Injector feed pipes- how tight?

With ~350K on my LB7, my injectors are looking grim. One shows -2.5 balance at idle and I'm starting to see smoke at the tail pipe (the others vary from +1.5 to -1.0). I'm getting tired of taking this to the dealership for better than $4K each time (I'm on my third set and I've only got ~67K on them). So, I'm doing them myself this time. Questions:

What's your take on replacing only the ones showing high balance rates? I'm doing the work myself, so it's down to parts cost and a tight budget.

How tight should the feed tube nuts be at the fuel rail and at the injector?

And what type of sealant would you recommend for the upper valve cover? Would a black hi-temp RTV be sufficient? (I assume the lower valve cover uses a gasket.)

The fuel injector pipe nut torque is 30 ft/lb.

DO NOT replace only the injector with the "high" balance rate. If you do, you'll likely replace a good injector, and not replace a bad one.

Permatex grey "Right Stuff" brand is the sealant to use on the valve covers, upper and lower. No gaskets. I like the "cheese-wiz" can. Do not use black RTV.

I recommend having the fuel injectors properly diagnosed, if you suspect you may have failed injector(s). The indication of one, or several injectors balance rates high or low is NOT an indicator of THAT injector being the bad one. In fact, an injector that's failing open (unable to stop/reduce the fuel flow, for whatever reason) will normally be the injector with the excessive NEGATIVE balance rate, and short PWM value (.2-.3 ms). The balance rates are fuel volume compensation values, and most often will show how it's compensating for an (other) injector out of spec. +/- 2.5 is not significant, and quite normal, even for new, healthy injectors. Balance rates compensate for much more than ONLY fuel injector imbalance conditions. There is also other data to examine during diagnosis, such as PWM, fuel return volume, pressure response, etc. These other values are often more indicative of injector health than the balance rates alone. Failed injectors are only one of several possible causes of smoke.

I believed I had an injector problem being that the odor from my tail pipe has been quite strong of diesel for quite some time. The "smoke" comes and goes. I work for the "General" and have access to a Tech II monitor. I can check the balance rates and pulse width values and report back. Does the Tech II report fuel return volume or is that something that is only determined on the bench?

I had the heads off about 4K miles earlier, but funds prevented me from adding more (injectors, water pump, etc). It is what it is. But even before the head gasket replacement, I was smelling raw fuel from my exhaust. Which is why I suspected injectors. Can you comment on what the Tech II will report?

And is the 30 ft lbs on both the nut at the injector as well as at the fuel rail?

It doesn't specify which end, just injector pipe nut, so I believe it's both, which makes sense. The nuts are difference in appearance, but are mechanically the same, or close enough. The cross-sectional area is the same at both ends, which means both ends see the same force.

Return flow rates are a mechanical test, and time consuming. The PCM will only detect fuel pressure loss, pressure that wasn't available where it should have been. If you aren't getting a P0093 or P1093 codes, then the test is usually not done.

With the Tech II, in addition to the BR and PWM values, you'll also be able to check the pressure response values, demand vs. actual, and stability. You can command full pump pressure at idle. If it is able to maintain stable full demand pressure for a period (1 minute), then it isn't losing much to the return. This really should be done by an experienced technician, and by the correct procedure. Otherwise, you could cause damage that a tech may recognize before it happens, and your data may not be properly logged and interpreted. If all you get is the BR and PWM values for each cylinder, it should be enough to at least see the general health of them.

Anyone buy these injectors from GMPartsDirect.com? They say they're selling a GM approved, rebuilt injector. However, they aren't specific on whether the 2 O-rings are present, they talk about a "gasket" (which looks like a valve cover gasket on their web picture), and they won't state if they're indeed Bosch rebuilts. I know DMaxMav stated "no gaskets" earlier....

Also, $200 S/H for a set of 8 is a bit steep and there's no return for such "specialty parts" if they're not what I expect them to be. Are these guys to be trusted?

