Compression test on '78 240D (first-timer)
 

I'd like to do a compression test on my 240D sometime in the next few days, which I have never done before (on either car). I've always kind of wondered where the 240's engine stands, since it has loads of blowby and idles rough on and off but starts fairly easily even in the cold. I'm getting discouraged with this car, again, and maybe some compression numbers would help me one way or the other.
I have the FSM and have done a fair bit of forum-searching, but just want to double-check a couple things.
1-I have a remote starting device my dad gave me a while ago. This is going to sound silly, but I'm not really sure how to use it. In the FSM it says to attach to terminals 30 and 50 ... does it matter which leads goes where? At that point do I just press the button and hold it as the engine cranks?
2-Since I only have two hands I can't hold down the stop switch, so was going to try to wire it down. How tightly does it need to be wired? I.e., is it going to try to pop up and start or is slight resistance enough to keep it from doing so?
3-The shutoff line is the one going into the very back of the pump, right? How much vaccuum do I need to put on it to keep it from starting, and will applying vaccuum once be enough?
I could figure some of this out by trial and error but I'd rather not have it start accidentally while I'm trying to take a compression reading.

if you pull all the gp's or injectors, one, it'll spin faster without draining the battery or straining the starter as much, and two, it'll NEVER start!
you should remove the injector lines from the injectors, but leave them on the IP, and wire up the stop linkage. not the stop lever.

Take all glow plugs out before doing compression. No way will engine start and run on one cyl.

remote goes to starter solenoid and + term of batt

jam a piece of wood cut to the right length between stop lever and IP

Hmm. I'm not sure you want to just hook to ANY terminal on the starter.
I'd hook to the battery side, and the small wire on the starter. both are on the starter itself. the large wire on the starter and the small wire on the starter.

I always use the junction box near the battery.

See pic courtesy of diesel911.
http://www.peachparts.com/shopforum/...1&d=1336290008

Connect the two leads on your remote starter on the outer two screws. Once you press down on that button the engine will turn over.


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240D does not have a junction box as I recall. There's a 50/50 chance she'll get the correct terminal. If it doesn't spin, go to the other terminal. The big terminal is + 12, if you connect the remote starter across the small and big terminal of the starter solenoid, there's no chance of shorting (if wrong batt terminal connection was made).

As I recall, the 240D has a lot more room than the 300D for glow plug compression testing. Removing the injector lines is not really necessary unless you have huge hands. #4 will be the hardest one with the IP in the way.

You can wire the stop lever shut but use a heavy duty bungee on the wire and hook it on the hood hinge. Wire alone has too much slop for complete fuel shut off.

I'd suggest doing both a cold and hot tests. More work but will provide more data. The cold test will be good practice for getting the glow plugs out fast for the hot test.

Have fun!

Thanks guys. I think I've got a pretty clear idea of the process now. Hopefully I'll be able to try it tomorrow or Tuesday.:)

Funola, I should have listened to your advice on doing a cold test first as practice on getting the glow plugs out! It took me so long to get them out (and I broke a vaccuum line the process) that the engine was not at all hot when I was done. Since it's all apart now, might as well wait until tomorrow and do a cold one, plug it all back in, warm it up, and then do a hot one. I don't think it will take me so long the next time.:) I did get the remote starter to work, but I'm having trouble wiring the stop lever in the right position. First I discovered it didn't even shut off the engine.:eek: I finally figured out (after a lot of reading) it was just because I had the idle cable adjusted too tight. Now it shuts off w/ the lever, but the bungie doesn't hold it up. I'll have to keep experimenting.

Just use a midivac on the shut off valve while you do the test.

It won't hold the vaccuum by itself, unfortunately, so I'd have to pump with one hand, push the starter trigger with the other, and read the compression gauge at the same time ... I guess that's possible but might require more coordination than I have! I could probably hold the shutoff lever with one hand though, I may try that.

There's always keeping someone in the car to crank it over at your command!!! Anyone think of that???

I always just put the compression tester in and hop in the car and crank it seven or eight times then go see what it reads.;)

You can use the key but since you have a remote starter, I'd say use that instead so you can see what the gauge is doing as you crank (be sure to wear safety glasses). The gauge needle should stay put. If it drops after you stop cranking, it's leaking.

