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Old 01-14-2012, 07:23 PM   #1
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Unhappy Intermittent power problem

Having a problem with my car.

I have an intermittent issue where tach drops, ems loses power, and injectors stop firing. Happens for a split second and then all is ok. If i am idling it is enough to make the motor shut off.

Any ideas on how to troubleshoot this? Im thinking it has to be impacting either a main power feed or the ems power since the ems goes offline.

Sad.
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Old 01-14-2012, 07:54 PM   #2
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You've been ------- around with the motor, right? Did you double check all your grounds are good when you put it back in?

I'd assume you checked the basics, but, this is Faeflora so obviosuly it makes sense to ask...a list of what you've checked so far ?
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Old 01-14-2012, 08:10 PM   #3
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Quote:
Originally Posted by EunosBen View Post
You've been ------- around with the motor, right? Did you double check all your grounds are good when you put it back in?

I'd assume you checked the basics, but, this is Faeflora so obviosuly it makes sense to ask...a list of what you've checked so far ?
Checked ground strap from tranny to engine bay
Grounds off harness onto intake
Battery negative and positive terminal
Alternator battery bolt and connector
Cam and cas sensor
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Old 01-14-2012, 08:43 PM   #4
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Fae, I know you've been messing with relays. Relays have a NASTY property. When they are turned off, they act just like an ignition coil and can send megaVolts through your wiring. This will do things like reset your ECU, make your tach go to zero, etc.

The term for this is "flyback voltage." The way to combat it is by putting a diode across the relay's coil to dissipate the voltage. I recommend that you carefully review any relays you may have touched/added and evaluate whether you need to add this protection. You'll recall that I talked about this on your build thread.

There's a good explanation of flyback voltage on Wikipedia, btw.
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Old 01-14-2012, 09:54 PM   #5
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Hmm i have read about that.

Heres what i did with my relays:

Take the switched 12v coming off my factory fuel relay and use it to trigger my bigun relay that is connected directly to my battery.
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Old 01-14-2012, 10:32 PM   #6
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Does that relay come on with the ignition switch and just stay on, or does it cycle?

Any others? For example, what is turning on your WI?

If you can get a good log of the event, it might help diagnose. Basically, where you see the event, analyze the conditions and see if the ECU would be turning anything on or off around that point.
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Old 01-14-2012, 11:06 PM   #7
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Another thought, if you can run your fuel pump off your stock relay for awhile, remove the bigun and eliminate that variable.
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Old 01-14-2012, 11:34 PM   #8
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Not turning on with my WI. was actually happening before i pulled mu motor and was on stock relay :(
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Old 01-15-2012, 04:43 AM   #9
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Definitely a cam or crank sensor. The fact that the tach drops to zero is the key here. If you are connected with the lappy toppy to the Hydra, do you lose comms?
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Old 01-15-2012, 05:50 AM   #10
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I just remembered that when I first got my car, it used to do exactly what you describe when under a hard launch from a standstill. I never did anything to fix it, it just stopped doing it eventually. However, the car had stood for a significant amount of time prior to my ownership (6 months+) so perhaps there was water ingress somewhere that went away once the under bonnet temps saw a few heat cycles.

Not much help I know, but it may assist your diagnosis. Bear in mind at this point the car was pretty much bone stock.
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Old 01-15-2012, 11:25 AM   #11
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Quote:
Originally Posted by Reverant View Post
Definitely a cam or crank sensor. The fact that the tach drops to zero is the key here. If you are connected with the lappy toppy to the Hydra, do you lose comms?
Yes i do lose comms.

Log shows all sensors dropping the minimum values.

Last edited by Faeflora; 01-15-2012 at 11:51 AM.
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Old 01-15-2012, 11:29 AM   #12
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Originally Posted by Faeflora View Post
Not turning on with my WI. was actually happening before i pulled mu motor and was on stock relay :(
Roger that. I thought that this just started happening. Sorry for the wild goose chase.
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Old 01-15-2012, 01:22 PM   #13
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Here's a log that shows some weirdness.

Attached as an .xls file because I highlighted two rows of freakout. One has sensors take a ---- and the next has RPM freak out.
Attached Files
File Type: xls wtfyarghgha.xls (51.0 KB, 89 views)
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Old 01-15-2012, 04:46 PM   #14
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You have high voltage spikes. Check grounds and all parts of the ignition system.
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Old 01-15-2012, 04:52 PM   #15
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Def not a crank/cam problem then. Does it happen often enough so that you can probe the +12V supply with a DMM?
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Old 01-15-2012, 05:18 PM   #16
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Also, think back and try to remember what you did to the car just before this started happening.
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Old 01-15-2012, 05:39 PM   #17
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Quote:
Originally Posted by Faeflora View Post
Having a problem with my car.

I have an intermittent issue where tach drops, ems loses power, and injectors stop firing. Happens for a split second and then all is ok. If i am idling it is enough to make the motor shut off.

Any ideas on how to troubleshoot this? Im thinking it has to be impacting either a main power feed or the ems power since the ems goes offline.

Sad.
EDIT, NM. delete please.
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Old 01-16-2012, 02:04 PM   #18
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Had a similar problem that only manifested at AutoX events and turned out to be a loose battery clamp which allowed the battery to move and grounded the +ve terminal to the clamp under hard acceleration.

Also, had a Main Relay go bad and just before it failed for good it gave intermittent power loss.
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Old 01-16-2012, 03:29 PM   #19
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Quote:
Originally Posted by hornetball View Post
Also, think back and try to remember what you did to the car just before this started happening.
Pull the engine and transmission out It was actually happening before that too, just not as often. I did also mess with the wiring under the dash which is a real rats nest. Hmm.

Quote:
Originally Posted by Reverant View Post
Def not a crank/cam problem then. Does it happen often enough so that you can probe the +12V supply with a DMM?
Yes, it does. What should I look for when probing?


Quote:
Originally Posted by BarbyCar View Post
Had a similar problem that only manifested at AutoX events and turned out to be a loose battery clamp which allowed the battery to move and grounded the +ve terminal to the clamp under hard acceleration.

Also, had a Main Relay go bad and just before it failed for good it gave intermittent power loss.
Hmm argh. Yes the same thing happened to me before too.

I guess I need to check ALL ground and hot wires that could be rubbing somewhere :(((((
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Old 01-16-2012, 03:41 PM   #20
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Quote:
Originally Posted by Faeflora View Post
Yes, it does. What should I look for when probing?
Look for the 12V line going nuts (high/low) when the problem happens. Then the ground. Then the 5V line.
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