Predetonation Q

[ARCHINSTL]

So - and pardon my denseness - you are saying that for even smoother driveability, I should reinstall the EGR system and associated vac tubes, even with the Weber?

MO has a "Historic Vehicle Tag" program as well. The requirements are:
1.To and from exhibitions and educational events without any mileage limitation;
2.To repair facilities within a 100 mile limit; and
3.Up to 1,000 miles per year for personal use.
My impression, though, is that these are pretty much wink-wink. I know a few people who flaunt this rule and use them as DDs. As well as being emissions-exempt, interestingly, they are exempt from safety inspections. I guess they figure an operator of such a vehicle will drive carefully and prudently...
Tom M.

[danzo]

Update on my pre-ignition issue: I removed/capped the larger hose on the EGR and it still pinged even at 10* timing with vac lines hooked up (3* retarded from stock). So I decided to put in cooler spark plugs. The NGK BPR5ES-11 plugs I had in it have a heat range of 5. I slapped in Autolite 64s with a heat range of 4. Extremely slight pinging can be heard if you really listen, much much less than before. It runs good enough so that I will leave it until my Sept emission test.

CO has the same 25 yr rule- only you have to pay 5 years of registration at a time (collector car tags). It only has to pass the first time through emissions, then you're 'free' to do what you will- Just don't sell it, cause it'll never pass the visual for the new owner.

So the purchaser can unknowingly buy a car without the correct emission controls and not be allowed to register a 30 year old car? I'm not saying you're wrong, but that sounds very unfair - once the car doesn't need to pass a sniff test it should be free and clear for the rest of it's life. Very few old cars on the road anyway.

This reminds me of a ridiculous law I experienced when I lived in Massachusetts. If you sold a car it must pass a "safety inspection" within (I think) 30 days of the sale. Doesn't matter if a given car changes hands 10 times in one year, it must be inspected every time. If the car doesn't pass, the buyer can force the seller to buy the car back - even if the safety malady is disclosed at sale. This happened to a friend of mine when he sold an old Cavalier with non working windshield wipers which the buyer knew about. Once the buyer found out how much the fix would cost, he forced my buddy to refund the money. The car at this point was unsellable and he eventually donated it. "Buyer beware" means nothing in MA.

Sorry to highjack your question, ARCH.

[sdoan]

The rough parameters for EGR valve actuation on almost any car are:

Engine warm
RPM above idle
throttle position BELOW about 80% of max

Besides, at WOT, there is very nearly zero manifold vac available to power an emission device. So the EGR, having no power source at WOT, is unable to function. Even cars with electric actuated EGR valves do not open them at WOT. At WOT the fuel mix goes rich (below 14.7/1 A/F mix) and ignition is retarded to guard against ping. The car mfr's are allowed to do this because street vehicles spend so little time at WOT that, in the grand scheme or things, the extra pollution emitted at those times is a non-issue.

EGR is most helpful at highway cruising speeds when ignition advance is cranked up a bunch, either by a vac advance can on the dizzy (carbed)or by the ECU (EFI)for good economy. A well calibrated EGR system will flow the most ex gas when you are cruising along at highway speeds and then crank in a small amount of extra throttle to accelerate a bit, as this is the time that most engines are prone to ping. Ignition timing will retard a bit at that moment also.

The introduction of EGR into the combustion chamber does not lean out the mix. It is neutral, as it has, in a good running engine, so little remaining fuel and O2. To lean out an engine you have to supply extra O2 or cut back on the amount of fuel in the induction charge. EGR flow has a damping effect on both how fast temps rise AND how far those temps rise during the combustion process.

So a good working EGR has an effect of providing a smoother & slower burning combustion process at part throttle cruise conditions, much like running a higher octane fuel. It is at these cruise conditions, when the engine is turning well below peak RPM's, that the engine is most able to efficiently turn a slower & smoother combustion event into mechanical power.

4wdchico,

That is the clearest statement of the purpose and working of the EGR system I've ever heard - Great. Thanks.

