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Rough idle - Running lean? #4754849
05/12/18 07:39 AM
05/12/18 07:39 AM
Joined: Jan 2014
Posts: 460
Australia
Spetz Offline OP
Spetz  Offline OP
Joined: Jan 2014
Posts: 460
Australia
Hi everyone,

Is there a product in a spray can that you can inject into the intake of a car to check whether a rough idle is causing by a lean condition?

I am not sure if butane gas in a can would work?


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 155,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Rough idle - Running lean? [Re: Spetz] #4754865
05/12/18 07:52 AM
05/12/18 07:52 AM
Joined: Nov 2008
Posts: 12,761
NH
supton Offline
supton  Offline
Joined: Nov 2008
Posts: 12,761
NH
Always thought anything flammable would work. WD40 on up. Usually one fogs in an area to see if recovers--pointing to a vacuum leak. Don't see why butane wouldn't work.


2011 Toyota Camry, base, 2.5L/6MT, 170k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 144k, ours
1999 Toyota Camry LE, 2.2L/4AT, 195k, his
Re: Rough idle - Running lean? [Re: Spetz] #4754868
05/12/18 08:00 AM
05/12/18 08:00 AM
Joined: Dec 2017
Posts: 3,035
SE British Columbia, Canada
Snagglefoot Offline
Snagglefoot  Offline
Joined: Dec 2017
Posts: 3,035
SE British Columbia, Canada
Carb cleaner, but it will increase your revs and possibly mask the issue.


If you want the job done right......do it yourself.
Re: Rough idle - Running lean? [Re: Spetz] #4754871
05/12/18 08:02 AM
05/12/18 08:02 AM
Joined: Sep 2015
Posts: 1,598
USA
mk378 Offline
mk378  Offline
Joined: Sep 2015
Posts: 1,598
USA
Check the fuel trims. Do a cylinder drop test to see if it is one cylinder misfiring or generalized.

Re: Rough idle - Running lean? [Re: Spetz] #4754922
05/12/18 09:04 AM
05/12/18 09:04 AM
Joined: Nov 2006
Posts: 20,594
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 20,594
MA, Mittelfranken.de
I use a propane torch with hose among other things when looking for a vacuum leak, just turn the gas on and move it around the suspected area the idle will smooth out when you find one (not it isn't OSHA approved so do it outside). It does not work well with fans that run all the time.

Like this one.


ASE L1, Master. Deutsch Meisterbrief.
Re: Rough idle - Running lean? [Re: Spetz] #4754953
05/12/18 09:42 AM
05/12/18 09:42 AM
Joined: May 2018
Posts: 120
California
Dave1027 Offline
Dave1027  Offline
Joined: May 2018
Posts: 120
California
Google "smoke test". +1 to the fuel trims idea.

Re: Rough idle - Running lean? [Re: Dave1027] #4755045
05/12/18 11:42 AM
05/12/18 11:42 AM
Joined: Nov 2006
Posts: 20,594
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 20,594
MA, Mittelfranken.de
Smoke testing is all well and good if you have one but most DIY usually don't happen to have one handy. Checking trim while looking for the leak is helpful when looking for a leak.


ASE L1, Master. Deutsch Meisterbrief.
Re: Rough idle - Running lean? [Re: Spetz] #4755536
05/13/18 02:31 AM
05/13/18 02:31 AM
Joined: Jan 2014
Posts: 460
Australia
Spetz Offline OP
Spetz  Offline OP
Joined: Jan 2014
Posts: 460
Australia
Hi everyone,

Thanks for that.

I've had a smoke test done before and it showed no vacuum leaks.

I was thinking perhaps the AFM or something was faulty causing a rough idle.
The car idles worse with colder ambient temperatures.

The butane/propane test was purely to isolate or exclude any fueling issue.
At least in my mind that's what it'll show as if idle gets better I know it's a fueling issue and if it doesn't I know it's not - Would that be right?


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 155,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Rough idle - Running lean? [Re: Spetz] #4755554
05/13/18 04:10 AM
05/13/18 04:10 AM
Joined: Nov 2006
Posts: 20,594
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 20,594
MA, Mittelfranken.de
Originally Posted By: Spetz


The butane/propane test was purely to isolate or exclude any fueling issue.
At least in my mind that's what it'll show as if idle gets better I know it's a fueling issue and if it doesn't I know it's not - Would that be right?


