Increasing Rail Pressure to Control Idle Haze

[blueshift]

Hello everyone.

I have an LB7 (that I tune myself) with some injector(s) going out. Main rate in the 5s, and balance rate on #8 coming in around -4.5 to -5.0. Confirmed that #8 is the primary culprit via DVT in EFI Live. The haze and smell has gradually gotten worse, to the point of being fairly noticeable (and embarrassing) at stoplights in the daytime. They have >100k miles on them, so no love lost. I will be replacing them as soon as possible.

That said, I have a couple of 12-hr round-trips planned to the mountains for ski trips in the coming weeks that I'd really like to have the truck for.

I remember reading a while back that bumping up the fuel pressure can help with the hazing at idle. Threw in a tune that raised it up to 50 MPa from the stock 35 MPa, which cleared up almost all of the haze. Other than being slightly louder at idle, I don't notice any ill effects.

Here's my questions:
1. Is bumping the rail up to ~50 MPa at idle going to hurt anything?
2. How long might this short-term bandaid hold up? Or am I pushing my luck and should just go ahead and park the truck until it's fixed?

I'd like to have the truck for another month / 1000 miles or so, but I also REALLY don't want to get stranded 6 hours from home in West Virginia banjo country....

 

[Chevy1925]

I mean, it’s not horrible yet. I’d probably drive it like that. The higher rail is probably helping stop the leak for now if it’s clearing up at idle.

#8 ain’t your issue though. You add 3 back to your balance rates (main rate at 5, should be at 8 so add 3 to all balance rates). That puts 8 closer to 0

 

[gmduramax]

I wouldn’t risk it especially being in cold weather. When I was driving an LB7 it started to haze and went to not drivable within 100 miles. That was on factory injectors at 125,000 miles. I was only doing short trips at the time so I didn’t care if it left me stranded.

 

[blueshift]

I mean, it’s not horrible yet. I’d probably drive it like that. The higher rail is probably helping stop the leak for now if it’s clearing up at idle.

I wouldn’t risk it especially being in cold weather. When I was driving an LB7 it started to haze and went to not drivable within 100 miles. That was on factory injectors at 125,000 miles. I was only doing short trips at the time so I didn’t care if it left me stranded.

Yea, that's exactly my dilemma. It seems fine with the bumped rail pressure, but I'm worried that I might be making their demise that much more severe / quickly onset....

The cold weather thing is a good point I hadn't thought of. Last winter when I made this trip, it was right at 0 one morning.....

For what it's worth, the balance rates all come down to +/- 3 at the higher pressure. I get that it's not a valid comparison to what they're "supposed" to be, but it's still a comparison to each other. Maybe I'll keep an eye on them over the next week or so and see if they change very much.

#8 ain’t your issue though. You add 3 back to your balance rates (main rate at 5, should be at 8 so add 3 to all balance rates). That puts 8 closer to 0

Am I doing my math wrong? I thought that the main being 5 basically equated to "-3" (from 8). And therefore, #8's real numbers would be (-5) + (-3) = -8. That not right?

Either way, turning #8 off cleared up most of the smoke. #8 off and 50 MPa was zero smoke at all.

 

[blueshift]

I'm definitely going to put 45% SACs in it, and I've got almost 3 weeks before the first trip coming up.. If I knew I could figure out the tuning fairly quickly, I might try to go ahead and get it knocked out beforehand. Just worried that getting them dialed in will take a substantial amount of time...

Are there any reputable tuners left that could write a decent 'stock' tune for 45% SACs, just to get me by until I had time to figure it out? (You don't have to answer, kinda a rhetorical question....). Seems that all the tuners I knew of from 8+ years ago when I got into it have closed up shop....

 

[2004LB7]

Yea, that's exactly my dilemma. It seems fine with the bumped rail pressure, but I'm worried that I might be making their demise that much more severe / quickly onset....

The cold weather thing is a good point I hadn't thought of. Last winter when I made this trip, it was right at 0 one morning.....

For what it's worth, the balance rates all come down to +/- 3 at the higher pressure. I get that it's not a valid comparison to what they're "supposed" to be, but it's still a comparison to each other. Maybe I'll keep an eye on them over the next week or so and see if they change very much.