The bungee on the stop lever must be strong and tight and pulling at the correct angle. I stopped using that method (because it's dangerous if the bungee let's go) and use a wooden stick to wedge the stop lever and keep the stick in my compression tester kit. I'll see if I can get a pic later.

Not sure what tools you're using for glow plug removal. For fastest results, you should be using 1/4 in drive ratchet, socket, extension on a universal on all except #4.

OK guys, I bravely tried a cold test tonight. I think on the first try I didn't have the stop linkage pushed far enough, because I smelled diesel after cranking (but it didn't start of course). After that I removed the idle cable so I could push the stop linkage farther, all the way. I used a socket bit between the pump and arm and it held fine. But I'm wondering if getting fuel in the cylinders in the first place messed up the test, even though I let it sit for a while after that try (and each try actually). My numbers don't sound right: Numbers 1, 2 and 4 were all around the 340 mark and number 3 registed 400.:confused: Does fuel injected during the test cause false highs? I don't mean to be a skeptic, but I don't feel like my 366,000-mile engine would have a COLD (has not run for three days) compression of 400 psi (I'm understanding cold compression test should yield lower numbers, right?). It does start pretty easily, but ...
Other observations: The first two glow plugs had light oil on them when i removed them, and a small bit of oil dribbled out of four glow plug holes during the test ... with a light fuel smell.:( During the #3 test, it looked like light smoke or steam was coming out of #2, but I did not notice it again while testing #4. I did notice light oil "spray" on the side of the IP from the open holes.
I want to do a proper full temp compression test tomorrow, but don't want to proceed until I know I've got the fuel shut off correctly. I did try pumping the MityVac on the shutoff while I cranked, on the final cylinder, but not sure if it made any difference. Thoughts? Is a little diesel smell normal during the test?
I guess once I get the glow plugs back in and the car warmed up, I can try starting it again with the same stop linkage setup ... if it doesn't start, would it be OK to assume the fuel is adequately restricted?
An alternative would be to try this with the injector holes instead of glow plugs, I suppose.:o

Fuel injected can result in false high readings. Make a jamb rod cut to the right maximum length instead of a socket to insure there is no fuel injected. I'll try to get you a pic soon.

One mod before you put the glow plug wires back on for the hot test is to make the ring lugs into spade lugs with a pair of dikes. This will allow taking off the wires without removing the nuts (just loosen them) saving time, and the engine is hotter.

Just disconnect the fuel line to the lift pump. It can't pump fuel if it's not being fed fuel.

The rectangular piece is the jamb. Notice the slot? It's for a positive fit. Use Oak or similar hardwood. Aluminum or steel will do also but take longer to make than wood. Oh and do not disconnect fuel line as suggested . Not only will you still spray lot's of fuel out the holes from the fuel that's in the IP. You will then have to do more work to bleed the air out.

http://i31.photobucket.com/albums/c3...519_104340.jpg

Jammed in place. Make it fit tight.
http://i31.photobucket.com/albums/c3...519_104224.jpg

Have you confirmed that via experiment? The engine will shut down if running and the fuel line is disconnected, suggesting quite strongly that the IP cannot pump fuel if new fuel is not entering it.

Hmmm, that's kind of similar to what I did (I can snap a picture in a bit), though my linkage is a little different. The first attempt I had it up as far as it would go against the idle cable stop (which I know was enought to stop the engine before, but maybe it was not stopping the fuel entirely). After that try, I took the cable off and put the stop linkage all the way up, so the lever sat against the valve cover. I'm not sure if it was still delivering fuel at that point, but the first try would have been enough to lubricate the cylinder (and comes out the GP holes) on subsequent tries I guess.
I didn't think unplugging the fuel line into the IP would help because the fuel left in the IP would still enter the cylinders, wouldn't it? Even though it's not much, it would do the same thing that happened last night, and provide a little lubrication and give high readings.
I'm going to put it all back together and run it a bit to get out any fuel that may have sat in the cylinders overnight. Then I guess I will experiment. What happens if it fires on the cylinder you're testing?:eek: I know it won't start because the other cylinders can't fire, but wouldn't that be pretty damaging to at least the tester?

It could be bye bye tester if you get ignition but that depends on the state of the engine and the tester - don't the really good testers have a pressure relief valve? Anyway according to the SAE OM617 development paper at idle the cylinder pressure is just under 40 bar - that's about 580 psi.

no I have not. have you?
we know that every time the fuel system is opened, air gets in. what you are suggesting does not seem like a good idea.

