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cam retard offset

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scott_duerring

Regular Contributor
Can someone explain to me how one can adjust the cam retard offset without messing up the timing? I found the following instructions for testing and adjusting the offset but it sounds like exactly what one does when you set your timing, so how can you set your proper timing and not screw up your offset, and visa versa???
"If you have a scan tool that shows the cam retard offset value you can set the distributor position. If you do there is nothing to setting the timing on these trucks. The specific rpm mentioned is just 1000 rpm and that is all. Here are some instructions that I found that are from GM.


Setting Timing
Camshaft Retard Offset Test
The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To insure proper alignment of the distributor, perform the following:

With the ignition OFF, install a scan tool to the DLC.
Start the engine and bring to normal operating temperature.

Important
Cam Retard Offset reading will not be accurate below 1000 RPM


Increase engine speed to 1000 RPM.
Monitor the Cam Retard Offset.
If the Cam Retard indicates a value of 0° ± 2°, the distributor is properly adjusted.
If the Cam Retard does not indicate 0° ± 2°, the distributor must be adjusted.
Adjusting Camshaft Retard Offset




With the engine OFF, slightly loosen the distributor hold down bolt.
Important: Cam Retard Offset reading will not be accurate below 1000 RPM


Start the engine and raise engine speed to 1000 RPM.
Using a scan tool monitor Cam Retard Offset.
Rotate the distributor as follows:
To compensate for a negative reading, rotate the distributor in the counterclockwise direction.
To compensate for a positive reading, rotate the distributor in the clockwise direction.
Repeat step 4 until 0° ±2° is obtained.
Turn the ignition OFF.
Tighten the distributor hold-down bolt to 3N·m(25 lb. ft.).
Start the engine, raise engine speed to 1000 RPM and recheck Camshaft Retard Offset."

​
 
If you go back a couple of threads ("low rpm") you should be able to answer your questions. But the key words in the GM instructions you quote are "The ignition timing cannot be adjusted". The engine computer sets the timing off of the crankshaft sensor (on the front, next to the harmonic balancer) and rotating the distributer has nothing to do with timing adjustment. The only way to change timing is to reprogram the computer. But turning the distributer cap (like you have done on other engines to adjust the timing) does determine at what post for a plug wire the rotor points when the spark comes. You must have it within plus or minus 2 degrees of correct or engine performance at either low or high rpm (depending upon which way you are off) will be affected. What is the correct value is a notional number, on Crusader engines with MEFI computers and a Rinda scanner it is 45 degrees. On GM automotive is comes up on their computer/scanner as 0 degrees. But it is really the same adjustment. Other than that the directions sound the same as they are for a marine engine.
 
scott_duerring said:
Can someone explain to me how one can adjust the cam retard offset without messing up the timing? I found the following instructions for testing and adjusting the offset but it sounds like exactly what one does when you set your timing, so how can you set your proper timing and not screw up your offset, and visa versa???
"If you have a scan tool that shows the cam retard offset value you can set the distributor position. If you do there is nothing to setting the timing on these trucks. The specific rpm mentioned is just 1000 rpm and that is all. Here are some instructions that I found that are from GM.


Setting Timing
Camshaft Retard Offset Test
The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To insure proper alignment of the distributor, perform the following:

With the ignition OFF, install a scan tool to the DLC.
Start the engine and bring to normal operating temperature.

Important
Cam Retard Offset reading will not be accurate below 1000 RPM


Increase engine speed to 1000 RPM.
Monitor the Cam Retard Offset.
If the Cam Retard indicates a value of 0° ± 2°, the distributor is properly adjusted.
If the Cam Retard does not indicate 0° ± 2°, the distributor must be adjusted.
Adjusting Camshaft Retard Offset




With the engine OFF, slightly loosen the distributor hold down bolt.
Important: Cam Retard Offset reading will not be accurate below 1000 RPM


Start the engine and raise engine speed to 1000 RPM.
Using a scan tool monitor Cam Retard Offset.
Rotate the distributor as follows:
To compensate for a negative reading, rotate the distributor in the counterclockwise direction.
To compensate for a positive reading, rotate the distributor in the clockwise direction.
Repeat step 4 until 0° ±2° is obtained.
Turn the ignition OFF.
Tighten the distributor hold-down bolt to 3N·m(25 lb. ft.).
Start the engine, raise engine speed to 1000 RPM and recheck Camshaft Retard Offset."

