90 240sx Engine Troubles

[rocksteady_racer]

I replaced my fuel pump and ignition coil but I still don't understand what's wrong with it. I think it's the MAF because I unplugged it and the car was running the same way but I'm not positive. How do you read codes of the ECU on the 90 computers? I have a OBDII reader but that doesn't work does it? I'm trying to fix it right now. I'm going to hook up my fuel pressure gauge and see if that helps me any.
Also does anyone know where I can find the voltage requirements for everything? I was going to check all the sensors with my multimeter and the fuel pump - the fuel pump is supposed to 12vs right?

The symptoms:
Motor keeps dropping off at idle - it bounces up and down from 500 to 800 rpm.
Also it bogs really really badly.
Even at full throttle it will reach 3000 rpm at most.

I have a suspicion that's the O2 sensor since I've never replaced it. But would that cause this symptoms?
Or maybe the MAF but I have another one I can try and since I unplugged it and it ran the same way I figured that might be the problem. Thanks in advance for all your help.
I know I sound like a noob but I just can't get anywhere with this and it's driving me insane. I was thinking maybe the fpr blew, would that be the same symptoms? I have an extra one if that's the case.

Or maybe the back line. Is there anyway to replace the rubber fuel lines in the back without dropping the tank all the way?

[rocksteady_racer]

When I swapped the pump, one of the lines seemed stretched maybe that's the problem. So I'm going to swap the back lines out tomorrow and hopefully that fixes my problem. Do you have to drop the tank to do that or are they right there behind the tank, clearly visible?

[SidewayZ-s14]

You don't need to drop the tank to change the fuel pump.
I've had a VERY similar problem to yours...Was my fuel filter.
Try purchasing a new fuel filter. Did the trick for me :]

GoodLuck!

[rocksteady_racer]

Yep I just put a new one in so it wasn't that. Thanks though. And I was talking about the rubber lines running to the fuel pump. I've swapped plenty of pumps.

[JohnnyDrfiter22]

Thats a sensor dude, your car is in "limp mode" I think on the obDI comps take a small screw driver and put it in the Port on the actual ECU itself turn it to left for 10 secs than to right and it should blink, count the blinks thats the code.

[rocksteady_racer]

O gotcha on the ecu code reading. That helps alot thanks. My guess is the O2 sensor then since it's the only sensor I haven't replaced unless my tps I got used blew already. Would a blown oxygen sensor cause the ecu to go into limp mode? Or would it need to be something else? Are you sure it's a sensor because it still hits like 3000 or 4000 rpm it just takes forever? And unplugging the MAf didn't make a difference so maybe I should try that first I have one laying around. Next I'll try unplugging the O2 sensor see if that makes it works better. And if it's not those too I'll check codes then replace the fuel lines in the back. I shortened the fuel line in the back a little because of tears in the front of it maybe that caused it to collapse inside or something. Well tomorrow I'll try all those things and tell you what I found out. Any more advice now will be awesome.

[rocksteady_racer]

OK. So I swapped in a new Oxygen sensor and that did nothing. So I threw in another MAF I had lying around and that did nothing. Also I checked the fuel pressure from the filter and it's a flat 40 psi from the walbro? Is that correct? That's with or without the vacuum from the fpr attached. I figured it doesn't change from the pump just the fpr right so I wasn't too worried about that. I think it might still be the FPR but...

New Symptoms:
Car used to bounce idle from 500 to 700 then bounce in idle alot. Now it idles at a steady 1100. So my guess now is the TPS Sensor, right? I just ordered a new one and gotta wait three days for it so I hope that's it. That's the last sensor I have left to replace. If it's not that, the only other thing I can think of is the FPR but that wouldn't screw with the idle would it? It's running really rich by the way with grey smoke coming out the back - crazy rich and misfires at high rpm. My friend said it might be the cat going because it smells like rotten eggs but I figured that was just from it being really rich? I have another exhaust and test pipe I need to install but I wasn't in a rush unless that could really cause these symptoms. I would think it's the cat if it had problems not at idle but since it idles steady now compared to the bouncing idle before my guess is the tps sensor at the point. Any help would be greatly appreciated. Still low power through the band including low and high rpm.

