COMPRESSION TEST

wingding333326 · Dec 22, 2023

immattj said:
No, not unreasonable, but in my opinion unnecessary.

i guess that i don't trust myself that i have done everything correctly. i learned that lesson years ago with my 4X4 truck. That is every time I thought I was right, i was wrong, and every time I was thinking that I may be wrong, I would be right, cant be wrrong wrong if you think your right... lol like for example, my truck died, fuel issue, thought to myself "oh ya, I know whats wrong cause it happened before, it's the carburetor," (at that point I had an AFB 650 Carter carburetor, much better & easier than the Rochester carburetor it had originally) so, I went and rebuilt the carburetor as I had times before, turned out I WAS OUT OF GAS!! LOL I learned a good lesson then. Just like when the alignment people told me that I had the tie rods upside down, I believed them. HOW can this most prominent shop in town be wrong and I be right?? It still blows my mind. I understand how this compression thing is what it is and not really much of anything to do about it, like not gonna make difference, it is what is expected, but, I think that it's really more about me… still wondering if I did this test right or not. And not so much about expecting anything different then what you, I and we already know… I guess the question is more like do I wanna spend $100.00 to see if all that I did was correct? lol Even though the out come stays the same.

immattj · Dec 22, 2023

wingding333326 said:
I guess the question is more like do I wanna spend $100.00 to see if all that I did was correct? lol Even though the out come stays the same.

You already know my answer to that.

If you were to repeat the test and do a couple of things differently, I think you would get higher readings:
1) perform test with WOT as it does make sense that more air would get sucked into the cylinders through the wide open TB which should result in more pounds of compression as more air is being compressed.

2) use jumper cables from your other vehicle to your Durango while testing, faster cranking speed may increase compression, but more importantly the cranking speed will be consistent from cylinder to cylinder. That shop you mentioned would probably use some type of booster on the battery when testing.

However:
It looks as if your passegers side is still going to read low. If you did it the same as the driver's side, regardless of whether you did it correctly, you did it the same, so the variance is still going to be there.

One of the very first replies I made to your thread, after I said that if it was me I wouldn't bother, was to say something to the effect of don't be crushed if you get some low readings. And that was when I thought you 'only" had 215k!

And again (because you have yet to answer this) how much engine oil do you actually add between oil changes?

wingding333326 · Dec 22, 2023

immattj said:
Okay, you missed post #77. I got that part about WOT putting it in 'flood-mode" and disabling injectors from a you-tube, but on further research, WOT allows more air into the cylinders while testing and should result in higher redaings. Here is what I posted in #77:

" With the throttle wide open at cranking RPM, the air pressure within the cylinder will be approximately 14.7 psi. Ambient air pressure minus some small loss.

With the throttle closed at cranking RPM, the air pressure within the cylinder will be less. Approximately 6 psi.

Compressing 14.7 psi by X ratio (say 10 to 1) will result in a higher value than will compressing 6 psi by the same ratio.

A four stroke will therefore show a higher pressure on a gauge with the throttle wide open than it will with the throttle being closed.

The motor maker will usually provide a minimum compression value and specify that the throttle should be wide open when performing the test. I suppose they could just as well provide a lower value based on the throttle being closed. But they don't. Not that I have ever seen anyway."

so, are you saying that if i have the gas pedal pushed down to the floor, that it would make a difference in the readings? because if so, it would be worth starting it over with the sequence you said of the cylinders.

and I think that I can get my electric seat to push a one of my collection of boards I have stored behind a small building next to my car (maintenance said that I can have my boards and stuff there) (these boards I use for when I jack up my car, high). I did this before when I was trying to check the bulb on my rear 3rd brake light, it worked so well, I just aligned the board with the brake pedal and pushed the electric button till it was where I wanted it really easy, I am sure that I can do the same with the gas pedal, what do you think? Should I do it that way? would that work?

wingding333326 · Dec 22, 2023

immattj said:
1) That means that the plugs were improperly torqued last time.

2) The drivers side isn't bad, the other side is getting unhealthy.

3) You are over 10% variance. 10% of 150 is 15.

you said "That means that the plugs were improperly torqued last time." what effect would that cause?

immattj · Dec 22, 2023

wingding333326 said:
so, are you saying that if i have the gas pedal pushed down to the floor, that it would make a difference in the readings? because if so, it would be worth starting it over with the sequence you said of the cylinders.

