IC 392 BAD Mileage, mistery detonation/pinging

Also,what did you mean by throttle open some? I took all measurements with the choke flap open, coil disconnected, engine warm, if that's what you meant.
 
cbmind said:
With vacuum advance disconnected, timing at idle is 10, at 3000rpm, 20.
Click to expand...

Only 10 degrees of mechanical advance is not right. Distributers usually have 20 - 24 degrees of centrifugal advance built into them. Start at 10 end at 30-34

did you keep increasing the rpm untill the timing maxed out (stopped increasing)? I say you need to buy a light and do this test again. 20* total timing and you won't get ping.


cbmind said:
Is the 35 degree spread with it connected normal?
Click to expand...


25 degrees of vacuum advance is a lot but not unheard of. With out knowing what parts your engine has on it it is going to be real difficult to know if things are working right.

Don't change anything yet.

I think a few pictures would be the next step. To many unknowns.

If you check the compression with the throttle at idle the engine might not get enough air to give you accurate readings or true max readings.
 
It's starting to sound a little like there's not too much about your timing that is too far off although, Robert is correct, a timing light and a vacuum guage are necessary, and your compression seems ok. You might want to have the centrifical advance springs looked at to make sure you are getting full mechanical advance and that the curve is set up right. The vacuum advance seems to be working right. Are you using ported vacuum btw or manifold vacuum?


There is one thing that nobody has mentioned yet... Hot spots caused by carbon buildup cause pinging. I know almost any water based liquid will do the same thing but a can of seafoam down the gullet will burn off any combustion chamber carbon build up and give you nice clean innerds to start with.

Another thing that will cause pinging besides too much timing is a lean condition. If let's say that your tq seems ok at idle but at part throttle developes an internal leak your mixture May become way to lean and ping ping ping. Tq's can be a bit touchy and the phenolic bowl warps and ya better make an appointment to have mm rebuild ya one.

Come to think of it so should I
 
Last edited:
Generally, it is "easier" to do a compression test with the choke plate and the throttle butterflies blocked wide open...

Based on your "timing specs", I think you need to supply / find the IH part number on the distributor that michael mayben asked for.

If you look in his distributor id post, I think you will find where to look...
 
Ok, so compression is ok, then that is not an issue at this point, one step in the diagnostic chain out of the way. And that's assuming the compression test was done both cold and hot, with all plugs removed, the choke plate and throttle plate blocked wide open, and the ignition system disabled. That was step one!

And from the beginning of this thread I see ignition timing numbers all over the place and nothing is right for a 392 that is "stock". And if it's "stock", then ya need to be using specs for a pickup/t'all not a dam Scout II that never had that motor combo oem. One more time, these engines/platforms are not "all the same"!

Loose the timing light right now...we're gonna fix this and move on. Power time it, just retard the distributor until detonation disappears!

Review this thread:

http://www.forums.IHPartsAmerica.co...es-pertronix-require-timing-readjustment.html

Mainly the portion regarding "power timing". Then go out and do it! Fuck a timing light for this!!! Your timing is way too advanced dude! I'll say it again, a 392 cannot use a base timing of more than 6*btdc on this akeegazz shit we call regular today, texas aint no different, e10 is e10.

But you must use a mity vac or something and verify that the vacuum advance is functional. Also, you must verify that all vacuum plumbing is correct, but I seriously doubt that everything is functioning properly, how do you know that??? Has each component been tested for functionality? Are the temp switches operating correctly? If the a.I.r. Pump has been removed, how was that delt with?? I have posted vacuum diagrams on this forum several times, do some research.

Open up the distributor and verify that all systems are operational also. At this point we don't even know which distributor is present so how the hell can we diagnose anything??? No tellin' what distributor is present, we need pictures of the engine bay from several angles and I gayrondamteeya I can pick it apart! Texians that ain't from cleburne do know shit! We must know the details and IH p/n for that distributor, other wise no progress is gonna be made here, plain and simple.

Distributor specs for these motors are all over the place, go review that "distributor I.d." thread and see how many there are, each has a different advance curve. "typical" curves for sv have a vacuum advance can that supplies 5*>7* advance at 10"hg and a mechanical advance of 14*>17" for a total of a nominal 22*>24* or so. But that varies tremendously by each part number and that is only if the distributor is fully functional.

If it's a Holley electronic, or prestolite electronic, then what you are describing (errant/erratic timing) is a typical failure mode, erratic timing all over the place due to component failure.

The spark plug heat ranges discussed here are all ballpark, plug heat range is not the problem!

No mechanic who is not very familiar with all variations of ihc schnizz (most especially emissions schnizz between '72 and '78) is gonna be able to deal with this in a cost-effective manner at a shop flatrate of $95 an hour in your market. Ya better open that checkbook wide and have a major interest in somma them gas wells arount cleburne.

It does no good and is useless to screw with the fuel delivery system until the ignition system is completely diagnosed and verified as functional.

