I have an '86 Olds Calais 2.5l with 5 speed. When I first got it the car had
been sitting for two years. I drove it home as it was. It ran well except
for a few minor things that didn't work properly (dashboard lights, etc.)
and the hydraulic clutch didn't work properly (bad master cylinder
methinks). The only other thing I noticed was that occasionally at lower RPM
(below 2000) the car would start to buck like I was in too high of a gear. I
figured a tune-up would fix that.
The first thing I did was change the oil+filter and air filter, as well as
hose down the throttle body with SynPower cleaner and put some SynPower
injector cleaner in with a fresh tank of gas. After that the car ran a bit
I then got the parts for a tune-up. I started to do the tune-up by replacing
the plugs. I removed the air cleaner housing and started by replacing the
two plugs on the drivers side which were easiest to get at. After struggling
to get the other two plugs out and failing I had to get going to work so I
cleaned up and headed out. The car ran very poorly, stumbling, stuttering,
bucking and knocking if I accelerated at anything more than a snails pace.
I checked my work and re-gapped the plugs to what the old ones were set to
(less than the gap stated on the emissions sticker). This improved the
problem a little bit. I also noticed that when I removed the air filter I
snapped a vacuum line running through the air filter and to the flapper door
in the snorkel. I replaced the line which also improved the problem. I then
put the old spark plugs back in which may or may not have made the problem
better. I then finished putting on the rest of the tune-up parts (cap,
rotor, wires) which helped the problem a bit. Now I can accelerate at a
reasonable pace, though I still have to go easy on the gas, gently easing
into it in each gear. Pressing the gas down quickly at any RPM in any gear
results in misfiring/shuddering/bucking/knocking. The problem seems to go
away if I keep the revs above 3500-4000... The engine totally smoothes out
above 4000 RPM.
The odd thing is that it has no problem whatsoever for the first minute or
so after I start it up in the morning. It runs great, just like it should.
It's got a decent amount of power for a 4 banger and I can jab the pedal to
the floor and it won't misfire or stutter/buck at all.
I'm thinking the problem is a vacuum leak. When I discovered the first
vacuum leak I mentioned earlier I also noticed a vacuum hose end connector
sitting in front of the valve cover. I could not figure out where it came
from. I must have broken/snapped it off when I removed the air filter
housing. That's my best guess at least. So I presume the problem is a vacuum
leak, and the only reason it isn't evident when the engine is cold is
because the computer makes the mixture obscenely rich (yet for some reason
still has a cold idle of just above 2000 RPM). In any case, where could this
vacuum line have connected to. I see no vacuum line that was snapped off or
any fittings without connectors. No obvious leaks in the hoses coming from
the throttle body or from the T/tree screwed into the intake manifold. Any
ideas as to where the leak could be? Or if there may be another problem
altogether here? Thanks.
I don't see any broken vacuum line though, that's the problem. It acts
almost as though a ported vacuum line is leaking in that it stumbles most at
part throttle under load (when ported vacuum is highest).
The problem is definitely related to something that was broken or damaged
when I removed the air cleaner housing to change the spark plugs. The car
ran very well before that and right after I put it all back together it ran
like crap. It would be quite a coincidence for a problem with the gas to
show up then, after I had already driven the car 300+ miles and immediately
after taking part of it apart to change the plugs. I'll still look into any
problems with gas, but I doubt that is the problem. I already ran some
SynPower through it which is pretty strong stuff. It's a CFI engine... No
carb or float bowl, just an electric pump that puts pressure in the line for
I seriously doubt it's the fuel pump as the car can go beyond the 85 MPH the
speedometer reads with no trouble and can sustain 4,500-5,000 RPM silky
smooth. Also, it's an electric pump.
I just can't wait until summer when I put a new short block in my '68
Galaxie. Then I'll have a nice reliable car again that at the rare times it
does break I can easily figure out what is wrong.
Anyway... Do you know how to pull trouble codes from the computer? Maybe
that could give me some insights?
From: Rick Colombo
Sent: Thursday, December 25, 2003 2:26 AM
To: Cory Dunkle
Cc: Rick Colombo
Subject: Re: '86 Calais 2.5l misfires/stumbles/bucks when warm...
Well at the very least, plug the broken vacuum line that you see. If
the line is coming from the engine, this leak will cause problems. If
it's on the side of the device that requires vacuum, well then that
device simply won't work.
