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Alright bear with me here, a bit of a novel coming.

Due to a lifter failure and resulting damage I had the engine rebuild over the winter. Previously the car was N/A with big cam and heads. As part of this build I installed a Harrop HTV1900 supercharger but went with a less radical cam. I've put on about 200 "shakeout" miles trying to get issues taken care of before I go to the tuner. I'm running the same injectors it was tuned for previously and I'm staying out of boost so it should be fine for this purpose. I installed a bigger fuel pump and did the 8.1L bucket mod which I am mentioning for later.

Most of the 200 miles I've driven have been uneventful, save for throwing a couple knock sensor codes which I believe I remedied with a new harness and one new sensor. One day I'm running errands in the car and I notice it's taking progressively longer to start each time I return to the car and eventually get a no start condition. CEL code is P0336 CRANKSHAFT POSITION SENSOR CIRCUIT RANGE/PERF. Have the car trailered home and replace it. Put things back together but the car now has a misfire. I figure it needs a CASE relearn so I schedule an appointment with a garage but they complete the procedure and no dice. They say it is running out of fuel but I don't believe them. Will explain below.

TL;DR
Newly rebuilt engine with new roots supercharger.
Car will idle perfectly fine for 30-45 seconds without throwing codes.
After a brief time it will misfire or stumble here and there, gradually becoming worse and then stall out within 2 minutes time.
When it starts misfiring it throws a P0336 code.

THINGS I HAVE DONE
-replaced CKP sensor
-verified air gap between the sensor and harness is .037"
-confirmed as best I could the reluctor wheel teeth are centered in the bore for the sensor. The 24X wheel has two sets of teeth fore/aft ad it looked like the set closer to the front of the engine was centered in the bore, thought I was lying on my back and looking through a mirror so I could have that backwards.
-replaced CKP sensor harness & ~7" of wire leading to the harness
-wrapped the wires in electrical heat shield, thinking that as the exhaust heats up the old wiring is building up resistance eventually leading to a insufficient signal, hence the gradual progression of the misfires
-tested pinouts of new ckp harness. I get a solid 11.5V on the 12V reference wire and ground on the low reference circuit (should this be a full 12V?)
-The garage believed it was running out of fuel. To check this I have
-verified fuel pressure @ the rails. I get a rock steady 63 PSI the entire time the engine is running including while misfiring and stalling out
-I have a Chinese Tech 2 clone and used it to perform a fuel injector balance test to see if maybe one or multiple injectors were not pulsing. Passed test with flying colors.

I'm about out of ideas here aside from bad PIM or mechanical issue with the reluctor wheel. Any of the gurus still here have thoughts on what to trouble shoot next? I think my manual says if all the pinouts test good then next step is to replace the PIM. Does anyone know of an actual procedure to test the PIM before I go to that step?
 

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Restarts both cold and "hot." Will not run long enough to get to operating temperature on one restart. Once it has started to misfire it will miss from the get go on each subsequent restart.

Of course I just went to verify this behavior today and now it will misfire immediately and not hold idle from cold more than about 10 seconds, if that.
 

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You've done just about everything i would have until this point.

Sometimes you do get a bad new sensor. IIRC the ECM reads the CKP directly as well as the CMP, i don't know how the PIM would factor in. That's more of a translator between two different protocols and the various modules in the car.

Gonna post the diag procedure from the service manual when i get home, if that will help.
 

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Discussion Starter #6
It can't hurt! The CKP sensor I'm running now is an AC Delco off Rockauto. I did briefly try a Duralast brand sensor from Autozone I bought as a precaution the day of the no-start in case I ended up having to fix it in the Lowe's parking lot I was in. If I recall I had the same issue with that one, but maybe I'll try it again since I have it on hand and see what happens.

Also befuddles me that it won't idle at all now. It was very repeatable that I could go to the garage and start it cold and it would run fine briefly. Even yesterday after I replaced the sensor harness it followed that exact sequence. I'm letting it sit with the battery disconnected for a little while to see if it will do it again after that.
 

