Very odd injector buzz test.

lmorris · February 21, 2013

Have a 2002 with some very interesting problems, first koeo I get 12 volts to the fuel pump for 20 seconds, then it drops to 6V. Checked at the inertia switch and it drops to zero, so I believe the CJB is ok. Removed the fuel pump relay fuse and I have 6 volts at the engine compartment connector as long as the key is on, so somewhere in the dash I have a short to power. Will run good for awhile then runs rough and stalls, restarts and stalls, let sit, restarts and will limp back to shop. Let sit for longer and it stars and runs good. Sounds like a fuel pump quitting to me. Yesterday I changed the fuel pump because I didn't notice the short to power. I am thinking the short may be robbing voltage from the pump. But that is not the main reason for my post.

When I fired it up this morning it was running rough, so I performed the injector buzz test. All buzzes sounded crisp, but I have one very odd thing happening. All the injectors buzz when it goes through the test. I even unplugged the right bank and got 8 buzzes from the left bank. Harness to engine is good and no codes are set. I have checked and cleaned all grounds as well.

I am suspecting an IDM, but have no tester to be sure. Any thoughts?

I am currently going to start pulling fuses to see if I can isolate the short to power for now.

Update: Pulling the PCM relay will remove power from the pump circuit. Somewhere, something that gets it's feed from the PCM power relay is feeding into the fuel pump circuit after the inertia switch. Wish me luck on this one. Posted Image

This is almost becoming a freaking blog. I removed the CJB and found a rats nest of scotch locked wires. Customer gave me the okay to remove the command start and look for green death.

Update: After inspecting the remote start I decided that was not the issue and discovered that the circiut splices under the hood and goes to the circuit monitor in the PCM.

DOES THE CIRCUIT MONITOR IN THE PCM PUT 7V INTO THE CIRCUIT KOEO WHEN THE PUMP IS COMMANDED OFF? DO I HAVE A MESSED UP PCM OR IS THIS NORMAL?

lmorris · February 22, 2013

I still haven't gotten around to figuring out the freaky buzz test.

Bruce Amacker · February 22, 2013

Even if you unplug both VC harnesses, you will still get 8 buzzes (?) from the IDM. It's been 10 years but I remember doing it a long time ago. I don't think I'd put an IDM in it at this time.

I'd put a small load on the 6v going to the FP and see if there is potential for current there or not. I'm wondering if there is a monitor circuit in there to verify circuit integrity through the pump? Just thinking out loud.

Many 7.3's will run (sometimes fine, sometimes rough) with the FP inop.

Posted Image

lmorris · February 22, 2013

More info on the buzz test may be needed. First it will buzz all 8 together. Then it will do them individually, and you can hear them go from side to side. This one does the all 8 first as normal, then when it does the individual injectors, you still hear all 8 buzz together, 8 times. I am pretty sure that is not normal. When I disconnected the right bank I can hear a crisp buzz from the one on the left bank that is supposed to be tested, then a lighter buzz from the left bank injectors which you should not hear. It's like all 8 are shorted to each other.

On the other topic, hotline states it puts a trace voltage into the system, so my 6v reading is normal. Still doesn't answer why I put a fuel pump in it and had the code return.

Aaron · February 22, 2013

If you pay the shipping and return it when you're done, I have a known good IDM in my toolbox. Probably won't be much from Ontario to Alberta, but the timeframe might not impress your customer.

As Bruce said though, I'm not sure you're into an IDM..but this is a head scratcher for sure.

lmorris · February 22, 2013

After putting the whole harness back together and putting the old pump back in, it has been flawless. 55 PSI under load, no codes. Maybe a bad connection that was inadvertantly fixed. It has a slight stumble at idle. flagged #8 but I don't trust that.

Read about PERDEL in another thread and has these: #3 2.5%, #5 1.4% #8 4.8%.

Can anyone interpret those here? I don't know much about them. Not sure if customer cares either, off idle it is good. Leaving IDM alone.

Thanks for the offer Aaron.

scott1984 · April 26, 2013

The IDM buzzes all 8 injectors at first and at in order all injectors do buzz it is designed to do that to keep from burning the IDM up. So yes if you pull connector off one bank the other bank will buzz.