1994 SHO hesitation problem
danSHO
04-20-2007, 05:19 PM
just wondering if anyone could offer some helpful advice. my SHO hesitates upon accelerating and seems to have an overall loss of power even at higher rpms. had oil on top of all six spark plugs but i changed the spark plugs and the valve cover gaskets...now there isn't any problems with the oil anymore but the hesitation problem will not go away...diagnostic checks were different at both mechanics i took it to. any ideas? thanks
shorod
04-20-2007, 10:27 PM
Did you replace the spark plug wires too, or just the plugs and gaskets? If not the wires, you probably should replace them too as there may be sufficient carbon tracing to cause them to short directly to the head rather than through the spark plugs.
Other areas to look at would be the Throttle Position Sensor (TPS), Mass Air Flow (MAF) sensor, dirty throttle plate, coolant temp sensor out of range, open secondary intake manifold butterflies, oxygen (O2) sensor(s), and the Crankshaft Position Sensor (CKP).
The TPS should provide a linear resistance/voltage when provided a steady opening of the throttle. Any non-linearities indicate a faulty sensor which can lead to hesitation.
A very dirty MAF sensor can lead to hesitation and decreased fuel economy. Often, if you have an oiled air filter, the oil will coat the MAF sensor elements and cause issue. CRC makes a cleaner specifically for cleaning the MAF. I've found it available at Advance Auto Parts. You will also need the security Torx bits to remove the MAF from the air intake tube.
If the throttle plate has quite a bit of carbon build up, it may contribute to hesitation when throttle is applied, but I wouldn't expect that to have much of an effect on overall power. The overall power issue could be partially psychological if the car is hesitating though.
If the coolant temperature sensor is out of range, it could be causing the air/fuel ratio to go way rich or way lean. This won't necessarily show up in the temperature guage on your dash though as that gets its reading from the coolant temperature sender (separate thermistor). If this is at fault, again I would expect a change in fuel economy.
If the secondary intake runners are stuck open all the time, this could cause a hesitation at low RPMs and reduced power below 3500 RPMs. My recall is that they are vacuum controlled on the '94 SHO.
If one or more of the oxygen sensors are not working properly, they could cause a hesitation and, again, change in fuel economy. The PCM will attempt to alter the air/fuel ratio based on the readings of the O2 sensors.
The CKP is a fairly common item to fail on the V-6 SHO engine. If the water pump begins to leak, the coolant drips right onto the CKP sensor. This corrodes and damages the sensor. In the early stages of failure, this could cause a hestitation and reduced power. The PCM uses this sensor, along with others, to alter ignition timing. If the sensor fails, the car will stall or no start. Replacing the CKP sensor is labor-intensive, so be real sure this is the problem before asking someone to replace it. If you need to replace it, you may as well have the water pump and timing belt replaced at the same time. I'd also recommend you replace the timing belt tensioner as well.
-Rod
Other areas to look at would be the Throttle Position Sensor (TPS), Mass Air Flow (MAF) sensor, dirty throttle plate, coolant temp sensor out of range, open secondary intake manifold butterflies, oxygen (O2) sensor(s), and the Crankshaft Position Sensor (CKP).
The TPS should provide a linear resistance/voltage when provided a steady opening of the throttle. Any non-linearities indicate a faulty sensor which can lead to hesitation.
A very dirty MAF sensor can lead to hesitation and decreased fuel economy. Often, if you have an oiled air filter, the oil will coat the MAF sensor elements and cause issue. CRC makes a cleaner specifically for cleaning the MAF. I've found it available at Advance Auto Parts. You will also need the security Torx bits to remove the MAF from the air intake tube.
If the throttle plate has quite a bit of carbon build up, it may contribute to hesitation when throttle is applied, but I wouldn't expect that to have much of an effect on overall power. The overall power issue could be partially psychological if the car is hesitating though.
If the coolant temperature sensor is out of range, it could be causing the air/fuel ratio to go way rich or way lean. This won't necessarily show up in the temperature guage on your dash though as that gets its reading from the coolant temperature sender (separate thermistor). If this is at fault, again I would expect a change in fuel economy.
If the secondary intake runners are stuck open all the time, this could cause a hesitation at low RPMs and reduced power below 3500 RPMs. My recall is that they are vacuum controlled on the '94 SHO.
If one or more of the oxygen sensors are not working properly, they could cause a hesitation and, again, change in fuel economy. The PCM will attempt to alter the air/fuel ratio based on the readings of the O2 sensors.
The CKP is a fairly common item to fail on the V-6 SHO engine. If the water pump begins to leak, the coolant drips right onto the CKP sensor. This corrodes and damages the sensor. In the early stages of failure, this could cause a hestitation and reduced power. The PCM uses this sensor, along with others, to alter ignition timing. If the sensor fails, the car will stall or no start. Replacing the CKP sensor is labor-intensive, so be real sure this is the problem before asking someone to replace it. If you need to replace it, you may as well have the water pump and timing belt replaced at the same time. I'd also recommend you replace the timing belt tensioner as well.
-Rod
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