N/A SOHC issues...any help would be appreciated :)

[schroder]

Hey guys,
I think this is my first thread that I've actually created. I recently purchased a 90 hatch from a buddy thats got some issues. When the car is warming up its able to idle fine, rev fine at all throttle inputs, and when put in gear (load) I can brake torque to 2100 RPMS easily - turning the tires over if I don't have enough force on the pedal. When brake torquing during warm up the AFRs read around 14.1-14.4. Once the car is up to operating temp the idle fluctuates (sometimes dies after being revved), revs fine at full throttle but at 50% throttle or less (give or take) it will rev initially but then try to die (wideband goes full lean when its trying to die...it sounds like its popping through the exhaust as well when showing lean and dying...), and when brake torquing it will only go to roughly 1800 rpms and will never turn the tires over. When brake torquing after its warmed up the AFRs are around 13.3-13.6. Below are things that are recently done to try and fix the issues:

PLX Wideband O2 (new) with the narrowband simulator hooked into ECU (wideband has a line specific for this function.)
AIV and EGR delete with all lines plugged
Vacuum line delete - only ones are from PCV, FPR, Brake booster, and lines to run Idle control/air regulator
New Intake manifold gaskets (IM to head and UIM to LIM)
A can of carb cleaner sprayed into lines for Idle Control/Air Regulator (multiple times)
New NGK sparkplugs that were indexed
New Coil
New 255lph fuel pump
Z32 fuel filter

All missing vaccum lines have plugs where needed in order to avoid vacuum leaks. The car is a SOHC auto that's stock save for a 3" catless exhaust. Any help with this would be great as I was thinking it was either going to be the coil or the fuel pump.

Thanks!
Justice

[IanS]

Are you sure the wideband is outputting the correct signal for the ECU to read?

When it comes to o2 sensors its not as simple as wide and narrow, there are 3 or 4 common narrow band signals. There are different high and low voltage limits as well as linear and progressive/regressive voltage profiles.

It sounds to me like the ECU is attempting to trim the fuel to reach a AFR target. Try disconnecting the o2 signal to the ECU. It should run in open loop mode, using a base fuel map. If your problems go away, then try rigging up a factory 02 sensor.

Have you tried pulling codes out of the computer?

[schroder]

The issues were the same before the O2 sensor was swapped out. The AFRs are also steady during warm up, idle, and under full load. I'll try disconnecting it again, and putting the stock o2 back in, but again...the problems were the same before and after.

[schroder]

http://www.plxdevices.com/AppNotes/PLXApp004.pdf - write up for narrowband simulation. Standard 0-1v replacement.

[IanS]

Well it really sounds like a sensor issue. It runs normally in open loop, but once it hits operating temp and goes to closed loop control it goes wacky.

You could have a short in the wiring, maybe even the wiring for the o2. You could also have a smoked ECU.

If it did it all the time I would say MAFS, but the ECU relies on the MAFS even in open loop to calculate base fuel trim.

[IanS]

Does it seem to be leaning out across the board? Or do the plugs show that some cylinders are worse then others?

Try unplugging the coolant temp sensor. This should force open loop mode. It may run a bit rich, but it should stop trimming, and therefore stop dying.

[schroder]

I'll try that tomorrow. If it hadn't been doing it before the wideband swap, I'd lean on that more than I do. As far as leaning out, its across the board. When under partial throttle it flashes to around 14.5 give or take, and then spikes lean...which is when it starts popping through the exhaust. But I'll try unplugging the coolant temp sensor and the maf, separately, to see if either of those clears it up.

[schroder]

Also, the other thing I was thinking of, is that after its warm the idle flutters from about 600-1000 rpms or so...could be an idle control problem (stuck partially open). If under partial throttle, it is initially spitting more fuel out because of tip in, but then leaning out because its not expecting as much air to be entering the motor as whats actually entering. I don't know how much of a possibility this is, so you're welcome to chime in on that as well...mainly just trying to think of as many things to test as I can.

[IanS]

Also, the other thing I was thinking of, is that after its warm the idle flutters from about 600-1000 rpms or so...could be an idle control problem (stuck partially open). If under partial throttle, it is initially spitting more fuel out because of tip in, but then leaning out because its not expecting as much air to be entering the motor as whats actually entering. I don't know how much of a possibility this is, so you're welcome to chime in on that as well...mainly just trying to think of as many things to test as I can.

Could be, I dont remember how the SOHC idle control system works. I just pulled mine off and used a throttle stop to set idle speed. It runs like poop when cold, but I wasn't worried about it. You could try plugging the IAC line, then just adjusting the throttle stop to temporarily get rid of the hunting idle, although it sounds like a symptom to me.