​
Click to expand...
All you are doing is ensuring that the rotor is lined up with the correct plug wire to avoid cross fire. The camshaft position sensor in the distributor is not controlling timing. It along with the crankshaft position and other sensors provide info that the ECM uses to control spark timing. From what I understand this adjustment only has to be done once to verify it is correct. It was checked before my engines were delivered to me. It is not something that will change unless the distributor was moved and their is no reason to do this except for replacement. I have never done the procedure. This is what I have.
11. Cam Angle Verification Procedure
The ignition timing cannot be adjusted. The distributor
may need adjusting to prevent crossfire. To insure
proper alignment of the distributor, perform the
following:
1. With the ignition OFF, install the scan tool.
2. Start the engine. Allow the engine to idle until the
engine reaches normal operating temperature.
Important: Cam Retard Offset reading will not be
accurate below 1,000 RPM.
3. Increase engine speed to ~1200 RPM while
performing the following steps.
4. Using the scan tool, monitor the Cam Angle Offset.
5. If the Cam Angle indicates a value of 705 degrees,
the distributor is properly adjusted.
6. If the Cam Angle does not indicate 705 degrees,
the distributor must be adjusted.
Adjusting Procedure
1. With the engine OFF, slightly loosen the distributor
hold down bolt.
Important: Cam Angle reading will not be
accurate below 1,000 RPM.
2. Start the engine, and raise engine speed to
~1200 RPM.
3. Using a scan tool, monitor Cam Angle.
4. Rotate the distributor as follows:
• To compensate for a negative reading, rotate
the distributor in the counterclockwise direction.
• To compensate for a positive reading, rotate
the distributor in the clockwise direction.
5. Repeat step 4 until 705 degrees is obtained.
6. Turn OFF the ignition.
Notice: Refer to Fastener Notice in Cautions and
Notices.
7. Tighten the distributor hold-down bolt.
Tighten
Tighten the bolt to 3 N•m (25 Ib ft)
8. Start the engine.
9. Raise the engine speed to 1,000 RPM and
recheck
 
Okay, now I am more confused than ever. I have 1998 era 8.2 MPI crusaders. It has MEFI 3 generation computer. I have personally adjusted the timing, and have watched several "professional" mechanics do the same. I have the shop manuals and there is a specific procedure to switch the plug that is by the CPU into a "timing mode" before you use the light to check/adjust the timing. What is the "cannot adjust the timing" refer to? If you can adjust the timing does that mean you cannot adjust the cam retard? The whole reason for exploring this is that I saw on the thread "low rpms" that a rough idle condition can be as a result of the cam retard not being set right. I have a rough idle in my stb engine (countless threads here in the past) I have not been able to resolve it. None of the numerous mechanics I have used ever even mentioned this as a possible cause. The folks at Pleasure Craft customer service never mentioned it either, the final suggestion they had was to send my ECMs in and they would reprogram them to adjust the idle rpms up from the present 650 to 750 or 800 rpms. I declined thus far.
 
Scott:

The short answer is you have no cam retard offset to adjust on your engine. The "newer" GM engines, mostly using the "crossfire" distributor, with both CAM and CRANK position sensors, have "this feature".
 
Please go to the internet and download a copy of the MEFI 3 Diagnostics Manual. It is free. The timing procedure with your MEFI 3 engine is different than discussed in the other thread (and different from the GM instructions you included in your inquiry).

Basically with your engine you put the controller in a service mode and then turn the distributer to get base advance correct. When you are back in the run mode the computer does the needed advance with rpm. When you turned the distributer to set the base advance you also got the orientation right so there is not a need for the famous "cam retard offset" adjustment on this engine. The manual explains it all in great detail.

The manual will also tell you many other things to look at to resolve your idling problem.
 
Also, when you referred to "switching the plug" I believe you are referring to the distributor (EST type) four pin connector...that plug, with its jumper wire, "locks" the timing advance the distributor module creates so set a base timing value. When you remove that plug and reinstall the one from the ECU, the module adjusts the timing based on what the ECU commands....
 
