ECM 1 fuse blowing when cranking does not blow when fuel injector connector is unplugged

COUNTRY8485

MEMBER
2004 CHEVROLET BLAZER
4.3L
V6
4WD
AUTOMATIC
175,000 MILES

Sorry for the novel, lol. I bought the vehicle listed above LS has almost 175,000 miles at the beginning of this year. Few weeks ago, had a p0200 and p0303 code and flashing SES light so replaced #3 spark plug and wire and replaced full spider injector with a remanufactured one from AutoZone along with the necessary manifold gaskets and the distributor cap. Codes cleared and she drove great. Few days ago, check engine light flashing again went to AutoZone around the block they ran codes got P0200, P0306, P0128, P0102. Driving home stalled out so started checking basic stuff found a blown 15a ECM 1 fuse. Replaced with another one cranked engine and blew another. Did that couple other times keeps blowing ECM 1 fuse. Unplugged spider fuel injector connector at the intake manifold and cranked the engine and it doesn’t blow the fuse. From my understanding this year of the blazer only the injectors, their connection components, and the senders or what not from the ECM are on this fuse and circuit with nothing else like the fuel pump or fuel relay tied into it. I read to test for 12v on the pins at the fuel injector connector and injectors or to look for open grounds or faulted injectors but wasn’t sure how to test injectors if negative terminal is disconnected before removing everything to access the injectors under the intake manifold. Wouldn’t that not do anything with no power to the vehicle? Also noticed no gas comes out of the little bleed valve on the gas lines. Not a mechanic by far but can’t afford parts and labor right now and can’t afford to keep replacing things that are most likely wrong. I can only buy basic testing tools, but I have tools to fix stuff or can get loaners and I’m pretty capable of repairing things so I’m trying to see if someone can please point me in the right direction on what to replace because I can’t pay bills when I can’t get to work. Is it possible it’s the remanufactured spider I just installed or can I rule that out cause supposedly it’s up to spec for reusing? Apologies for a question as long as the Nile but I’m just trying to put as much details in there that I can think of to help make answering easier.

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Monday, October 4th, 2021 AT 10:08 PM

14 Replies

COUNTRY8485

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9 POSTS

Chased the wires from the ECM 1 circuit found some damaged and completely exposed down at the exhaust.

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Tuesday, October 5th, 2021 AT 7:41 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

If you have exposed wires, it sounds like you found the issue. If you look at the pics below, I included the entire wiring schematic for the powertrain management. I highlighted the ECM 1 fuse and the wiring to the injectors and from there to the ignition control module and the distributor. The injectors have wires going from them to the PCM. I didn't highlight them.

The wires you found, what color are they? Are they pink by chance? If not, let me know what they are.

Based on the P0200, I would first suspect there is a short at one of the injectors. Disconnect cylinder 3 and cylinder 6 (one at a time) and see if the fuse still blows.

Here is a link you may find helpful when testing wiring:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know if the fuse still blows and the wire colors that are damaged.

Take care,

Joe

See pics below. Note: I had to cut each of the schematic pages in half to make them readable for you. I did overlap each page so you can follow from one to the next. Use this to trace the wires you found which are damaged.

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Tuesday, October 5th, 2021 AT 8:15 PM

COUNTRY8485

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Hi Joe! Thank you for the Info and schematics. The wires I found were green and a black one with a white stripe. Fixed those but still won’t crank. I also found a damaged black one around the fuel pump connector area and a purple one on the set of wires that goes to a relay near the A/C components (the harness running at the top of the firewall). Haven’t repaired them cause had to work yesterday. My maintenance man who’s a part time mechanic briefly looked over it and said what’s weird is the female ports on the harness injector connector shows 12v on the grounds of all 6 sets as well as at the ECM 1 fuse and a few other fuses just can’t remember which ones and when that’s disconnected and the I crank the engine it doesn’t blow a fuse so I’m wondering if it’s not the damage wires but something with the fuel injectors themselves. But would a new refurbished one do that as well or is there something shorting out the spider injectors possibly? I am financially already pinching pennies can’t afford mechanics labor too. I’m missing work trying to figure it out and when you remodel homes a vehicle is absolutely a necessity. So, I’m at my wits end on what to do. People say get what I can for it and get into a newer vehicle with a payment but from what I hear these Blazers have sound engines that will last to 300,000 and its fully owned so don’t want to sell it and regret it down the road if it’s something minor.

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Wednesday, October 6th, 2021 AT 12:16 PM

COUNTRY8485

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9 POSTS

First are the damaged ones I repaired.
Second are damaged wires going to the fuel pump connector.
Third are damaged ones near the firewall.

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Wednesday, October 6th, 2021 AT 12:35 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

First, make sure all damaged wires are repaired and insulated. Next, all pink wires going to the injectors should have 12v at all times. A ground path is provided via the PCM.

Is that what you are referring to?