Am I doing my math wrong? I thought that the main being 5 basically equated to "-3" (from 8). And therefore, #8's real numbers would be (-5) + (-3) = -8. That not right?

Either way, turning #8 off cleared up most of the smoke. #8 off and 50 MPa was zero smoke at all.

When the main rate is low, you add the "missing" amount to all the injectors because the ECM is pulling fuel from every one of them equally with the main rate.

Read more here:

Duramax Diesel Truck Balance Rates

If you’re big into diesel engines, especially the Duramax diesel engines, like we are, you have probably heard of balance rates. You are likely even familiar with checking them so that you can determine the health of the injectors in your Duramax. But do

www.schultzdieselsports.com

 

[Harshman]

I drove mine for several thousand miles like that. Some of it pulling 12,000 lbs. Other than the smoke, smell and rough idle when hot it ran really well.

 

[Bdsankey]

I'm definitely going to put 45% SACs in it, and I've got almost 3 weeks before the first trip coming up.. If I knew I could figure out the tuning fairly quickly, I might try to go ahead and get it knocked out beforehand. Just worried that getting them dialed in will take a substantial amount of time...

Are there any reputable tuners left that could write a decent 'stock' tune for 45% SACs, just to get me by until I had time to figure it out? (You don't have to answer, kinda a rhetorical question....). Seems that all the tuners I knew of from 8+ years ago when I got into it have closed up shop....

SAC45% are a great choice! They're an easy injector to dial in.

 

[wydopenLb7]

I drove mine for several thousand miles like that. Some of it pulling 12,000 lbs. Other than the smoke, smell and rough idle when hot it ran really well.

Me too..no problems towing 15k unless you were next to me at a stop light..

 

[Bdsankey]

My only worry running trucks with known leaking injectors is cylinder washdown. That's what would stop me from doing it.

 

[Chevy1925]

My only worry running trucks with known leaking injectors is cylinder washdown. That's what would stop me from doing it.

Well, if you tow and run bigger tunes, you run the potential of higher egt’s in that cylinder and may cause piston cracking.

That’s pretty much what did in a LBZ we replaced an engine in. Cracked cyl 7. Found it had a l5p glow plug in it (customer swears he was given all lbz), was running crap tunes from a well known shop in our area and his injectors were “Bosch new” from a local distributor here in town.

After getting a new semi built engine in with the right glow plug, we had the truck retuned with quality stuff but truck still smoked even on a stock tune. Talked him into biting the bullet on another almost 5k for good injectors and truck runs clean as a whistle.

Sometimes it’s a combo of bad things that take them out so keep that in mind with your truck OP. Injectors are cheap in the grand scheme of things

 

[Bdsankey]

Well, if you tow and run bigger tunes, you run the potential of higher egt’s in that cylinder and may cause piston cracking.

That’s pretty much what did in a LBZ we replaced an engine in. Cracked cyl 7. Found it had a l5p glow plug in it (customer swears he was given all lbz), was running crap tunes from a well known shop in our area and his injectors were “Bosch new” from a local distributor here in town.

After getting a new semi built engine in with the right glow plug, we had the truck retuned with quality stuff but truck still smoked even on a stock tune. Talked him into biting the bullet on another almost 5k for good injectors and truck runs clean as a whistle.

Sometimes it’s a combo of bad things that take them out so keep that in mind with your truck OP. Injectors are cheap in the grand scheme of things

Bolded is very very true as well.

 

[blueshift]

Update for anyone wondering.

I kept on driving the truck after bumping the pressure, albeit only for shorter trips close to home. I used this time to brush up on EFI Live and tuning; it's been a minute since I've touched any of this stuff!

Anyways, the smoke was minimal and balance rates were pretty darn good for a while (< +/- 1.5). Drove perfectly fine, too, minus the slightly louder idle. But I'm at about 1000 miles now, and the haze is quickly coming back, and the balance rates (especially #8) are heading out again (-4.2).

So I have a set of S&S SAC45's en route, courtesy of @Bdsankey. Planning to tear into it this weekend!