. . . um, yes, if you read that post, I am saying that theoretically sucking more air through the wide open TB should theoretically result in more air being compressed which should theoretically result in more pounds of compression.

But it still should not have an effect on the variance between cylinders.

As far as how to do it, the way you described should work. If you go to that PDF, it shows the aircleaner hat off and the TB being manually pinned WOT. But if you go that route, be careful nothing (dirt or any other foreign objects) get dropped through the throat of the TB.

wingding333326 · Dec 22, 2023

immattj said:
. . . once upon a time I was following a thread on another site and the subject of a compression test came up and a member who I am inclined tp have a great deal of trust in made the following observations about interpreting test results:

"I'm not challenging your observations, but wonder what 'plenty of compression' sounds like. Does the cranking process sound 'even' while you're cranking? Or does it speed up a little, then slow a little while it's cranking? [. . . ] If two adjacent cylinders are very low while the others are 'normal', suspect a blown head gasket. If one cylinder has no compression at all while the others are okay, suspect a broken valve or valve spring. "

I am also thinking that if a shop was to do a compresion test, they would probably hook the battery of the vehicle being tested up to some type of booster to insurr the same cranking speed which should make the readings more reliable.

you asked "Does the cranking process sound 'even' while you're cranking? Or does it speed up a little, then slow a little while it's cranking?"
the cranking was consistsant, until i got to the second to the last cylinder when i could tell that the battery was starting to get a little tired, i expected that so i stopped, charged the battery all night, next day was cranking good and consistant

immattj · Dec 22, 2023

wingding333326 said:
you said "That means that the plugs were improperly torqued last time." what effect would that cause?

Well, if you had a plug that had worked loose and was starting to back out, you would be losing compression up through there on the compression stroke of the piston, and then on the downstroke of the piston, I would assume that a certain amount of outside air (not air from the manifold) would be getting drawn in.

I guess the effect could be that slight miss you said you noted at idle.
Maybe/maybe not.
A lot of the actual effect would depend upon how loose it really was. You don't want to crank your plugs so tight that you break something or strip the threads in the head. Then you would be getting into the ugly territory, and if you thought those readings you first got made you want to cry . . . if you strip the plug threads in the head(s), you may be feeling suicidal.

But once again: how much engine oil do you have to add between changes?

immattj · Dec 22, 2023

wingding333326 said:
you asked "Does the cranking process sound 'even' while you're cranking? Or does it speed up a little, then slow a little while it's cranking?"
the cranking was consistsant, until i got to the second to the last cylinder when i could tell that the battery was starting to get a little tired, i expected that so i stopped, charged the battery all night, next day was cranking good and consistant

From that description, the cranking speed should not be having an ungodly horrific effect on the consistency of your readings.

immattj · Dec 22, 2023

Congratulations:
I just noticed that your thread now has over 2,000 views.

immattj · Dec 22, 2023

(Trying to do edits on this site is driving me crazy.)

. . . coming back to this:
first of all, my apologies for what I FIRST told you about testing at WOT. I am pretty sure I picked that up from one of the youtubes I skimmed through. However, after you posted your first readings (the ones you said made you want to cry) I did a couple of more searches and in the course of those revised my thinking on the rationale behind WOT while testing. See post #77. On one of the searches I did regarding why do it at WOT, someone else said that in his experience it didn't make any difference; BUT: there is an old saying that goes, "An engine is a pump and a pump is an engine," and what does a pump need? Something to pump, and in this application--air. So if you think about it, at WOT more air will be allowed to be sucked in through the TB when the engine is being cranked, and more air being compressed in the cylinder should, in theory, equal more pounds of compression and therefore higher readings.

However: the variance between cylinders STILL would not change as long as they were all tested the same, meaning ALL tested NOT at WOT.

So, once again, my apologies on that, and if it is any consolation, the few times I have performed compression tests on my stuff, I was apparently getting that part wrong.

Anyway, I did just go back through the replies on this thread and I edited out what was apparently misinformation regarding that subject that I mistakenly provided you with, and my understanding of the rationale for WOT has been revised and hopefully I have explained that rationale satisfactorily to you.

immattj · Dec 22, 2023

. . . and OOPS again!!

