When I changed to the colder nonextended ZFR6F plugs(NGK) I picked up a miss when the engine is cold right at 2200 rpm and no load on the engine. It is a pretty serious miss that feels like a lean miss, but the AF ratio is good. I am assuming timing is the culprit. It runs just fine when it gets warmed up. The timing at 2200 RPM and no load is 42 degrees, which seems to run fine when hot. There is a timing trim table which ads another 5 degrees into the timing when it is cold. This is adjustable, so it is likely running 47 degees advanced at 2200 RPM when it is cold. There is not a hint of preignition there, just the miss that mimicks a serious lean surge. Shift down a gear and it smooths right out when RPM and vacuum both drop.

The question is: Can this much advance cause a miss such as I am describing? I have this timing set at 42 because at cruise, the engine is turning 2200 RPM at 65 MPH. Since it seems to run well when it is warm, I am trying to figure out how to tune the trim tables to improve the cold start drivability without reducing the base timing table. Thanks for any and all thoughts on the subject.

Sam

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spo when it's cold the timing map adds another 5 degrees at the same point? maybe I'm just reading it wrong but doens't make sense to me that it would ADD another 5 degrees when cold. I rather have less ignition timing when cold at that revs... at least, the same that works OK for normal operating temperature. For what I'm reading sound like you can remove/modify that "add timing when cold" feature, can't you?

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

I think you are on the right track that the extra 5° cold advance might be pushing things over the line. 47° @ 2200rpm sounds like too much advance to me (just a gut feeling, so take it for what it's worth). Maybe you can cancel the cold advance and see what happens? Strikes me that with this much advance, the rotor's not going to be anywhere near the applicable cylinder's cap terminal and you may be getting spark misdirection under the cap. There are a couple things you can do to maybe get a fix on this. You might want to experiment with one of these wide-contact distributor caps. They were released in a package also containing a rotor with a narrower tip and a better-insulated coil wire in '62 to cure a cold/wet no-start condition on slant-6 engines caused primarily by improper spark jump under the cap. I wish someone had ever made these caps with brass or copper contacts; the factory used aluminum and it works OK but copper or brass is better, longer-lasting and more corrosionproof. The link above is to a kit of parts you don't need; contact the guy and ask him for just the wide-contact cap if you want to try it. You'd want to narrow the tip of a NAPA Echlin long-tip rotor # MO-3000 a little, say by 2mm on each side. (In case you're wondering: By 1966, the wide-contact cap and narrow-tip rotor had been superseded to narrow-contact caps and standard-tip rotors, but made out of better-quality materials than the initial-production caps and rotors that had caused problems.)

The other option would be to pick up a couple more rotors, selected for their tip configurations, and do some rotor component switcheroo to wind up with a rotor that has a tip "winged" on the leading edge. It's difficult to describe this in print...basically imagine looking down on the rotor from above, with it pointing to 12:00 position. Now think if the tip of the rotor were extended laterally to the right such that the end of the rotor were about double its present width, but only to the right. There are a few sources for candidate tip-swaps, and they're not hard to do; let me dig up some P/Ns for you when I get back to the office. This might well be the preferable way to go, since you could then use a cap made out of modern, higher-dielectric materials and good copper or brass contacts.

As to why this happens with the standard-tip plugs and not with the extended/projected-tip plugs...? Got me!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I can add or subtract any amount of timing I want for every temperature of ECT. Five degrees advanced is just the default that came with the calibration from the factory. That is gone by about 142 ECT or so. So you think it works better to take timing out when it is cold? Tell me more.

EDIT:
Dan, it seems I was typing as your were posting, and thus missed your post, even though it showed up before mine. Thanks for the thoughts. I think the extended tip just works better in marginal conditions, which this seems to be. I can easily take out the cold start 5 degrees if that seems wise. I can also take out 5 degrees from the base timing map at 2200 RPM, but it seems to runso well when hot, I would prefer another solution. I dont; know anything about how timing effects cold start drivability.

Sam

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if works good, really hood when warmed up, I'll just cut say 3 degrees for starters on that rpm band when below 142°F temp.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

For the warm up trim you can only cut or ad timing to the entire map by engine coolant temp. So for any given temperature, you can add or cut as many degrees out of the entire map as you want. I wil give that a try. But, I would enjoy a general discussion of how timing effects the warm up drivability of an engine. Why do you suppose the default trim table started with 5 degrees advanced?

ARgentina, why did you say you would retard the timing a little at warm up? Would this be better? I can remember thinking that I improved the warm up of one of my slants years ago by putting a bleed down style check vlave in the vacuum advance line which kept the timing up for a few seconds when you stepped into the throttle. This was bypassed in my system by an EGR switch, once it warmed up. This seemed to eliminate the cold bog that these engines were famous for. The only thing is, you did have to be carefull of detonation in that case. But with that set up the timing advance was backwards from where it is advanced now. Now the timing is advanced under no load conditions, so the mis happens when you let it wind up in RPMs in a light,lazy kind of way. Just as the vacuum gets back up it developes what feels like a lean surge, and then a real mis. But looking at the AF ratio, that is in a pretty normal, healthy range.

