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Won't run unless I pull the fuel pump fuse

Old 09-27-2018, 10:53 PM
  #16  
GPA951s
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FYI I had and issue one time with another vehicle (GM) and had the exact same issue... It was flooding out, I would un-plug the fuel pump, get it started...... then re-connect (quickly) and stumble home... Turns out it was the TEMP sensor, when it went bad the computer defaulted to full rich, Apparently General motors doesnt want their customers to walk home when its 10 below zero... But they are fine with you walking home when its hot out... Not saying thats your issue but it might be worth it to Either toss another one in or "Fool" it for diagnostic reasons. Im Sure you can find out ... Now that I am writing this I do recall that I found the Temp/Ohms scale somewhere. If memory serves I believe there are two in our cars, one if for the dash gauge or your M Tune has a Temp Function that lost signal.(Not Familiar with M tune.. HTH..- G s
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Old 10-01-2018, 07:27 PM
  #17  
Jacob AbuKhader
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Originally Posted by GPA951s View Post
FYI I had and issue one time with another vehicle (GM) and had the exact same issue... It was flooding out, I would un-plug the fuel pump, get it started...... then re-connect (quickly) and stumble home... Turns out it was the TEMP sensor, when it went bad the computer defaulted to full rich, Apparently General motors doesnt want their customers to walk home when its 10 below zero... But they are fine with you walking home when its hot out... Not saying thats your issue but it might be worth it to Either toss another one in or "Fool" it for diagnostic reasons. Im Sure you can find out ... Now that I am writing this I do recall that I found the Temp/Ohms scale somewhere. If memory serves I believe there are two in our cars, one if for the dash gauge or your M Tune has a Temp Function that lost signal.(Not Familiar with M tune.. HTH..- G s
Yeah I hear ya. One of the first things I replaced was the TEMP sensor. So thatís brand new.

tested my fuel pressure and itís within spec (37.5 psi with the pump jumpered) cranking with fuse in builds pressure into low 30s high 20s so itís normal. Gonna get injectors sent out soon here. Was there ever a solution found by OP?

Ive determined that the wiring for the pump is fine there is no shorting or anything like that. Iíve got a sick feeling in my stocmach that if the injector service doesnít take care of this issue itís going to be piston rings. Iím skeptical because the car does and has run perfectly. I donít want to continue to highjack this thread though so hereís the link to the one I started.

https://rennlist.com/forums/924-931-...-issue-12.html

Last edited by Jacob AbuKhader; 10-01-2018 at 07:43 PM.
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Old 10-03-2018, 01:15 AM
  #18  
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Originally Posted by Jacob AbuKhader View Post


Yeah I hear ya. One of the first things I replaced was the TEMP sensor. So thatís brand new.

tested my fuel pressure and itís within spec (37.5 psi with the pump jumpered) cranking with fuse in builds pressure into low 30s high 20s so itís normal. Gonna get injectors sent out soon here. Was there ever a solution found by OP?

Ive determined that the wiring for the pump is fine there is no shorting or anything like that. Iíve got a sick feeling in my stocmach that if the injector service doesnít take care of this issue itís going to be piston rings. Iím skeptical because the car does and has run perfectly. I donít want to continue to highjack this thread though so hereís the link to the one I started.

https://rennlist.com/forums/924-931-...-issue-12.html
Did you replace the correct temp sensor? The one with the two spade connectors is for the dash gauge only-----the adjacent temp sensor with the blue plastic connector housing is the NTC sensor for the DME.

Otherwise this sounds like a fuel injector is stuck open.
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Old 10-03-2018, 01:21 AM
  #19  
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Originally Posted by Droops83 View Post
Did you replace the correct temp sensor? The one with the two spade connectors is for the dash gauge only-----the adjacent temp sensor with the blue plastic connector housing is the NTC sensor for the DME.

Otherwise this sounds like a fuel injector is stuck open.
yes itís the correct sensor. Blue top that threads into block with fuel injector type connector.

All four of my plugs are caked in carbon
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Old 10-03-2018, 02:49 AM
  #20  
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Originally Posted by Jacob AbuKhader View Post


yes it’s the correct sensor. Blue top that threads into block with fuel injector type connector.

All four of my plugs are caked in carbon

OK. Something this drastic means that either a fuel injector or multiple injectors are physically jammed open, or the DME is bad or something else (short to ground in wiring harness) is causing them to get a ground signal all the time, which would also make them stick open.

