Ralentí inestable, pulsaciones durante el arranque y no arranca

[bergen]

Muy buenas,
Os comento, Yo tengo una T4 2.5i Aut.  del 2000, ahora tiene 260.000km.
De unos meses para acá el ralentí en caliente era algo inestable bajaba a 600-650 rpm con "saltitos esporádicos" de mucho menos de 1 seg como si se quedara el motor digamos que parado.
•   Comenzando por lo fácil: la primavera pasada cambie le filtro de gasolina, sin problemas, efectivamente estaba sucio porque después noté gran diferencia.
•   Comprobé la solenoide de arranque estaba OK pero por los temas de corrosión (las toneladas de sal que echan en este país y por la lluvia) limpie la zona de apoyo y arrancaba mejor.
•   En verano hice el trayecto Noruega-España-Noruega sin problemas y aparentemente sin este problema con el ralentí.
•   En septiembre comienza a aparecer el tema del ralentí pero poco a poco.
•   Cambie bujías, arranca mejor pero sigue con los "saltitos" en ralentí. Las bujías estaban en buen estado.
•   Hace un mes limpié la famosa mariposa que efectivamente tenía algo de chapapote, pero el problema del ralentí en caliente sigue apareciendo. A destacar que durante esta limpieza cayo liquido de refrigeración hacia abajo...
•   Me estaba preparando para seguir vuestros consejos (de T54motion sobre todo en otro hilo "ralenti inestable") en las próximas semanas  cuando:
Pues resulta que ahora no arranca, giro la llave, se encienden las luces del panel, hace el ruido de la bomba de combustible (yo creo que algo más fuerte), etc,...y cuando giro del todo para arrancar pues hace como que (el panel se vuelve como loco encendiendo y apagando bastantes veces por segundo, como pulsaciones) pero sin ninguna acción en el motor. Se me ocurre:
1 - Puede ser que la bomba de gasolina  este trabajando en vacío? Por eso del cambio de sonido aparentemente, a lo mejor son cosas mías.
2 - Fallo de algún relé: el 30 hace su "clik" y el de la bomba de combustible (no me acuerdo del numero ahora) también, de hecho la activa.
3 - Problema con motor de arranque?
4 - Sensor de detonaciones o sensor hall, que este estropeados? He leído que se suelen estropear.
5- Se habrá estropeado algún sensor causado por el "derrame" de líquido refrigerante?

Esta tarde después del curro me pondré a desmontar los sensores, a ver como están.
Cualquier idea o comentarios es bien recibido, pues tengo el coche parado y realmente me hace falta.

Gracias.

[Bulgrok]

Buenas,

Has comprobado la tension de la bateria?

Un saludo.

[bergen]

Buenas y gracias por la sugerencia.
si que  he comprobado la batería y esta OK.
Hoy me han traído los relés 30  y 167 (de la bomba de combustible) previo sablazo de la VW local (han tardado un día en traerlos desde la capital), espero que sea eso pues no me apetece nada trabajar debajo de la lluvia que va  a caer por la tarde.
de momento ayer intente arrancarla y nada, de hecho el ruido de la bomba de combustible ya no lo hace, mirare tb el fusible de la bomba.
a partir de ahí seguiré los pasos del link:
http://tech.bentleypublishers.com/se...%2092-96EV.pdf
saludos.

[bergen]

parece que el link no funciona pero es mas o menos, textualmente del documento en ingles (Copio y pego):


