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GT 3f running issue


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Hi,

When starting the engine from cold and even once it’s warm the car has bad throttle response. The revs die off under throttle and along with this the idle is slightly higher than normal about 1000-1100. The odd thing is, when turning the ignition off/then restarting the engine the problem goes away and it runs without any issues at all. It started out intermittently and now is doing it all the time from cold.

I have today checked all the earths and cleaned and lubed them. I have tested the ecu to sensor wiring for continuity and the temp plug, TPS, AFM are all okay. So is there anything else I can test before I begin replacing sensors/the ecu? Anyone else had this issue, there was a post a few years ago I found but the issue didn’t seem to be reported as resolved. Any help appreciated.

Thanks in advance,
Pete


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Have look at this https://www.clubpolo.co.uk/topic/357601-engine-idles-down-and-cuts-out/?tab=comments#comment-2728598I I've attached the printout from Autodata on what values you should have at the v

Swapped out the lambda for a new one and the problems gone. Haven’t tried my new VCDS adapter yet. But will bare that in mind for next time.   Thanks for the help! 

They represent whether the signal is an inbound signal from a sensor/power supply etc or an outbound signal to a unit/actuator etc

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Sounds similar to my temperature sender problems last year - the blue sender is a common culprit and is a service item really, they do deteriorate.

 

When you say you've checked the earths along with the ECU to temp sender connection have you checked that the relevant ground pin for the sensor (its pin 8 on mine, not sure if its identical on yours or not) is seeing a good ground?

 

 

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steveo3002

when i doubted the blue temp and its wiring , i made up 2 lengths of wire with the correct pins on and ran it direct to the ecu plug 

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684445034_TempSensorResistancetest.png.94903e835a4a7b9e1428dc68266dae54.png

 

This should give you an idea of the resistance you should see across the temperature sender - the same resistance should be seen across the relevant ECU pins too. Any breaks in the wiring etc will act to increase that perceived resistance which will lead to over-fuelling

 

If you do end up buying a new one make sure its a new OEM unit - they come up on ebay frequently. Pricier than ECP etc but worth it.

 

 

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I’ve had the engine up to running temp and seen 240 ohms, so I’m sure this is okay. I’ve just checked the earths on all plugs (multi meter against the earth terminal on battery then on the relevant sensor earth) with a value under 1 being ideal:

 

Blue plug, lambda, and injector rail all 1-0.8

All the earths on the inlet manifold about 0.8 

TPS was 1.4 and the black plug was 1.9

 

I think these are all okay.

 

So what’s the next thing to test?

 

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All sound reasonable. Did you check the blue temp sender resistance is being correctly 'seen' by the ECU? The way to test this is to pop your meter between the two relevant pins on the ECU plug. Disconnect the battery negative strap and then the ECU plug first, then measure between pin 8 and 9 (i think - double check that). 9 should be the brown/white earth that is shared with the throttle potentiometer and inlet temperature sensor (on mine - again, best check for yours). From steveo when i had this problem:

 

image.png.83c7d13ff0eac88fcf7f668e8652a8b3.png

 

The important thing is that the resistance you measure across the blue sender (i.e., across its own pins) is the same as across the relevant pins of the ecu plug.

 

 

 

 

 

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Thanks for that, it sounds like a good plan and something I hadn’t done yet.

I’ll post a pic of my ECU plug and hopefully you can tell me the right connections to test! 🙂 

does 8 and 9 on my plug correspond right to the pin out diagram?

 

 

0C1FB432-7B4D-4A8F-83BA-EE4889A24B0C.jpeg

Edited by Bawbag
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Update from this; 

With engine cold I have the MM on 20k Ohm setting. It’s reading 4.1 at the plug.  At the ecu harness, according to terminal side diagram connections 6 and 10 are the temp wiring, and they read 4.1 too.

The ecu also has good earth checked the 13 pin on 200 Ohms and read 0.7 

 

 

D8E7ACDB-3CD7-4E54-9A3E-E3D08C8D762D.jpeg

Edited by Bawbag
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I'm guessing that (if correct) 6 is the shared earth (brown/white wire) and 10 is the signal wire straight to the sensor then. Sounds unlikely that you've got a duff connection then which is good.

 

The temperature sender resistance sounds in the right range so its less likely that its totally duff.

