Car loses power during acceleration only (Limp mode)

BlakeS94

Hello everyone, car has been ripped apart recently a few big jobs the last couple months. All seems well now other than when I accelerate hard, almost every time the power will just go. Feels like I've hit a speed limiter the pedal does nothing from then on. Can drive the car just can't rev it high or accelerate much at all just cruise slowly up to 100 - 120km/h. When I leave it for a bit and turn the engine on it can take a good 5 or 6 seconds to fire up, but sometimes it fires up instantly. I have it booked in to go back to my mechanic, as a side note is trusted and I've been going to him for about 3 years and he's sorted a lot for me and does a good job with reasonable pricing. Fuel pump is good, fuel filter is new, cars recently had full service and all filters. The bit of knowledge I have on cars tells me it's either fuel or air that the engine isn't getting, or getting too much and when I go to climb the revs with the foot down its trying to pull in more air and fuel but something is wrong and the ecu is saying no and puts the car into limp mode. Its out of limp mode when I turn it off and start it again, until I go to rev it past around 2500rpm again. I think maybe a vacuum leak of something like that from putting the car back together after the head gasket repair a few weeks ago. Any advice is appreciated I know there's a lot of lads who know their stuff on here. Just don't tell me to scrap it, its not an option and I've put too much into it to give it away for something that may turn out to be a simple fix. Thanks

Truckermal

Have you tested the Pump? What Car is it?

The One Doctor

Limp Mode? I thought they called it Tubridy Mode nowadays.

BlakeS94

Truckermal wrote: »

Have you tested the Pump? What Car is it?

Hyundai i40. This isn't the first time its happened its been in before where they changed the fuel filter, at that time the car wouldn't start and then fired up after the filter so thought it was just clogged and sorted. But it couldn't have been if its still happening. Pump was tested at the same time and its good, strangely the car was driving perfect after work yesterday and again today, I don't get it.

fryup

could be ecu related, sounds like a job for a auto electrician

cournioni

BlakeS94 wrote: »

Hyundai i40. This isn't the first time its happened its been in before where they changed the fuel filter, at that time the car wouldn't start and then fired up after the filter so thought it was just clogged and sorted. But it couldn't have been if its still happening. Pump was tested at the same time and its good, strangely the car was driving perfect after work yesterday and again today, I don't get it.

What fault code are you getting?

randy hickey

MAF sensor or EGR valve would be worth looking at.

Fighting Tao

I had a similar issue with a Vauxhall Combo that I owned a few years ago. If I recall it was the ERG sensor...although may have been the valve itself. Have a Google, as the Combo was a known issue, and the i40 may have similar.

BlakeS94

cournioni wrote: »

What fault code are you getting?

I'm not getting any, ill talk to my mechanic when the cars in again

BlakeS94

randy hickey wrote: »

MAF sensor or EGR valve would be worth looking at.

I have considered maf sensor but didn't think of EGR being at fault. Car drives fine when its not revved high so not sure it would be the sensor , I could be wrong

cournioni

BlakeS94 wrote: »

I'm not getting any, ill talk to my mechanic when the cars in again

Very difficult to say, but usually if it was a fuel fault you would likely get a high or low fuel pressure fault if going into limp mode or open circuit fault if electrical on fuel system.

Would imagine it may be vacuum related but it really is impossible to say without seeing.

BlakeS94

cournioni wrote: »

Very difficult to say, but usually if it was a fuel fault you would likely get a high or low fuel pressure fault if going into limp mode or open circuit fault if electrical on fuel system.

Would imagine it may be vacuum related but it really is impossible to say without seeing.

My mechanic suggested a vacuum leak when I spoke to him to bring the car in when I described the systems, today its still driving well but its taking 3 or 4 seconds to fire up when I turn the key whereas before it would fire up almost immediately. There's never been any check engine light or any other light for that matter related to an issue. I would think its vacuum as what gets me is every single time its went limp was when the engine demanded more fuel and air, since we know fuel isn't the issue, must be air.

BlakeS94

Glow plugs were changed recently, could that cause all these issues?

MrFrisp

This has been happening to my i40 recently also.

However mine never went into limp mode under acceleration, it was only when I stopped at traffic lights, etc.

Mechanic scanned it and said Fuel Pressure Sensor was showing up.

