Jump to content



Weak injector pulse


  • Please log in to reply
42 replies to this topic

#1 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 22 March 2017 - 01:49 PM

I'm having a crank no start issue replaced the injector clips cleaned the injectors engine is rebuilt have 40 psi fuel pressure when cranking I put a noid light on the primary injector clip the light barely comes on im pretty sure that's my problem it's starts right up on either what would cause a weak pulse and how do I fix it





#2 Turbo Cary

Turbo Cary

    Established Member

  • Members
  • PipPipPip
  • 1,420 posts
  • Gender:Male
  • Location:Charleston, South Carolina
  • Model:Conquest

Posted 22 March 2017 - 05:50 PM

The ECU controls the ground side of the circuit. High resistance in the injector circuit can cause grounding issues. Did you solder the wires when redoing the injector clips?

Also check the grounds for your ECU, intake manifold, and make sure you are getting a full 12v going to the injector itself.

Is it just low power during cranking or is it not running at all?

#3 Chad

Chad

    noob

  • Moderators
  • PipPipPipPip
  • 9,094 posts
  • Gender:Male
  • Location:Lincoln City Oregon
  • Interests:Starquest Fanatic
  • Model:Conquest

Posted 22 March 2017 - 06:45 PM

The injectors are grounded to fire, and supplied constant +12 volts.  The ground is pulse width modulated, not just a simple ground.  Putting a lamp across the leads when duty cycle is only 25% would have an RMS equivalent of only 3 volts (voltage averaged @ 25%).

Verify good constant current when ignition is on.  If good, ground the other lead to a good ground, that should fire the injector as long as you hold it grounded.  It should dump fuel if the pump is running.

There is also a resistor pack on the radiator core support under the air box, check connections there, but that's not a common fail item.  They should measure about 3 ohms each lead to the common lead.

#4 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 22 March 2017 - 07:09 PM

It's not running at all I made sure it was getting good cranking power thought the might be it but even when jumped to my Jeep it made no difference unfortunately I butt connected them my cars in storage with no power the last ones were also butt connected and it was running a week ago I removed the fuel rail to tap it for a pressure tester adapter and installed two new injector clips I even tried changing them with other ones in case the clips were bad I haven't checked the ECU ground yet but that's next I have put a noid light on it before and the light was much brighter this looks like a flashlight with all but dead batteries

#5 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 28 March 2017 - 02:19 PM

Checked for power at the injector which is good grounded the primary it clicked the engine tried to start checked continuity between the injector connector and the pin at the ECU which is good has my ECU gone bad

#6 Turbo Cary

Turbo Cary

    Established Member

  • Members
  • PipPipPip
  • 1,420 posts
  • Gender:Male
  • Location:Charleston, South Carolina
  • Model:Conquest

Posted 28 March 2017 - 08:33 PM

What was the measured voltage at the injector?

Did you do a resistance check on your injector resistor box?

I had an ECU go bad due to a leaky heater core. It ran down the under glove box panel and onto my ECU connector. That's the only instance I have ever had of a SQ ECU failing. I know that the 3000GTs have issues where capacitors on the board burst causing ECU failure.

Do you also have spark? Have you checked ignition coil resistance and made sure it had battery voltage at the ignition coil?

Lastly just because the injector clicked when you activated it does not mean the injector is good. Check injector resistance. I would also try swaping the injector connections and see if it will spray fuel from the secondary injector.

#7 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 29 March 2017 - 02:57 PM

When I ground out the wire that goes to the ECU from the injector the noid light goes bright but I have 6 ohms between each leg and common on the resistor i have 11.5 volts to the injector and they're only about two years old

#8 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 29 March 2017 - 02:57 PM

I have spark it fires right up on either

#9 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 07 April 2017 - 03:01 PM

Changed the computer same problem also changed the distributor still still has a weak pulse the only thing left is the resistor box anything else? Also put another new connector on and tried putting it on the secondary

#10 scott87star

scott87star

    Technically Challenged, Daily.

  • Vendors
  • PipPipPip
  • 4,798 posts
  • Gender:Male
  • Location:Mandan, NORTH DAKOTA
  • Interests:Freezing, thawing, thunderstorms and constant wind.
  • Model:Starion

Posted 07 April 2017 - 06:25 PM

It's not the ECU, they rarely fail.  No such thing as a weak pulse, if you see a pulse it's trying to fire the injectors.  It may be weak looking because of crappy wiring job but if it's pulsing at all then the ECU is doing it's job, you have to fix whats in between.
Now selling true plug and play megasquirt!  Absolutely the best value in stand alone ECU's out there.

