low/mid range bogging, sputtering, hesitation.

[rsmithdrift]

K, so my car has been running crappily for quite some time, I've done alot to try and fix it but to no avail.

If the car is in neutral it seems to run fine, unless you go WOT from idle and then from 2500-4000 rpm the car misfires horribly and gains rpm VERY slowly. If you let off to about 1/2 throttle, the car will actually quit missing and gain rpm normally agian.

If you trying to accelerate however... you can't give the car more than 1/4 throttle or it will bogg out and start sputtering, missfiring, hesitating bad untill you finally make it to 4,000rpm at which point the power comes back to normal.

First thing to check is the codes... code 44 all clear. Crap.

I was thinking MAF, so checked the voltage but it is perfect. I even re-ran the wiring for the MAF just incase there was a bad wire somewhere. No difference. MAF is perfect.

The CTS is perfect, the 02 sensor is perfect, the TPS is perfect, and the voltage on the injectors is perfect.

I was thinking fuel system so I replaced the fuel filter and pulled the pump to check the sock, all good. Didn't make a lick of diference.

I decided to check the ignition, spark plugs are new NGK, cap/rotor are good, coil is a year old and good. Wires are a year old NGK, all good. Ignition is all good.

The only thing I could find that would get rid of the hesitation is putting on my old broken MAF meter that reads 10v at idle, and ofcourse the car runs pig rich to the point of pluming black smoke and gets 14mpg and wont idle with that configuration. MAF should read 1.2v at idle like my good one does, not 10v.... <IMG NAME="icon" SRC="http://images.nicoclub.com/forums/image ... es/eek.gif" BORDER="0">

I don't know where else to turn, I'm at my whits end.

What ON EARTH could be causing this. I can't even make it up Signal Mtn it's cutting out so bad.

*Edit* Check my newest posts. I fixed the cars problems. I had a bad fuel pump.
Modified by rsmithdrift at 2:33 AM 2/12/2010

[mcusmc007]

Try checking the groung from battery to chassis. It should read below 2 OHMS. If not then groun from the firewall to the block on both sides. There is a page to detail this in the 240sx technical page under hesitation. Good Luck and let me know if that might have fixed it for you.

[Vegascorbin]

Checking the grounds is a goods idea. The first thing I thought of is your fuel pump. I know you did a visual on it but hav eyou checked the pressure it is puting out?

[mcusmc007]

one more thing i forgot to add try switching to a hotter spark plug. Once upon a time i had the same problem. Well still, good luck.

[moyea]

I've got the same problem but grounds don't seem to be it. Car doesn't do it when I unplug the O2 sensor (brand new sensor).

[Mikesmax]

Check the back pressure from your exhaust. Your converter may be clogged from when you had the bad MAF sensor dumping fuel ito your exhaust

[fresno240sx]

maybe check timing? thats what happen to me, check timing and put it on t.d.c. this work for me and my car did not bog anymore...

[moyea]

It was injector #2 that was not firing. Whoever had this car before me installed venom injectors which are s***. I replaced all the injectors and the problem is solved. I did notice the the O2 sensor is inline with #2 cylinder only, that doesn't seem like the most logical place to put that.

[rsmithdrift]

FYI I finally fixed my cars problems. Turns out it was the fuel pump all along. It was putting out 15psi when it's supposed to be making 44 psi.

The low fuel psi was causing the car to run lean as f_(% making the car cut out and sputter horribly. Apparently these motors are tuned to run leaner untill 3500 rpm and then go into blind mode after that. Which is why it would still run (no power) but still run from 4k to redline.

[vmiramon69]

FYI I finally fixed my cars problems. Turns out it was the fuel pump all along. It was putting out 15psi when it's supposed to be making 44 psi.

The low fuel psi was causing the car to run lean as f_(% making the car cut out and sputter horribly. Apparently these motors are tuned to run leaner untill 3500 rpm and then go into blind mode after that. Which is why it would still run (no power) but still run from 4k to redline.

i was about to tell u that ....but i read and nevermind...glad u fixed it.

[my240sexy]

hey bro im having the exact same problem. just how u explained it. at first it wasnt so bad. but now it backfires, hesistates and boggs like crazy if i go full throttle passed 4000. im running the stock fuel pump in my 240. were u using the stock one before and just replaced it with a walbro 255?

[rsmithdrift]

hey bro im having the exact same problem. just how u explained it. at first it wasnt so bad. but now it backfires, hesistates and boggs like crazy if i go full throttle passed 4000. im running the stock fuel pump in my 240. were u using the stock one before and just replaced it with a walbro 255?

Exactly. Walbro 255lph all the way. Cost 88.99 shipped from ebay.

I'd say I've gained 20hp over the factory fuel pump when the car was new and ran perfect. It's just too weak to keep up even with stock n/a ka.

It runs so good now I'm afraid to power shift into 2nd gear because the last time I did it broke sideways and I almost went off the road gathering it back up. I have n/a ka24de btw. 248/232 cams with ignition timing set to 25* with intake and stock exhaust and electric fans (no more fan clutch). And Megan coilovers of course. I've ridden in my buddies 89 SR20DET 240sx hatch and it didn't pull that hard. It's flat out scary fast now.

[my240sexy]

damn ur saying u were faster than an sr20det? i have an sr20det and just fixed the problem. i just changed out my cas since i had an extra one just to see if it would do anything and it did haha. i shouldve done it before. thanks for the quick response ill have to get a 255lph pump now

[my240sexy]

oh btw how did u measure how much psi ur fuel pump was putting out?

[rsmithdrift]

damn ur saying u were faster than an sr20det? i have an sr20det and just fixed the problem. i just changed out my cas since i had an extra one just to see if it would do anything and it did haha. i shouldve done it before. thanks for the quick response ill have to get a 255lph pump now

Well I called him up and we raced last night. Just cause I was curious. I'm on his a**. lol. He put a z32 MAF on it and rebuilt the turbo since the last time I rode with him. But yes his car is *slightly* quicker than mine now. (we raced ~ 1/4 mile on a 3 lane one way street with no traffic btw) My front bumper is at his back bumper at 100mph ~ 1/4 mile. My car is 6 second 0-60, so is his.

Anyways, I took it to a nissan specific performance shop and they put an inline fuel preassure gauge on it to check it.