I referred you back to reply #77 for my revisions on rationale for WOT.
I am the King Of Typos.
I meant post #78.
So I will simply copy and then paste that post so it is right here:

#78 · 2d ago

. . . and, on another quick searck on why WOT on a compression test, I came up with this:

" With the throttle wide open at cranking RPM, the air pressure within the cylinder will be approximately 14.7 psi. Ambient air pressure minus some small loss.

With the throttle closed at cranking RPM, the air pressure within the cylinder will be less. Approximately 6 psi.

Compressing 14.7 psi by X ratio (say 10 to 1) will result in a higher value than will compressing 6 psi by the same ratio.

A four stroke will therefore show a higher pressure on a gauge with the throttle wide open than it will with the throttle being closed.

The motor maker will usually provide a minimum compression value and specify that the throttle should be wide open when performing the test. I suppose they could just as well provide a lower value based on the throttle being closed. But they don't. Not that I have ever seen anyway."

. . . however, WOT or not still would not account for the disparity between cyliners. But a tired battery would.

immattj · Dec 23, 2023

wingding333326 said:
No, but i think the relay under the hood is suppose to fix that, at first i unpluged two, couldnt find anything where the fuses are inside, but when tryied to crange it over it did nothing so i put one of the relays back in then it cranked over, at one point i thought i might smell gas,

. . . okay, catching up on my reading, and there was a bit to make sure that I was caught up on, and I forgot to respond to this.

Hopefully I have managed to clarify that I was wrong about the rationale for WOT and my explanation of why WOT is preferred was understandable, and I won't beat that horse any longer.

However, if it wouldn't crank after you pulled the relays, one of them was probably the starter relay, which was the wrong one.

The two I wanted you to pull were the ASD relay (disable injectors AND coi) and the fuel pump relay (obvious what that disables).

What I THINK probably happened is:
that "relay and fuse map" on the inside cover of the PDC lid can be kind of confusing. I was once wondering if I had dyslexia when I got it backwards. But later on I read posts on other Dodge Dakota sites by other people who were confused by it.

The way it SHOULD work is:
you should be able to set it right next to the relay/fuse panel and it should be identical and match up. But it is NOT. For whatever reason, Dodge actually drew it so that ilines up with the lid installed. In which case, I guess those @$$holes failed to take into consideration the "map" would be sort of hard to read because
a) with the lid installed you cannot see either the "map" or the panel
and b) not totally useless, I guess, as I suppose it would make some semblance of sense if one was to hold it above one's head and look up at the "map" and then look down at the panel to compare it with. Which seems idiotic to me.

And hopefully that last part made sense, because it is hard to put words to something that wacky.
But if I can figure it out, anyone can.
Since you now know which one is your starter relay, go by that to figure out which is the ASD relay and which is the fuel pump relay. You will get it, I have confidence.

And let me take this opportunity to ask (again) how much oil do you have to add between changes?

immattj · Dec 24, 2023

wingding333326 said:
No, but i think the relay under the hood is suppose to fix that, at first i unpluged two, couldnt find anything where the fuses are inside, but when tryied to crange it over it did nothing so i put one of the relays back in then it cranked over,

I was looking for something on another Durango thread, and I found this which also may be helpful to you for identifying relays in your PDC. It will make more sense than that "map" on the inside of the cover for the box. Note that it shows the ASD and fuel pump relay right next to each other. Theoretically it is applicable for Durangos '97 through '03. Theoretically.

Fuse box Dodge Durango

Locate fuse and relay. Fuse box diagram. Identifying and legend fuse box Dodge Durango 1997-2003.

fusesdiagram.com

wingding333326 · Dec 27, 2023

immattj said:
(Trying to do edits on this site is driving me crazy.)

. . . coming back to this:
first of all, my apologies for what I FIRST told you about testing at WOT. I am pretty sure I picked that up from one of the youtubes I skimmed through. However, after you posted your first readings (the ones you said made you want to cry) I did a couple of more searches and in the course of those revised my thinking on the rationale behind WOT while testing. See post #77. On one of the searches I did regarding why do it at WOT, someone else said that in his experience it didn't make any difference; BUT: there is an old saying that goes, "An engine is a pump and a pump is an engine," and what does a pump need? Something to pump, and in this application--air. So if you think about it, at WOT more air will be allowed to be sucked in through the TB when the engine is being cranked, and more air being compressed in the cylinder should, in theory, equal more pounds of compression and therefore higher readings.

