5.7 Vortec cold tap/knock HELP!

[Pinger]

I appreciate your advice here and I'm not trying to be antagonistic but I still don't understand everything.

1. It's really easy to be more than 2 degrees off, even when "aligning marks".
2. You don't know that the cam/crank alignment is correct now. Timing chain wear, cam gear wear, distributor gear wear, distributor housing wear can all affect the cam/crank synchronization.

Engine in question has done 43,000 miles and there's very little in the way of wear on the cam chain and no reason to be overly concerned about gear wear. For now, I'm prepared to accept that as it is it's good enough and all I want to do is not lose the current set-up.

The scan tool doesn't tell you that the TIMING is wrong. It tells you that the cam sensor isn't synchronized to the crank sensor. That has NOTHING to do with the ignition timing, but it does affect alignment of the rotor tip to distributor terminal.

But, as far as I can make out, all that can be lost is the synchronisation between the rotor arm tip and the terminals on the cap. I'm not seeing that as 'crucial'.

TIMING is set by the crank sensor and the reluctor on the crank snout. That signal gets modified by the computer, the computer controls the timing based on it's programming--but it all starts with the crank (not cam) sensor.

So the timing signal is from the crank (which won't change no matter what I do) and the cam sensor is there to tell when each cylinder is to fire (TDC combustion stroke not TDC gas exchange stroke - and even then possibly only on start up) and for identifying individual cylinder mis-fires. Independent of the cam sensor is the distributor shaft's orientation which can only affect the rotor arm tip's synchronisation wrt the cap. I just can't see why 2 degrees is so important. What am I missing?

I'm not sure how your location in the UK affects not being able to get a scan tool.

Not available in UK and expensive to import when I lost my job in December and need every scrap of money to finance new business. And I need the truck for work. No pressure then....

 

[Schurkey]

all I want to do is not lose the current set-up.

Then you're on the right track--mark the rotor position on the distributor housing, mark the distributor position on the manifold. Put it together the same way.

But, as far as I can make out, all that can be lost is the synchronisation between the rotor arm tip and the terminals on the cap. I'm not seeing that as 'crucial'.

The less-aligned the rotor tip-to-distributor cap terminal becomes, the more voltage the coil has to generate to fire a spark across the larger tip-to-terminal gap. If that voltage is less than the voltage needed to fire the plug, it won't make any difference. As the alignment gets worse, the ignition coil gets over-worked.

At some point, the rotor tip fires to the wrong plug terminal, and that's when the real problems start. When what should be #5 fires to #7 instead, the engine blows up.

Yes, that takes a fair amount of misalignment.

So the timing signal is from the crank (which won't change no matter what I do)

Yes.

and the cam sensor is there to tell when each cylinder is to fire (TDC combustion stroke not TDC gas exchange stroke - and even then possibly only on start up)

No.

for identifying individual cylinder mis-fires.

Identifying individual cylinder misfires, and preventing an arc-over that fires the previous or next cylinder in the firing order.

Independent of the cam sensor is the distributor shaft's orientation which can only affect the rotor arm tip's synchronisation wrt the cap.

I wouldn't say that the distributor shaft is independent of the cam sensor.

I just can't see why 2 degrees is so important. What am I missing?

The primary issue is that you're not guaranteed to be starting from "correct" synchronization. Maybe you are...maybe not.

It's a matter of a likely error compounding a possible error. The imprecision of reinstalling the distributor might get you closer to "perfect". Or it could make the synch error worse. You won't know until you verify with a scan tool.

Not available in UK and expensive to import when I lost my job in December and need every scrap of money to finance new business. And I need the truck for work. No pressure then....

But given your situation...mark the rotor position on the distributor, mark the distributor position on the manifold. Be as precise as possible (narrow lines that aren't ambiguous.) Put it together the same way.

Get a scan tool later to verify/correct synch; even if it's a year or two from now.