At present though, it's with the mechanic as it is as it's getting the timing chain replaced. He said it was slightly stretched. He also said because of the timing chain issue, that may have been causing the limp mode issue.

I'll let you know when I get it back, although it's going to be after the weekend at this stage.
.

BlakeS94

MrFrisp wrote: »

This has been happening to my i40 recently also.

However mine never went into limp mode under acceleration, it was only when I stopped at traffic lights, etc.

Mechanic scanned it and said Fuel Pressure Sensor was showing up.

At present though, it's with the mechanic as it is as it's getting the timing chain replaced. He said it was slightly stretched. He also said because of the timing chain issue, that may have been causing the limp mode issue.

I'll let you know when I get it back, although it's going to be after the weekend at this stage.
.

Please do, mines not going in until next week. Hoping its not timing chain related I don't have any sounds coming from engine and oil has been changed on or before due date every time

MrFrisp

BlakeS94 wrote: »

Please do, mines not going in until next week. Hoping its not timing chain related I don't have any sounds coming from engine and oil has been changed on or before due date every time

.
Mine went in as he said the chain guides were rattling bad. They were fairly noisy..

So no point in doing the guides alone so decided on the whole kit.

As soon as I get it back and drive it, I'll let you know.
.

greasepalm

Fault codes can be funny and not seen on machine but would try another machine to see if its seen on that one.

MrFrisp

BlakeS94 wrote: »

Please do, mines not going in until next week. Hoping its not timing chain related I don't have any sounds coming from engine and oil has been changed on or before due date every time

.
An update on this..

He done some further searching on this, and after deciding that the chain wasn't that bad, so not causing the limp mode issue, he's now 99% sure it's the Intake Manifold Runner/Sensor.

Said he's changed a few over the last 12 months or so and it's fixed that particular issue.

So something for you to look into.
..

Hellrazer

MrFrisp wrote: »

This has been happening to my i40 recently also.

However mine never went into limp mode under acceleration, it was only when I stopped at traffic lights, etc.

Mechanic scanned it and said Fuel Pressure Sensor was showing up.

.

A fuel pressure sensor fault on the I40 is almost always down to fuel filter needing replacement.

I used to see it all the time when non genuine filters were used.

Id suggest throwing in a genuine fuel filter before doing the manifold - In over 12 years with Hyundai I never did a manifold on any of them.

greasepalm

Also heard to use genuine ones when they had issues in winter.

fancy pigeon

Can you get diagnostics plugged in that will print out live data?

MrFrisp

Hellrazer wrote: »

A fuel pressure sensor fault on the I40 is almost always down to fuel filter needing replacement.

I used to see it all the time when non genuine filters were used.

Id suggest throwing in a genuine fuel filter before doing the manifold - In over 12 years with Hyundai I never did a manifold on any of them.

I had read up about that.

Fuel filter was replaced about a month ago. The check engine light no longer comes on now.

However, the limp mode problem still exists. 🙄
.

greasepalm

Was it a Hyundai fuel filter that was replaced with.
Does this car get motorway driving or only to shops and back.

MrFrisp

greasepalm wrote: »

Was it a Hyundai fuel filter that was replaced with.
Does this car get motorway driving or only to shops and back.

My apologies, I forgot to add that part.

Yes, it was a genuine Hyundai fuel filter.

It does both kinds of driving , but in all honesty, I'd have to say a lot of the driving is local.
.

greasepalm

Worst thing for diesels is short journeys as it can clog up exhaust components.

MrFrisp

greasepalm wrote: »

Worst thing for diesels is short journeys as it can clog up exhaust components.

Yes I understand that.

It's the worst thing I think with modern cars, especially diesels.

Trying to figure out limp mode problems can be a nightmare.
.

MAULBROOK

Could it be crap fuel. Was the car sitting up for long during lockdown.

greasepalm

Was it at main dealers diagnostics were scanned.

MrFrisp

MAULBROOK wrote: »

Could it be crap fuel. Was the car sitting up for long during lockdown.

No. Car driven every day.
.

MrFrisp

greasepalm wrote: »

Was it at main dealers diagnostics were scanned.

No, it was my local regular mechanic.

I hope you don't think I'm being rude, but the car is 8 years old.

It would only be a very last resort for me to bring it to a main dealer.
.

greasepalm

No not been rude but not all diagnostic machines pick up all faults on a car and garages normally have more than one machine to recheck on.

Are you based in Dublin?