So two years ago my 96' z28 developed a misfire and eventually it wouldn't start or run. I was a full-time college student living in an appartment 5 miles out from campus at the time so when it broke down I parked it in my reserved space where it sat for a long time.


I recently got a family member to pay for a new opti-spark install at a shop and it fixed all the issues I was having except now there's a p0336 code that won't go away. It's the only code I currently have on the computer right now and the car runs better than it's ran in probably 6-8 years (the last time I installed a new opti).


I went with an Autozone duralast for the lifetime warranty since I knew it would eventually break again eventually. The last time I did this job I used a new AC Delco unit that was incredibly good. Ran for years. And ran super silky smooth, but, it slowly ran rougher and rougher until it began misfiring over the course of 4-6 years.


That said, I feel like the chinese sensor in the Duralast Optispark is causing the p0336 code which is a problem because I live in california and I can't register the car with that code present -- regardless of it the Crankshaft position sensor actually does anything on the lt1 or not.


So, the first thing I figured was I'd just buy a bew crankshaft position sensor and try installing it to see if it solved the problem. Once again the Duralast lifetime warranty appealed to me. So I bought one and installed it this afternoon. The stock sensor was totally drenched in oil. Everywhere. Thing is, the engine leaks oil from every gasket but I couldn't ever afford the pricy labor costs to replace the leaking gaskets so I have really just let the car leak oil for the past 8 years because I literally couldn't afford the price of labour to fix it. So I thought maybe the wiring connection was being degraded by all the oil and grime caked on everywhere. But, to my surprise the new duralast sensor made the car run worse than it ran with the Delco crankshaft position sensor. So I swapped the Delco sensor back on and the car ran much, much more smoothly.


I'm kinda stumped by this because #1 I thought the crankshaft position sensor didn't affect how the car ran. So it really surprised me to see how back to back swapping the sensor caused the car to run noticeably different. So I'll be returning the Duralast crankshaft position sensor tomorrow.


Now, this is concerning to me because I worry that the rotor and cap on the new optispark are causing it to run good, but maybe the non-mitsubishi sensor is sending a bad signal to the PCM/computer which is causing the p0336 code. Which would mean, my optispark is preventing from registering my car. Which means I can't go apply for jobs because I don't feel comfortable using public transportation during covid-19. And, the icing on the cake is I just realized I can't find my receipt for the duralast opti spark which means I can't even return it and swap it out for another one.


So I'm feeling pretty low. The kicker is that, the car runs really good right now. The misfire is completely gone and it starts right up and drives great.


Though, it does get hot and flirts with overheating at idle if it sits for a long time without moving. If I let idle and just sat in the car and watched the temp guage it it'll go to 180 and sit there fir maybe 15-20 minuets, then it'll go to 200 and sit there for 10-20 more minuets but then it'll start to get real hot at the 1 hour mark. And it basically flirts with overheating. The gauge will go down again to around 200 and then climb back up to super hot and then go back down again. It's very anxiety invoking because when I was in highschool I overheated the engine once and blew the head gaskets which cost me $2,400 to repair.


So basically, I'm pinching pennies and I need to get this code gone so that I can go get a job so that I can get money. Hopefully then I can actually continue fixing things that I have neglected to maintain because I literally had no money.


I can take photos of the undercarriage tomorrow if anyone wants to see how it looks near the crankshaft position sensor and what not as well. I'm hoping that Autozone can see my purchase based on my rewards phone number. But given that I didn't get an email receipt luke I usually do (because I always lose track of paper receipts) that maybe I was in a rush and forgot to give them my phone number for my rewards account. Which would actually be really bad because I don't have any more money to buy a new optispark and since the car isn't registered if I park it I'll get a ticket and it'll probably get impounded. And, well, that would be bad.


