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Old 05-16-2018, 07:49 PM   #26
ZVOLV
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Why would bypassing a relay when there is already power do anything for you?
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Old 05-16-2018, 08:29 PM   #27
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Pull the fuel injector relay, then jump power to the output. If it starts and runs, the ecu has failed to provide a ground, a common failure. Replace it.
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Old 05-16-2018, 11:05 PM   #28
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Why would bypassing a relay when there is already power do anything for you?
Just because some voltage is getting to the relay doesn’t mean sufficient current is being supplied to the injectors
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Pull the fuel injector relay, then jump power to the output. If it starts and runs, the ecu has failed to provide a ground, a common failure. Replace it.
Jumping the fuel pump relay doesn’t work on a 7/9 because it also provides power to the RSR. So your pumps will cycle but injectors won’t fire. At least on the ones I’ve driven.
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Old 05-16-2018, 11:35 PM   #29
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There are two outputs from the relay and you jump power to both- I use a Y jumper.
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Old 05-17-2018, 12:15 AM   #30
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There are two outputs from the relay and you jump power to both- I use a Y jumper.
^ This. It's the same relay as an LH-based 240.
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Old 05-17-2018, 12:23 AM   #31
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There are two outputs from the relay and you jump power to both- I use a Y jumper.
Yes, important to make the Y instead of a U like normally.
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Old 05-17-2018, 10:01 AM   #32
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I'll make that Y jumper today and give that a try. I just don't see how that would make a difference if the relay is working properly.
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Old 05-17-2018, 10:26 AM   #33
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WTF. Looking at a diagram shows it's a standard 4 prong relay. What the heck is this Y crap?
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Old 05-17-2018, 10:44 AM   #34
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WTF. Looking at a diagram shows it's a standard 4 prong relay. What the heck is this Y crap?
Dang image quality got killed so you might have to google it. Pin 1 from the fuel pump relay runs up to fuse 9 (blue and yellow wire). Pin 2 from the RSR is also blue and yellow and runs to fuse 9. I think if the FPR does not energize, neither will the RSR. Just in my experience at least. On a 240 (where the RSR is absent), jumping the FPR works great as a temporary solution.
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Old 05-17-2018, 10:51 AM   #35
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WTF. Looking at a diagram shows it's a standard 4 prong relay. What the heck is this Y crap?
You’re looking only at the RSR I think. The RSR is a standard style 4 post relay. It gets a constant 12v, constant ground, then when the FPR is energized, the blue/yellow wire on the RSR is as well. This closes the contacts on the RSR and allows current to flow to the injectors. Someone please correct me if I’m wrong, this is how I’ve inderstood it in the past when I was dealing with wonky RSR stuff.
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Old 05-17-2018, 11:05 AM   #36
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Youíre looking only at the RSR I think. The RSR is a standard style 4 post relay. It gets a constant 12v, constant ground, then when the FPR is energized, the blue/yellow wire on the RSR is as well. This closes the contacts on the RSR and allows current to flow to the injectors. Someone please correct me if Iím wrong, this is how Iíve inderstood it in the past when I was dealing with wonky RSR stuff.
Thatís how I understand it as well. From what I previously tested, thatís exactly how it works.
The RSR, as has been mentioned, sends power to the injectors. My problem is not getting power to the injectors, itís grounding them.
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Old 05-17-2018, 11:12 AM   #37
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Oh fuel pump relay.

Try ether for science reasons.
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Old 05-17-2018, 11:48 AM   #38
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What needs to happen in order for the injectors to be grounded? ECU must be good, it must receive a signal from the CPS/hall sensor, grounds on intake must be clean and tight, resistor pack spades must be clean and tight, what else? You ohm checked resistance between the connectors on the resistor side, but did you check to see if the male spades were clean? I filed mine down until they were shiny and then the vehicle started
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Old 05-17-2018, 01:09 PM   #39
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I don't recommend using a file to clean terminals, but it sure will destroy any fretting.

Another way to test the ground side is to connect a test light to a positive source and to the injector control side of the circuit.