And we still don't have any ignition system detail!

This shotgun approach is gonna prevent any kind of meaningful resolution of this deal.
 
Here's the latest and greatest-
vacuum testing:
at a up to operating temperature idle of 750 rpm in park, 20"
in gear, foot on break, 600 rpm, 19"
at 65 mph, 2700 rpm, 12"
accelerating real hard from a stand still, 1, 2, 3rd gear, by new tires burnout, 5-6" vacuum.

Drove with the vacuum advance disconnected and the hose plugged, noise still present, extremely rough idle. Didn't really work out...


Here's the distributor numbers, tag was a red metal tag with a single screw affixing it to the distributor, reads"prestolite
1d114002w249 (the d is a maybe... 11 is questionable also) zeros might letter "o"s.

Carb id, carter thermoquad four barrel: number on driver side aluminum tag- 1700009c1
9g 09


hope this helps.
 
I really appreciate all the help everyone, I'm trying to accomodate all the "have you tried this yet?" and answer as many questions as possible. I have done my home work, read all the threads mentioned. Actually, half of the threads mentioned I had already searched and read before I started asking questions. Pretty busy day today, started a new job, don't have the time to fool around like I used to. Bad economy and a democratic president are bad for my kind of work. I took pictures this morning, as soon as I figure out how to post them, I will. Thanks for the help guys, have patience.
 
cbmind

Driver side vacuum

cbmind

Firewall vacuum

cbmind

Front of the engine vacuum hoses



cbmind



Passenger side vacuum hoses


cbmind

Distributor w/ vacuum advance, no cap or rotor installed.


I know, I know, couldn't resist. Had an edelbrock 1406 laying around, brand new, for my 65 lemans, decided to put it on here instead. I know I shouldn't have, but the idle is smooth now, acceleration is crisp and brisk, no stumbling as with the thermoquad. Egr valve is not hooked up, vacuum advance is plumbed into the thermo switch on pass rear block, the day after I bought it in calaforna, I had inspected and it passed with flying colors. I assume ( ass out of you and me...) that all emissions eguipment was working, but probably am mistaken. I have not physically pulled the distributor out and checked the shaft end play to verify wether or not the bushings are good, however when I had the cap and rotor, and "dust boot" off, I wiggled the shaft to and fro, did not check with a feeler guage, but I'm guessing (here we go again) hair under a 1/16th, or -.0625"
 
 
Just got done "powertiming" run's like a scalded ape. Can't hear the racket anymore, checked timing with my regular inductive timing light, at 4 degrees. Fyi. I'm going to run with it till the weekend and see what happens. Pull the plugs and take a look at them, big thanks to everyone. I didn't follow word for word, ignition/ carb thing, guess I'm stubborn, but everyon'es input is greatly appreciated. Thanks again.
 
Real texians (as in at least 5th gen) do know shit don't they???

Do not let that tq carb get away. And we're not "blaming" that carb for your issues which are multiple in actuality. But any carburetor running this e10 shit (and we now have no choice in that matter) will have a normal service life of about two years when used in daily service and not allowed to "sit" for an extended period of inactivity.

I'll post an analysis of your prestolite distributor when I've finished the research.
 
That ain't no tq on there....it's an edlebrock...probably a 1406

the distributor is a perstolite :mad5: ..........which in my mind presents a whole new set of problems. I'd kick that thing to the curb and get a Holley with a pertronix II. Opinions vary on repolacements.

Yeah I know throwing parts at a problem without proper diagnosis is a waste of money. For me some things just gotta go and the prestolite is one of them.
 
Tim...cb already posted that the tq carb originally discussed was swapped for the edelbrock 1406 just yesterday, and an "adapter" to do so can be seen in the pics!

And any distributor is the best one as long as it works as designed and the advance specs are matched to the motor it's being used in! While I am a Holley distributor fan for some IH schnizz just because they are more numerous, I work with just as many rotten prestolites and delcos as I do holleys. And the delco cast iron unit is far easier to service and repair when needed. Anyone with a "dial-back" timing light and a shop tach (accurate) can "tune" a delco using commonly available/inexpensive parts to do so.

Parts is parts...as long as parts are correct for the application and actually function as intended.

Imho, the prestolite electronic trigger unit is far superior technically to any other "electronic" distributor of that genre, the chrysler electronic sparker was equivalent in durability/performance.
 
Ok cb...first distributor data...

The prestolite number ya posted is "kinda" correct, good enough for me to make an id.

Attached is a spec sheet for several prestolite electronic sparkers right from a mts 2313 manual (late Scout II). By ciphering the number you posted, use the column on the far right for specs for your distributor when it was installed new. Notice the considerable specification differences in that distributor as compared to the 304 and 345 variations. And this is not all of 'em that were produced. This goes back to what I preach to you kids all the time...this stuff is not "all the same"!

Print this doc and retain for your IH service data collection.

And most especially, use a non-magnetic thickness gauge and verify the electronic trigger "air gap", it must be 0.008" before making any adjustments downstream.