[schroder]

It could be. The 240 is my toy, so the throttle stop could be a really good plan. I'll try the cts and maf first to see if that makes any difference. Well...thinking out loud, can you actually unplug the maf and have the car still run on the 240sx's? I know some cars will, other cars wont...I'm so used to the DSM scene...the eclipse won't run with the CTS unplugged, but it will with the Maf...it just wont rev.

[schroder]

Also, car feels like its down on power when revving after its warmed up. I haven't double checked the timing with a timing light yet since I just got the car. I can't remember, but isn't the timing advanced during warm up and then retarded back after its warm?

[IanS]

It could be. The 240 is my toy, so the throttle stop could be a really good plan. I'll try the cts and maf first to see if that makes any difference. Well...thinking out loud, can you actually unplug the maf and have the car still run on the 240sx's? I know some cars will, other cars wont...I'm so used to the DSM scene...the eclipse won't run with the CTS unplugged, but it will with the Maf...it just wont rev.

IIRC it will idle, but not rev without the MAFS.

Also, car feels like its down on power when revving after its warmed up. I haven't double checked the timing with a timing light yet since I just got the car. I can't remember, but isn't the timing advanced during warm up and then retarded back after its warm?

I believe you are correct with the timing. If the mechanical timing were off I would think that the AFRs would be more in line, and you would see other issues. An electrical timing issue could be the culprit, although if it was going full retard, then I would think the o2 would read rich, not lean.

[schroder]

I agree with you for sure. I tried unplugging the coolant temp sensor and it caused the idle to be even worse. The car was richer and still struggled with the same revving issues. BUT there was a difference between it being plugged and unplugged. I also hadn't realized until you said something that there would still be codes without a CEL showing up on these cars. I pulled the ecu out and showed code 13 and code 33 - Engine temp circuit (coolant temp sensor I assume) and Exhaust o2 circuit (o2 sensor I guess). I thought the code/codes may have been thrown from before and since the ECU wasn't reset, I was still having issues. I reset the ECU by going to setting 4, turned the screw back, and turned the car off. I turned the car back on, let it try to figure out its idle again, and after it had stabilized the idle I turned it off and checked the codes again...Same codes. I don't know if the Coolant Temp sensor would cause the O2 sensor to throw a code, because it has in my old DSM. The only reason I'm hesitant with either of these though is because the car acted exactly the same with the factory o2 sensor in place as it does with the wideband as its replacement, and the coolant temp sensor seems to be at least partially working due to the fact it caused a change when unplugged (changed to open loop...forced to run rich...etc). It got dark on me too quickly tonight so tomorrow when I get in from work (yay night shift) I'll try to make sure the narrowband simulator is simulating. I'm just getting tired of dumping money to fix the car and not having it fixed.

[IanS]

Interesting.

Check the resistance of the CTS, and the output voltage. You may be able to confirm it being bad. The voltage range chart should be in the FSM. Check it at ambient temp, then again at op temp.

And I would get a known good o2 sensor in it. Its possible it had a bad o2 before, and the wideband is not outputting the correct signal. You could have replaced broken with broken. Its happened to me at work, and it makes diagnostics infuriating.

The reason I dont think the wideband is outputting the correct voltages, is because I tried to use my AEM UEGO to output signal to the ECU when I had an SR20 in my S14. It hated it. Ran like death. The PLX may be different, but who knows.

[schroder]

I will. I researched the charts earlier but it was too dark to do any more testing. I may simply swap out the sensor since its God knows how old anyways. I'm also going to go ahead and check to make sure of what the output is. I figure the o2 voltage on idle, if it remains between 18:1-19:1 would be around .1-.2v's on the multimeter...and if I can manage to brake torque the motor to the 13.5-14.5:1, it should spit out something in the neighborhood of .6-.7v's or so. And if it doesn't show any voltage going to the ECU, I'll swap in a new O2 sensor. I really appreciate the help though man. I've had 2 240sx before, one of which ran...but this is the first I've actually been working on and its a bit different with no CELs.

[IanS]

CELs make life too easy sometimes. Sometimes i like kickin it old school, diagnosing with your senses and a multimeter.

Good luck.

