slight jerking/missing

[CMF_david (2)]

Hi all,

I have been experiencing some problems with my micra. My micra is dual fuel, but the problem only occurs when it runs on petrol. The symptom is that when under light/medium acceleration it sort of skips/hops/jerks along slightly.

After talking to various people I thought it might be the injectors are dirty, the O2 sensor might need replacing, or the timing might be out, or it could be dirty fuel.

So I used up the fuel tank and filled it up and it kept happening...so not dirty fuel.

Took it to the mechanic...who put it on his tuneup machine and said it was all fine (charged $110 ) and then said that it left the injectors or the O2 sensor which he said normally need replacing about the 100,000 kms mark anyway. (I have about 90,000) We then decided to put some injector cleaner stuff in the tank and try that...I am about 1/2 way through that tank and it appears to have improved it...but I can still notice it ever so slightly. Thus, I am thinking that I will need to get the injectors cleaned properly sometime in the near future.

Ideas/comments welcome. Or maybe at least it will save someone $100 for a tuneup that is not needed. ($25 for injector cleaner stuff... that he said was very good.)

 

[CMF_turbo march-rolling shell]

do a basic service on it first maybe? change all your filters/plugs, check out inside your dizzy cap, clean out your afm.

 

[CMF_david (2)]

Oh..I missed some stuff...he replaced the plugs and checked the dizzy cap (it was good)

What is an afm?

Air filter is nearly new....oil will be changed tomorrow (along with filter)

 

[CMF_nsm]

air flow meter...they get fairly tempremental at times...

 

[CMF_frank2]

david

why are you running it on petrol with all that cheap gas availiable ?
they might have altered the idle mixture when they setup the gas (had to do the same with mine)
it sounds like its hunting (overich) at low throttle, there,s a black plastic allenkey screw (o/s rear corner on the t/b) and if you screw it out it will run leaner at low throttle opening (haynes claims its a tickover screw, but its an air bleed, with a hole upsteam of the butterfly, exiting below the t/b)

frank

 

[CMF_darkfibre]

frank2 WROTE:

"david<BR><BR>why are you running it on petrol with all that cheap gas availiable ?<BR>they might have altered the idle mixture when they setup the gas (had to do the same with mine)<BR>it sounds like its hunting (overich) at low throttle, there,s a black plastic allenkey screw (o/s rear corner on the t/b) and if you screw it out it will run leaner at low throttle opening (haynes claims its a tickover screw, but its an air bleed, with a hole upsteam of the butterfly, exiting below the t/b)<BR><BR>frank

That adjustment is only for idle speed only as it bypasses air around the throttle plate. It does not alter the amount of air passing the air sensor. I have run these air flows on our test bench and the adjustment is not relevent.
There is no mixture adjustment.

 

[CMF_frank2]

darkfibre

yes i agree its for idle mixture only, but i find that on light acceleration the lambda readings are very scattered until the closed loop settles down
how precise is the closed loop system at short injector durations ?

frank

 

[CMF_david (2)]

Is the afm the same as the O2 sensor?

How do I clean it?

With regard to why I am running petrol...it is because the lpg guy says I need to and also it is set up to start on petrol and then switch to lpg....so if my petrol dies I'm stuck. I only started having this problem in about the last month...had the conversion done about 4 months ago.

 

[CMF_darkfibre]

frank2 WROTE:

"darkfibre<BR><BR>yes i agree its for idle mixture only, but i find that on light acceleration the lambda readings are very scattered until the closed loop settles down<BR>how precise is the closed loop system at short injector durations ?<BR><BR>frank

On light acceleration the readings will be anywhere depending on actual mixture. On cruise the system will be in closed loop and you should have a predictable cycle. Closed loop is always precise. Closed loop is only ever at zero load.

 

[CMF_darkfibre]

david WROTE:

<BR><BR>Took it to the mechanic..................... and then said that it left the injectors or the O2 sensor which he said normally need replacing about the 100,000 kms mark anyway. (I have about 90,000) We then decided to put some injector cleaner stuff in the tank and try that...I am about 1/2 way through that tank and it appears to have improved it...but I can still notice it ever so slightly. Thus, I am thinking that I will need to get the injectors cleaned properly sometime in the near future.<BR><BR>Ideas/comments welcome. Or maybe at least it will save someone $100 for a tuneup that is not needed. ($25 for injector cleaner stuff... that he said was very good.)<BR><BR><BR>

Injectors are always a problems when running gas, and are most likely to be the problem, if tank additive helps then it most likely is the problem.
Most mechanics tell you to replace the oxygen sensor at 100k but my advice is to wait till it fails as I have seen sensors go 200k If it responds quickly (cycles) in closed loop then leave it alone. And yes I am a mechanic And have spent many hours training other mechanics in vehicle electronics and injection.

 

[CMF_david (2)]

What do you mean by "If it responds quickly (cycles) in closed loop"?

 

[CMF_darkfibre]

david WROTE:

"What do you mean by "If it responds quickly (cycles) in closed loop"?

Oxygen sensors are designed to be very sensitive in a very narrow band (14.7 TO 1 air/fuel ratio) When in closed loop the sensor gives a signal (rich or lean) to the ecu which then alters the mixture to correct it. Because of the time taken (the changes need time to be compressed and burnt etc) the result at the oxygen will seem to be constantly trying to balance. The test for an oxygen sensor is responce time from rich to lean then from lean to rich. 300 milliseconds is considered good. (that information from an oxygen senser manufacturer).
So on a bargraph it the sensor cycles at around once a second in closed loop it is ok
Hope that was not too long winded, but thay are not exatly a simple device lol

 

[CMF_david (2)]

So you need a special machine to measure this?

What/How do you make a closed loop in a car?

Why do injectors tend to go bad on dual fuel vehicles? Is it because they get dry from lack of use? If so then that would not be helped by injector cleaner...am I correct?

 

[CMF_darkfibre]

david WROTE:

"So you need a special machine to measure this?<BR><BR>What/How do you make a closed loop in a car?<BR><BR>Why do injectors tend to go bad on dual fuel vehicles? Is it because they get dry from lack of use? If so then that would not be helped by injector cleaner...am I correct?<BR>

there are cheap led bargraph kits for measuring these. But anything that will show 0 to 1 volt should work. However an oscilloscope is best.
yes injectors get hot and dry on gas setups which lead to deposits on them, cleaner can help.

Closed loop basically happens at operating temp with no load (simplified a lot)

 

[CMF_fred]

um.... by yourself a air/fuel ratio meter...about $60 of ebay or you favourite autoshop....

 

[CMF_david (2)]

To anyone who has a similar problem to what I described....my problem seems to be gone now...thanks to the injector cleaner stuff (one tanks worth). Seems to be related to the fact that I run it on LPG as well so the injectors get stuff on them.