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Revision as of 08:54, 9 November 2011

Exhaust Gas Recirculation (EGR) was first used starting with 1974 B-210 (North American B210) models. Australia 1200 utes got EGR in 1982. Japan 1200 trucks got it in 1989. It recirculates a small portion of the exhaust back into the combustion chamber. Although this dilutes the the air/fuel mixture (reducing performance), it reduces burning temperatures resulting in drastic reductions of Oxides of Nitrogen (NOx).

1 Overview
2 Basic EGR System
3 Exhaust Manifold
4 Intake Manifold
5 EGI
6 Switches
- 6.1 Thermal Switch
- 6.2 Transducers
  - 6.2.1 BPT
  - 6.2.2 VVT
7 History

Overview

EGR is a key emission control technology. Even the new 2012 models use EGR, although now it can be effected by variable camshaft overlap and engine computer control. Datsuns use an early version of EGR which is heavy-handed regarding performance, but really does clean up the air.

The EGR valve simply mixes a little exhaust into the intake manifold.

Varying amounts of exhaust gas are let in by the pintle valve, which travel to the inlet manifold via the large square opening.

How much exhaust is recircutated depends on the vacuum signal, which comes from a port high on the carburetor. This is not the distributor vacuum advance signal, but rather it requires a signal that does the opposite: gets stronger as the throttle is opened.

EGR does not work at full throttle, due to the vacuum throttle. So it won't hurt peak HP. It only affect part-throttle performance. It also does not activate at idle. It only takes effect in-between idle and full throttle.

For a detailed explanation of EGR, see the AutoZine Technical School article.

Basic EGR System

Datsun EGR consists of:

Exhaust manifold with an EGR port tube
Intake manifold machined to take an EGR body adapter
EGR passage body, which bolts to the intake manifold
EGR valve, which bolts to the body
One or more switches
Vacuum hoses
Carburetor modifed with addition vacuum port for EGR signal

EGR parts in red:

Most basic EGR system

Generally speaking, the more complex the EGR system, the better. The complexity was to use less recirculation which is good for performance and fuel economy. This simplest implementations affected performance worse. There is little downside to this complexity because generally if anything fails, EGR fails to work and so doesn't hurt performance.

Models using the simplest basic system include:

1975 B210 AT North America (FED+CAL+CAN)
1975 B210 MT.CAL (MT.FED and MT.CAN add more switches)
1982 CAN all engines (A12A, A14, A15)

Exhaust Manifold

The only modification to the Exhaust Manifold to enable EGR is the casting is changed to add a threaded port to which a tube is fastened. The tube goes up to the EGR Valve.

First EGR (1974) -- tube goes behind manifold

Late A14 style

Early A14 FU style

Vanette Style

Variations consist of:

Size of the EGR port (diameter of hole and thread size)
Location. Early engine had it come straight out of the manifold outlet, while newer ones have it pointing almost up

Intake Manifold

Intake Manifold has a specially machined flat area where the EGR Body bolts. Nissan calls this adapter body the "EGR passage". In turn, the EGR Control Valve bolts to the body.

1981-1982 H95 EGR (valve not installed)

EGI

A14E and A15E EGI fuel injection engine manifolds use an EGR system.

Switches

These switches are to limit when the EGR works. Don't delete or bypass them otherwise your EGR will work full-time (not good).

Thermal Switch

This prevents EGR from working until the engine warms up. This switch is your friend.

Thermal Vacuum Switch

From 1975, a simple, reliable engine-coolant Vacuum switching valve is used by most implementations. It threads into the cylinder head and is warmed by the engine coolant. Nissan started calling this a TVV (Thermal Vacuum Valve) in the 1980s.

The switch has two ports. One hose comes from the carburetor signal, the other goes to the EGR valve.

The switch only opens when the coolant exceeds 134F (57C).

Thermal Electric Switch

For the first year 1974, instead of the simple thermal vacuum switch, an engine-coolant electric switch was used along with a relay and an electrically-operated vacuum switch. This was replaced in 1975 by the simpler thermo-vacuum switch.

The switch came on at an early temperature of 88-106F (31-41C).

