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Old 04-23-2018, 08:25 AM   #1 (permalink)
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Unhappy Epica 2007 start at 4000 RPM! HELP!!

HELLO GUYS!!

I am new here and have a HUGE problem with my epica 2008 2.5L. all days when I'm trying to start the engine, rev goes up to 4000 RPM and stay on it for more than 40 seconds!.
After that, the rev goes down but not to normal idle (700-800), the revs up & down continuously from 1000 to 1300 until Drive or Reverse is selected. Once the gear shift is returned to Park, idle revolution stays near "normal".
if engine is cool (first attemp to start) rev goes up to 4000 RPM.
once engine is warm, the engine starts and mantain this behavior above described.

please check the video.zip file attached

sorry for my bad english!!
Attached Files
File Type: zip epica 2008 rpm issue.zip (906.6 KB, 3 views)
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Old 04-23-2018, 04:19 PM   #2 (permalink)
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Hry franklin,
welcome to the forum.

Very strange indeed!

I have no experience with your car and can only guess.
If I was going attempt to isolate it, you mentioned that after it warms continues to act up?

Best of luck and your English is fine.



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Old 04-25-2018, 01:37 PM   #3 (permalink)
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Thanks a lot Don for fast response!.

In fact, once the chevrolet epica reach the "normal" temp range, the issue disapears, but i am afraid that the crankshaft can suffer in all starting attemps due all the oil engine remains in the oil pan before it start.

Could the Mass Air Flow (MAF) sensor sending a wrong info to the ECU??, and therefore the ECU try to start the engine in a higher idle rev??. is there a procedure that I can follow in order to test by myself the MAF?
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Old 04-25-2018, 01:57 PM   #4 (permalink)
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I think I read advice that Darrel had given for that.

I was wondering if the temperature sensor could be giving incorrect information.




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Old 04-25-2018, 04:24 PM   #5 (permalink)
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Quote:
Originally Posted by franklin perez View Post
Could the Mass Air Flow (MAF) sensor sending a wrong info to the ECU??, and therefore the ECU try to start the engine in a higher idle rev??. is there a procedure that I can follow in order to test by myself the MAF?
May be try unplugging the MAF sensor then start engine
If the engine behaves the same then info sent by MAF isn't the cause of the high idle
If the engine doesn't have the high idle anymore then MAF would then be suspect item
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Old 04-25-2018, 05:28 PM   #6 (permalink)
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I don't follow your logic - for the sake of discussion, let's assume the MAF IS defective - why would unplugging a defective MAF cause any change in symptom - it's defective - it's disconnected - what's the difference?

Also - shouldn't a defective MAF set a code?

Let's look at it from another angle - let's assume, for the sake of discussion, that the MAF is defective, and it is incorrectly telling the ECU that too much or too little air is flowing ...

- if it's saying there is too little air, what will the end result be? Under fuelling? Will that cause a significant increase in rpms? Not likely in my opinion. I would expect a lean mixture condition and possibly the engine stalling.

- if it is saying there is too much air, what will the end result be? Over fuelling? Will that cause a significant increase in rpms? Not likely in my opinion. I would expect a rich mixture condition, and again possibly the engine stalling.

In reality, since this is an OBDII vehicle, the fuelling is actually going to be determined by the O2 sensor, and neither of the above scenarios should result - I will also mention here that if I unplug the MAF on my Grand Vitara, which does not run an O2 sensor, and is dependent on the MAF sensor for fuelling data, the idle rpms do not increase, the mixture richens significantly, the engine starts to hunt, and will flood and stall unless I open the throttle and allow more air flow.

For a gasoline engine to have a significant increase in rpms, there must be a significant increase in air flow, the air flow is controlled primarily by the throttle plate (the MAF simply measures the airflow, it does not control it), and to a lesser extent by the engine's idle mechanisms which vary from one design to another - typically there will be some sort of idle air control valve which allows the ECU to control the idle speed, for warm up purposes, and to compensate for changes in load related to electrical load, power steering and air conditioning - in my experience this idle air control mechanism will not be able to flow enough air to allow the engine to run at 4000 rpm, maybe 2000 ~ 2500 rpm tops.

To flow enough air to get a 4000 rpm "idle", there is either a massive vacuum leak, which I doubt (I don't see the O2 sensor adding that much fuel, unless the MAF is saying there is that much airflow) - or - the throttle plate is most likely being held open, either because of a malfunctioning "drive-by-wire" throttle system, or possibly a malfunctioning cruise control actuator.

One last thing - I have seen a defective PCV valve allow sufficient air flow for the engine to idle at around 2000 rpm - most modern PCV systems draw air into the crankcase after the MAF, but before the throttle plate, so a leaking PCV can allow "metered" air to bypass the throttle plate and a subsequent increase in idle rpm.
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Old 04-25-2018, 11:15 PM   #7 (permalink)
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Quote:
Originally Posted by fordem View Post
I don't follow your logic - for the sake of discussion, let's assume the MAF IS defective - why would unplugging a defective MAF cause any change in symptom - it's defective - it's disconnected - what's the difference?
On some cars, when the MAF is disconnected, the ECU will use substitute values.
This is why I started with "May be".