Sam

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The added advance during cold operation is for driveability....

Although for a toyota, see page 5

http://www.grubinski.com/grubinski/auto ... als/40.pdf

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

I drove the DArt to Baltimore today to visit my 87 year old Mom, and discovered that 42 degrees advanced is too much for highway cruise even though it was warmed up. The same phenomenon happened at 2200 RPM under light load, which is actually 70 MPH. When ever we were drifting slightly down hill the miss came back, but more subtly. My wife was with me, and I talked her into triming the timing tables, which I had to talk her through to eliminate the miss. She was a valiant trooper, because while she supports my car hobby whole heartedly, she is not a computer person, nor a car person herself.

She did great though, and by the time she was finished she felt fairly comfortable with the process. She cut everything back to about 35 degrees advance at 2200 and brought the 2600 RPM advance back somewhat as well. The miss went away. So, for the record, you can have too much advance, without seeing any evidence of preignition. So simply pushing the advance until you get detonation and then backing it off is not good. The ideal is somewhere down below the detonation theshold.

Ems. that is a fabulous link. Thanks.

Sam

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You're welcome.


(go up a level, and there's more.... )

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

For sure! At one point after some distributor mods, I had a really strange symptom in my '65 which otherwise was a terrific runner: In Neutral, at engine speeds above idle, it would cough and skip and miss severely. Didn't seem to miss under load at speed, didn't ping, started and idled fine. I chased geese for a long time before accidentally leaving the vacuum advance hose disconnected and noticing the miss went away. I held the engine at an 1800 rpm idle -- no miss -- and reconnected the vacuum advance. INSTANT bucking and missing! Aha. Too much total advance; vacuum unit pushing it over the edge. I swapped in a less agressive vacuum pod and tweaked the mechanical curves and the problem went away. Pinging won't necessarily happen with excessive advance, sometimes the engine just runs poorly.

So OK, you had too much total advance and you've taken some out. What effect will this have on the engine's tendency to ping with ZFR5N plugs?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan, thanks for the confirmation. The detonation I have been working on all occurs at 7 lbs of boost or greater, and at 13 degrees of advance.I say and above, because 155 is the highest KPA value on the fuel and spark map, and the map reading goes right to the top of that by the time the engine hits 2500RPM or so under full throttle. It could be going higher as far as I know. The boost gauge failed, and needs to be replaced.

There are 144 cells in the timing and fuel maps, with vacuum boost on one coordinate, and RPM along the other. I can plug any advance figure I want into any one of them. So it is easy to run 35 degrees advance at 2200 and high vacuum while running 13 degrees at high boost and the same RPM. It is like having a vriable vacuum advance, and centrifigal system in the distributor, except it is all controled by the ECU, and when it decides to fire the MSD box. I know this morphed into EFI talk, but I thought you carb geniuses would maybe have reat useful information on timing, which did indeed happent o be true.

EDIT:(I went back and checked the fuel map and it is a 16x16 Matrix)

My AF ratio gauge seems to be working again, so I can now start looking at AF ratio when under WOT conditions. It really takes two people to tune this way, and I know I won't be able to talk my wife into that one. If the AF ratio is above 12:1, then I will likely ad some more fuel. But like I said earlier, going over the top rich mimicks lean on the O2 gauge, so you have to sneak up on the right VE figure.

BTW it seems as if the heater on the sensor was acting up for some reason. When it was new, it read fine, and as advertized, and then over night one day, it would take a few miles to start reading with anything close to making sense. Figures would all be off the chart lean, in territory that would not even run if they were correct. Now after 25 seconds of heatup time, it reads right once again.

For the record, I made the trip back home from Baltimore after the last post, and the mileage for a 100 mile round trip was 27MPG. I tried to get more fuel in the tank. I know it is possible that there was an air pocket in the tank, but I filled it up at the same station, and pump as last time.

Sam

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Gents Sam and SlantSixDan,

You saved me many hours of pulling my hair out by reading and reviewing your old posts last night.

I am trying to eek out every last drop of mileage on my daily driver and had overtimed the engine. In the driveway when it was cold it wouldn't miss until it warmed up. As I raised the rpm to 2000 it would start to miss then get worse on up past 3000. Cruising down the road it was un noticeable until I lifted off the throttle, and it felt like a lean surge. Press down a slight bit and it would go away........

After reading the Toyota article and what you both experienced it surprised me that you could overtime a car and not hear it ping. I was way over 60 degrees with the new recurve springs and didn't know it until I let off on the gas at cruise or slowly reved it up in the driveway.

Needless to say it can happen and not ping. It runs smooth as silk now.....I guess Doctor Dodge's long looped big block recurve spring idea made a huge improvement over the little stiff looped stock spring!

I have the initial timing at 16 degrees which seems very tame and less punchy.

Thanks very much for sharing! This post is worth a million!!!!!

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG