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Discussion Starter #1 (Edited)
Hey everyone, I'm stumped on this one...I have these two codes that will not go away, P0335 & P0336, fresh rebuild on motor and transmission, runs flawlessly and this is all that pops up, I replaced the crankshaft position sensor, checked for voltage as well and it reads 12 Volts on the power side, less than 1 volt on the ground side and 0.03 Volts on the signal side, with the engine running it pops up to 0.05 on the signal side and that's with the multimeter being set to the 20 DCV range, all others give nothing unless its in milivolts. I traced the yellow wire from the sensor back to the ECU and at the point about an inch away from the ECU side it still shows 0.03 Volts and 0.05 Volts respectively, also the insulation is not torn, or split in any way at all. I'm thinking the ECU has a glitch but I'm not sure. Any ideas? Also if I sent it out to have it tuned, would I receive the same ECU or a different one?
 

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Since the crank sensor on the 96-97 lt1 only reads misfires, don't go crazy because you have the codes. Go to the following link and download the 96 service manual. It will have troubleshooting, explanations of what causes code to set, wiring diagrams, etc. www.mediafire.com/?40mfgeoe4ctti

You changed the sensor, but that doesn't eliminate it as a suspect. This is because of the many defective new parts that make it into the supply chain.

My next prime suspect would be the wiring to the sensor from power, ground, & pcm. Use the wiring diagrams in manual to trace wires, connectors, & splices.

If you have an obd 2 scanner that reads real time sensor data, you might get lucky and be able to read some of the cks data as it streams live.

To monitor the signal of the sensor, you need an oscilloscope to properly see the square wave signal that crank sensor puts out You can buy a pc based oscilloscope on Ebay, Amazon,etc for around $70.

Don't think this will be a 1 time use tool. You can check your opti low & high resolution signals with it. Plus that pesky 50 hertz fuel enable signal sent from body control module (bcc) to pcm so injectors stay open.
 

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Discussion Starter #3
Thanks Cocobolo, certainly more involved than I was hoping for since I just finished rebuilding the motor and took it on it's first break in drive. This is the second sensor I've put in under warranty so I doubt it's that unless I'm just having some really bad odds with the parts store, the power is getting 12 volts and the ground is less than one volt (pretty much 0) What's weird is that tracking back the wiring it stays constant throughout the harness all the way to the ECU. If anything I'll just get the computer tuned as I planned on doing at some point anyway but I wanna be sure that I don't have an ECU that's failing and the tune gets done and a week later it's just dead.
 

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Discussion Starter #5
I think it's a AC Delco one, I replaced it a couple years ago and read about the BS that went on with aftermarket ones. It has no codes relating to the opti and has absolutely zero issues with performance. I plan on using an oscilloscope to check the signal but I find it rather odd that it's getting power, ground and low signal...Yet no opti codes. Just the crankshaft position sensor codes. If anything I'd rather just tune all that stuff out as it is but I want to be sure I don't have a failing ECU first.
 

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some off brand opti have issues with the slotted wheel being off which threw codes on obd2 cars with a cps which is why I asked
 

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Hi
I could be talking out of my arse but i was reading through a few threads on www.corvetteforum.com last night and a CPS was mentioned along with a re-learn procedure.
I can't recall which motor it was on until i read this thread.
Worth checking if there is one.

HTH
Mitch
 

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Discussion Starter #8
Thanks for the input everyone, I'm still not entirely sure what it is but one of my mechanics I work with thought at first the wheel that the sensor reads on the crank was installed backwards, I didn't think that would be possible but checked anyway...It's on good, voltage is still okay, I'm thinking maybe a glitched ECU but I'm still not 100% sure. As for the re-learn procedure, I thought that was only in OBD1 and certain vehicles that require the TPS to relearn it's setup, I could be wrong though. But it doesn't stall, act up, no lack of power, no issues in drive ability. Just this annoying light I need to get rid of to pass emissions.
 

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Discussion Starter #9
UPDATE: so I pulled the sensor to check and see if the wheel inside the timing cover was on wrong, it's on correctly but I noticed that it has a little bit of play in it...I would say about 1-2 milimeters, It's attached at the keyway as it should be but I'm thinking maybe the crank hub isn't pressed on far enough. It doesn't make any noise running or anything but I do notice that the front main seal might be leaking slightly. Not sure yet though...Could the hub not being pressed on all the way or correctly cause the wheel to wobble and create a poor signal on the sensors part?
 

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UPDATE: ...Could the hub not being pressed on all the way or correctly cause the wheel to wobble and create a poor signal on the sensors part?
Yes if hub is not flush against CPS wheel. Just see if you can turn hub bolt any. If M6 car put in gear...otherwise find a way to keep motor from turning while you tighten crank hub bolt.