Last time I installed the AC Delco opti I really screwed up the install because I'm not really a mechanic. I've just always been broke so I just slogged through it as best as I could because I couldn't afford to pay a mechanic for theur labour for the install. And so, I ended up breaking one of tge irigibal bolts to the opti off into the timing cover and when I tried to drill it out my drill bit broke off into the hole. And when I tried to drill it out again I broke a second drill bit in that same very hole. So I actually ended up just bolting on the opti with only two of the three bolts and somehow it worked and held together all those years. So when I got the offer from a family member to pay fir the install, I didn't tell the shop anything about the broken bolt and they didn't say anything to me about it after they finished the work either. And they finished the job pretty fast, so I just assume they drilled it out and got it on without any problems. Even so, I never got the p0336 code with the Declo opti even with only 2 of the 3 bolts holding it on there.


So it's a mystery to me.


The car has 161,000 miles and maybe the timing chain is worn out. And maybe that's what's causing the new p0336 code and that would mean it had nothing to do with the opti at all and was just a coincidence. But I'm not confident enough to attempt taking all that stuff apart to look at the timing chain only to put it back together right after paying someone to install the new opti for me.


So, any tips would be very useful and helpful.

 

You really are between a rock and a hard spot currently, when my optispark was going bad I also received a P0336 just before it spun its final revolution. I have no experience with the Duralast optispark, I can't imagine that there's a whole lot of good feedback for it. Hopefully, it truly is 'ok' and lasts you for a bit. You need to make sure that you don't have any oil leaks that will actually render the optispark useless, this may also be a possible cause of the code but I'll let Injuneer chime in on this. Now I wouldn't condone, especially because it's probably a crime where you live (definitely lol), you may be able to wire in a resistor of some sort just to turn off the P0336 code for the time being. You would have to do this at your own discretion, it's likely possible but I'm not sure what the PCM is looking for from that connector, so I'm unsure of the resistor range or if it's even possible. I don't understand how swapping the crankshaft position sensors back and forth would change how the car runs, the sensor is merely for misfire detection on the 96-97 cars. In no way could I imagine this effecting actual performance, are you sure there's nothing else that you messed with or changed between each time you swapped them? A picture of the optispark area and timing cover may be useful, if there's an excessive amount of oil or really any it should be fixed before it really renders the car useless. An oil leak on the front of the motor could be coming from a variety of sources, optispark seal, timing cover etc..
There's another multitude of issues that could cause the P0336 such as "excess timing chain wear, loose crank reluctor for the CKP, CKP sensor hitting the reluctor, reluctor hitting the timing cover, Opti indexed incorrectly to the cam dowel pin." (Injuneer), hopefully he won't mind me quoting him on this.
At this point, your main concern should be to get the job. But for that you need the car to pass emissions, so let's find a way to get it to pass emissions. If that's not possible public transportation may be the other option, or a ride from someone, if you plan on going public transportation a P100 Respirator and eye covering (shield or safety goggles) are your best bet lol

Goodluck, Grant

 

You know I was surprised too, but all I did was take off the factory original ac delco sensor and put on a parts store new sensor out of the box and it hard started and ran rough, so I let it run for about 10 min and turned it off and swapped back on the telco sensor and then it fired right up and ran very smooth. It was a night and day difference.

That's why I'm confused. You know, I should try just unplugging the sensor altogether to see what happens. If the sensor truly serves no mechanical purpose (which i question based on what happens when I switch the sensors), then maybe I'd try to see what I could do to finesse it to trick the computer.

 

First.... the output signal from the CKP sensor is a pulse, based on the 4X reluctor wheel on the crankshaft. You can't "fool" the PCM with a resistor.

Next.... All I can go by is the documents in hand.... two GM publications, including the factory service manual that says the CKP sensor was added in 1996 for OBD-2 only misfire detection. Also keep in mind that the 93-95 LT1's run fine without the CKP sensor. I've also reviewed PCM data logs from 100's of LT1's, including 96/97's with and without the CKP sensor hooked up, and never noticed a difference that I could attribute to whether the CKP sensor was hooked up.

P0336 sets when the PCM compares the crankshaft position indicated by the CKP sensor, to the crank position indicated by the camshaft position sensor in the Opti, and the difference in rotational degrees goes outside the range -10-deg - +7-deg. Yes, a sloppy timing chain can cause the code to set. Also, and this was one I picked up from some good data provided by the owner, if the Opti is not indexed correctly to the cam dowel pin, the code can set. In that case, the dowel pin was a bit too short, and slipped out of the correct index hole in the Opti. Interestingly, the owner did NOT detect any issues with performance when this occurred.

