new 944 owner. low compresion. worth fixing?

parish8 · 11-13-2007, 05:31 PM

just picked up an 87 944. i have a full size truck for bad weather but was looking for something with decent mileage that wasn't too boring or expensive and i dont mind working on it "a little" now and then.

i found this car and was blown away with how good of shape it was in. outside and inside are in great shape and it was only $1500. seemed like a good deal to me. after driving the car for a couple of days i really like the car.

now for the bad. about 1 out of 10 times it wont start. today i was able to roll start it and it fired right up. it cranks fine but just wont fire. 9 out of 10 times it fires right up. just reach in and turn the key and it fires right up. cap and rotor look good, plugs and wires look to be in good shape. fuel presure is around 40psi cranking and 30psi at idle.

the idle is prety rough but mostly steady. there is a big flat spot off idle and aproaching mid range but it runs good when reved up a little. cruises down the highway great at any speed. also has an oil leak that looks to be the pan gasket.

now for the big one. compresion from front to rear is 165, 175, 90, 145. put presure to it and most of the air seems to be headed into the crank case.

i dont think the compresion is to blame for the not starting but it might be the flat spot off idle and midrange.

should i bother keeping the car or is it going to turn into a big project. will the mileage suck with the low compresion. is there any point in changing the timing belt if the rings are shot? belt has 37k on it but is 7 years old. if i was to do the work myslef is there a cheap way to fix the lack of compresion?

thanks for the help and sorry for the long first post.

Jim

Dark Skies · 05:52 PM

The starting problem could well be down to the speed sensors being out of whack and / or bad earths. Rough idle might be the down to a combination of poor earth (or ground as you Americans like to say) accentuated by shagged engine mounts. The fact that it runs well when started suggests that the fuel system is reasonably OK (not saying it couldn't be tweaked with new filters / pump etc, injectors cleaned etc) but functioning. I'd try checking the sensors gaps and the earths first and see if it improves - because it's free to do. As for the compression issue - the cheap bit would be that you pulled the head yourself and had the valves checked over to see where you went from there. The rings and bore usually are good for a good 300K in my experience but it's possible the valve seats could do with some work if it's been exposed to some crappy fuel.

DMRK · 11-13-2007, 06:07 PM

First-welcome, you are in the right place.

Second-change the belt NOW before you need at least a valve job.

Third- might just be a head gasket, easy to change.

Fourth- check out http://www.clarks-garage.com/ and click on the garage shop manual link on the left to learn how to work on it.

parish8 · 11-13-2007, 06:19 PM

can you have a bad head gasket that blows combustion gases into the crank case with no other signs of failure? the typical leak down test pushing air into the crank case would make you think rings. never considered a head gasket.

idontknow · 11-13-2007, 06:45 PM

It's possible to have had the head gasket blow out to the oil return ports. Just a thought.

parish8 · 11-13-2007, 06:58 PM

Quote:

Originally Posted by idontknow

It's possible to have had the head gasket blow out to the oil return ports. Just a thought.

has anyone ever heard of this happening? if it is bad rings wich seems most likely i dont see any point in trying to save the motor. might as well not waste my money on a belt. just drive it till it dies is what i am thinking. then sell it for whatever i can get out of it. might get a couple of good years out of it?

maybe do some type of hybred motor swap down the road

i guess i am working thru some things in my own head. i will go thru one or two tanks of gas. if it still does ok on fuel and i can make it start/idle better then i will do what i can to keep it running for awhile(timing belt). if it gets worse mileage than my truck then the car isn't worth having for me and i need to look at other options.