No, I haven't but there was a post on here a couple of years ago that definitely proved that if you disconnect the fuel line, the engine shuts down promptly and doesn't use up the fuel remaining in the filter/IP etc. It was in regards to the options available when the engine runs away after a faulty shut off valve install. That's why I suspect that that the IP won't pump fuel if there's no fuel arriving at the inlet because the lift pump isn't pumping fuel to the IP.

It would probably allow air to get sucked in which would need to be cleared out with the primer pump.

We talking about a compression test, not how to stop a runaway. A fuel connection has to be broken, air will get in. If a new washer is not available, the old washer may not seal, more problems. So, still not a good idea.

I thought if you unplugged the feed line to the IP, it would still burn the small amount of fuel left in the IP before it cut out? Maybe I'm misunderstanding the way it works.
I will stick with fiddling with the stop lever for now. I didn't have time to try anything today, since my dad needed some help moving stuff around, which is fair because he helps me all the time. I'm tempted to go out to the garage and work now, but I've learned a few times not to start a somewhat complex (to me) project late at night.:o

Not sure what washer you are referring to. I said disconnect the fuel input line at the lift pump, the one coming from the tank.

The question as to whether the IP will continue to pump fuel with it disconnected is what is unclear in my mind. Evidence on this site so far is that it won't. Maybe it will still pump a small amount. It definitely won't pump the remaining fuel in the secondary filter and the lift pump based on what has been posted here in the past.

FYI
 

Cold compression test numbers are extremely inaccurate.

Heat expansion of the cylinder, rings, and piston can (depending upon engine condition) change individual readings by 200 PSI..

To prevent unwanted fuel entering the cylinders.
* Remove the steel injector lines from the injection pump and injectors.
* Cover the delivery valves and injectors with loose caps/condoms to prevent trash entering/damaging precision components.

IMO:

* It is easier to relieve cylinder pressure by removing the injectors, and a great excuse to visually inspect the nozzle condition.

* A wise owner keeps spare "NEW" heat shields on hand for injector work, and compression testing.

* You do not want to drain the injection pump, because diesel fuel is the only lubrication of the delivery valves + it will seriously increase the difficulty of restarting the engine after testing.

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Well, I did determine both the shutoff valve and the shutoff lever easily stop the engine. But I decided to try doing it through the injectors anyway, since like whunter said, I could also inspect the injector nozzles. Everything went surprsingly smoothly until I actually went to do the test. As soon as the guage reaches 250 psi, the connector pops off. There's only one quick connector in the kit that fits the injector adapter, so I can't try another one to see if it's just a bum connector. That would be my guess. Naturally I got the cheap Harbor Freight tester. It worked fine with the glow plug adapter (it popped off once on that round but I assumed I had not seated it right, and it was fine every other time). Frustrating. :(
Also my injectors came out covered in oil, especially Nos. 1 and 2. Not an encouraging day.

True for the VE pump and other fuel lubricated pumps, but not the inline Bosch pumps, which is lubricated by engine oil. Am I right or wrong?:)

It's popping at the quick coupler? That HF kit is not very good. The fittings are nickel plated brass (should be steel for such application) and tolerance is lousy. I did extensive work to my HF kit to make it work and leak free.

Post a pic of your injectors. Where is the oil coming from?

My fuel system is highly modified and not anything like a stock system. Maybe it's easy to disconnect the fuel input line at the lift pump on a stock system. I am not willing to try it on mine since it requires a lot of work. Can you try it on your car and report the results?

Answer
 

The internal lubrication of the delivery valves is diesel fuel, other components use engine oil.


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In the context of this thread, will cranking the engine to do a compression test while the fuel inlet to the lift pump is disconnected damage the delivery valves?

I just used a Mighty-Mite type vacuum pump on the stop valve. Just a few pumps is enough (~10" vacuum?). That lets you test the stop valve at the same time.

I also have the Harbor Freight Diesel Compression set (~$20), and it works fine. You probably aren't latching the coupler right. It is just a standard air-tool quick-connect. Insure you push it in fully and pull the collar forward, if the spring doesn't.

Answer
 

On a virgin NEW injection pump, not enough to matter.

On a used injection pump of unknown history, (the issue is not common) it has happened to me. :(

My point is why take unnecessary risk.

