This video will show you how I do a compression test on a automobile. This test was done on a Volvo 850 R. It will be the same on all Volvo 850, S70, and V70 cars built prior to 1999.

You should de-activate the ignition system and fuel system so that fuel will not be pumped into the cylinder chambers and the spark plugs wires are not trying to fire.

NEW VIDEO WITH IMPROVEMENT (and another 8 minutes).

 

1- PCV, not PVC.

2- You should have a battery charger on the car for the test. The battery can weaken from the cranking and cause false low numbers.

3- Instead of pulling the fuel pump relay, you can just disconnect the injectors. That way they don't open during the test and inject what fuel is in the rail.

4- No need to disconnect the coil.

5- Watching the gauge to see if it "bleeds down" is pointless. If you have a properly functioning gauge, it should never bleed down. There is a one way valve in the hose so that it holds the highest reading. So it should never bleed down. If the one way valve was not there, it would bleed down right away (unless you miraculously stop cranking when the valves are all fully closed).

6- You shouldn't assume bad rings just because there is low compression. A cylinder leakage test should be done to identify the source of the leakage if a wet test is inconclusive. I'd do a cylinder leakage test anyway to make sure you don't need valve work as well.

Too bad I'm blocked, at least someone will learn something while you continue to think that every car has bad rings because the compression gauge doesn't bleed down.

 

is that the R you just picked up with a broken pan?

 

Good job brother

 

[QUOTE=ES6T;356894]3- Instead of pulling the fuel pump relay, you can just disconnect the injectors. That way they don't open during the test and inject what fuel is in the rail.

Is there an easy way to disconnect the injectors ??

4- No need to disconnect the coil.

Why would you leave it to try and fire during all the cranking ?? If it finds a weak spot or carbon track to ground it's only going to reinforce that weakness and make it easier for it to fail in the future.

Wouldn't pulling the ECM fuse shut down the injectors and ignition ??

 

Yeah, pop the injector cover off and unplug them.

If the wires are disconnected from the plugs, they arent going to arc. Or, you can pull the ignition lead off the coil if you're really paranoid.

 

I guess I'll stick with pulling the fuse rather that unbolting the cover and disconnecting each injector.

"If the wires are disconnected from the plugs, they aren't going to arc."

Why in the world would you leave the coil to fire and work so hard at finding a ground or making one where there shouldn't be one. It's hard on the system and can cause a problem. 40 thousand or more volts are going to find a ground one way or another and the last thing I want is it arching from the coil tower to the windings and taking out my coil. Paranoid ?? I think not.

I've seen people destroy a coil pack trying to drive with a bad wire.
Burn down a coil tower because they had so much resisteance in the rest of the system the coil finally started arching to its case to ground.
At the very least put the plugs in the wires and lay them on the engine so they can "fire".

If you are a tech you've likely been bit by an ignition system more than once and that's the coil trying to find ground. It only goes to the spark plug if it's the easiest, if you are easier it hits you and if you leave the wires hanging in space it's going to find a path back to the battery through whatever it can and that's where you can do some damage to your system.

 

Nothing to unbolt. The cover pops off.

No, I haven't been shocked because when I'm cranking the engine, I'm obviously not holding the wires.

I'll give you the coil argument, I don't care. It isn't that hard to disconnect it. No need to disconnect the other two wires though once it is electrically disconnected.

 

Yes it is.

Other than that, this is how "I" do my compression test. I'm sure there will be another way for it to be done, which may be "more professional", take longer, give more information, show you exactly what's wrong. But lets face it, how many people reading this site or watching that video will have an air compressior that they can use to do a bleed down test? How many will be able to properly interpet the finding? How many will start breaking down the motor if 1 of the cylinders are bad? How many will change a piston.

The purpose of the video is to let someone know why their car won't start, why it's missing, if there is something wrong with the car, like worn pistons. Don't take a car with low compression numbers and put a $2,500 paint job on it unless you're going to find out why your compression numbers are low in 3 of 5 of your pistons. If the car has been run out of oil and compression is low, you likely have a damaged motor. If all the compression numbers are good, add oil and keep driving the darn thing.

If you have all of the spark plugs out and some fuel dribbles into the chambers, it will likely spray out or evaporate before you get the plugs back in. I have done several compression test like this and NEVER have had any problems starting the car afterwards.

The WWW is wide open for all. Feel free to post instructions on how to "properly do a compression test" for all to see. Hope they will be able to do it a. quick and easy; b. with very little expense on buying equipment; c. get the satisfaction they desire. For me, if I'm about to pay good money for a car and the compression numbers are low, I'm out!

 

That's all fine and good, and it doesn't really matter how you stop the fuel from getting in there. Disconnecting the injectors is actually quicker, but it doesn't matter. I don't care if you want to remove the fuel pump itself. But a battery charger should be used to get accurate results and if you are going to post a video like that, you should at least know how a compression gauge works so you don't give out wrong information, especially after your lofty claims you have made to me. If you explain it wrong, someone is going to have bent valves and think they have worn rings because the compression gauge didn't bleed down. Someone isn't likely to replace pistons but they might replace bent valves. Or who knows, maybe they replace the pistons. Then get it all back together and still have low compression because they have a bent valve but didn't know because the video on the internet was wrong.

 

The cover on mine has two bolts holding it down and then there is each injector electrical lead to disconnect.