AeroSS_87 · 11-13-2007, 07:21 PM

Hello again Jim. I'll keep off of two different threads and just keep any further comments here for you. Welcome to the site btw. These guys will know their ****. I almost forgot about clarks-garage.com also. Between there and here, you can't get much better info.

btw - you should throw up some material of the farm truck to let everyone know who you really are.

ronin · 11-14-2007, 10:57 AM

do a leakdown on the offending cylinders and see where the compression goes. has the car been sitting for a while? it is possible for cylinders to regain compression once the engine gets regular use again (i.e. rings re-seat, etc)

as for the timing belt: yes, it should be done regardless. if it goes, you have problems much worse than low compression

as for the fuel mileage: start with the injection system. the injectors could use a cleaning and bench test. then take it from there

parish8 · 11-14-2007, 02:49 PM

Quote:

Originally Posted by ronin

do a leakdown on the offending cylinders and see where the compression goes. has the car been sitting for a while? it is possible for cylinders to regain compression once the engine gets regular use again (i.e. rings re-seat, etc)

i did and it is going into the crank case. rings i assume.

you guys keep telling me to swap the belt but i just dont know if it makes sence money wise. if the car doesn't get better mileage then my truck(due to low compresion) then i need to get rid of it. if the bad idle or ocasional hard start is due to the low compresion then i need to get rid of it. if the compresion is going to get worse any time soon then i need to get rid of it.

belt is going to cost me at least $300. probably more. i am not going to drop $300 into it till i know it is going to run ok and get ok mileage with the low compresion. if the belt takes a dump on me it looks like i could get most of my money back just as a parts car.

i am going to clean up the grounds and test the tps sensor tonight. maybe test the coolant temp sensor too. is there just one sensor? if the dash looks to be reading corectly does the computer look at the same sensor?

mattdavis11 · 11-14-2007, 03:29 PM

Jim, if you aren't going to change an $8 belt then more than likely you aren't going to change the rings or do a head gasket. These folks can tell you what might be wrong with it until they're blue in the face, but until you put a wrench to the car, you, we will never know for sure exactly what the problem really is. Could be rings, could be a headgasket, who knows.

You might want to dump it.

parish8 · 11-14-2007, 03:52 PM

can i do a timing belt for $8. if so i will get started on it right away.

i am just here looking for some general info. thought maybe since this is a porshe board there might be some things that just go bad and the answers are simple. doesn't seem to be the case. i am not afraid to turn a wrench. just not willing to drop too much money on a car that i may not have a use for in the end.

not trying to offend anyone, just trying to make the best decision for me before i dive into working and spending on the car. from what i under stand if the rings are shot then the motor is prety much junk. if the motor is junk then the car is prety much done for other than for a parts or swap set up. no point in puting a belt on the car if that is the case but hell yeah, if i can do it for $8 i will get started right now.

ronin · 11-14-2007, 03:53 PM

Quote:

Originally Posted by parish8

i did and it is going into the crank case. rings i assume.

correct

matt is right, you need to actually start to do some hands-on diagnosis to get beyond your current stalemate. also, the timing belt is ESSENTIAL, no matter how much it costs. if you're squabbling over 300, then maybe this type of car isn't for you. remember, it's not a Honda Civic. if you're in the Pac NW (probably not) I'd love to have a look and maybe buy it off you

parish8 · 11-14-2007, 04:09 PM

you guys are funny. a little sensative about your cars i think.

i am not squabbling over $300. before i found the low compresion i was ready to order the parts and tools to get it done. the reason for this post is to determine if the car is worth spending money on now that i know it has low compresion.

i have a plan. going to run one tank of fuel thru it. if i get at least 20mpg then i put a belt on it and drive it. if i get less than that try and sell is for what i paid. should be easy if it still runs. if i kill the belt in the next tank of gas than sell it for a loss, a chance i am willing to take. from what i am seeing it should be worth $1000 or more even not running.

thanks for everyones help. i will report back on my mileage and if checking the grounds helped or not.

Dark Skies · 11-14-2007, 05:57 PM

Quote:

Originally Posted by parish8

...

thanks for everyones help. i will report back on my mileage and if checking the grounds helped or not.