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Discussion Starter #8
I bought a new Cloyes timing set for this build. Cam gear was CLOYES S826T (#12552953). The machine shop didn't charge me for a new reluctor wheel, nor did we ever talk about one, so I have to assume they reused the original. Since it ran fine for the first 200 odd miles I have to assume timing components are correct. Also I'm an 04, so the cam sensor is in the back of the block on top, doesn't read from the gear. If there is a cam an issue maybe cam bolts backing out?
 

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Yeah, your CSP reluctor is on the back of the cam, so that's not a bad thought. That would suck, though. It shouldn't move around much if the thrust plate is still ok, which it should be if you still have oil pressure, but still...

Easy enough to check.
 

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Well, after a quick search on good ol ls1t0k3, some more ideas to consider:

A reluctor installed backwards, aligned improperly, or bent

Crank has excessive end play
 

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Discussion Starter #11
Yeah, your CSP reluctor is on the back of the cam, so that's not a bad thought. That would suck, though. It shouldn't move around much if the thrust plate is still ok, which it should be if you still have oil pressure, but still...

Easy enough to check.
Yeah, like in your second post we're getting close to pulling the engine back out territory to check crank end play and reluctor wheel runout, so if I'm going to go that route anyway I might as well pull the front cover off first and see what's up. I would love not to do either so if you are still able to post the rest of the diagnostics I'll see if there more I can do before going there. I don't have an oscilloscope but maybe I can find someone locally that would hook me up to check actual cam and crank signals.

The running out of fuel idea intrigues me. It would be a simpler check than removing the engine. Shop's suggestion was that there was a fuel leak internal to the tank, which is possible because I monkeyed around in there enough. Some references I saw for P0336 causes included "running out of fuel." When I took it home from the shop it would not restart unless I primed the fuel pump via key on/off several times. It's generally exhibiting that behavior again. I just don't see how I could be running out of fuel when I have good pressure and functional injectors
 

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Discussion Starter #12
IIRC the ECM reads the CKP directly as well as the CMP, i don't know how the PIM would factor in. That's more of a translator between two different protocols and the various modules in the car.
You're correct on this. My book said PCM, I stored it in my memory banks as "PIM."
 

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Yeah, like in your second post we're getting close to pulling the engine back out territory to check crank end play and reluctor wheel runout, so if I'm going to go that route anyway I might as well pull the front cover off first and see what's up. I would love not to do either so if you are still able to post the rest of the diagnostics I'll see if there more I can do before going there. I don't have an oscilloscope but maybe I can find someone locally that would hook me up to check actual cam and crank signals.

The running out of fuel idea intrigues me. It would be a simpler check than removing the engine. Shop's suggestion was that there was a fuel leak internal to the tank, which is possible because I monkeyed around in there enough. Some references I saw for P0336 causes included "running out of fuel." When I took it home from the shop it would not restart unless I primed the fuel pump via key on/off several times. It's generally exhibiting that behavior again. I just don't see how I could be running out of fuel when I have good pressure and functional injectors
It's possible, although not something i would have ever thought of. Misfires from lack of fuel could affect crank acceleration.

But then i would think the ECM would interpret these as actual misfires and not a problem with the ckp circuit.
 

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I think i read of a way to verify the reluctor wheel placement is correct by looking through the ckp sensor hole and rotating the crank, will have to google later.
 

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Discussion Starter #15 (Edited)
Well this continues to be a fickle problem. I installed the parts store brand ckp sensor on Saturday. While I had it out I re-verified the position of the reluctor wheel in the sensor bore:
502728


That section checks out and aside from the day it no-started I know that it had been registering a crank signal because the tach works. I think the PCM relies on the ckp sensor for that, not the cmp sensor, though I'm not sure.

Anyway, I finished reassembling with the AutoZone sensor and it fires up. It's missing from the get go but instead of throwing the ckp circuit code there's a P0300 code so I use the Tech 2 to graph misfires and cyl. 7 is missing. This entire time it has not actually registered misfires until now. Then after a brief time it stops registering again and gives me only the P0336 code.

