stalling/idling problem revisited

[kumar]

original discussion here: http://fordgtforum.com/forums/showthread.php?t=9886&page=2

Over the past few weeks (since I removed the air block off plates in the clamshell), the surging and stalling has almost gone away. However, Ive noticed that the only time it happens is when its a windy day and there is a gust of air outside. It also happens when I come to stop very quickly. Im assuming thats the same cause since an abrupt stop causes a rush of air over the clamshell. So it seems as though Ive narrowed down the cause of the stalling to airflow inside the clamshell and not a fuel filler neck or IAC valve, etc.

To test this theory, I just used a leaf blower in the garage while the car was running. With the leaf blower pointed at the maf, there was a little surging at idle. When I pointed the leaf blower to either of the air intake openings, the car would surge badly and eventually die. Im not sure if that test means anything or not. I mean, a whole lot more air should play havoc on the MAF right?

Either way, what should I try to get the problem resolved? better idle tuning? change air filter? try a new maf?

Thanks,
Kumar

 

[tmcphail]

The turbulence from the leaf blower air moving into the airbox and picked up by the maf will cause voltage irregularities and cause that situation to happen.


The best way to rule out anything physical would be to datalog it.

 

[gtjoey]

One loop test on the machine will take allllllll the guessing away , dont risk your health, its still under warranty for the most part. :thumbsup stay alive to enjoy the ride gtjoey 1314:thumbsup

 

[kumar]

One loop test on the machine will take allllllll the guessing away , dont risk your health, its still under warranty for the most part. :thumbsup stay alive to enjoy the ride gtjoey 1314:thumbsup

Its not under warranty anymore.

+ i had it in to the dealer 4 times. Those guys dont have a clue.

 

[kumar]

The turbulence from the leaf blower air moving into the airbox and picked up by the maf will cause voltage irregularities and cause that situation to happen.


The best way to rule out anything physical would be to datalog it.

I even had a friend notice the same thing. I left the car running when I went to the bank.

He said the RPMs would surge from ~650 to ~400 every single time the wind would gust.

 

[tmcphail]

It should not do that in the wind at all. you need to gather sensor data.

 

[gtjoey]

Sorry my friend , didnt know, well the gt guys who built the thing from scratch would be my best bet:thumbsup. Dbk and I had a lesson on this whole vent side air thing along time ago in detroit, it does have to do with the mass airflow etc. interesting stuff, give dennis and rich a buzz, the car is a bullet proof ride, this shouldnt be happening. enjoy gtjoey 1314:thumbsup

 

[kumar]

maybe i need to ship it to michigan

 

[427Aggie]

Kumar,

Did you check and see if the inserts are inside the clamshell? There are 2 mesh screens inside the clam shell that each have a big plastic insert in them to control air flow.

Per the engineers these were added because when they got a cross wind the car would stall out.

 

[Silverbullitt]

I'm sure Matt would be able to bring his ride over so you can part swap until it is fixed. Then leave him with a rough idling car. He never drives it anyway.

 

[Blue GT]

History with racing and Modifying Vipers

I have over the years built race cars and modified Vipers. I don't know if you have moded your car. If you have the engine idle will continue to hunt for the proper air fuel mixture which will cause the engine idle to serge, have a rough idle and or die. My experience is that the mass air sensor and the stock PCM are not able to perform properly with the stock default settings if the engine has been modified. The PCM will need to be reprogramed to read the mods. Running a leaf blower over the air intake will cause a lean condition and cause the idle to rise. (be carfull). Also, if your car is stock, sometimes if you disconnect the battery and alow the PCM to return to stock settings this may clean up a funky PCM. Good luck, Dan

 

[kumar]

Kumar,

Did you check and see if the inserts are inside the clamshell? There are 2 mesh screens inside the clam shell that each have a big plastic insert in them to control air flow.

Per the engineers these were added because when they got a cross wind the car would stall out.

yep the inserts are there although i guess they could be kinda loose? since i had to take them apart to get the block off plates out

 

[kumar]

I'm sure Matt would be able to bring his ride over so you can part swap until it is fixed. Then leave him with a rough idling car. He never drives it anyway.

i like this idea

 

[kumar]

I have over the years built race cars and modified Vipers. I don't know if you have moded your car. If you have the engine idle will continue to hunt for the proper air fuel mixture which will cause the engine idle to serge, have a rough idle and or die. My experience is that the mass air sensor and the stock PCM are not able to perform properly with the stock default settings if the engine has been modified. The PCM will need to be reprogramed to read the mods. Running a leaf blower over the air intake will cause a lean condition and cause the idle to rise. (be carfull). Also, if your car is stock, sometimes if you disconnect the battery and alow the PCM to return to stock settings this may clean up a funky PCM. Good luck, Dan

it is modified and has a hennessey tune which is a generic tune i think

i might have a respected local tuner look at the idle settings. maybe i should quit putting that off.

 

[Blue GT]

Just a thought

If your settings are too lean any additional air flow will create a rise in your idle. Air fuel ratios will be different at idle than under normal operation. Also check your O2 sensors to see if they are conected and operating properly. And of course check for a vacuum leak. Just my 2 cents worth.... Dan

 

[kumar]

checked for a vacuum leak. that was my first thought

will definitely check on the idle tune. that might be it.

 

[paul b]

Try a different brand of leaf blower.

 

[Fubar]

Maybe the folks that modified that air grate did other modifications to the air flow system (just a thought). The next thing I would check is the tune... they may have adjusted the idle settings trying to correct the problem they created by blocking the vent.