'91 240sx -Starts but won't run...

[PMan_S13]

Well I just got done putting everything back together after replacing the valve stems and I have new problem (does it ever end?)..

91 kade, turbocharged, with the removal of some emissions systems, btw..

Anyhow, the motor will start and run without any problem for like 4 or 5 seconds and then it will slowly (about a second, i'd guess) idle down to 0 rpms. It starts again perfectly fine. I can keep it going if I jab the gas, once again it will stabilize for a few moments and then idle down to nothing. I've tried holding the pedal down to keep it alive, but it still won't work for more than a few seconds. It will do this temp idle at like 2000rpms at the moment, I don't know if it is because it's cold, or what, but that might be significant. I haven't been able to retime it yet of course, so the best it has is me eyeballing it up when I put the distributor back on. I've searched the engine bay several times in the last two days, I can't find anything unplugged or that looks wrong.

If I had to guess I would say it was either the a.a.c valve is stuck. Or I have some vacuum lines connected wrong. Both of which I haven't enough knowledge in except the basics. And I am quite reluctant to mess with needlessly.

Any help is appreciated...

[NISTECH]

set up the airflow meter so you can easily pull the connecotr off it quickly. start the car and once its running disconnect the airflow meter while its running and see if still does it. if it doesent something is wrong with the airflow meter. if it still does it check your pcv valve hose behind the altenator make sure its still connectoed as well as the brake booster hose.

[NISTECH]

hmmm also hook up a fuel gauge in the hose between the fuel filter and the engine see if it might be loosing pressure.

[PMan_S13]

Air meter is good and the fuel pressure is good. The line to the pcv valve is still connected, but I noticed some oil in the vacuum lines nearby.

I'm wondering if it could be shot. That little bugger is hard to get at too.

[PMan_S13]

Well, I've worked out some other issues but I am back to this one again...

I unplugged the AFM while it was running. It goes to a rock solid 2000. When I plugged it back on it died immediately.

I can still keep it alive by playing with the throttle a bit. I can even get it to somewhat stabalize at about 1000 rpms for about 10 seconds, but it still is a little rough and it always ends with the car dying with a jerk.

If you drive it around it is apparent that it isn't running right, it kind of jerks and stumbles even when you aren't changing throttle position.

I'm confused and tired from bleeding the darn hydraulic clutch..

[PMan_S13]

After some more tinkering...

The roughness I mentioned before seems like it might actually be the engine missing. Or at least it seems to be. It could very well be the effects of incorrect air/fuel, or very low idle air induction, or whatever the heck the problem is. It still seems to run alright when the maf sensor is unplugged but you can't add throttle, it just sputters.

As part of a "try anything" attempt we stuck a feeler gauge between the throttle body stopper and the (thing that the throttle cable attaches to.. can't remember at the moment) so that the car will get just a little bit of throttle on startup. It started up and revved to 3000 and then stabalized down to 2000. It didn't seem to stumble at all like how it does before. When the feeler gauge was removed it died immediately.

Is it possible that the stopper screw or the idle adjustment could have been knocked out of position? Is there a factory setting to return to as a baseline? Or is limping this to some mechanic looking more like a reality?

[NISTECH]

sounds like you have a bad airflow meter.

unplugging it is an old trick we use to determine if the meter is bad. You know anyone else with a 240 you can borrow a meter from to test it.?

[PMan_S13]

Hmmm, the only guy I knew with one moved away... I might be able to try the junkyard, I know they had an s13 at one point but it is pretty well stripped.

What would a bad meter be registering? Any ways I could further test it? With the car so modified I just want to work out one variable at a time.

[NISTECH]

at idle is what you need to measure should be around 1.2 to 1.4 volts.

[PMan_S13]

It measured about 1.45 at it's stumbling idle of about 900-1100 rpms. I'd venture to say that the element in the air meter is alright...

With the ignition on (but not running) it reads .0265 volts. Isn't it supposed to read .02 volts or less?

I also checked the ground wire at the back of the block. It reads 2.1 ohms. Couldn't find a measurement to check against, but that seems like a lot of resistance to me. Maybe a grounding problem?

Thanks for your help so far

[NISTECH]

The .2v or less applies to the ground wire off the airflow meter when its running not the signal wire you were reading. That reading doesnt sound to bad maybe only very slightly high but not to the point it would cause the car to die. you do need to check the ground circuit as well at idle.

[PMan_S13]

Well I need to go the store and get some stuff, but I figured I'd make a post on what little news I have now.

First off, I got the car running considerably better, not good, but much better. On cold start, it will start go to 2k for a sec then slowly idle down to about 1k-ish and then start to stumble. It wasn't even idling at all before. I was going to check the grounds and voltage readings but I'm out of batteries and the freakin timing gun is dead or something. All I did so far was add a new larger ground wire to the rear and found a small vacuum leak where two connections didn't mate up correctly.

