jwl

87' Bosch No. 0 438 140 036

AirCOOLme

alright... i checked for vacuum leaks around # five and found none...
static compression numbers were around 120# if i remember correctly..
i did a dynamic as the good Dr. instructed... this is what i found..


95psi on every cylinder except #5

#5 was 80psi.. there was 3% leak-down on this cylinder so I am guessing this is a valve adjustment problem?

thanks to PorschePhD and his dynamic test....I might have to buy something at imagineauto!


-Nick

PorschePhD

Ah, great!! That test is often over looked but can also be very effective. It is a pain in the rear though to do.

AirCOOLme

i found the only pain in the *** is reaching around a hot motor to screw in the tester.. ouch.

valves tommarow and i will let you know how it goes. thanks alot -nick

DonE

I assume with a twin plug, you need to pull the plug wire on the other hole?

AirCOOLme

alright... the valve adjust is SPOT on....


i have used a ton of carb cleaner looking for a vacume leak and found nothing...whats next? i have no idea where to go!

-thanks-nick

Stevie 77 930

After following this thread I am going on a limb and suggest getting your WUR rebuilt. You've gone this far without mentioning it is either new or recently rebuilt. I had a similar problem some time back and after a whole bunch of $$ and poor diagnoses from a local guy, I took the car back.... Had my old WUR rebuilt and problem solved. (I still have the new one I had to buy that didn't work for my car). Give John at Special T Auto a try.... http://www.specialtauto.com/porsche-parts/index.html.
It may prove to be cheap insurance against a faulty WUR and you won't spend a bunch on this fix. I hate when this happens Good Luck !

AirCOOLme

its new... out of the box new...6000 miles on it..... the shop that built it said they would send me another one.....

i dont know if im ready for the "shotgun" approach to fixing it yet :\

-nick

PorschePhD

System is 6 to 6.7bar

Control warm is 3.65 =/-.2bar

Full enrichment is 2.9bar
After 10 minutes shut down 1.6 bar
After 20 minutes of shut down 1.4 bar should remain.

Rob S

Nick, I'm going slightly off the main track here, but I'm interested in the "dynamic" compression test, and since you did one, I figure you would be too.

I've never heard of a dynamic compression test. And I'm wondering how well it works and what it really shows. Though I like the idea of measuring cylinder pressure while the car is running (which is when it really matters!) I would be concerned about raw fuel washing off the oil from the cylinder walls and giving an erroneous reading. With an EFI car, you could disconnect the injector at that cylinder for the test. With CIS, it's not so easy. I'd also worry that there might be characteristics of the mechanical gauge that would make its accuracy doubtful under those conditions. The typical mechanical gauge isn't meant to respond to pulsations at such a high frequency, and while that little check valve opens in the gauge, I can imagine all kinds of weird dynamics that might confound the reading.

Stephen, care to share more about where this idea came from (you said Bosch?), and what your assessment of it is as a diagnostic tool? For instance, Nick found consistent readings from cylinder to cylinder statically, but he found one that was down dynamically. Do you think that was significant?

Rob

AirCOOLme

i see your point rob. The test is new to me... hell... working on porsche's is new to me! so any other advice anyone could give would be helpfull.

DonE

Hi Rob

With an EFI car, I don't think an injector time of 1.55ms (my 72lb inj at idle) would do much to the gauge, especially if it only ran for 15 or 20 seconds to get a reading.

I don't know what the difference would be between a warm motor cranking and a warm motor running, for a compression check. Is it more consistent or accurate??

PorschePhD

I will try to find the actual tech papers. They were on a fax so let me do some digging.

It is something that was brought to my attention a while ago by a pal who owns a certified Bosch center, and a rather large one at that. They were using a 2.7CIS motor as a test bed.

The idea was much like a warm leak down the dynamic test would how any inconsistencies caused by the things being cold and did not represent smaller issues that would occur during running. This allows the motor to do what it does (run) and show live data verses doing it static.

I didn't make the procedure up but I have found it to be effective in pinpointing issues that are other wise masked.

The ring wash is not a problem at idle, or so they say. The only caveat was not to do this on a new motor or wash out certainly would become an issue.

Rob S

Thanks, Stephen

I'd be very interested in what you can share, if you have the time to dig that up.

I like the concept of a "live" compression test -- just had a few concerns about it. I'm wondering what you would make of Nick's data -- with one cylinder significantly lower than the other 5 when it's running, but all six equal when not running. It's also interesting that the values dropped from 120 to 95 psi when it ran. What do you make of that? Did his dynamic test make you say "Aha, now we know what's going on?" If so, what did you conclude?

Don, I wasn't concerned about the pressure impulse from an electronic injector skewing the compression numbers (plus, you can just unplug it). But I was thinking that washing down the cylinders with gasoline might be a problem for CIS. Sounds like that's not the case. But still, I wouldn't want to run it for very long that way!

WERK-I

If memory serves......(not lately though)
Aren't static compression tests done with the throttle body wide-open? Dynamic tests would draw air through the AAR thus reducing the efficincy of the engine(air pump).

Maybe the next step would be to pressurize cyl #5 at TDC and BDC and listen for air coming from either the oil tank or intake/exhaust tracts? Could be busted rings, cracked piston, others?

This is a great thread, btw.

Dave
'85 Factory Slantnose 930