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In the manual, I did a search for P0335 and it came up on page 6E-644. After reading up, I was confident I could find the problem. I knew I need to see live data to confirm info coming from the CKP sensor, Opti Sensor, and the CKP Lo Resolution Angle % and I'd be able to ascertain which of these was the problem ( CPS, Opti, or timing chain ).

Today, I go to Autozone to "borrow" a scan tool capable of live data. I scrolled through the 26 lines... and I have no idea which, if any, of them are for these three bits of info. I didn't write down everything I was seeing, but I can if it will help anyone willing to help me figure out what's going on.

It did have a "Freeze Frame" setting that according to the manual catches the relevant data at the time of the code. So for code P0335, it gives me the following:

Fuel Sys 1--------- 0L
Fuel Sys 2 -------- 0L
Calc Load ------- 3.9%
ECT--------------- 221 °F
STFT B1--------- 0.0%
LTFT B1---------- 0.0%
STFT B2--------- 0.0%
LTFT B2-------- 21.9%
MAP------------- 10 (inHg)
Eng RPM--------- 996
Veh Speed-------- 0mph
MAF ------------- 1.43 (lbs/min)
TPS ---------------- 0.0

Some of these I know what they are. The 5-8 are bank 1 and 2, but I'm sure exactly what they are reading. Seems odd though that 3 of them are 0 while 1 is over 20%.

There are 13 more categories when doing the live data. Besides any potential issues shown above, what should I be looking for in the live data? I need to figure out while I still have unusually warm weather to work on the car. Otherwise, it'll sit all winter...
 

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Try ebay, use "optispark distributor wiring pigtail" as your search query. There will be multiple sellers listing it.

About blown head gaskets. The symptoms of a blown hg, depends on where the gasket blew out at. water in the oil or oil in the water only occur if hg blows out in an area that communicates with a water passage. There are many symptoms of blown hg. Including exhaust manifold glowing red.

Do a compression test on all cylinders. 1 cylinder with low compression, or 2 cylinders with low compression, that are next to each other, are good signs of blown hg.

Also make sure the fuel injectors that serve the cylinders where exhaust manifold is red, are not clogged.

Since opti needs to be tested, you will need a $70 pc based oscilloscope to test low & high resolution signals of opti. That is if problem isn't wiring pigtail or blown hg. low & high res signals should be a well formed square wave, with no drop outs, or skewed waves.

And since your car is an obd 2 computer system, if you had a GM tech 2 scanner, it could run a test comparing output of crank sensor to output of opti. This would tell you if crank sensor or opti timing wheels are the problem causing codes 0335 & 0336
Okay, so I just replaced the timing chain and opti. I got an aftermarket one, but put a mitsubishi sensor from the junkyard in it. Car starts up just fine. Still give these codes on the second startup. I didn't manually clear the old ones, they just went away because the battery has been unhooked for like 2 weeks.

I used the service manual and the diagnostics tree only leads to a new opti if you also have the low or high resolution codes ( which I don't ). It says "excessive backlash in the distributor" can cause it, but I'd assume that's Crank timing gear was worn. Teeth were noticeably smaller than the new gear and that's where my slack was. The gear would move a little before contacting the chain. I was 99% certain that was my problem. I guess it wasn't. New chain is tight and movement of the two gears is instantaneous.

With a multi-meter, I checked at the sensor and I had good voltage, ground, and signal ( didn't use an oscilloscope, just checked voltage. Got an even 5 or 3 depending on crank position. Next I'm going to check the other end of the signal wire to make sure it's getting signal to the PCM.

Something I did notice today. The harmonic balancer has a bolt in one of the external holes going around and it's broken off in there. There are about a dozen of these holes, and only one has a broken off bolt in it. I'm sure that's throwing off the balance of the engine. Could that cause the code? I'm assuming previous owner tried to pull it off by putting bolts in those holes and one broke. Seeing as how they aren't threaded...
 

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Discussion Starter #24
I may be wrong but it's certainly a possibility. The biggest thing I noticed with the aftermarket distributors is that the reluctor ring inside was warped on every single one of them, some noticeable, others you would have to REALLY watch it as you turn the ring real slow, that's where I thought my problem was and it wasn't until I read a review on the aftermarket ones of a person that said it threw both those codes and they wouldn't buy another one. My main problem was that it would run just fine but on the second startup it would throw both codes. For whatever reason when I put the GM Delco unit in, problem solved.
 

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I may be wrong but it's certainly a possibility. The biggest thing I noticed with the aftermarket distributors is that the reluctor ring inside was warped on every single one of them, some noticeable, others you would have to REALLY watch it as you turn the ring real slow, that's where I thought my problem was and it wasn't until I read a review on the aftermarket ones of a person that said it threw both those codes and they wouldn't buy another one. My main problem was that it would run just fine but on the second startup it would throw both codes. For whatever reason when I put the GM Delco unit in, problem solved.
I think I'll pull the water pump and hub back off so I can open up the opti. After re-reading your post about the review, I thought maybe the reluctor wheel has the slots cut just a few degrees off. That would trigger the code. I have the OEM reluctor wheels from the junkyard optis I bought for the sensors. I'll compare them to see if the slots line up. The aftermarket one was pretty flat. Much like the oem. They both had a little warpage when laid on a flat surface, but flattened out when the rotor was tightened down on them.

If that doesn't fix it, then I'll put the original opt back on but with the cap and rotor from the aftermarket one.
 

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Update, didn't need to pull the water pump or distributor. Turns out it was actually a bad crank position sensor. Put that on and these codes went away. Water pump was leaking and the crank timing gear had worn teeth, so I don't regret doing those jobs. Opti seems to be fine so far.