Thanks for the short answer... got it. Cannot adjust Cam Retard Offset on my engines.
I do have the General Motors Marine Electronic Fuel Injection Troubleshooting and Repair (MEFI 3-1998 Software) manual. And yes I am referring to the plug that is actually marked "timing" on one end that you plug in that bumps the idle up and fixes the timing (disables the advance) so one can adjust the base timing.
The manual has a step that includes "A scan tool or MDTC tool to the DLC." I have never done that, nor do I actually know what it means. All I have done is switch the plug to timing and hook up the timing light to number 1 wire and shoot the light to check the timing mark, if I have to adjust I loosen the distributor hold down bolt and turn the distributor until I get 10 degrees BTDC. Am I missing something by not using one of those tools???
 
scott_duerring said:
Thanks for the short answer... got it. Cannot adjust Cam Retard Offset on my engines.
I do have the General Motors Marine Electronic Fuel Injection Troubleshooting and Repair (MEFI 3-1998 Software) manual. And yes I am referring to the plug that is actually marked "timing" on one end that you plug in that bumps the idle up and fixes the timing (disables the advance) so one can adjust the base timing.
The manual has a step that includes "A scan tool or MDTC tool to the DLC." I have never done that, nor do I actually know what it means. All I have done is switch the plug to timing and hook up the timing light to number 1 wire and shoot the light to check the timing mark, if I have to adjust I loosen the distributor hold down bolt and turn the distributor until I get 10 degrees BTDC. Am I missing something by not using one of those tools???
Click to expand...
Some scan tools or code readers have a set timing mode.Your not missing anything if your just setting base timing. You just don't have to use the timing plug with them.
When you say the timing plug "bumps" the idle up does the idle improve? That seems odd.
 
rfdlou said:
Some scan tools or code readers have a set timing mode.Your not missing anything if your just setting base timing. You just don't have to use the timing plug with them.
When you say the timing plug "bumps" the idle up does the idle improve? That seems odd.
Click to expand...
Yes, I cannot remember if it bumps the idle to 1000-1500 rpms but it automatically adjusts the idle up from the preset 650 rpms. And yes, my rough idle goes away generally after 800-950 rpms. Don't know where it goes..... but things settle down around that rpm range and above.
 
I don't think the idle is raised; its just a byproduct of the timing being fixed and the computer holding steady many adjustments it would normally be making...
 
Your post just made me think of this. Could a malfunctioning of the timing advance cause a rough idle condition? When the plug is put in timing mode my understanding is that the timing advance system is disabled. The rough idle improves in the timing mode...
But, I have no issues with the engine other than the rough idle. In other words if the timing advance is not working at idle it seems to be working fine at other rpms.
Barking up the wrong tree???
 
maybe not...the distributor module "owns" the timing advance function and makes its adjustments based on a signal from the ECU...

Are you sure the engine is sound mechanically? if you have access to a scan tool, I think the -3 ECUs have the cylinder power balance test...that's usually the quickest way to assess the engine's health.

The idle issue could also be from a marginal injector...the duty cycle at idle is usually quite low so any clogging/debris in an injector is most noticeable at idle, especially under load.
 
Can you explain the cylinder balance test as it relates to the ECU? I do not have access to a scan tool. I have had several mechanics with use their laptops to hook up to the ECU and run the diagnostic program. They never found any issues. Compression test supposedly revealed loss of compression thru a valve... had total valve job done. Didn't fix it.
I have removed all injectors and sent for testing and cleaning... nope. I have completely switched the top manifold with everything attached from the port engine to the stb engine.. still idled rough. Subsequent compression tests show no issue. Sent ECUs to Crusader through dealing with Mark Snyder (Sp?) who unfortunately is no longer there... they updated and made sure ECU was functioning properly..
All the standard stuff done, new plugs, wires, distributor cap... new IAC valve, new fuel pump, Three separate "Certified Crusader" mechanics...
Here is the weird thing about this. In 2006 I had to replace the transmission. Had a new tranny and heavy duty damper plate put in. Immediately after that was when the whole idle issue came up. It rattled and shook the whole boat when I put it in forward at idle... no problem to go in reverse. Thought it was a bad transmission, the transmission was pulled and sent to the distributor and they bench tested it... said it was fine. Had it reinstalled by different mechanic, still had rough idle rattle but much less... ever since then I have been looking at the engine to be the cause of the rough idle not the transmission... part of the issue was fixed when I had found out that the same mechanic who installed the transmission the first time had timed my engine to 2 degrees BTDC.
The past few years I have given up and just taken steps to adapt, if I have to idle through the marina or out to the open water I try to bump up the stb idle until the rattling goes away. I do not troll with my stb engine when I fish... which has resulted in a great disparity of hours on my engines... I am just worried that the torsional stress of roughness of the engine is shortening the life of my transmission. So I would like to fix it.
 
