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Old 07-13-2019, 02:46 PM   #1
92masonry
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Default No injector pulse, but the potential is there.

As some of you may have seen, I bought the 1990 780 that sat in the for sale section for a good while. So Iíve got it home and have spent the last week or so trying to figure out why it will not run. I have had a ton of leads on why by scouring this site and the others for answers, but every time I hop in and crank it over, cranking is all it does. So, it fires up with starting fluid through the intake manifold, thereís the spark. I pulled the fpr and got a ton of fuel out of the rail while cranking. I also replaced the dead in tank and put on a spare fpr I had just in case. Cleaned up a number of grounds, maybe not all or even important ones. I pulled the wires out of the radio suppression relay connector and connected the two that need to be (what I seem to have there is a brown wire straight to battery and a grey or white wire to the resistor pack) which doesnít match any other wiring diagram I have seen, but continuity has led me to believe that is exactly what they are. Now for the potential to pulse. I put the obd port deal to the setting that will pulse the injectors, and it did so perfectly across all 4, and turning the engine over right after even got me a moment of firing over. Iíve ran a wire from pin 18 I believe to ground to simulate a ground of the Ecu and got nothing from the injectors. I found corroded connections at the resistor pack, so I cleaned them, but it had already went through the diagnostic pulse thing, so that shouldnít have been the culprit, but Iím out of ideas here. A spare ecu was laying next to the original on that was still mounted in its chassis when I got the car, and the harness was plugged into it. Maybe I have 2 bad ecuís? Maybe the ecu has to be mounted to the chassis to work for grounding purposes? I appreciate any ideas you all could offer.
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Old 07-13-2019, 04:08 PM   #2
dl242gt
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If it's been sitting awhile. The injectors are probably clogged. They may open and put some fuel in there under testing. But it's not an atomized fuel spray. You also may have fouled plugs. Check out the plugs to get an idea of what's going on in there.
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Old 07-14-2019, 12:09 PM   #3
92masonry
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I’ve got a spare set laying around, so I’ll give that a shot today. Thanks for the reply.
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Old 07-14-2019, 01:40 PM   #4
philski o'flood
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Quote:
Originally Posted by 92masonry View Post
Maybe the ecu has to be mounted to the chassis to work for grounding purposes?
nope, they'll work fine flopping around on the floor mat
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Old 07-15-2019, 01:44 PM   #5
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"I pulled the fpr and got a ton of fuel out of the rail while cranking."

This is not a valid fuel pressure check.

"Maybe the ecu has to be mounted to the chassis to work for grounding purposes?"

I found one Bosch ECU that would not run if the case was grounded!


You need to diagnose the system, starting with the things it needs to inject fuel.
Its interesting that the ECU will test fire the injectors that really narrows down things.

But first there is a fuel pressure test that needs to be completed.

Then you need to look at the things that the ECU needs to turn on the fuel.
I don't remember/know what magical things Volvo did on your model.
I definitely recall Volvo had some nice diagnostic routines in the manual that will get you where you want to be.
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Last edited by Dirty Rick; 07-15-2019 at 01:54 PM..
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Old 07-15-2019, 03:26 PM   #6
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Once again, thank you for the responses. I traced voltage from where I deleted the rsr to the injectors and found a pretty significant drop. So I went back to the crusty connection I mentioned earlier at the ballast resistor. I picked at it some but decided to just splice right into it to eliminate the possibility. A quick check with a noid light gave me a big bright pulse I have yet to see, so I plugged the injectors in and it fired right up! I’m still confused as to how a got such a solid sounding pulse from the injectors in diagnostic mode, but I’ll get over that.
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Old 07-19-2019, 11:58 PM   #7
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Key on there's a lot more current available vs. cranking. That's probably why the injectors may have been able to click.
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