Correct, it is only to isolate the leak. If the idle gets better you have a vacuum leak in that area.


ASE L1, Master. Deutsch Meisterbrief.
Re: Rough idle - Running lean? [Re: Spetz] #4755557
05/13/18 04:22 AM
05/13/18 04:22 AM
Joined: Jan 2014
Posts: 460
Australia
Spetz Offline OP
Spetz  Offline OP
Joined: Jan 2014
Posts: 460
Australia
Trav,
I was actually planning on feeding the butane gas directly into the intake just before the throttle body to isolate or exclude a lean running condition that may be causing rough idle.

Would my theory be sound?
My tests so far have shown no vacuum leak however perhaps an injector is faulty or something causing a lean condition in one cylinder?

As the car does periodically idle smoothly I believe whatever is causing it must be able to be corrected


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 155,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Rough idle - Running lean? [Re: Spetz] #4755562
05/13/18 04:31 AM
05/13/18 04:31 AM
Joined: Jan 2011
Posts: 2,836
N.Ohio
Lubener Offline
Lubener  Offline
Joined: Jan 2011
Posts: 2,836
N.Ohio
I wouldn't do a thing till I checked the fuel trims first.


The "thinking" man's friend.
Re: Rough idle - Running lean? [Re: Lubener] #4755573
05/13/18 04:43 AM
05/13/18 04:43 AM
Joined: Jan 2018
Posts: 538
San Antonio, TX
das_peikko Offline
das_peikko  Offline
Joined: Jan 2018
Posts: 538
San Antonio, TX
Originally Posted By: Lubener
I wouldn't do a thing till I checked the fuel trims first.


What are we looking for when we check fuel trims?

Re: Rough idle - Running lean? [Re: das_peikko] #4755627
05/13/18 06:53 AM
05/13/18 06:53 AM
Joined: Nov 2006
Posts: 20,594
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 20,594
MA, Mittelfranken.de
Most engines have one O2/AFM (aka wide band O2) per bank, some inline have 2 and some modified engines use one per cylinder which is much better but more expensive and complex.
Given this V6 has one per bank fuel trims will tell which bank or both are adding fuel (eg +10) for a lean condition or taking fuel away (eg-10)because its rich.

If one bank is hovering around 0 give or take a couple of points and the other is +10 for example then that bank is running lean.
The problem is that bank has multiple cylinders making it difficult to pinpoint the exact one if the misfire count is the same for all.

Enriching the whole system through the TB wont help pinpoint the issue, checking the fuel trims to find out what is happening is the only real way to get a good starting point.
Back in the day when engines has secondary air system ports for each cylinder and no OBD 2 we removed them one at a time and put a gas analyzer probe down it to identify the offending cyl.


ASE L1, Master. Deutsch Meisterbrief.
Re: Rough idle - Running lean? [Re: Spetz] #4755750
05/13/18 09:11 AM
05/13/18 09:11 AM
Joined: Jan 2014
Posts: 460
Australia
Spetz Offline OP
Spetz  Offline OP
Joined: Jan 2014
Posts: 460
Australia
The car only has a single O2 sensor.

I know the test I am proposing won't pinpoint the offending cylinder but all I am trying to achieve here is to establish whether or not a lean condition (on a single, multiple, all etc cylinders) is the cause of the rough idle.

If the car idles better once I inject butane into the intake then I know I should be looking at a lean idle condition.

How do I check fuel trims?


2003 Mitsubishi Diamante 6G74 3.5L. 5 Speed auto. 155,000 miles. Shell Helix Ultra 5W40 at 6k OCI
Re: Rough idle - Running lean? [Re: Spetz] #4755847
05/13/18 10:59 AM
05/13/18 10:59 AM
Joined: Nov 2006
Posts: 20,594
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 20,594
MA, Mittelfranken.de
With a scan tool. This engine has both banks going into a single pipe with one O2? GM V6 engines were like like.
Yes enriching the mixture to see if it smooths out will tell you if you have a lean condition but you need some numbers.


ASE L1, Master. Deutsch Meisterbrief.
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