Whilst you're at it - try sticking in some of that petrol additive that's supposed to de-gum piston rings. You may find a bit of use frees things up a bit and improves the compression situation. Also, during your leak down test - did you find all the loss was going into the crankcase or was it spread about in other areas? It may be that a combination of valve leakage and stuck rings is responsible and things might not be as drastic as you seem to fear.

parish8 · 11-14-2007, 06:11 PM

Quote:

Originally Posted by Dark Skies

Whilst you're at it - try sticking in some of that petrol additive that's supposed to de-gum piston rings. You may find a bit of use frees things up a bit and improves the compression situation. Also, during your leak down test - did you find all the loss was going into the crankcase or was it spread about in other areas? It may be that a combination of valve leakage and stuck rings is responsible and things might not be as drastic as you seem to fear.

the car does smell stale as if it has been sitting for awhile. not sure how long but from the smell it could be a year or so prety easy. i am not aware of this additive, do you have any more info on it? it goes in the fuel or oil? when i did the compresion test it was after puting about 60 miles on the car so i dont know if there is anything to unstick but it might be worth a try.

as far as where the leak was going. i didn't do an actual leak down test with a gauge and all that. just took it to tdc and put 50psi to it. i put my ear up to the throttle body and could hear nothing, put my ear to the tail pipe and could hear nothing, pulled off the oil filler cap and could hear a loud hissing. put my hand over that and the breather tube going to right before the throttle body and the presure built quickly.

i do see a chance the low compresion might not get any worse and might not effect mileage or driveability. if that turns out to be the case i will swap the belt and enjoy the car. everyone that has seen the car is suprized at how nice it is considering it was only $1500.

Dark Skies · 02:11 AM

I've seen a number of these additives on the shelves in auto shops - made by brand name manufacturers. Can't remember an actual product by name off the top of my head at the moment but you supposedly put it in the fuel tank and it chemically breaks down the gum and frees the rings. A lot of products claim they'll restore the engine to 100% but of course that's bollocks. You can't replace worn metal.

However, breaking down gum chemically is entirely plausible - I've done it myself when I left a set of (motorcycle) injectors for a year and the fuel dried in them and gummed them up. I freed them up by hooking each one up to a feeder (syringe with a tube to the injector line in) filled with some miracle additive of some sort and then applied a 1.5 volt power source to each one and switched it on of off and 'rocked' the injector until this stuff flowed through it and cleaned it out. There's no reason to suppose that a similar result couldn't be done with stuck rings via the petrol source.

I would imagine one of those additives they sell for cleaning the injectors might have a similar knock on affect on piston rings - it has the same job - just lower down the engine.

Also, I believe a high quality oil such as valvoline contains similar additives. So you could try a two pronged approach - fuel additive and quality oil. It's worth a shot and the oil change is worth doing in any event on an engine that's been standing.

Finally ... this leak down check - did you warm the engine up to normal working temperature? That'd give you a more realistic idea of the state of the engine.

ronin · 11-15-2007, 11:38 AM

Quote:

Originally Posted by parish8

you guys are funny. a little sensative about your cars i think.

i have a plan. going to run one tank of fuel thru it. if i get at least 20mpg then i put a belt on it and drive it. .

no, we're not sensitive about our cars. we just know what happens when they're not properly maintained

you mentioned your timing belt was at least 7 years old. that means the belt could last you another few miles, or it could break on you the next time you start the car. and then the repair will be a lot more than $300 (by a factor of at least fifteen) and a car with a broken timing belt is worth next to nothing

that's all that we're trying to say

parish8 · 11-15-2007, 02:44 PM

good news. i did a mileage check. not very scientific since it was only 100miles but the car got 22mpg. as is it runs good enough to enjoy driving it but i think it will run better after a little tune up. this was about 50/50 highway/city, some spirited driving and starting it about 20 times just to see if it was going to start. lost a little fuel checking the fuel presure as well.

that mileage is good enough for me to want to keep it. i am going to put a belt in it and see if i can get it to idle a little better, also get it to start 100% of the time. so far it has failed me twice.

woohoo, i am excited. i am going to try and take care of the car. i do wish it had cruise, i found myself going over 80mph in a 65 today. it seems to be much happier at 85 then it is at 65.

AeroSS_87 · 11-15-2007, 02:47 PM

They're dog **** down low, but they just keep climbing up top. keep us posted

marky522 · 11-15-2007, 03:39 PM

If you want to make 100% sure its the rings, do another leakdown. Take your meausrement, now leakdown the same cyl, but first put a small amount of oil in the cyl. If the number increses dramatically it is rings.

Mark