 

[Pinger]

Thanks Schurkey, that's a big help. To summarise my predicament - i need the inlet manifold gaskets changed much more than I need to be checking cam sensor synchronisation. And this issue has been putting me off getting the gaskets done.

One point I'm going to get picky with you on though. Without a cam sensor, how, during cranking, does the PCM know if a piston approaching TDC is on it's compression or exhaust stroke. Pretty sure the cam sensor is required for that.
That a cam sensor is used for that purpose came to light in a discussion about how the 3 cylinder smart Suprex engine can identify which stroke to spark on during starting. Take a guess if you feel like it. (The answer isn't 'double ended coil' - only on cylinder groups of two is that viable).

 

[Schurkey]

The distributor rotor supplies spark to the nearest distributor cap terminal. With ignition timing signal supplied by the crank sensor, when the coil fires, spark it routed to the correct cylinder via rotor/cap position.

If the distributor is firing the wrong cylinder--or firing the right cylinder on the exhaust stroke instead of the compression stroke--the distributor shaft is misaligned to the camshaft, or the distributor housing is misaligned to the rotor.

Cam sensor has nothing to do with that misalignment, although it might report that misalignment via the P1345(?) code for cam sensor retard/offset. The Vortec computer cannot "correct" timing based on the signal from the cam sensor. When the coil fires, getting the spark to the correct cylinder is a mechanical, not electronic process.

OTHER computer systems may use a cam sensor to affect timing. From a certain perspective, the old "pickup coil and reluctor" was a cam sensor that DID affect timing.

 

[Pinger]

The distributor rotor supplies spark to the nearest distributor cap terminal. With ignition timing signal supplied by the crank sensor, when the coil fires, spark it routed to the correct cylinder via rotor/cap position.

If the distributor is firing the wrong cylinder--or firing the right cylinder on the exhaust stroke instead of the compression stroke--the distributor shaft is misaligned to the camshaft, or the distributor housing is misaligned to the rotor.

Cam sensor has nothing to do with that misalignment, although it might report that misalignment via the P1345(?) code for cam sensor retard/offset. The Vortec computer cannot "correct" timing based on the signal from the cam sensor. When the coil fires, getting the spark to the correct cylinder is a mechanical, not electronic process.

OTHER computer systems may use a cam sensor to affect timing. From a certain perspective, the old "pickup coil and reluctor" was a cam sensor that DID affect timing.

Spot on. I clean forgot we're not discussing a coil on plug set-up. Brain fade!
Coil on plug systems rely on the cam sensor for starting - once running they just use the crank. Exception was the smart. It recognised TDC on compression by the slight slowing of the crankshaft.

 

[Hogg]

I appreciate your advice here and I'm not trying to be antagonistic but I still don't understand everything.



Engine in question has done 43,000 miles and there's very little in the way of wear on the cam chain and no reason to be overly concerned about gear wear. For now, I'm prepared to accept that as it is it's good enough and all I want to do is not lose the current set-up.




But, as far as I can make out, all that can be lost is the synchronisation between the rotor arm tip and the terminals on the cap. I'm not seeing that as 'crucial'.



So the timing signal is from the crank (which won't change no matter what I do) and the cam sensor is there to tell when each cylinder is to fire (TDC combustion stroke not TDC gas exchange stroke - and even then possibly only on start up) and for identifying individual cylinder mis-fires. Independent of the cam sensor is the distributor shaft's orientation which can only affect the rotor arm tip's synchronisation wrt the cap. I just can't see why 2 degrees is so important. What am I missing?




Not available in UK and expensive to import when I lost my job in December and need every scrap of money to finance new business. And I need the truck for work. No pressure then....

I had 1/2 a dizzy gear worn almost to breakage, teh gears were knifedged badly, very sharp. Common issue, my engine had 58,000km when it required a new dist gear.
It'll be in your hands, easy to look at.