The problem started when the transmission and damper plate were changed, and it lessened when the transmission was pulled and reinstalled. The cause could be something else (which they have revealed) but those are two pretty good clues.

Does it run rough and "rattle and shake" when at idle out of gear or only when in forward? When you say "no problem in reverse" is it just like the port engine in reverse or it just better than it is in forward but still not right?

What is a "heavy duty" damper plate anyway?
 
I agree with CJ...could very well be coupled to the gear R&R...

The cylinder balance test is conducted on a running engine. What happens is one cylinder at a time has its spark cut off and the rpm drop is noted....and this continues until all are done. data is reduced and compared to reference values...if all is ok, a PASS is the result; if one or more cylinders fail, the overall test is FAIL and the guilty cylinders are identified.

Being as you have gone thru all (?) the standard service parts and had the topend off, there isn't much left...I suggested the cylinder balance test as it could show you a guilty cylinder or two...with the light you have shed on the gear issue, it appears highly coupled to that work...

If you have specifics on the damper, please share them....I have heard of the wrong damper (too stiff) plate being used but never got any details...
 
There is a very slight rattle at idle in neutral. It comes from the transmission. In reverse there is no rattle or vibration from the drive train, very smooth. Put it in forward gear in idle then the rattle starts and also a vibration. Kick it up to above 850 900 rpms and all goes away.
At the time I bought the new transmission it was represented to me that Crusader produced a "standard" duty damper plate, and a "heavy duty" damper plate... I bought the "heavy duty" one.. somewhere I have the part number on the paperwork for that job. I recall seeing pictures of the two different plates and the heavy duty one was quite a bit more robust. The distributor of the velvet drive trans in this area is out of Michigan.. I got "disenchanted" with the mechanic who did the install and had another come out to evaluate, he was convinced that it was a "bad gear" in his words and arranged through the warranty to pull the trans and send it back for testing at no charge to me. Well, they supposedly tested the gear and said it was fine. On the reinstall there was an improvement. I recall several discussions with the distributor representative, he wanted to know the specs of the damper plate which he was advised of, he did not seem to think that was an issue. Is there any way to test the gear while it is still installed? I am sure I will have to pay for any removal etc. at this late stage.
And yes I did a cylinder balance test, I just pulled one plug wire at a time with the engine running... I also have "noid" lights and tested the injector circuit.
The part number for the plate was CRU-98511
 
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The cylinder balance test is looking for a dead cylinder at idle (no rpm drop when the wire is pulled). I am presuming that you did see an rpm drop on every cylinder when you pulled their wire. I only bring it up because you have an Idle Air Control valve that the ECU opens and closes to keep idle rpm constant so the IAC would need to be disabled in order to run an accurate test.

I am really puzzled by the difference between behavior in forward and reverse. Maybe something about the Velvet Drive (like more compliance in the drive train in reverse) but that seems a stretch. Hopefully someone can weigh in on that issue.

Could the problem predate or be concurrent with the transmission failure? Did the engine hiccup and then the transmission failed (that actually happened to me) or was there some other cause (or no known cause)? With all you have done, and with the (hopefully) successful cylinder balance test I struggle to believe it is the engine....but then again that is still the most likely suspect.