Crank seal rarely leaks unless the hub got scored from seal. You would need to replace hub if that is the case. If hub is scored I would replace it vs using a speedi sleeve.
 

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Discussion Starter #12
Yes if hub is not flush against CPS wheel. Just see if you can turn hub bolt any. If M6 car put in gear...otherwise find a way to keep motor from turning while you tighten crank hub bolt.

Crank seal rarely leaks unless the hub got scored from seal. You would need to replace hub if that is the case. If hub is scored I would replace it vs using a speedi sleeve.
Yeah I don't think it's scored, I definitely believe this is the culprit here. I'll have to try and removing the hub again and re-pressing it back on...I strongly believe that it's just not in far enough.
 

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Sorry to bump an old thread, but I'm having the EXACT same issue with my 97. Freshly rebuilt engine and I'm getting the exact same codes. I'm guessing since there were no updates to the thread that the loose CPS wheel is what did it? I didn't check mine yet, but I will now. If the original OP sees this and could update with what his problem ended up being, I'd really appreciate it. Anything to make my diagnosis go easier would be great.
 

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Discussion Starter #14 (Edited)
Sorry to bump an old thread, but I'm having the EXACT same issue with my 97. Freshly rebuilt engine and I'm getting the exact same codes. I'm guessing since there were no updates to the thread that the loose CPS wheel is what did it? I didn't check mine yet, but I will now. If the original OP sees this and could update with what his problem ended up being, I'd really appreciate it. Anything to make my diagnosis go easier would be great.
In my case it happened to be due to the fact I was using aftermarket distributors, I caught on to it and bought three of them and opened them up to find they all had very badly warped reluctor wheels causing a misreading on the cam position sensor and since that engine uses cam position to determine crank position, I'm thinking that's why it triggered that code. Replaced with it an original true GM Delco unit and it seemed to fix the problem. The aftermarket distributors have had extremely poor reviews too, surprisingly even the MSD one had some bad reviews too but not as bad as the amount on a generic aftermarket Autozone or O'Reilly's part. If your using an aftermarket distributor I would start there by switching it back to a true GM Delco unit. If it still comes back, I would check the wiring harness and make sure everything is pressed properly together. I spent hours on end trying to figure it out and then I finally found a review on one of the aftermarket units that said as soon as they installed that part it caused that set of codes.
 

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In post # 2 I gave the link to 96 service manual. Get it and turn to page 6E-544. That is where code 0335 begins. Read up on the code and what makes it set. Besides the opti high resolution wheel being wonky, the timing set if worn can cause the code.

Unfortunately, you need a tech 2 scanner to read the crankshaft angle being sent out by cps. And need it to do most tests.
 

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The car still has the original opti on it. I was hoping it would still be fine to reuse since the car only has 104k on it and the previous owner ( who took it all apart ) never mentioned any issues. However, the wire that goes from that wide plug beside the fuel rail on passenger side down into the top of the opti was messed up. The plastic part that makes it click was broken and I could only push it in and let friction hold. The rubber part was acting like a spring and pushing it out some. So it may not be making good contact. I'll start there.

I posted another thread about glowing manifolds on the driver's side. Could this issue ( poor connection to the opti ) be causing that?
 

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Glowing exhaust manifold can be caused by a very lean mixture, retarded crank to cam timing, or retarded distributor timing. So yes, opti could be at fault. Blown head gasket can do it also.

My 90 3.1 car has a broken tab that locks map sensor connector. It gets poor contact and causes misfires in multiple cylinders. I open hood, reset connector, engine will run fine until connector wiggles out again. So your connector could be causing running problems.

New opti pigtail wiring harness is available for your car.
 

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Oh my, I hope it isn't a blown head gasket. I just put this motor together and THAT would be terrible. Though my oil doesn't have water in it and there wasn't any white smoke after the first warm up. I was a bit concerned with it except it wasn't as thick as when a gasket blows and it stopped after warming up. I assume it was either evaporating water from the exhaust or burning off the stp oil treatment from the cylinder walls.

I remember seeing that pigtail I need on rockauto months ago, but can't for the life of me find it now. Do you know what it would be specifically called on there? They don't call the distributor an opt, so optispark doesn't bring anything up.
 

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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
 

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Okay, so I replaced the pigtail and that did not fix the issue. I came in here to get the service manual page number ( which is incorrect, btw. 6E-544 is for code P0123 TP sensor ). While here, I have some more questions based on your earlier posts.

How do I know if the timing set has excessive wear? It did feel as though there was some slack in the chain when I put it on, but I didn't think it was significant enough to cause any problems. I'm pretty sure it's not supposed to be guitar string tight though, so how can I know how much slack is too much?
 
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