[Sileighty_85]

yeah O2 sensor has nothing to do with that.

Sounds like a vacuum leak check all hoses for cracks and make sure all unused vacuum ports are capped off.

Also inspect the intake pipe for cracks and holes.

[rocksteady_racer]

Vacuum leak could be it. I can't see anything that's leaking though. I checked all the lines and they look fine. Could it be the old emissions equipment might have given out causing the vacuum leak? I want to remove that stuff anyway just haven't got around to it.

[HS13KLS]

like everyone said its a vacuum leak..

clean your IACV its the smaller on the intake.

other than that..
get some crc cleaner and clean your MAF.

so if you floor it..does it sound like its on a 2 step?

i check all your wiring for the maf too.. but i cleaned my iicv and it helped.

[rocksteady_racer]

Yea if you floor it I've gotten it up to maybe 5 grand in idle. Then it drops to about 2 or 3 grand under load. It definately sounds has an audible pop at high rpms. And low RPMs the idle is very cranky. I tried three different MAF's and none of them helped so I'm pretty sure that's not it. I will check the IACV and clean it tomorrow. Think the gasket on it might've blown or something? Hopefully that might help. I got a new TPS sensor just for peace of mind since both of mine have 150k on them and I'm about to turbo it so I wanna make it run clean before I take the time and effort to rebuild it and strip the emissions controls off. The MAF is stock. I was going to check it with the multimeter to make sure it's getting the right power too but I think since I tried three of them I had that's not the problem. Do you have to remove the IAC to clean it or can you spray something in it? Or do you guys use sea foam and suck it directly into it? Confused about the cleaning process. Only vague info about it online and I don't feel like taking it off yet.

[rocksteady_racer]

So far I've used a 3/4 bottle of sea foam in the idle air control valve. It smoothed it out a lot but it's still a little twitchy. So I guess it's the idle air control valve. I'm going to throw in the new tps sensor and I cleaned my maf and am going to change the plugs since the seafoam probably fouled them up. Almost got it...

[rocksteady_racer]

Ok so I swapped plugs and cleaned the idle air control valve with seafoam and cleaned my maf. Still runnig weird. While I was swapping plugs, I read them. The first cylinder seems to be the problem. Maybe the injector is goin on it? All other cylinders had charcoal black cylinders , running too rich I'm not concerned about right now. However the first cylinder plug was weird. The side electrode is black on the inside towards the center electrode however on the outside it looks brand new. On the center electrode, it is black with white markings on the tip of the center electrode. The insulator tip is white with werid burn marks only on one side of it. Could this be the injector or should do a compression test on the cylinder? I have new 550's to install but need a couple more fittings for my FPR.

[soon2bs13]

have you checked your fuses?

[chrissyPOO]

Replace your Injector(s)!

Same thing happened to me. The first one by the front of the car was like...cracked
i just went through the same situation about 3 days ago!


I know the FSM has the resistance for injectors, so...

[rocksteady_racer]

Yea I replaced the injector. Still having trouble with power loss. I think it fixed that cylinder though. I think the other problem is either the IAC or the TPS sensor. I'm getting a new TPS sensor tomorrow. If it's not that it's the IAC, I ran a whole bottle of seafoam through it and it made it a little smoother but my idle is still bouncing(500-700RPM) all over the place before warm up. Then when driving warmed up it idles at 1000, then 1200, then 900, it's pretty eratic. So it's either the IAC or TPS I believe. I found a faq on 240sx.org on how to check the IAC so I'm doing that tomorrow to make sure that's not it. Or maybe I have to remove the IAC valve all the way to fix it. I've heard a couple people having that problem. I'm surprised a whole bottle of seafoam running through it didn't help that much so which makes me believe tps sensor. Or I have loss of compression in the first cylinder which I hope isn't the problem. When I do check the compression, if it's just loss in one cylinder and that means it's not the headgasket than what could it be?

[nissan-fanatic]

Idk if this thread still gets looked at but wat ended up being the problem?