It continues being able to run seemingly indefinitely on 7 cylinders at this point. Even though it was no long registering misfires on the Tech 2 I used it to deactivate individual cylinders via the power balance test. There was a noticeable decrease in idle quality for each cyl. I disabled except #7. I stop the engine to try testing some plug wires and moving them around, stuff like that, go to fire it back up and she will not run unless I keep my foot in the throttle. I'm talking 1-2 seconds of barely idling then nothing. I have a wideband O2 sensor in the odd bank header and when it does run it fluctuates every other second between showing no fuel and 14-16 AFR.

Besides checking the obvious stuff like plugs, coil etc I'm thinking I might pull the PCM and have it tested. There's a company called G7 computers and a few have posted about having them successfully rebuild BCMs for their GTOs and they're actually local to me. Besides trying to identify the source of the misfire as something other than PCM failure or ckp sensor related I'm basically out of ideas other than pulling the engine to check the mechanical parts mentioned in previous posts. Stick around if you want to follow this soap opera.
 

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if it was an 04 i would say just do a quick ECM swap. reflash with your calibration and kill the vats. they are cheap and easy to reflash.
 

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Discussion Starter #17
I am an 04! I don't tune on my own but if it comes to it I can have the tuner do it. Or is that something I would do with SPS?
 

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i've swapped out mine. you have to disable vats and reprogram the vin, both of which hptuners can do.

only issue is that you will have to disarm the factory theft system before starting, which is easily done by unlocking the doors with the key fob.
 

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Discussion Starter #19
Probably the last update on this for the weekend. This AM I swapped engine control relays around, checked fuses related to the PCM, and swapped in new plugs. Not real diagnosis work, I know but some process of elimination at least.

The old ones that came out were pretty black and probably on their way to being fouled. The #7 plug I noticed had a very silver electrode, and the #2 exhibited the same but to a much lesser extent.

1 - 3 - 5 - 7 left to right:
502731


8 - 6 - 4 - 2 left to right:
502732


Also noticed the #7 plug had cracked porcelain a couple places, though this could have been for just to how I removed it.

All of this was to no effect. It did run in the manner described in the thread title this time, with gradually more server stumbles until it stalled out and was difficult to keep running thereafter.

What was interesting that I noticed this time is when I would sit with the key on engine off going through menus on the scanner the fuel pump would prime multiple times randomly. Usually for the normal 3 seconds like on the first key on but sometimes for longer. I've only had this one GTO but I assume that is not normal behavior and another clue.
 

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Ok, so we have some new info.

your engine is running rich, even at idle. otherwise your groundstraps wouldn't all be covered in soot. either that, or your ignition is poor or improperly timed.

#7 has a weird issue.

fuel pump is priming randomly. the ECM should prime key on for 2 seconds, then quit if gets no ignition reference pulses. sounds like maybe the ECM thinks the engine is running momentarily.

misfire diagnosis done from using crank and cam sensor data indicating variations to the crankshaft sensor velocity.

the ignition reference pulses come from both crank and cam sensor data.

now, the cam sensor basically tells the ECM which stroke the engine happens to be on. so it can tell TDC for a particular cylinder from the crank sensor, but it uses the cam sensor to establish if it is TDC at the end of the exhaust stroke or the beginning of the power stroke. It will still run without the CMP sensor. from personal experience, an unplugged CMP sensor will make the engine crank forever and run like crap. But, it will set a CMP sensor code. if there is a mismatch between CKP and CMP sensor data, that will set a code too...

it still feels like the CKP circuit. The ECM is obviously getting a signal because it is running, it just sounds like it hiccups frequently.

the only other thing i can think of, if you've replaced the sensor, replaced half of the harness, checked the airgap and the reluctor wheel, besides being a bad ECM or a bad connection at the ECM, is some sort of electrical interference inducing some sort of current in the circuit.

now, i would think a bad connection would cause a drop in perceived rpm, not an increase. so that may rule out a bad connection... a spike in current at the wrong spot, where the signal should be low, would be interpreted as an increase in rpm.

that would screw up a lot of stuff, lol.
 
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