3.5" Hg vacume and Duramax barely starts

[Dave B]

My 03 Duramax was starting hard last couple few days. Last night low was 33F. By 9:00 it was in the med 40s. After glowplug light went out cranked for about 15sec. Nothing. Cycled the glowplugs again and this time cranked until starter kicked out. Nothing but a little smoke. Cycled plugs agian and cranked for about 15sec before it finally started.

Dealer keeps blaming the fuel filter. Only about 5000mi on filter. Checked fuel system vacume with my gage from Kennedy Diesel. Showing 3.5"Hg with 5/8 fuel level. Changed filter then had 2.5"Hg vacume. Starting was normal.

Do I have a fuel pump problem, glow plugs, or bad injector. No error codes have shown up. I have had my truck at the local dealer 3 times for the same problem and can't get them to look past the filter. Last time I specifically told them I wanted fuel pressure at the rails checked and fuel return check and the glowplugs and they still wouldn't look past the filter.

Any GOOD Duramax mechanics in Ks?

[DmaxMaverick]

Good luck finding a good shop.

Your problem sounds like a plugged filter. Simple as that. It only takes one fill up of less-than-ideal fuel to get there.

If you need to know your fuel rail pressures, etc, get a scanner, or someone that has one, and read it. A Predator will show you what you need to know.

Also, a poor battery condition (or battery connectors) can cause the symptoms you describe. The voltage requirements for the PCM and EDU are much more sensitive than your starter. The engine may sound like it's cranking fine, but the voltage drop may be too much.

[Kennedy]

Taking the pessimistic approach, it could be that there is sopmething weak or leaking in the fuel system. I would definitely watch filter restriction, and log it as you go. My suggestion is to check restriction at full tank for most consistent readings. I would also look at what the restriction is with a new filter at 2,000, and 3,000 rpm and log this for future reference.

From there (here's where I get pessimistic) it could be that you have the early stages of a failing injector which could allow excess return fuel. When an injector allows excess return fuel, it makes the injection pump's job much more difficult, and as I understand, the ECM will not begin to deliver fuel until pressure hits 5k.


One remedy is to pump the primer up when this happens and see if it helps.

[madmatt]

It should have started W/ 3.5". I'd check the glow plug system first then go on to pump and injector return rates. I'd suspect it's a pump or injector since it started normally after replacing the filter and subsequently pumping the fuel system up real good.

[madmatt]

try this...put your Vac gauge on it and pump the fuel system to 10psi. normal bleed down time is two minutes. if it falls to zero any faster you've got problems w/ something other then your filter. if thats the case, you can show that to you service dept who refuses to believe you have problems beyond your filter.

heres some vacuum specs that may help if you don't have them already:
LB7 Common fuel system vacuum gauge readings:

Engine Speed
Gauge


Idle
1"- 3" Hg VAC
normal

3000 RPM no load
3"- 5"Hg VAC
normal at operating temp

Hard acceleration
6"-10" Hg VAC
normal

[Kennedy]

FYI, 6-10" HG = 3-5psi drop. This reduced pressure combined with heat is what causes the fuel to begin to vaporize. Keeping it under constant pressure with a lift pump will cure this.

To add to madmatt's numbers, fuel level as well as gauge position (at least with the KM gauge) affect the readings as does the angle of inclination of the vehicle.

[madmatt]

Thanks for picking up for me JK! When you spend your days messing w/ these things you sometimes forget to add these details while explaning things to other people.

[Dave B]

Vacume level has not had a significant change with fuel level chage. I keep thinking that if their is a fuel restriction I should be getting higher vacume levels. It may have gotten bad enough to find the problem. Shut it off this afternoon and it wouldn't start at all. Had to have it towed to the dealer. I have been fighting this problem for almost a year now. I know I have put at least a 1000gals. through since it first started. Mechanic still tries to blame the problem on non-GM fuel filters as well. They don't belive Racor makes the filters.

Maybe it's time to go back to a Powerstroke. At least maybe the local Ford dealer has better mechanics!

[madmatt]

Have their parts dept call PARTECH and ask who makes'em ;)