Compression Problems

lordlinty · Post by **lordlinty** » Thu Jan 25, 2007 8:40 am

Hi there,

I'm desperately seeking some second opinions.

Over the past few months I've been working on getting rid of the little niggly things on my 94 2800 diesel Pajero. All in all it was going well until I got a compression test done. It came out 285 instead of the desired 400. I'm told this is pretty terminal although the clock is only showing 125k? I realise the clock could have been diddled but nothing else suggests the truck has done much more than this. Other than this problem it seems to have went really well since I got it in May last year. Ironic that I only just ordered some recovery gear shortly before this reared its ugly head.

My options as I see them are sell it at a huge loss, replace the engine or desperately seek to fix the problem. I realise the last is unlikely.

This is my first diesel, my first 4wd and my first car since moving to NZ. My knowledge of diesels is still a bit basic but I imagine it's going to get better really soon...

Cheers

Grant

NJV6 · Post by **NJV6** » Thu Jan 25, 2007 8:42 am

Out of interest what sparked you to do a Compression Test?

DieselBoy · Post by **DieselBoy** » Thu Jan 25, 2007 9:44 am

Are all the compression readings from all four cyclinders 285 give or take??

Provided they are all an even pressure, just drive it till it stops.

If its only one that is down on compression, get the cylinder head tested.

Other wise, it may have a glazed bore, as is common with alot of Jap imports.

Don't dispare, i bought my Safari with 134.000 on the clock. I knew it was a bit noisey from the tappets, and smoked like a 50 y/o booze hag, but i no matter what safari i bought, i was going to get the injectors and timing played with and replace the rocker shaft and resurface the rockers. After getting all that done, i was excited about picking it up from the work shop.

Alas, now i could hear everything more clearly now the valve gear was quiet, it showed up a new noise between idle and 1200rpm. Could have been execessive end float on the crank or worn and sticking lifters. After replacing the crank shaft thrust washers, i have had to admit defeat and leave the lifters to being randomly noisey when they feel like it. (not worth the effort pulling the head off to replace them when its not effecting the performance of the engine)

Three years later, its still going strong, and still makes a random and anoying ticking/knocking sound at times.( i quick burst at full rev'scure's it for a while)

Moral of the story, there's always something wrong with ya truck, or something your a bit worried about. Best thing is to stick with it and see what happens. If i craps out, then buy a second hand motor and throw it in. You can pick em up for a couple of grand.

So if its just one cyclinder thats down on compresion, and the heads all good, then just forget about it and drive it

lordlinty · Post by **lordlinty** » Thu Jan 25, 2007 10:01 am

Thanks for the replies. It's a comfort to have such a well of knowledge to tap in on.

It's 285 across the board

I decided to do the compression when I noticed black smoke when pushing the revs up. As far as I can remember it didn't do this a few weeks ago. It runs without smoke on steady acceleration. I also noticed the urban economy was down about 15-20%.

It's really just since I had the fuel and air filters replaced and an additive run through it that this all started.

DieselBoy · Post by **DieselBoy** » Thu Jan 25, 2007 10:53 am

What sort of additive??

It seems strange to me that all the compressions are down at that level. Could have been a faulty compression tester.

Compression loss, as you probably know, happens when the piston rings wear past a certain point and no longer seal against the bore. This is a very gradual process, not an overnight thing. I think its highly unlikely that the rings would have worn them selves out in a matter of a few thousand K's.

But, more smoke can be an indication of low compression. It can also be many other things such as dirty injectors, airleak in fuel line, valve clearences, clogged air filter, restricted air intake, worn injector pump, injector pump timing advance not working, injector pump timing set to advanced.

Things i would try are:(going through what was touched at the service after which the problems started)

Run Morey's Fuel Conditioner

Check that they have infact installed a good new airfilter.

Check the fuel filter for tightness on the filter housing, and for the correct type/size.

Give it an oil change, get some good diesel oil like mobil Delvac MX, or Caltex Delo Gold, use a Ryco or Repco oil filter and 1 litre or moreys heavy duty oil stabiliser.

Drive it for a few weeks, do some long hot runs in it out of town on the open road to get the fuel conditioner working on the injectors. Work the engine hard, such as up hills etc etc (working it hard doesn't mean reving the crap outa it all the time, just put it under load as you do at 100K's)

The idea behind that, is that hot running under load cleans some (not alot but some) of deposits that form in a diesel engine during slow running round town. It also helps with stuck/sticking rings and glazed bores, and injector cleaner works best underload on long hot runs.

Keep an eye on engine oil consumption over this time, as that is also an indication of piston ring and bore wear. A litre or so over 5000k's (or what ever the service interval is for your engine) is pretty normal.

After that, head into a different garage and get a compression check done.

OR,

Just say to your self, well, i have out it through its paces over the last couple of weeks, so there can't be to much wrong with it!!!!

Double check that the 400 reading is infact what is supposed to be for your engine.

