Working on a crate LS3. Changed cam, and had ecm reflashed. Car starts right up, and then blows the #2 fuse in the gmpp fuse box. All plugs, grounds and wires have been checked. Does anybody have a schematic of what the #2 (ign) fuse protects?. Could the cam postition sensor be bad? Is there something in the "flash" that could cause that fuse to blow?

Thank you!!!

Mike Coletta

 

You have a short somewhere.

 

Thanks for responding. Yeah, we know that, but the engine was running perfect before the cam swap (over 5000 miles), and it doesn't blow the fuse on ignition. I will start and run perfectly, for about 30 seconds, and then quit (fuse blows). If I knew what was on that fuse, it would be easier to track. The only wires that were moved, that are part of the GM harness, were the MAF, throttle, cam postition sensor. Anybody have any ideas?? Weird thing is that the motor will run fine for about 30 seconds. I would think that if I had a short, it would pop the fuse immediately. Any thoughts are appreciated.

Regards,
Mike Coletta

 

The ignition dwell setting in the flashed tune is wrong for your coils, been there, suffered that! If you have HP Tuners, you can easily fix it. Your dwell table should look like the one I attached. I bet your current table has much larger numbers in the 0 column.

 

Thank you guys. I’ve got my tuner coming out on Monday to resolve.

 

"The ignition dwell setting in the flashed tune is wrong for your coils,"
Unless the dwell was changed with the reflash, there's something else going on, as the engine has been in use for 5000 miles without issues.
I guess we may know when the tuner gets there............

 

Damn, I haven't thought about "dwell" since working with ignition points in the '70s. I've seen the dwell table in HPT but never seen a reason to change it. Had no idea it could pop a fuse with really wrong values.
Thanks for pointing this out, even if it turns out not to be the OP's problem.

 

Surprised the heck out of me! Since my engine is basically an LS9 clone, I tried flashing in the [ECM] 12650 - Base Dwell Time table. Engine started and idled fine for about 30 sec, then IGN fuse blew. Re-flashed with original dwell table and no more problems. Big difference between the two tables is in their column 0.

 

Still need help guys. The tuner (does it for a hobby), says it's not the tune. Since I can't seem to find a schematic for this fuse box/harness, I disassembled it to find the load side wire, and checked continuity. I'm working on this at a friends house, not my shop, so I have not checked to see if that 12v is on any of the lower components, ie; knock sensors, crank, or 02. I'm showing good connections to the coils, MAF. This is a 12v feed, from the #2 Ign fuse.

After my first post, and while waiting for the tuner, I replaced the fuse, and the car started right up.......and then kept running. Drove around the block, and let it run for about 15 minutes. No issues. I thought WTF?? Left it with the owner to reassemble. Called me yesterday and said that the car quit again after about 30 seconds. Blown #2 fuse. If I replace the fuse, it will immediately restart and run.......for about 30 seconds. Fuse gets hot, like there is short. When the car was running (for 15 minutes the other day), the fuse was cold. I'm going to do an amperage check on that wire this morning. The only wires that he messed with during the cam change was the cam sensor, and there is only 5v ref at that sensor, and the coil pack rail. I've inspected for damage, and run a power probe signal test on the top side of the motor, and everything looks good.

My knowledge of electrical is good, and I have excellent equipment, but I'm a total IDIOT when it comes to this PCM/ECU stuff. The "tuner guy" says that it can't be his flash, so I'm stuck. Again, this is a GMPP harness, fuse box, and ecu for LS3. Does the "dwell timing" effect the amp load on the coils?? Do I need to find a different "tuner"??? Central florida if you know someone? Thanks for you patience and help.

Regards,
Mike Coletta

 

Mike, is this of any help?
Looks like there's considerable info.
LS_Engine_Control_System.pdf

 

Mike, check your PM's.....

 

Thank you guys!! I'm doing more testing this morning. I will post outcome later today. If anyone else has an idea, I'll be checking in regularly.

 

Providing an update for anyone following. Here is what I found. Started the car this morning, with a clamp gauge on the 15amp ignition load wire. It turns out that this fuse only protects the coil packs and the MAF. I was getting intermittent negative spikes, so I checked all of the coils. One was shorted. This is probably what was causing the 15 amp fuse to blow intermittently. Getting the negative amp draw was not consistent, so the fuse heated up gradually, and then finally blew.

So, replaced the bad coil, and fired it up. No negative spikes, no codes set, ran perfectly. Let it run at idle for about 10 minutes. Then cool down. Fired it up again, and the entire left bank of coils not working. I had 12v, pink, key on. I had good ground on the black and brown wire. No codes set. I had a brand new E67 ECU, tuned for a 340 hp LS3. Installed it, and the car fired right up. Removed it, and reinstalled the original (tuner guy ECM). IT FIRED RIGHT UP?????? Ran perfectly,

As I said earlier, I'm a complete idiot when it comes to these things. My theory is that by unplugging the ECM (there were no codes set), and then reinstalling, I essentially "rebooted" it if there is such a thing. I'm thinking that there is something wrong it the flash. I advised the owner to get some run time on the engine, keep it close to home for a while. I also told him that I would re install the original tune, and find someone who knows what they are doing. Thanks for the help.

Last, does anyone have a tuner in Central Florida that they would recommend?? I'm about 30 miles west of Orlando.

Thanks again,
Regards,
Mike Coletta

 

Thank you !! for posting an update with the solution. Its these "solution" posts which make forums like this so useful.

 

Mike, call Don Cruz at Cruz Performance. He does a lot of custom stuff.
If he can't do it, he may know someone that can.
Cruz Performance, Tampa, Fl - Search

 

Any time I see Florida and electrical problem in the same sentence I wonder about corrosion at the connectors. This could be why plugging in another ecm, then switching back to the old ecm both allowed the car to run ok. The unplugging and plugging could have scraped the connectors enough to make good contact again. Just a theory, but you guys have a rough time with all that salt air.