Question: The EGR valve is clogged on one of my T4wds and I haven't been able to unclog it. Do I risk burning valves or ping cruising down the highway or do I just lose some mpg?

Thanks.

[4wdchico]

Danzo:

I checked and an Autolite 64 does replace a NGK BP4ES in some crossover charts & in others it is the same heat range as a BP5ES. The issue is that a lower heat range number in foreign spark plug mfr's heat scale is hotter. So those plugs you installed are either the same heat range or hotter than the ones they replaced.

Do you know that your base timing is really right? Simplest way to get a rough idea how the whole ignition advance system is working is to disconnect and plug both vac lines on vac adv can. Set the timing at 5 deg at no more than 800rpm. Then check that the timing advances smoothly up and back when you rev it up and let it go back to idle, vac lines still disconnected. Don't trust a dash tach as mine shows about 620rpm when it is actually turning 800rpm. Then reconnect the vac lines to the vac adv can, warm up the engine, and if you see 13 degrees at no more than 800rpm, your whole system is somewhere in the ball park of working correctly.

i am asking the above because there are so many ways that your vac system can be messed up and cause major errors setting timing. Without functionally checking every component of your vac system that can effect timing, and there are a bunch, you are really going far out on a limb when you time your engine with the vac lines attached to the vac adv can. Also, the mechanical advance can malfunction and send you chasing your tail also.

Are your combustion chambers clean? Dirty combustion chambers are a major, and easily fixed, cause of ping. I do a combustion chamber steam clean with distilled water just before every oil and filter change. Also the valve cover on the 3ac had bits of fiber mesh up inside the two PCV inlet/outlet chambers, if this fiber mesh is missing/degraded (likley) the PCV system will backflow large amounts of oil mist laden blowby gasses thru the PCV fresh air inlet tube at WOT and this will cause ping & lots of it. I had to change my valve cover and my JY sourced replacement has no fiber mesh in it at all. After the change I had WOT ping issues. I diagnosed this issue by diverting the PCV intake line to another line that ended in a fuel filter instead of pulling fresh air from the air cleaner. I capped the metal PCV intake pipe that runs into the bottom of the AF lower housing. This diagnostic re-route of the PCV intake eliminated WOT ping on a 110 degree day here in Chico. I also installed a cheap HD sourced catch can between the PCV valve and the intake manifold to help keep the engine internals clean. I still need to Install a nice after market UPR billet catch can on the PCV fresh air inlet side to totally solve the PCV causing ping issues. But, as temps are cool at the moment, not a huge hurry.

Tom:

Not for smoother driveability, a good working EGR system will not affect that. You could get better performance, mileage and reliability. If you are willing to tune your car to take advantage of the change. Are you running vac advance on your current setup?

[4wdchico]

sdoan:

Thanks & you are welcome.

If you time your car, with a clogged EGR system, so that it does not ping when accelerating lightly at highway speeds on a hot day you will likely be retarding the timing below factory specs. This will cause poor fuel economy as part of the burning charge will go out the ex instead powering you along. This is pretty hard on ex valves also.

The short term fix is is a higher grade of fuel.

[ARCHINSTL]

I installed the Weber pretty much "stock." I used the FSM setting of 5 degrees advance at 950 rpm with vac advance disabled. A vac tube from the manifold "gas filter" is going to the port on the lowest vac canister while the carb vac tube is going to the front port of the upper vac canister; the rear port is blocked (to the now-removed high-altitude gizzy).
I confess I have not given it a look in about a year.
Tom M.
EDIT: SEE MY NEXT POST.

[4wdchico]

I installed the Weber pretty much "stock." I used the FSM setting of 5 degrees advance at 950 rpm with vac advance disabled. A vac tube from the manifold "gas filter" is going to the port on the lowest vac canister while the car'b vac tube is going to the front port of the upper vac canister; the rear port is blocked (to the now-removed high-altitude gizzy).
I confess I have not given it a look in about a year.
Tom M.

