Hey guys,

With the winter blend of gas I experienced a drop in 20 miles to the tank. So I figured I try 92 octane gas. Right after I filled up and I started the car it stalled. So I was paranoid and just tried starting it again and same thing happen. About the third time I started to think and opened up the throttle once it started to idle and had throttle opened for a few seconds and let off and it was idling fine. Next morning it started up just fine. It appears it starts up just fine during cold start conditions. The problem I am having now is during warm start conditions. Ill go on a short trip to a store and once I am back in the car and fire it up it will stall without assistance with some throttle.

I asked my instructor and his first impressions based on my story would be that I would have leaking injectors and be flooding the engine.

So what I am wondering is would a higher octane gas cause these problems? Or perhaps they are unrelated and it is just a coincidence? Furthermore, can the Picoscope be used to help diagnose this problem? Any quick fixes?

Is it also odd that a code hasn't been set? I am still astonished with my ignorance :(

Almost forgot, I am driving an 2001 Nissan Sentra SE 2.0 liter

Hi and welcome

natefico wrote on Jan 10^th, 2008 at 3:00pm:

Hey guys, With the winter blend of gas I experienced a drop in 20 miles to the tank. So I figured I try 92 octane gas. Right after I filled up and I started the car it stalled. So I was paranoid and just tried starting it again and same thing happen. About the third time I started to think and opened up the throttle once it started to idle and had throttle opened for a few seconds and let off and it was idling fine.

If this happened whilst you were still at the gas pump it is not the fuel as you have a filter,rail and injectors full of your old fuel to consume before the new gas has a chance to be used.

My first tool would be the scan tool and look at fueltrims.

These vehicles have a problem with MAF sensors and ecm's Check your VIN number at the dealer to see it the updates have been done on the cam and crank sensors, and ecm.


natefico wrote on Jan 10^th, 2008 at 3:00pm:

Next morning it started up just fine. It appears it starts up just fine during cold start conditions. The problem I am having now is during warm start conditions. Ill go on a short trip to a store and once I am back in the car and fire it up it will stall without assistance with some throttle.

Just a coincidence at this time I think check the above first.

Mick

Nate also check the throttle body for coking.  If it's dirty, clean it out with a toothbrush and some throttle body cleaner.  Sounds like it may be lacking idle air supply.

Nate,
winter blend gas has lower flash point then summer grade gas/ you may be getting a case of vapor lock due to gas boil from winter blend gas in summer, or low fuel pressure.  Smitty.

If you are a member of iATN, there was a discussion about octane and RVP recently. I believe there was mention of Ford having a bulletin about what you are experiencing. I don't remember the thread name but it was in the last week or two.

Hey Nate,
try cycling the key-off-on a couple of times(prime the fuel rail) and see if it helps, fuel may be "perking" at a hot start-soak

Dave

Quote:

Is it also odd that a code hasn't been set?

Not odd at all....


Quote:

Any quick fixes?

On iatn, you'll probably get 30 quick fixes. Its just a matter of picking the right one.  :)


Quote:

I asked my instructor and...

At the risk of unintentionally offending you, I'm guessing this means your fairly new to the field. In which case I know its a tough road your facing.

One thing you have to keep in mind. Today instructors/educators tend to speak in terms of system operation in a "the computer monitors and sees such and such. Therefore, when this happens, the computer does this and that".

The problem is, older vehicles were equipped with technology far below todays and therefore much of the system programming only works as it should if current events/signals fall within certain "windows".

My comment above about it not being odd that a code hasn't set would also apply to much newer vehicles with much greater onboard diagnostic capabilities.

If there is no stored code, then other than an educated guess, you've got your work cut out for you. The absolute worst scenario is when the calibrators could not forsee a given fuel characteristic for a given situation and there is not yet a new calibration (or in some asian vehicles) or a new pcm to address the problem. Been there done that too many times...

I think though, the basics have already been mentioned. Throttle body coking, dripping fuel injectors, leaking regulator, fuel quality, etc...