Timing mystery

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mbaird

mbaird

mbaird
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I am getting more mechanical advance than my distributor is set up for !

I am running an HEI from trail beast and curved my dizzy for 14* of mechanical using the FBO limiter plate. But if I set my initial to 20* I get 45 ish total at 2500 RPMs with vacuum disconnected .......
I have used 2 different plates and double checked my reassembly.

What am I missing here ? Is the HEI throwing some advance at it ?
Would improper wiring cause this ?

STUMPED,
 
Might be "something else." Check for excessive vertical shaft movement, check for wear in dist. bushings and in the advance mechanism / shaft. Check for wear in the distributor intermediate shaft / bushing

And, what are you using for a light? "Dial back" lights are somewhat suspect.

Check for "rotor phasing" problems. Google it.

Maybe you are misreading the plate markings? What is the length of the slot in the limiter plate? "Somewhere" there are estimates of advance slot length to amount of advance.

And make sure you are not confusing distributor degrees with crank degrees

I think maybe crackedback found this, bear in mind these are DISTRIBUTOR degrees

Dimensions for Mopar distributor slots, in DISTRIBUTOR degrees

Modifying advance slots
degrees / slot size
6.............. .340
7................355
8................375
9................390
10...............405
11.5 ...........420
12...............435
13...............445
14...............460
15...............475
16...............490
17...............505
18...............520
 
Phasing is good.... plates are marked in crankshaft degrees....I have 2 timing lights that read same but one stops flashing above 3k and the other will intermitantly start changing the RPMs instead of the timing advance.... I just borrowed a 3rd and will check it tonight.
How much shaft play is too much?
 
I don't recall offhand. Play is addressed in the shop manuals
 
Im on the road at the moment but will check when I get home.....Do you know if HEIs will advance timing electronically ?
 
Sorry guy's just saw this.
HEI does not advance the spark, and it's most likely that you will need to pull the plate out of the distributor and set it to the next less advance slot.
That's why it's adjustable with multiple slots and even zero slot for full mechanical timing lockout if a person needed that.

I thought I sent this to everyone, but maybe I missed ya.
This is the instuctions for changing the total timing limit right from the people that make the plate. (4secondsflat.com) or FBO.

Mopar Distributor Tuning J685S
 
Trailbeast will have the answers, but in his absence the HEI is used in limp home mode without computer advance, because there is no computer. So, the mechanical advance controls the timing. In the GM design the distributor is locked, no mechanical advance, advance happens by computer, but if the computer fails, the ignition fires at base timing to limp home.

My thought would be to set the crank at 20, then pop the distributor cap, and observe if a reluctor tooth is near pickup nub. If not, the pickup polarity is reversed.
 
Thanks Trailbeast ....I have installed the plate properly and triple checked it.....

kit. ... THat was my next question. But I was under the impression that the engine would not run or run poorly if the reluctor wiring was backwards... The engine runs ok but is a bit of a dog....
 
KitCarlson said:
Trailbeast will have the answers, but in his absence the HEI is used in limp home mode without computer advance, because there is no computer. So, the mechanical advance controls the timing. In the GM design the distributor is locked, no mechanical advance, advance happens by computer, but if the computer fails, the ignition fires at base timing to limp home.

My thought would be to set the crank at 20, then pop the distributor cap, and observe if a reluctor tooth is near pickup nub. If not, the pickup polarity is reversed.
Click to expand...

Actually Kit the 8 pin module is in normal mode but minus computer controlled advance without the computer.
The application of 5 volts to pin D of the four pin plug sets "limp mode" which sets the timing back about 10 degrees.



mbaird said:
Thanks Trailbeast ....I have installed the plate properly and triple checked it.....

kit. ... THat was my next question. But I was under the impression that the engine would not run or run poorly if the reluctor wiring was backwards... The engine runs ok but is a bit of a dog....
Click to expand...

It can run ok, or bad, or not at all if the distributor wires are switched.
What happens is the spark still happens, and at full strength but the rotor is already so far from the terminal inside the cap that it is intended for that it can't jump it or it jumps to another contact in the cap instead of the one it is intended for and causing the engine to (break up).

Also, not all engines or driving styles are compatible with a modified advance curve.
Slow low RPM driving is not what the distributors are designed for, as they are a "performance" upgrade over the old lady grocery getter advance curve.
You may have the timing coming in too soon, or too much of it and even elevation makes a pretty big difference.
Or it may not have enough advance in later RPM's.
I set the distributors for a "Safe Range" of advance so they don't destroy someone's engine from detonation but the fine tuning is up to the engine tuner.

If you have or bought the HEI with your distributor then yes it is totally possible that it could be a wiring problem.
The most common one I see is low voltage to the HEI coil.
As a matter of fact now that I think about it, anyone who has ever had a problem getting the HEI kit to run good was from lack of good voltage and amps available.
This is why some use a relay to power their HEI instead of relying on their ignition wiring for enough power.

Then there's always the possibility that the problem is something else completely. :D
 
There is some advance that happens with variable reluctance sensors. The signal level increases with RPM, so the trigger advances some due to that, but typically only a few degrees. I use Hall, and optical sensing to avoid that, so timing can be accurately displayed real-time in car.

The comment about running ok, but a dog, raises the question of your timing light. Is it a set-back standard light? Also as timing changes, how is that? Smooth? Abrupt?

It is possible to rotate rotor, and scribe measuring marks or use fine point sharpie, then use those to estimate degrees via circumference measurements. The use of a small tape measure and a calculator. Crank degrees is 2x distributor degrees. Measured rotor movement, divided by circumference times 720 is estimated mechanical advance.
 
