after i read almost every single post on 4x4wire regarding the egr, im almost positive my egr valve is sticking open and causing my truck to die. but because my truck has had a slight miss at almost all rpm's even before this started, it leads me to believe my egr was stuck shut before. i wish thief was still around so he could give me some insight. i should mention that before i put on my eb street rv head and 268 cam my truck ran smoothly. so my cam likely plays a large part in my problem.

im running a carter electric fuel pump so i dont have any weep holes.

how do you fix a sticky needle valve, carb rebuild?

when you asked if my carb bolts are tight, that made me wonder. when i hit the gas my carb makes a sucking sound, almost like an air leak, just like the intake on my moms v8 camaro which has a k&n intake kit. but my truck didnt always do this.

EGR backpressure transducers are nothing new. Stand-alone EGR transducers first appeared in the earlier 1970s on domestic engines. Later on, newer domestic EGR valves designs eliminated the stand-alone transducer.

But today, nearly any Toyota, Lexus, Suzuki and many Mazda engines still have a separate EGR transducer (refer to the accompanying photograph). Shop manuals
may call this transducer and EGR vacuum modulator valve. Although this transducer works basically the same way a domestic unit does, many technicians overlook it when they troubleshoot a Japanese EGR system. Then they replace the EGR valve for a problem that is actually rooted in the transducer.

A backpressure transducer improves driveability by regulating EGR operation according to engine load. It does this by sensing exhaust gas backpressure and adjusting the amount of vacuum that goes to the EGR valve diaphragm.

The EGR transducer, which is spliced into the carburetor-to-EGR valve vacuum hose, has a spring-loaded bleed valve inside it. This bleed vavle leaks off the vacuum signal to the EGR valve. Therefore, the farther the bleed opens, the weaker the vacuum signal to the EGR valve and the less EGR flow the engine receives. Naturally, closing the bleed valve creates the strongest vacuum signal and maximum EGR flow.

The transducer senses exhaust backpressure through a hose connected to the bottom of the transducer. This backpressure operates the bleed valve. Under lighter engine loads, exhaust backpressure is relatively weak, so the spring loaded bleed valve remains open and weakens the EGR vacuum signal. As engine
load increases, exhaust backpressure increases, closes the bleed valve, and
strengthens the EGR vacuum signal.

A typical domestic EGR backpressure transducer only has one vacuum supply hose, but this Japanese unit has two. One hose feeds a ported vacuum signal to the modulator port that's usually marked P or 2. The other supply hose feeds venturi vacuum to the modulator marked R or 1. Under certain engine loads, the second vacuum signal boosts or helps the first one operate the EGR valve.

Check hoses first.

Whenever you check an EGR problem and you see an EGR vacuum modulator on the engine, be sure its vacuum hoses are routed correctly before you proceed. If someone has reversed the vacuum supply hoses at the modulator, the modulator will open the EGR valve too soon and make the engine hesitate, stumble, or surge.

Testing the EGR modulator is similar to testing a domestic unit. With the engine warmed up and idling, there should be no vacuum at the modulator's outlet port (usually marked Q or 3). When you rev the engine to about 2000 RPM, you should see a vacuum reading at the outlet port. If you don't see a vacuum reading, check for a clogged exhaust port before you condemn the modulator. A clogged port would prevent exhaust backpressure from closing the modulator's bleed valve. Meanwhile, a partially restricted port--or a substantial reduction in exhaust backpressure--may upset the modulator's calibration and weaken the vacuum signal to the EGR valve. This would reduce EGR flow and could cause the engine to ping.

Suppose the hoses are routed correctly and everything tests good so far but the engine still has an off-idle stumble or low-speed surge. Tee a vacuum gauge between the EGR modulator and the EGR valve. Watch the gauge while you road test the car. When you see a vacuum reading with just a tiny bit of gas pedal movement, the modulator is usually bad.

Remember that a restricted exhaust system could increase backpressure enough to trick the modulator into opening the EGR valve too soon. During your road test, note how the car performs during heavy-throttle and wide-open throttle driving. Perform the vacuum gauge test for a restricted exhaust. Depending upon how the customer drives a car with a restricted exhaust, he may only notice the off-idle hesitation or low-speed surge!