1993 240SX Fastback - MAF Problem?

[HSVDrifting]

My car is running rich as hell (to the point of fouling new plugs very quickly) and when I floor it, it hits about 5k RPMs and then backs off...not like your traditional rev limiter...just...it backs off. I'm thinking maybe that it's the MAF sensor. Does anyone have any good ways to test this? What other possible causes could there be?

Thanks in advance,Collin
Modified by HSVDrifting at 8:06 AM 4/19/2007

[vancouverbc]

Try disconnecting the MAF and see how car runs. Someone correct me but doestn it go into fail safe mode or something. YOu can also unplug the O2 sensor to see if that improves things. You can look at your injectors to see if they leak. See if your cylinders are wet.

[HSVDrifting]

there was no change when I unplugged my maf or my o2 sensor...though when I plugged the maf back in while the car was running, it died. I haven't checked the injectors yet...cause I'm not sure how.

[vancouverbc]

there was no change when I unplugged my maf or my o2 sensor...though when I plugged the maf back in while the car was running, it died. I haven't checked the injectors yet...cause I'm not sure how.

check your ecu malfunction codes. remove sparkplugs and check to see if cylinder are wet. take the injectors out and see if they are leaking fuel.I dont think it is wise to unplug something when it is receiving power. the arc is going to damage the terminals at the very least.

Removin the injectors in a bit of an art:zerothread?id=179725

[HSVDrifting]

check your ecu malfunction codes.

Did that. It's showing 11, 13, and 34. I've not been able to find a list of ECU codes for my year motor...and I'm not sure if the codes are the same for like the 95-98. Assuming they are, that's (respectively): Camshaft Position Sensor, Coolant Temp. Sensor, and Knock Sensor. (according to: http://www.240sx.org/faq/artic...h.htm).

Now I know the Knock Sensor's unplugged because the one of the wires was torn in half at the base of the connector, however, I've been told that I'll be alright without the Knock Sensor. As far as the Coolant Temp. Sensor goes, unless there's 2 of them on the motor somewhere...I'm baffled. I have the on that exists where the top coolant hose connects to the motor plugged in, and am reading coolant temperatures, so unless there's a second one...I don't know why the hell that code's been thrown. Lastly...camshaft position sensor? I wasn't aware that my motor contained such a thing...however...I suppose I could see how that would hamper it running correctly. I also don't remember it throwing code 11 when I wasn't able to start it. Funny.

remove sparkplugs and check to see if cylinder are wet.

I haven't checked the cylinders, thought I have pulled the plugs and they were covered with quite a bit of carbon, and if I remember correctly, I think one or two times, the plug was a little wet. The exhaust is almost always wet, however.

take the injectors out and see if they are leaking fuel.

I'll try that shortly.

I dont think it is wise to unplug something when it is receiving power. the arc is going to damage the terminals at the very least.

I didn't unplug while the car was running. I unplugged it and then started the car. I plugged it back in after the car had been running and it just shut off.

[vancouverbc]

Most of the faq for dohc ecu codes applies specifically to your car. The only thing that does not apply is the the beginning codes for the 95-98.

The codes for 1991-1994 are:

11 + Crank angle sensor circuit12 E Air flow meter circuit13 E Engine temperature sensor circuit14 E Vehicle speed sensor circuit21 + Ignition signal circuit31 E E.C.U. (E.C.C.S. control unit)32 * E EGR function33 E Exhaust gas O2 sensor circuit34 Detonation sensor circuit35 * E Exhaust gas temperature circuit43 E Throttle position sensor circuit45 * E Injector leak54 Signal circuit from A/T control unit to ECU (A/T only)55 No malfunction in the above circuits

There are two temperature sensors. One for the display gauge and one that supplies the ecu with temperatures. You might want to erase your codes because some of them might be old codes. It is interesting that you dont have code 45 which is for injector leak or rich condition. These codes can be totally misleading sometimes.

Article for testing ecu temperature sensor:

zerothread/26506
Modified by vancouverbc at 7:27 PM 4/15/2007

[HSVDrifting]

I think that the reason it's not throwing code 45 is because the ECU's telling it to run hellaciously rich. We checked the injectors...no leaks. I'm going to work on the other Coolant Temperature Sensor (currently, it is plugged ...and no...I didn't do it), however, what the duce is up with the Crank Angle Sensor? I've scoured my FSM and could not find it anywhere. Where's it located?

Also...how do I erase the ECU codes?

Thanks,Collin
Modified by HSVDrifting at 8:52 AM 4/16/2007

[vancouverbc]

To erase codes you first get into mode 2. Then you turn mode selector fully clockwise and wait 2 seconds and return so that you are in mode 1. You have now erased codes.