With the new sensor, I got P0300 code which I narrowed down to a bad fuel injector. Replaced it today and the car fired up with no codes. Drove it to church and back. As I was about to pull in the driveway, I stalled it since I couldn't see ( tint too dark and it's dark outside ). Fired back up no problem. Turned around and backed in with the windows down ( so I could see ). Check engine light starts flashing. I shut it off and it's code P0300 again. Cars been started and shut off a good 15 times before this happened. Raised the hood and now a new problem.

I could hear the coolant boiling. With the old pump ( before it went bad ), car would warm up, fans kick on, and then it would cool down. I couldn't see the fans to see if they were on or not, but the car was above the temp they should kick on. It climbed pretty quick to nearly the 260 redline and I shut it off. Since the fans weren't kicking on, it wouldn't do any good to let it run. If it's not one thing with this car, it's another. I guess I'll start a new thread about this.
 

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Update, didn't need to pull the water pump or distributor. Turns out it was actually a bad crank position sensor. Put that on and these codes went away. Water pump was leaking and the crank timing gear had worn teeth, so I don't regret doing those jobs. Opti seems to be fine so far.

With the new sensor, I got P0300 code which I narrowed down to a bad fuel injector. Replaced it today and the car fired up with no codes. Drove it to church and back. As I was about to pull in the driveway, I stalled it since I couldn't see ( tint too dark and it's dark outside ). Fired back up no problem. Turned around and backed in with the windows down ( so I could see ). Check engine light starts flashing. I shut it off and it's code P0300 again. Cars been started and shut off a good 15 times before this happened. Raised the hood and now a new problem.

I could hear the coolant boiling. With the old pump ( before it went bad ), car would warm up, fans kick on, and then it would cool down. I couldn't see the fans to see if they were on or not, but the car was above the temp they should kick on. It climbed pretty quick to nearly the 260 redline and I shut it off. Since the fans weren't kicking on, it wouldn't do any good to let it run. If it's not one thing with this car, it's another. I guess I'll start a new thread about this.
I hope you don't mind, but I'm bringing this thread back because I'm having the exact same problems on my 96' z28. Installed a new Durmast Opti and now have a p0336 code. Car runs really good. Car runs worse when I replace the crank position sensor with a new aftermarket unit so I put the factory original back on it.

I'm assuming the p0300 was caused by the aftermarket optispark failing. And I'm really beginning to wonder if the p0336 code isn't also caused by an aftermarket optispark as other posters have said. If so, that really sucks because the ac delco optispark is discontinued now. All i can buy are aftermarket units. And to be honest, I'm not very good at installing them. It's a little too much work for me not to wind up breaking something. But I've got a great running car with a p0336 and a new crankshaft position sensor didn't fix it. So I'm wondering how the process of diagnosing ended for the OP. What ended up causing the final p0300 code? Did it turn out to be the aftermarket opti all along?
 

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If you want to be 100% sure about optical section of opti, get a $70 PC based oscilloscope on Ebay, Amazon, etc.

With it and a laptop pc, you can have assistant drive car and you can monitor the low & high resolution square wave opti pulses as you go down the road. If pulses aren't a well formed square wave or if signal drops out, opti has problems.

While you can't buy a new GM, Delco, or Delphi opti, you can buy a rebuilt one. Also, I've heard good things about the Petris opti. But it costs $400. www.petrisenterprises.com

The crank sensor is only there to detect misfires. But I believe it can pick up on a misfire because of opti problems.
 

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Discussion Starter #29 (Edited)
What I finally realized and what fixed my problem (fingers still crossed it doesn't come back) is that it was a combination of not only a bad aftermarket Opti but also a wire problem. I checked continuity between the wires that go to the crank sensor and the PCM and they had continuity (had to repair the harness prior to all this) but the middle wire pin in the connector itself was bent just a little too far back causing intermittent contact within the pigtail/ crank sensor. Thus causing the code to appear. I replaced the pigtail and soldered it to the main harness and so far the code has not come back. Also yes in the 96 LT1 models the crank sensor does nothing but help the pcm detect misfires, if you have the 336 code PLUS a 300 code which means random misfire I would look into the ignition system, on mine I ONLY had a 336 code which drove me nuts trying to figure that out as everyone else on here had two codes related to the crank sensor. My first thought is that the opti spark is a major source of all kinds of problems on these motors, despite having a crank sensor it does not cause drive-ability concerns, I would personally install a true OEM Delco unit, ebay has them used which can be a hit or miss, they also can be rebuilt since I understand they have a Mitsubishi optical sensor in them and then check your wiring harness and make sure the pin tension is good between all the contacts also make sure that the opti you get is meant for a 96 LT1, doesn't matter if it's from a Corvette or whatever else. All in all I would say the aftermarket distributor caused all kinds of problems with crank codes, though at the end of the day it was in fact a wiring harness issue with me but again my motor still ran great despite having that code.
 

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Those multiple offender troubles will drive you up a wall.

I had a similar problem with my 90 3.1 car. Car died would not run. I traced the problem to the electrical part of ign sw, which wasn't sending power to the coil. Which in turn sends power to distributor.

Installed new elec part of ign sw, had power to coil, but engine still wouldn't run. Turns out wire pigtail from coil to dist failed also. Bought a new one and car cranked right up.

But I still had a regular miss that new plugs, wires, cap & rotor didn't fix. So I tested the pick up coil in dist and found it had a tiny break in one of it's 2 wires. This bare spot was grounding regularly and causing the miss. I could have replaced the pick up coil but a new distributor was only $20 more than pick up coil. So I replaced entire dist. Car runs great now.
 
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