 

On 23/11/2020 at 10:29, steveo3002 said:

when i doubted the blue temp and its wiring , i made up 2 lengths of wire with the correct pins on and ran it direct to the ecu plug 

 

This is a good thing to try as a double-check though. I've had wires that tested OK and then as soon as the plug was back on and the engine vibrating the break in them caused a fault again. Electrical gremlins are common in old wiring - degrading or abraded insulation, breaks in wire, corrosion at connections (although sounds like you've cleaned a lot of them up which is good) can often be to blame. For example I've run an extra earth from the lambda sensor directly to the battery neg for example which improved my running (albeit slightly). The original earth runs through the block and chassis so it can't hurt to clean it up totally.

 

It sounds like its either over- or under-fuelling enough to cause the revs to hesitate and die - what do the plugs look like?

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22 hours ago, nige8021 said:

Have look at this https://www.clubpolo.co.uk/topic/357601-engine-idles-down-and-cuts-out/?tab=comments#comment-2728598I I've attached the printout from Autodata on what values you should have at the various pins  

121465401_3FWiring-1.thumb.jpg.c1bc6fd195a85f0eb2fe3a99f3a95397.jpg

629100910_3FWiring-2.thumb.jpg.f30a8db98d86a7127569572c52d79353.jpg

890107981_3FWiring-3.thumb.jpg.1db599c25a7f18cc0d58d821117f8d94.jpg

1855890249_3FWiring-4.thumb.jpg.2d8227c21029cf4148da06586b3ddf0f.jpg

1375627050_3FWiring-5.thumb.jpg.f98fd2f2f109491386f98b90579eeb56.jpg

520212517_3FWiring-6.thumb.jpg.57e76fc145146affdd9f33f28ed73f7d.jpg

 

Filing this away for myself - this is really handy, thanks!

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On 25/11/2020 at 12:26, nige8021 said:

Have look at this https://www.clubpolo.co.uk/topic/357601-engine-idles-down-and-cuts-out/?tab=comments#comment-2728598I I've attached the printout from Autodata on what values you should have at the various pins  

121465401_3FWiring-1.thumb.jpg.c1bc6fd195a85f0eb2fe3a99f3a95397.jpg

629100910_3FWiring-2.thumb.jpg.f30a8db98d86a7127569572c52d79353.jpg

890107981_3FWiring-3.thumb.jpg.1db599c25a7f18cc0d58d821117f8d94.jpg

1855890249_3FWiring-4.thumb.jpg.2d8227c21029cf4148da06586b3ddf0f.jpg

1375627050_3FWiring-5.thumb.jpg.f98fd2f2f109491386f98b90579eeb56.jpg

520212517_3FWiring-6.thumb.jpg.57e76fc145146affdd9f33f28ed73f7d.jpg

 

Yeh spot on thanks. Dumb question - how can I check connections on the wire side of the ecu harness when it’s plugged into the ecu?

 

 

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On 25/11/2020 at 11:11, zob said:

I'm guessing that (if correct) 6 is the shared earth (brown/white wire) and 10 is the signal wire straight to the sensor then. Sounds unlikely that you've got a duff connection then which is good.

 

The temperature sender resistance sounds in the right range so its less likely that its totally duff.

 

 

This is a good thing to try as a double-check though. I've had wires that tested OK and then as soon as the plug was back on and the engine vibrating the break in them caused a fault again. Electrical gremlins are common in old wiring - degrading or abraded insulation, breaks in wire, corrosion at connections (although sounds like you've cleaned a lot of them up which is good) can often be to blame. For example I've run an extra earth from the lambda sensor directly to the battery neg for example which improved my running (albeit slightly). The original earth runs through the block and chassis so it can't hurt to clean it up totally.

 

It sounds like its either over- or under-fuelling enough to cause the revs to hesitate and die - what do the plugs look like?

Haven’t checked the plugs - will do. Yes it’s under or over fuelling and the revs are bogging down. After cleaning up contacts of earths and doing all that testing with the MM the last 4/5 drives have been no trouble. Might be coincidence!

I have ordered a better 2x2 adapter to hopefully read ecu codes, otherwise I feel pretty stumped with what to do next
 

will update what I find here.

 

thanks for the help.

