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3.0 with a miss on Cyl #3

R

rhays

Member
I have a miss on # 3 and need some help again from to figure out what in the world I am missing.
87 3.0 stock engine with points and 2 bbl Rochester -- has a miss at all rpms from idle to wide open with a load on cyl #3
this is both on the trailer and on the lake
miss is not intermittent, it Is always there,
I have tried every thing I can think of.
things I have done.

compression check - all plugs out, throttle open, hot and cold - 144, 146, 143, 144,
replaced plugs, no change , old plugs all looked ok.. even #3
new wires, new cap, new points - no change
checked fuel filter, fuel flow, new gas, no contamination or water in tank
changed the carb with another known good carb - no change
sprayed cleaner around carb base looking for vac leaks - nothing
changed the distributor with another known working dist to see if a lobe problem. no change
the miss is there whether I set it at 2, 4, 6,or 8, or 10 degees...
switched the wires and plugs to see if the miss would move - it stays with #3
pulled the valve cover to ensure all rockers are moving the same at idle,
all nuts are about even at 3 threads down on the top of the rocker.
adjusted all rockers again, 1/2 turn back till clacking, 1/2 turn forward after no clack.
checked intake with carb off, it is an open dump style and looked clean.
replaced the intake/exhaust gasket - no change
unhooked the tach from coil- no change
unhooked the shift interrupt - no change
no water in the oil
It has good spark to all cylinders, but only a very small change noticed when I pull #3 wire from the cap or at the plug.
All other wires when pulled really makes it stumble as it is now on two cylinders.

any ideas on what I could be missing, I will listen and try anything at this point.
thank you for your help
 
did this engine ever run correctly while you owned it?
Are you absolutely sure the firing order, i.e., connections from disti to plugs is correct?
 
Jeez, sounds like you tried it all! The only thing I'm thinking, is maybe you have funky valve on cylinder #3? It could be bent or split? One idea is to air pressure test cylinder #3 when valves are closed, and listen for air leaking on the intake, or exhaust side.
 
Another thought I had, was maybe you have a weak, or broken, valve spring on that cylinder? That may not show up on a compression test? But, physically you might be able to push down manually on the valve to see if it moves, and, or try turning the spring to see how much tension is on it?
 
Just bought the boat, as a Junker... for the lower unit and trailer,, the prior owner said it ran ok last year, but then it stopped running and wouldn't start this year, and he lost interest. as the boat had rotted stringers, and the interior Is shot.. I never had intentions of restoring it, but when I looked at the block, he had it winterized. I filed the points, spark came, and it fired up. with a miss, so before I pulled the engine, here I am..... firing order correct at 1342, points at .016, It starts right up fine, just the continual miss.
I hooked up an air hose, the cylinder has some blow by, but it sounds the same on the other three. I tapped the valve with a hammer and the popping of the valves sounds the same as the other three, I used 120 lbs of air pressure.,, I removed the valve springs, they look and feel normal. I do have other springs laying around, and will replace those two tomorrow....
I had another suggestion of replacing the lifters on #3, as one may be collapsing, ( I didn't think of that) Ill update more tomorrow.
looking inside ( through the plug holes with a flashlight ,, the tops of the pistons look dry and normal, the cylinder walls, from what I can see, look normal,,,

thank you again for all and any suggestions....I will try anything,,,,,,
 
Point gap should be,
gap .022"
Dwell 28-34 degrees

I would think if you had a collapsed lifter it would tick like crazy when cold starting.......

If you suspect a bad lifter try tightening the rocker arm more.

Also try closing the choke slightly when throttling up some and see if a little extra gas helps.

Also you say new this and that but you did not say a new condenser.
If you do a tune up replace all the point components. Points and condenser!!

WHen I was in the business I would have at least 2 one gallon zip locks bags filled with points, rotors and condensers every season.

A condenser can cause a host of issues..........

When checking valve springs one must use a valve spring checker (device that compresses the spring with a psi gauge telling how much force the spring produces per distance compressed).

Only thing one can do is to put them all side by side and see if any are shorter then another..........unless a gross difference one can not see a bad spring.

If nothing show ups after all your effort, maybe a burnt valve.........or combustion chamber/head issue.

Relook at the speak plugs and carefully compare number 3 with the others...if possible post pics and label number 3 for comparison.
 
