OK I'll start with my truck is a 99 24v auto. All stock aside from a beans sump and a fass 150. I had a edge ez but it's been removed. Also I just replaced the vp44 with a used vp44. Before I replaced it I had a hard set p1689 no communication between ecm and vp44. Once I put the replacement VP in the code immediately went away and right before I had all the injectors bled(almost had it running) it threw the p1694 in both ECM and PCM and then kicked me out of the bus connection. Still have power at the data link connector. 

Now I'm unable to connect my scanner(Autel Maxidas) to either, no tach signal while cranking, no wait to start light, no lift pump signal, and pin 7 on the vp44 isn't getting power. Likely because the fuel pump relay isnt getting the correct signal. If we put power to the wire from the FP relay that goes to pin 7 on the vp44 we can hear the VP click on. I've tested all fuses and grounds with my power probe 3 and all test good. I pulled the ECM plug and tested all the pins and it's getting correct power and ground from pins 48,49,50. I did notice all pins related to Cummins bus showed no signal or anything on the power probe. Pins 40 and 41 show 0.0 with key off and a little over 2v with key on. I may be making this harder than it should be but I'd like to rule out any other possibilities before replacing the ECM... Any help is greatly appreciated.

Well I decided to check my alternator for AC noise since that seems like a common problem on these trucks. It dropped to .01 and .02 a few times but seemed to consistently hold at 0.3 most of the time...  Took this picture where it was at 0.5... Gonna replace the alternator today and recheck.

Make sure they test it before you take it home.  It is really common to see 3 or 4 bad alternators in a row from a parts store.

OK I'll certainly do that. Thank you

AutoZone claims this as a pass.. and their new one tested at 0.40... Should i keep looking for another one?

Yep, you need to be at .03 or under.  More than that will cause issues.

OK I found one at another AutoZone and the guy said under actual ripple volts it showed 0.00 so I'm guessing that's the one I want? I'll have it tested again before I buy it just to make sure.

Well I've had 4 alternators tested and so far the lowest has been 0.33... This is proving to be more difficult than expected

Someone said the bench test wasn't testing AC leakage? And that's what's supposed to be below 0.03? This is so confusing....

Most auto parts stores when test alternator will only test if it's still charging very few test for bad diodes. Try to find a local starter and alternator Rebuilder they should be able to test it. When I rebuild my alternator changing diodes was half the problem, the other half was in Armature and brushes.  you can buy a new alternator that is not remanufactured, either Bosch or denso can't remember which one,  on line.

Took my original alternator to a local alternator shop and they tested it and the ripple was 0.03-0.04. they took the back off and checked the brushes as well and said they were real good. So I guess the alternator is not the problem... Guess I'll throw it back in and see if I can reproduce the original symptoms. 

Put the alternator back on and at idle I get AC voltage at the battery. Is that normal? 

That is high.  Typically it isn't the brushes but the diodes. 

 

If your alternator is disconnected at idle, what VAC do you show?

That was with the alternator connected. I'll have to check with it disconnected when I get home. I warrantied out the external voltage regulator because my voltage was jumping to 15.25volts.

4 hours ago, Shmokes24v said:

That was with the alternator connected. I'll have to check with it disconnected when I get home. I warrantied out the external voltage regulator because my voltage was jumping to 15.25volts.

 

The reason I asked is that I had bad relay that was making noise, once upon a time. 

 

So you are using an external voltage regulator?  Hopefully it isn't making noise, it really shouldn't though, but they aren't all clean. 

 

If your PCM's factory regulator was putting out that much voltage, it is probably toast.  Hopefully nothing else in the PCM are messed up.

Check vac directly from alternator not from the battery, it should be a more accurate reading. Note if you rev the engine up your VAC will also slightly come up. 0.03or less is for idle, you could see it higher when revd up. Also make sure everything is off like accessories, ect.

Edited March 15, 20178 yr by Dieselfuture

Marginal.... I've been getting .025 to .035 for alternators.

So here we are a year later. Tracked down a loose terminal in the under dash fuse block on fuse 9 which i was able to kill the engine from wiggling it. Pulled it out swapped pins out and now it has a tight connection. Thought i had found the problem so i hopped in and tried to take it to work this morning for a test ride and i didnt make it but maybe 5 miles and sure enough died on me and ecm turned off. I previously tracked down a popped capacitor on the PCM board and had it replaced by a friend who does that for a living and that changed nothing, cant for the life of me figure this out and cant get any hard evidence that its the ECM. I opened the case on the ECM and found nothing out of the ordinary. Been through the harness shaking and wiggling and nothing. However these last couple days something has been completely draining my batteries and noticed the grid heater codes again so i wonder is it possible the grid heater relays are shorting out causing transfer of positive voltage to the engine block grounds which in turn freak the ECM out and cause it to turn off? Ive just removed the wires off the battery and shall see if the batteries still drain. Truck runs great when it runs but something is causing the ECM to just shutdown. Im running out of ideas here. Just to recap on whats been replaced,

Ignition switch

Crank sensor and pigtail

Cam sensor and pigtail

Used vp44

Coolant temp sensor and pigtail

External voltage regulator

Pins on fuse 9 of the dash fuse block

Asd and FP relays

Oil pressure sending unit

Checked and cleaned all grounds i could find

Recalibrated apps

And just disconnected the grid heater relay wiring from the batteries.

@Shmokes24v what is that in the picture?

Pins inside the under dash fuse box.

Did ya get it fixed?

 

 

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