When is it appropriate to look for carbon deposits

Joe Diagnostician Jersey City, New Jersey Posted   Latest  

Hello everyone. I have a question for all of you driveability techs. First, let me start by saying I am a huge fan of the ats scan tool and especially the training dvd that is included with the kit. Needless to say the topic of this dvd is on using your time efficient and yielding solid diagnostic decision you can use facts to back up. Here is my question...

With any vehicle that sources gasoline for fuel (especially GDI fueled engines) how do you prove carbon build up is present. ??? 

I know several engines may require the service more often than necessary. So some use mileage as reason to take a peak. Has anybody come up with a dso test to point them in the direction of carbon build up prior to inspection? You know so when you use your videoscooe your not wasting your time?

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Jeffrey Manager
Yuma, Arizona
Jeffrey
 

Joe, I haven’t, but I haven‘t had many GDI engines in for service yet. Maybe the dry climate here is less conducive to carbon buildup. I think I’d rather know what customer concerns, fault codes, and fuel trim/VE data would indicate a need for an intrusive look at the intake valve faces. A DSO seems like the long way IMHO. What usually leads you there?

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Ray Diagnostician
North York, Ontario
Ray
 

There was a post in Autonerdz with a 4 cylinder GDI engine with misfire codes. A pressure transducer was connected to the intake manifold while cranking and the waveform showed some cylinders were pulling less vacuum then the other cylinders during the intake strokes. A photo showed the carbon buildup on the intake valves. My experience with misfires in GDI engines is that the injectors drip

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Jim Curriculum Developer
Frederick, Maryland
Jim
 

Without mentioning specific vehicle in this reply, an often overlooked resource is scan tool data. There can be PIDs related to "throttle trim" or modifiers like "loss flow control" available. These can be an arrow toward changes in air flow expected under specific operating conditions. The culprit could be carbon.

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Rudy Technician
Montebello, California
Rudy
 

I like that line of thought Jim. Can you elaborate a little more?

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Jim Curriculum Developer
Frederick, Maryland
Jim
 

Hi Rudy, Sorry I missed the detail of a "reply to me" in the email alerts. Still getting used to this beta. To elaborate a little more I will provide on example from one manufacturer. This is the type of data that is starting to show up in vehicles that we may not yet be looking for. The example I will use is a late model Toyota. Toyota has a series of PIDs related to ISC (idle speed control)

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Ray Diagnostician
North York, Ontario
Ray
 

I haven't seen it myself, but In the scan tool Generic data, the MAF and the Calculated Load percentage would read lower with carbon on the intake valves. Ray

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Albin Diagnostician
Leavenworth, Washington
Albin
 

That should be reflected in the engine load, which would be easy to find on a FRTD (flat rate test drive).

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