"Kent" <immortala2 (AT) yahoo (DOT) com> wrote

It sounds like the fuel pump.

Andy

"Kent" <immortala2 (AT) yahoo (DOT) com> wrote


Methinks thou mayest be in need of a new distributor or a new Hall Effect
Sensor (pickup) on the distributor assembly. Also, take it to a mechanic
and have a fuel pressure test since you seem concerned about this, but I
doubt its your problem.

Oh yeah, on a car that's this old (pushing 20 years no?), I would have the
exhaust system checked out, specifically the catalytic converter which may
be broken or plugged. What can happen is the little screens inside break
off due to the accumulated effects of temperature and vibration, they can
wedge together creating a plug. Of course, this may not be your problem at
all, but I did have that problem on my car ('95 Jetta GLS) and it would
totally kill power since the engine could not exhaust. The car would idle
okay since the engine could squeeze a small amount of exhaust through the
remaining portal, but giving it some gas would cause it to bog down in a
most distressing fashion.

Yes it was intermittent for a fashion, but then one day it became permanent,
on a Friday afternoon, at 5:10PM, in the middle of a 4-way intersection. It
was great fun pushing the car through the intersection, fortunately another
driver did get out and help me. I could start the car, it would idle, but
putting it in gear and giving it some gas cause it to lurch forward a few
inches then die.

In rec.autos.makers.vw.watercooled, Nik&Andy wrote:

<snip>
You think that the fuel pump suddenly pumps only enough fuel to
idle, and then suddenly returns to full capacity?

"Tom's VR6" <no (AT) mail (DOT) please> wrote

I'm not sure about a CIS car but would think it's not that different than
Digifant as far as fuel pumps are concerned. The fuel pump gives more than
enough fuel for any running condition. On a Digifant car the fuel pressure
regulator is vacuum-activated according to the engine's need for fuel and it
routes any unnecessary fuel back to the tank. On a CIS car I'll bet the
fuel distributor probably does a similar thing...the pump provides constant
pressure and probably the fuel distributor determines how much fuel to send
to each injector and then the excess is sent back to the tank.

However if the pressure from the pump is too low, it's possible that the
engine is getting enough fuel for idling but at higher loads/speeds the car
might not be getting enough fuel anyway.

In rec.autos.makers.vw.watercooled, Tom's VR6 wrote:

And if that were the case, I suspect flooring the throttle with a
limited fuel availability would probably stall the engine rather
than having it idle. That would be a form of "response".

"Tom's VR6" <no (AT) mail (DOT) please> wrote

Yes but it does depend on how he's "coasting" to the side of the highway as
he said. If it's shifting to neutral before the engine totally stalls it
might have time to recover to idle speed w/o stalling. Or if he's leaving
it in gear and takes his foot off the gas the car could also be restarting
itself. It'd stall probably only if he continued to leave it in gear and
mash the throttle to the floor but if he's taking his foot off the gas
*very* soon after noticing the power loss or shifting to neutral very soon,
that might prevent an actual stall.

Tom's VR6 wrote:

<snip>

I have once been able to drive ~50 miles home with a failed transfer
fuel pump ('87 Gti 8V) The car would idle just fine, cruising at 50 mph
on flat road was no problem, but going up hill or going faster, the car
would sputter and loose power.

Interesting development in my troubleshooting of this problem over the last
few days. Many of you may know that the KE-Jetronic CIS-E system on my car
includes two throttle switches, one for full throttle enrichment/RPM
limitation, and the other an idle switch for deceleration fuel shutoff. The
idle switch also provides input to the idle stabilizer valve. Whenever the
throttle valve is closed such as when decelerating or coasting, the idle
switch is closed (continuity), sending a signal to the computer. If the
computer receives this signal AND engine speed is above 1600 RPM, the
computer cuts off fuel to the injectors by reversing current to the
differential pressure regulator. Fuel flow is then restored by the computer
once the engine speed drops below 1300 RPM. This function is intended to
improve fuel economy.