Loosening the steel line nuts on all of the injectors, will prevent:
* Unwanted fuel entering the cylinder during testing.
* Excess wasted labor.
* Potential damage.

There will be minor external fuel drooling, to be cleaned later.

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Yep it's popping off at the quick coupler. It is a different quick coupler than the one used for the glow plugs, so I'm guessing it is the quick coupler that is causing the problem. I definitely have it fastened as solidly as it will go ... I tried several times, but each time it would pop off. I think maybe I could rent a tester from Pep Boys and see if it works any better.
Injector pics ... the oil was all over the tips. Some of it was fuel (those droplets on the cardboard were partly fuel that dripped out):
http://compressionignition.files.wor...33_o.jpg?w=450
http://compressionignition.files.wor...3316.jpg?w=450

There is only one quick coupler (the brass thing at the hose with a spring loaded collar). The part that goes on the injector adapter is a fitting. Check the shape of that fitting compared to the ones for the glow plugs to see if it is different. Also check the quick coupler o-ring to make sure it has not unseated itself. If it has, lube it with some oil then pop it back in. Also lube the collar with light oil to make it work smoother.

There shouldn't be oil on injectors in a good running engine. What you have maybe fuel from your compression test with the fuel not shut off completely + soot which together look like oil. One way to find out is put the injectors back in, run the engine till fully hot and take the injectors out. They should be dry with just a thin layer of soot.

While your injectors are out, might as well get them pop tested for opening pressure and spray pattern and correct it if there are problems before putting them back in. Don't forget new sealing washers (heat shields) every time an injector is R&R'ed. You gotta plan what to do when pulling injectors and do as much as possible and not use up too many sets of heat shields which add up and gets expensive.

Ah, I was using the wrong terminology. I think it's the fitting that's bad (but it is the quick coupler that's popping off). I'll inspect the fittings and the inside of the coupler.
The engine was fully hot before I took the injectors out. After the first test attempt, I put the GPs back in, started it up and drove it around the neighborhood until full temp. Then I removed the lines and injectors. So something must be amiss ... I guess that should not surprise me by now. I will take them to my mechanic and see if he can pop test (or recommend a shop to do it). I do have one set of heat shields I planned to install after the compression test, but now I need another set if I want to try the compression test again.
At the moment my project for the day is removing the mouse that has ended up in my home office ... fun ...

Update: I took the injectors to show my mechanic. He could not find his pop tester ... he said he never uses it anymore because he finds it more cost/time-effective to replace the injector than rebuild it. He did not think the oil on the body of my injectors was a concern, but that the fuel leaking from the nozzles was. His advice was get remanufactured ones, install them with new heat sheilds, forget about the compression test for now and see how it goes. I.e., if it runs smoother, the problem was the leaking injectors. He had a set of injectors in his store room he said he could give me for a good price but when we checked the numbers, they were for a 602.
I have to admit I'm kind of confused by what injectors to buy or not buy, even though there have been a ton of threads on it. The dealer searched for remanufactured and new ... the former showed none in stock and the latter showed 15 in Germany. But, the ones listed as new in Germany also said "remanufactured" under them. I've heard mixed reviews on the Bosch remanufactured units, but I've also read a couple posts saying the ones from the dealer are a safe bet? My indy also thought the Bosch units from the dealer were the best route. I know I could try to rebuild them myself with Bosios or Monarks, but I don't have a shop to balance them, and I don't have a ton of time. I.e., IF the Bosch units from the dealer are dependable, I'd rather go that route, but if they're going to be off-balance or stream I guess I have to come up with a different plan.
I kind of hijacked my own thread ... :rolleyes:

He can't find his pop tester and don't use it anymore?:eek: See if you can buy it from him cheap! It'd be a cool tool for you to have.

If you send me your injectors I can pop test them for you. I can shoot video of the pattern. I can also rebuild them if needed (if you supply the nozzles).

Unfortunately, he couldn't find it.:eek: I suppose I could mention to him that I'm interested in it if it ever turns up.
If I send them up for pop-testing and possible rebuild, how long would that probably take? I suppose I'm not in any huge hurry, but just curious as I weigh my options.:o

You should be able to find a local shop to check your injectors. Do a search for "diesel injection". Ask them if you can see it while they pop test them. If there are none by you, I can pop test them in a day or 2. Rebuild in about a week if you supply the nozzles.