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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / December 2007Stumped with a rich mixture/lack of power problem
I have a stock 93 MX-6 V6 KLDE with a definite lack of power and rich mixture. It idles OK with a slight fluctuation of the needle. Engine is OBD1 and was thowing codes 17 and 24, indicating o2 inversion errors on both sensors. I have replaced both sensors, CEL has not come up again, but the engine continues to drag upon acceleration. Plugs are reddish brown. No fluctutations in engine temp. Engine starts easily. Poor mileage. Here is what has been done or checked: Compression 175 to 185PSI across all 6 cylinders Entire ignition system has been replaced during troubleshooting - plugs, wires, distributor. Vacuum is at 20hg/in at idle, thoroughly checked over for vacuum leaks by myself and a shop - found none. Injector resistance spec is between 12 and 16 ohms - all read at 14 Timing belt has been changed recently - valve timing has been triple checked. Fuel pressure spec is 30-36psi at idle. Current pressure is at 34psi idle. Fuel filter is new, pump is nearly new, fuel return line is not clogged. VAF meter tested OK Intake manifold and throttle body cleaned and installed with new gaskets. Coolant temp sensor checked OK Crank position sensor NE-1 checked. OK Throttle position sensor set within factory spec - .65v at idle, 3.75v wide open. air filter is stock, and clean. All VRIS valves working No obvious signs of head gasket failure. - Temp fine, coolant level maintained. What would my next step be? The engine used to run closer to the lean side when it was in top shape. Intermittent misfire? Bad injector spray pattern? EGR? bad cat converter? Thanks, Brad Nobody have an idea, or am I asking a dumb question? Checked my new o2 voltage readings. The before cat left hand o2 sensor for the front 3 cylinders is fluctuating between .51v and .62v while the rear is moving between .42v and .51v I've also noticed that a quick tap to the gas pedal will cause the rpm to drop for a sec before picking up, more obvious when the engine is cold. Anyone? > Nobody have an idea, or am I asking a dumb question? > [quoted text clipped - 6 lines] > > Anyone? You claim a rich mixture problem and lack of power yet your O2 sensor readings indicate a normal mixture ???? How are you getting the voltage reading from the O2 sensors ? Is the engine fully warm ( closed loop ) when these readings were taken ? You also calimed a drop in mileage, how much of a drop ? What is the weather like were you are, winter ?? I am getting the voltage reading from the o2 sensors by tapping in to their signal wires with 2 digital multimeters (one on each). The engine was fully warm when testing them, it had been driven for a half hour on the highway. I used to get 24mpg, and now I am getting about 18mpg. It is winter here, but I didn't think the mileage change would be that drastic. Also when I come in off the highway and stop at the end of the ramp I can smell rotten eggs. My cat was replaced about 6-7000km ago. It just feels like there is something not quite right. I have been driving this car since '97 and got to know it quite well. Is there a way of measuring fuel trim in this OBD1 car? Brad >I am getting the voltage reading from the o2 sensors by tapping in to > their signal wires with 2 digital multimeters (one on each). The > engine was fully warm when testing them, it had been driven for a half > hour on the highway. I used to get 24mpg, and now I am getting about > 18mpg. It is winter here, but I didn't think the mileage change would > be that drastic. That is a considerable drop in mileage. The cold weather shouldn't cause that big of a drop unless you let it warm up for 20 minutes or more. > Also when I come in off the highway and stop at the end of the ramp I > can smell rotten eggs. My cat was replaced about 6-7000km ago. You normally can't smell your car's exhaust while driving unless you have a leak. Are you sure the rotten egg smell is comimg from your car. > It just feels like there is something not quite right. I have been > driving this car since '97 and got to know it quite well. The only things that come to mind that you can check are the ignition timing and check the EGR valve makimg sure it is not sticking open. You also metioned that you did a tune up during your daiagnosis, what brand plugs and wires did you use? I ask this because Bosh spark plugs will cause all kinds of problems like you mention. I would use a good plug like NGK or DENSO > Is there a way of measuring fuel trim in this OBD1 car? You would need a scan tool that is capable of reading that info. It may be a good idea to take a ride with a scan tool hooked up so that you can look at sensor values while the car is being driven. > Brad >I am getting the voltage reading from the o2 sensors by tapping in to >their signal wires with 2 digital multimeters (one on each). The [quoted text clipped - 5 lines] >Also when I come in off the highway and stop at the end of the ramp I >can smell rotten eggs. My cat was replaced about 6-7000km ago. Rotten egg smells are caused by contaminated fuel, almost always. If there's too much sulfur in the gas, you'll get this sort of smell and it's actually possible to poison the catalytic converter this way. I have experienced this with gas in the third world before, but never in North America. There's another kind of dry smell that is caused by the engine running too lean, and there's a raw gasoline smell caused by the engine running too rich, but I wouldn't call either one of these a rotten egg smells. >It just feels like there is something not quite right. I have been >driving this car since '97 and got to know it quite well. Where did you buy gas last? Stay away from Pemex Verde.... --scott  Signature"C'est un Nagra. C'est suisse, et tres, tres precis." |
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