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Mike S.
Mike S., Chevy Mechanic
Category: Chevy
Satisfied Customers: 7500
Experience:  ASE Certified Master Technician
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2000 chevy 3500hd 7.4l the other day i was driving and i

Customer Question

2000 chevy 3500hd 7.4l
the other day i was driving and i noticed that my voltage meter was dropping when i accelerated. it would usually come back up to normal when idling or coasting. I made it about 10 miles and then the ecm1 fuse blew. replaced fuse but truck wont run. it tries to start, and every once in a while it will fire up but run poorly for a very short time and then die. alternator checks out good. i also have fuel pressure, i must have some spark too as it sometimes starts. need help quick, it is my work truck. Ive also been chasing wires looking for shorts.
Submitted: 4 months ago.
Category: Chevy
Expert:  AMEDEE replied 4 months ago.

Hello and welcome!

My name is ***** ***** I can assist you with your question.

Expert:  AMEDEE replied 4 months ago.

I am very sorry your having this issue with your vehicle.

I will try my best to answer all of your questions.

However, before we get started, please let me mention a few things.

1. If at any point you would like to speak on the phone, please feel free to request a phone call on your end and I can call you right away.

2. If you dont understand any technical terms or anything that I mention (component tests or theory or operation), please let me know and I will provide you with a more in debt explanation or answer.

3. Please understand that I am here to help you any way I can.

Expert:  AMEDEE replied 4 months ago.

Can I start by getting your VIN, any stored codes in the computer and the exact fuse that keeps blowing?

Thank you!

Customer: replied 4 months ago.
1gbkc34j2yf518757
no codes
ecm1
Expert:  AMEDEE replied 4 months ago.

Thank you for that information.

Are you aware of everything on this circuit?

Do you have a wiring diagram for this ECM 1 fuse circuit?

Customer: replied 4 months ago.
i dont have a wiring diagram.
Expert:  AMEDEE replied 4 months ago.

Would you like one?

Customer: replied 4 months ago.
the fuse is no longer popping, but like i said it still wont run
Expert:  AMEDEE replied 4 months ago.

Ok, if the fuse is no longer popping, then I suggest we move on to something else.

So the engine is cranking over but not starting?

Customer: replied 4 months ago.
please reread my question
Expert:  AMEDEE replied 4 months ago.

So it starts up and then stalls and or runs poorly?

Customer: replied 4 months ago.
it rarely starts, when it does it runs poorly for a short time then dies
Expert:  AMEDEE replied 4 months ago.

Thank you for that information.

What is the fuel pressure at?

Customer: replied 4 months ago.
60
Expert:  AMEDEE replied 4 months ago.

Excellent!

Does it drop down at all when the engine is turned off?

Customer: replied 4 months ago.
all is normal as far as leak down. im sure the issue has something to do with whatever is causing the voltage issues
Expert:  AMEDEE replied 4 months ago.

What is the battery voltage at with the engine turned off?

What is the battery voltage at with the engine cranking?

Customer: replied 4 months ago.
12.4 when off
it drops to 9-10 when cranking, sometimes lower than that
Expert:  AMEDEE replied 4 months ago.

You might just have a bad battery.

It should not drop below 9.6 volts while cranking.

Customer: replied 4 months ago.
battery is only a year old. why would it start sometimes? once started the alternator should keep it running, but it doesnt, why?
Expert:  AMEDEE replied 4 months ago.

First, it does not matter if the battery is new or not. I have seen bad new batteries right out off the shelf.

Second, if the engine is cranking over just fine, this has nothing to do with the electrical system.

Third, it is most likely going to be a an air/fuel ratio delivery issue.

Expert:  Mike S. replied 4 months ago.

Charge the battery, then try a few shots of starting fluid into the throttle by. If the engine starts and runs for a few seconds with the starting fluid, then you have a fuel system issue. If it still won't start with the starting fluid, then most likely you have no spark.

The problem with the fuse blowing and the gauge dropping down might or might not be related to the no start or poor engine running but it sounds as though the charging system voltage regulator is sticking and if the pcm is actually used as a voltage regulator than that may also be the reason that fuse is blowing and you may have a faulty pcm. If so that may be the reason for all of these problems. It don't always work but once you get the engine running tap on the pcm with your finger tips and listen if that tapping changes the way the engine runs, the gauge moves or if the fuse blows. If so, there is something loose inside that pcm and it's intermittently causing these problems.