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Electrical issues/ fuel injection

 
Old 01-05-2019, 10:42 PM
  #1  
Dylan_928
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Default Electrical issues/ fuel injection

Hello, this is my first post on here. I am fairly new to 928s, and currently i am working on a 1980 928 i got off of a trade with my 944. Anyway i have been trying to figure out how things work and what i need to do to get the car running. Right now i am not getting and pulse from my fuel injection. I know i have 12v going to the injectors, i replaced the XVI relay, however im not sure what the issue is and im looking for some assistance (im no proffesional as im only 17, so basic terms please). Also, wondering if anyone has a diagram for what the plugs on the bottom of the fuse panel are for (the alphabeticaly labeled ones). Any help is appreciated.
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Old 01-06-2019, 12:18 AM
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Wisconsin Joe
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First off, Welcome. You've found what's probably the best resource for these cars. Lots of helpful, knowledgeable people. Ask nicely, answer the questions asked, post outcomes and say 'Thank you" and you will get all the help you need.

80, US model, right? That would be L-Jet. Green wire ignition. So diagnosing spark (or lack of) wouldn't help much.

Are you getting 'tach bounce' when you crank it? I'm not 100% sure, but I think you should be.
Does the fuel pump come on when cranking? IIRC, this one won't energize the fuel pump until the ECU 'sees' rotation.

This is leading to questioning the reference sensor. It tells the ECU where the engine is in it's rotation and when to fire the injectors. If it's bad (or if the connector is bad) then the ECU doesn't know the engine is turning.

It's located at the back of the engine, on top. Under the air filter box.

Wiring diagrams are in the WSM (work shop manual). There's a fairly complete one available for free. There's a link for it in the "New Visitor" sticky. You should read that in any case.
There's also a better version of the WSM available on CD-ROM from Roger at 928s R Us. Complete WSM, updates, tech specs, lots more.

And, last but not least, a bit of a tradition on here:

THIS...
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Old 01-06-2019, 02:36 AM
  #3  
Dylan_928
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Originally Posted by Wisconsin Joe View Post
First off, Welcome. You've found what's probably the best resource for these cars. Lots of helpful, knowledgeable people. Ask nicely, answer the questions asked, post outcomes and say 'Thank you" and you will get all the help you need.

80, US model, right? That would be L-Jet. Green wire ignition. So diagnosing spark (or lack of) wouldn't help much.

Are you getting 'tach bounce' when you crank it? I'm not 100% sure, but I think you should be.
Does the fuel pump come on when cranking? IIRC, this one won't energize the fuel pump until the ECU 'sees' rotation.

This is leading to questioning the reference sensor. It tells the ECU where the engine is in it's rotation and when to fire the injectors. If it's bad (or if the connector is bad) then the ECU doesn't know the engine is turning.

It's located at the back of the engine, on top. Under the air filter box.

Wiring diagrams are in the WSM (work shop manual). There's a fairly complete one available for free. There's a link for it in the "New Visitor" sticky. You should read that in any case.
There's also a better version of the WSM available on CD-ROM from Roger at 928s R Us. Complete WSM, updates, tech specs, lots more.

And, last but not least, a bit of a tradition on here:

THIS...
thank you for the help and quick response! I will go outside and check the connections tomorrow, and i will also check the fuel pump and if i have “tach bounce”.
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Old 01-06-2019, 02:50 AM
  #4  
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And yes it is the US model. What do you mean by “IIRC”?
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Old 01-06-2019, 03:50 AM
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IIRC is a web abbreviation for If I Remember Correctly.
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Old 01-06-2019, 04:15 AM
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Originally Posted by Hey_Allen View Post
IIRC is a web abbreviation for If I Remember Correctly.
gotchya, thanks
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Old 01-06-2019, 07:03 AM
  #7  
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Hi welcome your going to learn a lot about a 928 here.
From your info first thing you need to do is post a picture of the engine bay.

Your car uses a green wire to run ,
this goes from the distributor to the connector at the hot post area then to the computer on the right fender well located at the area under the 14 pin connector hot post .
This green wire is the fail point as the end will crumble and the wire insulaton can fail.
A new wire is about 132.00 don’t try to fix the old one if the ends are crumbling or it’s not green anymore.
Note your car doesn’t have a reference sensor at the back of the engine
But you should check the passenger cam cover to verify the 2 brown ground wires are attached these ground wires run the fuel injection system if they are loose then the computer won’t have a solid ground
Anyway set the engine at TDC remove the passenger timing cover verify the timing mark lines up then remove the cap and the rotor and gray cover.
put the rotor back on and verify it’s pointing to the hash mark on the distributor body.
Note pictures will assist in more accurate answers
Make sure the battery is charged up with a battery charger a 2 to 6 amp charger will work disconnect the ground strap in the hatch area before charging the battery

Last edited by Mrmerlin; 01-06-2019 at 07:19 AM.
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Old 01-06-2019, 01:44 PM
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Wisconsin Joe
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Originally Posted by Mrmerlin View Post

Note your car doesn’t have a reference sensor at the back of the engine
Oops.

Apparently I didn't "RC" on that.
Not super familiar with the L-Jet on the early 80s US 928s. I have a 944 with similar (but not the same) setup, It has a crank sensor.

Stan - For future reference, how does the L-Jet in the 928 'see' rotation and 'know' when to pulse the injectors, if not a reference sensor?
Is it from the green wire? Or something else?
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Old 01-06-2019, 02:52 PM
  #9  
Dylan_928
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Originally Posted by Wisconsin Joe View Post
Oops.

Apparently I didn't "RC" on that.
Not super familiar with the L-Jet on the early 80s US 928s. I have a 944 with similar (but not the same) setup, It has a crank sensor.

Stan - For future reference, how does the L-Jet in the 928 'see' rotation and 'know' when to pulse the injectors, if not a reference sensor?
Is it from the green wire? Or something else?
i believe thats what the green wire does, not 100% sure but pretty positive
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Old 01-06-2019, 06:52 PM
  #10  
Dylan_928
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Originally Posted by Mrmerlin View Post
Hi welcome your going to learn a lot about a 928 here.
From your info first thing you need to do is post a picture of the engine bay.

Your car uses a green wire to run ,
this goes from the distributor to the connector at the hot post area then to the computer on the right fender well located at the area under the 14 pin connector hot post .
This green wire is the fail point as the end will crumble and the wire insulaton can fail.
A new wire is about 132.00 don’t try to fix the old one if the ends are crumbling or it’s not green anymore.
Note your car doesn’t have a reference sensor at the back of the engine
But you should check the passenger cam cover to verify the 2 brown ground wires are attached these ground wires run the fuel injection system if they are loose then the computer won’t have a solid ground
Anyway set the engine at TDC remove the passenger timing cover verify the timing mark lines up then remove the cap and the rotor and gray cover.
put the rotor back on and verify it’s pointing to the hash mark on the distributor body.
Note pictures will assist in more accurate answers
Make sure the battery is charged up with a battery charger a 2 to 6 amp charger will work disconnect the ground strap in the hatch area before charging the battery

Ground for my injectors, (although it looks clean it isnt)

This is the green wire plug (may need replacement?)

She is a dirty girl

is there any way to test the green wire? I dont really want to spend $100+ on an insulated wire with some fancy connectors. Thanks
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Old 01-06-2019, 08:03 PM
  #11  
SeanR
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Originally Posted by Dylan_928 View Post



Ground for my injectors, (although it looks clean it isnt)

This is the green wire plug (may need replacement?)

She is a dirty girl

is there any way to test the green wire? I dont really want to spend $100+ on an insulated wire with some fancy connectors. Thanks
Replace the wire and forget about it for 20 years.
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Old 01-06-2019, 08:11 PM
  #12  
Dylan_928
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Originally Posted by Wisconsin Joe View Post
First off, Welcome. You've found what's probably the best resource for these cars. Lots of helpful, knowledgeable people. Ask nicely, answer the questions asked, post outcomes and say 'Thank you" and you will get all the help you need.

80, US model, right? That would be L-Jet. Green wire ignition. So diagnosing spark (or lack of) wouldn't help much.

Are you getting 'tach bounce' when you crank it? I'm not 100% sure, but I think you should be.
Does the fuel pump come on when cranking? IIRC, this one won't energize the fuel pump until the ECU 'sees' rotation.

This is leading to questioning the reference sensor. It tells the ECU where the engine is in it's rotation and when to fire the injectors. If it's bad (or if the connector is bad) then the ECU doesn't know the engine is turning.

It's located at the back of the engine, on top. Under the air filter box.

Wiring diagrams are in the WSM (work shop manual). There's a fairly complete one available for free. There's a link for it in the "New Visitor" sticky. You should read that in any case.
There's also a better version of the WSM available on CD-ROM from Roger at 928s R Us. Complete WSM, updates, tech specs, lots more.

And, last but not least, a bit of a tradition on here:

THIS...
i am getting no tach bounce, and the fuel pump is not running when cranking btw. However, i know my cold start valve is working because whenever i crank it over it will fire for about 5 seconds and die. How does the cold start valve know when to turn on? or does it just prime when you turn on the ignition
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Old 01-06-2019, 08:27 PM
  #13  
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Ok thanks for the pictures
Please follow these instructions
you need to replace the green wire .
you need to clean the grounds on the cam.tower .
you need to service the CE panel fuses and relays with deoxit 100
you should follow this advice before further testing
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Old 01-06-2019, 09:44 PM
  #14  
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This is an L-jet? I agree with all the above advice and, if that doesn’t solve it, then replace the fuel injection relay.

The L-jet works by supplying 12v to the injectors full time and switching to ground for the duty cycle. So grounds are critical. And per your description, I and many others have had the exact same problem solved with a new relay (if ground cleaning doesn’t do it).
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Old 01-06-2019, 10:15 PM
  #15  
Mrmerlin
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NOTE poor electrical connections will damage a new relay,
this is usually due to an underpowered feed thus the relay contacts don't close as well and arc.
so you can decide if you want to test two new relays first or last.

Joe the green wire gets the signal from the distributor signal fingers think early electronic ignition systems.
The MAF systems then went to having a reference sensor timed to the flywheel.
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