wire harness to ECU connection
 

I am having a problem with the connection between my wire harness (red and blue) connectors and my GM ECU. I have 12 plus volts going into the ECU but the output lead from the ECU to the fuel pump measures only 9.8 volts. My fuel pump won't turn on with the low voltage, and the car won't start.

I suspect that I have a bad connection between the wire harness and the ECU. What can I do to improve the connection? The wire harness has been plugged in and unplugged several times and I think the connections are a bit loose now. The engine is a GM LS2 with a GM ECU.

I am looking for Ideas on how to restore a good connection between the wire harness (red and blue connectors) and the ECU. Thanks.

Do you have that 9.8v lead going to the pump directly or to a relay? pictures please.

You can pull each pin out and carefully compress them with pliers.

I am running a Vaporworx DC controller and a GM CSTV fuel pump. I have one 12V connection directly from the battery to the 12V input on the DC controller, and a second "switched" 12V connection that goes from the ECU to the second "switched" input on the DC controller. Normally when I turn the key on you can hear the fuel pump turn on.

Yesterday when I tried to start the car... the fuel pump would not turn on. The trigger wire from the ECU measured only 9.8V. Next... I rigged up a switch from the battery with a full 12 volts and connected it to the DC controller and the fuel pump turned on... so I know the DC controller and fuel pump are working.

I think there must be a bad connection between the wiring harness and ECU. The voltage going into the ECU measures 12.5V. I'll try crimping the female connectors like you said and see if that fixes the problem. Is there some kind of gel or spray that you use on the connection that prevents corrosion or do you put them together dry?

Thanks Vince!

Thanks Sieg... I'm going to make sure all the pin connections from the wire harness to ECU are good... and then use some of the dielectric lube on the connection to prevent future corrosion.

If this does not solve the low voltage problem... then I will have to go through each leg of the wiring harness to make sure there is not a short somewhere. The computer control engines are great when everthing is working properly, but not so good when things go wrong.

:hairpullout:

Dale,

What about crimping a new terminal on to the wire that goes into the harness? I have some for the older Gen3/24T ECM's. I don't know if they work for the later Gen4.

There is very little power needed to turn on the VaporWorx controller. Less than a relay.

I just re-wired the whole car for the exact reason you mentioned. I hate things like this.

Thanks Carl.

I am also using a Gen3 24T/ECM. The VaporWorx digital controller will not turn on the fuel pump with only 9.8 volt input from the ECM. When I supply 12 volts to the digital controller the fuel pump does turn on, and maintains the correct fuel pressure. I know there is no problem with the VaporWorx controller or CTSV fuel pump... it's something else.

This weekend I will check all the power supply connections, ground connections, and the terminal connections between the wiring harness and ECM. Hopefully it will be something simple. It's a learning experience... at some point I may rewire the car like you did. Right now my car has a combination of old and new electrical circuits.

We'll see how long that lasts.........:whistling:

Having the confidence of knowing the car will fire and fuel properly 99% of the time is a priority!

It just never ends...does it! Lol.

:sieg:

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

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...

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.

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 :thumbsup:

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

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 :relax:

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!

Correct Greg, it's PWM controlled.

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+. :headscratch:

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

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.

http://photos.smugmug.com/photos/i-7...7whhLZH-XL.jpg

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 :headscratch:

http://i1048.photobucket.com/albums/...ps0ca45fc4.jpg


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.

http://i1048.photobucket.com/albums/...ps6bc7956e.jpg

http://i1048.photobucket.com/albums/...ps78a5c71c.jpg


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

Star washers should be used to "cut thru paint" etc --- rather than a "split ring washer" that is used to keep a bolt/nut from backing off....

They should also be used to keep two pieces from rotating - so put between say a leg of a table and it's base - it would help to keep the leg from moving.

As such -- a STAR washer should be used between the electrical connector and the body to which it's being attached. Or between two parts that you want to keep from moving. Used that way - the star washer will cut into the metal and make a good connection. Or cut into to two surfaces and provide "grip". Once used - they should be tossed and a new one used because they flatten and loose their cutting ability.

I sound like mister washer expert the way I wrote the above but it's hard to explain it any other way. And here's the weird part -- I can't even remember why I know this stuff in the first place!! HAHAHAHAHAHAHA

What I'd like to figure out is why some star washers have the "star" on the outside edge vs the inside!! And my only conclusion is "surface area"?? Therefor holding ability??


So glad you found this problem Dale! I use the back of SBC heads for a ground source and the blind holes in some of them are quite shallow -- so I too have had to shorten a bolt in order to not bottom it out. That and it makes it easier to install and remove when it's so tight to the firewall in some applications.

Leave to Mr. Microscope to point out the finite details. :D :thumbsup:

What I've learned is to dry fit the bolt, if it doesn't bottom without washers or connectors, one issue addressed.