Why would swapping CKP sensors affect the way the engine runs? One way would be an electrical problem with the sensor. The CKP sensor and the Opti cam position sensor low resolution signal use the same "reference" (in effect, ground) from the PCM. The cam position sensor uses a 5-volt positive reference from the PCM. The CKP sensor uses a 12-volt power supply from fuse #11 in the under hood box. It's conceivable that an internal short in the CKP sensor could affect the cam position sensor, and make the engine run rough. Just a theory, but a plausible explanation.

I would suggest you download a free copy of the 1996 factory service manual, courtesy of member GaryDoug. Look at Volume 2 of 2, Part 1 of 2, page 6E-649 for the detailed description of P0336. It lists all the things that can cause the CKP sensor crank angle to differ from the cam position sensor angle. Also look at P0335. That code will set for a much larger deviation between the crank and cam signals, and also sets if there is no signal from the CKP sensor.

http://www.mediafire.com/?40mfgeoe4ctti


With your description of excessive oil leaks on the front of the engine, oil entering the Opti could cause problems with the pulse signals the PCM requires to run the engine. Have you found oil in the Opti, if you opened it up?

 

Photo of opti on car. Hard to see much, but it's dry from the front. not sure from the back. Oil tends to leak from the bottom of the timing cover and from the oil pan, but not from the top of the timing cover.


CKP after cleaning. Before cleaning it looked black like charcoal. Totally covered in gunk and grime. The white plastic was not visible. Neither was the bracket.


Reference to show how the sensor looked before cleaning. It looked like how the rack and pinion looks in this photo, black grime caked on. Even so, I'm thinking it's a defect on the autozone opti. I don't have an oscillometer but I have a milimeter and an obd scanner that supports live data graphing. If the scanner can show and graph the optical sensor on the opti that'd be cool. But I don't know if it can, it appears to only graph stuff like manifold pressure, 02 sensors, MAF and timing.


Shot of wiring harness.

Another shot.

Will upload photos of sensor scuff and try to take a photo of the reluctor wheel and my voltage readings on the wires.

 

Oil can enter from the back of the Opti, through a faulty Opti seal on the timing cover.

 

These are the codes I had before installing the autozone optispark.

When I payed a shop to install the opti, I also installed a new mass air flow sensor to take care of the p0100 code (and it's gone now). I installed new upstream 02 sensors and cleaned my filthy k&n air intake filter (I hadn't cleaned the filter once in the last 8 years, it was black and now I an hear the audible whistle of the filter pulling in air again so that was cool) with a recharge kit which took care of the p0172 and p0175 codes.

I replaced the corresponding coolant temperature sensor and that took care of the p0118 code.

That left only the p0300 code and the bad misfire that the car had. That's why I bought a new optispark. I was 'this close' to buying an ac delco remanufactured opti from the parts store but at the last minuet I went with the lifetime warranty part figuring it'd be nice to never have to spend money buying a new one again figuring that it'd break often and need replacing often. But then I lost the receipt so the warranty is probably lost.

But sure enough the new opti fixed the p0300 code and now it runs like a champ. But, after a few days of testing, I got the new p0336 code.

I've got a video showing the car idling after a cold start to show no misfire. I need to switch from my phone to my mac to upload it.

 

OP

I hope you saved the old AC Delco opti. Its Mitsubishi sensor is gold.

After market optis are mostly crap. There has been evidence shown the the stamped metal wheel is "slightly" off compared to a original AC Delco. This will cause the code you have.

