LB7 idle and cold start issues

[TILMSTR]

Ok guys, this one will burn up some brain cells. My 02 injection pump failed at 371,000 miles. Wrapped up the new install and now I have a long crank/no-start issue on our last cold day(40 degrees)here in FL. I have no problem with warmer weather starts.(other that issue #2) I have checked everything connected to the glow plug system. Ohms test on each glow plug was stellar @ 3ohms each. Controller, both intake heater and glow plug relays, are functioning normally. The fuel heater hasn't been tested but it is a brand new complete filter head unit so I am 99% confident its ok. (There's always a chance of a lemon)

That's issue #1

#2....I also have a idle issue with it pulsating until it reaches 170 degrees. As soon as she reaches full temp the pulsating goes away.

There are no codes, no smoke present. So give it your best shot! I'm stumped.



Thanks in advance!!

[DmaxMaverick]

Welcome aboard!

Forget about the glow plugs and intake heater, especially in FL, at least for now. At 40F, the engine won't miss them for a start. Mine starts just fine to sub-zero temps with them completely disconnected (I tested it). Any issues with the glow plugs or intake heater will set codes and trigger the SES lamp.

It sounds like you have air getting in, or the pump isn't getting the pressure high enough, or just barely enough. You'll need a capable scanner to observe fuel pressures. You can try bleeding the fuel filter and pressuring it up before a cold start. If this helps, start looking for an air leak.

The higher temp smooth idle is likely the (fuel injector) cylinder balance engaging. This is normal operation, but a really rough idle may indicate problems with the system. You can verify this, once up to temp and smooth, by applying 1% throttle angle (step on the skinny pedal slightly, but only enough before the RPM's increase). This disables the cylinder balance (it should return to rough idle), and it should remain rough for a couple seconds after you let off, before smoothing again. If this is the case, the fuel system (injectors) may be significantly out of spec (a cylinder balance test is in order).

[TILMSTR]

Thanks for the reply Dmax. I did all the checks prior to tearing her down to verify that it was the pump that failed. The supply side held 15lbs from the tank thru the filter so no air getting in unless its the sender itself.

I also have a Snap On MODIUS scanner and have been able to view all the parameters. It's crazy to watch but just as it warms up the idle smooths out and all the values falls right in place where it needs to be. I did notice, however, that the FPR command was a tad low. IIRC, it was at 38 and the normal parameter is 40-45. It's not a rough idle either, just more of a surging.

What gets me is I can plug the truck in, warm her up for a bit and she will fire up. It'll still surge while idling but at least running. Our first 40 degree morning she wouldn't even fire up. As for the skinny pedal test, it's quite the opposite. If I give it more throttle, it will smooth out and again the values hit their mark and stop jumping all over the place. Plus the injectors are only 3 years old and not a lot of miles, probably less than 40k on them now.

[Kennedy]

Back in the day when these trucks were new (and I think limited to 2001 models) the rolling idle flow chart was this:

1) Rolling idle cold= software
2) Rolling idle warm= regulator

Now all of this should be old news and the model year does not fit, but I would also be looking at the fuel filter and say that you need a lift pump. The CP3 has been known to last seemingly forever.

My other thought which is the most likely is the source of the reman pump. I see LOT of sub standard stuff especially if "reman" by anybody other than Bosch Factory. I won't name names, but I suspect the answer will be coming soon.

More reading on lift pumps: http://www.kennedydiesel.com/docs/Duramax%20lift%20pump.pdf

[TILMSTR]

Thanks for the reply John. I'm under the same thoughts on the pump. I've already contacted my vendor to see what we can do. At the very least I'd like to swap out the FPR to see if it makes a difference since none of these issue were present before the swap.

IF, I have to swap this out, Is the new Bosch pump available? I see you have it listed on your site.



Thanks!

[Kennedy]

Thanks for the reply John. I'm under the same thoughts on the pump. I've already contacted my vendor to see what we can do. At the very least I'd like to swap out the FPR to see if it makes a difference since none of these issue were present before the swap.

IF, I have to swap this out, Is the new Bosch pump available? I see you have it listed on your site.



Thanks!

if we don't have one on the shelf I'm sure I can get one shipped direct. If your supplier is in state (FL) I have VERY high suspicions. I have never seen a Bosch regulator bad from new so I would consider not wasting my time swapping it.

[TILMSTR]

Ok, I think may have be unclear trying to respond before having to get out the door. I was talking about swapping out the entire pump again. That was my question, if you had a new pump in stock. My concern is that if I do anything to this pump, including just swapping out the FPR, that it will void my warranty. Just waiting on them to respond now. Thanks!!

[Kennedy]

Did you ever get anywhere with the current pump?

We have LBZ/LMM pumps in stock and LB7 are easily obtainable as well.

[TILMSTR]

Hi John, the cold start issue has seemed to resolved itself but I still have a lopey idle and it's worse on colder days. I gotta say though; the pump itself has gotten my towing issue and throttle response back to where it was from the start. Now if I can just get the idle issue worked out I'd be happy, I've just been too busy to deal with it at the moment, and will definitely order a new pump from you if I end up sending this one back.