"Three critical items for ignition get battery voltage when the key is on:
- the Camshaft Position Sensor, switched by the ECM
- the Coil, switched by the key
- the ECM, switched by the key and though the ECM relay (Relay position #3, often
with "30" printed on the relay)
These must also have good grounds. The Coil has a brown ground wire, the CPS has a
brown wire with a white stripe. The ECM has four grounds (see the listing further down)
A good ground is no more the 1.5 ohm resistance, preferably less than 1 ohm. When I
was finished cleaning up my grounds, they were all under 0.5 ohm. The same applies
when checking for a good connection from one end of a wire to the other.
What is supposed to happen:
- When you turn on the ignition, the coil gets 12v though the key, the ECM gets 12v
through the Ignition relay, and the CPS gets 12v through the ECM.
- As the engine turns over, the CPS sends a 12v pulse to the ECM.
- The ECM takes this information, modifies it based on input from other sensors, and
switches 12v to ground from the coil pack. Timing of this grounding is the ignition
timing.
- The Coil sends a spark (much more than 12v) to the distributor. (Note: The Coil
pack has a primary and secondary side: however replacements are sold as both
parts integrated together, and I think most shade-tree mechanics would just replace
both at once).
Simple stuff to check first if your van cranks but won't start:
- You should hear the fuel pump run briefly when you turn on the ignition (after it
has been off for at least a couple minutes).
- Got gas? (this sounds silly, but I have seen it happen).
- Check for spark at the spark plugs.
- Check for good tune-up parts (distributor cap, rotor, spark plugs and wires)
Fuses & Relays (pull down the small tray right by the driver's door, under the dash)
- Check Fuses 15 and 18 (Fuel and ECM Relay)
- ECM relay (for AAF engine - third from left, second row up, often has "30" written on
it) - you should feel it click when you turn the key to on.
- Fuel Pump Relay (for AAF engine - bottom row, right hand end) - you should feel it
click when you turn the key to on.
Ignition System Tests:
The Bentley manual says that the following tests should be performed with the Cold Start
Valve connector removed and the Fuel Rail connector removed. Otherwise fuel will be
injected into the motor while cranking during testing, and will get pumped out as
(potentially explosive) vapors. Plus, it will condense in the cold engine and wash down
into the oil. That being said, I did my tests with these connected and lived to tell the tale.
This is the order I would recommend doing the tests, from what I gather the most common
fault is tested for first, and so on in order:
1 - Start with the coil, located in front of and below the battery.
Coil packs are said to be common failure items on these vans.
Checking for power to the coil:
- Disconnect the three-wire connector from the ECM to coil pack.
- Look for battery voltage from terminal 3 (black wire) going to ground on terminal 1
(brown wire) with the ignition on.
- If no voltage, check for voltage to the negative terminal on the battery (or other
known good ground). Check that the brown wire has a good ground. If everything
checks out and there is no voltage to the coil, you may have a defective ignition
switch.
Checking for signal to the coil:
- Disconnect the three-wire connector from the ECM to coil pack.
- Connect an LED 12v tester or 12v LED between Terminal 2 (Green/Black) and
Terminal 3 (Brown)
- Turn the ignition on, LED should light up, stay lit for a few seconds, then go out.
- Crank the motor, LED should flicker (quite obviously). The flickers are the trigger
signal: if you get the trigger signal the problem is most likely either the coil or the HT
system (plug wires, distributor cap, spark plugs: not on right, worn out, timing way
off, etc.) Or, you have good spark and something else is wrong - fuel problem,
compression, timing belt slipped, etc.
- If there is no trigger signal to the coil, go on to step 2
2 - Check that the ECM is getting a signal from the CPS.
The Hall Senders are also a known weak point on these vans, although they are more
reliable than the coils.
The signal comes from the CPS (Hall Sender) in the distributor. Pull the shield off the
distributor by lifting straight up to get access to the connector. .
- Disconnect the three-wire connector
- Check for battery voltage between the side terminal towards the front (red/black
wire) and ground (Brown/white wire) with the ignition on. If no voltage, check for
voltage to the negative battery terminal or known good ground.
- Check for good ground on the Brown/white wire.
- Pull back the rubber covering on the three-pin connector, and insert probes (I used
chunks of wire from household wiring - the solid copper wire makes a good probe)
into the back of the centre signal (green/white) wire and the ground (brown/white)
wire.
- Re -connect the three pin connector
- Hook up the LED tester to these two probes
- Crank the motor, and look for flashes. The flashes are the signals to the ECM.
- If no flashes, make sure the probes are connecting inside the plug, and not to each
other: if you still get no flashes this points to the CPS as the problem.
If you get flashes from the CPS but not at the coil, then the problem is likely in the ECM or
the ECM wiring. There is nothing else that would prevent the signal getting to the coil - all
the other sensors only modify the spark timing; none of them eliminate it.
Check the ECM wiring before ordering a replacement!
Checking the ECM wiring:
- turn the ignition OFF before removing the ECM Plug.
- to remove the ECM plug, squeeze on the clip at the back of the plug, and lift the back of
the plug up. When it comes free at the back, swing it up until you can unhook the front of
the plug from the ECM.
- remove the small slotted screw from the front of the ECM plug and separate the cover
from the plug base.
- First thing to do is check the grounds, and check for good circuits to the coil and CPS.
(See below or a Bentley manual to know which wires).
- To do the full series of tests, you will need a Bentley Manual, a multimeter, and a
