Glow System Info

[charlieb]

I WAS GOOGLING FOR THE PERFORMANCE SPECS ON THE PUP DIESEL, AND CAME ACROSS http://www.sae.org/technical/papers/811271. IT'S A PAPER TITLED "THE ISUZU P'UP - FULLY REMODELED SMALL PICKUP TRUCK", WRITTEN BY JAPANESE ENGINEERS. I BOUGHT A COPY, HERE'S A SUMMARY. FIRST HALF OF THE PAPER IS AN OVERALL COMPARISON OF THE EARLIER MODEL TO THE NEW MODEL. COVERS STYLING, INTERIOR ROOM, SUSPENSION, MANUFACTURING, AC DESIGN. EVERYTHING GETS BETTER WITH THE NEW DESIGN (NO SURPRISE). SECOND HALF COMPARES THE 1981 GAS AND DIESEL. HERE'S THE GOOD STUFF:

QUARTER MILE ET (CURB WEIGHT + 2 PASSENGERS): 20G/22D SECONDS
QUARTER MILE ET IN 4TH GEAR, STARTING AT 25 MPH: 22G/22D SECONDS
SOUND LEVEL C-WEIGHTED, 4TH GEAR WIDE OPEN THROTTLE: 90G/90D DB

THE SOUND LEVEL TEST IS A GRAPH FROM 25 - 80 MPH, BASICALLY FLAT AT 90 DB FOR BOTH FROM 30 - 60 MPH, AND SLIGHTLY HIGHER OUTSIDE THAT RANGE. THE GRAPH STOPS AT 76 MPH FOR THE DIESEL, 78 MPH FOR THE GAS, SHOWING WHAT THE ENGINEERS THOUGHT THE TOP SPEED WAS.

THERE IS ALSO A DESCRIPTION OF THE QUICK ON SYSTEM (QOS) FOR THE DIESEL. PRE-HEAT TIME AT -4 F: 20 SECONDS WITHOUT QOS, 3.5 SECONDS WITH. STARTING TIME TO 2000 RPM: 40 SECONDS WITHOUT QOS, 17 SECONDS WITH.

SO IF YOU WANT TO KNOW HOW FAST, OR LOUD, OR QUICK TO START YOUR PUP WAS BY DESIGN, HERE'S WHAT THE ENGINEERS INTENDED. SHOULD BE INTERESTING TO SEE HOW THEY PERFORM AFTER 200K MILES. CHARLIE

[charlieb]

Based on the technical report http://www.sae.org/technical/papers/811271 and measurements on an 82 Luv, here’s how the glow system works. If you don’t want the details, skip to the conclusions at the bottom.

There are two separate circuits: the electronic Quick On System (QOS), and a manual circuit. The QOS controls Relay 1; the START position on the ignition switch controls the manual circuit through Relay 2. Both circuits connect the battery to the sense resistor; Relay 1 directly, and Relay 2 through the dropping resistor. The sense resistor is in series with the glow plugs. The sense resistor is 0.027 ohms, and the dropping resistor is 0.12 ohms.

The glow plug resistance is proportional to absolute temperature. At 300K (about 80 F) the four glow plugs in parallel measure .033 ohms. When the ignition switch is turned ON, QOS closes relay 1. The voltage at the glow plugs is shown in the chart below. QOS senses the temperature of the glow plugs by comparing the voltage at the glow plugs to the voltage at the sense resistor. QOS uses the ratio of voltages, rather than absolute voltage, to compensate for battery variation. When the ratio of these voltages is 5:6, indicating 1173K, (about 1650F) Relay 1 drops. Because the ignition switch is in the START position, the voltage drops from 7.5 to 5V since Relay 2 is engaged. If the switch is ON, the voltage drops to zero.

If Relay 1 is unplugged, only the manual circuit operates. This is shown as Without QOS in the graphs. With the ignition switch in the START position, Relay 2 engages, and connects the battery through the dropping resistor to the sense resistor. Because the dropping resistor is in circuit, the voltage at the glow plugs does not go above 5 V, and the glow plugs heat much slower

The temperature of the glow plugs is shown in the second graph. This graph is developed by using the voltage and current at the glow plug to determine resistance, and therefore temperature. The current is determined by measuring the voltage across the sense resistor just before and just after Relay 1 drops. Just before drop it’s 59A, just after its 38A.

Conclusions:
1. The QOS gets the glow plugs to operating temperature in 5 seconds, the manual circuit takes 15 seconds.
2. The glow plugs are rated for 5V continuous. QOS takes them briefly to 7.5V to heat faster, while monitoring temperature. Unless the temperature is monitored, use the dropping resistor to avoid burning out the glow plugs.
3. All Pup/Luv diesels include the manual circuit. If QOS fails, just hold the ignition switch in START, clutch out. After 15 seconds, push in the clutch. This manual circuit is the same one shown by Jerry and others on the forum, except it uses the ignition switch to engage.
4. The sense resistor dissipates 38 Watts, and the dropping resistor dissipates 169 Watts steady state. That means both get hot quick. It also means there is no practical substitute available from Radio Shack. You need both of these original parts to get the complete glow system working. You don’t need the sense resistor if you only use the manual circuit; however the glow voltage will be go up to 5.5V. This will shorten the glow plug life a little, probably not enough to notice.

[charlieb]

The SAE paper is 20 pages, but only one page covers QOS, so there's not a lot of detail. There are a few key points that let you figure out the rest:
- Glow plug resistance is proportional to absolute temperature.
- Target temperature is 1173K.

[charlieb]

Here are the schematic and a picture showing component locations. The theory of operation is at viewtopic.php?f=1&t=2613

[StevePT]

I have this picture on my computer, I can get a better picture later, but maybe this will work for you.

I'm seeing gold - brown - black - gold

[Paul]

Hi All--

Here is my schematic for the QOS glow control card. It may assist those who want to repair their card.

Paul

Edit: If you want to get a clearer view and /or print this schematic click on it to download the full size file.

[JoeIsuzu]

This thread is some of the best glow plug info that has been assembled from several old threads. If you see others that should be included here, please PM me.

Jack