KA24DE bad distributor diagnosis sanity check

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tankboy1138
Posts: 2
Joined: Mon Mar 05, 2018 10:57 am
Car: 1991 240sx S13

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Hello everyone. I was originally going to toss this in the "I'm new and have a simple question" thread, but after typing this up, not sure if it fits the "simple" bill anymore. I have been chasing down an overheating issue for the past month on-and-off, and I'm close, but I am missing some information I need to diagnose the problem fully and commit to buying a couple hundred in parts. I want to hear what someone else with more experience with these things has to say if at all possible to see if my diagnosis is good or I may be going astray somewhere. If this is the wrong place to post this, I'd be happy to delete and move, but I think I'm in the right place here.

I have looked at as many articles about distributors and problems mirroring my own experiences, but it has been slim. the closest thing I found was a mustang owner who had his timing go stupidly advanced for no apparent reason, but the thread was never truly resolved so I am still in the dark. I have been upon many forums, I understand the search etiquette very well. But this problem seems to be outside the realm of common repairs and I have been unable to get anything similar to this on a 240.

Background:

I'm a mechanical engineer with lots of experience in electrical control systems, so I have plenty of technical aptitude to work on the car and I understand how it all works, but I am unfortunately lacking on car specific troubleshooting knowledge. Spent a lot of time with the FSM and trolling through forum articles to learn, but I don't have raw intuition of what is happening. But the 240 is my dream car, and I'll learn whatever I have to learn to keep this car running for as long as I can.

Car: 91 SE hatch, KA24DE, engine is stock but does have an emissions delete. (no EGR, PCV venting is blocked off, no cats, charcoal canister and all that is gone. So not really stock, but it's not turbocharged nor does it have different cams and all that stuff). previous owner was trying to make a drift-missile out of this beautiful, rust-free hatch that's only fault was a cheap-O Macco paintjob and worn interior, my goal is just to restore this wonderful car to a good fair-weather daily driver. (my love for this car knows no bounds. I always knew I wanted one, but I never imagined that a car would be as fun to drive as my 240.) Got the usual "Stock" 240 welded diff, coilovers, and fart can, but that really doesn't apply to this problem. 250K on the chassis, but I have documentation showing that the engine received a rebuild 50K or so ago and my own inspection of the internals confirms this.

Only other thing to note that I'm not really sure at what codes I can trust with this car. Since the emissions have all been deleted, there are plenty of things no longer hooked up to the ECU. So I have been taking the approach of diagnosing everything without reading codes as I don't want to be chasing phantom stuff that is being thrown because the engine has been "simplified." I also wonder what effect that has on my check engine light, as a missing EGR is probably something that will cause a check engine light to pop. (interestingly the check engine light seems to be functional on startup, but it has never popped on me while driving, so I wonder if my ECU has been chipped? I don't know a ton about the emissions delete, as I didn't do it, so that's an unknown factor that I may be considering improperly)


Diagnosis:


Bought the car, ran really great when I bought it, and continued to run like a charm for about 500-700 miles or so. Compression check was really good when I bought her, and remains good to this day even after issues. Took it out one day for a sunday cruise (cold day), noticed the temp gauge was riding a bit high, pulled into a gas station, and shut down the engine, started puking a ton of coolant out from under the intake manifold due to an overheat. Probably should have let it idle down with the hood open, but I wasn't thinking. Did all the usual troubleshooting for overheating, put the system back together (along with a secondary water temp gauge to have a backup reference of what's going on), cleaned out the cooling system twice with distilled water, fresh coolant back in, no leaks, thoroughly bled, and plenty of pressure under the rad cap... and the car still overheated. (BTW: aftermarket radiator with electric fans, and I rigged the fans to be always on for testing purposes. No effect)

Getting very puzzled, I remembered something my dad had told me, and I shot my ignition timing. The crank was reading something like 20 degrees of timing advance, but oddly enough, I didn't hear any pinging (that said, I do run 91 octane in that car, so that may have helped me out). I reset the timing to factory spec (followed the proper procedure, warmed it up, unplugged TPS, restarted car, then adjusted timing), but oddly enough, the timing appeared to be a hair retarded when I did that (backfiring downhill when I left it in a high gear and foot off the gas). So it's possible that somehow the markings on the crank are a bit off. Regardless, I advanced the timing bit-by bit until the retarded symptoms seemed to be gone, and my timing appears to be set roughly 5-7 degrees advanced from factory settings. Seen plenty of people run that, and it was a lot better than before, so I figured I was safe.

Car ran perfectly: no overheating, temps held right at spec on the stock gauge, and in the 175-190 range on my aftermarket gauge which seems to be correct. Drove around for about 45 minutes that evening enjoying the experience again, watching the gauge like a hawk, no problems. mix of both city and highway driving, both gentle driving and mashing the pedal to the ground. The point was to do a shakedown cruise, and it was all going well.... until I roll into a drive-through to get a quick burger, and by the time I get back onto the road, I was reading 205. Started driving, assuming that idling around was causing temps to spike, trying to get airflow through the rad. Temps just continued to gradually climb till it hit 220, at which point I pulled over to let the car cool. Shot the timing just before I turned the engine off, and the 20 degrees of timing advance at idle had magically returned. The distributor had not physically moved, I had previously cranked down on that bolt and then marked it with a pencil mark to check that it hadn't shifted.