"3. Changing Modes

Note: Switching Modes is not possible when the engine is running.

* Turn the Ignition Switch ON.* The ECU is now in Mode I.* To switch to Mode II:

Turn the ECU Mode Selector fully CLOCKWISE, hold for at least 2-seconds and then return the Mode Selector to it's original position. You are now in Mode II.

* Return to Mode I by turning the Mode Selector fully CLOCKWISE again, holding for another 2-seconds and turning it back to the original position.

Note: Doing this will ERASE any Malfunction Codes that are stored in the ECU for Mode II.

Example: If you found a Malfunction Code of 34 when you very first switched to Mode II and then cycled back to Mode I, then again to Mode II, you'll get a 55 (everything's OK) code. This is assuming that you didn't start the car between changing modes. When you start the engine, any current malfunction codes will be store by the ECU until you erase them or they get dumped.

Malfunction Codes are stored by the ECU for 50 times of cranking the starter. Then they are erased. If the same conditions are present, the Malfunction Code will be stored again for 50 cranks of the starter. And so on..."


Modified by vancouverbc at 2:14 PM 4/16/2007

[HSVDrifting]

So I called Nissan back and bitched them out today for giving me the wrong gauge...I suppose it's not really their fault. I've seen their parts program...the diagrams suck very much. I'm trading in the incorrect sensor for the right one today and we'll see if this helps anything.

Now that I've got the Coolant Temp Sensor covered, and I'm not worried about the knock sensor...what's throwing this Crankshaft Position Sensor code? If I'm not mistaken, isn't that sensor part of the distributor? I thought it was in that 4-wire plug that plugs into the distributor...but I could have misunderstood the diagram in the FSM.

[vancouverbc]

I know zero about crankshaft position sensor. It is discussed in section EF EC in fsm page 10 and 159. The ecu temperature sensor is the big thing. The temp gauge sensor means nothing.
Modified by vancouverbc at 12:55 PM 4/16/2007

[HSVDrifting]

I think you're thinking of the Knock Sensor. The plug for it is pretty close to the coolant senors, though the actual sensor is in between cylinders 2 and 3 on the intake side.

The crankshaft position sensor is a basic component of the entire ECCS. It monitors engine speed and piston position and sends signals to the ECM to control fuel injection, ignition timing and other functions.

This right here makes it sound like if the distributor timing is off...then so is fuel injection...couldn't this, in conjunction with the missing coolant sensor, cause the car to run hella rich?

Also...how does the coolant temperature sensor for the ECU affect richness?

Thanks,Collin

[HSVDrifting]

The guys at Nissan told me that since the ECU wasn't seeing a signal, it was thinking that the motor wasn't warming up so it was trying to give it more gas to warm it up...which makes sense. Anyway, I got the sensor and installed it, as well as wired up the knock sensor. I wiped the codes, as you suggested and gave it another try...got 55 this time. When I tried to start the car, then checked the ECU codes it was throwing 11 again. I'm assuming that the Crankshaft Position Sensor code is just telling me that my ignition timing is off. I need to get hold of a proper crankshaft pulley so I can time it effectively.

One of the guys in the Nissan Parts Department here was telling me that I shouldn't use a timing light, but that I should use a vacuum gauge. I don't really understand this. Can anyone shed some more light? If I could somehow get this thing timed right...I'd be SO happy...

Thanks,Collin

[vancouverbc]

Thanks for reporting back. Good to know that a faulty temp sensor can cause rich condition.

Youd prolly have to start new thread somewhere else to find out about timing and vacuum. From my superficial knowledge, I would say your distributor is not vacuum controlled so your only option is a timing light.Most people use a timing light so it cant be that inaccurate.

[HSVDrifting]

Right...but some genius had the idea of putting an SOHC crank pulley on my DOHC...so I have no way of using a timing light for real..

[HSVDrifting]

okay...so I dropped (another....ugh) $50 at a junk yard on a DOHC Crank Pulley (off of a '93). Yay! Time to get that gay, bright red (no, I didn't paint it...) SOHC piece of **** off of my motor. I'll keep you posted after I get it on and use a timing light...it's gonna be interesting to see how I get this back on and torqued down to spec (~150ft. lbs) with only one person...lol..the car tends to move when you put it in gear and turn the crank, lol.

- Collin

[HSVDrifting]

lmao...so it turns out that it wasn't an SOHC pulley...it was just yet ANOTHER piece that didn't come with the motor...any takers? The key for the pulley/crankshaft. It's getting ridiculous...all the things that are missing.

