Injectors: Front Vs. Rear

[Jeepsinker]

I have been noticing my truck losing power little by little over the past couple of months, so i decided that with now over 2000 hours on them it was time to change the injectors or have them rebuilt. The easier option for me was to change them out because I had some low hour ones on hand. I noticed when I removed my old ones that the back three were carboned up, not coked, just some very soft carbon that wiped off with a paper towel. The front three were absolutely clean. No carbon, no coking, nothing. Clean silver steel. I know that the rear three cylinders are said to receive more fuel than the front three, but I'm just curious if the clean injectors is normal or if it may signify an issue that I am unaware of like a failing metering part in the injector pump or Hydraulic head.

 

[m-35tom]

all receive the same amount of fuel, anything else would be an impossibility. where did you get that info?

 

[Jeepsinker]

I have seen it mentioned multiple times that the rear three cylinders get more fuel and that is why thermocouples for pyrometers should be placed in the path of the exhaust of the rear head just before the turbo. Apparently the rear three cylinders get hotter. I haven't substantiated that claim, just have seen it a few times on here, and then found my rear three injectors carboned and my front three clean.

 

[m-35tom]

sadly, much of the info on the internet and also on this forum is simply wrong. all injectors get the same amount of fuel. now it is conceivable that since it is an inline engine, the rear cylinders may run hotter, but from a practical sense, not enough to matter.

 

[WillWagner]

If the tips of the injectors have no carbon on them, they ain't firing and never have. No one cylinder gets more fuel than another. diesel fuel injection is a very precise event.

 

[Jeepsinker]

I understand what you mean, and perhaps I exaggerated when I said no carbon. There is a very small amount on the very ends of them, but none on the sides of the tips, whereas there was on the rear injectors. I know my truck is running on all cylinders. It runs pretty smooth even at a low idle. All that I have noticed is a reduction in power and throttle response. I have not seen any other indication of an issue, but I didn't get my power back when I changed the injectors either. I also changed my turbo yesterday after finding that the thrust bearings in my D turbo had some fair wear on them. I installed a C turbo I had as a spare and I'm still seeing the same top end boost numbers. Topping out around 7 lbs.

 

[m-35tom]

7 psi boost is very low and indicates a fuel or tuning problem. it is just not getting enough fuel to make any power. stock setting is 9 psi and is very conservative. what was your boost in the past?

 

[Csm Davis]

Hey jeep did you change your fuel filter? I am not trying to dig at you but even the the best of us forget the little things.

 

[porkysplace]

Are you running straight Diesel or waste oil ?

 

[Jeepsinker]

Yeah Jeff I change all three filters regularly. My in tank pump and all is working fine and all that good stuff. I run straight Jp-8 with some Tcw-3 and sometimes, mainly on longer distance trips I will add ten to twenty gallons of on road diesel. I never added a boost gauge until I started losing power. I still don't have a pyro. I did bump my smoke cam up just a bit this morning ( moved the end up toward the sky) and got 8 lbs on the top end. The truck used to nearly put me back in the seat accelerating through 1-3rd gear and still had plenty of pedal response left at cruising speed in 5th. I don't have any of that now.

 

[Jeepsinker]

I just read through the sticky on turning up the fuel again to refresh myself because it has been a while since I read through it. I already turned up the main fuel the other day and only saw a small difference, then today I messed with the smoke cam adjustment and got a bit more boost. I guess I'm just going to turn up the main fuel up some more and readjust the smoke cam and then the droop screw to my liking. I'm just still trying to stay conservative with it because i pull a lot of heavy loads in some fairly hilly terrain sometimes, and I do go pretty far from home.

 

[welldigger]

I wonder if fuel isn't starting to bypass the hydraulic head from wear. Also do a compression test. One of your head gaskets may be starting to fail and loose compression. Or some other problem leading to low compression. It will at least tell you if it is your engine or fuel system causing the problem.

 

[whatadeuce]

Hello Everyone, In an effort to follow this thread what is boost pressure, and where is the gauge installed?

 

[Jeepsinker]

I wonder if fuel isn't starting to bypass the hydraulic head from wear. Also do a compression test. One of your head gaskets may be starting to fail and loose compression. Or some other problem leading to low compression. It will at least tell you if it is your engine or fuel system causing the problem.

I believe you may have called it out on the HH comment,not sure if things work that way but it seems plausible and likely in my case. Remember my badly rusted fuel tank causing me trouble for the first little while I had the truck? May have damaged the HH from that. On the other hand, I did notice a film of what was obviously engine oil residue in the radiator filler neck when I did my cooling system flush and fill last week. No oil in my coolant or in my coolant expansion tank I added though. The front headgasket has had a very minor oil seep at the front since I got it. I dont see that as abnormal at all after owning Jeeps with inline six cyliders. They all seep oil at the headgaskets.

 

[Jeepsinker]

Oh, I forgot, I was getting 7lbs boost. Gauge mounted by the Windshield center post angled towards me. I just went out and adjusted the droop screw and smoke cam and drove it again. This makes the fourth time I have adjusted the fuel in the past few days and I finally got the performance that I remember back. I'm getting right at 10.5lbs boost now and I'm content with it. Now to just see if it stays this way.

 

[welldigger]

Pull the shut off cover on the injector pump with the engine running. Use a mirror to see if fuel is leaking down into the pump housing.

 

[Jeepsinker]

Wouldn't it contaminate the engine oil with fuel if it was doing that?

 

[welldigger]

Yes.

 

[Jeepsinker]

ok. I have yet to notice my engine making oil, but will check tomorrow with a mirror.

 

[mhassett]

If you are making oil, then diesel fuel is leaking past the fuel density compensator. By-pass fuel density compensator.
MHassett