Need help with some issues after no. 6 cylinder replacement...

[Mopar1973Man]

Alright gentlmen.. I got my results for compression test. Injectors were pop tested and all checked out to be working normal.

Cylinder

1 - 245 psi

2 - 250

3 - 250

4 - 250

5 - 250

6 - 255.

I still have that whomp whomp sound thru intake. and as far as I know still burning oil.. I just figured out the edge has settings within each setting. Going to mess with that to see if it gets rid of some idle haze. I'm going to top off the oil and run it some more to ensure it still burning oil. Thnx for any more suggestions u have... And appreciate you guys that following up.

sent from my cell...

Ummm... Think its time to rebuild. If I'm not mistaken you should see between 400-450 PSI on a good tight engine and no lower than 350-375 PSI on a wore engine.

As quote here...

http://articles.mopar1973man.com/general-cummins/34-engine-system/144-compression-testing

In general, you are going to want to see at least 375 psi all across the board. In real life, 9/10 when you check a motor that runs good it will be above 400 , 450 500 psi depending on the motor. Shouldn't see too much of a variance between two adjacent cylinders, if you do it is often indicative of a head gasket combustion leak. Normal to do both a leak down and a compression test if you are trying to find a problem.

AFe cold air

You might want to check that AFe I think you had a dust leak and ruin a set of rings.

[ISX]

The whomp sound and the fact that #6 is the same compression as the rest even after you replaced it makes me wonder. The oil consumption is also interesting. You bought the engine with #6 messed up so who knows what else could be wrong but nevertheless #6 should have tested good. Just sounds like all 6 intake valves are leaking or are just flat out all timed wrong but the cam is on a gear so the only possibility there would be the cam is a tooth off which I doubt but who knows. Just seems like something the previous owner did seems to have thrown everything off.

[freedomisntfree]

Ummm... Think its time to rebuild. If I'm not mistaken you should see between 400-450 PSI on a good tight engine and no lower than 350-375 PSI on a wore engine. As quote here... http://articles.mopar1973man.com/general-cummins/34-engine-system/144-compression-testing You might want to check that AFe I think you had a dust leak and ruin a set of rings.

If 400 psi is normal than I guess this motor is on its last legs. I keep hearing that 250 - 300 is ok or good... I'm going to take a closer look. It looked good few months back ... sent from my cell...

[freedomisntfree]

Yeah I know the PO tried to do some shady ____ and hide a lot of issues I found later ... Sucks that I didn't run a compression test prior to pulling the motor and I have $3k into it now. Should have just rebuilt the whole damn thing regardless.. I would like to k ow more about the timing possibly being off. I will look into that. sent from my cell...

[MnTom]

I would like to k ow more about the timing possibly being off. I will look into that. sent from my cell...

That is pretty easy. Just pull the front cover and make sure the timing marks are lined up. Oh, here is what I have been able to dig up about compression: New rebuild: 350psi Good Used engine: 300psi max allowable variance: 100psi

[ISX]

Can you go into more detail about #6? I assume it was melted? Did you drive it like that? You said in the original post "Now it smokes" which makes me think it didn't smoke before even with the bad #6. More info we can get on what brought it to this point the better

[dripley]

I have had the whomp whomp sound out of mine for at least 11 years if not 12. I noticed it when I put my _k& in. The day I put it not years down the road.

[freedomisntfree]

Can you go into more detail about #6? I assume it was melted? Did you drive it like that? You said in the original post "Now it smokes" which makes me think it didn't smoke before even with the bad #6. More info we can get on what brought it to this point the better

The no. 6 was not melted at all it had those scrapes on the piston and walls. It didnt smoke before but it does now... I'm going to try take some video and catch the sound... I just figured out how to adjust low boost fueling on the Edge Comp but haven't tried it out yet .. but even then it hazes with box off... Also I will pull the AFE off to see any difference but I think I had already tried that and sound was the same. sent from my cell...

