Voltage drop at operating temp during idle cruise in my 7m

leftynridge

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So over the last several months I have been trying to diagnose the voltage drop that I'm experiencing at full operating temp at idle cruise. I'm currently running fic bluemax 1800cc injectors and they will only stay happy between 12.6 to approximately 14 volts. It becomes a serious problem when the voltage drops below 12.6 at wot. I originally started of by checking all my grounds. I have a 2ga ground strap from the head to the chassis. The battery has been relocated to the trunk and has 0ga ground strap from the battery to the chassis there. I decided to run a 4ga ground from the alternator to the block and additional 4ga power wire from the front fuse block main power source to the power distribution block that I have in the engine bay. I also replaced the 120amp ebay alternator for the 160amp alternator from supra store. Those 2 things seem to help but only mask the problem. The engine also has a brand new wiring harness. At this point I'm open to any possible ideas or suggestions. Has anyone had a similar problem?
 
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jetjock

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Idle cruise? And voltage drop is easily found by doing, wait for it, voltage drop testing. Now if you're complaining of low alternator output at idle that's a different story...
 

leftynridge

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While driving the vehicle at low rpm. It's even worse under boost. I have an aem so I can see the voltage drop and I have logs that I use as a reference. The alternator output is fine at idle. I did drop testing at idle on my power distribution block, the alternator, and battery. All came back fine.
 

3p141592654

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How about posting some data. How much drop do you see? Even the stock system shows some voltage drop at high injector pulse widths.
 

Zazzn

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i've always had low voltage like 11.x volts when at idle until i rev it up. Just though ti was normal because it happened on 7m/1j/2j
 

hvyman

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What are you tuning with? There should be a voltage/injection adjustment.
 

leftynridge

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How about posting some data. How much drop do you see? Even the stock system shows some voltage drop at high injector pulse widths.
I don't have any data as of right now but the fic bluemax injectors are very sensitive. The car would break up on anything below 12 volts. Which under wot I would expect a drop in voltage and then quickly jump back up. However, while driving around town I would see voltage drops of approximately 1.5 volts for no reason. It's almost like a surge that you would get from the fans coming on. After a while the alternator seemed to struggle with keeping up with the drop in voltage and the battery would slowly drop from 13.5. volts to sometimes 10.5 volts depending on how long I drove around. This is why I purchased another alternator from suprastore which is rated 160 amps hot. This should have been more then enough but the problem still is there. It has made a difference at the rate at which voltage drops but did not fix the problem.
 

leftynridge

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Even with battery voltage correction, if the voltage drops too low the deadtimes become unmanageable.
That is what was happening!

The alternator could not keep up with the problem. When the car was originally tuned it's was hooked up to a battery charger while on the dyno. It received a constant voltage even under wot. The problem didn't happen right away. Didn't start until maybe 3-4 months after being tuned.
 

Poodles

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So over the last several months I have been trying to diagnose the voltage drop that I'm experiencing at full operating temp at idle cruise. I'm currently running fic bluemax 1800cc injectors and they will only stay happy between 12.6 to approximately 14 volts. It becomes a serious problem when the voltage drops below 12.6 at wot. I originally started of by checking all my grounds. I have a 2ga ground strap from the head to the chassis. The battery has been relocated to the trunk and has 0ga ground strap from the battery to the chassis there. I decided to run a 4ga ground from the alternator to the block and additional 4ga power wire from the front fuse block main power source to the power distribution block that I have in the engine bay. I also replaced the 120amp ebay alternator for the 160amp alternator from supra store. Those 2 things seem to help but only mask the problem. The engine also has a brand new wiring harness. At this point I'm open to any possible ideas or suggestions. Has anyone had a similar problem?
Where is the AEM grounded? Not a fan of relocated batteries for a number of reasons, but this is one of them. Stock, the battery is grounded directly to the block, with your current setup it's going through the entire chassis (rust and all).

i've always had low voltage like 11.x volts when at idle until i rev it up. Just though ti was normal because it happened on 7m/1j/2j
Not normal (we went to alternators from generators for this exact reason)

That is what was happening!

The alternator could not keep up with the problem. When the car was originally tuned it's was hooked up to a battery charger while on the dyno. It received a constant voltage even under wot. The problem didn't happen right away. Didn't start until maybe 3-4 months after being tuned.
Given it didn't immediately happen, it's probably corrosion (if power to the injectors is your issue at all)

Datalogs would help immensely here...
 

leftynridge

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Poodles the AEM is ground to the intake manifold at the head.

Also when you said, "it's probably corrosion." What were you referring to. I have plans of cleaning both fuse blocks just for that reason to try and eliminate a possible source.

Also the battery is grounded to the strut tower in the rear. There is a ground from the head to the chassis. I've added a ground form the alternator to the block and additional ground from the the fuse block to the block.
 

Busted_Knuckles

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Run a voltage drop test. I had a similar problem with a voltage drop from the alternator to the battery, and managed to isolate it to bad fusible links and connectors.
 

leftynridge

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I've already tried a voltage drop test. Everything is good there. At least at idle it's good. Problem is only present while driving.
 

Busted_Knuckles

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A proper voltage drop test should have the suspect circuit loaded up and the engine running at 2000 rpm. I'd turn on everything, stereo, lights, electric fans if installed. Run it all full blast and run the test again. That's how I found the voltage dropping on mine across the fusible links between the fuse block and battery and fuse block and alternator. With the extra loading, the bad connections really show up.
 

atmperformance

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Poodles the AEM is ground to the intake manifold at the head.

Also when you said, "it's probably corrosion." What were you referring to. I have plans of cleaning both fuse blocks just for that reason to try and eliminate a possible source.

Also the battery is grounded to the strut tower in the rear. There is a ground from the head to the chassis. I've added a ground form the alternator to the block and additional ground from the the fuse block to the block.
cor·ro·sion (kə-rō′zhən)
a. The act or process of corroding.
b. The condition produced by corroding.
2. A substance, such as rust, formed by corroding.
electrolysis speeds this up, you can google that word if you don't know it.

I feel you have poor grounding points, try running a ground wire up to the block rather than on your strut tower.
as for your AEM ground find something better than your intake manifold which is having to pull all that current though bolts that might be coated in oil. your paper gaskets do not conduct electricity.

I'll be back to check up on the progress of this thread.
 

leftynridge

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A proper voltage drop test should have the suspect circuit loaded up and the engine running at 2000 rpm. I'd turn on everything, stereo, lights, electric fans if installed. Run it all full blast and run the test again. That's how I found the voltage dropping on mine across the fusible links between the fuse block and battery and fuse block and alternator. With the extra loading, the bad connections really show up.
Well I guess it's worth another shot. I'll try it tomorrow and let ya know what I come up with.
 

leftynridge

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cor·ro·sion (kə-rō′zhən)
a. The act or process of corroding.
b. The condition produced by corroding.
2. A substance, such as rust, formed by corroding.
electrolysis speeds this up, you can google that word if you don't know it.

I feel you have poor grounding points, try running a ground wire up to the block rather than on your strut tower.
as for your AEM ground find something better than your intake manifold which is having to pull all that current though bolts that might be coated in oil. your paper gaskets do not conduct electricity.

I'll be back to check up on the progress of this thread.
This issue has only been resent. The ground locations have been the same for the last 2 years or so with no problems. I've actually added grounds since the issue. Only thing that has changed is that the car is making more power then before. But i would agree the grounds could be in a better locations. There are few things that I'm going to try that won't cost me any money . 20ft of 0 gauge wire isn't cheap.