Golf 3 1.4 - rpm drop

[alessioblaupunkt]

Golf 3 1.4 - rpm drop

Year 1992, petrol.

Car has two faults, related or not.

1) Sometimes no start

2) Rpm drop occasionaly in this situation:
a* Shifting from 2nd to 3rd gear, also 3rd to 4th
b* Entering a roundabout or at the center of the roundabout or in some curve,
with or without braking

Parts that has been changed with new spare that don't solve the problem:

- crank position sensor
- fuel filter
- 70° corner pipe in vacuum line


Parts that has been changed with USED spare that don't solve the problem:

- idle motor in throttle body
- idle control valve

Parts that has been changed months ago:

- new fuel pump (April 2017)
- new ignition switch (August 2015)
- new throttle body gasket (June 2013)
- new water temperature sensor (April 2015)

If engine no start there are two rapid solution:
- keep cranking and press accelerator pedal half way, in a few seconds engine will start, and stay on.
- key in off position then crank again.

If engine engine drop rpm while driving:
- engine will solve the problem in 2 seconds, driver have to do nothing.
Only one time engine shut off very quitely while downshifting.


Suspect of internally broken central exhaust silencer that sometimes clog the engine.

All other driving condition are good: overtake, rapid acceleration, etc.

Please suggest other thing to do.

[ollync]

what fault codes?
What engine type? ABD, AEX, APQ?


Sent from my iPhone using Tapatalk

[alessioblaupunkt]

ABD.

Didn't do a scan yet.
Also a scan in OBD1 car tells very very little.

[autoden]

Can you do throttle body relearn?

[xoom]

TB actuator i guess V70 if remember correctly

[ollync]

Check for air leaks, replace tb actuator with new one


Sent from my iPhone using Tapatalk

[alessioblaupunkt]

@autoden
Can you do throttle body relearn?

Year 1992, OBD1 vehicle, it has metal cable from pedal to throttle body, so I guess there is no relearn for this.
If I am wrong about it please tell me.


@xoom
TB actuator i guess V70 if remember correctly
Has been changed but it wasn't faulty.
In post #1 here it is:
- idle motor in throttle body

@ollync
Check for air leaks

Forgot to mention in post #1, when there is rpm drop ( usually 1500 to 200 rpm )
there is a buzz noise coming from the fuel pump I guess, the buzz noise last 2 seconds.

In the next two weeks I'll wire a voltmeter in fuse box with
+ after fuel pump fuse
and
- in the ground point near driver door
and put the voltmeter near the dash to see if it is the voltage that is missing or the fuel that is missing (maybe for air leaks).

Fuel pump has been changed in April 2017, new pump.

---
Air leaks chapter:
apart pulling the throttle body to hear for hissing noise while engine is running,
can you suggest other things to do to find air leaks?

[rideon]

Throw away oe fuel cap and fit cheapest aftermarket...

[ollync]

Spray some brake cleaner around the throttle body with engine running and see if rpm is increasing , check fuel pressure with fuel pressure gauge


Sent from my iPhone using Tapatalk

[alessioblaupunkt]

Left the car out for the night on a ramp inclined at 30 degrees, in the morning start ok BUT after 2 seconds engine die.
Tried to start but sound like no fuel/air leak (ghegheghe_ghegheghe_ghegheghe)
So I stop cranking.
I disconnected lambda sensor and water temp sensor.
Tried to start again with throttle open and after cranking for 20 seconds the engine
try to start firing 1 then 2 then 3 cyl ok engine start running on 4 cylinder
but have to rev up to 2000 rpm otherwise it will idle very low.

2 minutes later I left the foot gradually so the engine stay to idle,
but one minute later the idle drop from 850 to 600 even 400 rpm
and it continue to stay on!!!

Then automatically return to 850 rpm.
Tried to do a short trip and engine works well even with 2 sensors disconnected.
I stop the engine and reconnect the sensors.
Restart after 1 minutes and everything ok.
Done a trip of 20 minutes/15 kilometers, everything ok.
I drove back then I wired the voltmeter in parallel to fuel pump.

Three days later car has been outside for 72 hours in the inclined ramp, start ok,
drive for 20 minutes/15 kilometers and engine dropped rpm two times
while downshifting from 4th to 3rd, fuel pump buzz when there is rpm drop.
Voltage of fuel pump is costant to 13.2 Volt so fuel pump has supply voltage.
Left the car in park for 90 minutes and as I expected,
key on, fuel pump DO the prime, you crank and get only crank,
I stop cranking then key on again then crank and engine start correctly.
Drove back with engine nearly ok apart two or three rpm drop while donwshifting with buzz noise
from fuel pump in that particular moment.

---rideonseatednexttome
Throw away oe fuel cap and fit cheapest aftermarket...

Nice idea.
I have one original used that I can fit.
Only one doubt: I am very disrespectfull expecially at the gas station so
everytime I refill partially I do it with engine running.
The engine does not change behaviour if I open or close the fuel cap,
also there is no hissing sound while releasing the cap.