Gmpartsdirect is a real dealership, and they sell OEM parts. They also sell aftermarket parts, but will state that in the description. If you locate them by part number, they will be OEM, or clearly state otherwise. I've bought from them many times, but you have to be creative about it, or get stuck with a $200 shipping charge for 8 injectors. When I saw that, I ordered over the phone and it was more realistic. It's been a while, so I don't know if they still do that. I haven't bought from them in a while because of (unrealistic) shipping snags. If you have questions, they do well to answer emails. Make sure you include your full VIN when asking about model/engine specific parts. Their "no return policy" applies to restock parts, not defective parts. However, when it comes to parts such as fuel injectors, if you have a failure, they'd likely claim you caused the failure during the install. You'd do better getting them at a local store, if you can use your GM employee association to get them at/near wholesale. Otherwise, go with a reputable supplier, such as Kennedy.

There are other good suppliers that don't play the S/H game.

I don't know about the gasket. I've seen them in the "kits", but don't know anyone using them. It is tempting, though, in case you intend to be back in there anytime soon, such as a valve adjustment (I'd use them, in that case, but seal it up after). I've never used VC gaskets on any GM (or most any) Diesel. They ALL leak, eventually.

Any tips or recommendations on replacing the injectors on a LB7 on the left (driver's) side? I pulled some of the hoses and wiring off of the engine recently to get a feel for what's involved. Looks like a lot more crap to contend with on the left side. The right side doesn't look quite so bad.

Any tips to lessen the grief that awaits me? Looks like draining the radiator and pulling the upper hose/pipe is mandatory. Is pulling the glow plugs or removing the interconnecting power strip on either side necessary?

I think I've resigned myself to either renting or buying a beater in the meantime because I'm not completing this job in a weekend- being this is my first time into the job.


On the reason for the injector replacement:
Originally, I reported smelling raw fuel in the exhaust and seeing smoke from the tailpipe- the smoke comes and goes. DmaxMaverick responded with input on BR vs. PWM. I've borrowed a TechII from work and recorded some values over the course of a few days. The data may not seem too bad:

Cyl Ave BR HI Lo Ave PW Hi Lo
1 -0.5 0.2 -0.9 0.30 0.32 0.27
2 -2.0 -1.4 -2.5 0.26 0.27 0.21
3 0.6 1.5 -0.3 0.33 0.37 0.27
4 0.1 0.7 -0.3 0.32 0.35 0.27
5 1.7 2.2 0.8 0.37 0.40 0.31
6 -0.2 0.1 -0.5 0.31 0.34 0.26
7 -0.2 0.1 -0.7 0.30 0.32 0.27
8 0.4 0.9 0.0 0.33 0.35 0.29


Cylinder 2 varies a bit, occasionally at -2.5 and I've seen the PW sit at 0.21 for some time. Cylinder 5 often times remains at 2.0 but has been less. All cylinders seem closer to 0 +/- 0.5 after a long 4 hour hiway cruise. Although the BR haven't approached the +/- 4.0 in park, the smoke at the tail pipe still comes and goes. I don't know; maybe I'm worrying too much. Maybe the smell and smoke should be tolerated for a while longer. Oil analysis hasn't shown any fuel and I haven't seen any using the paper toweling test from the dip stick. If I have to get into this engine, I'd rather do it now with the summer weather (and before the hunting seasons start).

Any comments?

Data table in previous post lacks formatting-
attempting a more readable view (may/may not work)....