The latter is easy to verify. Turn the ignition on and see if there is continuity to ground on the ground side of the injector connectors.
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Old 10-03-2018, 02:06 PM
  #21  
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Okay so I pulled the fuel rail and pulled all 4 injectors. One at a time I connected them directly to the battery. All 4 open and close. They shot out whatever tiny bit of gas was in them. Obviously werenít pressurized so I canít accurately tell you if the spray pattern is good.

Per your short to ground testing on the wiring harness instructions, with ignition on I have continuity at all four injector harness plugs.

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Old 10-03-2018, 03:57 PM
  #22  
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Originally Posted by Jacob AbuKhader View Post
Okay so I pulled the fuel rail and pulled all 4 injectors. One at a time I connected them directly to the battery. All 4 open and close. They shot out whatever tiny bit of gas was in them. Obviously weren’t pressurized so I can’t accurately tell you if the spray pattern is good.

Per your short to ground testing on the wiring harness instructions, with ignition on I have continuity at all four injector harness plugs.


The fuel injectors should always have +12V on the power side when the ignition is on. The ground side is switched by the DME. If you have a solid ground signal at the ground pin of each injector connector with key on, engine off, then either the DME is shorted internally or there is a short in the wiring harness. Again, easy to tell which. If the ground signal goes away when the DME is unplugged, then the DME is faulty. If the ground stays, you've got a short in the harness, which may not be so easy to find!
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Old 10-03-2018, 05:14 PM
  #23  
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Okay we are on to something here.

I have 12 volts at battery.

With DME plugged in, ignition on engine off I get continuity (zeroed our reading and beep from meter) at all 4 harness plugs and I get 7 volts when I connect the power to the ground on the back of the firewall.

With DME disconnected key on, ignition on, engine off

I no longer have continuity (OL reading on meter) at any of the four injector harness plugs and I no longer get any voltage reading at all when I measure the power side of the harness plug and the firewall ground.

So if im understanding you correctly, there must be an issue with the DME correct?
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Old 10-03-2018, 11:20 PM
  #24  
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Jacob,

I believe Chris is talking about the *ground* pin of the fuel injector connector, not the power pin. I don't believe he means the harness has +12V at all times on the power pins if DME disconnected; but if the ground side is showing 12V at any time (key on but engine not running), then you have a problem.

You should only be checking the injector ground pins and if you see 12V, check DME plugged / unplugged to figure out if it's DME or wiring.
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Old 10-03-2018, 11:35 PM
  #25  
Jacob AbuKhader
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Originally Posted by Dan Martinic View Post
Jacob,

I believe Chris is talking about the *ground* pin of the fuel injector connector, not the power pin. I don't believe he means the harness has +12V at all times on the power pins if DME disconnected; but if the ground side is showing 12V at any time (key on but engine not running), then you have a problem.

You should only be checking the injector ground pins and if you see 12V, check DME plugged / unplugged to figure out if it's DME or wiring.
okay so maybe I tested wrong. Just to be completely clear,

when testing continouity i set the multi meter to resistance.
I plugged both test leads into both pins on the injector pins.

With DME ignition on I got all zeros and tone, which indicates continouity correct?

Under same testing conditions this time with DME unplugged I got OL and no tone.

When i tested for voltage, I plugged the red lead into the positive plug on the injector harness and the negative lead to that ground point on the firewall, just to ensure thereís power in the harness. Again I donít know if 7 volts is okay but thatís what I got. thatís how I got my voltage reading. Am I plugging in the test leads incorrectly?

Im not sure if the pins get 12V with the DME unplugged, I donít see how they could since essentially each injector plug is a positive and a ground that both plug directly into the DME so the fact that Iím not getting any voltage with the DME unplugged should be normal. I think if I was seeing voltage with the DME unplugged that would indicate a harness short somewhere am I correct in that thinking?

Let me know and Iíll go back and retest properly

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Old 10-03-2018, 11:47 PM
  #26  
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"when testing continouity i set the multi meter to resistance."

Nope--continuity is a little symbol like this and the result is a beep:



And you don't check continuity between the two pins anyway.

"I plugged both test leads into both pins on the injector pins."

Why? One injector pin is fed power +12V and the other is grounded (by the DME--a different connection)

"With DME ignition on I got all zeros and tone, which indicates continouity correct?"

