I have a 1992 Nissan 240SX convertible that runs great when it wants to but sometimes (randomly) it will not start. When it does it, the car tries to start and stumbles real bad like its trying to run on one cylinder. It usually will do it after I have been running a while then stop for something and get back in it to crank it up. I was on a trip where I ran about 200 miles. It ran great the entire time until I stopped to get something to eat. When I get back in the car it did the stumbling and wouldn't crank. I went back inside and waited a few minutes then tried it again and it cranked up and ran fine all the way home. SO far it hasn't quit while driving. When its about to act up I can sort of tell because when I pull up to a redlight I notice the idle seems to be slightly lower and fluctuation like it will go down to about 500-650 rpm with it in gear (automatic trans). When its running good the idle will be steady. It does it randomly so I never know when its going to act up. I have checked all the wiring connectors which seem to be ok. It has a new fuel pump and ignition switch. When its running I can grab the wiring harness in front of the head and pull on it and sometimes it will affect the idle speed. I thought it may be a bad water temp switch that sends a signal to the controls but I replaced it and didn't seem to affect it. I didn't want to just throw parts at it until I could narrow down the problem. If it would just die I could troubleshoot it better.
Thanks,
Zoom45

Doesn't sound like a parts issue to me; sounds like a wiring issue.

The part of the harness you are talking about contains the wiring that carries the cam angle signal from the distributor to the ecu. Without this signal no fuel or gas.

I had a similar issue with one of my hatches where I had a broken wire in that signal wire where it entered the firewall into the cabin. It was a nightmare to diagnose because it was so intermittent. The car ran beautifully then just randomly shutoff, sometimes while driving. Its so hard to diagnose because it seems like you can't reliably replicate the problem.

What I would do is, with the car idling in the driveway, try to jiggle or mess with the wiring harness in various places and see if you can try to narrow down a place where, when moved, you can cause the symptoms again. Thats where you need to get into the harness to look for the broken or shorting wire. Or... if you narrow it down to that and validate a harness problem, save yourself some future headache and just replace it with a wiring specialties harness altogether. I've bought a number of things from.them and have nothing but great things to say about all of the stuff I've bought from them.

Great response thank you. Sounds like you had the same problem. I'll try your idea.
Zoom45

Keep us posted. The wiring in these cars is old and brittle. Doesn't take much to cause an issue. On a similar note, how do the ground wires connecting the engine harness to the engine look? Are they cracked and frayed? May not hurt to get a little back into the harness and solder in some new wire for the grounds if you aren't planning on getting a new harness. The ones on my s14 were pretty bad wheI went through mine this past weekend.

Also, have you tried pulling codes from your ECU? Might turn up a good lead on what to look for as well.

https://240sx.org/faq/articles/ecm_codes_doch.htm

The grounds all look clean and no brittle wires. I don't know how to pull the codes. Got any instructions? I cranked it today and ran it for about an hour. I pulled and tugged on wires all over the motor and could not make it mess up. I started and restarted about 50 times. Seemed to run perfect. If I drive it to work in the morning (supposed to be storming) I'm sure it will decide to stumble and quit at a red light.
Zoom45

Found this video explaining how to pull the codes so I will try it tomorrow night and see what I get.https://www.bing.com/videos/search?q=ho ... ORM=VRDGAR

Dude, i literally posted a link at the end of my last post haha.

Hopefully the ecu yields some idea of where to look next.

The car was running good today so I drove it 50 miles. Ran great. Go to a store got out for 20 minutes then got back in the car and drove the 50 miles back home. Ran great the whole time. When I got home I cut it off then in about 1 minute tried to crank it and it wouldn't crank. I waited 30 minutes and then it cranked up and runs great. I pulled the codes. It has code 13 then 33. Does that tell anything that would cause my problem? I guess that is coolant temp and oxygen sensor codes.
Thanks
Zoom45

The coolant temp sensor... when it stumbles and has hard starts, listen carefully and see if you can hear the electric radiator fan kick on. If that's the case, you have a bad connection between your coolant temp sensor and the harness. If that sensor fails open or you have a bad connection, the ecu reads it as a super high value like 200+ degrees coolant temps and pulls timing and adds a ton of fuel. It also kicks on the electric AC fan because it thinks you are overheating.

Alternately the coolant temp sensor could be bad and reading abnormally high when you let the car sit after running. A new sensor is less than $20 at most parts stores and typically in stock.will take you maybe 5 mins to change with a 17mm combination wrench I believe. Thats also in the same location as the harness you were referring to in the OP. Sounds like the connector just has a bad connection. It's going to be the red plug down near your upper radiator hose connection on the head. If it's missing the metal clip that thing can slide on and off from vibration.

*edit - I see you already replaced the CTS sensor. Did you lose the metal U shaped rod that goes around the harness side connector to secure it to the sensor?
You replaced the red one, from this pic, right?

