Too much back pressure? Idle issues?
02-26-13, 07:34 PM
#1
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Too much back pressure? Idle issues?
1987 gxl n/a. Racing beats header to the stock cat piping that has been gutted, to a 3" cat back. my 5th and 6th ports are ALWAYS open, im afraid to test with open header cause id hate to have too little back pressure, or just so happen to shoot a flame and start a car fire. do i just need to do a full 3" from the header?
and the second,
when i start my car, i have no accelerated warm up (removed by last owner) thats not the problem, the problem is the car never heats up past a 1/4 pf temp gauge and idles around 1500 rpm most the time, while sometimes it will idle right at about 700-800 rpm. while it idles never 1500 depending on the temp (mostly when its colder) the engine with rev to 1500, hold for about a second, then drop back down, rev to 1500 for about a second....... on and on and on... i have no idea on the path to take to fix this?????
thanks for the help.
and the second,
when i start my car, i have no accelerated warm up (removed by last owner) thats not the problem, the problem is the car never heats up past a 1/4 pf temp gauge and idles around 1500 rpm most the time, while sometimes it will idle right at about 700-800 rpm. while it idles never 1500 depending on the temp (mostly when its colder) the engine with rev to 1500, hold for about a second, then drop back down, rev to 1500 for about a second....... on and on and on... i have no idea on the path to take to fix this?????
thanks for the help.
02-26-13, 07:41 PM
#2
The only reason to want a little backpressure is to move the actuators for the 6PI system (aux. ports / 5th 6th), but they only need ~2 psi. Engines don't need backpressure. If your ports are wired open, it would be a good idea to get them functional again to regain low-end torque.
1/4 of the gauge is 180 degrees and normal operating temperature on an S4.
If your idle bounces, it's most likely a TPS problem. See FAQ for idle troubleshooting. The sensor can be misadjusted or have dead spots in the sweep that can cause "hunting".
1/4 of the gauge is 180 degrees and normal operating temperature on an S4.
If your idle bounces, it's most likely a TPS problem. See FAQ for idle troubleshooting. The sensor can be misadjusted or have dead spots in the sweep that can cause "hunting".
02-26-13, 07:48 PM
#3
Normal operating temperature on the S4 temp gauge should be 1/4th to 1/3rd at the most so you're not encountering anything wrong here.
The TPS is at the front of the throttle body. Has three wires from it running to a connector about a foot away. One of these wires is Green/Red. Wire runs to the ECU and receives this signal from the TPS. W/the car as hot as possible ( 30 minutes of driving time), and w/the key to on, measure the voltage on the this Green/Red wire (again, w/key to on and car as hot as can be). Voltage should be 1 volt DC. If not then adjust the TPS screw (flat head screw, one inch in length, surrounded by a spring, and part of the throttle linkage resting up against the TPS plunger).
The TPS is at the front of the throttle body. Has three wires from it running to a connector about a foot away. One of these wires is Green/Red. Wire runs to the ECU and receives this signal from the TPS. W/the car as hot as possible ( 30 minutes of driving time), and w/the key to on, measure the voltage on the this Green/Red wire (again, w/key to on and car as hot as can be). Voltage should be 1 volt DC. If not then adjust the TPS screw (flat head screw, one inch in length, surrounded by a spring, and part of the throttle linkage resting up against the TPS plunger).
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