How do you get "tone" with your VOM set to resistance?

"Under same testing conditions this time with DME unplugged I got OL and no tone."

With DME unplugged, there's no way those two pins have a signal travelling through the DME and back

"When i tested for voltage, I plugged the red lead into the positive plug on the injector harness and the negative lead to that ground point on the firewall, just to ensure there’s power in the harness. Again I don’t know if 7 volts is okay but that’s what I got. that’s how I got my voltage reading. Am I plugging in the test leads incorrectly?"

I think so. You can just touch the neg lead to any good ground point ex. intake manifold, bolt attached to body, etc

"Im not sure if the pins get 12V with the DME unplugged, I don’t see how they could since essentially each injector plug is a positive and a ground that both plug directly into the DME so the fact that I’m not getting any voltage with the DME unplugged should be normal. I think if I was seeing voltage with the DME unplugged that would indicate a harness short somewhere am I correct in that thinking?"

Yes, that is what Chris is suggesting. You still haven't checked if the *ground* pin has voltage with key on, DME plugged in.

PS. Have you replaced your ignition wires? Tested your coil? Looked at your cap?
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Old 10-04-2018, 01:40 AM
  #27  
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Originally Posted by Dan Martinic View Post
"when testing continouity i set the multi meter to resistance."

Nope--continuity is a little symbol like this and the result is a beep:



And you don't check continuity between the two pins anyway.

"I plugged both test leads into both pins on the injector pins."

Why? One injector pin is fed power +12V and the other is grounded (by the DME--a different connection)

"With DME ignition on I got all zeros and tone, which indicates continouity correct?"

How do you get "tone" with your VOM set to resistance?

"Under same testing conditions this time with DME unplugged I got OL and no tone."

With DME unplugged, there's no way those two pins have a signal travelling through the DME and back

"When i tested for voltage, I plugged the red lead into the positive plug on the injector harness and the negative lead to that ground point on the firewall, just to ensure thereís power in the harness. Again I donít know if 7 volts is okay but thatís what I got. thatís how I got my voltage reading. Am I plugging in the test leads incorrectly?"

I think so. You can just touch the neg lead to any good ground point ex. intake manifold, bolt attached to body, etc

"Im not sure if the pins get 12V with the DME unplugged, I donít see how they could since essentially each injector plug is a positive and a ground that both plug directly into the DME so the fact that Iím not getting any voltage with the DME unplugged should be normal. I think if I was seeing voltage with the DME unplugged that would indicate a harness short somewhere am I correct in that thinking?"

Yes, that is what Chris is suggesting. You still haven't checked if the *ground* pin has voltage with key on, DME plugged in.

PS. Have you replaced your ignition wires? Tested your coil? Looked at your cap?
Dan thanks for the info helped a lot I was lost. I was infact using the right setting. So that was correct.

I retested everything correctly this time. Hereís what I got. Picture is for orientation.



Terminal on the left gives me 11 volts DME plugged in or disconnected. Doesnít matter.
Terminal on the right gives me 7 volts with DME in and nothing with DME disconnected.
These are consistent for all four harness plugs.



The guys at the dealer checked my cap and rotor those are in good working order. Havenít tested plug wires yet.

The ignition coil is brand new.



Last edited by Jacob AbuKhader; 10-04-2018 at 02:09 AM.
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Old 10-04-2018, 08:03 AM
  #28  
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I think you are getting the 7V on the ground side, in which case according to Chris' post 22 you have an issue. Continuity on that same pin is also according to Chris' post 20 a problem.

You may have found something.
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Old 10-04-2018, 11:29 AM
  #29  
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Originally Posted by Dan Martinic View Post
I think you are getting the 7V on the ground side, in which case according to Chris' post 22 you have an issue. Continuity on that same pin is also according to Chris' post 20 a problem.

You may have found something.
I think so too. The voltage reading goes away when the DME is disconnected. So that leads me to think that thereís a short within the DME. Which would explain a lot of my symptoms. Hopefully this is the big issue that has kept the car down for so long. Theoretically then, should I be able to plug in a good DME, top up the gas tank and get my car back on the road? It canít be that easy....
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Old 10-04-2018, 11:49 AM
  #30  
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Later today, I'll pull an injector plug and see if I get some Vs on the ground pin & report back
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