Hesitating and lack of power in high revs

**Finn** · 05-08-12, 07:02

My Q4 doesn't pull cleanly in the top range. It lacks obviously some power and the boost gauge says it only has 0,5bar of of boost. It ticks over nicely and pulls good under 4000rpm, but full throttle acceleration is disappointing.

The car runs on a temporary exhaust at the moment and it is quite restricting. I have also checked the vacuum and inlet pipes for cracks and leaks. It has new plugs and an air filter.

**Steve Webb** · 05-08-12, 08:57

First things first, is this something that has just happened, or have you changed something with the car and now you have this problem?

How restrictive is the exhaust? What size is it?

And are you sure the pierburg valve is connected the correct way round?

**Finn** · 05-08-12, 11:38

The fault has been with the car since I bought it. I've just replaced the plugs and air filter and went through the hoses.

The exhaust is quite appalling. The front and rear sections are stock. The middle section is replaced by one cat and is made with 2 1/2" pipe. Both the front and middle cats are useless and the cores are loose. The plan is to get a MOT first and then have a 3" custom exhaust made with one removable cat and one silencer at the rear.

I'll have to check the Pierburg valve and make sure it is connected correctly. I'll also try a different fuel pump and replace the fuel filter.

**Steve Webb** · 05-08-12, 12:25

Is the engine standard at the moment? And what plugs did you use? I had a problem a long time ago with the plugs not being able to cope once the car produced a lot of boost at @4000rpm.

Sounds to me at the moment at though there might be a problem with the pierburg not allowing any more than the base boost.

**Finn** · 05-08-12, 15:01

Engine is standard and the plugs are NGK BP6ET's. Spark plugs showed signs of lean mixture but I haven't detected any detonation. All the cylinders were similiar. I found out that the Pierburg valve vacuum pipes were the wrong way and corrected that. Now the base boost is higher 0,6-0,7 but it still doesn't give full power and it doesn't overboost.

Have to measure the fuel pressure and figure out why the engine is running lean.

**AlfaJack** · 05-08-12, 17:06

Could your exhaust be blocked at all?

**Steve Webb** · 05-08-12, 17:57

Loose cats could mean that they have collapsed and are partially blocking the exhaust.

**Finn** · 05-08-12, 18:03

Could a blocked exhaust cause lean running? It is indeed quite restrictive

I found a Walbro fuel pump from the tank. I thought the stock pump is a Bosch.

**colibry** · 05-08-12, 18:34

Walbro is uprated pump. its was changed by someone before you buyed the car i guess.

**Steve Webb** · 05-08-12, 18:45

Maybe you ought to open up the ECU and check you have a standard chip in there.

**mpampis_** · 07-08-12, 18:07

Check the turbine mate. I had same problem. The most possible is a broken turbo specially near the wastegate port. At high revs the gases goes from the broken area of the turbo

**Finn** · 09-08-12, 07:30

I'm still waiting for the adapter for measuring the fuel pressure but I have found out the knock sensor is hanging loose as the threaded part is broken.

I identified the loose sensor as I was reading Brul(tm)'s thread. I thought it was part of the EGR-system...

It looks like the inlet manifold and most likely the head will have to come off

And to add to that I broke the quick connector on the fuel tank for the fuel return line.

It is more and more likely I will do a full head refurb with new exhaust valve guides.

**Steve Webb** · 09-08-12, 11:03

Is that a pic of your head? Doesn't look too bad, apart from #3 of course.

Not sure what effect a dodge knock sensor would have (either no sensor reading or reading you have knock all the time) but if it was sending a signal to the ECU that you had a knock all the time, you'd get the problems you've been having.

Did the remains of the sensor come out ok?

**Finn** · 09-08-12, 11:18

The picture is from Brul(tm)'s thread and not from my engine. My engine is still in one piece. And I'm just assuming I don't have enough space to pull out the remains -> so the head will have to come off. But I know more when I take the inlet manifold off over the weekend.

Edit: I think the sensor tells detonation at load and retards the ignition sharply and therefore it feels sluggish.