[fire176969]

Alright gentlmen.. I got my results for compression test. Injectors were pop tested and all checked out to be working normal. Cylinder 1 - 245 psi 2 - 250 3 - 250 4 - 250 5 - 250 6 - 255. I still have that whomp whomp sound thru intake. and as far as I know still burning oil.. I just figured out the edge has settings within each setting. Going to mess with that to see if it gets rid of some idle haze. I'm going to top off the oil and run it some more to ensure it still burning oil. Thnx for any more suggestions u have... And appreciate you guys that following up. sent from my cell...

Those numbers do seem kinda low. They are good readings showing the cylinders are even, but do seem low. I just tried looking the specifications up from Cummins, however they don't have a compression test shown. It would be a good idea to check the crankcase pressure, that will give you an idea of how well the rings are sealing. I know thats the point of the compression test, however the crankcase pressure gives you an idea with the engine running. The easiest way I can think of to check your cam timing would be to remove the breather from the front of the engine. Line up the mark on the vp44 gear with the front cover and check the valves. I know you have to remove the valve cover but it beats pulling the front cover.

[ISX]

The fact that it didn't smoke before and does after they fixed something seems counterproductive. I would take the breather off and mark TDC on the dampner then rotate the engine clockwise (from the front) and watch valve overlap (watch the exhaust valve go down then back up but before it is fully up, the intake valve will start to go own, the instant you see it go down, stop) as it should overlap pretty close to the mark on #1 or #6. A cam that is a tooth off would put it pretty far off. When I was experimenting the other weekend, the valve overlap puts it realllly close to TDC (with stock 10/20 lash settings). It would be an easy indicator

[vineyardmh]

RE: Compression testing ....I am a simple engineer ...and I like simple concepts that can be done 'back of envelope'.If I have a piston moving up and down - and it has about 16.3:1 compression - then I would expect a compression buildup to be 16.3 x 14.7 psi - or about 240 psi is the pressure in the cylinder when the piston reaches TDC - and it won't go higher unless there is burning/combustion of fuel. {For a High Output HO engine with 17.0:1 compression ....then 17.0 x 14.7 = 250 psig. ] That number is assuming that the turbocharger isn't really spinning fast enough to add any real boost.If I got a mere 1 psi boost - then my air in as 15.7 psi - and I would get 256 psi. (But the starter motor is spinning the engine at maybe 200 rpm, there are no exhaust gases to expand out and spin the turbo - so I don't expect much boost!)When doing a compression test, it is necessary to turn the engine over 4 or 5 times - because on the 1st or 2nd stroke - there is some small bleed off of the pressure past the rings, and the compressed air volume now needs to include the volume of the gauge and air line to the gauge - and therefore it takes several cycles to get a reliable measurement. BUT - after each cycle of the piston - the pressure is trapped in only the compression gauge - the cylinder pressure will bleed off as the exhaust valve opens - so it is difficult to have the compression gauge get a much higher reading than what the cylinder pressure can build up to....I haven't done a compression test on my Cummins - but on my old (and long gone) GM with a 6.2L engine that had a 22:1 compression ratio - I saw about 320 psi on my compression tests...matching my simple concept analysis. (And for my gasser 4.3L V-6 with 9:1 compression - the compression checks give me about 130 - 140 psi...which is what I have seen when doing compression checks.)Bottom line ...I am not sure that 350 to 400 psi on compression checking a Dodge 5.9L engine is reasonable...but I remain open to alternate explanation!

[rancherman]