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1 minute ago, Bawbag said:

Haven’t checked the plugs - will do. Yes it’s under or over fuelling and the revs are bogging down. After cleaning up contacts of earths and doing all that testing with the MM the last 4/5 drives have been no trouble. Might be coincidence!

I have ordered a better 2x2 adapter to hopefully read ecu codes, otherwise I feel pretty stumped with what to do next
 

will update what I find here.

 

thanks for the help.

 

No worries. The codes (in my experience) won't tell you much but if you can get VCDS to read out the sensor data in real time while its misbehaving you'll be able to track it down very quickly. Never had much luck with the 'free' version of VCDS myself but at the end of the day if its intermittent between drives its more likely to be something physically getting loose i'd say.

 

 

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  • 3 weeks later...

Swapped out the lambda for a new one and the problems gone. Haven’t tried my new VCDS adapter yet. But will bare that in mind for next time.

 

Thanks for the help! 

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Oh crap I thought that had solved it. It came back today first time since changing the lamda, but also first time in quite a few journeys. Really not sure whats causing this, as it made sense it was overfuelling on throttle as the revs die off a lot.

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Is it bogging down when you rev it in neutral, or just under load?

 

Earthing can be a significant issue on GT's. If it's not idling well or having problems when revving in neutral, try putting a jump lead between the inlet manifold (or anwhere that sort of side of the engine) and battery negative and see if that improves the job. It's worth running a more direct earth wire from the lambda in addition to the existing one. 

 

Have you tried setting the ignition timing using this procedure? https://www.clubpolo.co.uk/topic/109802-how-to-set-the-ignition-timing-and-idle/Earthin

 

 

Not saying it's definitely going to be that, but it generally makes a difference on most GT's. 

 

 

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It’s bogging in neutral most noticeable at idle when pulling away for example and even when pushing throttle at cruising speed it hesitates. As soon as I switch the engine off and back on it goes away instantly, idle speed is back to 950 rpm and the whole thing has gone and engine performance is bang on.

 

With it doing this it could be earth related, or fuel pump relay (also new from Max RPM) or something else over fuelling related?

 

I have cleaned up the earths on the inlet and the new lamda obviously had a new earth. Run a separate earth from the lambda plug directly (like spliced in?) to the negative or from the inlet earth mounting point?

 

Timing shouldn’t have changed much at all, was set up as per that post a about 5 years ago. Worth doing again?

 

Edited by Bawbag
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Fuel pressure could be a culprit, as it might be why it resets after ignition off / on? I’m not sure what to check on this though?

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Took a video of a cold start this morning, this is not always what it does before it starts having shitty throttle / overfuelling.
 

In the video on first start it coughs and doesn’t catch then second turn of the key it does, the pump doesn’t prime for that second start. But doubt this is related. The engine sounds like it’s overfuelling as I gently open up the throttle. Some kind of safe map?
 

Could this be TPS or Airflow meter related? Neither have been tested or replaced. Got spares but maybe worth a test with multimeter for their signals?

 

As soon as I turn it off and re-start it behaves... Does this help narrow it down?

 

Help!
 

 

 

Edited by Bawbag
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On 25/11/2020 at 12:26, nige8021 said:

Have look at this https://www.clubpolo.co.uk/topic/357601-engine-idles-down-and-cuts-out/?tab=comments#comment-2728598I I've attached the printout from Autodata on what values you should have at the various pins  

121465401_3FWiring-1.thumb.jpg.c1bc6fd195a85f0eb2fe3a99f3a95397.jpg

629100910_3FWiring-2.thumb.jpg.f30a8db98d86a7127569572c52d79353.jpg

890107981_3FWiring-3.thumb.jpg.1db599c25a7f18cc0d58d821117f8d94.jpg

1855890249_3FWiring-4.thumb.jpg.2d8227c21029cf4148da06586b3ddf0f.jpg

1375627050_3FWiring-5.thumb.jpg.f98fd2f2f109491386f98b90579eeb56.jpg

520212517_3FWiring-6.thumb.jpg.57e76fc145146affdd9f33f28ed73f7d.jpg

 

Hi what do the various symbols in ‘signal’ column mean?

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nige8021

They represent whether the signal is an inbound signal from a sensor/power supply etc or an outbound signal to a unit/actuator etc

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