1.9 dci massive hesitation at 3000rpm

[mrvandango]

Hi guys, my Meggy is suffering from a big stumble at 3000rpm. Everything is fine below that point, pulls like a train, excellent mpg (55-60 calculated not computed on a run) and as smooth as silk. The turbo was replaced by the previous owner 2 years ago.

I know the maf is shot, as unplugging it doesn't affect the idle at all. I've just done a complete service on it, including fuel filter.

When I get to the 3000rpm point it's like I've hit something it's that harsh. It moves you forward in your seat. It doesn't matter if you rev hard to that point or creep up, it still occurs. It refuses to rev in neutral past that point also. No warning lights come up.

Could it be the maf? Or possibly the egr? I also thought that it could be something related to the breather system. It would be great to get to the bottom of it, as I love the car to bits. Smooth, powerful to a degree, and miserly on diesel!

Any ideas/suggestions would be most welcome!

[ad0mas]

Could be an MAF problem, our family has a Peugeot 807 that had a badly clogged MAF and was actually inverted- it would pull like a stoned slug below 3k but anything above 3k was simply delightful. Unplugging the sensor would simply make it not pull at all. Of course such rpm wasn't healthy for a diesel so after diagnosing the problem we got it quickly replaced and now it pulls nice and smooth. The sensors are not that expensive (around 20 quid on ebay), I suggest you start diagnosing the problem by replacing it.

[mrvandango]

Cheers for that. I had the same issue with a dead maf on an mgzt cdti a few years back. Sluggish under 2500rpm then picked up. I did try a maf off ebay but still the problem persisted. Where are you seeing maf's for £20? The cheapest genuine unit I have seen so far is closer to £70. Can pattern maf's work ok?

[ad0mas]

Ok, maybe I exaggerated a bit, this one is £26: https://www.ebay.co.uk/itm/151259578580
My dad purchased a non-genuine one for £35ish at a local parts store 2 years ago and it's still going strong as. If any of your friends have a healthy 1.9 dci Megane, Clio, Laguna, Espace, Master or Kangoo, you could ask them to let you fit theirs before buying a new one just to test it as renault seems to use the same MAF for its 1.9 diesels since late '90s, as the eBay compatibility chart shows.

[mrvandango]

The link is much appreciated, and it's good to hear of a pattern one still going strong. I will order one right now.. I have no friends crazy enough to own a Renault, so I'm on my own with this one

Thanks for taking the time to get back to me!

[ad0mas]

Been away for a week while so couldn't come back to the forum but just wondering if you got the part yet and if you did, has it fixed the problem? hehe fair point there, my friends think I am crazy for getting myself a Megane...

[MilosB]

The cheap maf is not worth the money!! They either come broken or they read slightlly of.
The correct maf to buy is VDO and the cheapest one i found on ebay was 75€

You can check if the maf isnthe actuall problem in two way.
1- disconect the maf, if the car goes fine though the whole rew range then it is maf
2 - go on diagnostics and let them plot a maf value.

But actuallz I really doubt it is a MAF as my was dead it read sometimes zero, and it was all ower the place. The only thing I noticed was slightly raised fuel consumption.

[AlexB]

I'm with MilosB regarding that it's not MAF. MAF in diesels does not affect idle. I tried this with F9Q-800. It sounds more like the ECU cutting off the power, unless the figure 3000rpm is not exact. Just think, what's the chance that essentially an analogue system would glitch at exactly 3000, not more, not less? It's the OBD time!

[mrvandango]

So if it's potentially the ecu cutting off the power then this would suggest it's one of the engine sensors perhaps? I did order an ELM unit, but it wouldn't connect to the ecu. Apparently I need one designed for a diesel, whereas I didn't know there were different kinds. I have ordered a new one, so will see what comes up. I figured that a fault like this would trigger the engine management light.

I'd love to get it sorted, as besides this issue and the steering lock it runs beautifully.

Thanks for the input and help guys!

[MilosB]

you need a proper diagnostics tool, not cheap adapters. dont waste your time or money.
dont believe the sellers.

get to some garage that does know how to use a diag tool and take the car for a run,
plut values like :
Maf,
Map,
injection quantity
rpm

[AlexB]

Set ELM327 to scan all protocols - it will find the appropriate one. Almost all data mentioned by Milos are accessible by ELM, because it's an open standard. More advanced stuff is proprietary and needs Clip computer. Compare the ELM datasheet to the factory workshop manual for this car to see what is accessible and how. If ELM327 doesn't connect, then there's likely to be a fault either in the connector or the device.