A bad PCV system (allowing too much air in at idle) could also cause rough running at idle but I would think all the testing would have discovered a weak vacuum. Still, everything in these MEFI systems depends upon having the correct vacuum since that drives injector timing. It is too bad you do not have access to a Rinda scanner so that you could do a line by line comparison with the good engine.
 
Yes, I did the cylinder balance test, but I did not disable the IAC valve. Not sure if the engine will run with it unplugged? Put a vacuum gauge on it, I believe it was pulling a 12 or 14, whatever number it was I relayed that to the Crusader tech with their customer support and he said it was ok. It is the same on the port engine and that idles fine. I have been told that some rattle at idle is not unusual for the Velvet Drive 5000 trans, but as I said this is much more than a little rattle.
No hiccup when the trans went... actually was cruising to Chicago and the engines kicked into the "safe mode". After everything cooled it ran fine, but kicked into the safe mode again when almost back. My mechanic said it threw a code indicating that the trans was overheating, and he said it needed replaced. I went with his recommendation. But like I said the engine purrs like a kitten and anything above an idle...
How do I get a Rinda scanner... right now I am so "mechanic" shy I am trying to do everything my self these days.
 
$400 for a tech-mate self contained or just under $600 for the s/w & cable to convert your PC @ www dot rinda dot com
 
As for the cylinder balance test (a.k.a. power balance test) if you saw an rpm drop every time you pulled a plug wire then you are OK. If one did not drop then that is the bad cylinder. So if your IAC is active then I would expect it to adjust to try and hold rpm constant and spoil the test. The IAC is only a stepper motor that changes the air bypass opening and when you unplug it there should be no further movement so I would expect the engine to run fine for the test without the valve working.

My manual says do the test at 1500 rpm under "moderate" load but not while underway. I haven't figured that one out! But that rpm would get you above where the IAC valve is active. But since you believe you problem is only present at idle those instructions don't really work for you and it is worth trying the test at idle.

The Rinda website provided by Mark also lets you read the manuals before you buy. I got the Techmate for my MEFI 4. It gives the same information as the PC version but you have to scroll it line by line. I made up some forms with all the data line titles and blanks to fill them in. This way I could record all the data from both engines with dates and rpms for study and as a permanent record. You get actual output voltages on your sensors which is much better than just a thrown code. It is $400 but cheaper than most things about a boat, and a lot cheaper than just throwing parts at a problem. The PC based version is much slicker, but costs more and requires you to haul your PC to the boat every time you want to check something. I haven't used the PC one, so I can't speak to how much more convenient it might be to have all the data displayed at once.
 
Thanks for the link, felt kinda stupid after I posted that question as to where to find it, these days just google it and there it is. Yes the p.c. version is pretty neat, I recall watching it when the mechanic would hook it up and it would display the data. Your right, at 400 dollars that is a bit cheaper than throwing parts and mechanics at it. Been there done that...
I guess the one plus is that I have learned a hell of a lot by working on this one problem. But apparently not enough as I still have it.
thanks again gentlemen, your input is much appreciated.
 
Well, good luck on finding the resolution to the mystery problem. Let us know.

As a final thought....I have been thinking about the two strange parts to the problem. What is rpm dependent so that the issue is only there below 900 rpm? You changed out all of the likely suspect parts so you may be left with the "weird electrical sh*t" cause. Others have suggested that a bad tach can feed back problems to the ECU and the check is to disconnect it and see what happens. Also bad alternators can cause electrical noise. If you have some time you might try swapping them and see if the problem moves. And I am not sure why bad grounds should be rpm dependent but they could be a source of electrical noise as well.

And as for the bigger strange clue, what is different about reverse that make the problem seem to go away? The only thing I can think of is the load on the motor mounts is different in reverse. A broken (or perhaps incorrectly installed) motor mount could cause a lot of rattle and shake at low rpm. And the problem did start after a transmission change so that could tie in. So they are worth a careful look and a comparison of movement to the ones on the good engine.

Both long shots but that is about all you have left.

CaboJohn
 
2X on the motor mounts - good call John! Very possible for a rattle though it won't help with the idle being rough.

Have you cleaned the IAC valve...I clean mine on the truck about ever 50K-60K to give rid of irregular idle issues...the carbon-varnish crap collects on it a lot faster than I think it should...and clean the throttle plate where it seats in the bore of the body, too.
 
