that be less seeing as thou the car is powering 2 wheels instead of 1????


^^ My personal favourite

TwinCam16
Post #19

Please though, let us know which workshop employs you, for the sake of every poor bugger out there.

We would hate to see someone have to have an injector cleaned cause the power steering is a little stiff.

J-train
Post #20

So back to the original question, even though I am enjoying the wise cracks, I am guessing it is more likely to be an oxygen sensor rather than the Map sensor. If so I am going to get a new O2 sensor and plugs and see what happens.

TwinCam16
Post #21

On topic - there is a few things you need to check.
Plugs is the numebr one.

Having a sticky injector, believe it or not can cause it to act like you are talking about.

Id look at this before you go replacing map sensors, or sensors etc.

You can unplug the o2 and it will not cause it to miss.

J-train
Post #22

I have a new set of plugs so I will chuck them in tomorrow and see whats going on. Normally I think I am alright at medial mechanics but this one has got me stumped.

TwinCam16
Post #23

The more i read it the more it sounds strange.

Plugs would "generally" give you a miss right from start up.

The ACC motor may be up the duff (idle control)

They do stiffen up and are a very common part (last time i repalced on it was 70 bucks from memory on an 13 pulsar, which is the same as the dunnydore)

If it was me?

Check for vac leaks, first, that's a given, being that its, free.

Change the plugs.

pull out the acc motor and clean it.

Get the injectors cleaned.


There is much more apart from that, unless you start looking at sticking valves / head gasket issues.

iamhappy46
Post #24

Remove spark plugs
Disconnect CAS plug
Turn over engine and find the cylinder spraying wet fuel out of the spark plug hole. This cylinder has a damaged injector(dirt in fuel system has caused a pintle to be jammed open etc)

Since disconnecting the CAS + removing plugs means that no injection pulse is given to the injectors and no coils are fired the free flowing injector will be easily indentified.

If this is not the case, disconnect O2 sensor and if idle becomes worse, then its the Map sensor. If idle improves, its the O2 sensor

J-train
Post #25

Thats exactly what I need thanks mate.

low96
Post #26

check your fuel pressure reg.it controls how much fuel goes in the motor

TwinCam16
Post #27

Actually it doesn't

It controls how much fuel is taken away from the motor.

49AZM
Post #28

from expeirience i would bet on acc if you want to check the map just disconect the vac line and see if it changes

MaccaColt
Post #29

We had a VS commodore once

Kept stalling at idle and stuff

Turns out the return line to the fuel tank from the fuel pressure regulator was blocked causing high pressure in the fuel rails obviously.

I would also check that shouldn't be too hard, remove return line add another piece of hose and blow down it with the fuel cap off.

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