chaseincats Posted May 31, 2022 Share #1 Posted May 31, 2022 Hey gang, My friend picked up a 75 280 and its not running all that great. We found that injectors 5 and 6 have 10.3 volts with the key in 'on' (but not running) but injectors 1-4 have something like 0.3v. According to the FSM, there are two dropping resistors, one that covers injectors 1-4, and one that covers injectors 5-6 so I'm assuming those (or the connectors) would be the problem. I have never heard of those going bad or causing problems though. I thought the injectors were supposed to get 6v after the dropping resistors - anyone know how they could be getting 10.3? Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/ Share on other sites More sharing options...
Roberts280Z Posted May 31, 2022 Share #2 Posted May 31, 2022 The resistors won't drop the voltage until the injector is activated. I think in this condition (ignition on, not running), you should see full voltage on all injectors. 1 2 Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641098 Share on other sites More sharing options...
SteveJ Posted May 31, 2022 Share #3 Posted May 31, 2022 There could be corrosion at the connector for the dropping resistors for 1-4. Also where are you measuring voltage? Don't measure across the injector. Measure from one side of the injector connector to ground. When the car is running, you should see the voltage fluctuate rapidly. Also, the best way to test injector firing is with a noid light. If I don't miss my guess, I would say this one would work for you: https://www.amazon.com/OTC-6266-Noid-Lite-Bosch/dp/B0050SGHMW Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641099 Share on other sites More sharing options...
chaseincats Posted May 31, 2022 Author Share #4 Posted May 31, 2022 22 minutes ago, SteveJ said: There could be corrosion at the connector for the dropping resistors for 1-4. Also where are you measuring voltage? Don't measure across the injector. Measure from one side of the injector connector to ground. When the car is running, you should see the voltage fluctuate rapidly. Also, the best way to test injector firing is with a noid light. If I don't miss my guess, I would say this one would work for you: https://www.amazon.com/OTC-6266-Noid-Lite-Bosch/dp/B0050SGHMW We measured across the injector connector. Wouldn't that be the best place to measure it since it would isolate the plug itself? Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641101 Share on other sites More sharing options...
Zed Head Posted May 31, 2022 Share #5 Posted May 31, 2022 Nissan wrote a book. It covers all years through 1980. Many possible reasons for not running great. 1 Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641103 Share on other sites More sharing options...
SteveJ Posted May 31, 2022 Share #6 Posted May 31, 2022 25 minutes ago, chaseincats said: We measured across the injector connector. Wouldn't that be the best place to measure it since it would isolate the plug itself? No, it is not. If you want to test if the injector is getting the pulse to fire, use a noid light. Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641105 Share on other sites More sharing options...
chaseincats Posted May 31, 2022 Author Share #7 Posted May 31, 2022 34 minutes ago, SteveJ said: No, it is not. If you want to test if the injector is getting the pulse to fire, use a noid light. Gotcha - it's getting pulse to fire, its just very weak. Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641108 Share on other sites More sharing options...
SteveJ Posted May 31, 2022 Share #8 Posted May 31, 2022 That merits looking at the connectors for corrosion. Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641109 Share on other sites More sharing options...
Zed Head Posted May 31, 2022 Share #9 Posted May 31, 2022 Have you calibrated your eyeballs? Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641110 Share on other sites More sharing options...
chaseincats Posted May 31, 2022 Author Share #10 Posted May 31, 2022 7 minutes ago, SteveJ said: That merits looking at the connectors for corrosion. The injector connectors have been replaced and look fine - I will let him know to check out the dropping resistor and ECU connectors. What is the connector you circled on the bottom of the chart - I don't see it labeled Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641112 Share on other sites More sharing options...
SteveJ Posted May 31, 2022 Share #11 Posted May 31, 2022 That is the electronic fuel injection relay. Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641113 Share on other sites More sharing options...
chaseincats Posted May 31, 2022 Author Share #12 Posted May 31, 2022 11 minutes ago, SteveJ said: That is the electronic fuel injection relay. Is that one of the relays located in the under-hood relay bracket? Link to comment https://www.classiczcars.com/topic/67538-injector-voltage/#findComment-641114 Share on other sites More sharing options...
motorman7
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