Author Topic: G40 Engine Diagnostic Guide  (Read 20449 times)

Offline z3i

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Re: G40 Engine Diagnostic Guide
« Reply #15 on: April 22, 2013, 06:30:58 pm »
Is there anyway to check the air temrature sensor inside the co pot?

Offline Andy

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Re: G40 Engine Diagnostic Guide
« Reply #16 on: April 22, 2013, 07:46:57 pm »
Air temp sender is pins 2 & 3 in the CO pot/air temp assembly.

Resistance should be circa 5k7 at 0°C, 2k6 at 20°C and 180ohms at 100°C.

Offline z3i

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Re: G40 Engine Diagnostic Guide
« Reply #17 on: April 22, 2013, 08:09:08 pm »
Air temp sender is pins 2 & 3 in the CO pot/air temp assembly.

Resistance should be circa 5k7 at 0°C, 2k6 at 20°C and 180ohms at 100°C.

brilliant! Thanks mate

Offline Andy

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Re: G40 Engine Diagnostic Guide
« Reply #18 on: April 22, 2013, 09:24:35 pm »
That's based on measurements from a couple of sensors, rather than a spec - so don't worry if yours doesn't match exactly.

Offline Alexis

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Re: G40 Engine Diagnostic Guide
« Reply #19 on: August 15, 2013, 08:04:03 pm »
Does everyone get values matching this guide? I've got juddering at 2500-3000 and juddering at low revs when cold, which will also not respond to the idle speed screw.

I tested the old sensors, for the coolant temperature sensor I got 46 ohms cold, going to 26 ohms hot, so replaced the sensor and got 70 ohms cold, 25 hot.

Also just tested the co pot/air temperature 1-3 gets 103 ohms, 2-3 gets 44 ohms. The adjustment screw doesn't change anything on the 1-3, but the 2-3 will go to 66 ohms and no higher. Is it worth replacing?

Offline Yoof

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Re: G40 Engine Diagnostic Guide
« Reply #20 on: September 17, 2013, 01:54:49 pm »
Carl,

In response to a mail from Carl asking about some running problems, thought I’d post this in here as it might helps someone else (and save my fingers).

Presume the Golf GTi uses a high pressure >3 Bar fuel pump? It should be adequate for the G40 engine.

I would approach this with the basics in mind, spark, fuel and air.

Spark:
-   Check plugs, and plug gap. G40 uses a W5DPO Bosch plug, you can use NGK BP7EVX too.
-   Rotor arm / distributor cap condition (worth replacing if they’re unknown, cheap from VW)
-   Coil/Hall sender health, hard to know by looking at them, swap for working components (or new)
-   Earths – clean connections, fresh wire/crimps, replace as necessary.
-   Ignition timing

Fuel:
-   Fuel pressure under load (gauge on the end of fuel rail) remember fuel rail pressure will differ to maintain injection pressure (elta pressure across injector) at 3bar. I.E at idle with 1 bar vacuum, fuel pressure will be 2 bar. At 1 bar manifold pressure, fuel pressure will be 4 bar.
-   Colour of plugs – plenty of charts online to indicate mixture strength
-   Sensors, the ECU is regulating fuel based on the information it is able to collect. Is the CO Pot set correctly (550-650 Ohms, Pin 1 – 3)
-   Filter clogged, injectors clean, fuel pressure regulator has a good vacuum source with no leaks

Air:
-   Leaks, common ones are injector o-rings, throttle body, and degraded boost pipes.
-   Vacuum lines (important ECU and fuel pressure regulator)
-   Idle speed adjustment, this is important, the ECU will try to achieve a stable idle speed (~850rpm) by altering ignition timing, useless if the screw is wound out and engine at 1100rpm!
-   Charger health, oil in boost pipes, air filter cleanliness etc
-   ISV- located on the main water pipe, below the inlet manifold. Can be cleaned with carb cleaner if full of crud. Make sure pipes to/from are leak free.
-   Compression check across cylinders

Other:
-   Sensors & Wiring, are sensors in good health, a bad blue temp sender, or lambda can give very rough running problems and poor fuel consumption. Try to replace with OE quality parts Bosch/VW.
-   Sensors are plugged in correctly, favourite is throttle body (white) plugged into knock sensor (black)
-   Throttle switches working correctly (idle micro switch and full throttle micro switch)

These are the basics, and will probably lead you to find most common running problems.

CO Pot is located on the plastic boost pipe, it houses a temperature sender and is held in with a c-clip, has 3 wires running to it, and looks like this:

http://farm6.staticflickr.com/5118/7438288060_fd3735168c_n.jpg

Hope this helps,

Pete

Offline FORCEDINDUCTION

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Re: G40 Engine Diagnostic Guide
« Reply #21 on: September 17, 2013, 09:06:11 pm »
Much appreciated Pete, as replied by email...I'll have GOOD look about and plumb in a boost gauge ....
I've found today a crushed ( but not completely flat ) metal fuel line ..looks like supply !

Then I'll get a base rolling road session and take it from there regarding coming to see you guys for a freshen up

Again cheers Carl

Offline Ross36

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Re: G40 Engine Diagnostic Guide
« Reply #22 on: April 19, 2018, 07:39:49 am »
I had a juddering at 2000rpm when on light throttle, turned out to be the knock sensor and co pot plugs were swapped, also a broken earth going to the co pot plug.

The ECU still went into service mode with these plugged in incorrectly, wasn't until checking the colours of the wires against a Haynes it was obvious.