So, a perplexing issue.

[Alisaihin]

Alright, I've searched high and low for answers on this, but nothing seems solid, concrete, or well-defined, so I might as well list off what I am experiencing to the T.

I, about a month ago, got myself a well-used 1990 Nissan 240sx. Practically bone stock except for an exhaust (it was already on there). Now I knew when acquiring it, that it'd be a bit of work. And I have most all the kinks worked out or know what to do to work them out except for one...

Now, at part throttle, the KA24E will rev as high as you want it. But when you put it at Wide Open...is where it gets kinda strange. It won't rev past, on average, 4000 RPM's. It'll vary some, anywhere from 3400-5000. Now, it's not just dying out...it's like I hit a cut-off. When I hit a certain rev, unless I back off the throttle, it won't refire until about 2500 or so. I've ran through diagnostics, and I did pick up a code 11, for Crank Position Sensor. I cleared it and it hasn't come back (Didn't fix the problem, to my dismay), but I plan on replacing that...juuuuuust in case. Also fuel pump is DEFINITELY working as during part throttle it's pretty peppy (It better be, replaced the exhausted factory pump with a Walbro 255, boy what a difference that made!).

Far as I'm concerned MAFS and TPS are working (tested both a couple times). And I know if MAFS was a dud I would be getting killed at 3500 consistently. 5th gear switch is functioning as intended (unplugging that didn't change a damn thing). I've heard the VSS can be a prime culprit in this...but diagnostics showed it normal, and I don't wanna replace sensors willy-nilly here (That and I think the speed is pretty accurate-I've had cops tailing me at 25 mph in a 25 zone and nothing...and cops here can be pricks about speed), that and my speedometer doesn't have glitchings out or nothing. Seems to work just fine.

Any suggestions would be helpful so I can narrow down my searching and avoid blowing hundreds on this, especially since I have a little vacation planned with my beau and wanna save up for an eventual RB25 swap (though from how this motor keeps making me WTF all over the place I just don't know).

I -do- have a leaking valve cover gasket that I intend on replacing once I get the funds this Thursday. Doubt it has anything to do with that but from what I gather there are vacuum hoses connecting to the valve cover for some odd reason (My 01 Elantra, the daily driver, doesn't have that hence me being perplexed).

Hopefully this is enough information to help you guys help me because I've been pulling my hair out over this since I got this thing...

[blkvrtswp]

Focus on ignition: 1) spark plug gap; 2) grounds; 3) plug wires & coil condition.

My guess is your spark is not strong enough and is getting blown out at higher rpms.

Good luck.

[Alisaihin]

Focus on ignition: 1) spark plug gap; 2) grounds; 3) plug wires & coil condition.

My guess is your spark is not strong enough and is getting blown out at higher rpms.

Good luck.

Sounds reasonable, I can give it a shot. I know it isn't the plug or wires-both are brand new (I replaced them with good stuff, NGK yeah!), so I guess it's time to break out the multimeter and check EVERYTHING. After all...this is a 24 year old car, some wires are probably s*** out.

[blkvrtswp]

Did you gap the plugs? They can be WAY off straight out of the box.

[Alisaihin]

Did you gap the plugs? They can be WAY off straight out of the box.

Gapped and everything. Frankly I think the car needed new plugs and wires, ran smoother after the replacement.

So, I went in and did a little poking with my multimeter. It seems the ignition coil harness itself is fine...it's recieving proper power and everything (harness connector is recieving 12V as per FSM. That leaves me...the ignition coil? Unless the dizzy's input terminal is bad...

[blkvrtswp]

Yes, I would try a new coil for sure. Weak spark from a bad coil is not uncommon. Hopefully not too much money - in 18 years of playing with 240SX's I have not ONCE had to buy a coil ha ha ha! (SR spoiled here....)

[Alisaihin]

Yes, I would try a new coil for sure. Weak spark from a bad coil is not uncommon. Hopefully not too much money - in 18 years of playing with 240SX's I have not ONCE had to buy a coil ha ha ha! (SR spoiled here....)

Well, in my case the first owner had it for 20 years and used it as a daily (140,000 miles, not too bad for age but still...). So I guess it wouldn't be a shocker. Ill see if I can't pick one up sometime and throw it in.