Looking at page 91 of our online FSM , I think that you have the hoses reversed. The lowest vac can should be connected to the carb vac port and the upper vac can should be connected to the gas filter via a hose with a check valve in it. Also you should connect to the to the rear port on the upper vac can and cap off the front port. The front port on the upper vac can has a brass restriction in it and was supposed to be connected to the HAC gizzy on a stock setup.

Zooming in on the vac schematic, I see that the port on the carb that provides vac to the lower vac can on the dizzy (and also one side of the vac modulator of the EGR system) is a ported vac source. This ported vac setup is SOP in controlling dizzy vac cans on most carbed cars. A ported vac source will read zero vac at idle and then show higher and higher vac as the throttle opening is increased until that point at very high throttle opening where available vac dissipates. So, I would make sure that the port on your Webber that you are going to use to energize the lower vac can is a ported vac source by attaching a vac gauge to it and making sure that it acts as I state above.

I'm fairly sure that switching the hoses mentioned will give you more advance (the upper vac can is limited to providing only about 8 degrees of vac advance)at cruise conditions on the highway so you will need to listen carefully for ping (or get a ping aware younger set of ears to listen for you...)at the all important time of light acceleration from a highway cruising condition, then repeat this procedure when the weather gets hotter. This is because the lower vac can is able to advance the timing more than the upper can.

If you study the vac diagram you will see that you could reinstall the EGR system even with the carb change. You may now need it, in hot weather, to help eliminate ping once you start getting full highway vac advance by switching those vac lines to the dizzy vac cans.

Also, did you time the car at 5 degrees with all vac lines disconnected from the dizzy vac cans? If not I would do so. Since it is possible that by timing it per the FSM procedure of removing only one hose, and having the hoses mixed up, you timed it wrong.

Your highway fuel econ should be better with full highway vac advance.

As Sheldon would say: Enough??

[danzo]

Thanks for the tips chico. Withthe new Autolite plugs it did start to ping just like before, maybe I just did not warm up the engine enough the other day.

What you refer to as 'base timing' I assume means the 5* with vac lines disconnected. My car right now is at 10* with lines connected (don't what it the disconnected setting is), and before this it was 13* connected and I believe 5* with vac lines disconnected. I'll double check soon. Also it does advance alot with higher engine speed, but I didn't check this with the lines disconnected. This is why I'm confused - it shouldn't be pinging. Since it only pings at light load I guess I should check the other vac system components?

I'll check my PCV ports (I did replace the valve about a year ago), and I have SeaFoamed the car twice in the past year so the combustion chambers should be Carbon-free.

Again thanks and I'll let you know if I discover anything else. For now I'm going to smurf in some 93 Roctane to and see if that helps as a temporary solution (no pun). Damn I miss fuel injection. Go Saints.

[ARCHINSTL]

4wdchico -
I am embarrassed - my earlier post was incorrect (memory) - I just physically checked the car: I DO have the carb vac going to the lower canister and the manifold port going to the front port of the upper.
This is the setup per the Federal system (and the Canada MT system, which has no HAC).
On my upper canister, the rear port has the restriction in the tube for the HAC - not the front as you mention. This is per the illustration on the site's IG-14 page.
So my original hookup, while I misstated it earlier today, was correct:
Carb vac to lower canister;
manifold vac, with check valve, to the unrestricted, fully open, port of the upper canister, which in my car (and the spare new canister I have) is the front port.

I confess - I do not recall if I plugged both vac sources when timing it; I'm pretty sure I just disconnected one, per the FSM, on IG-14 of our site's FSM.
You are stating I should disconnect and plug both vac lines and retime - right? I did do it per the plugged 5 degree and reconnected 13 degree FSM note.
I have noticed no ping in hot weather - someone mentioned this last Spring, and I kept my ears open.
Thanks!
Tom M.