Cyl____ Ave BR___HI_____Lo__________Ave PW___Hi_______ Lo
1_____ -0.5_____0.2____-0.9__________0.30_____0.32_____ 0.27
2_____ -2.0_____-1.4____-2.5__________0.26_____0.27_____ 0.21
3_____ 0.6_____1.5_____-0.3__________0.33_____0.37_____ 0.27
4_____ 0.1_____0.7_____-0.3__________0.32_____0.35_____ 0.27
5_____ 1.7_____2.2_____0.8__________0.37_____0.40_____ 0.31
6_____-0.2_____0.1_____-0.5__________0.31_____0.34_____ 0.26
7_____ -0.2_____0.1____-0.7__________0.30_____0.32_____ 0.27
8_____ 0.4_____0.9_____0.0__________0.33_____0.35_____ 0.29

In my opinion, according strictly to your data and other comments about them, I suggest looking elsewhere for your smoke and odor. That table of data looks quite typical, approaching ideal. Add to that, if a bad injector causes smokey exhaust, it will typically always cause smoke, not come and go, as you say. Another test you can do is, at normal operating temperature, at idle, in D (E-brake on), A/C on, disable the engine idle balance. To do this without a Tech II, simply apply 1% throttle angle, or enough to disengage the balancing, but not enough to increase engine RPM. If the "change" in sound and feel is not significant (loping engine), then the injectors are not greatly affected by the balance program, and not a problem. Replacing injectors at this point would possibly, and perhaps likely, leave you with worse numbers that you are seeing now. Unless you have some extra cash burning a hole in your pocket, and are really anxious to get some experience, I wouldn't touch them. The injectors in my 2001 have been replaced twice, and they've NEVER looked that good. Not once.

The "paper towel" method of checking the oil is only necessary if you suspect the oil level is increasing. If the level remains normal, there's nothing to suspect, or check, in the oil. If you have enough fuel to show on paper, the level will be increased. By the time increased oil causes smokey exhaust, the crankcase is full, with at least an additional 5-7 qts. of fluid. When this happens, the smoke will be rather overwhelming, leaving little doubt. The engine will also run very rough at idle, and there will almost always be an alarming drop in oil pressure. Unless you are seeing these symptoms, continue your diagnosis elsewhere.

In the absense of related DTC's, I suggest looking more closely at fuel quality as a cause of idle smoke. Perhaps try a good lubricating and cetane boosting additive, and another fuel source.

DmaxMaverick you're reply to chessy56 got me to thinking about my truck. It smokes sometimes and sometimes it doesn't at idle. So I ran the fuel down to 1/4 tank and added 40 oz. of Power Service ( sorry don't have any Standyne) to that 1/4 tank and drove it around and is stopped smoking at most stops, but did return when I got back to the garage. Can a dielsel injector get dirty or carboned up on the tip and not close properly? If it can, would one be able to clean it by using extra cleaner and cetane booster?

Back in my 6.2L diesel days, I found that during the winter and a few K miles of light-duty commuting type driving, the engine would gradually begin idling rougher and smoke differently than it did during the summer.

When spring and camping season arrived, we'd tow our travel trailer to an area campground. This extra load (and much higher average exhaust temperatures) on the engine always-always produced a smoother running and less smokey engine.

My LB7 is sorta in the same situation now. I've not towed with it for a quite a while, and I almost always drive for fuel economy - light on the pedal. I ask myself, is this contributing to a rougher running engine? I dunno...

The "valve" that controls the fuel flow to the nozzles is internal. The external soot buildup will have no affect on how the valve works. It will either close, or it won't. If it's intermittent, due to valve damage (ball seat erosion), no amount of cleaning will change that. If it's fouled, it can be cleaned, internal or external. Excessively sooted or damaged nozzles can cause issues with spray patterns, which can affect combustion quality, which can cause some smoke. This can be more pronounced at idle, with significantly lower injection pressure.

"Extra" cleaner won't help. 40 oz. of Power Service in 1/4 tank is WAY overkill. A double recommended dose is overkill. Also, the jury is still out on the affects of biodiesel. I've seen the affects of it on older Diesels, including 6.2, 6.5, 7.3 and several foreign small cars, and the result is fairly consistent, regardless of the perceived quality or concentration (25% and more): Residue buildup will foul the injector nozzles, every time, over time. The internal fuel supply condition, before high pressure, can't be much different. I don't know if the much higher pressure seen in later model Diesels makes it better, or worse, but I suspect it will have some affect.