The improvement is subsantial but not enough. I think this merely patched a far worse problem. Since I was at a dead end anyway I decided to let the car warm up so I could check it away from the cold loop. I had to sit and blip the throttle every now and then so it isn't idling enough for me to tinker with alone. With it warmed up the O2 sensor (I have an A/F ratio meter) doesn't even respond at 2k, so it is dead too. It doesn't idle at all when it is warmed up either. I noticed today that the boost gauge was responding slow, that's what lead me to the leak, but it didn't change after I found it. That makes me wonder if there is another some place.

So I'm off to get a new 02, batteries, and some carb cleaner to spray around and search for leaks. And some taco bell...

[PMan_S13]

Ok. Still not running right but here's some data...

The AF meter has the following readouts. Black Wire -with key on 14 omhs -with key on and 2nd ground wire 5.6 ohms -while running(unplugged harness) 2.6 ohms -with attached 2nd ground(unplugged again) 1.6 ohms

Black Wire with White line -14 volts regardless

White Wire -with key on .05 volts -at ~1k ~2k rpms ~1.3 volts +/- .2 (fluctuates a good bit)



Got the readout of the timing finally. ~25 BTDC at 1k rpms. There weren't any marks that far over of course, but I eyeballed it.

I also checked the spark plugs for spark, the gap, the connections, ground for the coil, new O2 sensor, checked the vacuum lines, checked fuel injectors, tried adjusting the i.a.a. up and down (only mild changes surprisingly), checked the intake for leaks, checked every electrical connection I could see. Drove it around the block, not fun. It kicks and pulls and stumbles pretty much the whole time.

With the AFM unplugged it runs at about 2k just fine, except for it trying to readjust every few seconds. But with the larger injectors being controlled though the AFM it runs rich and stumbles with throttle.

[NISTECH]

I wanna think you still have a vaccum leak somewhere. Is your 02 reading full lean at 2k rpm? I dont use the ratio sensor you use so I cant interpit what those readings mean. If it is reading full lean I am thinking its gotta be vaccum BUT the accel problem in conjunction with the lack of idle does indicate AFM.

[PMan_S13]

Well it doesn't seem to be reading much of anything, just sits at slightly rich. The A/F gauge isn't all that accurate a device anyway, but when it works it just bounces back and forth from green to red. But at the moment it just sits at green (it does this when it is cold).

I've thought it could be a vacuum leak as well, but as I have no emissions there are very few lines to check. I used a vacuum tester to pressurize the line for the FPR, Boost Gauge, SCV from where it attaches to the manifold. It held pressure. The 2 idle control lines seem to be fine.

I now think you were right initially. The AFM might be kaput. It just seems too fishy that it runs great (even with the larger injectors) when it is unplugged. It just sucks I have no way to test it before forking out some cash... o well, maybe a nico member will give me a break

[PMan_S13]

Update.

Got the new AFM installed. It starts up and runs great now. I drove it up and down my driveway (I have a long driveway) and it doesn't kick or miss anymore.

However, I am still having some trouble with the idle. On cold startup it sits at 2k, no problem. But when it starts to warm up it acts a little strangely. It stays in the range of about 1200-1600. It will hold for a moment then climb till it stops and slowly drops again.

Another and possibly linked problem is the O2 sensor is not reading at all. This is a brand new sensor with maybe 15 minutes run time on it. Possible that it could be a dud?

I may still have some air in the radiator giving false temp readings and I'm pretty sure I need to reset the ECU and my S-AFC2. Just looking for advice from someone with a lot more experience =) Thanks

[NISTECH]

hold the rpm at 2000 and watch for O2 response. It may be that its just not hot enough. if it still doesnt respong check for power to it if its a muti wire O2

[PMan_S13]

Well during it's warm up it runs at 2k. I let it warm up all the way, but maybe the exhaust temp just isn't hot enough. I'd imagine it would be designed with this in mind however...

It's just a generic bosch 02 sensor with a single wire.

[p00t]

if you have a turbo you dont want your timing advanced to 25 btdc... you will detonate very easily... make sure your knocked back to about 20 at max... lower if you plan to use higher boost (stock timing is 22btdc) i am asuming you have the KA motor as well... SR should be lower.. like 15 btdc

AFCs can be tricky, double check that your injector correction % is right, and that your MAF settings are correct for your maf type, since 300zx maf will need different settings than a stock 240 maf etc..... which maf are you using? The maf setting needs to be perfect...

NGK O2 sensors works the best for our cars, but I have a bosch unit on mine and no complaints yet.... i doubt that would cause a problem

[NISTECH]

Most of the nissans now use Bosch O2 sensors.

As far as your O2 getting hot enough. this is the reason the FSM says to test it at 2000 rpms. to be sure it is in the correct range to read accuratly.