This tells me that somehow, my timing is getting advanced and not resetting itself. However, I am puzzled as to how it's happening. The ignition is based off a distributor, so as far as I'm aware, the only thing that can advance timing is either a vacuum advance system or centrifugal weights in the distributor. There's no vacuum advance on this thing, so my guess would be springs holding weights on the distributor are bad. But every manual I have doesn't show the inside of a distributor for a KA, so I don't even know for sure if it has centrifugal advance. But if it doesn't, what advances the timing on that engine to cope with higher RPM operation? It doesn't appear that the ECU has any ability to directly control timing.

I also pulled the upper timing cover, and the chains/sprocket markings are where they should be when I get the engine to TDC. Cams were even in the right place, so I'm reasonably certain that I didn't jump a tooth on the chain. (interestingly enough, the upper chain guides are still on that motor, so that should also help prevent jumping teeth)

Knock sensor on the block seems to be in mediocre condition (plastic cracking and all that, probably the stock sensor) so I did buy a replacement for it (have not installed yet) but as I understand, the knock sensor on S13's is just a, "oh crap, we're knocking, illuminate the check engine light" warning sensor, and doesn't effect timing. (again, there doesn't appear to be a way for the computer to advance or back off the timing as far as I can see)

Car is down for a repair right now (waiting for some hoses to arrive, want to eliminate any possibility of a coolant leak) But are there any theories out there about what could be causing my timing to advance like that? Something that I have not considered? Or does the problem seem to be isolated to the distributor? I'd prefer not to spend $150 if I don't have to, so I just wanted to sanity-check my diagnosis before I start throwing more money at the problem. Got no issues throwing money at a problem, just as long as I have some indication that it might be leading me on the right track. My dad has spent a lot of time on the phone speculating with me, but he's more ore a european car guy, MG's, VW's, Jags, volvos. He doesn't have 240-specific knowledge which might be able to help me out here.

If you made it this far, thank you for reading, I know I can get long-winded. I just like explaining with as much detail as possible to give the most complete picture of what is happening. I'm eager to learn, so I'd be happy to take any advice or troubleshooting recommendations, thanks for your time. Again, I hope this is a reasonable question to ask here, I don't want to be that person that asks a stupidly obvious question before researching it. But again, I've been chasing this down for almost a month now and spent many hours trying to answer this myself. I figured it would be wisest to defer to those with more experience. Take care.


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PapaSmurf2k3
Site Admin
Posts: 23998
Joined: Thu Nov 21, 2002 3:20 pm
Car: 2017 Corvette, 2018 Focus ST, 1993 240sx truck KA Turbo.
Location: Merrimack, NH

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Holy crap man, that was a novel.

Cliff notes - car overheats, and also the timing moves around.

You've really only got 1 issue here, and that's overheating. The timing moving around is normal. You are mistaken when you assume the ECU can't control timing, because that's exactly what it does. It will advance or retard ignition timing based on coolant temps, load (MAF reading), RPM, throttle position, knock sensor, etc. Why do you think it has all these sensors? How does it change timing when you unplug the TPS sensor (when you're setting the base timing per the FSM)?

The overheating could just be a bad thermostat or bad water pump... or there's a gasket failing and you're getting air in the system somehow. KAs are a bit notorious for being fickle about air being in the coolant system.

flartius
Posts: 138
Joined: Sat Apr 01, 2017 9:19 pm
Car: 1996 - Nissan 240sx SE RB25DET
2008 - Yamaha YZF-R6 - SOLD
2007 - Ford F150 FX4
Location: Huntsville, AL

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I had the same exact problem with my ka last spring. Car suddenly overheated going down the highway, when I stopped coolant was pouring out from under the manifold. Turned out I had a huge air pocket in the cooling system. Once I got that burped out it ran great the rest of the summer.

tankboy1138
Posts: 2
Joined: Mon Mar 05, 2018 10:57 am
Car: 1991 240sx S13

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Thanks for the reply Smurf. Sorry to suffer you though war and peace.

Now that you say that about timing, that does make sense. The ECU can probably control the frequency of when it charges the coil to advance or retard timing. I was under the impression that the distributor was operating under a simpler, "when the gap between rotor and coil get close enough, instant spark" methodology. Thus skewing my diagnosis of the problem. Maybe that's how it worked in older distributors before ECU's.

I'll start by testing all of my sensors and replacing anything that's off, and then I'll double and triple check my coolant for air pockets, thanks for the info Flartius. Been replacing hoses, the pump, tstat, and cleaning up pretty much anything that I can to reduce the potential causes for problems.

Again, thanks for the replies, I was probably over-complicating things. I'll go back to basics and see where that gets me.


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