Thank you for your help.
Pulled the valve cover, pulled the springs, they feel the same, (I don't have a tester) they are all the same height, so I switched them with #1 cyl.
Also, as the lifters were easy to get to, I pulled the two from cyl #3 and replaced with two others from another engine.
Still got the miss on #3
my apologies for the condenser, I did put a new one on also. I set the points to .022 with feeler gauge. My duel meter quit working a long time ago, so I haven't been able to check that.
Closing the choke up more while throttling didn't make any change except to make it want to stall out,, I was hoping to find a vac leak or something but didn't,
bummer...
Thank you again for your advice and knowledge...
I did try another working distributer with cap and wired and no changes,,
Will post a pic of the plugs in a minute ..
 
My experience has been that a constant miss on one cylinder, usually showed a valve problem in that cylinder.
Bert
 
Plugs are left to right 1,2,3,4
these are what was in it, The new plugs don't show anything yet, as I have only ran them once around the lake and maybe 15 minutes on the trailer...
Thank you again for all your help...
 
MikDee said:
Another thought I had, was maybe you have a weak, or broken, valve spring on that cylinder? That may not show up on a compression test? But, physically you might be able to push down manually on the valve to see if it moves, and, or try turning the spring to see how much tension is on it?
Click to expand...

bertg said:
My experience has been that a constant miss on one cylinder, usually showed a valve problem in that cylinder.
Bert
Click to expand...

My thoughts as well, either a valve or an ignition problem, if only on one cylinder. maybe a split, or cracked valve?
 
I have not worked on heads in relation to valves, other than replace valve seals, and set the rocker adjustment,, I have always had the local machine shop do the work, then bolt them back on,,
I have had a few 140's easily show head issues between cylinders 2 and 3, due to bad exhaust valve seats, burnt valves or bad head gaskets, but this was always easy to diagnose, as the compression would be in the 60s to 90s for those cylinders ,,, but with good compression showing, I just hadn't come across a miss in a cyl due to a head issue, My plans are to take your advice and pull the head tomorrow and take it to the machine shop to be checked out.
Today, I disconnected everything to isolate any issues. The coil is running solid 12 volts from a jumper wire from the battery to the hot side,, there is only the black wire from the coil to the distributor, jumping the starter to start it, no changes, I have switched out coils, distributors, wires, plugs, I even installed the distributor at 180 degrees and ran the wires at 180 degrees to try that, with no changes.....
I appreciate everyone's help with this,,, I will update again soon,,,,
 
Why is number three plug look rusted on the metal body? Do you have a small water leak?

If any water is reaching this plug while running it can and will short the plug to ground........very common problem with closed cooling systems when antifreeze makes its way to the plugs on the old 470's......

It just may be coincidence but need to ask.
 
I found it,,, (i think) and am surprised it didn't show up earlier,
ill post a pic as soon as I can.. I pulled the engine as it was coming out anyways,,, as I was getting ready to pull the head, I pulled the manifold off.. And found that it was a small port intake head, and had a big port manifold gasket on it... (It is a 3.0, but appears to have the 2.5 head on it) This wrong gasket combo allows the intake on #3 and exhaust on # 2 (side by side) to have a small gap about thickness of two dimes of exhaust air to enter that intake port from the exhaust. It never affected pressure, as the cylinder was always getting air, just exhaust air,, and when I sprayed the gasket looking for vac leaks, it never showed as it was sealed from the outside as there was enough gunk on top of it between manifold and the engine.
Now that it is out of the boat, ill get the correct gasket and see if that fixes it for good.
I really appreciate everyone's help on this,,
thank you again. Ill post soon if that fixes it.
 
Wow! Imagine that! It should run like a top after this! Glad you found this, and thanks for letting us all know.
 
I have cheated in the past with a large port gasket on a small port head before myself, but I have always used a name-brand gasket and it has always covered both ports well and I have not had an air leak,
the gasket that was on this was rock hard, and obviously a very cheap no-name.. I would have thought saturating it with carb cleaner looking for air leaks would have identified it... anyways, the root cause was it had a small port head put on it in the past, and both the manifold and the gasket were large port, with a cheap gasket that didn't seal it.. I will probably switch the manifold to an older style small port, with the proper gasket, and use this engine else where...
Is there a known name brand gasket that will work for either? I have heard of adapters, but always try to stay with original safe proven things.. I am not a certified boat mechanic by any means,, just a general auto mechanic from the past that has a shop and gets into these every so often, and likes to read this forum....
thanks again for all your help and guidance....
 
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