Toyota MR2 Message Board - View Single Post

mr2greasemonkey · 05-23-2007, 09:26 PM

The biggest complaint in the automotive world is driveability. Now that you've figured out how to make the engine start and run we are moving on to making it driveable.

The first thing we'll start off with is engine performance. The engine must be able to rev smoothly in neutral and in gear. There are all sorts of engine performance driveabiltiy complaints so we will begin with the basic diagnostic terms.

stumble/misfire on acceleration = it seems like it jerks and bucks when starting from a stop or accelerating from a lower speed. May not be as noticeable in neutral as when in gear. Typically an ignition misfire when it is not limited to a certain rpm. Do the ignition/spark system basic tests. If it always seems like it happens at the same rpm's then check the throttle position or map/afm sensors.

Hesitation = it seems like it takes more time for the engine to pull at certain rpms. This can be a result of improper timing or not enough fuel/air delivery. Depending on how long the duration it is in the rpm range or if its at the top or at the bottom will point you in which system to check first. Typically at the bottom of the rpm range you should be checking: tps, afm/map, timing, vacuum leaks. In the middle rpm range: tps, afm/map, timing, egr. At the upper rpm range: tps, afm/map, timing, egr, fuel.

Lack of power = when you step on the pedal and it seems like the engine doesnt pull like it's suppose to. Check the basics. An engine that pulls slowly at the bottom rpm range and then seems to "pick up" at the top is generally a sign of retarded timing( now is a good time to use that new timing light you just bought). If it seems to start pulling but then just flat lines like it's out of breath, suspect restricted exhaust or lack of fuel. Holding your hand a few inches form the tailpipe while somone revs on the engine, there should be a nice flow. Sometimes removing the O2 sensor from before the catalytic convertor can be enough to make a noticeable change with a plugged cat. A basic fuel system test will determine if you are supplying enough fuel to the rail. Give the spark plugs a good visual to see if they are running lean. Even a partially open EGR valve can return enough exhaust to bog the engine down.

05-23-2007, 09:26 PM	#12 (permalink)
mr2greasemonkey Once again....yups Join Date: Sep 2005 Location: Portland, OR Posts: 1,440 Thanks: 4 Thanked 54 Times in 39 Posts iTrader Rating: (0/0% )	Driveability: Engine performance. The biggest complaint in the automotive world is driveability. Now that you've figured out how to make the engine start and run we are moving on to making it driveable. The first thing we'll start off with is engine performance. The engine must be able to rev smoothly in neutral and in gear. There are all sorts of engine performance driveabiltiy complaints so we will begin with the basic diagnostic terms. stumble/misfire on acceleration = it seems like it jerks and bucks when starting from a stop or accelerating from a lower speed. May not be as noticeable in neutral as when in gear. Typically an ignition misfire when it is not limited to a certain rpm. Do the ignition/spark system basic tests. If it always seems like it happens at the same rpm's then check the throttle position or map/afm sensors. Hesitation = it seems like it takes more time for the engine to pull at certain rpms. This can be a result of improper timing or not enough fuel/air delivery. Depending on how long the duration it is in the rpm range or if its at the top or at the bottom will point you in which system to check first. Typically at the bottom of the rpm range you should be checking: tps, afm/map, timing, vacuum leaks. In the middle rpm range: tps, afm/map, timing, egr. At the upper rpm range: tps, afm/map, timing, egr, fuel. Lack of power = when you step on the pedal and it seems like the engine doesnt pull like it's suppose to. Check the basics. An engine that pulls slowly at the bottom rpm range and then seems to "pick up" at the top is generally a sign of retarded timing( now is a good time to use that new timing light you just bought). If it seems to start pulling but then just flat lines like it's out of breath, suspect restricted exhaust or lack of fuel. Holding your hand a few inches form the tailpipe while somone revs on the engine, there should be a nice flow. Sometimes removing the O2 sensor from before the catalytic convertor can be enough to make a noticeable change with a plugged cat. A basic fuel system test will determine if you are supplying enough fuel to the rail. Give the spark plugs a good visual to see if they are running lean. Even a partially open EGR valve can return enough exhaust to bog the engine down.