Check your vacuum lines! - "bad" EGR valve

[waynehoc]

Just went through annual AirCare testing a couple of weeks ago (Lower Mainland, B.C., Canada) and was wondering how readings would be after having replaced a faulty vacuum advance and HIC valve. HC and CO on both idle and driving tests were great - no real change from previous years, and still on the original Toyota cat converter. But, NOx was up a lot, close to the fail limit, but under enough to pass.

So, considering my wagon has approx 250,000k (± 150,000 miles) on it, and still with the original, untouched EGR valve, I suspected that it must be plugged pretty badly.

So this past weekend I pulled it off and had a look, expecting to have a major cleaning job ahead of me. To my surprise, it looked as though it was almost new, hardly any carbon buildup, and the port into the intake manifold was totally clean/clear/NO carbon.

Checked the modulator and it was working fine, so figured I must have some problem with a bad check valve or bad vac line or who knows what.

Could have knocked me over with a feather when I discovered (and double and triple checked as I just couldn't believe it) when I found that two vac lines were wrongly interchanged. The port on the carb that should have been connected to the orificed port on the EGR modulator (and also tees off to connect to the EGR diaphragm on the distributor vac advance) was connected to the Charcoal Canister and vice versa! In other words, the EGR had not been functional for many years.

Until last year, when I found this group, troubleshooting a backfire on deceleration problem, I had been paying the local Toyota dealership, and more recently, general mechanics to repair the wagon. I had only been doing my own regular oil changes and simple things up until then.

There are only two times that the carb could have been off the engine and all the vac lines disconnected. First was when Toyota rebuilt the carb back in August 1996 and second was when my mechanics at the time did rings, con rod bearings and valve stem seals in August 2000. So I suspect the EGR has been non-functional for either 10 or 6 years, thanks to either Toyota or the other guys.

Incidentally, I found in my records that the vac advance diaphragm assy had been replaced by Toyota in April 1995; I also replaced it myself late last year. As my wagon is an '87, it looks like the vac advance units are only good for 5 to 10 years befor they fail.

Now that I have the EGR working, I'm impressed with the improved driveability. The engine is more responsive with very little hesitation and no noticeable surging. For years there was noticeable intermittent hesistation at just off idle and slightly more open throttle positions. No wonder, with the high vacuum from the carb port that was intended for the EGR modulator being routed to the Charcoal canister, I can only imagine what kind of a fuel/air mixture I must have been getting at those low throttle opening driving positions.

Looking back, I probably could have saved myself a lot of time by checking the vac hoses connections before tearing the EGR off the engine, but would not have learned nearly as much. In the end it was a real eye opener.

Wayne

[GTSSportCoupe]

Excellent writeup - thankyou!! Will prove to be a great reference.

[Mac]

Yeah, my tercel had a few problems like that, either from my dad and me when we resurected it, or the mechanics that messed with it in the past.

-dizzy advance and retard lines were mixed
-one on the vacume hoses close to the top radiator hose on the engine side leaked (heated and cracked)
-EGR was plugged
-various control diaphrams and check valves were installed backwards or non-functional

it dosn't exactly purr nowdays (i suspect uneven compression) but its a night and day differance between how it idles now and when i first got it.

[kaji]

When I checked my ignition timing yesterday, the mark was at about 7-8 btdc with the vac line disconnected and plugged. I was getting about 30 mpg with this setting.

I reset it at 5 btdc, but when I hookup the vacuum line again it does not advance to 13. My vacuum advance only has one port. I noticed in your pics waynehoc that the new one you purchased had 3 while your old one had 2.

With the timing set at 5 btdc I notice a lack of power.

I was wondering what the most likely culprit would be for having no advance. (clogged EGR valve, leaking vac advance diaphragm, check valve?)

After reading your excellent post I will be checking all my vac lines also but was wondering which drawing you followed to figure out what line goes where?

I have had this tercel since new and it has 430k on it. (3a engine)

[waynehoc]

I was wondering what the most likely culprit would be for having no advance. (clogged EGR valve, leaking vac advance diaphragm, check valve?)

After reading your excellent post I will be checking all my vac lines also but was wondering which drawing you followed to figure out what line goes where?

kaji, I would first check the diaphragm in your vac advance unit on the distributor. If you pull off the vacuum hose (which goes to the distributor) right at the rear of the engine (where it attaches to the metal tubing routing it along the carb side of the cyl head) and suck on it, it should hold a vacuum. If the diaphragm is ruptured (= no vacuum advance is functional), it will not hold a vacuum. Easy to check.

As far as what drawing I followed to be certain of the vacuum hose mixup, I referred to the 'Emission Control Systems' 'Component Layout' indicated in the original Toyota factory service manual I have for the exact year of my wagon (1987 Tercel 2WD wagon m/t). The component layout is a more pictorial representation which shows pretty clearly the actual locations of emissions items and vac hoses/connections.

The fact that your Tercel distributor vac advance has only one port suggests that your engine is indeed, as you have stated in some of your posts, a 3A engine, and not a 3A-C. As I understand it from the local Toyota dealership, the 'C' means that a catalytic converter is installed. The 3A has no cat converter. My 1986 Tercel 4-door parts car had a 3A engine with no cat converter, and also, as with your Tercel, only one port on the vac adv on the distributor.

If you do not have a Toyota FSM for your Tercel, they are selling quite inexpensively on ebay (where I got mine, along with an original Chiltons for the 1984 - 94 Tercels). There is also the FSM you can download from tercel4wd.com, and a repair manual for free on-line use at the autozone site at http://www.autozone.com/servlet/UiBroke ... epairGuide

Wayne

[ARCHINSTL]

kaji - I would like to add to Wayne's recommendation of the Autozone site. It is, in many ways, much better than the FSM, as it has photos instead of just line drawings, and I like the text better.
It also has full specs/diagrams/piping for torque, dimensions and emissions, including those specific to the Canadian version.
The link was set for my '86, but covers all of the Gen 2 Tercels.
Congrats on keeping yours since new - I had one of the first in St. Louis in late '82, and it was always one of my favorites, whence owning Goldie now.
Tom M.