engine and drivetrain Help Diagnosing Very Poor Running O2

[esty]

the past few days i've been driving the o2 truck to work, about 100 miles a day...yesterday on the way home it started running like crap, missing...popping on decel and the engine is shaking violently

 

steve changed points, rotor and condenser & plugs, leaving the almost new wires with no change in behavior...this morning he changed distributors, same behavior

 

there's no oil in the radiator & no water in the head...my neighbor came over while steve was working on it this morning and said he thought that it seemed like a vac leak but testing for leaks found none

 

thoughts, ideas, suggestions

[ecpreston]

You said vacuum was tested... as in, with a gauge or just visually?

My case sounded a lot like yours, it was a vacuum port cap that jumped iff the intake:

http://www.bmw2002faq.com/topic/134669-suddenly-running-as-if-on-3-cylinders-but-not-help/

[FunkyLaneO]

Sure sounds like a vacuum leak, I would double check that.

['76mintgrün'02]

I had new Bremi wires that were defective.  Bought a set from Kingsborne and problem solved.  "It can't be the wires, they are new..."  I was wrong.  You can check them with a timing light on each wire to check for consistent spark.  Just a thought... although it does sound like a vacuum leak.

[esty]

all the plugs and caps are securely on the vac ports on carb & intake

[c.d.iesel]

Rule # 1 :  Compression Test Readings

 

Cyl. 1___________ psi

 

Cyl. 2___________ psi

 

Cyl. 3___________ psi

 

Cyl. 4___________ psi

[esty]

what does these readings indicate and what needs to be done to fix it

 

compression test results

 

cylinder:

 

1.....150 psi

 

2.....150 psi

 

3.....150 psi

 

4......85-90 psi

[M3M3]

not good.....all readings should be withing a few psi of each other.  #4 obviously has a problem.  my next step would be to do a leadown test to see where the issue was.  it can tell you if it is rings, intake valve or exhaust valve.

 

pull valve cover and look at the rockers for #4.  if the intake valve rocker is broken, valve will stay closed.  the cyl cannot pull air in and will show a low compression.

 

if it is valves, head needs to come off.  if rings, engine comes out.

[esty]

rockers look good, not broken or repositioned...we'll have to buy a leakdown tester before that can be done

[LimeySteve]

Sounds like lean running to me spray carb cleaner around carb/intake while running , see if idle rises , check booster & hose  too for vac leak .Also you can cover air intake on carb with hand if idle rises , vac leak if hand sucked onto carb no vac leak. Also is fuel filter blocked, are you getting enough gas  ?, blocked jet in carb !

[esty]

something that just occurred to me that i remember...there was/is a ticking, rattling sort of sound in the area of number 4 cylinder....i used a pipe as a amplifier listening around the engine and it was at the rear of the engine

 

a blown head gasket maybe?

 

"Sometimes a blown head gasket will cause a whistling or wheezing sound"

http://wiki.answers.com/Q/What_are_the_signs_of_a_blown_head_gasket

 

also water and heavy soot were blowing from the tailpipe which i belw off as normal because of the outside temps at the time

 

"Often (but not always), a blown head gasket will also cause deposit of water on a piece of cardboard held an inch from the tailpipe output while the engine is running"

http://wiki.answers.com/Q/What_are_the_signs_of_a_blown_head_gasket

[Pamola]

Could be a head gasket if oil getting in the combustion chamber. What does the #4 spark plug look like?

[FunkyLaneO]

Sticking valve?

[esty]

we bought a leakdown tester last night and...

 

after reading old threads, we set number 4 cylinder to TDC...or believe we did....the piston was all the way up, using the wire in the plug hole method, cam lobe pointing down

 

when pressure was added it sounds like the air is coming from under the plug wire heat shield or the rear lower side of the head...i couldn't detect air coming from a valve, the exhaust or carb

 

 

i suspect a blown head gasket with the air escaping at the point of the breach in the gasket...when this problem occurred, i was hearing a ticking, clicking, rattling sort of sound from the same are near cylinder number 4

 

and was getting water from the tail pipe....what do you guys think

 

 

 

for my next adventure, i'lll be helping hubby, steve figure out how to change a head gasket

 

 

EDIT

 

i just had a neighbor over and had him listen to the escaping air...he said it's coming from the rear bottom of the head, where the head meets the block, near cylinder 4 and believes it's a leaking head gasket

Edited June 21, 2013 by esty

[M3M3]

i believe you found the issue....