**Steve Webb** · 09-08-12, 18:39

Well at least it looks like you know where the problem lies, just a shame its going to be a real pig to fix.

**Finn** · 10-08-12, 19:01

Threads were clean and no sign of sensor remains in the head. I really hope it solves the sluggishness problem.

Manifold was ok to take off but I dread "the putting it back" -part. I think the manifold is from a lancia but maybe someone can recognise from which one.

**Steve Webb** · 10-08-12, 19:38

Looks like the standard Q4 manifold to me. Were the clips in the right place to be able to get at them?

What Wrinx wouldn't give to have is coilpacks as accessible as those as they are now.

**Finn** · 13-08-12, 09:45

Ok, a standard manifold. The clips were accessible and quite easy to open. I think I'm going to move the battery to the boot at this point and relocate the coilpacks where the battery is now. To help reinstallation. I'm in the middle of changing the cambelt and cursing the previous owner as all the bolts are feckin tight.

Oh, and I seem to have "lost" the air temp sensor as I can't find it anywhere

I thought the pressure switch for the water injection was the temp sensor until I read the article about the water injection system. Where does the wire come from for the sensor so I can start looking?

**Finn** · 15-08-12, 07:58

I found the plug for the air temp sensor but the sensor was nowhere to be found

Have to get a new one and plug it in. Should help even further to make things right. I've managed to finish the cambeltchange last night. I also put the knocksensor in place. So if I'm lucky I might be able to test the Startrek and the car over the weekend. And then MOT next week if I'm really lucky and get my hands on a wing mirror - like that's going to happen

**Steve Webb** · 15-08-12, 08:45

Sounds like you are sorting out all those little problems that add up into a big problem with the car. Good luck getting it all back together, should drive like a completely different car.

**Finn** · 17-08-12, 18:51

I bit the bullet and coughed up the dosh for a brand new mirror.

I put the car back together and went for a drive with high hopes. First test and there was a massive leak and no water temp signal. Next test went better but there's only the base boost and the lack of power. I'm convinced there's something wrong with the Pierburg -valve. And the blocked exhaust isn't helping. Maybe someone could help me interpret the log from startrek. I think I have to check the earths as there's some weird fluctuation in the values and the voltage is lowish.

I think a break is in order...

**Steve Webb** · 19-08-12, 17:45

Hi Mika,

just taken a look at the startrek file and compared it to mine.

First off a couple of questions.

1. Was the car upto temp when you captured that data? Had you been driving it around before you connected it to the pc?

2. Was the data capture done with you driving the car around or just sat there idling?

The air pressure reading looks a little strange to me (Column D) you don't seem to be getting much vacuum when the car is idling. I'd check the small bore hose going to the MAP sensor.

Also the figures for the timing (column J) seem vastly different to the ones I got when I collected data from the car.

I posted up a startrek file in this thread http://forum.berlinasportivo.com/sho...?t=2383&page=2

Looks like there might be a timing issue with the car as well.

**Finn** · 20-08-12, 06:48

Thanks Steve,

I took the log with a warm engine and I drove it a bit. I will change the hose for the MAP -sensor as I somehow skipped that one when I changed the other small bore hoses. Then I'll try it with a new temp sensor as the values seem to fluctuate erratically. I also found that there's a Squadra chip inside the ECU.

There's still a definite leak somewhere and just have to go through every possibility. Will test the cooler for leaks and have to recheck the BOV -hose.

The timing issue keeps bugging me. It's quite hard to track down what's causing that. For example Startrek doesn't allow for monitoring the knock sensor signal. But I guess if I eliminate all the possible causes (airleaks, wrong sensor -signals and the usual) I'll get it to work properly.

When I get to drive it next time I'll try it without exhaust as it might be totally blocked

**Finn** · 25-08-12, 15:39

The problems are sorted

I checked the intercooler for leaks, changed the turbo and the temp sensor and now the car pulls like a totally different car. I'm not sure what caused the lack of power but most likely the main reason was the blocked exhaust.

The short drive was a revelation

Brilliant cars - Q4's.