Wiring mystery
 

Today my 2005 ZR2 Blazer wouldn't start. I'm checking fuses and find a wire connected to a ground relay plugged into the ECM fuse. First time I'd looked there since I bought it 2 months ago. So I'm checking the coil and I connect the pink wire to my tester and ground it to see if there is power and nothing. What I do get is the continuity light and buzzer going off telling me I have continuity between the pink coil wire and the neg of the battery. Everything else works fine and it's showing no engine codes. Can anyone help me with this as I haven't a clue where to start. Thanks.

1. I'm not sure what you mean when you say "ground relay"?

2. Did you have the key in the run or start position when you were checking the pink wire? The pink wire receives power from the ECM1 fuse which is hot in RUN or START.

3.How did you check the PINK wire? Did you unplug the connector from the coil or did you backprobe or pierce the PINK wire with connector plugged in?

4. You should start by checking fuel pressure. See the link below my signature block and follow Captain Hook's directions.

1. A ground relay meaning when 3 or 4 ground wires are connected together on the firewall.
2. Both
3. I unplugged the connector so I could get a clean test
4. Why would I check my fuel pressure? I'm having a "no spark" problem, not a "no fuel" problem. I did the fuel or spark test when I began with a "not starting" problem but after eliminating fuel issues anhd establishing spark issues I am only focusing on why there is no spark.

My answer may be more than you want but I hope to help others doing a search. You need spark, fuel and air to run correctly. You are focusing on spark so lets start there:

Using a spark tester, test for 1" of strong blue spark at the end of a plug wire to ground.

If no spark, using a spark tester check same at the lead from the coil that is unplugged from the distributor.

If no spark, then determine if its the coil, signal to the coil from the ICM, signal from The PCM to the ICM, sensors to the PCM, power or ground.

Since you are focusing on the pink power wire, lets start there. With the key on, probe the pink wires into the ICM and again into the coil for 12V. If so check the ground. If not, check ECM1 fuse.

Check ground by one of two methods. Positive DCV meter probe to battery 12V and negative probe to Black/white wire on ICM or unplug the ICM harness and check the same wire and its continuity to ground using ohms or continuity beep.

If you had no spark and power and ground are good then we need to check the switching signals to find out if its the coil, ICM, PCM, or sensors.

Report back.

George

I have no spark at the coil lead to the distributor. When I checked for power to the pink wire with my tester I didn't get any volts. What I got was the continuity light and buzzer going of meaning there is a connection from the pink to the ground. From that I'm thinking something is grounding out the ignition. At the ECM fuse {15 amp} there is a wire with a probe on it stuck into the front facing terminal of that fuse. That wire is going to a plastic relay box with 3 other wires 2 of which go to the firewall ground. The 4th {white} I can't find follow as it goes into the dash somewhere. That strange wire has been there for the 2 months I've been driving the zr2 trouble free. I pulled it out and no power at the fuse but continuity to the ground again.

OK, a little bit of info, a relay is a switch which has power and ground. There are ground-switched-relays but they also have power. What you were looking at seems to be simply a ground junction.

You state that you checked the PINK wire with the key in both run and start position. Is your engine cranking?

Also, you did not state all the information in #4 in your original post. All that info is very good to put in a first post to help us narrow down diagnosis in the first responses.

Just use a regular old fashioned test light not one of those (bleeping) continuity testers.

If no spark directly out of ignition coil: Disconnect coil connector and 1) test for voltage on pink with a test light with KOEO. 2) Back-probe white/black with test light powered by 12V while cranking. If test light flashes, coil is bad and the rest is all good. If test light doesn't flash, check RPM while cranking with a scanner. If RPM displays, then crank sensor is definitely not the cause and PCM appears to be working OK. In that case ignition module is your best bet.

Hope this helps

If something were "grounding out" the pink 12v power source to the ICM and/or the coil then the ECM1 fuse would be blown and would keep blowing upon replacement. As Lesmyer said, do not test a live power wire with a continuity tester, use the DCV function of a meter or a test light.

You mention what sounds like extra wired added to the fuse box at the ECM1 fuse. What is the purpose of this wire and how is it connected?

George

I'm wondering the same thing. Can you post pics?

I have been working on the problem for 2 days testing and retesting everything. Now I am left only with the crank sensor but need someone to do that for me because my legs are handicapped and I can't get myself up if I go on the ground. If the crank sensor works does that mean the pcm is gone. I did the ignition switch test as well.