Mechanical Ignition Timing Adjustment Procedure (MITAP)

4062 Views 13 Replies 6 Participants Last post by Sailing_Faith, Dec 12, 2021

Sailing_Faith

Discussion Starter · May 8, 2020

Mechanical Ignition Timing Adjustment Procedure (MITAP).. :lol:

We all know that ignition timing on our vans is not "adjustable" but electronically adjusted by the computer. :dance:

That said, many have reporting obtaining improvements in performance and distributor cap life by opening up the bolt hole in the distributor hold down to manually "tweak" the mechanical relationship between the rotor and pickups in the cap.

From a thread "Burning through distributor caps";

Sailing_Faith said:
Ok, I have a theory.....

So, we know there is not officially any adjustment on our distributors. The computer adjusts the timing... BUT. There is no getting around the fact that there is a hard relationship between TDC as seen by the crankshaft position sensor and the alignment between the rotor and the poles on the distributor.

So, if the computer is adjusting the timing, and the rotor is not exactly over the contact (let's say it's because of a minor stretch of the timing chain, or slightly misaligned gear in the dizzy....

Saying all that to say, some grind an oval in the hold down clamp and play with minor tweaks... and report performance gains. Maybe the computer working to throw a spark across a larger then ideal gap is taking a bite out of your cap....

Just a theory, I'll await others ideas.

While we know if the "gap" is greater then ~2degrees the computer will throw the 1345 code.... but if the timing is being adjusted to cross a gap created by a 2degree difference it's going to weaken the spark and eat up caps. :screaming:

The mythical "case relearn" procedure can correct the 1345 code, but I can't see how it could fix the mechanical alignment issue... :think:

In that thread;

TurnNburn said:
.....I over drilled my hold down bracket to dial in my timing, totally do-able...

I remember Leeann and others referring to doing this...

I image at least three approaches;

'Seat of the pants' adjustment... tinker with it and see what you get.

'Align the marks'.... set the engine to TDC by the mark and see if the rotor points exactly to the contact.

Or maybe even;

'Read the reported advance and compare to timing mark with a light'... not sure what this would look like, but would like to hear what others have done...

I also thought about drilling a big hole in an old distributor and using that to manually adjust while watching the spark increase or decrease.... I can think of problems with this, which is why I am posting this...

What procedure did YOU use? Long term results?

Thanks in advance (pun intended)... :ty:

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Sailing_Faith

Discussion Starter · #2 · May 8, 2020

Background

I replaced my distributor drive twice (in over 200,000 miles). The Skip White (United brand) distributor drive went a long time with its original cap.. maybe 30k.

Since replacing that drive (rotor plate stripped out, and did not reliably hold rotor in place) I have gotten less miles out of distributors.

Last three;
Knock off brand distributor with brass contacts - 14k
Another knock off with brass contacts - 12k
AC Delco with aluminum contacts - 9k
And my current AC Delco with aluminum contacts is failing at 8k.

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Leeann_93

· #3 · May 8, 2020

I used a Dremel to wallow out the hole, then I checked the CKP correlation. When it was 0° at 1300 RPM, I locked it down and performed the relearn. It was still 0° at WOT, so that was perfect.

Of course, you're not supposed to have to adjust the timing, but needs must.

Performing the relearn lets the computer know how far apart the two are and it adjusts spark timing accordingly. It can only adjust so far, however, so mechanical adjustment to get as close as you can to 0°, then perform the relearn, is the best way. On my '02, I simply stabbed the distributor in one tooth off; when I rotated it one tooth counter-clockwise, it was dead on 0°. On the '05, one tooth made it 40° or so and back a tooth made it something like -10°, so I left it at -10° then manually adjusted to get to 0°.

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Sailing_Faith

Discussion Starter · #4 · May 8, 2020

Leeann_93 said:
I used a Dremel to wallow out the hole, then I checked the CKP correlation. When it was 0° at 3200 RPM as per the book, I locked it down.

Of course, you're not supposed to have to adjust your timing, but needs must.

Brilliant! I hope that number is available with my scanner. Thank you! :ty:

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sixsix

· #5 · May 8, 2020

'92 - CPI - Gen I - OEM dist - Fully adjustable radially ( just an edge clamp, no specific 'hole' ).
Chevymayer adjusted ours as we tooled around the neighborhood till it sounded good to him and felt good to both of us. Didn't 'clatter' and then didn't 'bog' - it is just right. Couldn't tell ya' where we ended up-angle wise anyway.

