73 450 sel. no injector pulse - Mercedes-Benz Forum

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post #1 of 52 (permalink) Old 11-28-2015, 04:45 PM Thread Starter
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73 450 sel. no injector pulse

It's a friends car and I'm stumped. Here's how far I am. The fuel pump is working and I believe the trigger points are in working order. Using a multimeter as I turn the distributor by hand the fuel pump turns on. I have a noid light to test for pulse and I'm getting nothing. They were working earlier this summer and the car was running.
It had been sitting for a long time. The tank was so filled with brown tar it had to be cleaned. I realized after several gallons of gas it was not going to do it.
Anyway, I'm not sure why no pulse at the moment. Seems all injectors are affected.
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post #2 of 52 (permalink) Old 11-28-2015, 08:48 PM
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Hi
Have you checked continuity in all the wires?
I'm assuming the fuel filter was changed? Also is there any extra inline filters? I just had a starting problem with my 4.5. It turned out to be a few bad plug leads, but also a very badly clogged inline fuel filter. I installed one before the fuel pump to protect it. The car had sat for many years so I cleaned the tank as well as I could. changed the stock filter and added an extra one.
Cheers John
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post #3 of 52 (permalink) Old 11-28-2015, 09:14 PM
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If the trigger points are good and you have no pulse, look to the ECU. It's either out of commission or the power to it is...
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post #4 of 52 (permalink) Old 11-28-2015, 09:20 PM Thread Starter
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It's an electrical problem. Not getting injector pulse. Pump, pressure, filter, regulator are all good. As I mentioned I checked the trigger points and they appear to open and close that part of the circuit. As I turn the distributor by hand the trigger points activate the fuel pump so I know that much is working. New injectors, had to replace some of the connectors.
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post #5 of 52 (permalink) Old 11-28-2015, 09:22 PM Thread Starter
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So if I can activate the fuel pump turning the distributor would it still do that if no power to the ecm?
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post #6 of 52 (permalink) Old 11-29-2015, 06:41 AM
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The distributor doesn't activate the fuel pump. The ecu senses engine rotation and activates the fuel pump relay. Seriously, look at the wiring to the ECU and see if you have power going to it. I also suggest you go into the Online Resources portion of the forum - there's a ton of tech data on your fuel system including how to troubleshoot it.

Was it recently running, and no longer is? If such is the case, look at your fuses too. I feel strongly your issue is with the computer or its power.
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post #7 of 52 (permalink) Old 11-29-2015, 08:19 AM Thread Starter
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Well then that means the ecu is getting power if the pump activates while I'm opening and closing the trigger points by turning the distributor.
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post #8 of 52 (permalink) Old 11-29-2015, 04:47 PM Thread Starter
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Ok, doing some more checking. While cranking the cold start injector circuit fires. The noid light is constant while cranking, but still no pulse from regular injector circuit.
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post #9 of 52 (permalink) Old 11-29-2015, 07:39 PM
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See above. I can provide a link to the troubleshooting section if you wish.
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post #10 of 52 (permalink) Old 12-05-2015, 03:29 PM Thread Starter
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I've tested everything I possibly can to this point. The wiring is good, good spark. Cylinders 1 and 5 which are paired in the circuit fire but they're the only ones working. I'm guessing whatever drives the other injectors must've crapped out. Anybody have an opinion before getting another ecu?
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