Joe

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Wednesday, October 6th, 2021 AT 8:10 PM

COUNTRY8485

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Yeah, the pink wires going into the connector piece at the harness that plugs into the actual spider unit are all reading 12v and the ground ports on that connector are also reading 12 V and to my understanding from what that guy was saying the grounds are supposed to show zero not positive. It's damaged on one of the middle ports where it looks like the pin hit the edge and cracked it a bit. It’s also showing 12 V on the ECM fuse but also 12v where it is supposed to be zero for a ground. I was looking at the schematics trying to see where all the grounds go thinking one of those grounds coming off the PCM are touching a positive somewhere along the lines. I know when doing electrical houses, it’ll read a hot neutral when it’s making a connection with a positive somewhere down the line. Being the second spider injector unit and it being an open circuit is there a need to open that all back up? How likely is it the issue stems from there? Thank you so much for helping. I’m really up a creek if I can’t figure this out so all your insight is greatly appreciated.

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Thursday, October 7th, 2021 AT 6:32 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

If you are getting 12v to ground at all of the injectors, there is a chance the PCM has failed. Do me a favor. Disconnect the PCM and see if the power from the grounds goes away. If it doesn't, there has to be a short to power at some point between the PCM and injectors. However, for all of the injector grounds to have power, there has to be a common fault because each injector has its own ground path. Make sure the connector at the PCM is good, not damaged (pins), and has no corrosion.

Let me know what you find.

Joe

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Thursday, October 7th, 2021 AT 2:53 PM

COUNTRY8485

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Sorry for just responding, just got time to get back to the Blazer. Before disconnecting the PCM I repaired all visibly damaged wires. I double checked the harness injector connector for 12v and now I get nothing on any of the 12 ports. Maybe I’m not getting as good of a connection with my meter as the guy was who tested it before. The fuse box also isn’t testing 12v on the ground side of the ECM 1 fuse anymore. Still blew the fuse though when koeo so unplugged the pcm and left everything else plugged in and koeo and blew a fuse still. Unplugged harness injector connector and fuse doesn’t blow. Someone who noticed me testing and he checked the spider injector pins and both # 6 injector pins as well as both ports on the actual injector connector are getting.025 ohms on one pin and.028 Ohms on another pin and the others only show.01 on both pins of each injector. The injectors were being tested without the ECM connected. From what he said the injector has a ground fault and needs to be replaced? It has a warranty so I can replace it no problem but would like your knowledgeable input before putting all my chips into that bag. Thanks again for all your time helping solve this issue.

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Sunday, October 10th, 2021 AT 10:06 PM

COUNTRY8485

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Installed new spider assembly no SES light drove 10 minutes and SES flashing and now says p0200 and p0305. So, at this point I’m going to assume it’s the PCM and just replace it or sell this thing before my head explodes.

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Monday, October 11th, 2021 AT 1:40 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

As far as the codes, you likely already know it's cylinder 5. Here is how it works: The control module enables the appropriate fuel injector pulse for each cylinder. Ignition voltage is supplied to the fuel injectors. The control module controls each fuel injector by grounding the control circuit via a solid-state device called a driver. The control module monitors the status of each driver. If the control module detects an incorrect voltage for the commanded state of the driver, a fuel injector control DTC sets. That is the P0200.

Let's try one more test.

Disconnect injector 5 and see if the fuse blows. If it doesn't there is a chance the ignition 1 voltage is shorted at the injector. If it does blow, then the short is before the injector and after the ignition 1 fuse.

If it doesn't blow, probe the ignition 1 power supply to the cylinder 5 injector. With the key on and the engine off, you should have power.

If you do, connect the tester to the control wire (PCM) and the ignition 1 voltage wire. Crank the engine. Does the test light flash?

Let me know.

Joe

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Monday, October 11th, 2021 AT 8:47 PM

COUNTRY8485

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Thank you for explaining how the injector circuit operates. Apologize for leaving out that I have not blown a fuse since replacing the spider. Warranty replaced the injector assembly with another one we installed it and it started up fine and drove for 20 minutes before the ese light started flashing again and those two codes popped up. No fuse is blowing and it’s still cranking over as of now. I will go ahead and do that test in the morning and let you know what I get. Thank you for all the help you’ve given.

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Monday, October 11th, 2021 AT 9:08 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

No problem whatsoever. I just hope to help. Since you have the cylinder 5 misfire code, that is the injector to focus on.

Let me know what you find or if you have other questions.

Take care,

Joe

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Tuesday, October 12th, 2021 AT 4:32 PM

COUNTRY8485

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Hi Joe, well the craziness continues. I disconnected the battery while I was looking for more damaged wires just in case and then the codes cleared for maybe 5 minutes then returned but with no misfire code just the p0200 code now so I’m beginning to think I’m just going around the mulberry bush. Not sure what to think. Actually, I think it’s spazzing out and wants a new owner.

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Tuesday, October 12th, 2021 AT 5:05 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

The P200 is related to a variation in voltage to the driver (injector). Something is causing an electrical issue. It could be a wire, corrosion, a faulty injector, a bad PCM, and so on. We are missing something simple.

Take a look through the diagnostics below. I've walked you through some of them already. However, follow them step by step. Also, let me know if the cylinder misfire code came back as well (cylinder 5).

Take care,

Joe

See pics below.

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