Anyway...so I got the pulley on there right. And pulled it to TDC according to a straw in the #1 cylinder...lol. Looked on the crank...it was TDC. So that's good news. I pulled it to 20º advanced on the compression stroke, and slipped the distributor in correctly and lined it up so it was sitting on the #1 post on the cap. Then I put everything back together and tried to crank it. It would start pretty easily...but it was running like ***, so I tried to keep it running and decided to rev up to about 2k RPM and it started to choke some and then the check engine light came on solid, so I let it go and it just died. I checked the codes and the only code it's throwing is for the CKPS (code #11).

I don't know why it's dying now...

Anyone that has any ideas...I'd really appreciate it.

Thanks in advance,Collin

[rogoman]

The guys at Nissan told me that since the ECU wasn't seeing a signal, it was thinking that the motor wasn't warming up so it was trying to give it more gas to warm it up...which makes sense. Anyway, I got the sensor and installed it, as well as wired up the knock sensor. I wiped the codes, as you suggested and gave it another try...got 55 this time. When I tried to start the car, then checked the ECU codes it was throwing 11 again. I'm assuming that the Crankshaft Position Sensor code is just telling me that my ignition timing is off. I need to get hold of a proper crankshaft pulley so I can time it effectively.

One of the guys in the Nissan Parts Department here was telling me that I shouldn't use a timing light, but that I should use a vacuum gauge. I don't really understand this. Can anyone shed some more light? If I could somehow get this thing timed right...I'd be SO happy...

Thanks,Collin

The crankshaft position sensor sends signals to the ECU to control fuel injection, ignition timing and other functions. Check the harness connector and check the engine ground that's near the temperature sensors.

By all means use a timing light for the ignition timing.

[HSVDrifting]

The crankshaft position sensor sends signals to the ECU to control fuel injection, ignition timing and other functions.

I don't mean to come off like a smart ***....but I know what it does. Where it's located is what I'm not 100% sure about. If I'm not mistaken, it's located in the distributor, correct?

Check the harness connector...

You mean make sure all the wires are still good? It'd also be helpful (methinks) to know which wires do what. If it's the plug I'm thinking that it is, (the 4-wire one side of the distributor) then I can't imagine what the 4th wire is for. I'm sure there's a power, a ground, and a signal wire...but the 4th? I guess I could be totally off and it could be somewhere else...but I seem to remember that that's what the slots in the plate inside the distributor are for and that they opperate off of an LED and a Photo Diode.

...and check the engine ground that's near the temperature sensors.

You mean the one that looks like it's supposed to connect to a valve cover bolt, right?

By all means use a timing light for the ignition timing.

I plan on it...but I can't get it to idle or even run right so that I can do that.

A little clarification would be greatly appreciated. Thanks, too, for your reply.

- Collin
Modified by HSVDrifting at 8:20 AM 4/23/2007

[DammitBobby]

I am getting a code 11 and 34. Car starts fine drives fine except in WOT. Timing is set to 20 degrees. It seems to miss and have no power. So have you done anything else yet?

[HSVDrifting]

code 11 means that your timing's off, at least I think so. I fixed my timing and it went away. As for code 34, a believe it's discussed earlier on in the thread...but it means your collant temp sensor that goes to the ECU is either missing, disconnected, or bad. That sensor's the one that has 2 pins. I found out from Nissan that if you don't have it, your car is always in like "cold-start" mode or something and it dumps extra fuel...this could be, perhaps why your car's running like crap at WOT. Another possibility (and something that helped me significantly) is a vacuum leak. Buy a cheap can of carb or brake parts cleaner (as long as it's flammable) and start spraying (systematically) things around your intake manifold.

Good luck!

- Collin

[HSVDrifting]

As for my car. It's idling great, now. We fixed a vacuum leak and it's nice. It's still making no power through what should be the power band. I understand that straight 2 1/4" piping for an exhaust is pretty unrestrictive...but there should still be power...when I start out in first and floor it...it takes probably a good 4 or 5 seconds to get up to 6k RPMs, which is where it doesn't wanna go past (again, let me reiterate...not like a rev limiter...it's either flooding out or leaning out (methinks).

** EDIT: By the way...it's not fouling plugs anymore...nor is it throwing code 11 (CKPS Error)...it's just still slow and crapping out at about 6k **

Any ideas or help would be appreciated...if I can't fix this damned thing soon, I'm going to cut my losses and sell it.

Thanks- Collin

[DammitBobby]

Set timing with timing light and disconnected the TPS. It is set to 20 degrees. Code 34 is the knock sensor code.

[rogoman]

I don't mean to come off like a smart ***....but I know what it does. Where it's located is what I'm not 100% sure about. If I'm not mistaken, it's located in the distributor, correct?

Yes, it's in the distributor. The harness connector is under the base of the distributor body.