At first the car ran and drove not starting issue?

1991 PONTIAC 6000
74,500 MILES • 3.1L • 6 CYL • 2WD • AUTOMATIC
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SNOWINDIESEL
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I got this car on a trade a few months ago.

At first the car ran and drove, it ran rough, would “loop” at idle. I drove it around like that until it gave me a no start. The car will fire up, you’ll hear all 6 fire off and then it shuts off. If you give it fuel trying to start it, it won’t even try to start. I was able to get the car to start by pumping the peddle like a carb but now that doesn’t work anymore

It has fuel pressure (43psi) it’ll run off ether,
I’ve replaced ICM, ECM, Ignition coil packs, TPS, MAP, IAC Valve, CPS, Fuel filter. I’ve got a used throttle body coming in the mail for my next attempt. Any recommendations?
Sep 20, 2024 at 5:32 AM
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STRAILER
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Are the injectors getting a trigger signal? This guide can help you:

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Also, when you crank the engine over hold your hand over the exhaust pipe, you should feel the pulses of the cylinders, if not then you could have a clogged exhaust system.

Please go over this video as well:

https://youtu.be/lXLJbuAZ4CE?si=aCNzQRvsH2OFvROF

Please go over these guides and get back to us.
Sep 20, 2024 at 11:05 AM
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SNOWINDIESEL
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I don’t have access to a multi meter right now but when I unplugged an injector and tried starting it you can hear it missing. I’d think that means it would be getting a signal? No?
Sep 20, 2024 at 11:33 AM
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STRAILER
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If you unplug the injector and it is running worse than it is probably working. Can you upload a short video of what the problem is? That way I can se what's going on.
Sep 20, 2024 at 1:47 PM
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SNOWINDIESEL
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I’m surprised it started! When it’s running and you give it fuel it stumbles over itself for a second and then revs up.
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Sep 20, 2024 at 3:46 PM
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STRAILER
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Thanks for the video, it helps. It seems like the fuel pump is weak and it needs to be replaced.

Here is a guide to help check the fuel pressure to confirm the issue:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

FUEL PRESSURE:

Ignition ON Engine OFF .................... 40.5 to 47.0 psi

With Regulator Vacuum Applied [1] .................... 3.0 - 10.0 psi Less than Ignition ON Engine OFF

You can rent a fuel pressure gauge from the auto part store for cheap or free. Here is how to change the pump out in case you need it. Check out the images (below). Please let us know what happens.


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Sep 21, 2024 at 10:43 AM
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SNOWINDIESEL
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Replaced fuel pump. Still same issue. Could it be a bad fuel regulator that’s causing this?
Sep 27, 2024 at 12:30 PM
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STRAILER
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hmm, when it shuts down will it run on starting fluid? We need to see what the engine loses spark or fuel? Also is the security light flashing?
Sep 28, 2024 at 10:15 AM
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SNOWINDIESEL
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No security light. It does run on starting fluid when it’s shut down. It will fire for a split second and die when it’s acting up. When the car is running it runs really smooth as long as you keep your foot on the peddle. If you let off it starts to drop in rpm and struggle to idle. If you don’t keep the gas going it won’t idle.

I have a fuel regulator coming and I’ve got a donor throttle body. Those are my next guesses…
Sep 28, 2024 at 10:26 AM
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SNOWINDIESEL
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That and if you try to floor it when it’s running it will lose all power, it’ll still stay on, but you lose power until you restart the car. I found that out trying to pass a car when i was able to get it started.
Sep 28, 2024 at 10:28 AM
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STRAILER
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The IAC valve seems to be bad for the idle problem but not the no power issue. Lets run the codes to see if any are stored.

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

You may have a clogged catalytic converter, please go over this guide as well:

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Please go over this guide and get back to us.
Sep 28, 2024 at 11:05 AM
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SNOWINDIESEL
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It flashes code 12 to me 3 times and then flashes code 43 - Knock sensor or electronic spark control circuit fault.
Sep 29, 2024 at 8:22 AM
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SNOWINDIESEL
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Also I’m pretty sure the Catalytic Converter was deleted. This car was straight piped when I got it. I put a muffler back on it
Sep 29, 2024 at 8:23 AM
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STRAILER
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Okay, when you installed the new fuel pump did you replace the fuel filter as well? And when it wont start can you sue starting fluid to make it run?
Sep 29, 2024 at 10:09 AM
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STRAILER
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I have seen the ICM cause strange problem like this as well FYI.
Sep 29, 2024 at 10:10 AM
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SNOWINDIESEL
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I had a shop replace the pump. I’ve replaced the fuel filter before the pump was replaced. I was able to get the car to run off starting fluid before I replaced pump or filter. I’ve replaced ICM, ECM, Coil packs, TPS, IAC Valve, MAP Sensor, and CPS.
Sep 29, 2024 at 10:13 AM
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SNOWINDIESEL
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The car fires up no problem at times or doesn’t fire up at all. It’s bipolar. haha
Sep 29, 2024 at 10:16 AM
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SNOWINDIESEL
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Here’s a video of me trying to start it this morning. It fired up. I could smell gas out of the exhaust, and it had a blue cloud leave when I first fired it up. I also drove it around and got video of how it’s acting while driving.
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Sep 29, 2024 at 11:04 AM
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STRAILER
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Yep, that is an intermittent problem, they can be tough track down, did you run the codes? This might give us a clue on what is causing it. Since it has a new fuel pump and it didn't change anything I am leaning towards the ignition system, and more specifically the ignition control module.
Sep 30, 2024 at 9:42 AM
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SNOWINDIESEL
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Yes I ran the codes. I got a code 12 and a code 43. The link you gave me says 12 means everything is normal and 43 is a bad Knock sensor.

It does have a new Ignition control module and new coil packs on the ICM. The plugins on the ICM looked fine, no corrosion. Again, I've replaced ICM, ECM, Coil packs, TPS, IAC Valve, MAP Sensor, and CPS.
Sep 30, 2024 at 4:16 PM
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STRAILER
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Yep, those codes are typical. So when the engine does not start we need to see what it is missing, either fuel or spark. Use starting fluid for fuel and this video will show you how to check for spark.

https://youtu.be/baq_aEWNQ0Y?si=9MWDPgLYuuPAD6Ms

Please go over this guide and get back to us.

Oct 1, 2024 at 9:53 AM
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SNOWINDIESEL
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Starting fluid keeps the car running.
Oct 1, 2024 at 12:33 PM
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STRAILER
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So, it is losing fuel pressure, you said you installed a new fuel pump and filter, correct? Also, I have seen the oil pressure sender switch cut out the fuel pump due to low oil pressure. Here is the location so you can bypass it to see if things change. Check out the images (below). Please let us know what happens. Connect the orange and grey wires.
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Oct 2, 2024 at 9:04 AM
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SNOWINDIESEL
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Ended up being a bad injector shorting out causing the ECM to go into a safe mode by shutting all injectors off. Put in 6 new injectors. it fires up and runs like a top now. I guess early GM MPFI systems all do this?
Nov 23, 2024 at 7:23 AM
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Yes, I have heard of this problem, thanks for letting us know, we are here to help, please use 2CarPros anytime.
Nov 23, 2024 at 9:50 AM