[schroder]

Thanks I was able to test at home by pulling the sensor out, but couldn't find a thermometer so I went off a guess. Ambient temp inside was actually 67 degrees and the sensor checked out fine. Running straight hot water from the tap (set around 135-140) the resistance looked like it could be either way. Without a thermometer though I couldn't get the water to the 176* or whatever that its supposed to be to get an accurate test. Another big issue I had was making a good connection. There were spots on the sensor itself that I couldn't get an actual reading on the multimeter so it could be corrosion. I didn't get as much testing done today as I really wanted to because of work and the fact it was 37 when I got home and I have no garage. Tomorrow should be a better day. I didn't think about the reset of the codes not being done right so I think that could be why I'm still throwing o2 and coolant temp sensor codes (if o2 was bad and was never reset, and I checked codes after I disconnected the coolant temp sensor without resetting any possible codes). I have to change the battery anyways, so I'll go ahead and reset the codes when pulling the battery out, toss the old coolant temp sensor back in, and let it idle for a bit to see what codes come back. After it starts idling I'll check the voltages as well.

And I agree, CELS USUALLY make life really easy. Unfortunately, some cars will trip a CEL that says one thing, but means another. I guess thats the joy of testing everything in the circuit. Thanks again for all your help with this man...its been a pain trying to figure this one out.

[schroder]

Also, kind of off topic with these problems, but I can't seem to find any info. Do you know how to remove the speed governor on an Auto? I plan to toss a turbo on it this winter/spring and in the 1/4 mile I'm hoping to actually trap over 110-115.

[schroder]

Ian, I don't know how much you hate being right, but you were...although my guess at the problems being related also was right. I replaced my coolant temp sender today to continue having these issues. The code continued to come back and after staring for a while I gave up, frustrated, and decided to look at the ECU pinout in order to see if the o2 sensor on the car somehow tied into the grounds/power for the cts. Usually, they don't. However when I was searching for a switched 12v around the ECU for the wideband I located one which turns out to be a pin including the 12v switched power for the CTS. Now mad at myself I retreated to the car and broke the connections I had for the power and ground for the WB02 and reset the ECU. Code 55. I'm still a little confused with how I'm getting code 55 when I don't have an o2 sensor hooked up currently (getting ready to get a new one after this post), but I'll take it. Turned the car over, perfect idle. 700 rock solid. Revs, for the most part (I assume theres still a bit rich mixture due to no o2 sensor) like butter. I still can only turn 1900 RPM when brake torquing it, but I haven't driven the car yet so I doubt its really found where it needs to be...plus, there's no o2 sensor.

So the problem I had initially was PROBABLY due to a bad CTS, and possibly ONLY a bad CTS. But I'm replacing the o2 sensor to air on the side of caution. Also, had I not been hunting for the problems, I wouldn't have replaced my fuel pump. Before replacing the fuel pump the car gave up the ghost and would not idle no matter what. After I replaced it, it would struggle, but still idle. However, when I pulled the old pump, the sock was garbage and I found a lovely little gift (sorry no pics) from the rust fairy: the lower hose clamp that secures the hose to the fuel pump was broken...and part of it missing. Also, when I went to remove the clamp it shattered and there was no tension on the hose between the hose and the fuel pump outlet (would spin freely). I know I've spun my wheels with this, and alot of it is my fault, but in the end I've gained a good bit on the car that I probably wouldn't have done otherwise:

No butterflies
No EGR/AIV
Minimal vacuum lines
Replaced upper/lower IM gaskets
new fuel pump
new coil
new CTS
new o2 sensor
indexed spark plugs
and a new z32tt fuel filter.

Thanks again for all of your help through this process, and I hope this is all that I really need to get the car where I want it. If you could still get me with my final question regarding governor removal on an auto I would greatly appreciate it!

[IanS]

Sweet deal. Glad you got her figured out, hopefully.

Ive got nothing for you on the govouner front. The closest i have come to automatic 240s, is the auto parts car parked next to my garage, and it came to me with the engine in pieces.

Glad to be of help.

[schroder]

LOL...Thanks anyways man. I'll probably kick off a new thread on it. If I can't find anything I'll try to find the pinout for the TCU and study it vs the ECU pinout I have. Thanks again for all the help man, I'd say I owe ya one...but I don't know how much I can be to ya, lol!

[IanS]

LOL...Thanks anyways man. I'll probably kick off a new thread on it. If I can't find anything I'll try to find the pinout for the TCU and study it vs the ECU pinout I have. Thanks again for all the help man, I'd say I owe ya one...but I don't know how much I can be to ya, lol!

Pay it forward sir.

you're welcome.

[Fenris]

Last i knew, there was some wire sniping involved, search the forum to find it

[schroder]

I have searched. Everything I keep turning up is M/T specific.