Low boost below 2000-2500 rpm 1.9 dci FAP

[megowner2k]

Hey fredcamp, both EGR and MAP sensor were replaced at some point. Don't know about wiring, what am I supposed to check? Gah, this car is pulling more money out of me than the state

[AlexB]

I mean, I did not see the "Commanded Boost Pressure" parameter in the OBD in my 53 plate diesel. If you are getting these readings, then you are right - the turbo is not boosting enough. As the ECU can see the difference between the commanded and actual pressure, then it operates the actuator as far as it goes, but somehow this is not not enough in your case. It can be the intercooler leaking, exhaust plugged, a vacuum leak, solenoid valve, actuator mechanically sticking, the turbo itself... At this point my experience stops.

Yes, 1300 mbar is a lot less than the commanded 2000 mbar.

What do you mean by print out of the engine map? What do you mean by downgrade?:) The values were gathered and compared live while on the motorway using a KTS scan tool. If I'd have a recorded graph, it would look something like this (6th post) https://uk-mkivs.net/topic/218399-low-bo ... con-turbo/.

[megowner2k]

I'm at the point where I'm thinking of replacing the turbocharger, but as I said, I would check for leaks first. Also you're saying the exhaust manifold might be plugged. I ran the car with the exhaust pipe downstream of the turbocharger removed and it ran just as bad; could it be plugged upstream of the turbocharger? Is there anyway I can check this without removing it? Any particular signs, like rough idling, stuff like that?

Also, I read somewhere that a car is supposed to have vacuum in the intake manifold at idle, whether it's turbocharged or not. Mine blows air at idle, I checked when I removed the MAP sensor for cleaning, is this normal?

I thought about fiddling with the turbo rod at one point, try and shorten it by a 360 degree turn and see where that takes me, is this safe?

Look, sorry for bothering you guys with so many questions, it's just that every single thing I want to try costs me, and I'm at the point where I don't want to waste another penny on this car without results, so I just want to narrow the problem down as best as I can before taking another wrong decision.

[AlexB]

Morning megowner2k,

Gas flow resistance in obstructed pipes is a non-linear function of the flow or its speed. Let's say it is approximately quadratic for mild obstructions. At idle the exhaust flow is, say, 1% of the flat out flow, and the exhaust is still able to let the high flat out flow through (with resistance or not). The quadratic function looks pretty flat in the area of low argument values, hence one can neglect the effect of mild obstructions at idle. Basically, if it is coping with the full flow, at least somehow, then it will be OK at idle.

Regarding vacuum in the manifold. You are, probably, confusing this with petrol engines, where vacuum is created behind the throttle when the latter is closed. In petrols they also use a dump valve to avoid a situation when the turbo is blowing into a duct plugged on the far end with the suddenly closed throttle. Without a throttle valve it is not needed, so diesels do not have a dump valve usually, and there is no vacuum behind the throttle due to absence of such.

Fiddling with the turbo rod. I don't know. The turbo is not working properly, so it is not a standard situation. Check first that it is not stuck due to soot deposits inside. A risk is that if the intercooler is leaking, then an adjustment may cause overrevving the turbine under a high load mode. If it is not leaking with the noise of a whistle of a boiling kettle, then it should be safe to try.

Regarding costs and the whole approach - it is the first time you are working with this engine, you are learning, so do not expect it to be cost-efficient. If I were in your place, then I would have tried attaching a string to the rod, "helping" it to move to meet the commanded boost pressure. Thus one can eliminate the control circuit faults. The same you can achieve by adjusting the rod temporarily (just be careful with the accelerator).

[megowner2k]

I will take the turbo off and I will check the exhaust manifold upstream of the turbocharger on the way. I'll also check for leaks in the intake as best as I can and will also check voltage output for the boost controller. Thanks so much for your time and I will post here whenever I'll have the time for these operations.

[vanko25]

Meganeowner2k, did you manage to fix the problem? I am having similar issue on F9Q 800 120hp. Thanks in advance!

[megowner2k]

Hey Vanko, have given up for now, I was thinking of going big and replace the turbo, but haven't had the time or money. Could you detail your problem a bit? How did it appear, any lights on the dash, is the car smoking, etc?

[vanko25]

It is the strangest diesel car I have ever had. When I bought it was alright and after an oil change all these problems seemed to happen. Running really rough which I suggest is something to do with the Fuel Supply system and it does not pull as it did before. I have changed fuel filter(BOSCH),air filter,ELF oil with OEM Renault filter,intercooler. Cleaned the EGR, MAF, MAP, all intake pipes. The strange thing is that if I turn it off and on when is warm it seems to become a bit better. Has been at Renault specialist and he said there is nothing wrong with it except the turbo boost is slightly low than normal and that the cam shaft sensor error popped up for second but then went away. I am planning to bring it to diesel specialist to check pump and injectors as the charges seems to sound alright. Thanks!

[megowner2k]

That's really weird, how much have you drove it before you drained the oil and how severe is the lack of power? Also, the values for MAP, MAF and any other sensor for that matter should be checked on the road at various speeds and rpm. My car was all good when the service people just revved it at idle like idiots but turns out it doesn't build up enough boost pressure when you're actually moving the car.

[vanko25]

I have one of these ELM327 based Bluetooth OBDII scanners. I have been monitoring it for a while and all seems fine. It will turn to be mechanical error I think. I am planing to buy one of these Delphi CDP OBD scanners and check how are the Injectors compensation values. Now need to sort out my rear bumper as have been rear ended during the week.

[megowner2k]

Wow, they just keep on coming, don't they? I've got water all over driver's side, it will be the third time this season I'm taking it apart.

[vanko25]

After I had opened the N/S door to fix the electric window have a little surprise in the doors pocket every time it rains. Still do not have time to fix it. I have some 17 inch wheels that need to be prepared by spring time and a GF moaning that I am spending too much on the car. Well I think with a Renault we will never stop spending money on them.

[Colster]

I'm currently having similar issues with my car. I've just changed fuel supply line between filter and fuel pump, as this was drawing air. I'm interested in the Renault comment about turbo hissing. I can hear hissing when driving from the brake servo. I wonder if this is causing reduced vacuum to turbo circuit?

[taffyhl]

Vanko25 - I have exactly the same with my 1.9dci (no FAP). If I've done a long motorway run followed by a slow city journey the car is a little rough when stopped at lights etc. Doesn't misfire but vibration can be noticeable. If I can switch it off for a few minutes and then it's fine. If I do a series of city journeys it's fine too. Garage suggested changing the engine top mount but only cos they couldn't find anything wrong and OBDC has no error codes. My instinct is the EGR valve but I have changed that once (no difference) and clean it every 6 months of so. Get's a little sooty but not too bad. I'm also pretty sure my turbo isn't kicking in when it should and even a mildly heavy foot producing a puff off grey unburnt fuel and a bit of lag.

What does help is putting my foot down hard occasionally. Most journeys are motorway at 1800 - 2200 revs and I'm certainly no boy racer in town so car rarely goes over 2500 rpm.

[MilosB]

I don't know. Please feel free to have look at my OBD diagrams. It's F9Q-800, 1.9dci, 120hp, 8 valves, no FAP.
https://www.tboneandporcini.pwp.blueyond ... strun1.jpg

Alex, i see you MAP spiking at 2.5bar, I don't remember is you car mapped ? and more that im interested in is whether the 2.5 bar should remain more or less constant under full throttle or is it only for a short period of time beetween 2ooo and 25oo rpm ?