HDI 90 Jerky / Hesitation / Flat Spot

[adam03031980]

Well title sort of says it im not sure how ypu describe it but when you change gear theres like a delay in power or may even be noticed as Jerky / Hesitation / Flat Spot when changing gear not a smooth change like my old 110 is this a common problem or has anyone had similar

[piglet]

Adam,
Mine too.
1300-1500rpm flatspot, hesitates, kangaroos. Makes town driving painful.
So far I have blanked the EGR, changed all filters and flushed with injector cleaner.
My next step is to get local garage to read codes and pass his opinion.

I had an aircooled RD250 that was just the same. That makes me sound very old.

[adam03031980]

I kept thinking inkectors but the leak off was pretty much perfect as the car sounds like an old transit, it got better once when i disconnected the battery and the ecu for about 30 minutes when i was replacing a sensor and dropped a clip ahem i am wondering the throttle position sensor is playing up just need to figure out whats best to clean it. Tried a couple of garages but to be honest round here they know less than i know and thats saying something

[piglet]

RWB suggested changing throttle position potentiometer, see my earlier thread:
'2003 56K Siemens Hdi90 poor slow running' it's on page 2 now.
It's a possibility, but so is the MAF, clutch sensor, LAMDA (if it has one).
Could easily end up buying a lot of expensive parts and still have the problem.

Interesting about the ECU, and yes my local guy is much the same, good at fitting clutches and getting MOT's but no rocket scientist.

Are you on Bosch or Siemens? What are you getting to the gallon? I'm only getting low 40's

[Gary406]

low 40s sounds right for town driving ?

[piglet]

Mostly rural commuting, don't do too much heavy traffic.
40-50mph mostly.
I had hoped for better.

[adam03031980]

on average about 43mpg which is less than my 110 that could get nearer 60 on a run and all i do is sit on the A1 most of the time, mines a siemens. I have replaced a lot of parts but luckily my brother gets parts at cost i might try and clean up the TPS see if that helps just gets a ball ache spending every weekend trying to cure and unknown problem as mine also has an issue starting when cold ie below about 7c

[piglet]

Same, 43mpg, 40 if I'm towing.
Have you had a new MAF?

[adam03031980]

Yeah new maf didnt make a difference from the old one but kept it anyway new coolant temp sensor and filters too, i have noticed after a long drive that if i pull over and just gently blip throttle with the window down i can hear a very faint whistle but i dont think its the turbo might try disconnecting the egr saturday and go on a 10 mile drive see if that has any affect

[piglet]

Fitting the EGR blank plate did improve low revs, but it was marginal.

[adam03031980]

Just checked today as i fitted the new maf and after my work run i managed 58.39 mpg but that was doing 60 - 65mph, im going to enquire how much i can get a throttle position sensor and if not too much i will just change i also think that maybe the lower engine mount may be perished causing some of the sensation

[adam03031980]

btw the maf was fitted last weekend so probably wasnt too easy to tell the difference at first

[Blubayou]

Hi there,

My HDi 90 with Siemens control has had flat spots all the time I've had it too. Not a major issue, when I get them I give the priming bulb a good pump before starting then when running for a couple of days. There's always loads of air comes thro' and it's always a lot better after.

I guess the engine mounted pump is drawing in air somewhere.

I suspect the Siemens system is a bit of a lemon.

Hope this helps.

[martint]

Just think diesel 406's are quirky & all have certain flat spots to a degree, but when folk start blanking egr's i just dont get it. What benefits did doing it, give you? Was it because of smoke?

[piglet]

Adam, 58 is a massive mpg improvement on your 43, how's the flatspot, just the same?
How much was the MAF, and was it OEM or pattern?

Martin, blanking the EGR was just a cheap & easy place to start. The rational was if the EGR is blanked off it can't be interferring with low speed running.
Fitting the plate gave a tiny performance improvement but made difference to my poor running, I wouldn't consider it a tuning mod by any means. I may well take it out when i've 'finished' fiddling.

Interesting idea about air bubbles Blubayou, that would go with the surging feeling though wouldn't explain why it's so rpm specific.
Out of interest, tell us what your Siemens set up is giving to the gallon.
Don't like the idea that I've bought another lemon. What's in the 407's?