selection of probes. Check that you are working with the right test procedure for your van.
There are differences depending on the month it was built, automatic or manual, California
or 49 state/Canada. The wire numbers in the Bentley diagram match the wire numbers on
the plug as well as the socket numbers on the VAG tool described in the manual. You can
cross-reference by checking the colors against the number. The number scheme in the
wiring diagram is Txx/yy where xx is the number of pins in the connector (38 for an AAF
engine, more for the later ACU motor) and yy is the wire number. I have laid out the wiring
scheme for my 5 speed, 49-state, Pre-1993 Eurovan at the end of this document.
If the ECM wiring passes the tests, you are getting a trigger signal from the CPS, but no
trigger signal at the coil, consider replacing the CPS before dropping big dollars on a
new/used/rebuilt ECM. In my case, I had an intermittently failing CPS which always
passed the test. I installed two "known good" ECMs, yet the problems did not finally go
away until I replaced the CPS. Coincidence? Maybe... or maybe I should have replaced
the CPS much earlier. Bottom line is, the CPS is a "known failure" item (i.e. you might
need to replace it one day anyway), and it is easier to get and much less expensive than
an ECM.
Other Digifant System info
This only matters once your van starts and runs (or at least idles, see #2 below for Jan
1993 and later)
There are 10 sensor/senders on the Digifant system. None are needed for ignition to work
(the engine will run / idle, and waste a lot of fuel, without any sensors attached; the
resulting "default mode" is rich to make sure the motor starts and doesn't run too lean/hot.)
1 - Oxygen sensor
2 - throttle position sensor (TPS)
3 - coolant temperature sensor (blue, two wire)
4 - CO potentiometer (before January 1993) or Closed Throttle Switch (Jan 1993 and
after)
5 - Air intake temperature sensor (the IAT unit)
6 - idle control valve
7 - cold start valve
8 - evaporative emissions frequency valve (valve allows air to flow though from Charcoal
Canister)
9 - power steering pressure sender (sends data to ECM so ECM will raise idle when P/S
fluid is cold and thick)
10 - Manifold Absolute Pressure Sensor (MAPS), inside the ECM, connected by vacuum
line to the intake manifold
The 5 key inputs are the TPS, the IAT (2 inputs), the MAPS and the coolant temperature
sender. You could disconnect all the rest and the motor would basically run the same. It
would be harder to start when cold, might stall when turning the steering, would idle too
high and would release more emissions, but once warmed up it would run the same with
the following 5 as it would otherwise run with all 10.
1) TPS: the ECM uses info from the TPS for...
idle air control
deceleration fuel shut-off
wide-open throttle enrichment
Mine reads 2.7kilo-ohm at closed throttle, drops quickly to 2kilo-ohm in the first part of of
opening the throttle, goes to 1.14kilo-ohm at wide-open throttle. Makes sense that the
potentiometer would be more sensitive when close to closed for better driveability. I took
the readings at the TPS between the red-blue and the blue-black wires.
2) IAT (Intake Air Temperature) unit
- Pre- January 1993 this is comprised of a thermistor that loses resistance as it heats
up and a CO potentiometer...
- January 1993 and after this is comprised of a-thermistor that loses resistance as it
heats up and a Closed Throttle Position Switch
- ECM's are not interchangeable between before and after January, 1993. With a
newer ECM in an older van, the motor will start and idle, but not rev.
The signal from the thermistor is used by the ECM to modify fuel injection duration for
richer mixtures when cold and leaner mixtures when hot. Early Eurovans tended to go into
"rich mode" too often, which caused problems with passing emissions tests. The Aircare
emissions program in Vancouver, Canada identified this problem and worked out a
solution. This is posted in the files - look for "ev_smog".
The signal from the CO potentiometer does the same thing (change injection duration) but
does so as a result of throttle position (its maximum affect is at idle and it's also affective at
partial load).
The Closed Throttle Position Switch is important to the ECM. Without the signal, the
engine will not rev beyond idle.
3) MAPS
The vacuum line to the ECM is connected to the MAPS (Manifold Absolute Pressure
Sensor), which is built into the ECM. The ECM uses info from the MAPS to determine
engine load and, along with the engine speed signal, helps determine ignition timing and
injector duration.
4) Coolant temperature sensor:
There are several coolant sensors on these vans; this one has a the Blue Connector, a 2-
wire connector, and is located at the motor end of the top radiator hose. It does not control
the radiator fans, the temperature gauge on the dash, air conditioning cut-out or after-run
pump. The ECM uses info from this Coolant Temperature Sensor for...
- cold-start enrichment
- acceleration enrichment
- after-start enrichment
- deceleration fuel shut-off
- idle air control during cold start
The coolant temperature sensor is particularly important. If it is not working or
disconnected, the engine runs in default rich mode. You will get very poor mileage, a
noticeable smell of unburned gas, and very high HC emissions. The engine will start and
run, however."

[marcus]

A mi me daba relentí inestable,fue rectificar la bomba inyectora y adiós.Por km no le tocaría en principio pero nunca se sabe.

Saludo.

[bergen]

Buenas,
aparentemente todo arreglado, solamente con el cambio de los relés, la bomba suena normal previo al arranque.
después conecté a la batería el "arrancador auxiliar de batería" que previamente había pre-cargado al 100% para asegurar el tiro.
Hoy hice cerca de 40km, todo bien, arrancó a la primera, ralentí estable.
pues de momento ya esta todo OK (toquemos madera), hasta la próxima, que llevo ritmo de actualizaciones en la T4 durante el último mes que vamos (tubería hidr de frenos a cobre, repartidor de frenada, gomas de estabilizadores delanteras, bujías, filtro combustible (por si acaso)...)
gracias por los comentarios.