If you have the old opti use the sensor and slotted wheel in the autozone opti

your CPS wires are bare as they enter the connector...could easily be corrosion on the connection as a result

front motor oil or WP leaks will kill any opti so until you fix those you will just keep killing optis. The most common leak source is from the WP drive seal ESPECIALLY once it is disturbed by changing opti as the WP is removed

Short of paying "cash" to a smog shop that does....."altered" smog tests you need to fix the core problem causing the code. Also every time you use a scan tool to clear a code or disconnect a battery the IM monitors in your PCM need to "learn" again and that can take several hundred miles of various driving speeds to accomplish and in CA you are only allow 1 IM monitor to show not ready. EGR and CAT Heat are the two IM monitors that are very stubborn to read ready

 

And are you 100+% certain that the cam dowel pin is correctly indexed to the Opti?

http://shbox.com/1/opti_back.jpg

 

Interesting to know that. I don't know if I'll be able to pull the thing apart. It'd be easier for me to get my hands on an oscilloscope. I have a relative willing to help finance diagnostic tools. So, if i could get an oscilloscope to check the high and low resolution optical sensor signals from the optispark digitally that would be much easier and better.

Here's that video of the car starting up cold and idling smoothly. Absolutely no misfire at all. The watermark is due to free software to covert to a compatible format and file size.

 

You know, I thought about that. But the old shop said they threw it away. Once I start working again I can source a Mitsubishi sensor to keep on hand. My local parts stores still sell remanufactured AC Delco units. So hope is not lost yet on that sensor. I should have told them not to toss it honestly. But on the other hand, I'm annoyed that we can't walk into a parts store and buy a working part and put it on without worrying about it. It's not really right to have to horde discontinued products just to maintain a vehicle with no mechanical failures.

 

No I'm not really sure. I didn't do the work and I'm a little traumatized about doing it since the last time I damaged a bunch of stuff in the process by breaking bolts and drill bits. Plus I don't have a harmonic balancer puller on hand. But if by some stroke of luck my lifetime warranty is still findable via my phone number then I'll certainly be trying to do the replacement myself i suppose if nothing else appears to be causing the problem. I hate to rip apart a good running setup though. I still don't have an oscilloscope to use right now so I'll need to order one on Amazon tonight, but when I get one I can use it to check the optical sensor in the AutoZone opti. But I guess even that won't detect slight manufacturing defects that could cause a misalignment of the internal parts. So if I do wind up pulling the one on there off, then at that time I can verify whether or not everything is exactly the way it is supposed to be (which is why I will always dislike taking my car to a shop, but for the big jobs it's the best way for me).

I might just start going to dealerships for big jobs I don't want to do myself going forward from now on. I've got good dealerships in my area. At least then I can trust that they have all the GM specialty tools and diagnostic procedures and flow charts, as well as the original factory documentation on maintenance, a bias towards using factory engineered parts and all of that good stuff. It seems on this car that it's best do go to dealerships for work done for the guarantee that the work done will actually be done correctly as it is supposed to be done strictly according to the book. I honestly just believe that the GM engineers are a cut above the rest of their direct competitors in the industry. And that the car's design confuses ordinary aftermarket manufactures and mechanics because their engineers just aren't good enough to figure out the design the GM engineers put together. That's both good and bad. it's part of the reason why I've insisted on hanging on to the car over the past 10 years and why I don't have any intention of getting rid of it at the moment. Had it been nothing special engineering wise I would have gotten rid of it a long time ago. But I do believe that it is actually special.

Just seems like the really great parts of this car also make it unserviceable by the majority of auto technicians out in the wild, which is very annoying. It's like owning a $5,000 Ferrari in many ways.

 

I wouldn't chase anything further before repairing the bare wires at the crank sensor connector. My troubleshooting motto is to repair anything that is obviously improper before going on to other more obscure paths.

 

Okay so an update. My oscilloscope came in the mail this morning and I tested both the high res and low res signals on the opti... and it looks just fine on the scope. So my opti is okay. See my attachments for the videos I filmed where I show the readouts on the scope. So this rules out the opti.

So what else could it be? I haven't used a multimeter to check wiring connections yet, so that will be my next step. Anyone know what the crankshaft position sensor's signal wave pattern is supposed to look like on a 'scope? I may as well check the CKP sensor's wave pattern to see if it looks good/right.

 

You can have PERFECT Opti signals and a PERFECT CKP signal, and still get P0336. Read post #4, 3rd paragraph.

The GM dealer Tech-2 scan tool can read the difference in degrees between the CKP sensor and the Opti signals.