[PMan_S13]

p00t -Thanks for the insight but I'm well aware of the timing needs. If you reread I wrote that the 25btc was recorded at just over 1k rpms and since the motor advances timing with engine speed, this should be very close to normal, and at least close enough to not be a real problem with the idling and certainly not a problem wth the distributer off a tooth. Thanks anyway bud. I just got another s13 maf. I was planning on resetting the AFC back to factory and start over when I get a chance to work on the car again. Just to make sure that isn't a variable, it is just too controlling to overlook.

I'm going to venture to say that the o2 sensor was a dud from the store. It's getting a good clean connection with dylectric (sp?) grease, it just simply doesn't change reading the whole time it runs. How much does the o2 sensor affect idle control? If I let it warm up again and then disconnect the sensor and it doesn't change, is that a good hint as to the problem?

[PMan_S13]

Well, I got the AFC back to factory settings and redid it from the beginning. It should not be a variable anymore. Topped off the radiator and overflow resevoir so it should be good now.

The 02 sensor has a warranty so I'm switching it out here in bit.

Still idles high, doesn't drop down now, just sits at 2k or around there. Thought it might have been the air regulator not shutting. But that hose is too tough to squeeze so I just unplugged it, nothing changed. I can make it idle down if I squeeze the main idle control line enough, I can even kill it. That would make me think it would have the idle set too high... if it weren't for one thing. If you race it and let it idle down it gets down to like 1400 (maybe less, can't remember) or so and something changes. It sounds like it is running really rough on all cylinders. Not stumbling or anything, just "brrrrrr". Then no more than a second later it switches back (smooth again) and idles up to 2000.

That one kind of has me confused. I'm going to dig the timing gun out again, maybe p00t was right. It seems like the computer is messing with something and then switching back, no engine light, but I'll see if self diagnosis finds anything.

Other than that the car runs fine, drives nicely, runs smooth, has plenty of power. Just the idling and the strange momentary roughness to figure out.

BTW I appreciate all the help, I know this must seem like a bother sometimes, but you have my thanks

[PMan_S13]

Ok, this is a little strange.

I checked the timing again. At 2k it was at 20btdc. Obviously this is wrong, but I know it was very close just a few days ago so I figured it is pulling timing. I retarded the timing as far as I could, turned it off and turned it back on. The Idle is significantly lower, about 1400, but the timing light showed 5 *A*TDC, It also will rev up and idle down without the "brrr" at the end. But since this is at least 25 degrees retarded it can't be right, it doesn't idle well either. I moved it back to somewhere close to where it should be, the engine speeds up as I do this. At about 25btdc it is at 2k rpms. When it revs up it "brrrr"'s again...

The ECU seems to be pulling timing. All I can really get from all this is the "brrrr" roughness is related to timing, but to get rid of it involves pulling a lot of timing, far more than is normal. I took my time reassembling everything, I have pictures of when I put the chains back on, I doubt they where put on out of time. Although it is a possiblity.

[NISTECH]

I just blew through this thread,maybe I missed it but did you ever check your tps adjustment?

[PMan_S13]

If you are talking about the stopper on the throttle body, yes. It was at .465v but I moved it to .500v, if anything it raised the idle about 500 rpms

[NISTECH]

you do not adjust the stopper screw. you loosen the 2 bolts holding the tps on and adjust it from there. if your start moving the stopper around you start changing the throttle opening. you never want to move that screw. that is a calibration screw for the throttle body to throttle plate clearence. any tps adjustment is to be done with the sensor itself.

[PMan_S13]

Ouch, that sucks. This is a stupid question since you said you are never supposed to move it, but is there a way for me to line it back up? I suppose I just move it back to .465

Anyway, the TPS didn't change anything with me messing with it. It reads from .5v up to 4.06v, I don't think it was an issue.

[NISTECH]

yea before you start moving the tps around by its bolts try to get that screw back to where it was.

The point of moving the TPS around is not to "fix" the voltage variance through its travel. Its to make the hard idle switch close[the other connector on the tps]. If that switch where to open at idle it would make the ecm think you where stepping on the gas and increase the opening in the idle air control mode and increase the injector pulse width to match the air intake measured by the airflow meter. In other words, When the idle air control valve opens the mass air flow meter sees the increase in airflow and tels the ecm the ecm then determines it needs to supply more fuel to keep the air fuel ratio correct. After which the ecm then takes a look at the O2 sensor to fine tune the changes. This all happens in a matter of millisecs. So as you can see this would increase the idle if it thought the throttle plate was open.

[PMan_S13]

Alright, sounds like something to look into. One of the symptoms I'm having is idle speed not changing from hot to cold always 2000. But when I disconnect the air regulator nothing changed.

So what exactly am I trying to adjust? I am tring to rotate the TPS until the hard idle switches off, right? Is there a way to tell this happens other than the motor finally idling down?

Also you said you skimmed through yesterday. Did you catch the part about rough running after it is revved past 2000?

[NISTECH]

yea I remembered that and I was thinking it was your airflow meter or a vaccum leak. Several of your symptoms do still point to that but you need to be sure all your other control sensors are correct.