wire harness to ECU connection

[GregWeld]

Just my quick 2 cents ====



ECU's etc aren't made to run pumps --- THEY MUST BE connected to a RELAY to run the pump. 9.8V is more than enough to run a relay....


I didn't go back to read the thread so maybe this isn't even worth mentioning...

[GregWeld]

Sorry Dale -- Went back to look at the thread and see you're running to a controller / relay.... so my info is useless! Normal for me, I know.


Just to be sure -- is that pin out 12V POSITIVE or NEGATIVE --- lots of times people fail to see these are ground outputs (or actually that they just go to ground)... So again - I know it USED to work -- but just tossing out stuff to look for.

[DaleTx]

Originally Posted by Sieg

Sounds like you'll be in the garage this weekend? I might get a wild hair and give you a call.

I will be home Saturday afternoon and most of the day Sunday. Call to make sure I'm here... if you get the wild hair

Originally Posted by GregWeld

Sorry Dale -- Went back to look at the thread and see you're running to a controller / relay.... so my info is useless! Normal for me, I know.


Just to be sure -- is that pin out 12V POSITIVE or NEGATIVE --- lots of times people fail to see these are ground outputs (or actually that they just go to ground)... So again - I know it USED to work -- but just tossing out stuff to look for.

Greg... I appreciate you tossing stuff out. My controller outputs to the fan relay, and the fault light are both negative outputs.

[GregWeld]

Sounds to me you might have isolated the issue already.... unless I'm just all messed up. Which is usually the case.


The ECU pin out is NEGATIVE -- so it doesn't actually put out any "voltage" -- it just goes to ground - thus grounding the relay actuating it. The relay would have a big gauge wire ground - big gauge load positive - ignition 12V positive - and a ground. In this case the ground would go to the ECU...

correct me if I'm wrong -- so then the RELAY operates some kind of pump controller??? Or does the pump "controller" run the relay??

It's so hard to troubleshoot without a schematic to follow so I'm just picturing in my head - your particular set up and I'm unfamiliar with the Vaporworks (other than I know Carl and he and his stuff are GREAT!).

[DaleTx]

Originally Posted by GregWeld

Sounds to me you might have isolated the issue already.... unless I'm just all messed up. Which is usually the case.


The ECU pin out is NEGATIVE -- so it doesn't actually put out any "voltage" -- it just goes to ground - thus grounding the relay actuating it. The relay would have a big gauge wire ground - big gauge load positive - ignition 12V positive - and a ground. In this case the ground would go to the ECU...

correct me if I'm wrong -- so then the RELAY operates some kind of pump controller??? Or does the pump "controller" run the relay??

It's so hard to troubleshoot without a schematic to follow so I'm just picturing in my head - your particular set up and I'm unfamiliar with the Vaporworks (other than I know Carl and he and his stuff are GREAT!).

Greg... I don't know all the details of how Carl's digital fuel pump controller works, but I'll try to explain it. One 12 volt + input wire with a 25 amp fuse goes from the battery to the digital controller. One 12 volt + input from the ECM "fuel system relay arming source" goes to the digital controller "signal conditioning module"... and one ground wire goes from the chassis to the digital controller.

When the key is on... the digital controller then puts out whatever voltage is required to run the fuel pump and maintain the desired preset fuel pressure. My pump runs in the range of about 7-12 volts to maintain a fuel system pressure of 58 psi..

You do have to be careful when wiring devices to the ECM. Some pin outputs are negative and some are positive. My fuel system relay arming source was positive. The best bet is to get a schematic like you said.


I was finally able to get the car running today after 2 days of trouble shooting!! The problem was a bad ground. There is main ground for the ECM that is grounded at the back of the engine block next to the head. The bolt securing the ground was tight.... but it turned out the bolt had bottomed out in the hole before the ground connection was completely tight. I cut 1/8" off the end of the bolt... and then re-tightened the connection and that solved the problem. The voltage output from the ECM to the "signal conditioning module" went from 9.8 to 12 volts!!

It was not obvious that the connection was loose... so I feel very lucky that I was able to solve the problem. It's great to be up and running again

[GregWeld]

AH HA!!!



I like discussions like this just because I learn something.


I've always found wiring to be just like a motor --- basics --- fuel/air/spark...


Wiring always seems to come down to voltage/connection/grounds....


So I'm going to assume that Carls/Vaporwork controller is PWM (pulse width modulator)?? Where it really doesn't drop the voltage -- but rather, modulates the 12V to reduce pump speed... which saves the pump in the long run...

Or does it reduce voltage to the pump (which in my ever so humble opinion isn't a good way to run electric motors...) Which is why I would assume it's PWM based.


Glad you got it! Because these kinds of little issues can be really "trying". Amazing how nothing more than a bad ground can keep your car from running!

[Ron in SoCal]

Correct Greg, it's PWM controlled.

[CarlC]

Yup, closed loop PWM control. When using the ECM output the controller mimics what the ECM would see in a traditional system, hence all of the safety features remain. The power requirements to turn on the system are less than a relay, so there's no ECM overload concerns.

For some reason GM ECM fuel pump output is BAT+.

[Sieg]

The car appears to be working well. Dale met me in Wilsonville for lunch today and made it home with no issues.

The car in person is awesome! All business and well thought out with great attention to functional detail. That 427 revs quick right off idle and sounds great.

[DaleTx]

Originally Posted by GregWeld

AH HA!!!

Wiring always seems to come down to voltage/connection/grounds....

Exactly right... with the LS engines the wire connections and grounds are absolutely critical! I think a volt meter and some type of device that plugs into the OBDII port for reading codes is a must for diagnosing problems on the LS engines.

In my case there were no codes... so the problem was a bit more difficult to diagnose. I used a volt meter and found that the voltage to the fuel pump trigger was low. After two days of checking connections I found out the problem was a bad ground connection between the ECM and engine block.


Here is a shot of the ECM ground connection at the back of the engine next to the passenger side head. The problem I had was the bolt bottomed out in the hole before the ground was completely tight. The connection was tight but when I pushed on the wire hard I could move it. Another 1/8 turn on the bolt and there would not have been a problem




I ended up cutting 1/8" off the length of the bolt and then re-tightened, and this solved the low voltage problem. I also used star washers and some loctite on the bolt to prevent loosening of the ground connection.






Problem solved... thanks for the star washers Sieg.