6.6turbo compression

[Bowtie4life]

I am new to the diesel world I've taken control of my fathers 2002 2500 HD 66 Turbo. Did a compression test over the weekend and all cylinders are between 775 PSI and 800 PSI is this normal? The only thing I can find online is that there should be a minimum of 300 PSI any advice and help would be greatly appreciated trying to get this thing back on the road. Also did a balance rates reading and have for bad injectors thank you very much for your help

[DmaxMaverick]

Welcome aboard!

You need to run the test again. The engine should be up to operating temperature, and this time, shut off the fuel. Just cranking with the key won't do that. You're lucky you didn't blow the gage (most have a small enough orifice that prevents that, but not all). The Duramax engine will compression-fire the fuel without any heat help, even on a cold engine. Pull all the glow plugs, and use a starter switch tool (a momentary, hand-held button/switch with alligator clips that connect to the starter solenoid --get one at parts store or Harbor Freight) for cranking during the test. KEY OFF. 6 puffs (needle jumps) exactly for each.

[Bowtie4life]

Thank you very much. I had a mechanic friend of mine help me do this we did disable the fuel after we've been running it in his driveway we pulled all 8 glow plugs to do the test first couple tries blue the release valve on his compression gauge and then change to new needle and did the test again and that's when we came up with the seven 75 and 800 PSI I will try it again with a starter button and leaving the key off probably won't happen until this weekend and I will let you know on an update from their thank you much

[Bowtie4life]

By the way what should an average compression be for that motor it has 240000 something miles on it and is been driven like a grandmother owned it

[DmaxMaverick]

The mileage isn't relevant unless you have symptoms of something. Compression should be above 300, all within 10% of mean and/or a 15% maximum spread. If they are all within 775-800, the actual pressure value is irrelevant. What is important is the range, high to low, and departure from mean. 3% is well short of an industry standard 5% margin of error, so they are essentially the same. With those numbers, I'd not look at it until another 240K.

Is there a symptomatic reason for testing? Curiosity?

[Bowtie4life]

My father has dementia and ran unleaded gasoline in this truck we do not know for how long would you not know how much I was mainly concerned before spending the money on injectors to make sure that he didn't hurt the Rings or the Pistons and let me say this again thank you very much for the info it is a very big help I'm new to this and need to learn a lot

[DmaxMaverick]

If the engine starts, runs and sounds mostly normal, there wasn't enough gas in it to do significant harm, if any. If you get enough to hurt something, it will run horribly, and not start cold. There have been some extreme cases noting some damage, but I'm fairly certain we didn't get the whole story. I know of one that burned pistons and injectors, but it was very full of unleaded, and they ran through about a dozen battery charge cycles trying to get it started with ether, then ran the pee out of it when it did start (the rest of the story). The late models were designed to run on low sulfur fuel, which has not much more lubricant quality than unleaded. If it starts and runs normally, or close, just get some good fuel in it, change the oil and filters, and don't look back.

[Bowtie4life]

That is a big load off my mind I was so worried that I would be ended up replacing an engine hi we did do a balance rate test and while it was running I've got three injectors that are definitely shot and one that wants to work and then goes way high and then goes back to normal and way high again so here are the next couple weeks it will be getting a new set of injectors and all that goes with that a lift pump and an artboard computer so I can watch this Beast run like it needs to thanks again

[DmaxMaverick]

Post your balance rate values, as well as the PWM values. These have been routinely misread since they were a thing. A very high or low rate of the balance alone rarely indicates an issue with that specific cylinder. Add to that, many of the early aftermarket scanners mislabeled the cylinders (the Duramax cylinder banks are opposite that of typical previous GM engines --apparently, they simply never actually looked), so chasing individual cylinder issues was a fools errand. The balance rate (fuel volume rate) must be read with the PWM (dwell) and interpolated as a collective. A very high or low, long or short event is most often balancing (compensating) another cylinder, or one or two cylinders bouncing up and down off of zero is often a misread by the scanner, or the scanner resolution is too wide or narrow. What's the difference in feel between balanced and unbalanced mode? Cold idle is usually the most profound, but disabling the balance mode when hot can also be helpful. Applying 1% throttle angle on a warm engine will disable balance mode without increasing commanded fuel volume. 240K is the likely suspect on old injectors if they haven't been replaced in a long time/miles, but sometimes not. The injectors may be due for replacement, but I think I'd hold them out for last, and start at the other end of the fuel system (lift pump, etc.). If you truly have injector(s) coming and going, it should be generating some codes, at least cylinder balance complaints (don't rely on the scanner, let the PCM tell you where it hurts), along with a very noticeable engine lope and/or knock. This can also be cause by other issues the PCM doesn't monitor.

[Bowtie4life]

After I got the truck I went to Gilchrist Chevrolet in Tacoma and had them look at their computer to see what all they have done to that truck my father bought it from brand new and always took it to them for service never let anybody else touch it they as far back as him buying that truck has never replaced any of the injectors and like I said it has no lift pump so that's what I figured we would start I'd have to check again on the balance rates I don't have that info with me it does smoke at an idle pretty decently when you give it throttle going down the road I'm pulling it looks like a jet fighter pull up blowing smoke behind me it's just massive if it sits at an idle too long it does start loping I don't know if that might helpi

[Bowtie4life]

Also when I first got a hold of this truck and noticed that it was hazing we immediately change the oil fuel filter had to change out the water separator cuz he had broken the wires to it and the truck has not gone more than 10 miles because of the smoking still happening I have told the fuel-cell and have that cleaned out and put back in so yeah I don't drive it I don't want to hurt it so it's only got maybe ten miles or so on the new filter and oil

[DmaxMaverick]

Forget all that balance rate mumbo-jumbo. With that many miles on original injectors, and that much smoke, you probably have a crankcase full of fuel. This could also explain your high compression numbers. Stop where you are. Don't run or drive it until the injectors are replaced (along with new fuel return lines, which have a high likelihood of cracking, if not already), and the oil has been changed. Once the oil level goes over, it will completely drench the underside of the truck with fuel/oil. Fuel in the oil isn't good for the engine either, but minimal use hasn't shown any damage.

[DmaxMaverick]

The "water separator" is just a float in the bottom of the filter. It's passive, and if disconnected or with broken wires, does nothing and doesn't trip the WIF lamp (although it may if the wires are shorted). The only water separator is gravity and the filter element media.

My WIF sensor wire has been broken off since the truck was about 5 years old. Never missed it.

[Bowtie4life]

At least I know not to never look for the light on the dash hey this what happens when a newbie starts working on a diesel thanks much I'll let you know about the flow rates and what we come up with thanks again

[Kennedy]

The blue haze at idle is injectors. We have a cure for that. Standard injectors tend to repeat in about 40k.

Many just eliminate the water in furl sensor and put in a billet plug with a drain valve that actually works.

[Bowtie4life]

I checked the oil level the other day when I did the compression test and the oil level is full where it should be is actually quite clean since it hasn't ran very long since I did the oil change on it and does not have any diesel fuel smell whatsoever and to Kennedy I figured we were having issues with injectors but I just want to check everything else out before I spend that kind of money here in the next couple weeks it will be getting all new injectors and the parts they also go with that and I'm going to enjoy this truck thanks a lot guys