No power to my injectors!

Tiny
CHARLESWITHTHE900SE
  • MEMBER
  • 1995 SAAB 900
  • 2.0L
  • 4 CYL
  • TURBO
  • 2WD
  • MANUAL
  • 111,000 MILES
I just got a 95 saab 900se givin to me by some very cool people and it has sat for 7 years. I put a new battery did a tune up and oil change and went to start it but the engine just cranks so I took out a spark plug to see if there was any fuel on it and nothing but I know for sure my fuel pump is good because I have real good pressure at the rail so I checked for power at my injectors and nothing so if you could tell me what could cause that if it could be a security issue or maybe the ecu? I dont know but I really need this car to get to work. Its making me insane!
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Sunday, March 27th, 2016 AT 6:18 PM

13 Replies

Tiny
CARADIODOC
  • EXPERT
If this is like most other car brands, the first thing you must do is check for spark. If that is missing, it is likely 12 volts for the injectors and ignition coil(s) comes from the same source, and that relay is not being turned on. If that is the case, start by checking the wiring for the crankshaft position sensor to see if a mouse made a meal of it.
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Sunday, March 27th, 2016 AT 10:28 PM
Tiny
CHARLESWITHTHE900SE
  • MEMBER
I made sure to run thru all of that and it has spark the only thing that is lacking power is the injectors plus I found out that other people have tried to figure this same problem out on this same car without very good results and that's probably why it was givin to me. Is there even anything else I can try?
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Monday, March 28th, 2016 AT 3:51 PM
Tiny
CHARLESWITHTHE900SE
  • MEMBER
Maybe the ignition? The key will turn fine for a few turns then will get stuck to where I cant turn it past on to engage the starter.
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Monday, March 28th, 2016 AT 3:54 PM
Tiny
CARADIODOC
  • EXPERT
Check for 12 volts on fuse # 16B, a 30 amp, in the left side of the instrument panel. That feeds the injectors, but it also feeds the "ignition discharge module". Voltage for that fuse comes from the main relay, and that one is fed from fuse # 2, a 60 amp maxi-fuse on the right side of the engine compartment.

If you have spark, all that has to be working. That leaves splices buried in the harness. It seems very unlikely all four injectors would be missing their 12 volt supplies while the ignition system still works.

Let me know where you have 12 volts, then I'll check back on the diagram to see where to go next. By the way, that 12 volts at the injectors is on the green / red wires.
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Monday, March 28th, 2016 AT 8:04 PM
Tiny
CHARLESWITHTHE900SE
  • MEMBER
Ok just tested that fuse and it has 12 volts and I retested the injectors and cylinder #3 is getting 12 volts but 1, 2, and 4 are only getting close to 3 volts

P.S. Thank you for taking the time to help!
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Tuesday, March 29th, 2016 AT 9:46 AM
Tiny
CHARLESWITHTHE900SE
  • MEMBER
Could that be the ecu? Does my car have an ecu? Haha
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Tuesday, March 29th, 2016 AT 3:27 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. All four green / red wires are spliced together in the harness. Assuming your probe was making good contact with the terminals, so your readings are to be believed, pull the tape off the harness and look for a splice that's green with corrosion.
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Tuesday, March 29th, 2016 AT 8:21 PM
Tiny
CHARLESWITHTHE900SE
  • MEMBER
Is that only under the hood or do I need to go under the dash too?
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Tuesday, March 29th, 2016 AT 9:47 PM
Tiny
CHARLESWITHTHE900SE
  • MEMBER
Ok so I found that splice and it looks really clean with no green at all and there is 12 volts at that splice but still cant get 12 volts to 3 of the injectors. So is there maybe a place I can check the other wires instead of the red and green maybe they have a problem?
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Wednesday, March 30th, 2016 AT 2:06 PM
Tiny
CARADIODOC
  • EXPERT
Nope. If your Christmas tree lights don't work, you don't go over to your neighbor's house to diagnose his lights. When there is a problem with the red / green wire, you don't go looking for a problem with other wires. If you have 12 volts at the splice, those wires only run a few inches to each of the injectors. The problem has to be a broken wire right next to where it is crimped to a terminal in the connector or your meter probe isn't making good contact. At this point it is acceptable to unplug a connector from an injector, then touch your meter probe to the terminal on that side. If you find 12 volts that way, your meter probe wasn't making contact. I've been in tv repair since the early '70s, and as an "expert", I can't tell you how many times I've gone in the wrong direction after getting an incorrect meter reading.

If you do not find 12 volts that way, tug gently on the red / green wire. If it acts like a rubber band, the wire is broken inside the insulation. That is not too uncommon, but it would be very unusual to happen to multiple wires at the same time unless the car was previously flood-damaged.
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Wednesday, March 30th, 2016 AT 8:27 PM
Tiny
CHARLESWITHTHE900SE
  • MEMBER
Ok so I ran negative on my wire tester from the battery and tested the positives and they all go straight to 12 volts but still having an issue with no power so what is the other wire on the injector? Does that tell it when to fire or is it a ground? Because I can't get any reading from that one at all not even using it as a ground so its like a dead wire right now!
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Thursday, March 31st, 2016 AT 10:55 AM
Tiny
CHARLESWITHTHE900SE
  • MEMBER
I just used the only injector that is still working to see if I could get a negative off of it and it gave me a reading of 12.85 volts so it has to be those negative wires right? The other 3 dont show a reading at all.
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Thursday, March 31st, 2016 AT 11:06 AM
Tiny
CARADIODOC
  • EXPERT
There's a red / green wire at each injector that supplies the 12 volts. I'd have to dig out the diagram again to know for sure, but that 12 volts will be there either with the ignition switch on or only during engine rotation, meaning cranking or running. The other wire for each injector gets grounded by the Engine Computer only when it wants to fire it. When the injector is off, that control circuit is open, so the 12 volts from the red / green wire will go through the injector and be seen on the other wire. You can't measure the firing with a digital voltmeter because of how they work. You have to use a scanner to view the number of milliseconds listed that the computer is holding the injectors open during each pulse.

You can't measure the voltage on the control wire to determine if the injector is being pulsed on due to the way digital meters take a reading and display it. I have a web page that explains this but I can't find it at the moment. I'll try looking again tomorrow when my laptop battery is charged up.
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Thursday, March 31st, 2016 AT 10:11 PM

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