[v12-engine] Sluggish at start

V12-Engine
1

My thanks to all that have been helping me thru this. To Kirby, I do
have vacuum at the ECU in the trunk. My problem is getting progressively
worse. This is really strange…
Driving down the road about 50-55 MPH, take my foot off the throttle
quickly and it acts as if the key has been turned off, but the weird
part is if I put it in neutral while still coasting at the same speed,
once the engine RPM drops to 1200, the tach jumps up quickly about
another 200 RPM and then settles back down to 1200. At that point I have
full throttle control to rev it up to any RPM as long as I don’t put it
back in gear…all of this happens while still coasting at highway
speed. If I put it back in gear it dies again. If I leave it in gear and
let it coast down to 1200 it does the same thing, but by then I’m only
going about 25 MPH or so. Absolutely no power anymore. Could it possibly
be the cats are burned up and causing a tremendous amount of back
pressure on the fuel system. Is there some type of shutoff device built
into the system to cause this.

Thoroughly Stumped.

Tom Drakos

2

My thanks to all that have been helping me thru this. To Kirby, I do
have vacuum at the ECU in the trunk.

Whether or not you have vacuum isn’t the question. The question is
whether or not the line is clear. If full of liquid, for example,
you would get vacuum – but it would be delayed, and that delay would
make the engine run really badly.

My problem is getting
progressively worse. This is really strange… Driving down the road
about 50-55 MPH, take my foot off the throttle quickly and it acts as
if the key has been turned off

If the vacuum line were obstructed, like full of liquid, then when
you let your foot off the throttle quickly the vacuum in the manifold
would rise but the sensor wouldn’t pick it up for a while. The
engine would then run way too rich, which would effectively shut it
off.

but the weird part is if I put it in
neutral while still coasting at the same speed, once the engine RPM
drops to 1200, the tach jumps up quickly about another 200 RPM and
then settles back down to 1200.

The vacuum finally gets through to the ECU, and proper fuelling kicks
back in.

At that point I have full throttle
control to rev it up to any RPM as long as I don’t put it back in
gear…

That’s because manifold vacuum is high as long as you’re in neutral,
no matter what RPM you’re at, and as long as it doesn’t change
significantly the engine will run OK.

all of this happens while still coasting at highway speed. If
I put it back in gear it dies again.

As soon as you put it in gear and apply load, the vacuum drops, the
ECU doesn’t get the word, and the engine leans out.

Could it possibly be
the cats are burned up and causing a tremendous amount of back
pressure on the fuel system.

I suppose. I only suggest blowing out the vacuum line with
compressed air because it’s easy to do and it seems to jive with the
symptoms reported.

Is there some type of shutoff device
built into the system to cause this.

No. In fact, these cars don’t have many shutoff devices of any kind.

– Kirbert | Palm’s Postulate:
| If anything is to be accomplished,
| some rules must be broken.
| – Kirby Palm, 1979From: bebeep bebeep@mediaone.net

3

<< Could it possibly be the cats are burned up and causing a tremendous
amount of back pressure on the fuel system? >>

The catalytic convertors being clogged up definitely IS a possibility. I had
an American auto exhibit similar symptoms; nearly total loss of power which
rapidly got worse and worse. I could “rev up” the engine when in neutral,
where there was no load on it; however when the transmission was engaged in
“drive,” I could barely do 35 mph with the accelerator to the floor. Heavy
application of the “loud pedal” resulted in a “hissing” sound emanating from
under the car.

After limping home, I grabbed the biggest hammer I owned, crawled under the
car, and beat the living daylights out of the bottom of the single catalytic
convertor, for about an hour (Caveat emptor; your mileage may vary; I’m not
responsible for anything you do with this information). After the beating, I
started the engine, and revved it up a few times. Numerous ceramic beads
were expelled from the tailpipe. However, the power was completely restored,
and the problem did not recur for as long as I owned the car.

Before you try something like this, I’ll vouch for Kirbert’s suggestion, and
blow out the ECU vacuum line. While you’re doing that, I’d suggest as well
that you perform a vacuum check at the ECU to ensure that the internal MAP
sensor hasn’t sprung a vacuum leak. It certainly couldn’t hurt; and you
might very well track down the source of the problem. Even if you think
you’ve found the problem, go through Kirbert’s checklist in “The Book”, and
make certain that all the major points (at a minimum) are covered.

Hope this helps…
Steve Wilke
'88 XJ-S H&E Conv.,57kmiles

4

Tom,

Pinch of the vacuum to the distributor and see if this causes any difference
in engine response.
The things that come to mind is: the distributor body is moving (loose),
spark plugs s/b replaced, or system has massive vacuum leak. I did not
speak of the ignition module because I am sure that you have cleaned all of
it’s contacts to ensure good electrical contact. Poor electrical contacts
on the older cars generate malfunctions that defy analysis.

If your car is not old, never mind :o).