[waxdnuggz]

Definitely sounds like a coil. Seems like the spark is getting blown out somehow. I've had a problem with a coil on my only sohc 90 and that's almost what happened except it didnt 2 step on me. It just had way more acceleration on half throttle then on full throttle. I changed the plugs and wires and fuel reg and coil. I doubt its the fuel reg tho for your case. I changed mine because I was having a hard time starting it after it ran down the highway for a bit

[Alisaihin]

Well...new coil put a little more pep in the 240's step. I was able to spin the tires during a U-turn in second gear...(I made a last second decision to turn around and felt cheeky), which I couldn't do before...but the underlying issue still is there.

So, a small victory, but the war still rages on.

[Alisaihin]

So, since I'm in Des Moines this weekend I decided to go to the Nissan Dealer there, Hummer's Nissan (Who after this visit has my admiration, they're exceptionally helpful, even if I'm not having to pay for their assistance!), and directed me to a service guy who has a 1993 240sx with a KA24DET and has owned it for 10 years! He was saying that two very likely things might be my issue-Dizzy's going bad and can't keep up the load (He says he's found his particularly prone to failing, though he drifts his with an MSD Ignition coil so that probably doesn't help longevity for him-that and since I found a code for crank position, which is integrated as I found, might as well just replace the damn thing entirely regardless), or there's a nice dead spot in the action of the TPS causing the ECU to freak because it's not reading the voltage it should when I'm at full, throwing it in limp at WOT (He's found that sometimes along the action there's a burnt spot, typically, that does that. It just doesn't normally throw a code because under normal driving it just doesn't hit it.)...which may explain why it might only prove to do that under WOT.

Well, at least all this, you guys and my experience today is narrowing this b**** of a problem down into something I can purge from this car...

[waxdnuggz]

The tps sounds alot more like the culprit if the coil helped. Usually if the dizzy is bad then a coil change will result in no change. Test your tps its pretty easy and there relatively cheap to replace. ~50$ new. If you have an advance auto near you go on there website and buy it and select pick up in store there's an online coupon for 20$ off a 50$ purchase that i always use trt25 is the code and another code is trt41 which is 40$ off of 100$ it helps out alot.

[Alisaihin]

The tps sounds alot more like the culprit if the coil helped. Usually if the dizzy is bad then a coil change will result in no change. Test your tps its pretty easy and there relatively cheap to replace. ~50$ new. If you have an advance auto near you go on there website and buy it and select pick up in store there's an online coupon for 20$ off a 50$ purchase that i always use trt25 is the code and another code is trt41 which is 40$ off of 100$ it helps out alot.

It's worth a shot then. A discount makes this rather worth it...

So TPS is now on order. Excellent!

[Alisaihin]

Well, I may as well make this my general, "fixing time/build/restore" thread because I'd rather stick this all in one thread than swamp the forum with threads over time SO

I may as well mention a couple updates:
-Next paycheck, provided the new TPS does well and my little oil change is all that was needed to fix initial knock...I'm getting a welder. Because I need to desperately repair the frame. It's just bad.
-I found my engine may have been merely low on oil (what a shocker with how bad I found out the valve cover gasket was leaking...and had been leaking for a while from the looks of things), hence the initial engine knock. Just was having trouble getting oil to where it was needed. Regardless, I didn't just add some, I f*** did a full change. Because I'm anal and very prone to overdoing things (even if I don't think I am doing such a thing).
-TPS was sent...to the wrong address. Thankfully, it was merely my parent's house, and it's only an hour's drive away. This does mean I'll have to head into town tomorrow and pick up the sensor from their house. I'll throw it in and give it a whirl...if it's also the fix I've been desperately needing then I will declare that (for now) the 240's motor has been brought back to full running order. And thus will end Stage 1 of the 240's overhaul...

The welder is what Stage 2 will be all about. Buying a f*** of various steel pieces, cutting them up, and welding them to the frame and sheetmetal of the 240 in various places. I MAY wait until I can buy the RB25 before I do this-1. excuse to pull the KA24 from the engine bay 2. If I manage to sell the KA24 (for cheap, this motor is old and it's merely SOHC. Mostly to cover some of the RB cost). Pulling the KA24 before I do this will give me excuse to remove fuel lines and the like, too. I want this a fairly clean shell for when I hack and weld the s*** out of this car. I might also head to salvage yards to see if I can't pull off some more intact side skirts (or maybe just save for some aftermarket ones. I just wanna get rid of the s***, rusted out ones!).

Anyhoo, that's all for now :3

[Alisaihin]

New TPS...nada. It did nothing. But my idle is smoother...

Also fixed a knock. Valve Cover Gasket was leaking more than expected. Replaced gasket, change of oil and voila, no more knock!

