AGU 1.8T miss as it comes on boost

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Modjo
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AGU 1.8T miss as it comes on boost

Post by Modjo »

Hi All,

Hope you could advise,

Ive recently purchased a Golf 4 GTi, the car has stage 1 software, with a 63mm exhaust,previous owner advised that the car had a miss but that was due to the MAF.

(A)The car does the following,
1. Misfiring as it comes on boost,then,
2. Backfiring, as you let off throttle,
3. Jerks at low revs if you in 3rd gear and higher,
4. Quite heavy on fuel, even while babying the car due to the miss

(B) Whats been done since i bought it,
1. Been for a full service,
2. New MAF (bosch)
3. Diagnostics done (bosch service centre), no errors picked up apart from central locking on 1 of the doors

However, the car still does the same (A), could anyone perhaps point me in the right fault finding direction

Thanks
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Re: AGU 1.8T miss as it comes on boost

Post by Kyle »

Coil packs usually cause the "Coming into boost misfire" symptom, but they usually show up on the error logs.
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Re: AGU 1.8T miss as it comes on boost

Post by Modjo »

@ Kyle,

Thank you for the advice, anyone that you could recommend to run diagnostics on the car (again)
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Re: AGU 1.8T miss as it comes on boost

Post by Kyle »

Modjo wrote:@ Kyle,

Thank you for the advice, anyone that you could recommend to run diagnostics on the car (again)
Where are you based?
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Current:
'03 BMW E46 330i Individual

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Re: AGU 1.8T miss as it comes on boost

Post by Modjo »

Hi Kyle,

JHB south, but dont mind travelling
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Re: AGU 1.8T miss as it comes on boost

Post by Nikz_tsc »

Check out that Engine speed sensor as well bud
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Re: AGU 1.8T miss as it comes on boost

Post by panic-mechanic »

Very rarely does an engine sp ed sensor know thatbthere is now boost and stops working becuase of that.
What is affected though is fuel pressure and spark. For fuel pressuryou have to use a good old school mechanical gauge becuase the computer on those don't know it.
ONCE MORE - looking for fault on the vcds log is NOT DIAGNOSING.

And it can be a spark plug and or a coil, both of which can fail without the computer knowing or caring.
But start with fuel pressure checks. The pumps are starting to fail now. Have done a few recently.
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Re: AGU 1.8T miss as it comes on boost

Post by Pynoxim »

AGU Coil Packs seldomly die, in fact I've never seen one die. What does act up is the ignition coil module that's usually located on the Airbox or close to it if running a cone filter.

Also, AGU's will give a very harsh cut if MAF reading hits its limit or Injection time hits a certain limit, generally due to unseen boost leaks or whatever.

As panic also mentioned, check fuel, get a fuel pressure gauge on the fuel feed line and check it FP drops when going into boost. It should rise by the exact amount of boost that you're putting in and also have a base pressure of 3 bar if running the stock FPR.
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Re: AGU 1.8T miss as it comes on boost

Post by THANAS »

Checked sparkplugs?
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Re: AGU 1.8T miss as it comes on boost

Post by Donavan »

Mine had the exact same issue.

In the end it came down to a simple spark plug gap issue. When the car was serviced it started with the above mentioned issues.

When the plugs was changed they simply just dropped in the new plugs and did not adjust the gaps.

The gaps was roughly about 0.8 and it should be in the region off about 0.45 iirc.

This solved the misfire under boost issue for me.
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Re: AGU 1.8T miss as it comes on boost

Post by Pynoxim »

0.4mm is very VERY close together. 0.8mm on a 6 or 7 range plug sounds right.
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Re: AGU 1.8T miss as it comes on boost

Post by G-man11 »

Pynoxim wrote:0.4mm is very VERY close together. 0.8mm on a 6 or 7 range plug sounds right.
I had the same happening when my AGU was still standard. Turned out to be the OEM boost controller.

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Re: AGU 1.8T miss as it comes on boost

Post by Modjo »

HI Guys,

Thank you all for the advice, appreciated,

Spark plugs were replaced, and ignition coil module checked when the service was done, i was initially advised that MAF was faulty, so i bought a new Bosch unit, but car is doing the same thing,

All boost pipes were checked for leaks, but nothing there as well,

Thanks Panic-Mechanic, will check fuel pressure this weekend,

will low fuel pressure still cause the car to be heavy on fuel ?
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Re: AGU 1.8T miss as it comes on boost

Post by panic-mechanic »

Yes possibly worse as you use a lot more throttle while trying to get somewhere
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Re: AGU 1.8T miss as it comes on boost

Post by Modjo »

Hi Guys,

Checked the fuel pressure, its 3bar,

but found the following errors, throttle body actuator valve, and water temp sensor, could this be the cause/contribute as well?
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Re: AGU 1.8T miss as it comes on boost

Post by panic-mechanic »

Water temp yes. Cause incorrect fuelling. Throttle body no. Will just perform badly but not missfire.
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Re: AGU 1.8T miss as it comes on boost

Post by panic-mechanic »

Fuel prssure must be 3 bar plus whatever you boost. So if you boosting 0.8 bar it should be 3.8 bat at that stage.
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Re: AGU 1.8T miss as it comes on boost

Post by Modjo »

@ Panic-Mechanic, could i maybe just bring the car to you to diagnose and check up?
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Re: AGU 1.8T miss as it comes on boost

Post by panic-mechanic »

Sure. Just crazy atbrhe moment so depends on how much of a hurry.
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Re: AGU 1.8T miss as it comes on boost

Post by Modjo »

Thanks Panic-Mechanic, i dont mind waiting at all, PM sent :-)
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