LB7 Glow Plugs

[DmaxMaverick]

A couple days ago, The SES light paid me a visit. No problem. Plug in the Predator, and pull code P0380. OK, Glow Plug circuit malfunction. The engine has 2660 hours and 91,000 miles on it. This morning, I grab my ohm meter and tools. Done this dozens of times on every Diesel vehicle I've owned. Wait. Maybe I better consult the book. Could be some very valuable info there. Sure enough. 5 pages of diagnostics. Hmmmm. Looks like a bunch of unnecessary steps. It's just glow plugs. No surprise, but the ECM is very involved, moreso on CA trucks...Darnit! The diagnostic chart has some very useful info, and tells you how to use it. During glow plug operation, feedback voltage is monitored by the ECM. Fortunately, it is one of the parameters displayed by the Predator, "DIAGNOSTICS, REAL TIME DATA, ENGINE DATA 1, GLOW PLUG VOLTAGE". On a cold engine, the activated voltage will be displayed during the "WAIT TO START" cycle. When feedback voltage isn't within the range, something is wrong with the circuit, and the ECM orders the SES light to show up. The following voltage table will indicate the failure:

SIGNAL VOLTAGE.................GLOW PLUGS FAILED OPEN
5.00 - 6.00...........................NONE
2.00 - 3.00...........................1
1.00 - 2.00...........................2
0.80 - 1.70...........................3
LESS THAN 1.30....................4 OR MORE

In my case, 2.9 volts were indicated. Cool. That means one plug is open. This could either be a failed plug or a poor connection. On the early LB7's, the controller and all the wires are easily accessible. Should be a no-brainer.

Now, I pull the fender liners and have a look. Passenger side looks like a piece of cake. Driver's side, not so. All kinds of stuff in the way. Reflecting on my history of wrenching, I'm absolutly certain, whichever plug is suspect will be the 8th one I check, and it will be the most difficult plug to access. I are smart, so I do it backwards, starting with the driver's side, most difficult plug to check. I remove the nuts retaining the wires, and hit them with the ohm meter. 45 minutes later, all 4 on that side are good. Take a break (it's already 90

[More Power]

Good stuff... Thanks for the insight! smile.gif

Jim

[DmaxMaverick]

Update

Sunday morning, I had the chance to change out that failed plug. JK was kind enough to hand deliver the new plug to TDP Rendezvous. Thanks again, JK!

The replacement was extremely uneventful, so I won't bore you with details. 2 wrenches and 4 minutes.

Feedback voltage indicated 5.9 volts, at the upper end of the scale. No SES, and a smoother idle on a cold start (I didn't count on that).

One thing I did note was the insulation on the power stud. They are a soft mount insulator. Care should be taken not to overtighten the nut. It could damage the internal connection if overtightened, as the stud will twist. I could feel the softness when tightening, kinda' "spongy". The old plugs didn't seem as soft, but that could have been due to the mileage and heat cycles. Under the circumstances, a spade type connector may have been more practical.

[Kennedy]

Glad things worked out simply for you.

[DmaxMaverick]

TTT and opened for reply.......

[BozDMAX]

Maverick - Interesting narrative and got me thinking about having to do the same thing someday.

I presume that living in CA you have a CA truck. The wiring on the Federal trucks is different, with a relay instead of a controller feeding individual glow plugs. So I guess the rest of us just follow part one of your procedure?

Also, tell me more about the 'Predator'

Boz

[DmaxMaverick]

Maverick - Interesting narrative and got me thinking about having to do the same thing someday.

I presume that living in CA you have a CA truck. The wiring on the Federal trucks is different, with a relay instead of a controller feeding individual glow plugs. So I guess the rest of us just follow part one of your procedure?

Also, tell me more about the 'Predator'

Boz

Yep. Found that out almost immediately. I started another thread on that at the time. Diagnosis is similar, but on the Fed trucks, the plugs are wired parallel on each bank. This requires additional steps, but still similar enough to get the job done. Guess this is one time where CA emmissions actually does anything positive, for the wrencher, anyway.

Predator.....
It is a programmer/scanner. I bought mine for diagnostic features, reprogram for larger tires, and increase the speed limiter. It has some nice power adding programs, as well. Very easy to use, and programming is very fast, and idiot proof. The display is very large, compared to others. 8 line LCD with backlighting. If you are a DIY'er, it is priceless. It will display most all PCM/BCM DTC's in plain terms, and can clear the codes. It also displays over 100 realtime engine parameters, including injector balance and fuel delivery values. If you are considering one, I don't think you will be disapointed.