i have a 90' 240sx that is bone stock, i love it. been driving it the last 5 years. sometimes it takes a long time of cranking to finally start. recently it flooded out. i checked spark; it was good. the vahicle has newer plugs,wires, rotor and cap. the fuel pressure is around 45psi. now the problem is getting worse and it's doing it more often. i also notice the engine stumble when i quickly press the accelerator, this is accompanied by black smoke puffs. sound like a bad MAF or TPS? what's a good thing to test for? and what should my readings be?

 

1)your fuel pressure should not be that high unless your vaccum is off the FPR... stock fuel pressure with vaccum is in the area of 38psi

also if you are having to crank that many times, you may want to just check the connections ( rust, frayed wire etc) with-in your ignition system for wear and tear. these things break down over time. your plugs in all can be awesome but if the wires are bad, you will not get the best connection/ any at all..

I would run a ecu diagnostic also becuase your CAS ( Crank Angle Sensor) could be on its last leg. right before a CAS goes completly out you will get the symptoms that you are having right now.

you want to test the voltage and resistance for the TPS and MAF.

but your TPS would have the effect of an unstable Idle. and you would be able to really test that by allowing the car the idle and measuring the resistance and voltage.



2) the flooding is occuring becasue when you are cranking, fuel is being injected. the black smoke that you are getting is raw fuel at an result..

Ill put diagrams up after work

(MAF)


(TPS)
you want to measure between ground and signal

while moving the Throttle Body Plate from close to WOT
your voltage should be as low as .4v and as high as 4v

 

Dont forget the temp sensor, if thats bad the ecu might flood the engine thinking its a different temp.

 

Moving this out of the "Engine Management" section and into the "Naturally Aspirated" section.

 

thanks for all of your suggestions. i went to the library and got some info on pulling flash codes out of my ecu. the codes stored were for coolant temp and o2. I then checked the connections of both and found corrosion inside the connector for the coolant temp sensor. i cleaned out the sensor connector end with battery terminal cleaner and electrical contact cleaner and blew it out with compressed air. then i cleared the stored faults out of my ecu at the ecu. i started it multiple times hot and cold and it seems to be starting fine. my idle issue seems to still be jumping around. I think the first step should be to perform the o2 sensor test as part of the ecu diag test plan. does this sound good? also; anybody know where to find wiring diagrams online for this thing?

 

hey ill get that for you but in the mean time you should get familiar with the fsm allll of your answers are there.. just google 240sx+FSM and you will need Adobe reader to see it

 

Replace the O2 sensor, then clean the IACV with carb cleaner through the IACV hose located on the intake. If the idle problem is still persistent check the clutch fan, and the electrical(spark plugs, wires, rotor cap) that should solve your problem.
If not check ecu codes again.....

 

^ i would do that, but also change the temp sensor.

 

What you said also, "the temp sensor", they do show wrong readings without ever throwing codes sometimes....
The temp sensor can cause idle to fluctuate because the A/F ratio at idle would constantly change to variable temperatures...

 

I'm having a similar problem with AIR/FUEL and MAF

I was being a retard the other day cleaning some stuff on the air filter and box on my 93 240SX 5 Speed, SE

So when I was removing the MAF I unscrewed the 2 small screws on the top of the MAF near the connector and broke the connection taking it off, ( I didnt know how to get the clip off, but now I do! )

I cranked the car after trying to fix it and the connection was bad and the car was running like crap and dying at idle, I only ran it for about 30 Sec. Obviously dumping way to much fuel into the motor. Naturally as I broke the MAF and it was running without one.

Also when I playing with the connection that I broke with the car on (ON, but not running) i could hear the connection clicking when I moved it back and forth, however the clicking sounded like it was coming from somewhere to the left. Like click on then off, So I take apart the MAF and soder the connectors back to working order.

I install the old MAF back on the car, start it and it doesnt die at idle however it does run like crap (RICH) still and doesnt rev over 2000, there is also a large amount of smoke coming from exhaust, smells like it's running rich. It also runs very very ruff and the motor shakes badly. I tried to let it run some of the fuel out but it didnt get any better after about a minute i turn it off.

So I buy a new MAF from a reliable source. Install it, Put BRAND NEW NGK Plugs in, start it up. SAME PROBLEMS! So I take it there is something else wrong. I check the plugs, Im getting plenty of spark, the plugs smell like gas badly so I know it's running rich.

I get no check engine lights. I tried to see if I could hear the clicking noise again by unplugging and plugging the clip from the MAF. I cant get it to do that.

I also took the battery out for about 3 days waiting for my New MAF so unless I need to reset the ecu another way... I thought that would reset it.

PLEASE HELP ME I'm NEW TO NISSANS!