Mechanic number 3 said that my front motor mounts were stripped and needed to be replaced... so new motor mounts went in for the front. He said the rear mounts were ok. The new mounts did not correct the problem. I will though take a real careful look at the rear mounts again as what you said makes sense, especially since the rear mounts have to be removed for a trans replacement. Mechanic number 2 said the IAC valve needed replacing so a new one went in. No change. I also switched the intake manifold with everything attached from the port to the stb engine myself last year when I was reinstalling the fuel injectors, just to see if there was anything at all that could be causing the rough idle but no change. I thought perhaps the tach issue could be a source as occasionally the stb tach got erratic, but I put in new digital Floscan instruments last month and no change. I have not thought about the alternator as a source, but what the heck, might as well give that a shot too.
 
Not a Crusader question, but I have been scared to tackle removing the transmission myself and checking the condition of the damper plate... how hard is that? I have basic tools, nothing fancy...
 
I'd be more inclined to think any "noise" is due to a bad ground....the environment anywhere close to an ignition system is "noisy" due to the sparks occurring. Sure won't hurt to spend the little bit of time to swap alternators - just be sure to check the fans if you have the counter-rotating engines...

Not hard to pull the gear at all...much bigger challenge to re-install it. more physically intense as they aren't light. a couple of the right size studs helps the re-install go smooth...
 
The real question on the transmission is "how big of a boy are you?". After wrestling manifolds and heads by myself I decided I was not big enough and paid to have my flex plate done. Billed for 6 hours of labor and most of that was removal and reinstallation of the junk....heat exchanger, starter, exhaust, fluid cooler lines, linkages, prop shaft, etc. So it is not that big of a job. Only real trick is finding some way to jack up the rear so as to get the weight off of the rear motor mounts (which you may be doing anyway if that diagnosis is correct). My Mexican crew used a little hydraulic jack with a remote pumping cylinder. Some folks lift from above. All depends upon your boat and what you have to work with. Motor mounts were then removed and the engine was supported by the exhaust manifolds resting on wood blocks on the stringers. Transmission was pulled out by a really strong kid. I second Mark's suggestion of using studs on anything heavy. Easier and cuts the risk of damaging the shaft or the splined hole in the flex plate.

Once you get it apart it is doubtful there will be much to see when it comes to checking the condition of the damper but the general consensus seems to be if you go to the trouble to pull it apart, you always put in a fresh flex plate no matter what it looks like.
 
makomark said:
I'd be more inclined to think any "noise" is due to a bad ground....the environment anywhere close to an ignition system is "noisy" due to the sparks occurring. Sure won't hurt to spend the little bit of time to swap alternators - just be sure to check the fans if you have the counter-rotating engines...

Not hard to pull the gear at all...much bigger challenge to re-install it. more physically intense as they aren't light. a couple of the right size studs helps the re-install go smooth...
Click to expand...

Going back to this issue... one very odd thing that happens that I never thought could be tied into a bad idle is this. My boat came with a stereo system installed. It is wired through the ships panel, on the twelve volt side. Originally it worked as designed, turn on the breaker, go the the head unit and turn on the stereo, music would come out of the speakers. Now, in order to get it to work I have to "bump" the starter switch for the starboard engine (the one with the bad idle), after bumping the switch, the music starts. Odd enough, but the stereo unit turns on, but no music comes out of it until you hit the start switch. Very strange electrical anomaly. Is it possible that what ever is causing this weird situation may be causing the engine to idle poorly? Any ideas on how to fix???
 
I have no idea. What I do know about the truly "weird electrical.......stuff" is that even if you "fix it" you still never know for sure what it was. Most of my experience in this department is on old cars (except for my windlass) but I think maybe boats are worse. I would try to totally (as in trace every connection back to something common to the system) disconnect anything that you think might contribute to the problem and see if it goes away. But you might do better hiring an exorcist. Perhaps the same odds of success. And I still like the motor mounts because of the forward/reverse issue discussed earlier.

Good luck. Many of us are living with some gnawing issue that seems to have no solution. So I am focusing my energies on how to get some really big tuna this fall.

CaboJohn
 
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