98 Tahoe ECM-1 fuse blowing

[m2q]

98 tahoe, 2wd, 4dr. Need help determining why the ECM-1 fuse continues to blow. Wouldn't start after being parked for an hour. Found the ECM-1 fuse had blown; replaced fuse and it blew again as soon as I turned the ignition on. Checked fuel pump relay, tested good. put a test lamp in the fuse slot and sequentially disconnected the ECM, crankshaft position sensor, ignition control module, and ignition coil -- no joy; test lamp stays lit, fuses still pop. wires to CKPS, ICM and IC all tested good as well. Interesting find is that the test lamp goes out when the IGN-A 40A fuse is removed. Anyone have any ideas on what the problem is and how to fix?

Thanks

 

[SunlitComet]

Ecm-1 and some others are fed from IGN-A thru the ignition switch. Ecm-1 feeds the pcm and positive side of injector so if the all the things you listed above are still disconnected along with the injector body connector removed this time and the fuse still blows then it is the wiring harness. Seem like the only part you have not tried on that fuse circuit is the injector body.

 

[m2q]

Thanks. I'll check that one out.

 

[m2q]

That was it! I pulled the connector off the throttle body injector assembly and the test lamp went out. After checking continuity on the wires, it appears I have a faulty injector assembly.

Thanks for your help.

 

[SunlitComet]

you mean continuity from spider connector to ecm on same color coded wire? just wanted to be sure. did you try each injector to see each resistance was courious to how it failed specifically. Had not seen an injector body fail like that but if you do replace it get the new improved style one you won't regret it. Wouldn't mind some pics of the old one to if you see any obvious damage or you decide to tear it down.

 

[m2q]

Yes, I hooked a multimeter to the ECM-1 fuze and checked each individual pink wire running to it and confirmed continuity on each. I didn't check resistance on each but will do that tonight. What i did find was that one injector of the bunch seemed to have a short across the connectors that the others did not have. what I had planned to investigate was replacing just the single injector vice the entire assembly.

 

[SunlitComet]

A single injector non-oem will cost about $64 and the original design has been detrimental to the v6/v8 engines that use them. You have to pull the body of to get the injector out and at that point the bracket is not usable if you bend it to far to get it off. They start dumping to much fuel causing misfires among other symptoms and enventually wash down your cylinders and yopu start loosing compression. Besides one new against 7 old will not have the same flow rates. A new injector assy with all new injectors with improved design with new regulator already installed as well as new mounting bracket costs $215 at amazon. Auto parts store will most likely charge $450+ and you have to buy bracket seperately. Throw in the fel-pro plenum gasket in case yours is damaged and it is $230. It is from Delphi itself. Like I said you won't regret it.

If money is the worry try and hold off repair a little longer if you can.

Try and check for shorts or resistance on the negative trigger wires heading back to the ecm to be sure as well.

 

[m2q]

I checked resistance on all the injectors; the one I was concerned about registered 11.9 ohms as did one next to it, the others were 12.0 or 12.1. Looks like I'll need to trace the other wires as you suggest to see if I can find any shorts. I did seriously consider repalcing the one faulty injector vice the whole assembly; if it comes down to it I'm just going to replace the whole assembly.

 

[m2q]

just finished checking the continuity on the rest of the wires back to the ECM. all checked out so I guess that leaves me with the fuel injector assembly. also, I did a circuit test with the ECM disconnected the fuel injector assemble connected. with the FI assembly connected the test lamp remained lit, when I disconnected the FI assembly the light when out. Thoughts?

 

[SunlitComet]

if you are hooking the test light to each injector negative side and the other terminal to ground while the positive side has voltage they should all light up. How about disconnecting the injector body, power fuse and ecm connectors get the multimeter on the ecm side with one test probe on injector wire and the other grounded as well as on the other injector circuits looking for ground or cross shorts. And the injector supply wire on the connector supply side to ground as well as fuse conector side to ground. 10-4. I have to admit I am unclear how you are hooking up the test connections.

---------- Post added at 06:59 PM ---------- Previous post was at 06:52 PM ----------

Yes, I hooked a multimeter to the ECM-1 fuze and checked each individual pink wire running to it and confirmed continuity on each. I didn't check resistance on each but will do that tonight. What i did find was that one injector of the bunch seemed to have a short across the connectors that the others did not have. what I had planned to investigate was replacing just the single injector vice the entire assembly.

One other thing if I missed it. With fuse in and power applied did you see the same voltage at each feed terminal. Not sure if connector is labeled but my diagram show letters b, c, p, r, g, f, and k as the pink supply in the injector connector.

 

[m2q]

Here's what I did:

• with FI assy, ECM disconnect and fuse out: checked each FI pink feed back to the ECM-1 fuse to check continuity; checked ea FI colored wire back to ECM to confirm continuty
• with FI assy disconnected, checked resistance across each injector's connectors; res registered 11-9 to 12.1
• with FI assy connected and ECM-1 fuse in, fuse blows when power is turned on whether if ECM is connected or not
  
  I'll try what you suggest on the wire voltage check and additional injector checks and let you know what I find

 

[m2q]

With ECM fuse in-place, ECM connected and power on, checked voltage from each FI pink supply wire; with multimeter to ground, voltage measured 12.11v for each wire; with multimeter connect to pink wires and corresponding wire to ECM, essentially across FI connection, voltage measured 11.93v.

Power output at ECM fuse to ground was 12.12v.

With fuse removed, FI body and ECm disconnected, resistance from FI connector to ECM connect was about 4 ohms for each wire; continuity verified.

resistance across fuel injector connection pins was 12.1 ohms for 6 injectors and 11.9 ohms for 2.

ECM fuse still pops when ECM and FI body are connected and the power is turned on; disconnect the FI body and all is well.

 

[SunlitComet]

Then yes the injection body would seem to be at fault. Just can't see that with all the injector almost the same readings although they may be breaking down electrically when there is power on the unit. The only other farscape idea I can think is the pcm drivers are kepping all the injector open at one but that is still not enough current to blow the fuse.

 

[m2q]

The FI body was my conclusion as well. Thanks very much for your time and assistance.

 

[Spikesdaddy]

Then yes the injection body would seem to be at fault. Just can't see that with all the injector almost the same readings although they may be breaking down electrically when there is power on the unit. The only other farscape idea I can think is the pcm drivers are kepping all the injector open at one but that is still not enough current to blow the fuse.

I'm having what seems to be the same issue with my 1999 GMC YUKON ( L31, 5.7). I unplug the main plug to the fuel injectors (on top of the manifold), replace the fuse and it doesn't blow the fuse. Plug the harness back in and it instantly blows the PCM-1 (20 amp) fuse. Mine was replaced 4 years ago by a dealer in Georgia with part number 19210687. I'm thinking I have a bad injector or a short at one or more injectors? Does it sound like I'm correct?

 

[Spikesdaddy]

I'm having what seems to be the same issue with my 1999 GMC Yukon ( L31, 5.7). I unplug the main plug to the fuel injectors (on top of the manifold), replace the fuse and it doesn't blow the fuse. Plug the harness back in and it instantly blows the PCM-1 (20 amp) fuse. Mine was replaced 4 years ago by a dealer in Georgia with part number 19210687. I'm thinking I have a bad injector or a short at one or more injectors? Does it sound like I'm correct?