Fuel pump engages, but it will not start?

Tiny
AQUIGG79
  • MEMBER
  • 2000 GMC JIMMY
  • 4.3L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 300,000 MILES
I replaced the fuel pump twice over the course of 3 years. When I turn the key, I can hear the fuel pump engaging. It won't start. Starter fluid will cause it to try to start, might start for two seconds, then shuts off. Could it be the fuel pump relay or fuse, and not the fuel pump itself? My wife seems to think since the pump obviously engages, but there's really no spark, that it could be the ignition coil. She says to look into ignition coil replacement. Truck has multiple misfires and codes. Plugs and wires were changed within the last 2 months. But no coil packs. Should I continue on my possible fuel pump replacement for the 3rd time or maybe give my wife some credit and look into the ignition coil?
Friday, July 14th, 2023 AT 2:50 PM

3 Replies

Tiny
AL514
  • MECHANIC
  • 4,637 POSTS
Hello, if there is a weak spark when testing, then replace the coil. Weak spark will cause misfire codes and it will eventually cause the Catalytic Converter to fail. So, it's best to do a coil now before that happens. I'll put up a guide to help
The ignition coil on this vehicle is controlled by an electronic ignition module which is usually bolted to the top right side of the engine or the distributor in the engine compartment, The right side being the passenger side. There is also a cam position sensor (or pickup) inside the Distributor that signals when the spark should occur. The module, pickup and coils will all eventually fail, so if there is still weak spark after replacing the ignition coil, you may have to replace the Distributor and Ignition module as well. They only last so long and this vehicle is 23 years old. So, if it hasn't been done yet, it's best to do all 3. That way you won't end up stranded somewhere. Replacing the Ignition coil and the ignition module is easy, but the Distributor is a bit more difficult, it has to be put in exactly where it came out, and then the base timing needs to be set afterwards. So, if you have never done that before, you may want to take it to a shop for the Distributor section. If the ignition timing is not set correctly with the correct procedure the vehicle will either never start or run extremely badly, potentially causing damage to the engine.

Here are the instructions for replacing the ignition coil. It looks like the ignition module is bolted right to the coil on this model., So that makes things much easier.
There are also a couple of guides below, one is for checking ignition spark and the other is for checking fuel pressure. Remember to change the Fuel Filter every 15,000 to 30,000 miles, which will save on fuel pump failures.

https://www.2carpros.com/articles/how-to-check-for-ignition-spark

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
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Friday, July 14th, 2023 AT 3:19 PM
Tiny
AQUIGG79
  • MEMBER
  • 2 POSTS
Thank you. The underlying problem is ultimately the fuel filter. When my husband changed the first fuel pump, he did not change the fuel filter. The fuel filter not being changed, when it should have, is more than likely what caused the need to replace that fuel pump. We're getting spark. The fuel wasn't being distributed evenly. I've read up on this. Over consumption of gas, due to fuel pump working harder to push gas. Loss of oil, not from a leak, hard initial start etc. I believe that's what is the culprit.
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Friday, July 14th, 2023 AT 11:47 PM
Tiny
AL514
  • MECHANIC
  • 4,637 POSTS
Yes, not changing out the fuel filter will cause a pump to work harder, but something to keep in mind, when a fuel system/pump is struggling and there isn't the fuel volume that should be there, the air/fuel mixture will be lean, meaning more air than fuel, the computer will compensate for this by adjusting the fuel injectors, but a lean mixture also stresses the ignition coil(s). So, if you change out the filter and you are still getting misfire codes, first buy one of these Ignition Spark testers. This type you can see is adjustable, and that's what you want, you need to stress the coil and see if you still have good spark, there may be spark when testing with the spark plug grounded to block and plugged into the spark plug wire. But that spark is not under combustion pressures and temperatures, everything changes when the spark has to jump a gap under pressure. This tester just plugs into either the wire coming right off the coil, or you can plug it into a plug wire. It has two numbers on it, 20k (20,000volts) or 40,000. You will need to test about halfway up to the 20,000 mark for your vehicle.10-20,000 to stress the coil some and see if it can still jump the gap.
Since you have cylinder misfires occurring now, you should also change the oil, due to blow by gases past the piston rings (and every vehicle does this), during cylinder misfires the oil becomes contaminated with gas and must be changed. Diluted gas leads to premature failure of bearings. What other codes were you getting besides misfire codes? Any P0171 or P0174?

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

https://www.2carpros.com/articles/symptoms-of-engine-misfires-a-step-by-step-guide
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Saturday, July 15th, 2023 AT 10:24 AM

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