You'll never be able to get your distributor base installed in the same exact orientation, even if you mark the dist base with the intake manifold, its impossible get installed correctly the first time. I can eventually get the SES to go out, but it takes patience.

A loosened holddown bolt will allow the dist body to be clocked, this adjusts the CMP Retard(camshaft position sensor retard) It MUST be at Zero degrees, plus or minus 2º.
The accuracy is required for missfire detection, giving the CKP sensor(CranKshaft position sensor) the ability to detect exactly which cylinders are misfiring based on the minute accelerations detected at the crank snout.

When re installing the dizzy, after you get the cam and dizzy gears meshed and you find that the dizzy wouldnt drop all the way down. Thats your oil pump drive not meshing, with the holddown loose bump the starter a few times til it drops down.

Its way more complicated for me to type than it is for me to do unfortunately.

peace
Hog

 

[east302]

Thanks Schurkey, that's a big help. To summarise my predicament - i need the inlet manifold gaskets changed much more than I need to be checking cam sensor synchronisation. And this issue has been putting me off getting the gaskets done.

Search this site for “CMP Retard” and you’ll find threads going over use of a Bluetooth OBD adapter and cell phone apps DashCommand and CarGaugePro. If you don’t have access to a good scan tool, either of those two apps can be used to read the offset so that you’re done with it.

It’s maybe $50 for all of it over here, not sure what it is on your side of the pond. I’ve seen somewhere (think it is in the manual) that P1345 will not trigger until the offset is outside of 14-degrees of so. Meaning - you may not have the DTC set but can still be out of spec.

YouTube has videos of the process as well. It only takes a few minutes to do.


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[Pinger]

A loosened holddown bolt will allow the dist body to be clocked, this adjusts the CMP Retard(camshaft position sensor retard) It MUST be at Zero degrees, plus or minus 2º.
The accuracy is required for missfire detection, giving the CKP sensor(CranKshaft position sensor) the ability to detect exactly which cylinders are misfiring based on the minute accelerations detected at the crank snout.

Moot point in my case though.
Without a scanner I can't read misfire codes anyway. And if (or when) I have a scanner, I can get the required synch. Chicken and egg!

 

[99Classic]

So another really late update. Sorry yall. Got my lifters in the mail. Rockauto "ultra power" lifters. They seem really decent. Got them for 7$ each. Gonna see if it helps. On the cam timing aspect I was using a 1200$ scanner and the computer automatically advances the timing based on its cam sensor reading. As long as you arent off a whole tooth it will run good. Its tough to get a good setting with high miles due to gear wear. Especially in my situation with 200k+ miles.

While it was on a lift I saw it needed ball joints, cv axles, and a passenger front axle seal on the outer part. She definitely needs some lovin lol.

Oil is real dirty after only about 1k miles of driving so that marvel mystery oil really loosened up some gunk and the knock is slightly better now. Its -40C today and the knock is better than it was at -20C.

Going to try and keep you all posted more often from now on.

Side note: how tough is a passenger outer axle seal to replace on these?

 

[Schurkey]

On the cam timing aspect I was using a 1200$ scanner and the computer automatically advances the timing based on its cam sensor reading. As long as you arent off a whole tooth it will run good. Its tough to get a good setting with high miles due to gear wear.

No. The computer does not change the timing based on the cam sensor. The base ignition timing comes from the CRANK sensor. The distributor/cam sensor needs to be aligned with the crank sensor so that the rotor phasing is close--otherwise the spark could jump to the wrong distributor cap terminal. The computer uses the cam sensor to determine which cylinder is misfiring, and nothing else.

So, no, being way off on the "Cam Retard" or "Cam Offset" or whatever the scan tool calls it is NOT compensated-for elsewhere. It needs to be within tolerance (+ - 2 degrees.)

Its -40C today

Got me beat. Only -20F overnight here, but with high relative humidity and 12 mph wind, the candyass wind-chill is considerably "colder"

Side note: how tough is a passenger outer axle seal to replace on these?

I can't even picture that.