And back in the day, if you sourced a replacement part distributor through an IH dealer, it would not have carried that exact same part number, service parts carried somewhat different numbers to denote..."service part", not oem part. Many reasons for that, not important here!
 

Attachments

  • Prestolite IDN 4002A Specs.PDF
    1.7 MB · Views: 535
Likewise, the IH p/n ya supplied for the tq carb is not accurate. If that number was on an aluminum tag under a screw head, those can be impossible to read correctly most of the time. But that was good enuff for a starting point, dealing in all this kinda shit is an investigative process!

The "c1" suffix tells me that was an oem carb, not a "service part replacement". I believe if ya look at it again, you will see that the first digit is really a "4", not a "1".

Here is a scan of the actual replacement parts list page for what I "think" is your carburetor, you can see all the variations that were used. And this is just for the "normal" versions, not the "low compression/export" stuff. This is directly from the IH parts list for '74/'75 pickall.

These tq carbs never had every small part available though ihc, if a carb required any other part, then it had to be replaced with new, that was a warranty/emissions requirement and not uncommon at all.

And the "kickdown" stuff for the tq when used in pickalls was completely different from the system I see in the pic of your engine bay, that has the Scout II kickdown linkage set up. Since you had to use that carb adapter, the linkage is now working at a fairly extreme angle (as compared to oem), so ya need to "re-adjust or at least verify the kickdown travel adjustments.

And with that carb adapter, hood clearance is really close to the air cleaner top!
 

Attachments

  • 74_75 392 TQ Carb App.PDF
    781.5 KB · Views: 498
Thanks for the hard work & homework. I used the carb adapter pn edelbrock 2696 and yesterday was able to get the throttle linkage adapter, pn edelbrock 1481. Corrected the angles somewhat. The previous owner put a 2" body lift on the traveler, only thing besides wheels and tires that isn't original (and now the carb...) so there's plenty of room for a tall air cleaner. The thermoquad is at my building in town, it'll be tomorrow before I can verify the numbers on the carburetor and distributor. I never doubted your displaced texan wisdom for a minute mr. Mayben:) I think part of my problem is solved, but I'm wondering something I forgot to mention before, when I pulled the old rj12yc plugs a couple weeks ago and replaced with a new set of 12s, they were white in color. Indicate a lean condition or poor timing? Also, when I pulled the rotor off the distributor yesterday, the "metallic bump" towards the end had wht kind of looked like welding slag hanging off of it. I'm guessing the metal bump partially melted. I replaced with an identical part the po gave me. The cap looked, fine, clean, no visible cracks.
 
Now we're gittin' there dude!

That weldin' slag on the tip of the rotor is a normal condition for a rotor with many rotations on it! That's caused by "arcing" from the rotor to the cap terminals along with metallic transfer, perfectly normal, that's why the need to be replaced periodically.

Rotors like that can be rejuvenated if need be by using a quality file or a product referred to as a "flextstone", (even emery cloth works well), those are used to dress breaker/contact points such as in distributors or in oldskool electro-mechanical voltage regulators, motor contactors, etc.

The sharper/cleaner the "edges" are of the rotor tip, the easier the path for electron flow, same as regards a spark plug.

While I'm not a fan of body lifts, they do make life with an air cleaner and all much more pleasant for a Scout II/traveler! Opens up a whole new range of air cleaner options!

If ya need a replacement distributor cap, don't let any parts house bs ya. The Holley cap and the presto cap do not interchange anywhere near correctly, they don't locate correctly, and they don't "index" correctly (very slight difference but enough to screw with timing in some cases)! I really think the male terminal configuration on the presto caps are far superior to the much more common female terminals as used on the Holley and delco caps.

I'm still looking at your pics as I see a few more areas ya might wanna look at, you May have already done so but I'll throw it out anyway prolly tomorrow.

For help with the tranny kickdown adjustment if needed, check this link, post #23:

http://www.forums.IHPartsAmerica.com/transmission-tech/588-torqueflite-727-guapo.html

Also...robertk called to my attention a point that I overlooked regarding that spec sheet for the distributors. All of that information is based upon the use of a some type of "distributor machine", such as an allen synchrograph or the old sun electric units. And the data is in "degrees of distributor rotation", not crankshaft rotation! You can see that notation up at the top of the page. The info he posted earlier regarding "typical" degree set points reflects crankshaft rotation!

If you want to screw with that thermoquad in the future, I can post a similar page of "specs" for those mixers as used in the IH apps, those would be specific by carb part number also. That kind of info is what differentiates the IH carbs from the mixers used in chrysler oem service...and of course the differences in the 49 staters vs. The kalifornikate units!

I also just came into possession in the last few days, of a large document originally prepped by carter just for the chrysler thermoquad product dealer mechanic training. I'll attempt to post that in a new thread just for tq info over in the carb tech sub-forum.
 
You must log in or register to reply here.
Back
Top