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Leeann_93

· #6 · May 8, 2020

Sailing_Faith said:
Leeann_93 said:

I used a Dremel to wallow out the hole, then I checked the CKP correlation. When it was 0° at 3200 RPM as per the book, I locked it down.

Of course, you're not supposed to have to adjust your timing, but needs must.

Click to expand...

Brilliant! I hope that number is available with my scanner. Thank you! :ty:

I used the wrong nomenclature - it's CMP Retard (just looked). And then I did a CASE Relearn, which probably isn't on your scanner; I have the cheap Tech 2 knockoff....

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Sailing_Faith

Discussion Starter · #7 · May 13, 2020

Leeann_93 said:
Sailing_Faith said:

Leeann_93 said:

I used a Dremel to wallow out the hole, then I checked the CKP correlation. When it was 0° at 3200 RPM as per the book, I locked it down.

Of course, you're not supposed to have to adjust your timing, but needs must.

Click to expand...

Brilliant! I hope that number is available with my scanner. Thank you! :ty:

Click to expand...

I used the wrong nomenclature - it's CMP Retard (just looked). And then I did a CASE Relearn, which probably isn't on your scanner; I have the cheap Tech 2 knockoff....

I checked both of my scanners to make sure, but neither gave CMP retard.. just
"advance"

Good discussion of Reader types here in 'Adjusting Distributor' thread.

So I pulled the cap and noticed (again) that the burn marks were on the portion of the contact Nearly 90 degrees before the center... looks like the spark is coming well before the mechanical "closest point" of the rotor .... (I know I took a picture, but must have deleted it).

Without the scanner data I went with the "seat of the pants" adjustment method, I removed the hold down and ground out a oval (turning the pictured slot into more of a + mark).

Putting it back together, adjusting it I could hear a change in the spark "tick"... and a smoothing out of the idle.

Drove it and I can feel a difference.... did not change the cap, or do anything other then the adjustment. :thumbup:

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MechBob

· #8 · May 13, 2020

Me thinks there is some misinformation and/or misunderstanding here. The sensor in the distributor is a cam sensor.it tells the PCM which cylinder needs it's injector "fired".It also is used for detecting which cyl. has a problem for misfires. It also can determine which cyl. gets the spark, but not relevant, as we are using a cap and rotor for this.Also, built into the programming is parameters that can determine if the crank and cam sensors are out of wack.Don't have a clue what you mean by "the gap" determining this.So, the crank sensor is what actually determines "when" to fire the coil. As far as the rotor lining up with the terminal in the cap,you are right,can cause weak spark to plug,wrong injector timing and possible misfires.Also, the increased gap can burn out a dizzy cap much faster. Now, the misalignment can occur naturally, because it gets further behind as the timing chain wears. Also, GM made some bad dizzys, so did "Skip White", some of his china imports were made poorly.This happens when the shaft is not quite drilled properly,where the pin holds the gear to the shaft.Also remember, as the dizzy gear wears, makes the gap bigger also.If you wanted to do it perfect, you would have to put the cylinder you wanted to use at TDC, then rotate it to TDC in the normal rotational direction,because of wear in timing chain and gear, notch out the hole and rotate dizzy till the rotor and the cap electrode line up.The closer it is, the better engine will run, and cap life will be at it's best. Fell free to correct me if you think I am wrong.

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AstroWill

· #9 · May 14, 2020

Leeann_93 said:
Sailing_Faith said:

Leeann_93 said:

I used a Dremel to wallow out the hole, then I checked the CKP correlation. When it was 0° at 3200 RPM as per the book, I locked it down.

Of course, you're not supposed to have to adjust your timing, but needs must.

Click to expand...

Brilliant! I hope that number is available with my scanner. Thank you! :ty:

Click to expand...

I used the wrong nomenclature - it's CMP Retard (just looked). And then I did a CASE Relearn, which probably isn't on your scanner; I have the cheap Tech 2 knockoff....

I think the Tech2 clone($300) is really the way to go as it can do virtually everything, and being done standalone. With the VX Diag for GM($100) running Tech2Win being second best(Tech2 software emulated on the computer).

Other scanners can show it, typically the higher end scanners. I just came across this recently where it seems that with the proper software and an el cheapo ELM based bluetooth adapter can do it as well.
https://www.scantool.net/forum/index.ph ... ic=10382.0

It would be cool if someone could figure out the ABS brake bleed in a similar fashion so it could be done with a cheap ELM device. Cheapest way I have seen for that is that is the VX Diag for GM running Tech2Win.

Edit2: Deleted link to app, too many negative reviews.

Be careful if you are going to adjust the timing by wallowing out the holes, a lot of times the distributor drive gear is worn out or a replacement has the gear 180degrees off. See Pancake Distributor Disease
In other words you shouldn't have to make the non-adjustable distributor hold-down adjustable if the parts are not worn and are installed properly.

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Sailing_Faith

Discussion Starter · #10 · May 14, 2020

MechBob said:
Me thinks there is some misinformation and/or misunderstanding here. The sensor in the distributor is a cam sensor.it tells the PCM which cylinder needs it's injector "fired".It also is used for detecting which cyl. has a problem for misfires. It also can determine which cyl. gets the spark, but not relevant, as we are using a cap and rotor for this.Also, built into the programming is parameters that can determine if the crank and cam sensors are out of wack.Don't have a clue what you mean by "the gap" determining this.So, the crank sensor is what actually determines "when" to fire the coil. As far as the rotor lining up with the terminal in the cap,you are right,can cause weak spark to plug,wrong injector timing and possible misfires.Also, the increased gap can burn out a dizzy cap much faster. Now, the misalignment can occur naturally, because it gets further behind as the timing chain wears. Also, GM made some bad dizzys, so did "Skip White", some of his china imports were made poorly.This happens when the shaft is not quite drilled properly,where the pin holds the gear to the shaft.Also remember, as the dizzy gear wears, makes the gap bigger also.If you wanted to do it perfect, you would have to put the cylinder you wanted to use at TDC, then rotate it to TDC in the normal rotational direction,because of wear in timing chain and gear, notch out the hole and rotate dizzy till the rotor and the cap electrode line up.The closer it is, the better engine will run, and cap life will be at it's best. Fell free to correct me if you think I am wrong.

We have the same understanding... the procedure I am after is a way to "reliably " make that adjustment...

As you say "the closer it is, the better the engine will run".... exactly what I am going for here. :thumbup:

I understand my using the term "gap" is not clear.. I mean to say the space between the rotor and the appropriate contact in the distributor cap... the space that the spark must jump when the computer is telling it to fire and apply the spark.

Leeann has the best answer, her procedure makes perfect sense...

Leeann_93 wrote:
I used a Dremel to wallow out the hole, then I checked the {CMP Retard}. When it was 0° at 3200 RPM as per the book, I locked it down.

Of course, you're not supposed to have to adjust your timing, but needs must.

. I don't have a Tech 2 scanner (I appreciate AstroWill's suggestions above). :thumbup:

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Sailing_Faith

Discussion Starter · #11 · Jun 4, 2020

Last 2 fill ups the mileage was up. 18.6 and 19.2 mpg.... pretty happy with the results.

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Leeann_93

· #12 · Jun 4, 2020

Sailing_Faith said:
Last 2 fill ups the mileage was up. 18.6 and 19.2 mpg.... pretty happy with the results.

Sweet!

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pbgbottle

· #13 · Jun 28, 2020

I had done this readjustment a few years ago mine was at around 6degrees. Original distributor, I dialed it back to 0. I just checked it last week I'm at 2 right now I will be removing dog house to change cap and rotor I will try to set it back to zero. I use an elm wifi dongle and scanxl pro. On a laptop. It can read all kinds of info program is old. It can also be found on the internet if you look hard free. Just saying. I'm at 236,000 kilometres on a 2004 Original distributor only changed cap and rotor once this will be my second time also only changed plugs once. All has been fine.
Just changed fuel pump for the first time also last month. His van has been pretty reliable for sure and did the EBCM reflow nothing else. My oem distributor has still been hanging in there for the long haul. Cheers.

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Sailing_Faith

Discussion Starter · #14 · Dec 12, 2021

So there have been a lot of “my van won’t start” threads…. The procedure in this thread is helpful…. The basic problem is classic “pancake distributor disease”.

The gear (and or the shaft bushings) get worn in the distributor. Sometimes a misfire code either a P0300 or even one cyl code (like a P0304 for example) will come up.

changing the distributor cap fixes it for a little while…. Because the computer is electronically adjusting the timing…. BUT!

the spark is jumping across a larger gap…. This leads to arching and traces of carbon build up on the terminals, inside the distributor…. Everywhere.

then you get a moist day, or even a dry day and a temperature change…. The carbon attracts moisture from the air AND your van won’t start.

Checking / replacing the gear, the distributor drive, and then getting the mechanical alignment as close as you can is the only way to properly address this.

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