EGR Troubleshooting[1]

8/14/2019 EGR Troubleshooting[1]

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tr ophies won by pas t students in stat eand na t iona l au tomot ive t rouble -shooting competitions.

“Most do-it-yourselfers overlook theEGR because they don’t kn ow how itworks,” he says. “Unfortunately, it

frequently gets neglected at the ga-

rage. too.”

Steve and other pros suggest thatthe EGR system be checked every12,000 to 15,000 miles and at everytuneup. You should specifically re-quest t ha t it be checked at t un eup, orcheck it yourself. We hope to demon-strate here how important it is tokeep your EGR functioning.

What EGR does

To redu ce hydr ocar bons an d car bonmonoxide to an acceptable level. engi-neers have designed engines to run onleaner fuel mixtures. But that in-

creases combustion temperatures,which increase furmation of nitrogen

oxide (NOx), another pollutant. Tokeep NOx at an acceptable level, theydeveloped the EGR system. It recircu-

lates exhaust gases into the combus-tion chambers, reducing combustion

tempera tures , thus reduc ing NOxformation.

At engine idle, the EGR system



should be inoperat ive. It is designed tooperate at cruise mode, in the 20-70-mph area. It, may rely on a va r iety of inputs-engine vacuum (carburetor

venturi vacuum coupled with mani-fold, or por ted, vacuum), coolan t tem-perature, ambient temperature. and

exhaust back pressure (see draw-ings).

If the EGR valve sticks partiallyopen (a common malfunction), or if it

opens too ear ly, driveability willsuffer.

This can be dr a ma t ica lly i l lustrated

when the car is idling by manuallyopening the EGR valve with your fin-gers. The engine immediately dies or

runs extremely rough.

On t he other h and. it ’s impor tanttha t the EGR valve not rema in closedall the time. This way, engine drive-

ability doesn’t su ffer . But detonat ion

(spark knock or pinging) can occur.

And because fuel mixtures are lean,the engine may run hotter than itsh ou ld , s in ce combust ion-chamber

temperatures are not being reducedby the exhaust gas. Eventually the re-

sult may be burned valves and blis-tered spark-plug electrodes.

Checking the EGR

How do you check the EGR system?

Basica lly th ere a re two ways.Method one. Let’s t ake the easier

way first-using only a tachometer.

Ident ify the system in your car (see

drawings). It may not be exactly like

any of t h e four typical systems shown,but may incorporate some compo-

nents from each. Use a shop manual if

available. If not, check the vacuum-hose routing label on your car. Many

later-model cars have this label at -t ached .

The engine should be cold. FirstContinued



Check your EGR

[Cont inued)

A poppet va lve (top photo) controls the

EGR. Unit in bottom photo.uses a taperedvalve to do the job. Both valves workokay--just two different ways of doing thesame job. By depressing the diaphragm,bottom photo, you can see if the stem be-

tween the diaphragm and valve is broken(the valve should open).





Typical manifold vacuum tap atthe

base

of the carb i s shown. When removing the

vacuum hose f r om any t ap , espec ia l l y

with older hoses, rotate the hose back and

forth with your fingers until it breaks free

of the tap-before pu l l ing the hose o f f . ’Any vacuum hoses that don’ t f i t snugly

should be replaced.



diaphragm and see if you can feel it

move. (Be careful: you may burn yourfingers if the engine is hot.)

If you can neither see nor reach the

stem, remove the v a c u u m h o s e a t -tached to the EGR valve and put yourfinger over the end of the hose. You

should be able to feel suction when theengine accelerates.If the valve stem moved, the EGR

valve is working. But is it doing its

job? To find out, disconnect the vacu-

um line that goes to the air cleaner atthe ax-cleaner connection. On older

cars, where the hose has hardened and

doesn’t come off easily, take care thatyou don’t damage the nipple it’s at-

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EGR Troubleshooting[1]

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