Predetonation Q

[Petros]

cars for many decades ran without EGR, race cars, boats, airplanes and off road vehicles run without EGR, so should the tercel.

It lowers the peak temp and pressures of the combustion cycle to reduce emissions by mixing exhaust gas into the intake mixure, but it also lowers the efficiency. You can disable it, or remove it all together (plug the holes) and it will run fine. Some think it may increase the chance of detonation, but I have not found that to be an issue, if so just back off the timing.

Good luck.

[danzo]

Am I correct in thinking that removing/plugging the vac port from the EGR will disable it? I did that and left everything else alone, but my car still pinged at 13* ignition timing (everything hooked up), so I backed down to 10* and it pings very very slightly. This leads me to believe something else is amiss, but I just don't know what. In fact it runs good enough so that I prolly won't bother anymore.

[4wdchico]

Sorry for the delay - I think I do have an EGR leak since the idle changes when carb cleaner is sprayed on it. Not sure how to get Propane down there since you can't hold a Propane bottle upside down, right?

Anyway I was wondering if I could override the EGR and basically keep everything else stock? Would the car run OK? This may not be possible, but new EGRs are fuh-reakin' $185 and I'm not sure how fruitful it would be to get a j-yard one esp since I would most likely need to get it from a different year/model. Maybe someone on the forum has a good one they don't need? Thanks for any advice/help.

OK, have you verified that the diaphragm in the EGR valve is not leaking? If yes: take a propane torch & unscrew the mixing/burner head off of it. Put a hose on what remains. When you open the valve on the torch you should have raw, undiluted propane coming out the hose. Adjust the flow so it is a fairly slow flow out of the hose and then put the end of the hose up to the underside of vac diaphragm housing of the EGR valve. Right up to one of the holes in the underside of the housing. If your idle changes you have a vac leak at the pintle shaft/EGR body housing. While you are at it, put the propane flow up to both ends of the throttle shafts in the carb and every vac hose and diaphragm there is while the car is idling to see if it changes the idle.

A functioning EGR valve will reduce pinging & combustion chamber temps at all times when accelerating at less than about 90% of wide open throttle, providing that the engine is fully warmed up. Those who say that an EGR valve reduces max HP are self deluded as the EGR system does not work at WOT.

[Petros]

but the EGR does reduce efficiency, and fuel economy, at part throttle.

[4wdchico]

but the EGR does reduce efficiency, and fuel economy, at part throttle.

This is true, but remember that an engine with a good EGR system requires a different state of tune than one without one.

However, if an engine that has a good functioning & well designed EGR has had it's timing optimized so that it runs right on the verge of ping onset, with a given fuel, it will be running several degrees more ignition timing advance than it would be able to without the EGR system. More timing advance equals more power and efficiency. More than an engine without an EGR system? I think so. So what I'm saying is that the EGR system is a big part of the tuning strategy that the 'yota engineers implemented on our cars.

Toyota has done some very sophisticated tuning to optimize the tuning of our little 3ac engines. For example the HIC valve: have you ever noticed that it has a much bigger hose connecting it to the intake manifold vac than the hose that runs from it out to the diaphragm that controls the hot air intake metering flap? That bigger hose allows the HIC valve to bleed air into the intake manifold under hot air intake conditions to lean out the A/F ratio a bit below what the carb jetting would normally provide. Otherwise the carb jetting would be providing a too rich A/F ratio under those conditions. Pretty trick setup. No, not nearly as sweet a system as EFI, but way more sophisticated than a '60's Chevy with a 4 barrel sitting on top of it.

[danzo]

OK, have you verified that the diaphragm in the EGR valve is not leaking? If yes: take a propane torch & unscrew the mixing/burner head off of it. Put a hose on what remains.

Yes, my EGR will hold 15 inches of vacuum no problem. So I guess it's still possible for it to have a vacuum leak? I'm assuming you mean to stick a fuel/emission hose onto a propane torch - why is this better than using carb cleaner?

If I'm not going to damage anything by leaving my EGR the way it is, then I would prefer to leave it. It sounds like my car would get better mpg with it unhooked anyway. It only needs to pass emissions this coming September, then it's free and clear thanks to Texas' rolling 25 year law.

Thanks for the help!

[4wdchico]

OK, have you verified that the diaphragm in the EGR valve is not leaking? If yes: take a propane torch & unscrew the mixing/burner head off of it. Put a hose on what remains.

Yes, my EGR will hold 15 inches of vacuum no problem. So I guess it's still possible for it to have a vacuum leak? I'm assuming you mean to stick a fuel/emission hose onto a propane torch - why is this better than using carb cleaner?

If I'm not going to damage anything by leaving my EGR the way it is, then I would prefer to leave it. It sounds like my car would get better mpg with it unhooked anyway. It only needs to pass emissions this coming September, then it's free and clear thanks to Texas' rolling 25 year law.

Thanks for the help!

Carb cleaner is hard on rubber components like vac lines and diaphragms. Carb cleaner can splash around and then vaporize and confuse the vac leak diagnosis. Carb cleaner can ruin your paint.

By putting a smaller diameter chunk of flexy copper in the end of the hose and using a low flow of propane I can really pinpoint the item that I am checking. I usually use clear vinyl tubing from the hardware store on a propane torch with the mixer/burner removed. Thinner walled and easier to get into small places.

Since it sounds like it is fairly certain that you do have a pintle shaft leak in your EGR valve, if you are not going to replace it, removing it will eliminate a vac leak. Blocking off the point where the EGR valve feeds to the intake manifold is fairly easy. Then blocking off the flow of EG up from the ex. manifold would also be needed. Pretty sure you can figure that out.