RE: Compression testing .... I am a simple engineer ...and I like simple concepts that can be done 'back of envelope'. If I have a piston moving up and down - and it has about 16.3:1 compression - then I would expect a compression buildup to be 16.3 x 14.7 psi - or about 240 psi is the pressure in the cylinder when the piston reaches TDC - and it won't go higher unless there is burning/combustion of fuel. {For a High Output HO engine with 17.0:1 compression ....then 17.0 x 14.7 = 250 psig. ] That number is assuming that the turbocharger isn't really spinning fast enough to add any real boost. If I got a mere 1 psi boost - then my air in as 15.7 psi - and I would get 256 psi. (But the starter motor is spinning the engine at maybe 200 rpm, there are no exhaust gases to expand out and spin the turbo - so I don't expect much boost!) When doing a compression test, it is necessary to turn the engine over 4 or 5 times - because on the 1st or 2nd stroke - there is some small bleed off of the pressure past the rings, and the compressed air volume now needs to include the volume of the gauge and air line to the gauge - and therefore it takes several cycles to get a reliable measurement. BUT - after each cycle of the piston - the pressure is trapped in only the compression gauge - the cylinder pressure will bleed off as the exhaust valve opens - so it is difficult to have the compression gauge get a much higher reading than what the cylinder pressure can build up to.... I haven't done a compression test on my Cummins - but on my old (and long gone) GM with a 6.2L engine that had a 22:1 compression ratio - I saw about 320 psi on my compression tests...matching my simple concept analysis. (And for my gasser 4.3L V-6 with 9:1 compression - the compression checks give me about 130 - 140 psi...which is what I have seen when doing compression checks.) Bottom line ...I am not sure that 350 to 400 psi on compression checking a Dodge 5.9L engine is reasonable...but I remain open to alternate explanation!

You are very correct in your math, but you forgot to add the temp variant! your calculations are correct when temp remains constant... but change dramatically when air is heated. Some dude named Boyle came up a bunch of laws on this years ago...

[ISX]

RE: Compression testing .... I am a simple engineer ...and I like simple concepts that can be done 'back of envelope'. If I have a piston moving up and down - and it has about 16.3:1 compression - then I would expect a compression buildup to be 16.3 x 14.7 psi - or about 240 psi is the pressure in the cylinder when the piston reaches TDC - and it won't go higher unless there is burning/combustion of fuel. {For a High Output HO engine with 17.0:1 compression ....then 17.0 x 14.7 = 250 psig. ] That number is assuming that the turbocharger isn't really spinning fast enough to add any real boost. If I got a mere 1 psi boost - then my air in as 15.7 psi - and I would get 256 psi. (But the starter motor is spinning the engine at maybe 200 rpm, there are no exhaust gases to expand out and spin the turbo - so I don't expect much boost!) When doing a compression test, it is necessary to turn the engine over 4 or 5 times - because on the 1st or 2nd stroke - there is some small bleed off of the pressure past the rings, and the compressed air volume now needs to include the volume of the gauge and air line to the gauge - and therefore it takes several cycles to get a reliable measurement. BUT - after each cycle of the piston - the pressure is trapped in only the compression gauge - the cylinder pressure will bleed off as the exhaust valve opens - so it is difficult to have the compression gauge get a much higher reading than what the cylinder pressure can build up to.... I haven't done a compression test on my Cummins - but on my old (and long gone) GM with a 6.2L engine that had a 22:1 compression ratio - I saw about 320 psi on my compression tests...matching my simple concept analysis. (And for my gasser 4.3L V-6 with 9:1 compression - the compression checks give me about 130 - 140 psi...which is what I have seen when doing compression checks.) Bottom line ...I am not sure that 350 to 400 psi on compression checking a Dodge 5.9L engine is reasonable...but I remain open to alternate explanation!

I don't want to shatter your theory but that is not how you calculate pressure of compression. You might read up on the Ideal Gas Law The spreadsheet I attached makes it easy as it also calculates temperature. The simple PV=nRT is too simple as you will have a constant temp or constant pressure which simply isn't the case. But with 16.3 CR and 100F intake temp, 0 boost, the pressure is 731psi at TDC. With all the leakage that is why 350ish is more normal.

Compression.xls

[rancherman]

I don't want to shatter your theory but that is not how you calculate pressure of compression. You might read up on the Ideal Gas Law The spreadsheet I attached makes it easy as it also calculates temperature. The simple PV=nRT is too simple as you will have a constant temp or constant pressure which simply isn't the case. But with 16.3 CR and 100F intake temp, 0 boost, the pressure is 731psi at TDC. With all the leakage that is why 350ish is more normal.