I would make sure your ECU is powered up.
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Old 05-17-2018, 01:14 PM   #40
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I used a flat head screw driver and a harbor freight pick on site to clean them. Got it running, drove it home, then used file. At this point in my 940s life it doesn’t matter what I use. Maybe something a bit less abrasive is recommended but I didn’t really care. It worked.
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Old 05-17-2018, 01:30 PM   #41
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Yeah no kidding. Slap some dielectric grease in there to prevent future oxidation and to promote a good connection. There was a bulletin to slap grease in the ecu connector on these cars.


Like I said in your other thread, these mid 80s 740s have the biodegradable wiring. It may have shot wiring under the intake or at the firewall.

Have you checked continuity between the injector ground wire terminal and the ecu!? Do so and wiggle test the engine wiring harness and see if the resistance goes open or high.


One MORE test....use a test light between injector ground and a known good ground. Make sure is does NOT light up=short to voltage. Do it with key on.
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Old 05-17-2018, 03:36 PM   #42
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Tried ether just now... didn't start, but there was definitely ignition... I probably just used too much. All I got was a pop, which nearly ignited what dripped into the intercooler hose. Crisis averted. Tried again with the same result. If I cranked longer, it probably would have started but I didn't want to take any chances.
Tried the Y jumper relay bypass, no difference at all.

The male terminals from the ballast resistor are good and clean, that's where I tested the resistance because I didn't want to pull the spades off the resistor pack. That was the issue with the previous resistor I had on the car and I was unable to fix it at the time.

I have already checked continuity between the ECU connector and the injector connectors, all good. I moved around the harness and there was no change, so we're good there.

I will try the test light in a little bit.
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Old 05-17-2018, 03:52 PM   #43
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It should have ran on ether.
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Old 05-17-2018, 03:55 PM   #44
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Quote:
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Just because some voltage is getting to the relay doesnít mean sufficient current is being supplied to the injectors

Jumping the fuel pump relay doesnít work on a 7/9 because it also provides power to the RSR. So your pumps will cycle but injectors wonít fire. At least on the ones Iíve driven.
This takes a 2 pronged approach. Power needs to be jumpered to both the pumps and the rsr.
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Old 05-17-2018, 04:39 PM   #45
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If it doesn’t start on ether you have more than just a fuel problem. It (probably) won’t blow up in your face..I’d see if you can get it to somewhat idle on ether. But that’s just me
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Old 05-17-2018, 06:04 PM   #46
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Okay... pardon my total stupidity... don't know how I didn't catch this sooner.
When I tested the injector ground with the test light, it DID light up. I quickly realized what I completely missed before... there is power on both injector terminals. That led me to once again test resistance from the injector connectors to ECU pin 13. 0 ohms on ground, and anywhere between 9 and 15 on power side. Didn't seem quite right. Then I realized that I have 12 volts on pin 13... and I'm pretty damn certain there isn't supposed to be any voltage there! Maybe I didn't fry the ECU, but I'm betting I did.

Anyway, I'll be pulling the wiring apart under the intake manifold to look for where the wires are making contact... because that must be where it is. ZVOLV has only mentioned it a few times...

In the meantime, I appreciate everybody's help and for sticking with me through this!

What's the best way to pull that harness out? Just pull it forward? It doesn't seem to have much flexibility without removing the manifold.
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Old 05-17-2018, 10:17 PM   #47
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Unplug the ECU and see if short goes away.
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Old 05-18-2018, 09:23 AM   #48
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With the ECU unplugged, there is no voltage on either (no power going to RSR) but still continuity on both wires.
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Old 05-18-2018, 01:58 PM   #49
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I gotta look at a diagram, but the i think the ecu powers up the RSR, therefore, one could power up the RSR circuit manually and see if there is still a short to voltage on that injector ground circuit.

You gotta figure out if the short is internal to the ECU, or in the wiring.
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Old 05-18-2018, 03:56 PM   #50
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NO the ecu powers up the FPR which powers the RSR.
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