88 Caravan 3.0 Engine Gallops

My 88 Caravan auto 3.0L has developed an unbalance. It felt like at
least one cyclinder was not firing. So I replaced the rotor, the cap
and all the high voltage wires.

The same symptom persists! The exhaust has a regular pulse to it
(every revolution) and a strong smell of unburned fuel.

The symptom is not readily apparent until after 15 seconds of idling.


What could this be?

 

Maybe you replaced the spark plugs butjust forgot to list them?

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

Whoops! I did check the spark plugs but forgot to list that. I was
hoping to find a fouled plug,

I had three brand new plugs around so I replaced the back 3. I
checked and regapped all old ones to .040 (they were all .048). All
six were the right light brown color with no oil fouling, no soot, no
deposits.

The back middle one did have a faint smell of gas, but that was before
I replaced the cables.

I will next make sure there is a spark at each plug. Not sure how I
will get back there for the back 3 - will have to check at the
distributor.

-gw

 

Just pull each wire and hold it close to ground (the frame) using a
screwdriver, if necessary. Also, pull the codes.

 

Oops, I had replaced the spark plugs in addition to the HV wires and
cap and rotor but I forgot to mention that first time around.

Well, I went to check the spark at the distributor to each cylinder
and they are all getting a nice fat 3/4" long spark. This was in a
dark garage and I would have seen or heard other places it could be
leaking - but this is a new wire set anyway so not likely.

Anyway when I started the procedure it to check the spark it ran fine,
with no gallop at idle! So, either

a) there was a sticky valve that got unstuck again
b) One of the old front plugs I re-used decided to unshort itself
(assuming it was shorted) - but I had just checked, filed and gapped
it the other day!

Question: Is there some additive I can use to unstick sticky valves?
At this point I don't know which cyclinder it was. I know there is a
bewildering assortment of miracle cures on the shelves but which can
be recommended?

-gw

 

It has likely either worn out or dropped a valve guide. Makes a valve
not close ptoperly - and the engine misses. Do a compression test.
Common problem on 3.0 MitsuShitty engines. My '88 New Yorker is on
it's third set of heads.