I remember it being inversely proportional.... (calculating pressure/volume)... I agree now that his 'starting point of 14.7 psi' is the wrong value. But you have to consider the net gain temp , not just the intake temp??

[ISX]

I remember it being inversely proportional.... (calculating pressure/volume)... I agree now that his 'starting point of 14.7 psi' is the wrong value. But you have to consider the net gain temp , not just the intake temp??

The intake temp determines how many moles of air can be in the chamber along with just setting a starting point. The ending compression is the same but the ending temp is vastly different. Going from 0F to 100F IAT creates a 305F ending temp difference. I think 14.7 is the right starting point given you are cranking the engine with the starter (slow) so the chamber easily equalizes. In this spreadsheet (more detailed) you can see 0-100F also has a 21% mole number difference. So you lose a 300F and gain 21% of air.

CAI Proof.xls

[freedomisntfree]

Interesting. I need to re read these to make sure I understand this right. I never cared to understand compression until now :banghead:sent from my cell...

[rancherman]

this shows pressure of '1' at max volume... then pressure of '2' at min volume. Pressure is doubled, volume is halved. TEMP is constant. I just assumed his CR calculations would apply... volume is 16.7 times smaller at tdc than bdc. This assumes 100% volumetric efficiency too. Someone out there have a formula for temp variations? Would the 'starting' value be 1 (atmospheric pressure) instead of 14.7? (we don't feel 14.7, because it's inside us too)

- - - Updated - - -

The intake temp determines how many moles of air can be in the chamber along with just setting a starting point. The ending compression is the same but the ending temp is vastly different. Going from 0F to 100F IAT creates a 305F ending temp difference. I think 14.7 is the right starting point given you are cranking the engine with the starter (slow) so the chamber easily equalizes.

In this spreadsheet (more detailed) you can see 0-100F also has a 21% mole number difference. So you lose a 300F and gain 21% of air.

yep.. the hotter the air, the less moles going in! BUT, with less moles, the less it will INCREASE in temp during the same compression period too. (given the same piston speed) I was considering the NET temp gain on ending psi.

[ISX]

BUT, with less moles, the less it will INCREASE in temp during the same compression period too. (given the same piston speed) I was considering the NET temp gain on ending psi.

I thought about that. I went over the formulas forever but it didn't make sense to me and I just grew tired of working on it. I'll research it more.

[vineyardmh]

You are very correct in your math, but you forgot to add the temp variant! your calculations are correct when temp remains constant... but change dramatically when air is heated. Some dude named Boyle came up a bunch of laws on this years ago...

Ah..yes...I forgot to use Boyle's law. (P1 x V1)/T1 = (P2 x V2)/T2 Assume P1 = 14.7 PSI, V1 is 16 and T1 is ambient - 20 deg. Celsius or 293 deg. Kelvin Assume V2 is 1/16th of V1 ...or 1 ....and assume T2 is autoignition temp. of diesel - which is 483 deg. Kelvin - and solve for P2. P2 comes to 388 psi.

[rancherman]

I have a suspicion that no matter what the intake air temp.... the final 'compressed' temp will be the same, if not pretty dang close. (as long as everything else is constant). cold AiT = more molecules to 'excite' during compression...more heat gain. Hot AIT = less molecules to compress, less heat gain. where: where

P is pressureV is volumen is the number of molesR is the universal gas constantT is temperature (K) So, lets say we compress this cylinder (with a perfect seal, no leakage) at the speed cummins cranks their engines to start. Then suddenly stop the piston at TDC, and we have a 'hot' cylinder gas of 650 degrees, with a psi reading of 750 psi. ( in a perfect scenario). Then we allow the gas temp to return to ambient. the law above says 'double the temp, double the pressure'. But that assumes instant compression, not a slow compression (our engines during cranking) which is already dissipating heat to the head and cylinder walls! The OP statement was correct on his calculations....WITHOUT temp factored. My question was his original value of 14.7.... because our compression gauge reads 'zero' at atmospheric idle, not 14.7 Is this becoming a chicken or egg first... need heat to make psi, or psi to make heat? Maybe the dude just needs to rebuild his engine:lmao: