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Suspect DME died... Can anyone lend me a DME?(WI) (Read 606 times)
jsneeb
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Suspect DME died... Can anyone lend me a DME?(WI)
Sep 3rd, 2020 at 3:34pm
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Troubleshooting a no start after the car sat for a year.

Put in a new battery car would crank but misfire, Able to get the car to rev, up to what sounded like 2 or 3k rpm, but the tac barely moved, showing 500 rpm and would go up to 900 when I rev the engine, misfiring horribly.


Eventually stopped starting all together.

Tested the Reference sensor and one was not the correct Ohms.
Replaced one sensor.

No change car wont start at all, sometimes it does but will barely idle.
No tac bounce.
Tried to unplug an injector ( seen somewhere that helps if the issue is a fuel pressure regulator )
No change
jumpered DME relay, can hear fuel pump running. No change

Right now I suspect the ECU is acting up or just died.
I would like to see if anyone is around WI or Minnesota and could lend me an ECU to try and swap in? Just want to try it to rule out another possible issue.
I could buy one if someone has a known working spare but right now I just want to know what is wrong with the car.

Stuff I haven't tried but will next time I am at the car ( stored in WI )

Clean up grounds behind the dash.
Replace the other sensor ( one tested bad ones tested ok )
New ECU / DME

Any other ideas?
  
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OhioTom
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Re: Suspect DME died... Can anyone lend me a DME?(WI)
Reply #1 - Sep 3rd, 2020 at 7:11pm
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PM me..

  

Tom Simpson&&VW/Porsche freak.
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Dave W
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Re: Suspect DME died... Can anyone lend me a DME?(WI)
Reply #2 - Sep 4th, 2020 at 6:14pm
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no tach bounce means no reference signal.  either the sensor is bad, the harness side connector is bad, the two sensor connectors are swapped, or the gap is wrong.
  

Dave - black 84 no longer exists. Sad 83 self destructed. All better now. Smiley
... Let's go hit some twisty roads! ...
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jsneeb
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Re: Suspect DME died... Can anyone lend me a DME?(WI)
Reply #3 - Sep 24th, 2020 at 2:47pm
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Hello.

So Im back at the car and got two new reference sensors put in.
It didn't start, No tac bounce.
so I swapped the cables in case I had them wrong.

Got tac bounce and the car started, but it ran very poorly.
Gave it some throttle and it died.
Started back up again and I let it idle for about 5 min while I checked for oil or fuel leaks.

Shut the car off.

Tried to start it again and no tac bounce. Tried about 6 times. No tac bounce no start.

Checked the connectors and used a small screwdriver to nudge the pins in the connector a bit tighter in case the connection was poor.

Still wont restart.

What gives?

I really think something is up with my ECU, where can I get one to try and just swap??
  
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jsneeb
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Re: Suspect DME died... Can anyone lend me a DME?(WI)
Reply #4 - Sep 24th, 2020 at 2:57pm
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Im going to replace the connector.
I dont have OEM connectors but have other waterproof 3 pin plugs that I can use.

Will try that but on inspection the wires at the harness side look just fine. Maybe they are broke internally?

Everything started to go wrong after the car sat for about 2 years and I put a new battery in it and since then havent been able to get it running.
  
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Dave W
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Re: Suspect DME died... Can anyone lend me a DME?(WI)
Reply #5 - Sep 25th, 2020 at 4:34pm
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Here's something that might help and that you need to do anyway:

1. Clean all of the grounds, including the engine to firewall ground strap.

2. Clean all of the fuse holder tabs.

3. Clean the ends of the fuses or replace the fuses with new ones.

Things don't work well without good voltage and current.
  

Dave - black 84 no longer exists. Sad 83 self destructed. All better now. Smiley
... Let's go hit some twisty roads! ...
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jsneeb
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Re: Suspect DME died... Can anyone lend me a DME?(WI)
Reply #6 - Sep 25th, 2020 at 8:09pm
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Ok.

Got a O-scope and checked the speed and reference sensor outpus.

Getting a strong spike once per cyl rotation on the reference sensor ( about 4 V ) and a sine wave on the speed sensor ( about 3.3V peak )

Cleaned fuse holder, and fuse ends.

Cleaned the ground behind the dash, and the one on the back of the engine. Cleaned the large strap ground that goes between engine and firewall.

Added a 6 guage jumper cable from the neg of the battery, to the engine & to the ground point on the firewall & onto the ground block behind the dash, all connected via jumper cables.

Car started 3/10 times but eventually got to where it won't start at all.

When it did start it would idle poorly, backfire, or just die.

Tacometer increases are revs increase, but not enough, For example it shows idle at about 500rpm, but then when I rev the engine up to what sounds like 3k rpm, it's only showing about 2k rpm.
Revving higher creates erratic backfiring.

Im extremely convinced this is an issue with the DME, but I'm so done pouring money into this car that I really want to just try and swap a DME in before buying one for 200$.

  
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OhioTom
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Re: Suspect DME died... Can anyone lend me a DME?(WI)
Reply #7 - Sep 28th, 2020 at 7:00pm
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PM me.....

I have one I can loan...

Will need it back thou..
  

Tom Simpson&&VW/Porsche freak.
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Dave W
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Re: Suspect DME died... Can anyone lend me a DME?(WI)
Reply #8 - Sep 30th, 2020 at 4:21pm
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A couple of other things to check that won't cost anything:
1. check if you accidently knocked a vacuum hose off.  But this usually causes surging idle rather than rough idle.
2. check if you forgot to reconnect the wires to the AFM.  easy to forget and causes engine to die if given any throttle.
3. check the j-boot for the usual tear on the bottom side of the first rib by the throttle body.  maybe you've moved something and opened up the tear.
4. inspect the speed/reference sensor connectors on the engine harness side.  Sometimes the problem is in there.
  

Dave - black 84 no longer exists. Sad 83 self destructed. All better now. Smiley
... Let's go hit some twisty roads! ...
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