[4wdchico]

4wdchico -
I am embarrassed - my earlier post was incorrect (memory) - I just physically checked the car: I DO have the carb vac going to the lower canister and the manifold port going to the front port of the upper.
This is the setup per the Federal system (and the Canada MT system, which has no HAC).
On my upper canister, the rear port has the restriction in the tube for the HAC - not the front as you mention. This is per the illustration on the site's IG-14 page.
So my original hookup, while I misstated it earlier today, was correct:
Carb vac to lower canister;
manifold vac, with check valve, to the unrestricted, fully open, port of the upper canister, which in my car (and the spare new canister I have) is the front port.

I confess - I do not recall if I plugged both vac sources when timing it; I'm pretty sure I just disconnected one, per the FSM, on IG-14 of our site's FSM.
You are stating I should disconnect and plug both vac lines and retime - right? I did do it per the plugged 5 degree and reconnected 13 degree FSM note.
I have noticed no ping in hot weather - someone mentioned this last Spring, and I kept my ears open.
Thanks!
Tom M.

I am saying to time it w/ both lines off the dizzy vac cans (plug the lines) to make absolutely sure that no vac advance is happening when you time the car to 5 degrees BTDC. Also, when you time it, get the idle down below 800rpm's actual, not dash tach, as the springs in an older dizzy can weaken and allow mechanical advance to occur at a lower rpm than the designers originally intended.

Ok, I was going from memory also, and yes, after looking at my '85 t4, the unrestricted port on the upper vac can is the front one & that is where the vac line from the gas filter should go. Mine being a CA car, the restricted port is capped.

Do you have a vac gauge so that you can check if the vac source that your lower vac adv can is attached to is ported vac?

EDIT from Archinstl - I do have a vac gauge - I also have a tach/dwell meter which I use for reading RPMs in tuning. Well, the vac to lower should be ported - it's from the port on the Weber itself. Will follow your method when I retime. Thanks!
Tom M.

[4wdchico]

Thanks for the tips chico. Withthe new Autolite plugs it did start to ping just like before, maybe I just did not warm up the engine enough the other day.

What you refer to as 'base timing' I assume means the 5* with vac lines disconnected. My car right now is at 10* with lines connected (don't what it the disconnected setting is), and before this it was 13* connected and I believe 5* with vac lines disconnected. I'll double check soon. Also it does advance alot with higher engine speed, but I didn't check this with the lines disconnected. This is why I'm confused - it shouldn't be pinging. Since it only pings at light load I guess I should check the other vac system components?

I'll check my PCV ports (I did replace the valve about a year ago), and I have SeaFoamed the car twice in the past year so the combustion chambers should be Carbon-free.

Again thanks and I'll let you know if I discover anything else. For now I'm going to smurf in some 93 Roctane to and see if that helps as a temporary solution (no pun). Damn I miss fuel injection. Go Saints.

Getting a tank of 93 octane fuel is also a good idea as a diagnostic tool. if your car still pings with your base timing (no vac advance at all) set at 5 degrees, mechanical advance proven to be working smoothly, clean combustion chambers & high octane fuel, your odds the ping being related to a vac leak is much higher. Putting a solid plate under the EGR valve, as Tom suggested earlier, to block it off completely would be a good diagnostic test as well.

[danzo]

Let me start by saying that it's a great day to be alive! I've finally solved a problem that been dogging me for months. Here's a recap/update in case somebody has the same problem and doesn't want to read the whole thread:

My car started predetonating around the first of the year, but at the time it was very slight. Playing with the ignition timing and various spark plugs did nothing, and all the vaccuum advance/timing control subsystems checked out. Once summer temps hit (100* F almost every day now) the pinging got much worse, albeit it only happened with a warm engine and under light throttle (high vaccuum/light load). This led me to believe there was a vac leak, but I didn't find any.

I saw in the FSM on page 148 a Heat Control Valve (HCV) described. It directs hot exhaust gases onto the intake manifold at a cold startup to help driveability. As soon as I saw a bimetallic spring (i.e. moving part) was involved I decided to check mine. You can only see this spring and associated counterweight from underneath the car as it's between the ex manifold and the block. Sure enough, my spring was worn out allowing the counterweight/valve to flop around as it pleased. It seemed to hover midway between closed and open thereby partially allowing the intake manny to be heated. So I took a page from the British Car Fix It Manual (BCFIM) and coat-hangered the counterweight in the "down" position, which prevents it from heating the intake. Shazzam! Zero point zero pinging!