Unfortunately, this does mean I have one last option...replacing the dizzy. Ehhhhhhhhhhhhh fuh. New experiences all around with one of these...

[waxdnuggz]

Its easy. Take the cap off and figure out which way the rotor is facing you dont even have to make it top dead center. Pull the distributor and put the new one in with the rotor in the same place turn it a little clockwise before installing because the gear is swirled and will twist the rotor slightly on install. If the rotor is in the same place your good. It cant be kinda close its either on point or its not. If your on the wrong spline youll be about +1" off maybe even 1.25-1.5 but it wont be small to wear your eyes cant tell. Then time it +20* done. It should be the 2nd to last mark on your crank pulley (2nd to last on the right) and make sure your gun is set to zero. MAKE SURE YOU FOLLOW PROPER TIMING SEQUENCE THERES PLENTY OF WRITE UPS

[Alisaihin]

Its easy. Take the cap off and figure out which way the rotor is facing you dont even have to make it top dead center. Pull the distributor and put the new one in with the rotor in the same place turn it a little clockwise before installing because the gear is swirled and will twist the rotor slightly on install. If the rotor is in the same place your good. It cant be kinda close its either on point or its not. If your on the wrong spline youll be about +1" off maybe even 1.25-1.5 but it wont be small to wear your eyes cant tell. Then time it +20* done. It should be the 2nd to last mark on your crank pulley (2nd to last on the right) and make sure your gun is set to zero. MAKE SURE YOU FOLLOW PROPER TIMING SEQUENCE THERES PLENTY OF WRITE UPS

Well, one last question...think I should just get a new rotor and cap, or just the rotor? Or get a completely new assembly? Getting just the cap and rotor (which the rotor is likely causing the issue) seems FAR CHEAPER but eh...I wanna get this right the first damn time.

Also, since I plan on replacing the radiator soon, I think a new alternator and water pump just in case might be a good idea...

[Alisaihin]

I'm about done trying with this motor. The ENTIRE ignition system is replaced now. Still...the same damn issue! (Though the rotor was in pretty sorry shape, the contact was burnt...the car runs MUCH smoother now).

Out of desperation I tried testing the MAF again. It works. 4th and 5th gear switches disconnected. Still the issue.

I'm not doing anymore big fixes. A couple more smaller ones. If those don't work I'm just going to pull this motor. I'm not throwing thousands into a motor I'm going to just yank out likely a couple months from now. This way I can focus more money on getting the swap (changed mind, not doing RB25, instead RB20...mostly because it seems more practical), and getting materials to sleeve out the frame rails. Cause I've about had it...

[waxdnuggz]

Have you checked your fuel pressure reg? What about the actual injectors?

[Alisaihin]

Have you checked your fuel pressure reg? What about the actual injectors?

I guess that'll be part of the work on my day off tomorrow. It does emit a white puff of smoke (Smells HEAVILY of gas) when this happens-ONLY when this "cutoff" occurs. And it doesn't smell sweet. That and when I changed the oil it looked like...oil. Nothing milky. So may as well.

[waxdnuggz]

Too much fuel will cause this usually puff of grey black smoke is fuel white is usually steam/water. Check your injectors. Search the proper way to do so as idk how to test sohc injectors

[Alisaihin]

Too much fuel will cause this usually puff of grey black smoke is fuel white is usually steam/water. Check your injectors. Search the proper way to do so as idk how to test sohc injectors

I might also test out vacuum, lack of it can apparently make FPR's go haywire and f*** up.

[waxdnuggz]

If you had a vacuum problem you would know it. The car wouldnt idle for s***. But its worth a try. Im leaning alot more towards a fuel problem. Like too much of it some how. If youve broken down all the ignition and it all tests right then next would be fuel. Test before you replace that way you DONT dump $ into a short term motor.

Rb20s sound amazing and yes are cheaper. However 1200$ is not alot of money and thats about the difference between having a solid 20 vs a 25.

[Alisaihin]

If you had a vacuum problem you would know it. The car wouldnt idle for s***. But its worth a try. Im leaning alot more towards a fuel problem. Like too much of it some how. If youve broken down all the ignition and it all tests right then next would be fuel. Test before you replace that way you DONT dump $ into a short term motor.

Rb20s sound amazing and yes are cheaper. However 1200$ is not alot of money and thats about the difference between having a solid 20 vs a 25.

I literally...have replaced every ignition component...and even tested the harness that runs up to it. So I'm leaning towards fuel now.