BTW: Another indication of worn piston rings is excessive crank case blow-by. You can see this by removing the hose that comes out of the top of the rocker cover and goes to the intake after the aircleaner. If, when the engine is hot after a long trip, you pull this hose off, and its billowing vapour and steam at quite a high pressure and rate, the the rings may in fact be knackered. A visible steamy hazy looking stream of vapour coming out of the breather at a reasonable pressure is normal for a diesel engine thats traveled 100,000 or more. Kinda hard to judge if you haven't actually seen a vehicle with a knackered engine and just how much blow-by they create :wink:

tallsam66 · Post by **tallsam66** » Thu Jan 25, 2007 6:20 pm

Ive heard it better to get a leak down test done as it gives a better indication of how good the rings are sealing against the cylinder walls....im no expert but thought id throw that in to confuse things.
Trev

DieselBoy · Post by **DieselBoy** » Thu Jan 25, 2007 9:29 pm

Well, there's nothin like a second opinion from another garage with these sorta things :wink:

Send it in to some where else and get another test done

adventures_more · Post by **adventures_more** » Thu Jan 25, 2007 9:54 pm

That Moreys diesel conditioner is good stuff i reckn , my wee 2LT seems a little bit more responsive with that stuff in the tank , i use it all the time now ( just have to buy another bottle ) .

Also "Beware" that some garage's put the scare tactic on the innocent & ill aware , purelly to get more work out of you and more money , when alot of the time you car doesn't need it . Alot of the time i act dumb /unmechanically minded when i go to a service centre , just to see what they are really like ,its suprising at times to say the least . i like to be sure when people do work on my vehicles , etc . When you find a good place , stick to them .

tallsam66 · Post by **tallsam66** » Thu Jan 25, 2007 10:32 pm

Hi
Ive had a look on the net & found some info on leak down testing.
Basically a leak down test is a way of finding out what is causing the cylinders to loose compression.
Follow this link to read about it.

http://en.wikipedia.org/wiki/Leak-down_tester

Cheers
Trev

lordlinty · Post by **lordlinty** » Fri Jan 26, 2007 8:37 am

So much information!

Cheers for the help. And thanks for the link. I will update and how I get on.

Toyhatsu · Post by **Toyhatsu** » Sat Jan 27, 2007 6:52 am

There is such a thing as a wet compression test wherein a small amount of oil is placed in the cylinder and the compression test carried out. From memory if the compression is improved then the issue is with the piston rings/cylinder wall, if not there may be leakage associated with the head or valves. That said from reading the Wikipedia article it would seem that a leak down test may allow you to differentiate between the leakage being caused in the cylinders as opposed to the head. My 2c.

adventures_more · Post by **adventures_more** » Sat Jan 27, 2007 8:11 pm

Most mechanic's know that little trick with the oil, every mechanic i know does this , sure some don't . Plus you need to make sure the engine is warm 1st ( different expansion rates of different steels & alloys inside the engine, etc )before you do any Compression tests .

plus i am sure there are alot of different and more accurate ways of checking compression , probably most accurate one would be with the head off, pressure testing the head , valves& seats and then the cylinders & pistons , etc

lordlinty · Post by **lordlinty** » Tue Jan 30, 2007 9:31 am

Thanks for all the advice guys.

I have a couple of people to approach regarding the problems, hopefully sometime in the next couple of weeks I will have a plan.

Cheers.

Aaron · Post by **Aaron** » Tue Jan 30, 2007 2:00 pm

Definatley get a leakdown test done if the compression is down it will tell you where it going. If the leakdown test comes up good but the compression is down then you may have bent rods so the pistons dont come all the way up. Or its had a head gasket replaced with one thats too thick.

adventures_more · Post by **adventures_more** » Tue Jan 30, 2007 7:52 pm

"If the leakdown test comes up good but the compression is down then you may have bent rods so the pistons dont come all the way up"

saying bent rods is a bit extreme , don't want the poor bugger counting all his pennys in his piggy bank now do we -LOL

Is it blowing black smoke under power ? if its not , the compressions are not that far down .

Rollux · Post by **Rollux** » Tue Jan 30, 2007 9:47 pm

Just a side point, a few years back i foolishly put "motor-up" in my 2LT. 3 weeks later i had the head off to hone the bores - It was chewing thru 2 litres of oil in 600kms :shock:

Bores were so well polished you could see your reflection...
My motto is now - Never use an oil additive to prevent bore wear/reduce friction.

Aaron · Post by **Aaron** » Wed Jan 31, 2007 7:16 am

saying bent rods is a bit extreme , don't want the poor bugger counting all his pennys in his piggy bank now do we -LOL

If the compression test is correct @285, then its not a happy camper!

lordlinty · Post by **lordlinty** » Wed Jan 31, 2007 2:30 pm

Smoke under power, yes. Quite a bit of power though i.e. heavy acceleration.

That reminds me, I will find out what additive was run through it during the service.

