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2005 Volvo S40 II 1.8 Pb - no faults, high fuel trims while accelerate

  • dudek17
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08 Apr 2019 17:45 #28521 by dudek17
Hi everyone,

I have a issue with my car. It usualy work fine, engine start with out any problems, but on iddle engine speed I can feal lot of vibrations from engine on all car body, so I started looking for what can be wrong.
I found o-rings rubbers on injectors that was destroyed, but problem still occure.
On graph below you can see quite big positive long and short fuel trim, while acceleration.
What it is mean?
Fuel pomp or fuel regulator is damage, or what else?

Another question is why ignition angle is falling down for a moment at first after throtle pedal pressed, because i can feel that small gap while I try accelarate?

Car data log

Thank you for help with that.

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  • Andy.MacFadyen
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09 Apr 2019 06:40 - 09 Apr 2019 06:41 #28537 by Andy.MacFadyen
All cars go open loop & rich when the accelerator pedal is pressed, this has the same function as the accelerator pump on a carburettor.

The ignition advance angle normally lies in the range 8 to 17 degrees at idle speed it will probably vary up and down a little within this range as many engine computers use ignition advance partly to control idle rpm. Also on any car engine over about 2500 RPM the ignition advance will max out somewhere between 36 and 46 degrees depending factors to do with engine design and the fueling strategy.

Normally when the engine is running closed loop at idle or constant speed cruising the total fuel trims (average STF + LTF) should work in the range -10% to +10%. Most cars with a few miles on the clock show some fuel being added say +6%.

"There's always a catch ---- Catch OBD2 ."


Last edit: 09 Apr 2019 06:41 by Andy.MacFadyen.

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09 Apr 2019 07:01 - 09 Apr 2019 07:02 #28538 by Andy.MacFadyen
The fuel trims at idle and at raised idle say constant 2500rpm can tell you a lot. High fuel trims at idle that improve at raised RPM point to a vacuum leak. If the high + fuel trims don't improve at constant 2000 to 2500 rpm tend to point to a MAF or fuel pressure issue

What I would want to see is the output from the MAF sensor in kgs/s , the signal voltage from the TPS this should be a smooth progression with no glitches as throttle is moved.

NB If the car has any modifications to air inlet or air filter this can cause issues when the accelerator is depressed

"There's always a catch ---- Catch OBD2 ."


Last edit: 09 Apr 2019 07:02 by Andy.MacFadyen.

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09 Apr 2019 12:52 #28540 by dudek17
Thank you for help,

This car have original air inlet without any modification.
Also unfortunatelly, this engine have only MAP sensor (without MAF).

I attachments i've put screens shot with constant speed driving on 3 gear and around 3200 RPM. It looks that car have quite big positive LTFT in that moment.
Second one show data with 5 gear and arround 2000 RPM.

Also, I've found something strange, that on iddle speed the RPMs, Speed, LTFT are litle jumping up every exacly 2.2 sec. Maybe it is a problem with my diagnostic tool, but it is strange that this make reaction in LTFT. You can see that on last photo.

Unfortunately, I didn't prepare logs with smooth acceleration yet.

Another thing, is it normal that engine load is increse so fast to 100% with small throttle open angle? I can feel that, if I press throttle pedal harder then car isn't speed up well, but then if in that moment I will take leg little back, then it is much better?

Sorry, for that many explanation from me, but mayby it will help resolve problem easier.
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