If the smog inspection in TX has a visual component, doing the above will cause it to fail. A big vac leak like a pintle shaft leak in an EGR valve will cause a sniffer failure almost every time. Leaving a leaking EGR valve on your engine will eventually cause engine damage like all vac leaks do. So I suggest that since you do need to get it thru smog one more time, getting a new EGR valve soon would be wise.

If you do decide to replace the EGR valve, once you have done so, I will give you the very easy procedure to test it like a smog tech will so that you can be sure of passing that part of the smog test.

Here is what most folks do not understand about cars becoming "smog exempt" by age: Most states do not ever drop the requirements that all original smog control components be installed and working correctly. They simply stop requiring the cars be tested, so the term would really be "smog test exempt". Big difference, as most cops can easily tell if the basic smog systems have been modded and then they send the car to a state referee for further inspection. That is when the fun really starts. All it takes to start the process is to piss off a cop enough for him to pop your hood...

[ARCHINSTL]

Here is what most folks do not understand about cars becoming "smog exempt" by age: Most states do not ever drop the requirements that all original smog control components be installed and working correctly. They simply stop requiring the cars be tested, so the term would really be "smog test exempt". Big difference, as most cops can easily tell if the basic smog systems have been modded and then they send the car to a state referee for further inspection. That is when the fun really starts. All it takes to start the process is to piss off a cop enough for him to pop your hood...

OT, but...
As the late, great, Arte Johnson's character would say..."Very interestink..."
Missouri has had no emissions inspections* for '95 and prior-year cars for a couple of years now, and when I installed the Weber I removed all of the emissions items - but kept them. But since Goldie spends most of her time in the right lane - I guess the only time she'd PO a cop would be if she ran over his foot. But I really wonder how many are that familiar with '86 Tercel emissions systems...?
I'll watch the feets...and not discard the emissions stuff.
Tom M.
* This inspection applies only to the STL Metro area - nowhere else in MO...

[danzo]

I guess I just need to know if there is a way I can leave the EGR on the car without it functioning or vacuum leaking. Like mentioned previously I have plugged the vac port. Do I just remove/plug the larger (about 1/4") port and call it good? I don't really want to remove the EGR and risk causing some other leak.

Your talk of smog tests certainly gives me flashbacks of when I lived in CA. Here in TX 25 + year old cars must pass a visual test, but I have never ever seen a testing station even so much as pop the hood of an old car. They will pass any old car as easily as the local school district will grease through a dumb kid!

My old Triumph may as well of had three pigmy clowns on a treadmill for an engine and it never had a problem passing. The thought of a TX cop scrutinizing an old car sounds so absurd - why would they waste their time when they can be writing tickets for people smoking in bars?!?

[ARCHINSTL]

How about just fabbing to proper size a blocking plate out of stiff, yet thin, aluminum with an extra gasket and installing it between the EGR and the manifold - and then blocking the vac ports to all with BBs in the tubes? You can use the gasket to cut an exact o/s match from aluminum.
This way, visually at least, the system is intact; if it flunks, then you can start over (a thrill, I know).
I used the above blocking plate when I removed the EGR (and all emissions plumbing, including the big manifold-to-EGR tube).
Tom M.

[Petros]

We have a similar law here in WA, it is exempt from requiring a test after it is 25 years old (which exempts both of my Tercels), but I already live in a part of the state that does not require testing anyway. I have tried to see if that means I can actively remove all the emission control crap (including the EGR), but I have not gotten a strait answer, the law is not clear.

One thing I was told was it is a way to allow people to keep older cars on the road since it can become difficult to find replacement parts for the emission control systems. This would seem to me that means you can remove them, presuming they are not working anyway. But how are they to know? Can we dump the Catalytic converter too?

[ARCHINSTL]

But how are they to know? Can we dump the Catalytic converter too?

This is interesting - at some point in time I will have to replace the exhaust pipe from manifold back - what would be any driveability/other probs, if any, if the converter were not reinstalled? Note that I did not include legal problems in the question...
Tom M.

[4wdchico]

But how are they to know? Can we dump the Catalytic converter too?

This is interesting - at some point in time I will have to replace the exhaust pipe from manifold back - what would be any driveability/other probs, if any, if the converter were not reinstalled? Note that I did not include legal problems in the question...
Tom M.

Since your car has a Weber on it now, even a new cat would not be fully effective. A cat needs to be fed an ex. stream that is switching back and forth, rich and lean, to efficiently reduce pollutants in the ex. As far as driveability goes, you should see no changes as even the original cats on our cars had minimal back pressure effect & newer ones have even less.

[Highlander]

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. I plan on pulling all of the emissions off of the '83 when I get the new engine and weber setup installed- that includes putting the exhaust that I had to take off of the '85 when I bought it 'cause there's no Cat. Blocking the EGR off seems a bit excessive though, even with the weber and no ECU idle circuit, the EGR only opens at WOT to lean out your high end -I guess it could be a power problem- or as the thread is titled, predetonation??

[4wdchico]

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. I plan on pulling all of the emissions off of the '83 when I get the new engine and weber setup installed- that includes putting the exhaust that I had to take off of the '85 when I bought it 'cause there's no Cat. Blocking the EGR off seems a bit excessive though, even with the weber and no ECU idle circuit, the EGR only opens at WOT to lean out your high end -I guess it could be a power problem- or as the thread is titled, predetonation??

Pretty cool about the collector tags out in CO. I knew there were some states that were mellow about older cars, makes sense that CO is one of them.

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.