Yes I did replace the CTS a while back and the wire clip is still on it but maybe I have a bad connection at it. I will troubleshoot more. My gauge sender terminal is loose so I ordered a new one for that. Sometimes the gauge needle jumps so maybe that's the cause of that issue. Thanks for the info. What about the oxygen sensor code 33?
Thanks
Zoom45

bad forward O2 sensor will cause you to use more gas but should not cause the starting problems you're describing. I'm leaning toward a wiring issue or connectivity issue with your coolant temp sensor at this point. Electronic issues are a real pain when they're intermittent like this. Might as well replace it though and clear that issue up. They don't cost much, I believe yours is one of the single wire variants.

If your metal retainer is on the clip, there shouldn't be an issue at the actual connection. I don't know what else to try at this point but to get the car warmed up and see if you can get the problem to reappear and mess with the harness at the cts and around the front of the valve cover like before and get it to clear.

if you get it narrowed down to a bad harness side connection, Wiring specialties does sell individual pieces too. https://www.wiringspecialties.com/ka24de2.html

Hopefully someone else will chime in with an idea. Once you are able to reproduce the problem I'd check for spark on all cylinders when it won't start. You can do that pretty easily with a timing light on each of the plug wires in sequence.

What's the situation with the AC fan? does it come on when this problem is happening?

Haven't noticed the cooling fan on. My gauge sender came in today so I put it on. Now the gauge is reading correctly and not jumping. So far its running great. I guess time will tell. Thanks for all the help.
Zoom45

Drove it yesterday to work and ran great in the morning at lunch and on the way home. Got in it to run to the store this morning and it would not crank. At least its dead now. I had my wife try to start it while I checked for spark at the plugs and it does have spark. I just had a screwdriver stuck in the end of the wire and held it close to ground. The spark looked a little yellow but was good. I didn't hear the fuel pump running but its pretty quiet anyway. At least it died in the driveway and not out on the road somewhere. If I'm getting spark at the plug it must not be sending fuel. Could this be a bad coolant sensor or computer problem? Would it help to check codes again now that its not starting? That red sensor connector is cracked where the wire clip goes so I ordered a new pigtail for it from that site you listed. Hopefully that's where the trouble is. Its a good thing I have some other cars I can drive.
Thanks
Zoom45

If the electric fan isnt on solid it isnt the coolant temp sensor
unless the fan is dead too... i'd absolutely pull codes again and see if you get anything new. Good luck!

Code 13 and 33. It stumbled one time trying to crank after I reset the codes but its still dead. Now the battery is down so I'll have to charge it and try troubleshooting later.

Yeah coolant temp sensor related again. Hmm... curious to see if the new pigtail for the CTS fixes it.

Funny thing. After the battery was down I put a charger on it for 30 min and I went back out and it cranked up and runs great. I can't make it stumble. Seems to run perfect. I cranked it several times. Same as usual. I guess it will run until it decides to quit again. Does anyone want to buy a 1992 240 convertible?

Yeah you've got a wiring harness issue. Get that cts pigtail replaced and I think you'll stop having this problem. Maybe check your ac fan when you have a chance to make sure it isnt frozen too.

AC fan is working good. It comes on when you turn the air conditioning on. The car is still running good. I just don't trust it to hit the road yet. I wonder if when I stuck the battery charger on it could it have boosted something that was stuck because it started working fine after that. If it quits again I'll try that first thing. That plug should be in this week but I have to fly out of town so will have to wait until next week to put it on.

Update: After installing the new coolant switch plug and harness it seems to have fixed it. I have been about 200 miles without it quitting. Now my shifter was stuck in park and wouldn't release when I push the brake so I had to push the red button in front of the shifter to release it. Is there a switch on the brake pedal that may be bad?

Re shifter stuck in Park. I went through 3 of these before I sold my 240SXSE. They would on occasion self cure for a while but soon revert to non-shift status. It's not an external brake pad switch, the shift mechanism just screws up, The new buyer just put his weight to the shifter and got it working [for now].

Thought I had the intermittent starting fixed. Drove it to work all week and it did fine. Drove it about 25 miles this morning ad stopped for gas. It did it again when I tried to crank up and leave. It would try to start but stumbled real bad and never got going. This is twice its done it after filling the tank. I pushed it away from the pumps and let it sit about 10 minutes then it cranked up like nothing was wrong. Drove it back home and it ran fine. Really aggravating.

It seems to be running great now but I have decided to sell it so I can get a vehicle with more room to travel and see my kids. I have the car posted on craigslist in Jackson MS in case anyone is interested in buying it. You can see 24 pictures of it there.
https://jackson.craigslist.org/cto/d/te ... 56873.html

Zoom45

very clean convertible, glws! you might also try posting this up in the for sale section if you haven't already.