compression test results

[[email protected]]

i just did a compression check on my 79' 2000 cc engine, and the results were as follows rear left=120 lbs/front left=105 and rear right=120/front right 117 does this seem "not to bad" ?? i dont have my bentley to check specs and see what its supposed to be , cuz im stuck at work , and forgot to bring it with me

[[email protected]]

ok, im home now, and my bentley says 114-142 is within limit, so even the cylinder thats at 105 is still only a hair below "normal" range... 100 being the "minimum allowable"
So in theory should that not even really affect it that much?
SHOULD this run have anything to do with why it wont run for crap?
Its idling terrible and will only stay running is if i keep swatting the throttle and barely putts if ya put it in gear and try to go .
it almost seems liek it bogs when i give it gas, but im not sure.
plugs looked bad, not really oily, but pretty caked with thick dry black carbon
plug wire ends come out of the wire itself
I stop swatting the gas, it dies.
Heres what all ive done so far. keep in mind this IS a 79 engine eg code if it matters
1)compression check, as noted above
2)checked intake air sensor results as follows
A)potentiometer - (6 & 9)=312 and (8 & 7)= 158 .. all ok
B)Stator Flap- (Closed )= zero and (Open)=varied ..just like it said it would
in Bentley
C)temp sensor =(6&27) didnt check yet, forgot to when I was checkin "the box"
any advice/past similar experiences would be appreciated

[[email protected]]

Check timing, idle and valves, replace plugs and wires...How clean are your injectors? How's your fuel pressure (should be 28 psi)? Filters good?

[[email protected]]

cool, thanks for giving me soem kind of lead to go off of, i got the wires and a set of plugs at work, just didnt get that far yet, dont run to be able to check timing, hopefully the wires and plugs will be enuff to keep it runnin, ive seen so many ppl on here say theyre runnin on 3 cylinders, and it runs fine (aside from the fact that its 3 cylinders, thats why i was kinda suspicious about it not nessesarily <SP? being just the cylinder being down causing the problems.

[jeremysmithatshawdotca]

check the temp sensor
Jeremy

[[email protected]]

ill have to check it when i get to work, AND take my manuals with to check it . Ill get this figured out yet. thanks Jeremy.

[bljones]

plugs and wires. it is amazing how many times i have seen a poor running engine 'recover" with just that one simple step... the next part is a little tougher- solving the plug fouling problem
"curing symptoms is easy- it's preventing the patient from dying of the disease that is difficult."

[[email protected]]

oh by the way, is the 120 per cylinder pretty good? or does this mean the engine's about shot?

[[email protected]]

oh shoot, i forgot to ad, the compression check was with the engine cold. due to the not wanting to run factor, so would that make the compression higher because of the expansion of the metals or would it go down ?

[ratwell]

You need to warm up the engine before doing the test and during the test hold the throttle wide open otherwise your results will be skewed.

I think you misread the Bentley slightly. For all Type IV engines, 100-135 psi is normal compression and you need to rebuild when it drops below 85 psi. Of course the performance will go down until 85 psi but people still drive with cylinders at 80 psi and lower. I was in a bus like that just 3 weeks ago and it ran and that's about all.

Those readings in Bentley were taken at sea level so you need to adjust them for your altitude. Here's the multiplying factor:

0500 ft. 0.987
1500 ft. 0.960
2500 ft. 0.933
3500 ft. 0.907
4500 ft. 0.880
5500 ft. 0.853
6500 ft. 0.826
7500 ft. 0.800
8500 ft. 0.733

So for example if I lived in Denver and I got a reading of 85 psi I would be making a mistake deciding on a rebuild because it would really mean 100 psi at sea level and that would be ok.

[[email protected]]

ok, i just checked my intake air sensor "temp sensor" and it read 5330 instead of 2500 or less, so im assuming ;-)its shot would this effect the way it would idle right from the getgo?

[ratwell]

You mean the cylinder head temp sender (temp sensor II) by #3? It should read about 2500 at 68F. I graphed the range of values it produces:

http://homepage.mac.com/ratwell/TempSensorII.html

If you've run the car recently the value will be lower than normal. Since the reading you've got is so high it's going to tell the ECU that the engine is very very cold when it's not.

Make sure you are getting an accurate reading with your ohm meter and replace it. New ones are as low as $20.

[[email protected]]

i mean i tested the ohms on #6 and # 27 on the airflow sensor, and it actually said 5.33 , but i believe i have to move the decimal point to the right 3 places ( or am i wrong?) and i used 2 differnt ohmeters, so im sure that teh reading is correct

[ratwell]

BY replacement I meant the sensor not the ohm meter, sorry.

[[email protected]]

ok, ya lost me somewhere along the way.

[[email protected]]

by testing the ohms between 6 and 27 what did i just test? i thought it was the intake air temp sensor? am i mistaken ? to test the cyl head temp sensor, id have to either take it out or use the plug that plugs into the computer to check right? not the airflow "box" ??

[[email protected]]

im tryin real hard here, bear with me

[[email protected]]

help !

[brackish]

There is a good way to set the timing without having to have the engine running. It's found in "How to keep your volkswagen alive." It sounds to me like timing would be a good thing to eliminate as a possible source of the problem before going too far on the injection system. My '77 bus had a similar problem which was cured by setting the timing.