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Lupo gti running rough when hot


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Hi guys, wondering if anyone can shed any light on a problem with my gti. 

I had it sat on the drive for a year as it needed a rebuild. Started occasionally with no issues. I took it for a engine rebuild a few months ago. Ran fine on the way there although I was nursing it due to the engine problem (blowing oil out exhaust). It had a full rebuild, all put back together and now as per title it runs beautifully until full engine temperature is reached then it won't rev past about 3k. Its almost like its got a rev limiter. It's still with the engine rebuild shop but it's been months now and we're all pretty confused. No codes thrown up. So far it's had new :- coil pack, leads, plugs, new head, temp sensor, timing pulley, both o2 sensors, had the egr/throttle body/anything needed recalibrated.

The engine has been rebuilt twice now as the shop wanted to make sure they hadn't missed anything (they fitted new head 2nd time round due to being not being 100% happy with a valve seat). 

I'm not sure if the car gained this problem when it sat for a year I know before I parked it up other than the oil out the back it was running like a dream never had any power or running issues (although obviously it wasn't being pushed hard). 

Any of you gurus got any other ideas what else to check? 

Cheers. Simon 

 

Edited by lupo_s_i
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What was lambda saying as it approached 3k? Any misfiring or just gutless and wont go over 3k ish?

you checked timing belt? A tooth out? Although dumb question- ecu would flag a code.

what's idle vac like when hot?

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23 minutes ago, mk2 said:

What was lambda saying as it approached 3k? Any misfiring or just gutless and wont go over 3k ish?

you checked timing belt? A tooth out? Although dumb question- ecu would flag a code.

what's idle vac like when hot?

Cheers for your response. Not sure what lambda was saying but it runs like normal till hot, then when hot at around 3k ish it goes completely gutless like it hits a limiter and the car starts spluttering, doesn't seem like a miss as such it's like it's not getting enough fuel. Timing belt done, checked, new vvt pulley fitted as it squealed slightly on restart after first rebuild but didn't make any difference. 

Again not sure on idle vac, the garage is doing the work I was hoping for questions like this so I can ask the garage about it. I have a relatively good mechanical understanding but I'm no car mechanic. I'll ask about the vac when I next pop in. Are there figures it should be? Cheers

Edited by lupo_s_i
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Could be that the cat is blocked like @Sausage suggested. Or fuel pump? Try running it briefly without exhaust connected if you're in a workshop.

if you're 100% sure all the mechanical stuff is ok, and not the above, it can only be ECU controlled output. The ecu thinks the car is simply heavily loaded and just can't go "uphill" any faster. This is all being done on a rolling road I'm guessing?

the lambda output figures/plot always tell you everything you need to know.

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2 hours ago, Rich said:

Cam sensor or something related to the vvt is buggered.

I've been here before.

Yeah i thought the same, but wouldn't ecu flag timing fault if more than 3/4 of a tooth out?

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20 hours ago, mk2 said:

 

Thanks for all your responses. I'll pop by the garage next time they are open and do some digging. I was wondering about the fuel pump does it get a signal from the ecu to change its output when warm? Just couldn't see how it would run so well when cold. Plenty to get my teeth into though thanks 🙂

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I'd be tempted to try a green temp sensor, cheap enough and gives the ECU it's temp feed.

Fuelling doesn't change when warm, always regulated by the fpr.

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Diagnostics would pick up dodgy temp sensor... when cold all sensors should be about the same. When hot, water around 90 and air around 25 in this weather. Yeah check the temp sensor.

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Diagnostics never pick up a temp sensor but it is such a prevailing problem.

How many blue temps on old Bosch management?

How many black?

Now they're combined into a green four pin the temp reading part seems to last but the other part doesn't.

When mine went on the GTi it ran like absolute spanners when hot and cold.

Surprising the effect that it had. 

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I have already had new temp sensor but will check and make sure a green sensor has been fitted when I visit the garage. That was my first suspicion but its definitely been changed and didn't make any difference to the running 

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On 12/20/2018 at 9:18 PM, lupo_s_i said:

It had a full rebuild, all put back together and now as per title it runs beautifully until full engine temperature is reached then it won't rev past about 3k. Its almost like its got a rev limiter. 

Does it rev's past 3k cold? 

has it been driven + has normal power cold or is this all just in the garage ?

Coilpack on the way out? - have they tried a good spare?

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On 12/22/2018 at 11:07 PM, LR5V said:

Does it rev's past 3k cold? 

has it been driven + has normal power cold or is this all just in the garage ?

Coilpack on the way out? - have they tried a good spare?

Yes it has been test driven and runs completely fine until reaches temperature. Obviously not redlining with being fresh rebuild but definitely runs as it should until warm. It has had a brand new coil pack which didn't make a difference, I'll pop by the garage in the new year and check what vcds is saying 

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  • 4 weeks later...

Just a little update incase anyone is Interested. Popped by the engine shop today and they have found what they believe to be the issue. Their supplier sent pistons that were slightly different and didn't have enough clearance  cut out at the top of the pistons for the valves. Engine is back in pieces it's totalled the head and is currently being rebuilt for a 3rd time now with the correct pistons so we will see how we go. The builder recogns it was running fine when cold due to extra fuel but once hot correct air fuel mixture couldn't be achieved due to valves not seating properly. Just thought I'd post seen as so many threads don't get closed out. If anything changes (ie there's still a problem once finished) I'll post end findings for future reference. Cheers for everyone's help. Si 

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As Rich said - what was wrong with the old pistons?

Hope they are replacing your valve / valve guides

seem to recall testing valve clearance to piston is done without head gasket, pretty easy on a traditional head, but our cam box + vvt  makes it a bit harder.

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Old pistons were shot, I bought the car with a knackered engine after strip down it was assessed to need rebore and pistons (I was shown them and fully agreed) Engine was rebored with new pistons and then was having the issues above. I have seen the damage done to both head and block and completey believe their story it all matches up I have Compared the pistons supplied with original and can see the slight difference. Admittedly they should have noticed it on first build but hey mistakes happen. Car is back with me now after all the fun and games they had (4 months it's been with them with rebuilds and diagnosis) has had all new valve guides (twice for what it's worth) running like a dream now. Saw my engine completely stripped down on Monday and I don't think there is any way if there was further problems in the electrical system that they would have had time to diagnose after rebuilding and reinstalling the engine. 

Edited by lupo_s_i
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