Ned

bebeep wrote:> My thanks to all that have been helping me thru this. To Kirby, I do

have vacuum at the ECU in the trunk. My problem is getting progressively
worse. This is really strange…
Driving down the road about 50-55 MPH, take my foot off the throttle
quickly and it acts as if the key has been turned off, but the weird
part is if I put it in neutral while still coasting at the same speed,
once the engine RPM drops to 1200, the tach jumps up quickly about
another 200 RPM and then settles back down to 1200. At that point I have
full throttle control to rev it up to any RPM as long as I don’t put it
back in gear…all of this happens while still coasting at highway
speed. If I put it back in gear it dies again. If I leave it in gear and
let it coast down to 1200 it does the same thing, but by then I’m only
going about 25 MPH or so. Absolutely no power anymore. Could it possibly
be the cats are burned up and causing a tremendous amount of back
pressure on the fuel system. Is there some type of shutoff device built
into the system to cause this.

Thoroughly Stumped.

Tom Drakos

5

In a message dated 4/24/2000 5:24:14 PM Eastern Daylight Time,
bebeep@mediaone.net (Tom Drakos) writes:

<< I plan on trying to blow the line out and see if anything comes out. >>
Good!

<< Where does it connect under the hood. >>
Umm… I dunno. But rest assured, it’s the only vacuum line attached to the
ECU!

<< How do I know which one to disconnect before I blow it out. >>
If you unplug it from the ECU end, and apply compressed air, the other end
should pop off under the hood. Might be helpful to have someone else watch
for a snake rearing it’s ugly head underhood during this procedure.

<< Can I just suck on the ECU side to check for the Map sensor leak. >>
Well, I suppose you could. However, your tongue would not be sensitive
enough to detect a significant pressure differential over a prolonged period
of time, and you might wind up with a “tongue hickey” as well, which isn’t
particularly healthy.

<<Should it hold a vacuum if I suck on it? >>
Yes, it should. However, it would be much preferable to utilize a vacuum
gauge and apply roughly 30 in. hg. to it, and see how long it can hold that
much vacuum. If, starting out from 30 in. hg., it can hold within 10% in 5
minutes, I’d say that it’s OK.

<< My gas mileage has been terrible since I’ve owned the car, which has only
been about a month or so. If it has been the vacuum to the ECU all along, and
causing it to run that rich, I suppose I may have burned up the Cat’s with
all that excess fuel.>>
Rather than “burning them up,” I suspect it’s much more likely that you’ve
coated all of the ceramic balls with a very heavy layer of carbon, which has
now glued them all together in a near-solid mass, and there’s nary an exhaust
gas path in sight.

<< If so, aren’t there some after markets that are not as expensive, or do
you know. >>
There have been previous threads about low-cost catalytic converters which
you can search for, along with other threads about removing them entirely
with something like “maintenance bypass” pipes; something I neither recommend
nor condone due to Federal emissions requirements. However, if you’re doing
some “bracket racing” or “circuit racing,” you may be able to convince your
local muffler shop to weld you up some “bypass” pipes, with the understanding
that these pipes will never be used on the street. :o)

Hope this helps…
Steve Wilke
'88 XJ-S H&E Conv.,57kmiles

6

Tom,

If the problem is a sensor that extends the duty cycle of the injectors
causing the car to use excessive gas, we can resolve it. The poor gas
mileage is a good start. I am sure that there are “List members” that have
detailed knowledge of each contributing input sensor. I am also sure that
they can give you reference parameters for each sensor input.

If you have an oscilloscope, you may be able to observe the injector pulses
as each input sensor and feedback loop are eliminated.

My 87 and 88 are different for your 89. So, I will not be of much help,
except to help interpret the oscilloscope displayed data should you need it.

7

Well it’s no longer sluggish. Apparently after rebuilding the dist. the
adjustment screw came loose and the timing was the main culprit. The
engine is very responsive now and runs quite strong. “NEW
PROBLEM”…now at startup on a cold engine, it cranks right up and
idles very smoothly but at an accelerated idle…about 1800 rpm or so.
It remains at that speed for about 60 seconds, and then starts it’s
ramping up and down. Up to 1800 and then down to 800 over and over. I
pulled the AAV and examined it without taking it apart, and used some
threaded rod into the plate in the bottom with the holes in it, and was
able to move the piston freely up and down. When it’s ramping up and
down the idle screw has no effect.

I setup the TPS as per the book, setting the stop voltage at .036, and
checked full motion for any inconsistent voltage…all is well.

I setup the throttle linkage as per the book, following all five steps
and that appears to be fine as well. In reading the book, I came across
similar symptoms under the
“Overrun Cutoff” section.

Any and all suggestions will be greatly appreciated. I feel I’m almost
there, just a few more adjustments hopefully.

Tom Drakos
89 XJS

8

At 09:56 PM 5/16/00 -0400, you wrote:

I setup the throttle linkage as per the book, following all five steps
and that appears to be fine as well. In reading the book, I came across
similar symptoms under the
“Overrun Cutoff” section.

I am considering removing and blocking off the overrun valves on our V12,
but am unsure if it would affect this problem or not. Regardless, I am after
simplifying the engine compartment in various ways, and this one is on my
list…
Does the cold air valve on the back of the Right air cleaner have any affect?
Perhaps it is producing the high idle on startup, but what does it do next?
Just my $0.02

Kelly Spongberg
Rocky Mountain House, Alberta, Canada
<@The_Spongbergs>

1987 Jaguar XJ12 Vanden Plas
2001 Ford F150 SuperCrew XLT 4X4
1995 Nissan Pathfinder XE 4X4
1949 Ford F-1 pickup (someday project)
1997 Polaris Trail Boss Quad