Thanks for the explanation on the flow control valve, make sense to me. Also experienced the same situation with my LB7. When towing really heavy, hot climate, long grades, after a day or so of that when I stop, the engine idles silky smooth, but most of the time it doesn't. I noticed the slightly rough idle when I first drove the truck for a test run before I bought it new, it does not normally idle smoothly unless it's worked hard. Maybe I'm getting paranoid about the old 02, wondering if it's getting time for something new, but I always said I was going to put a million miles on that one. Now I'm wondering why, with dual filtration, would there be anything wrong with the replacement injectors? There is so much to consider! Especially the fact that I don't have smog pumps, catalytic converters, exhaust recirculation, and exhaust fluid and particulate traps to be concerned with. Do I really want to go there?

Chessy56 before you consider doing an injector replacement yourself, you might want to locate a Helms Manual which takes you through all the steps, special tools, adhesives and lubricants, sealers etc. to do a correct job. The ole put some RTV on it it will hold ain't gonna work. Just the amount of items to remove, wiring to tag, fluids to drain, parts to get out of the way just to get to the injectors is a major job in itself. I've wanted to tear my engine down and go through it and check everything out just to see what condition everything is in, but ever time I consider how much time It would take me I change my mind. The older I get the more, if it ain't broke don't fix it has more meaning. I'm not suggesting you wait until it breaks, because that is way too expensive, just be sure it needs something before you jump in there to replace it and I think as you continue to search for the answer you will figure out for sure what needs to be done.

My commanded vs. actual pressures are pretty close to each other. I've seen a bit more variation in my BRs lately and have noticed that I blow a puff of smoke at startup and virtually none when the engine is cold. It smokes with greater frequency (nearly all the time) after the engine has warmed up. Yet, my BRs would appear to be under the 4.0 limit in park/neutral. If I give it 1% TA (and cheat the balance program), I hear and feel a "subtle difference" if anything, but nothing I'd describe as "definitely noticeable". I didn't try commanding the FP to max at idle as I don't know what I'm doing with a Tech II to force abnormal conditions w/o causing damage. My oil pressure appears normal. I've changed both fuel filters (primary & secondary) and have changed my fuel supply to a local Kwik Trip truck stop. No reduction in tail pipe smoke.

The Power Service (gray can) doesn't do anything to eliminate the smoke and for that matter, neither did the use of Seafoam. Haven't tried ATF fluid like I've seen elsewhere on this site. I've been running the Stanadyne Performance additive- haven't tried the FPPF yet to see if it'll make a difference. (I suspect at this point, no "additive" is going to make a difference.) The smoke I see is mainly at idle with a small cloud initially as I accelerate from a stop; I don't see anything cruising in daylight, but do see the smoke as I accelerate at night with headlights behind me. I was thinking of disconnecting the return line near the firewall and hitting it with compressed air to see if there was any blockage (JK mentioned that he found something along this line in an earlier post). I don't believe the '01 has a PCV or EGR valve- it's just a breather to a collector. I've cleaned the MAF sensor after cleaning/oiling my K&N air filter- no difference. If there's any other suggestions as to what to look at, I'm open to ideas.

There's other things I'd rather being doing with my time than replacing the injectors, but I've looked it over and have found some nice step by step instructions on the web. My "edge" (if any) is being a GM employee, so I can get the injectors @ ~$210 ea from my local dealership. Replacement OEM feed tubes are pretty reasonable too. I looked at GMPartsDirect.com, but their shipping is outrageous (and they won't let me place a phone order to attempt lower shipping). I've been thinking of a subscription to AllData DIY; might not be a bad idea unless someone thinks a Helms manual is superior.

Other thoughts?????