Doesn't that seem a bit much compared to just pulling the fuse

 

Yeah, if you want to remove the fuel rail to disconnect the injectors. You don't have to pull the rail or remove the injectors. The 850 should have a metal cover that clips into the fuel rail and covers the electrical connectors. It pulls off, then you can disconnect the injectors. No bolts. No tools needed. Or four bolts to remove the cover and then relay. But really, who cares?

The big gripe with the video is the fact that a battery charger should be used and a compression test cannot tell if there is a valve problem by watching for it to bleed down. If you have something about that to refute, then go for it. Otherwise, I don't care how you disable fuel. Pull a fuse. Pull the relay. Remove the injectors. Remove the fuel tank. I don't care.

I realize you and Robert dislike me for whatever reason, but you are missing the more important point.

 

If you don't care why are you making such a big thing out of it ??

Pulling the fuse is easier.

 

Hey, if you're going to nit pick about the difference between PVC and PCV like anybody reading or listening to the directions wouldn't know it's a typo then you should be helpful enough to explain how you do something without me having to go out and take things apart to figure it out.

It sounded to me like you were talking about taking the cover off I had a photo of in my response and pulling each injector connector.

If you want to try and be helpful don't get all twisted because someone asks you a question about something you are presenting as a better way.

 

First, I nit pick about PCV vs. PVC because of the lofty claims made to me by Robert.

I was simply talking about disconnecting the injectiors, which is obvious in my replies. I never said pull the whole fuel rail. You're the one making a big deal about something so insignificant. I know you take Robert's side, but holy hell... if you really want what is right for the people of the site who read this, why chose to nit pick about how to disable the fuel injection system rather than the other totally wrong things about this video?

 

Ok, the video has been improved. Hope it helps people understand more about doing a brief compression test.

 

ES6T: I am surprised at you; you talk like you know it all (and usually you are correct) but you missed some points here.

2 - Done many a compression test in my day; never jumped the battery before. If your battery voltage is drooping that much during a compression test (remember, the plugs are out so only one cyl is building compression at a time), then it's time for a charge and/or new battery. That's just silly.

3 - Whatever; seems to me it would be easier to pull one relay than get to the injectors. You really shouldn't use the ignition switch to do a compression test anyway; it's remote starter switch time - then you don't have to worry to fuel or spark (see next item).

4 - Whoa, this is bad! You know I was the guy that informed rspi (on his original vid about compression tests) that it's very bad to leave the coil live while doing this test. I guarantee you that hundreds, if not thousands, of ignition coils have met their demise because of shade-tree (and dealership) techs doing compression tests by not using a remote starter switch and leaving the coil connected. What KFrog said here and more. If you're interested in learning more than you'd ever want to about the topic, ck out this thread (post 23): https://volvoforums.com/forum/volvo-...t-67195/page3/

5 - Like you said (I think?) if you see your comp gauge bleeding down after the cranking stops, then that one way valve in your gauge is bad (or the gauge itself).

Another comment on your posts: please quit sniping at specific people and holding grudges; it's shows lack of maturity and is un-attractive...

Other than that, really appreciate your posts!

 

You really shouldn't use the ignition switch to do a compression test anyway; it's remote starter switch time - then you don't have to worry about fuel or spark (see next item).

I didn't catch that. You're 100% there.

And I'm the same with the battery charger. Never remember hooking one up. To be technically correct you should but I've never had a problem without one.

Thanks for pointing out about the coil. That to me is very important so someone isn't leaving a coil "hot" to try and fire in a way that can damage itself or something else. ES6T might give us that one because he doesn't care but I do as it can damage components.

 

I've learned a lot from Robert's videos and do appreciate them, too. I also appreciate the fact that if someone makes a mistake or omission in an online 'how to guide', that someone else notices it and corrects it. I know I'm not the only guy who has used these videos to help them complete a task and save a few bucks over going to a mechanic.

Having said that, ES6T, you're abrasive! Offer some friendly suggestions, discuss your opinion, but you come across as a jerk, and I am not going to put any weight behind your suggestions if you come across that abrasive.

In general, with very few exceptions, Volvo people have been top notch. Other cars I've owned, there have been online forums similar to this, but people have been jerks. There's no reason for that. We can all get along, have fun, and discuss the cars we enjoy.

The people on this forum, along with other Volvo resources have made me feel *welcome*, and have made me *want* to improve my car. I enjoyed the car before I came here - but I enjoy it *more* because of the people.

While we are on this subject, how would I hook up a remote ignition switch for doing a compression test? What do I need, and how do I hook it up?

 

2- It isn't silly. A battery charger should be on the battery so all things are equal during the test.

3- Good point. Cranking directly from the starter would eliminate any discussion about fuel and spark.

4- I never claimed to know everything- no one can know everything. And, unlike some people, I have no problem admitting when I am wrong. And in this case, I was wrong. Very good post you linked to, also.

However, I doubt thousands of coils have been fried from this. I doubt it for two reasons: First, I have been doing compression tests with just the leads disconnected and have not personally fried one (I will do it differently from here out). Of course, me using that as an example is the same as you saying a battery charger is not needed simple because you haven't used one. And second- coils aren't even that common of a failure. Yes, they go bad... but not nearly as often as other things.

Either way, I was wrong.


As for being abrasive- I am not usually abrasive. There is a situation here that you don't know about which is the reason for my "tone". I will not explain it any further. If you think I'm a jerk and don't want to listen to any of my advice, that's fine. But if you would like some advice, here it is:

To use a remote ignition switch, you just hook one lead to battery positive and the other to the solenoid on the starter. Press the button on the switch and it will supply power to the solenoid to crank the engine.