Quote:
Originally Posted by fordem View Post
Also - shouldn't a defective MAF set a code?
Have seen plenty of cars that have defective MAFs but no codes.
Don't know why?

Quote:
Originally Posted by fordem View Post
Let's look at it from another angle - let's assume, for the sake of discussion, that the MAF is defective, and it is incorrectly telling the ECU that too much or too little air is flowing ...

- if it's saying there is too little air, what will the end result be? Under fuelling? Will that cause a significant increase in rpms? Not likely in my opinion. I would expect a lean mixture condition and possibly the engine stalling.

- if it is saying there is too much air, what will the end result be? Over fuelling? Will that cause a significant increase in rpms? Not likely in my opinion. I would expect a rich mixture condition, and again possibly the engine stalling.
I understand your logic. However, I don't believe I said it was possibly a bad MAF sensor.
Just answered a question about how one could possibly test a MAF.
There are other ways but require an oscilloscope with known good wave forms available to compare.

Quote:
Originally Posted by fordem View Post
In reality, since this is an OBDII vehicle, the fuelling is actually going to be determined by the O2 sensor, and neither of the above scenarios should result - I will also mention here that if I unplug the MAF on my Grand Vitara, which does not run an O2 sensor, and is dependent on the MAF sensor for fuelling data, the idle rpms do not increase, the mixture richens significantly, the engine starts to hunt, and will flood and stall unless I open the throttle and allow more air flow.

For a gasoline engine to have a significant increase in rpms, there must be a significant increase in air flow, the air flow is controlled primarily by the throttle plate (the MAF simply measures the airflow, it does not control it), and to a lesser extent by the engine's idle mechanisms which vary from one design to another - typically there will be some sort of idle air control valve which allows the ECU to control the idle speed, for warm up purposes, and to compensate for changes in load related to electrical load, power steering and air conditioning - in my experience this idle air control mechanism will not be able to flow enough air to allow the engine to run at 4000 rpm, maybe 2000 ~ 2500 rpm tops.

To flow enough air to get a 4000 rpm "idle", there is either a massive vacuum leak, which I doubt (I don't see the O2 sensor adding that much fuel, unless the MAF is saying there is that much airflow) - or - the throttle plate is most likely being held open, either because of a malfunctioning "drive-by-wire" throttle system, or possibly a malfunctioning cruise control actuator.

One last thing - I have seen a defective PCV valve allow sufficient air flow for the engine to idle at around 2000 rpm - most modern PCV systems draw air into the crankcase after the MAF, but before the throttle plate, so a leaking PCV can allow "metered" air to bypass the throttle plate and a subsequent increase in idle rpm.
That is perfect logic. And I would follow that line of troubleshooting.
Clean the in-take and throttle
And check other things which affect the idle.

Please note that a suspect item is a part that needs to be tested to verify it is faulty.
I am wondering if I just should have not said anything??? Probably.
Please delete my posts if you feel it is not helpful.

Last edited by avisitor; 04-25-2018 at 11:29 PM.
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Old 04-26-2018, 01:03 PM   #8 (permalink)
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Guys... the previous car's owner said me that he changes both oxigen sensors ( before & after catalytic converter) because these pieces are a common failure point on this car model. Should I assume that the first owner had to face a similar issue and change both O2 sensors as a result??
The car have a broken piston ring in cylinder #6 and loses compression for the same, but THIS is a MECHANIC problem and it has nothing to do with the acceleration in the start procedure? or it does?. Some weeks ago i saw in youtube a guy checking a throtle body with a scanner and the equipment shows a wrong aperture angle of the plate (not 0 degrees, something like 8 or 10), when the guy start the engine, its beahvior was exactly the same of mine. then make a software reset of the plate's angle (return to 0 degrees) and the engine start normal, quiet and smooth (obviously not my case with a faulty cylinder)
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Old 04-26-2018, 01:50 PM   #9 (permalink)
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Quote:
Originally Posted by franklin perez View Post
Some weeks ago i saw in youtube a guy checking a throtle body with a scanner and the equipment shows a wrong aperture angle of the plate (not 0 degrees, something like 8 or 10), when the guy start the engine, its beahvior was exactly the same of mine. then make a software reset of the plate's angle (return to 0 degrees) and the engine start normal, quiet and smooth (obviously not my case with a faulty cylinder)
Was the vehicle in the youtube video an epica? I've never set eyes on an Epica, but looking at the parts manuals it appears to have a cable operated throttle, which would mean, there's no software involved.
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Old 04-28-2018, 06:43 PM   #10 (permalink)
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Could the throttle cable be sticking?
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