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Re: It's a really good Saab only shop that has worked on Posted by Justin VanAbrahams [Email] ![]() ![]() In Reply to: It's a really good Saab only shop that has worked on, KB88900T, Tue, 17 Sep 2002 22:48:49 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Please do, as I'd be interested to hear.
On a carburated engine, fuel is released purely based on the volume of air coming into the engine. As a result, when the car is cold, there may be insufficient fuel to keep the engine running. A choke restricts (get it? "chokes") the incoming air, thus achieving a relatively richer mixture at the expense of performance.
On a fuel injected engine, pretty much no matter *how* it's fuel injected, various sensors measure the incoming air more accurately, compensating for things like altitude, air temperature, and velocity. In addition, nearly all of them incorporate some form of engine temperature sensor - on a c900 that's the oft-talked-about NTC (negative temperature coefficient) sensor or coolant temperature sensor. This sensor reports back to the ECU the current engine temp, and allows the computer to make adjustments to the mixture to compensate for a warm or cold engine. This is superior to a choke, as you are not restricting airflow and thus not affecting (seriously) the performance of the engine.
This being the situation, installing any sort of conventional choke on a fuel injected engine would seriously affect its ability to properly measure the air, and would have an adverse affect on the running of the engine. If a Saab is having problems running when cold, there are two likely candidates - the NTC sensor not accurately reporting the engine temp, or the air mass meter (AMM) not accurately reporting the mass of the incoming air. Barring any physical problems - like vaccum leaks or electrical breaks - 90% of the time one of these will be causing the problem. Some people install a resistor inline with the NTC sensor to fool the computer into thinking the engine is colder than it actually is, which causes the computer to richen the mixture. From a cold-start perspective, this can help smooth out idle and running when especially cold. From a performance perspective, this will increase fuelling under all situations, helping to stave off detonation. From a fuel-economy perspective, you're consuming more fuel than you would be otherwise. Personally, I think fixing the real problem is better than fooling a computer, but that's my $0.02...
Well, that's more than you asked for, but I still wanna hear what you mechanic has to say about installing a choke on a fuel injected car, much less a Saab.
-Justin
posted by 64.166.4...
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