As for sitting for two years, I would guess that there is bad gas in the
tank/system. I would drop the tank and drain it (I hope you replaced
the gas filter once or twice by now) or put in some "Heet" to take up
any water in the gas and/or add some gas stabilizer to help dissolve any
old gas. I don't know this engine (throttle body?), but if it has
anything like a float-bowl then you should drain it.
I had this sort of problem with an old MGB that sat for a few years. I
drained everything related to gas, eventually I bought a new gas tank
because I could see it had rust inside. Just filling the tank with
fresh gas doesn't get old gas out, but if you add gas stabilizer (which
I mentioned earlier), this might help to dissolve the old gas. I should
mention that I never tried this method myself (so I can't promise it
will work), because I remove the tank and drain it. It was then that I
saw the rust inside so I bought a new gas tank.
I thought of something else. I had another vehicle that ran fine around
town, but I couldn't get it up to highway speed. That turned out to be
a bad gas pump (the mechanical kind mounted to the engine vs. the
electrical unit that is mounted in the gas tank or along the frame.
Cory Dunkle wrote:
I changed only two spark plugs and after that it ran like crap. I changed
the plugs back to the old ones and it ran slightly better but still very
poorly. When the engine started to run poorly I did not change the plug
wires. In any case, the plug wires should be on the proper plugs... I doubt
if the plug wires are even long enough for me to mix them up as they are
sized to the length needed for each cylinder.
When it misfires it will misfire a bit then for a split second it will pull
strong and smooth like it should, then repeat.
Dont know if this is a problem similar to what happened to my car. I had to do
some work on the engine and disconnected the battery. After I started driving
again the engine ran terribly. Would stop when I slowed down, no power. My
mechanic told me that the computer lost all its memory and just to tough it for
a few weeks, till the computer learned my driving habits again. You know, he was
right. Car runs 100% now.
So, if you disconnected the battery, maybe your engine will straighten itself
Did you ckeck the plugs for the correct gap or did you use them right
out of the box? If you unplugged the computer, it will only take about
ten miles of driving to re-program it. You should do the reprogramming
at lower speeds with no jack-rabbit starts (just drive like you were
taught for ten miles). Could be that you damaged a wire or vacuum
connection while working on it. Sometimes, the plastic vacuum T's and
Y's, etc. will crack at the junction. Make sure that you don't have a
cracked insulator on the plugs also.
I gapped them to the gap specified on the emissions label. I then tried
gapping them to what the old ones were set to, which was slightly less than
teh emissions label. At the moment the old plugs are in the engine gapped at
what they were at when I got the car (though I have new wires cap and rotor
on the engine).
I'll have to thoroughly go over all vacuum lines and connections... I only
briefly looked them over the other day, but I found nothing obviously
leaking. I will check that and the plugs.
Nah, I didn't disconnect the battery, though it was dead when I got the car
600-800 miles ago. In any case, there is something mechanically wrong with
teh car. It's not a matter of the engine not running optimally because the
computer isn't operating the engine management controls optimally. No car
would run like this from the factory and actually sell.
What I'm thinking is taht when the engine warms up the computer allows
vacuum (most liekly ported vacuum) to flow into some line that it doesn't
when the engine is cold. This line must have a leak. The engine runs great
when cold, only after a minute or two of driving/running will it run like
crap. Now that I think of it maybe the EGR is disabled when the engine is
cold? I'm going to try plugging the vacuum line to the EGR from it's course.
If anyone has any ideas as to what the problem may be, please let me know.
I very much doubt your vacuum hose theory. If it's a vacuum leak it's
probably there all the time. The computer richens the mixture for cold
running situation (just like your automatic choke used to do on old
carburated engines) and then leans it out to mormal mixture once operating
temp achieved. You could go out with a water squirt bottle and start
looking for it, you spray water at the intake to head joint etc and listen
for changes in the engine speed/smoothness, but there's a few other things i
would look into first.
You issue with the spark plugs has nothing to do with the particular plugs,
new vs old, or gap or anything like that. You probably broke the internal
core of the plug wire when pulling them off. If you're not inclined to go
out and replace them, get an ohmmeter and check the resistance in all of
them. Start with this. Ensure all of the ign side is functioning properly
first. The fact that there was change when you handled the plug wire is
telling you something. Richer mixtures are easier to ignite, which could
explain your warm to cold issues.
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