Well, it seemed to me that a malfunction of the idle switch might be sending
erroneous signals to the control unit, resulting in fuel cut-off at
inappropriate times. So I thought I would check out the idle switch (which
is buried out-of-sight under the throttle body) to see if anything was
amiss. First off, I noticed that the full throttle switch made a very
definite clicking sound when engaged. I expected the idle switch to do the
same, but it didn't. I then removed the throttle body to get a better look
at the idle switch. It was almost completely covered with grease and grime.
(Long story, I recently repaired a leak in the intake system at the bypass
hose for the air-shrouded injectors. It exits from the bottom of the rubber
bellows that connects to the throttle body. Not only was this leak allowing
unmetered air to enter the system, but small amounts of oil from crankcase
ventilation was exiting in the vicinity of the idle switch. I didn't notice
this when I repaired the hose as I removed the bellows and repaired the
connection off the car).

I cleaned the idle switch as well I could, and after poking it a bit, the
plunger started to make the clicking sound I expected. I checked for
continuity when the plunger was in, and it checked out. When I reassembled
everything, I left the throttle switches disconnected just to see if the
power loss problem recurred. I've driven the car over 250 miles since then,
in all kinds of traffic, and the problem has not recurred. This is by far
the longest I have gone without the power loss problem since it began many
months ago. Not only that, but the car no longer stalls at stop signs. Sure,
the idle bounces around a bit since the ISV isn't receiving the proper
signal from the idle switch, but the car never comes close to stalling.

I definitely think I'm on to something here. My theory is that the idle
switch was malfunctioning by intermittently sending a closed signal to the
control unit even when the throttle was open. This behavior was probably
caused by a combination of wear (it's the original switch), oil/dirt
contamination, and engine vibration. Since the RPMs would be well above 1600
(especially while cruising down the highway, where the problem tended to
occur) the erroneous signal would cause the control unit to cut off fuel to
the injectors until engine speed dropped below 1300 RPM. This is why the car
always returned to a proper idle after I coasted to a stop by the side of
the road, or pushed in the clutch to disengage the engine from the
drivetrain. If I just let the engine turn with the wheels while frantically
pressing the accelerator, power would not return.

I'm going to drive around for a week or two with the throttle switches
disengaged just to make sure I've isolated the problem. Once I'm satisfied
that the problem is gone, I'll install a new idle switch. I'll provide an
update indicating success or failure at a later date. Right now I'm
optimistically assuming success.

THANKS TO EVERYONE FOR THEIR THOUGHTFUL CONTRIBUTIONS TO MY TROUBLESHOOTING,
ESPECIALLY THOSE THAT SENT DETAILED RESPONSES TO MY EMAIL. YOU DEFINITELY
GOT THE WHEELS IN MY HEAD TURNING. I COULDN'T HAVE DONE IT WITHOUT YOU.
--
Kent
1987 VW GTI 8V, original owner, 222,000+ miles

"Kent" <immortala2 (AT) yahoo (DOT) com> wrote

Kent wrote:
Good thinking! And thanks for posting back, reading (pending) solutions
is always interesting, not to mention educational.

I had the opposite problem about a year ago, my idle switch was broken
and would never close. This caused idle to be way out of spec,
particularly with the A/C on. From the dealer you can get the switch
only with the full throttle switch and the wiring harness, priced the
wrong side of $100.

At the junk yard I found a number of CIS-e engines, but they all had
broken idle switches. If you are handy with a soldering iron, you can
use the switch from a Digifant engine. (The California variety of
Digifant (I?) uses switches, I believe the 49 state variety (II?) uses a
potentiometer). The switches are the same as CIS-e, but they are wired
differently. For Digifant the two switches are wired in parallel and the
connector is 2-pin. CIS-e uses a 3-pin connector. I cut the idle switch
out from my harness and soldered in a "new" one from a Digifant engine.

"Randolph" <trash (AT) junkmail (DOT) com> wrote

Other way around (sort of).

You are correct that California is Digifant I and 49 state is Digifant II.
But it's Digifant I that uses the potentiometer and II that uses the
switches.

And this distinction only applies to 1991-1992 vehicles. 1990 and older
Digifant cars were Digifant II nationwide.