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View Full Version : 1990 240sx Bad mileage and idle


jerryk
08-06-2008, 10:21 PM
I have a 1990 Nissan 240sx hatchback with 183,000 miles. The compression results 155-160 dry range and only 2+ on the wet test. My gas mileage is very erratic and I have conducted numerous tests. Highway at 60MPH the best was 20-23MPG stop and go city 14-16MPG. I do not think this is appropriate mileage for this car. I am on 17” wheels and a web calculator shows a small odometer error 59 miles = 60. The car on a test dyno produces very high levels of hydrocarbons but the rest of the pollutants were within specifications. It has a brand new Cat so the engine is really spilling gas. I have replaced fuel filter, injectors, spark plugs, spark plug wires distributor cap, rotor, temperature coolant and O2 sensor, and corrected ground weakness. The EGR has also been tested. The idle is 750rpm, but it cannot go 30 seconds without a stumble some more violent then others this alternates sometimes with an idle hunt between 650 and 850 rpm. The car is equipped with a wrapped stainless header, random flow cat and a Borla Cat back. It has a K&N filter on the standard intake pipe. I suspect the TPS and the crank angle sensor, how do I test them, or where else should I be looking? I also suspect an overly hot engine compartment because of the header and thinking of making a heat shield. I am getting ahead of myself; I had the idle and mileage problem before the upgrades. Which areas should I look at next and what test can I perform without replacing all fuel and emission components blindly. I want to get this car working correctly and I am investing money and time.
I have my original 240sx, rusted out bottom, parts car with 230k on it and I have swapped the MAF. Many engine builders I have spoke to, thinking of another SOHC rebuilt, say my mileage should be better.

Please do not use abbreviations or fail to describe the wire colors and locations for tests.

drftthatshit
08-07-2008, 05:27 PM
well dude i would start with the tps if you unplug it and it dies or falls on its face for like 4-5 seconds then its working you might have to set the tps sensor use a dmm and set the tps sensor at idle to 0.45V this should fix you idle prob as for you fuel millage i would start by checking for a vacume leak i know its shitty and theres alot of vacume lines but just look one maybe rotted or jus not hooked up anymore i hope this helps let me know

jerryk
08-07-2008, 08:40 PM
well dude i would start with the tps if you unplug it and it dies or falls on its face for like 4-5 seconds then its working you might have to set the tps sensor use a dmm and set the tps sensor at idle to 0.45V this should fix you idle prob as for you fuel millage i would start by checking for a vacume leak i know its shitty and theres alot of vacume lines but just look one maybe rotted or jus not hooked up anymore i hope this helps let me know


I need more information the vacuum lines I understand, the tps I do not.

Unplug while the car is at Idle? How do you set the TPS dmm is a meter? What lines can you do I tap be precise, give more detail?