I think something might be starving the motor of fuel at WOT. Even when I still had that old factory fuel pump (which was wheezing) it was doing this.

[Alisaihin]

The issue...is a f*** exhaust restriction. I had someone else look it over, and they found other pecuilar things (like the timing was off, which doesn't shock me at all with how lumpy it ran), the diagnostics connector...was shoved under the dash for some bizarre reason, and that people have been trying to weld on the exhaust in various places. Which brings me to the root cause...

I have done further burrowing myself, and have removed the exhaust from the catalytic converter back. All that did was make it loud and smell (which I expected), but thing is...it's rather upstream. I know it is the exhaust because when the whole thing was unbolted from the block at the manifold it revved high. Which means that I'm probably going to, when I actually get free-time (I'm working almost 60 hour weeks for the forseeable future. f*** me) head someplace to see if I can't bum some old exhaust from another KA. Because until I do...this thing will just cause me trouble just due to the noise. And how it might gas me out.

[Alisaihin]

SO. I made a thread a while ago about how I was having odd issues, hm? Where at WOT I couldn't go past 4000~ RPM. Well...I've replaced the stock manifold/downpipe as suggested and it's still doing it.

Original thread here: so-a-perplexing-issue-t590558.html

I feel like I'm running out of options. I have a new O2 sensor now (was necessary as the old one was FROZEN into the old manifold big time), as said before MAFS is great, ignition is practically brand new, I have new fuel pump and filter, and FPR and injectors both check out. New, properly calibrated TPS in place...so needless to say I'm wondering something...

Would a partially stuck open, or ill-functioning EGR or BPT valve cause this? I wonder if something in that system is misbehaving and simply causing too much exhaust to be dumped into the engine (I know the BPT is actuated by exhaust pressure, and should only allow EGR to operate from about 2000-3500 or so, ergo, while cruising under light-throttle applications). I know the AIV isn't malfunctioning cause...well...needless to say I accidentally busted up the line for it when removing the old manifold (oops) so it's blocked off for now.

A bit of extra info-when I unhook the vacuum line from the BPT to EGR the car runs really ragged, even if the nipple is sealed off. Would this be normal? I've looked everywhere for answers on this...

Anyone got some ideas to throw at me, or maybe see if my theory is even remotely valid?

[Rogue One]

Per NICOclub's ToS, please do not create new threads for existing topics.

Thank you.

[AZhitman]

I'm gonna read back through this one - bear with me, I want to take my time on it... and maybe pass it along to get another few sets of eyes on it.

Hang tight, Ali - don't give up yet.

[rotorimp]

Sounds like you pretty much have the ignition sorted...I have a feeling that it is fuel too. Have you changed the fuel filter (I didn't see it in there...could have missed it). From reading it sounds like the car is pretty rusty....Have you cleaned...down to bare metal all the grounds? MAF, TPS, ECU, Ignition...all need specific voltage so re-check all grounds and positive terminals.

[Alisaihin]

Sounds like you pretty much have the ignition sorted...I have a feeling that it is fuel too. Have you changed the fuel filter (I didn't see it in there...could have missed it). From reading it sounds like the car is pretty rusty....Have you cleaned...down to bare metal all the grounds? MAF, TPS, ECU, Ignition...all need specific voltage so re-check all grounds and positive terminals.

Yeah, this car is a bit worn but that's why she's a project...

Checking all grounds wouldn't be a bad idea in the end. Though something I've finally noticed now that I got it back running as usual again-when it hits the cut its apparently backfiring into the exhaust as it's dying (I've heard that enough before to recognize THAT sound ). That and the smell of fuel really makes me think it's not burning things right...

And yes, fuel filter is replaced.

Also sorry for that Rogue One ^^;

[Alisaihin]

New information! I think I might have a bad FPR. Hear me out on this.

I recently, if mostly to make this motor a bit easier to diagnose, pulled off most everything vacuum operated that isn't used to help the car run. Which means, versus the little rat's nest on the back of the motor feeding vacuum to the FPR, it's running straight off the manifold.

Now, the car is acting like it's what I believe to be flooding-it idles horribly, sputtering, spewing smoke out the tailpipe. It struggles to get started (I need my foot in the throttle to get it to live after a start), and it's shaking bad.

Would running the vaccum for that directly exacerbate a pre-existing problem, considering there's fewer potentially leaky lines and sources sucking the vacuum from the FPR? Vacuum is so new to me...as my Elantra has significantly fewer vacuum operated things and uses different sensors so it isn't as keen to screw up.