Knowing that an overheated intake charge can cause predetonation was key. It's seems strange that modern car makers don't try to control the intake temp. Maybe they do and I'm just not privy, and maybe water injection is in my future, though it would only be really effective during the summer. Either way I'm glad to once again have a great running Terc!

BTW, last week I also replaced the exhaust, front struts and sway-bar-to-control arm bushings. To quote Dr. Evil the car drives "like a frickin' laser beam!" I'm kicking myself for not doing this sooner, it's a totally different car. Now I just need to get that blasted a/c to work.

Time for a 24 ounce Colt 45....

[ARCHINSTL]

BRAVO !
Tom M.

[dlb]

hey fellas. i'm in a similar boat as danzo was, here's the scoop:

put the 4A in the terc. set the timing at 10* BTDC but it pinged a lot regardless throughout entire driving range. did a huge seafoam treatment, the exhaust puked black filth for 4 or 5 minutes, cleared up, and ping was decreased to only occurring during acceleration and hills.

retarded timing to 7* BTDC, pinging decreased again but still present.

played with the heater control valve that danzo mentioned (it's quite easy to access with the smaller weber carb), zero effect.

sucked on the vacuum advance hose as per sdoan's instructions (blech), vacuum functions fine. disconnected the vacuum advance anyway just for fun, ping was almost non-existent but car ran a little shitty--idled rough, hesitated on acceleration. not psyched about that.

thought that maybe 4As actually have different timing even though the difference between them and 3As seems to be limited to piston and cylinder size. turns out they are also set 5* BTDC stock and most cats advance them to 10* as well so no luck there. set the timing to 5* BTDC and hooked the vacuum assist back up, pinging on acceleration and hills returned.

i just did a compression test to check for a damaged valve and the results were 1 - 180, 2 - 169, 3 - 171, 4 - 171 so that seems okay.

and that's where i am now. so while the vacuum assist does not leak, it does attribute to the pinging. running without it sucks though so i'm not content to just leave disconnected and am searching for the cause of this problem. i never had pinging issues with the 3A so i'm looking for things that have changed since the engine swap. a port on the EGR and one on the carb were unblocked so i blocked them, zero effect. on the valve cover there are two ports, one has the PCV and a hose that leads to the air intake but the other one... i had it blocked off on the 3A but when we put the 4A in he said not to block it, that i should get a hose with a vent on it so it can breathe but will prevent crap from getting into the valve cover. i never got around to so it's just had a 6" hose on it that achieved the same effect but my question is, what is that port for? I just blocked it now and will see if that helps but if anyone has any suggestions on where i should look i would really appreciate it. the pinging isn't too bad but i don't want to keep running it like that and risk burning a piston.

thanks!

[4wdchico]

Don't run your car with one of the PCV ports on the valve cover plugged. You could build up crankcase pressure and blow a main seal. There are two sides of the PCV system: (#1)the fresh air intake side pulls filtered air from the air cleaner into the valve cover. That fresh air is then mixed with blowby gasses and then pulled thru the (#2) PCV valve and then into the baseplate of the carb by manifold vac.

The above description is correct as long as manifold vac is present. At full throttle there is no manifold vac to pull the blowby mix thru the PCV valve & into the intake manifold. So the blowby gasses will back flow thru the fresh air intake side of the PCV system up into the air cleaner assy. and then down the carb throat.

I have installed two PCV catch cans in my PCV system, on both sides #1 & #2, to prevent the blowby gasses from carrying any oil mist or other liquid contaminates into my engine. Those mists will cause ping in the short term by their having much lower effective octane than gas. In the long run they also cause ping my raising compression and causing carbon hot spots due to carbon build up. They also cause the engine oil to get contaminated much faster than than it would w/o their presence.