I can upgrade your Fuel Injection Pro firmware

Performance Coatings!  Pistons, manifolds, bearings and more!

Now a graduate of EFI University!  www.efi101.com

ECU Vendor link:  http://www.starquest...howtopic=137426

#11 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 07 April 2017 - 06:52 PM

Ok well I've verified the circut is good between the injector and ecu the only thing left between them is the resistor right?

#12 Chad

Chad

    noob

  • Moderators
  • PipPipPipPip
  • 9,094 posts
  • Gender:Male
  • Location:Lincoln City Oregon
  • Interests:Starquest Fanatic
  • Model:Conquest

Posted 07 April 2017 - 07:34 PM

They shoudl be 2.5 to 3 ohms each channel, there are 2 with a common lead.  2 wires are the individual channels, and one is the common.

#13 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 10 April 2017 - 11:29 AM

Ya I got six ohms on each

#14 Turbo Cary

Turbo Cary

    Established Member

  • Members
  • PipPipPip
  • 1,420 posts
  • Gender:Male
  • Location:Charleston, South Carolina
  • Model:Conquest

Posted 12 April 2017 - 05:19 AM

View Post88turboquest, on 10 April 2017 - 11:29 AM, said:

Ya I got six ohms on each

If you have 6 ohms on each wire that is double the resistance causing less current to make it to the injector. Think of like there being a kink in a garden hose with the injector being a spray nozzle. If you needed X amount of water to come out, but there is a kink less water will come out.

I would recommend running new injector wires for the whole fuel injector circuit. You could have corrosion or short to ground somewhere. Use the FSM and redo the wiring to match the original layout.

#15 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 16 April 2017 - 09:26 AM

I think you're right I replaced the resistor same issue tried cleaning all the grounds i think I'm going to have to run new wires from the ECU

#16 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 16 April 2017 - 11:04 AM

Ran a wire from the resistor to the injector and from the injector to the ECU still same problem I'm guessing​ the ECU ground is corrodied in the harness some where should I cut the two grounds on the ECU tie them to a new wire and rub them to the ground on the battery?

#17 Turbo Cary

Turbo Cary

    Established Member

  • Members
  • PipPipPip
  • 1,420 posts
  • Gender:Male
  • Location:Charleston, South Carolina
  • Model:Conquest

Posted 17 April 2017 - 05:59 PM

View Post88turboquest, on 16 April 2017 - 11:04 AM, said:

Ran a wire from the resistor to the injector and from the injector to the ECU still same problem I'm guessing​ the ECU ground is corrodied in the harness some where should I cut the two grounds on the ECU tie them to a new wire and rub them to the ground on the battery?

I think Chad was saying that each injector itself is supposed to be 2-3 ohms. I asked if you had gotten 6 ohms on the wires. That is my bad. Any wire should have less than 2 ohms of resistance for it to work properly. Ideally less than 1 ohm.

The resistor box itself also has specific ratings for how much it should ohm out to.

You could have bad injectors, a bad resistor box (unlikely as I haven't ever seen a bad one unless someone else has), or a wiring issue.

Like stated before the ECU controls the grounds. Meaning the ground circuit for the injectors goes directly to the ecu. You can always run new wires from the injector clips behind the motor and inside the car. Then run a crimp splice and see if it fixes the issue. If it fixes your concern you'll know that there was high resistance in the ground circuit for the injectors and then clean up the wire install. Otherwise you'll have to look at other possible failures.

Edited by Turbo Cary, 17 April 2017 - 06:03 PM.


#18 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 19 April 2017 - 03:16 PM

I ohmed out the resistor box and got 6 ohms between each wire and common haven't done injectors it's getting some fuel I pulled the ovcp and had someone crank the motor it's just not enough to run just sputters and dies I'm starting to think it's the TPS since I have replaced everything else and ran new wires

#19 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 20 April 2017 - 07:20 PM

The injectors have 2.6 ohms each I took a video of the noid light while cranking

https://youtu.be/xLBzbcDW33M

#20 88turboquest

88turboquest

    Member

  • Members
  • PipPip
  • 122 posts
  • Location:connecticut

Posted 20 April 2017 - 07:20 PM

The injectors have 2.6 ohms each I took a video of the noid light while cranking

https://youtu.be/xLBzbcDW33M




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users