I have an 85 which has done 80,000 miles it is idling rough and when I accelerate it badly hesitates and has lack of power. I have recently had the injectors cleaned, checked fuel rail pressure, changed spark plugs, leads, new ignition control module and distributor cap.

I have checked the compression yesterday and came up with the following readings, second reading is compression test with some oil spayed into Cylinder

1 150 155
2 150 160
3 150 155
4 150 165
5 145 150
6 155 157 (plug cover with oil deposit)
7 150 150
8 149 150



The oil deposit on number 6 plug seems to indicate oil leakage into the cylinder. If it was the valve guide the second compression reading should have been a lot higher but the first reading is in-line with the other cylinders.

Is the compression in the ranged expected any clues to the problem would be appreciated.

Thanks

Andy

Perth
Western Australia

 

I would clean the throttle body and the IAC.

 

A typical 'rule of thumb' is there shouldn't be more than a 10% range between the highest reading and the lowest reading.

Your compression looks great to me.
If the valve stem seals haven't been replaced that could very easily be the source of the oil in the cylinder you mentioned.

You can expect the compression to come up a little on any engine when you put oil in the cylinder and check the compression.

You can change the seals pretty easily. It requires a valve spring compressor that bolts to the rocker arm stud and compresses the spring so you can get the retainer locks out.
Remove the rocker arm, bolt on the spring compressor, compress the spring, remove the two retainer locks. Pull the old seal up off the boss in the head out and over the valve stem.
Put on the new seal and put the retainer & rocker arm back on.
Do one at a time until you get'em all changed.
Adjust the valves with it running if you can. Put a bunch of newspaper over the exhaust on the sides of the engine.
Don't run it but a few minutes at a time and it won't get too hot to work on.

It's a pretty straight forward job.

 

I disagree with your conclusion on #6. Number 6 is already higher (dry) than the others because it IS getting oil from the guides. It doesn't go up as much on the wet test because it was already wet on the dry test. Do you follow that?

Either way, those readings are great. A little tired, maybe, but quite healthy.

RACE ON!!!

 

Look okay to me. Check the IAC as mentioned earlier.

 

Have you checked the fuel pressure while driving it? It may have plenty of pressure, idling, but the fuel system may not be able to maintain sufficient pressure while trying to supply the increased volume of fuel, demanded by acceleration.

RACE ON!!!

 

Thanks for the advice.

I have checked the fuel pressure even bought the gauage, 38psi to 41 psi.

I'll try the IAC next, the throttle assembly has recently been cleaned.

Good news a did fix my cluster a dry joint between the DC to DC power supply daughter board and the main board.

Andy

 

Forget someting about keeping the valves in place???

 

Lucky I have an air compressor!

 

I'd also check/clean the EGR system. Make sure the vacuum is connected correctly.

 

compression looks absolutely great!

 

Thanks all

I'l let you know how I go with fixing the hestiation problem hopefully its simple.

Thanks again

Andy

 

All the way through a full power run? You said you checked the pressure in your opening post, but have you checked it as I suggested in post #6?

RACE ON!!!

 

Forgive me. As CLint Eastwood said "You just never know when some awhole is going to be offended", no offense intended.

Why didn't ya just go ahead and fill in any blanks left out of the explanation and try and be helpful?
Just trying to see whether I REALLY know how to do this or not?

Here it is for'ya tmax the second:


FORGET the air compressor.
FORGET the 'rope trick'.


This 'works for me' and has never failed on a SBC engine.
It's quick, easy, logical, cheap and reliable.

Disclaimer: This information is backed by a 100%, no questions asked, money back guarantee. If you are not completely satisfied with this information, return it, along with your proof of purchase, for a complete refund of the purchase price..


/**************************************** ********/
Here's how to keep the valves from going anywhere with absolutely nothing but a helper to run your starter motor for ya..
/**************************************** ********/

(1)Remove the spark plugs just to relieve a little load on the starter/battery.
(3) This is for you TMAX
Remove the valve cover(s)
(2)Select a cylinder you want to work on.
(3)Have your helper:
a. Open the left door.
b. Get in and sit down
c. Instruct your helper to listen to your commands to
activate/deactive the starter with the cars ignition key.
c. Command your helper to 'Bump' the starter while you watch the rocker arms.
(4) Watch the rocker arms as your helper 'bumps' the starter.
What you are looking for is the compression stroke.
After the intake rocker arm depresses the intake valve, the compression stroke will occur. It's very easy to 'see' when the piston is coming up on the compression stroke. Both rocker arms will be in the 'released' position and both intake & exhaust valve will be closed.
If you want more assurance it's on the compression stroke place your finger in the spark plug hole and 'feel' the piston compress the the air in the cylinder as it comes to the top. Have your helper immediately stop the starter at that point.
Both intake and exhaust valves will be closed, the lifters will be on the 'heel' of the camshaft.
With a little practice you can do this very quickly and consistently.
No compressor, no rope in your cylinder, nothing at all.

Compress the valve springs, remove the retainer locks, release the valve spring compressor and have at whatever you want to do.

The valves can't go anywhere without 'bumping' into the top of the piston.

'Most' of the time there will be some oil deposits that have built up on the top of the valve stem that will keep the valve from dropping anyway.
But if the valve does drop it can't go far enough that you can't pull it back up.


/**************************************** ********/
Here's how to keep the valves for going anywhere with ABSOLUTELY NOTHING.
/**************************************** ********/

(1) Buy yourself a 10 buck remote starter switch and forget about having a helper or issuing commands to your helper.
This is the *PREFERRED* way of doing anything to your engine that requires it to be turned by the starter while you work on it.
OR... use a couple pieces of wire and do the same thing.

(2)Complete all the other steps listed above.

BTW, this technique works equally as well for adjusting the valve lash.
A little twist I use, at times, is to adjust the intake/exhaust during the time the 'other' valve is starting to open.
Example: When the intake valve is starting to open on the intake stroke, the exhaust valve WILL be fully closed and on the heel of the camshaft lobe. The respective exhaust valve lash can be set at this time.

Using the above described techniques the valve train can be worked on without all the machinations of putting 'stuff' into your cylinders or installing an air hose adapter to 'pump up' the cylinder all the while hoping there's not so much pressure that it presses the piston down and moves the crank/cam/valve actuating mechanism from where you want it to be.
This method is substantially quicker and easier to use for setting valve lash than any other I'm aware of.
If there's a quicker/easier way somebody please tell me about it.

YMMV but "I" have done it this way since the 60's when I started working on SBC's.

Anybody want/need more details????????????????

Tonymax#2 ?????????????

 

A little touchy tonight or something?

I posted so the new guy didn't rush out and get himself in real trouble with a dropped valve. I figured you just forgot to include it being that it sounded like you knew what you were talking about and I didn't want to hijack the post with any additional. I agree the "TDC" method you recommend is the best-have used it for about 30 years after pissing around with compressed air once or twice way back. I also agree it's not a good idea to have a "buddy" involved, unless he's a better mechanic than I am; even then I don't like to if I have a choice. Besides, the best line DH ever said was, "A man's got to know his limitations".