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I almost forgot to remind that these distributors are set to run about 16 initial for a 34 total, and not 20 for a 34 total.
It does sound like you are into it far enough to see that and change it if needed.
 
Where do you recommend running the hot wire from ?
Or should I say a good key on power source......
 
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mbaird said:
The distribute is not from you.
Click to expand...
Well there ya go then. :D
Just kiddin ya.

There really is no recommended good source because it relies on all the individual wiring of each vehicle and it's possible high resistance spots in the wiring.
This is why some use a relay to make sure they have one.
My own HEI runs perfect right off the old ballast wiring from the harness, and some people can't get a decent supply there.

Try just pulling 4 degrees out of your initial timing and see if it runs better (doginess gone), and if it does but likes 20 initial then bring down the total with the plate settings so you can run 20 initial.
Sounds like you might have done this and still getting too much total for some reason?
 
I have the plate set at 14* advance.... Initial at 20*
Wired HEI to old ballast wiring . All wiring in car is new.

It should not be physically possible .....dizzy is in good shape . All I can figure is I messed up or HEI is faulty....

Would weak power source or reversed pickup wiring allow the car to run decent (not a monster but smooth) yet cause the spark advance like it is ?
 
mbaird said:
Would weak power source or reversed pickup wiring allow the car to run decent (not a monster but smooth) yet cause the spark advance like it is ?
Click to expand...

Not that I have ever seen.
You might measure the voltage at the coil while the car is running and see what it says.
New does not always mean adequate.
 
I have suggested a way to verify correct phase by observing reluctor to pickup location at observed timing, in static test.

I also suggested a way to measure advance by rotor angular deviation estimate.

The HEI triggers on trailing edge of reluctor tooth, as it is on the way off of pickup nub. That of course is when phase is correct.

The HEI module without ecu, does not have the ability to control timing.

A scope can be used to monitor peak coil current and trigger point, using low value shunt on one channel and pickup signal on the other. That would easily prove correct operation of module and wiring, or not.
 
Kit....I haven't checked the phasing using your method yet because the damn timing tape flew off my balancer again even though I clear coated it on .....Urghh
I don't know why I didn't get my dampner marked.....
Will swap dist. wires next to see if it makes a difference .
I checked voltage with key on and am getting 11.8 volts
( engine not running) and ran a ground direct to the battery....

One step at a time and I will figure it out.
 
11.8V means too much voltage drop or weak battery. Need to measure battery, too. That will not change timing, it may reduce top end ignition energy because time necessary to charge coil increases, with reduced voltage. At high RPM, less time is available.

I would not swap distributor wires as test. Fix timing marks first. Then see what light says, verify reluctor based on that.
 
Kit , are you referring to the reluctor phasing as related to the rotor /terminal post? If so I have verified that using a cap with a window cut away....and I have several multikeyway reluctors .

This has got to be something simple that I am missing.
 
Ok....so here is the plan. I'm going to install the plate at
0 advance and see what happens. If it still advances....
Then I will_________ ?????
 
mbaird said:
Kit , are you referring to the reluctor phasing as related to the rotor /terminal post? If so I have verified that using a cap with a window cut away....and I have several multikeyway reluctors .

This has got to be something simple that I am missing.
Click to expand...
No, I thought my description was clear. I am talking about the polarity of the connections to pickup sensor. I assumed you were reading and understanding my prior posts.
Relucto_pickup.jpg

See where the brass feeler is inserted? It is between a reluctor tooth and the nub on the pickup. When the tooth is just starting to leave the pickup from being centered with it is where spark happens. If the polarity of the pickup coil connections are reversed, then the spark happens somewhere between the teeth in a very erratic way because between the teeth, is smooth with no sharp edges. The teeth on the reluctor have sharp edges.
This is the signal that comes out of the pickup at the distributor shaft turns, and a reluctor tooth goes past.
MoparVRCorrect (800x552).jpg

For the HEI to trigger, the signal goes low, then quickly high that is the trigger point. The trigger point varies slightly from HEI module, and with MOPAR ECMs, and the amplitude of the signal increases with RPM, so timing advances slightly sooner. Timing also varies slightly from cylinder to cylinder because of run-out ( in out wobble of teeth). Mopar distributors are far from perfect.

If the pickup polarity is reversed the signal is flipped, not backwards! If one imagines that, and understands the trigger, you will be able to see why polarity is so important. I am not saying yours is off, but a check is so simple. Line the ballancer to whe spot where you see the timing light at idle. Pop cap observer where a tooth on reluctor is to the pickup. That is just a few minutes. Then you know for sure ....
 
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Actually, Dave, that amounts to some of the same thing. "Relative timing" of the ignition trigger to the rotor

Do you have ANY other module like a 4 pin HEI or Mopar module that you can temp wire in and compare? I'm doubting, frankly, that it's a module problem.

It would be possible, I'm sure, for a magnetic pickup to have reversed magnetism or wired wrong from the start, IE polarity wrong in relation to "should be"
 
Yes that is true, it is not a module problem. With incorrect poparity the rotor phase may be off enough that it is in-between cap towers with cross fire galore. Step 1 of any ignition install, should be: start engine with a static timing setting. If it does not start, then use timing light, and see where spark happens. If it is not correct, it might be the pickup polarity. With a scope it is easy to view coil signal and pickup to determine where spark triggers.

Here is a picture of a using MS paint to flip waveform, I posted it years ago. Results vary where trigger happens.
MoparVRIncorrrect (800x566).jpg
 
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