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Old 11-09-2015, 02:45 PM   #1
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Default Main relay - Car won't start

Just wanted to confirm before I commit into buying a new main relay.

Jump F/p and GND in the diagnostic box and the fuel pump turns on. The car still doesn't fire.

Went further into my diagnostic and found out I get no voltage from the injector connector, and no spark (hooked up a timing gun and did not fire). I checked the fuse box in the dashboard for the 15amp engine fuse, it was not blown, but my 10amp room fuse was blown, I replaced it and still won't start.

Removed the main relay in the engine bay and checked if I get +12V. The main relay terminals do see +12V, which makes me believe the main relay went out.

Does my reasoning make sense? Also, what about the other relay in the dashboard? Any way to check that? Forgot to add this is for a '92 and with a mspnp1

Last edited by .one lane; 11-09-2015 at 02:55 PM.
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Old 11-10-2015, 09:37 AM   #2
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I am pretty sure if the main relay blew you would not get the fuel pump to turn on.

Does it turn over (starter works)? Does your MS fire up and display data on your laptop? Do you get the fuel pump priming pulse when you turn the key on?
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Old 11-10-2015, 09:41 AM   #3
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The starter works, but the car gets no spark or fuel. The mspnp turns on as the red light can be seen through the case.
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Old 11-10-2015, 09:57 AM   #4
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Have you hooked a laptop up to the MS to see what data it is displaying? I had a MS get its firmware corrupted once and it would not start or prime the pump. Red light still came on because it was getting power, but didn't work right. If the MS light comes on it means you get 12V and your main relay should be OK.
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Old 11-10-2015, 11:38 AM   #5
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Backstory

The car was fully functional before, I recently installed a gm iat and was having some issues. I bought a replacement sensor and just to be sure I reflashed the mspnp with diyauto's gm iat and stock clt temp/ohms values with easytherm.

I flashed the unit at my desktop as my laptop was having issues with the download-firmware.bat, due to 64bit windows (weird because I downloaded the same fix on my desktop and it works). Anyways, the flash didn't encounter any errors. I did, however, forget to unplug the battery (stupid mistake) when I removed/reinstalled my mspnp. Probably explains the blown 10amp room fuse.
  • Fuel pump does not prime or start. Jumped F/p and GND, and the fuel pump turns on when the key is in the on position.
  • No power to the injectors when I checked with my multimeter.
  • No spark
  • Besides the 10amp fuse, there was no other fuse that blew. (dashboard or engine bay)
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Old 11-10-2015, 12:39 PM   #6
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Because the forum-image-resizer was maliciously destroyed by IB Nolan, click here for full size:


(oh, for ***** sake. Now I can't even hotlink to the URL of an image without the forum ******* it up even more. IB Nolan, fix the god-damned thing, already!)

Let's see if this works:

http://i.imgur.com/KKQT3Ms.gif

There we go, noparse to the rescue. Open that in a new tab then continue reading. This forum software is really starting to **** me off...










Room fuse explains loss of power to ECU. It does not explain loss of power to injectors, main relay, etc. Furthermore, the fact that jumping F/P to GND in the diagnostic box turns on the pump verifies that the main relay is operating correctly. This means that you do have power to your injectors, but you're measuring it wrong.

I'm pretty sure your ECU is just fucked up somehow.
Attached Thumbnails
Main relay - Car won't start-kkqt3ms.gif   Main relay - Car won't start-80-fuelsystem_c103636df375ed9d04915889dd79aa4d7c9cd48e.gif   Main relay - Car won't start-kkqt3ms.gif   Main relay - Car won't start-80-fuelsystem_c103636df375ed9d04915889dd79aa4d7c9cd48e.gif  
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Old 11-10-2015, 12:46 PM   #7
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Thanks for the reply, Joe. I'll see if my stock ecu will start the car.

edit-

firmware on the mspnp was corrupted. reflashed and now the car starts.

Last edited by .one lane; 11-12-2015 at 02:43 AM.
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