Cheers again

adventures_more · Post by **adventures_more** » Wed Jan 31, 2007 9:16 pm

the shinyness is not from a additive , but something else all together - most diesel mechanics know what its from !

mudhaw · Post by **mudhaw** » Wed Jan 31, 2007 10:21 pm

Black smoke from a deisel is excess fuel or not enough air in other words a fuel rich mix this can be fixed with turn of a screw on the injector pump if it is lacking in power it could be lack of air. Yor wagon should be fited with an intercooler these I have found somtimes to be blocked with oil and gunge deposits and restricting air flow (black smoke, lacking power)
Pull the inter cooler off and flush with kero, you should be able to see inside if it looks oily flush it!

. This is inexspencive and a good place to start.
As for the comp test if all the cylinders are almost the same, and you have no problems with coold start there is nothing wrong (just drive it)
Have found with 4.2 landcruisers if you driver like a nana the inlet clogs up and does the same as yours. And they dont have an inter cooler with small air ways that block easaly
I have done lots of comp tests on deisels and dont very often go by the presure they put out just how even they are
Good luck and start with the cheep bits first

Aaron · Post by **Aaron** » Thu Feb 01, 2007 4:07 pm

I have done lots of comp tests on deisels and dont very often go by the presure they put out just how even they are

The whole idea of a compression test is to find out the pressure, if it is low it doesnt matter if they are all the same it just means they are all low!

Get a good compression and leak down test done that gives you an accurate reading, diesels rely on compression if you dont have enough then you wont get power.

mudhaw · Post by **mudhaw** » Thu Feb 01, 2007 6:28 pm

The whole idea of a compression test is to find out the pressure, if it is low it doesnt matter if they are all the same it just means they are all low!

Yes thats right, but when was the comp tester last calabrated and how old is it. As long as the comp is all even and still in the ball park it should be fine
If compresions are low as in bad it is rear to get them even
Also depends on where you get your figures from some turbo motors have lower compreson because the use diferint pistons, or a thiker head gaskets

long · Post by **long** » Fri Feb 02, 2007 8:04 pm

Hey mudd wheres the air screw on a nissan mistral pump ?

mudhaw · Post by **mudhaw** » Fri Feb 02, 2007 9:26 pm

Sorry not quite shure what u mean injector pumps dont have an air screw,they have a fuel screw, If they are not an EFI pump.
Manual pump will have the excelerator cable going to the injector pump and the EFI system will be going to the inlet manifold
EFI pumps are controled by the computer

Toyhatsu · Post by **Toyhatsu** » Sat Feb 03, 2007 12:04 pm

Do you mean the bleed screw sometimes found on the fuel filter housing? I recently bought a Mistral. How have you found it for reliablity, mileage etc?

long · Post by **long** » Sat Feb 03, 2007 2:34 pm

Ive only had one prob with my Mistral it was running outta power on hills and wouldnt rev over 3k after checking all the usal remidys for the problem i went one step more n thought back to the last time i owned a diesel that had this prob n i took the bolt out of banjo on top of injector pump being careful not to lose the 2 copper washers inside there u will find by useing a ball pen a smal spring reinsert ball pen u should snag a very small fine filter mine was so cloged up with grunge n crap it wasnt funny n after a good clean out it was 100% better n power and pulling capability it will now red line n more ifn i was to push it
Cheers
Gary

Toyhatsu · Post by **Toyhatsu** » Sat Feb 03, 2007 6:06 pm

Yeah I heard about the blocked filter thing on the nissan owners site. Along with MAF faults seems to be quite common. What sort of economy are you getting out of it?

Tony

mudhaw · Post by **mudhaw** » Sat Feb 03, 2007 6:29 pm

Been thinking about it and the pump on your wagon is a rotory pump
and they dont have an air bleed
The inline injector pump could be what your thinking about cause they have an air bleed
If you think you have air in your pump, pull the hose from the leak off rail that goes to the pump, and pump the primer on top of the fuel filter.
aloso pays to check the fuel filter for air first, if it doesnt have a bleed screw on it pull the out let hose off and do it that way.

long · Post by **long** » Sat Feb 03, 2007 7:18 pm

im gettn from Hawera in Taranaki up to west gat in Auckland on $40.oo at that time diesel was $1.03 a liter and that is a 5 hour drive for me towing a traler with 3 dogs and my race rig on the top of it all since doing the filter in the fuel pump

adventures_more · Post by **adventures_more** » Sat Feb 03, 2007 7:19 pm

if an engine is worn & you get a compression test done , it is extremely rare that the cylinders will have similar compression , mostly each cylinder will vary a bit from each other , as each piston/rings /liner are never precisely same within their structures.

the same reason that if you have 2 identical engines built precisely the same , put them on an engine dyno , they will vary a wee bit in Hp & TQ ratings , 2 engines are the rarely the same , same with individual cylinders within an an engine-( unless its been precisely blueprinted with individual cylinders cc'd & equalised) .

so i reck'n your internal engine could possibly be in good condition , turbo engines , especially "Direct" versions have distinctly lower compression ratios than natural ( Non forced induction ) versions,

Compression Problems

Compression Problems

air screw

it good

mileage