3-port Thermal Switch

This switch looks similar to the Thermal Vacuum Switching Valve, but has a third port which goes to the air cleaner. It bleeds off the carburetor vacuum signal, thus de-activating EGR. It is used in conjuction with a vacuum-delay valve in the hose that goes to EGR valve, which smooths out the reponse on quick throttle changes.

1982 FED & CAL models

Transmission Switch

Some models de-activated EGR when in nuetral or in top gear. This made use of the transmission Nuetral switch and transmission Top switch.

1975 Manual Transmission FED & CAN

Transducers

Transducer Valve gets a backpressure signal. One metal tube connects to the exhaust, and a vacuum line Tees into the EGR line. This allows the Transducer Valve to fine-tune the EGR signal.

BPT

Starting in 1977, a BackPressure Transducer (B.P.T.) Valve was added to USA models. The metal tube connects to a port on the EGR body, near where the main EGR metal tube came in.

Tube variations

1977: BPT tube threaded on both ends on two-piece tube. Joined by rubber hose in the middle.
1978 up: threaded on the manifold end, used a rubber hose on the Valve end

BPT was used with 2-port OR 3-port Thermal Switches

VVT

Venturi Vacuum Transducer replaced the BPT valve on 1981 models to fine tune how much Recirculation is used. Instead of the crude early systems without VVT, the 1980s implementations use the VVT valve as an amplifier for input signals from backpressure and carburetor signal.

If you run EGR, then VVT is your friend.

History

1974: EGR fitted to North American B210.

Australia

Late-model utes were fitted with EGR.

Japan

1980-1981 EGI engines used EGR

1989-up 1200 Sunny Truck used EGR

North America

Keep in mind that intake & exhaust manifolds changed almost every year, for reasons not usually related to EGR. Also the EGR valve specification changed every few years, and differed by Transmission. Bolt pattern remained the same.

1974: EGR first fitted to North American B210. This was the A13 engine.

It used a basic system, except the switch was a complicated electric system.

1975: EGR continued on the new A14.

Simpler 2-port Thermal Vacuum Switch replaced 1974's electric switch, relay, solenoid and wiring.
On-temperature activation point was raised.
(FED + CAN) Manual transmission cars added Vacuum Switching Valve which enable nuetral and top gear EGR de-activation. CAL cars did not use this, nor did AT cars.
FED cars used a separate EGR warning system that did not interact with the EGR system. It simply notified the driver via dash light at 50,000 miles.

1976: 1975 system carried

B210 adopts same Thermal Vacuum Switch as Datsun 610 and Datsun 710 (minor change)
EGR tube shape changed

1977: For USA, EGR flow increased to reduce NOx

EGR warning system discontinued
Canada unchanged. CAL + FED is changed

FED + CAL NOx emissions tightened

NOx emissions
1976 all: 3.1 
1977 CAN: 3.1
1977 FED: 2.0 
1977 CAL: 1.5

Exhaust Manifold has larger EGR port, otherwise is same as 1976.
Larger EGR Tube to manifold
BPT valve added

USA Exhaust Manifold EGR 
Tube inner diameter 11.8mm (8mm 1976)
Manifold boss dia.: 32mm (25mm 1976)
Thread size: M22 (M16 1976)

1978:

CAN adopts large EGR tube (and Exhaust manifold), even though NOx requirements did not change
CAN retains basic EGR
BPT Tube (USA models) simplifed one-piece design
FU models retain 2-port thermal valve
USA non-FU changed to 3-port thermal valve

1979: no changes from 1978

CAN models: Basic EGR
FU Engine models: Basic EGR + BPT Valve
USA except FT: BTP Valve + 3-port TVV

1980

Switched back to 2-port thermal valve

1981

USA NOx emissions further restricted

NOx emissions - Passenger Car
1977-1980 FED: 2.0
1981 FED: 1.0 
---
1980 CAL: 1.0
1981 CAL: 0.7

USA replaced BPT with VVT
FED EGR secondary air passage increased from 11mm to 18m
FED EGR Tube mounting screw increased from M20 to M22
USA uses VVT and 3-port TVV
CAN MPG (A14 FU engine) adds VVT and 3-port TVV, all other CAN models remain basic

1982: No changes

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