No one of you have to replicate my action.

---olly
Have to beg downtown for a fuel pressure gauge.

[alessioblaupunkt]

I'm sorry to contradict such an international mechanic as rideoff
but fuel cap is not responsable, because the buzz sound from the fuel pump is still present
and it happen in some curve or sometime up or downshifting.

In the next month I'll change fuel pump.
I have one with 150000 km that has been removed
but was working and there were no buzz sound while taking
a roundabout or curve or up/downshifting.

[ollync]

Any updates? Come on , its an old car with mono-point injection, it must not be so hard.


Sent from my iPhone using Tapatalk

[autoden]

I have had a few some time back with faulty ignition switch when a non start. Did not have poor idle but we could have 2 faults.

[Meat-Head]

ON TOPIC:-

1) fuel pump relay dry soldered joint
2) remove the pipes (leave wires) seal both ends of the EVAP solenoid under the hood

[alessioblaupunkt]

(1st scan for this fault) Scanned the car yesterday found:
00519 - Intake Manifold Pressure Sensor (G71)
31-10 -- Open or Short to Ground - Intermittent

Unfortunately in this engine 00519 makes no sense for these reason:
1) year 1992 engine code ABD doesn't have Pressure Sensor in Intake Manifold
2) G71 refer to nothing in Elsawin for this engine (no Pressure sensor = no name for non existing part, simple)
3) Autodata for this engine doesn't have the 00519 code in the list (no Pressure sensor = no fault code, simple)

Please give me an hint.
All the stuff to control fuel pressure will arrive in June.

ollync->Haven't changed fuel pump yet because if you full throttle breafly just after the rpm drop the engine reach 4000 rpm.
autoden -> Ignition switch is relatively new (2years) and a new one didn't solve the problem.
Meat-Head -> 1) fuel pump relay has been changed, no cure.
2) I have clogged EVAP, no cure.

[synkrotronic]

I sorry,did you confirm throttle position potentiometer,on central body injection?
TB actuactor work with information from this sensor,based on that information and relanti contact on actuator give the correct rpm.
If you have incorrect value the engine rpm could drop.
What scanner did you use?Try another tool to confirm faults.
This is a old injection version,could not adapt tb actuator,when release acelerator (relanti),throttle make contact with tb actuator and give relanti contact ( 0 ohms) and when pressed infinit.The other tb actuator, two connections are from internal motor could measure 5 or more ohms.
If you try with another central body injection,see if is same number,because position potentiometer could have differet values.

[alessioblaupunkt]

VCDS Lite and VAG-COM 409.1 both give the same code with blue chinese KKL cable.

Throttle position potentiometer: I don't have one specific for ABD engine,
I have two from ABU, and one from an unknown engine.

Next week I will use one of these even if they differ in resistance response in the low, medium and high position.

If problem persist I'll swap the "central body injection" as you said,
because the problem could be in the very thin moving contacts that is part of the throttle body.

[alessioblaupunkt]

Rpm drop solved: throttle valve potentiometer G69, also known as TPS.
No more buzz noise coming from fuel pump as you release throttle pedal,
because now ECU has the correct reading so it can activate throttle valve positioner
at the exact right time.

The other fault is still present:
drive as much as you want, park the car for 40 minutes or 1 hour,
it will not start at first attempt (it cranks with dash light on)
it will start at second attempt.

I'll do another scan the next month.

[Meat-Head]

Chuck bucket of ice on rpm sensor

[autoden]

I dont know if this is relevant but, had a 1995 polo 1.4 in a few times but no for his problem. when you got to start, the car would crank but not fire. Take key out, rotate key 180 deg. Put key back in and car would start. Customer knew about it, and was happy to leave it alone. Strange.

[alessioblaupunkt]

^
Maybe immo recognition problem. Not my case.

MY CASE:

Checked fuel pressure several time, I have a tube with a fuel gauge to check pressure, gauge is before the fuel filter,
IT IS NOT IN SERIE with engine fuel rail.
Fuel pressure is 0.8 or 0.9 Bar while engine running, It should be 1.2 Bar but I have 0.8 or 0.9 with a new pump or with an old one.
Fuel pressure is 0.5 Bar when engine is off and the pressure remain for 60 or 90 or even more minutes.
It should be 0.5 Bar so this is ok.

Problem is still here: you left the car sit for 40 minutes or 1 hour it will not start at first attempt.
It will start if you repeat fuel pump prime 3 or more times.
Sometimes it will start at first then die after 1 second, and you have to repeat pump prime.
While repeating prime, the pressure is ok: 0.5 Bar that will increase to 0.9 Bar when pump
is operated by ECU via the relay for 1 second.

It's not an ECU fault.
It's not a fuel pump RELAY fault.

More tests in the next months with another fuel pressure gauge, as this one is a chinese 10 bar fuel pressure gauge and might gave inaccurate readings in the low range.