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Late 1993 Egr Issues


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#1 dogwin

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Posted 15 February 2012 - 03:11 PM

So my stepfathers late 1993, (OBD1) Corolla DX Auto Trans with 265K miles started throwing Check engine lights. It is CA registered, so a CEL is a problem to transfer, and Smog, but otherwise it runs fine, with a *solid* 33-35 MPG, on regular gas. No knocks, no pings and runs cooler than any other car I own.

Ran CEL diagnostic routines, and EGR system was the culprit., with a 71 error code. I reset the code several times, and it would send the repeat code, (typically) after about 300 miles of driving at highway speeds. There is also a auto trans ECM code present, but that is another issue...

For those not familar this particular EGR valve, is one of those parts, where I truly hate that we have child labor laws.. .because my 8 year old's hands, are perfectly sized, for the EGR Remove and Replace, where mine are kinda of a nightmare.

The EGR is towards the Rear of the engine, almost against the firewall. After much swearing and even contemplating cutting a wrench in half to try and fit it between the bottom (25mm?) nut and the fire wall, we ended up taking the EGR *and* its (exhaust Manifold) riser pipe off, as one unit. Less swearing, less drama. Once the EGR was off, here is where the fun began.

Upon manually applying positive air pressure to the vacuum diaphragm (read: Take hose in mouth and blow), *water* came out of the other end of the 2nd hose on the Diaphragm hose *only*. Slightly rusty, and about 2/3 of the volume of the diaphragm space itself. I.E. "enough to make the valve not actuate--- probably, or worse "sometimes". Note this only happened with the diaphragm was upside down. I had applied vacuum and positive air several times when it was in the car... no fluid expelled. to quote a phrase: FRACK!

Once I spent an hour or two soaking the entire assembly in brake cleaner, (except the diaphragm of course), the valve started to work normally with "manual vacuum applied". (read: Suck on one hose, plug the other). Gave the N2 sensor a solid cleaning and scrub brushing, and pushed Q-tip sticks into the various narrow diameter pipes and hose connections. (Also spent about 5 minutes manually sucking the broken Q-tip end *out* of a vacuum hose connection with a shop vac...). Lesson learned, right tool, right job. Shot gun cleaning brushes worked fine by the way, for the larger bore pipes.

The vacuum control unit filter was *totally* clogged, but water free, (washed, rinsed, dried, re-installed). The hoses were dry, to and from the diaphragm.


The car is located in a moist climate where fog, is common.

Is it possible that over the course of 16 years, that enough water vapor collected in the diaphragm space, that eventually it actually became a pool of water? Even more weird is it possible that there was not enough engine heat, to actually boil off the water captured in the EGR diaphragm space?

No other part of the system is throwing water, and (to be frank) I plan on selling the car shortly, so a 167 dollar new EGR valve is not a good investment. Once the water was removed (and *much* air was blown through the actuator), it works perfectly normally "out of the car"..

My labor cost is free. I needed the help of a neighbor master mechanic, for one particularly nasty reach.

So, unless I hear a suggestion otherwise, I will re-install the unit tonight and see if the system throws another CEL, over the course of a week. I will probably force the computer into diagnostic mode *first* just to see if I can convince it to throw another CEL.. saving much drive time.

Suggestions? Did I miss something?

Thanks in advance.

#2 the99contour

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Posted 16 February 2012 - 01:19 PM

BUMP up due to a move to this sub forum.

#3 tashirosgt

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Posted 09 March 2012 - 01:03 AM

I'll be interested to see if your fix works. I've changed both the vacuum modulator and the EGR valve on my 1990 Corolla 4AFE, which may be the same engine as yours. Changing the vvacuum modulator didn't stop the code 71. Changing the EGR valve stopped the code 71 for about a month of around town driving. It came back the first highway drive I took. Fortunately, there are no emission requirements here.

I changed the EGR by putting a board across the engine compartment and doing a belly flop across it to peer down the firewall at it. I removed one bracket that was in the way. Of course, the body style on the '90 is different than yours.

We may not have the same EGR valve. It didn't seem plausible to take my old one apart. I checked the resistance of the EGR temperature sensor that screws into the valve and it was in spec according to the service manual for the '90.