So as some may remember my questions. Im building a LQ4. It broke a rod etc.
Well i got a few new rods .020 over pistons. Bought new heads. Cast iron. Then i bought a LQ9 cam. (cant remember the number on it) to put in. New lifters new trays etc. Went to put on intake found a huge crack melted part. Bought new dorman intake. I know not the greatest but its a "stock" motor in a 00 chevy truck 3/4 4x4. Got it all put together and it has good oil pressure etc..(should mention i did replace the reluctor with a homemade tool and im 99% POSITIVE it is spot on and i measured the run out)

Now the bad. When it runs it runs GREAT. but it acts up. Just cuts out misses however you want to say it.. No check engine light. Finally it ran SO bad that it came on. Knock sensor low voltage(1&2) (guessing because it took SOOO much to get them to come on) and then Crank sensor. Well i didnt replace that so i bought a new one Installed it (i know shouldnt hang parts) well it ran GREAT. Pulled to 5k no problem ran up down highway being moderate at first then getting on it. Finally going up hill under load maybe 45 mph it does NOT like. And it started bucking running like crap. No MIL again.


I just dont get it. If i did get the reluctor in the wrong spot why would it run great 85% of the time. by great i mean GREAT!! Good power. Maybe not to some of your standards but for a "stock" motor great.

Im leaning towards intake leak. Whats the best way to test it? EGR should only effect idle in gear stopped right? Just not sure what to do or where to go from here. It has me frustrated. I have access to a good scan tool.

**i now remember the reason i dont work on cars for a living.

Sorry its so long but i wanted to give full details. Thanks.

 

If I remember correctly, on the old school EGR it is circulating gas at cruise or light throttle and should be closed under power/load. That might be something to look at.
I hope I got that right. It has been a while since I messed with that.

 

since you replaced the reluctor wheel, you need to do a crank relearn on it. find someone with a GM tech II or take it to the dealer.

 

also, the EGR is only active at low load crusing RPM's ~2000 RPMS.

 

Ok. So please explain this to me... Why would the ECM need to relearn the reluctor if its in the same spot? And how is this done?(besides a tech 2, I have access to one but when i call in the favor i need to tell the guy more what i need) And if i changed cranks wouldnt i of had to do the samething? Why does it run good for half the time and is very intermittent?

Just trying to get a grasp on what you are saying.

55-60 mph is ~1800 rpms most of the time it seems like speeds under 45 is when the real problem shows up.

 

The crank sensor looks for the cam and crank sensor to determine timing. If you installed the crank wheel half a degree off it will mess with it. Even changing cranks will mess with it. Just tell your favor provider you need a crank re learn. That seems to be the most possible cause right now. If it doesn't help, at least you can rule it out.

 

Ok. called in my favor. Guy is going to do a crank relearn for me. It honestly makes no sense to me because isnt that why you have the gaps and spaces and crank sensor in the first place?

 

No. It has a reference tooth, it tells the computer exactly where each cylinder is in relation to the cam, then uses that information as well as engine load, temperature etc to adjust fuel, timing...etc. that would explain why it is intermittent.

 

**UPDATE** took to a shop. It died on way there and wouldnt run (thats a first) well it sat over night. Guy went out started right up ran fine like normal. He attempted to do a crank relearn and it would not do it...

The first time it threw a generic Crank Pos code. This last time it threw a CPS performance code. I replaced the crank sensor hoping it was the problem(before i was aware of a crank relearn) Think the new CPS could be bad not letting it do a crank relearn. My old sensor had like 2 grooves in it (not deep but there) where it looked like the reluctor ring hitting it. Never thought anything of it. But now im wondering if i need to shim it and if maybe the new sensor got hit..

Whats the thoughts on this? Why it wont relearn.. What your next step would be.. I know what the shop is going to do but i want more opinions or ideas.

 

no one?

 

No one has any ideas or comments?

I dont think the shop has had time to mess with it yet. He was going to watch on the scan tool and see what all changes and when. Because when he started it up it ran GREAT.


If the reluctor ring is in the wrong spot or off. Is this common symptoms? Or when they are off are they usually OFF. meaning run like crap all the time. Not just when cold.

 

I think something is wrong with your CKP reluctor, it should not cut a groove in the CKP sensor.


