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Terrible Gas Mileage Posted by Dana [Email]  (#2822) [Profile/Gallery]
(more from Dana) on Sun, 1 Aug 2004 07:35:40
In Reply to: 84 Saab... very bad gas consumption, andy [Profile/Gallery]
, Sat, 31 Jul 2004 00:10:44
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You have done quite a bit on the standard stuff, but they have only little effect on the gas consumption compared to the fuel enrichment system (CIS) on the 84. I would look at the following items in the following order:
1. Thermo Time Switch....failure causes the cold start injector to be on all the time and the normal injectors to have too much enrichment as sensed by the fuel enrichment control system. Easy to test for with ohm meter (pull off plug, 40 ohms resistance from one of two electrical pins to engine body, 40 ohms between the two electrical connector pins, 0 ohms between the 2nd pin and the engine body if <115F...40 ohms between 2nd pin and engine body if >115F. Test when engine is cold then stop engine and retest after running to normal operating temp.
2. Old Oxygen sensor: more than 60K miles on the same sensor. bad sensor will tell fuel enrichment control system to lock onto a richer default higher enrichment. This year has single wire connection. It puts out 0-1 VDC. Normal CIS controls the oxygen level to maintain .5VDC after the car has warmed up. After the car has warmed up and idling you can pull off the single sensor wiring connection. If the sensor is working you can hear the engine idle move to the default enrichment position. If it does not change then the control system is already locked in the default mode before you pulled the wire and the sensor is bad. You can also monitor the sensor output voltage on the wire while running and connected. It moves around the 0.5 VDC level but you may need an old analog voltage meter to see the average reading...moves too quickly for digital meter. Just reconnect the wire when you are done.
3. Cold Start Injector Leakage....have to pull out of intake and then go through the normal injector test procedure for leakage drips.
A description of these devices, the CIS system/description/wiring and much more can be found on my web page listed below.
posted by 172.163.122...
, Sat, 31 Jul 2004 00:10:44, Sun, 1 Aug 2004 11:04:47, Sun, 1 Aug 2004 07:35:40 <-- Viewing This Message
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