1990 240sx bogging problem

[WESIDE]

Just want to say this site is awesome and full of great information. I have been having this frequent problem for some time now and cant figure it out. I am driving about 75 mph or so and rpms are at about 3500 or so. When I start to go up a grade it will bog like I let my foot of the gas. I get no pedal response until rpms drop to 3000. This also happens sometimes under heavy acceleration, high rpms, in 3rd and fourth gears. I read a topic about a possible chassis ground and will check that out. But I have replaced fuel pump, tps sensor, plugs, wires, cap, rotor, fuel filter, o2 sensor, and more. Can someone please enlighten me. Thanks

[NateDogg]

Clean all engine grounds especially the one on the back of the head to the firewall.

[WESIDE]

cleaned every ground that I could find and stll the same. Also realized that it bogges in 5th gear going up a grade at 3500 rpms and doesnt come back until it drops to 3000rpms. Also, my odometer and speedometer doesnt work but all my other gauges work if that helps any........

[NateDogg]

These RPM limits sound like a MAF fuel cut. Is your MAF getting the right readings at idle? Should be about .2V with the key 'ON' and about 1.1V with the engine idling at ~750 rpm.

You can also try unplugging the speed sensor connector.. It is a black cable that should be near the back of the engine on the transmission, intake side.

[smokin240]

try cleaning you MAFS with some carb cleaner or maybe even replace it. Does it run fine for awhile then bog down after warming up? If so you might also try your coolant temperature sensor, about 10-15$ at autozone.

[WESIDE]

cleaned up the mafs yesterday. didnt look that dirty but did it anyway. Where exactly is the speed sensor? back of motor? side of transmission? by just unplugging this will my car still run... is it needed to send info to my cpu in any way? Oh yea, coolant temp sensor was replaced bout 6 months ago for a bad idle and hard starts when the car was warm.

[Kenrik]

my 240 bogs sometimes in first gear. 3500 rpm at 75mph is off for 240s mine runs 3500 rpm at 80mph on the dot, that's stock anyway.

[unsoshabl]

ok mine does the same. I cant past 5000 rpms in first or second and goes down from there in each gear there after. It has to do with your hud not working. Once in awhile when my hud works, I can get full redline in my gears except for fuel cut at the cut off speed of 112. I know it sounds wierd that your hud would affect it, but somehow it does in mine.

taking for granted you have hud, here is a site of how to fix your hud. I am going to attempt it here in a couple weeks, or I might just go analog.

http://multi-index.myonlinesit...o.htm

[WESIDE]

I dont have a heads up display on my 240. But I do know that my analog speedometer doesnt work. sometimes it bounces from zero to 115 and back. It really flips out sometimes. Maybe this could be why im having a similar problem. Any suggestions???

[MAKAKO]

he heads up has nothign to do with it.

i'm having bogging with my motor as well. but. i think it's somethign different. at times i have throttle response. then it gets hott and i have nothing. so i bought another 12inch fan. but now she is temperamental with the throttle. whenever i press on it she bogs adn dies.. why does she not liek me?... i also ended up removing everythgin the motor does not need. as far as to make this more simple to work on.

yesterday i took her out for a spin when i was confident that she kept adn idle. i rode 1st over a spee dbump adn slamme d2nd with the throttle at WOT. scarred the **** outa me. she was faster than expected. i feel that if i can get it responding the way it should it will be one fast 240. for stock.. i'm willign to pay anyone down here in south fl mismi. to help me with this . if you get it running i'll spot you a few hundred. its' been kickign my *** for teh past 2 months.

[NateDogg]

Hey why don't you read my post up there about unplugging the speed sensor. You odometer wont work but it may help with the bogging while you get a newer used gauge cluster.

[WESIDE]

I have a cluster off a 91 dohc. swapping this out might cure my problem?????????

[NateDogg]

Well if the speed sensor circuit is all screwed up and the computer thinks you're going 108mph (fuel cut) but you're really only going 35mph and it cuts out...then yes it can cure your problem.

OK After researching a similar problem on freshalloy a long time ago I found that a member had a similar problem. He wasnt getting enough voltage at the fuel pump causing the engine to run lean and the ECU pulling back timing. You may want to check the voltage you are getting at the fuel pump or just ground the pump to the trunk area instead of it running through the stock voltage regulating system which lowers the voltage to keep the pump life up. Sometimes when that fails you can run lean and the engine will pull timing.

Here is the link: http://forums.freshalloy.com/u...14487

You may also want to pull your codes and check for a Knock sensor malfunction.
Modified by NateDogg at 11:59 PM 5/1/2005

[nissilvat]

hey that ground u r talkin bout, the one from the back of the head to the firewall, is it on the drivers side of the car or the passengers?

[WESIDE]

drivers side , from the block to the firewall, right by the brake lines

[NateDogg]

WESIDE: if everything checks out ok check out the MAF. Check the voltage on the Maf ground from the terminal on the connection to the ground on the intake manifold. Should be less than .2V drop. I would add one anyway. They are known to go bad.

Only other thing I could think is the knock sensor circuit, or large vacuum leak.

[unsoshabl]

alright check it out. We had a Tech Day here in Phoenix, and a master at electrical helped me out.

The cure for my problem of fuel cut at 5000 rpm's was disconnecting the 5th gear sensor. It is located on the very front of the engine bay on the passenger side. it is a blue and yellow wire that is in a harness there. just pull the harrness apart and pull out the white center piece. then take a paper clip or something in similar size and push it in the whole where that blue and yellow wire is connected to release that wire. once the wire is out tape it up and put the other stuff back together. now my vehicle still fuel cuts at 5000 in 3rd gear and up. This could be the neutral sensor which is the green and yellow wire. I am going to test this out in the next few days and I will keep you posted.

give this a shot. if it doesnt work, I really dont know what to tell ya.

[WESIDE]

I have fixed my problem. It was my speed sensor in the back of my odometer. I just happened to have a 91 that I have been parting out. Swapped them and it hasnt given me any trouble for like 4 days now

[tiger]

hey, I just ran across this thread searching... my ecu is giving me 2 codes.. ignition signal and vehicle speed sensor...my car kind of crapped on me when I was going down the road.. in the end, it would idle and I could drive about 10mph but it would not even go up the slightest hill. Thank goodness it got me about a quarter mile from home so my sister towed me back. When I try to rev it.. it sounds horrible, like a bogging, dog growling underneath his breath when you're trying to steal his bone... it doesn't really rev at all.. do you think my speed sensor crapping has anything to do with this?