The CKP relearn is for the purpose of priming the misfire detection algorithm (i.e. it allows the PCM to learn the rate of crank deceleration that would occur on a misfire).


Without a CKP relearn, your engine should run (at least as good as the tune) since the CKP reluctor identifies the crank position to the PCM (as long as the reluctor was installed correctly).


You might want to check that the reluctor is not wobbling or walking/spinning relative to the crankshaft (your description of the symptoms sounds like this is what may be happening).

You might also want to check the condition of the 3 wires, they are very thin and may be fractured or may be shorting.


You need to find a shop that has an oscilloscope with which they can view/compare the CKP/CMP signal waveforms against known good waveforms.

 

To me your post kind of argued with itself.

You said the engine should run if the reluctor was in the right spot. Which it does. (now only when cold before 90% of the time) It started as a hiccup every now and then. And continued to get a little worse. Then we replaced the CKP (before knowing about a relearn) and now its gotten alot worse. I think the new CKP has to be working some. But 100% or not is the ?

Then you said you think my reluctor is moving or causing an issue. If it was then by your other post it wouldnt run. But it does.

They are going to check the waveform of the CKP.

It is a well known problem on the LS engines that the block is made a little shallow. The reluctor a little big and it will graze the sensor. GM actually makes a shim kit for this. So it doesnt nec. mean there IS something wrong with the reluctor.

Im really looking for someone to come in and say: when my reluctor was messed up here is what mine did.

(sorry if the post sounds like im arguing with you,, im not i appreciate the reply just trying to learn more and discuss)

 

Which part, let see if I can clarify myself...?


Another thing I've seen is worn out thrust bearing allowing crank to walk causing CKP signal to become degraded... especially under conditions where torque converter may have been ballooning.

 

I stopped reading at this part. Either defective replacement reluctor or your 1% error probability came true.

 

Without a CKP relearn, your engine should run (at least as good as the tune) since the CKP reluctor identifies the crank position to the PCM (as long as the reluctor was installed correctly). --- It DOES run. So by this i would say it is installed correctly.

You might want to check that the reluctor is not wobbling or walking/spinning relative to the crankshaft (your description of the symptoms sounds like this is what may be happening). -- but if the reluctor is in the wrong spot or moving. Would it still run good?


Yes i do understand that there is a chance i got it in the wrong spot. Even though the tool we built was located off of the previous reluctor. And is the exact same design as the goodson except i used the dowel pin hole and 1 flywheel bolt. (used the flywheel bolt as an extra measure so it had 2 points to locate it)

I really just need a sure fire answer if i need to pull this motor back out or not. It seems 50% says if the reluctor is off it wont run. BUT it does. So i dont want to pull the motor change cranks (because im not going to chance changing it again since no one has the tool in my area) then have the problem still be there.

Crank endplay was good.

What is the syptoms of a bad reluctor? Or installed wrong? Run bad all the time? Only when warm? Only when cold? Wont do a relearn?

 

If the reluctor spins relative to the crank, it may or may not spin back to its original position (it usually does not).

If the crank walks (due to excess endplay), the crank usually walks back to its original position when the load is removed/reduced.


Before pulling the motor there are various checks/diagnostics you should do:

- check crank endplay (worn thrust bearing);

- remove the CKP sensor and observe the reluctor as you rotate the crank (does it wobble...? can you spin the reluctor relative to the crank...?);

- look at CKP and CMP waveforms and analyze their relationship (compare to known good waveforms) [ but do this only if the oscilloscope operator knows how to do this; it may be hard to obtain a scope and an operator ];

- you mention an intake leak... this would have the most effect at idle, and its effect starts becoming negligible as rpm increases and engine pulls more air; you should fix this but it will have no impact on the problem;

- you said the knock sensors registered knock... did you check the various things that may cause this (lack of fuel, overheating, wrong plugs); did you analyze a scantool log to see what injectors/LTFT/MAP/MAF/RPM were doing when knock happens and/or when problem happens...?

There are other questions... did you tack weld the reluctor to the crank...?

 

I checked crank end play when we put the motor together. We did not tack weld the reluctor. I was going to but everyone suggested TIG and we only have a MIG.

Im not saying there IS an intake leak. Its a new manifold and gaskets with proper torque sequence. So theoretically it shouldnt be the culprit. Will check on the rest. Thanks for the reply.