However: the variance between cylinders STILL would not change as long as they were all tested the same, meaning ALL tested NOT at WOT.

So, once again, my apologies on that, and if it is any consolation, the few times I have performed compression tests on my stuff, I was apparently getting that part wrong.

Anyway, I did just go back through the replies on this thread and I edited out what was apparently misinformation regarding that subject that I mistakenly provided you with, and my understanding of the rationale for WOT has been revised and hopefully I have explained that rationale satisfactorily to you.

Well, I decided that im just gonna clean the spark plugs up a little and put it back together, see how that goes, and if im still wanting to find out what I have in comparison to what the shop would find, maybe I will take it in.

I started with the spark plugs and after looking at them I decided to just get new ones. None had any oil or were wet, no cracks.

Got it back together and runs well, so far I don’t feel the miss that I used to, but I haven't drove it much. when I take that gauge back, I will get another PVC valve.

Next im planning on changing the transmission fluid…..

immattj · Dec 27, 2023

Well . . . I guess that's all good?
But you still have not told me how much engine oil you actually have to add between changes.

wingding333326 · Dec 27, 2023

so very little, im trying to put some special stuff in the engine, but i can only put just a tiny bit in at a time, most of the time, i check it and i cant put more in. because i know that it is worse to put too much than not enough.

immattj · Dec 27, 2023

wingding333326 said:
so very little, im trying to put some special stuff in the engine,

"Very little" means that the engine can not be all that sick.
And, for the record, I am not a fan of engine oil additives.
But that typed, I've never had anything that made it up to 315k.
What were your final compression readings?

wingding333326 · Jan 7, 2024

immattj said:
"Very little" means that the engine can not be all that sick.
And, for the record, I am not a fan of engine oil additives.
But that typed, I've never had anything that made it up to 315k.
What were your final compression readings?

Sorry it has taken me so long to respond, been really busy with the season & all. Im sure you understand.
So, After I got those low readings on the passenger side, (#8: 95 PSI, #6: 90 PSI, #4: 95 PSI, #2: 90 PSI). I decided to just go ahead & clean up the spark plugs a bit & put them back in & everything else back together again, still pondering if I want to have someone else that knows what they are doing, going over what I got.
Then after looking at the spark plugs I figured I would just go ahead and replace them all, so after I did that. I found a friend of a friend of a friend who had a shop (kinda) located in a back yard, but I had been there before when I had a friend help me change the belt. He said $30.00 for the compression test.
So he tested the passenger side, and got readings of 110+PSI on those cylinders that read for me 90-95PSI. Which was cool!! The guy was amazed at the readings (from his snap-on gauge) He said "factory specks". and the "quenkie-dinkie was that when I drove to his shop, the odometer was reading exactly 315,000!! right on the nose!
Anyways, he continued to comment on his amazement at the over all health & condition of my car. He said that he thought that if I keep on taking care of the car as I have been, he is sure that it will go another 100,000 miles, no problem….
The last thing he said was that it was his opinion that the engine that I have "5.2" was the best engine that was out there/is out there............

wingding333326 · Jan 7, 2024

I am feeling really good about this whole ordeal, yesterday, in the snow storm, I drove many a mile to return the gauge to auto zone, bought a new PVC valve and the rubber grommet that goes with it.
I love the snow, my car and I are from California.

wingding333326 · Jan 7, 2024

So, driving home yesterday was an amazing trip driving through the snow storm, really was enjoyable! car drove like a dream! so smooth, almost floating, and with most of the roads being the first to drive on, then on the "more traffic roads" the car felt like it was on "auto pilot" lol.
Really, I was a bit bummed when I arrived home & the trip was over… I could have drove all day!! just for the pure enjoyment of the snow and driving a car that really handles so well, better & better as what I put in, comes back to fruition.
But like I said before, none of this could have been accomplished with out your help. I cant thank you enough!! fact is that this car is the only car I have and I have no way of getting another if this one is gone, that’s it.. no way to afford another!

COMPRESSION TEST

wingding333326

immattj

wingding333326

wingding333326

immattj

wingding333326

immattj

immattj

immattj

immattj

immattj

immattj

immattj

Fuse box Dodge Durango

wingding333326

immattj

wingding333326

immattj

wingding333326

wingding333326

wingding333326

Top Contributors this Month

Recommended Communities