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Weird engine cutting out

  BMW 320d Sport

I know someone had this same problem a month or two ago but I cant remember who. Anyway it just started happening as I was on my way down from York tonight. At first I thought it was my imagination or Id gone over a bump in the road, but what happened was just for an instant the engine missed a beat. Ive had weird things like this happen before; while racing Simon and caning the nitrous the engine cut out totally when I let off the power, today it was doing it while the engine wasnt under any load really just normal slowish driving in A1 traffic, usually at only a quarter throttle, gentle acceleration - it would just cut out for a fraction of a second, enough to feel the jerk, then come back straight away.

Any ideas? Looks like an electrical problem to me cos its not a constant thing and keeps coming and going.

Sounds like a bad connection. Ive had this a long time ago. The wire was very worn - like a couple of strands left, so cut and rejoined. But to find it was a bummer !
  Skoda Fabia vRS

well i had the returning to idle problem, but this doesnt sound like the same thing

You should check your engine faultcodes. My 16v did just the same thing, and faultcodes showed throttle potentiometer to be blamed for. Changing it helped, no more jerking. But it wasnt a cheap one, so you should first check the codes.

I had the same problem in my RT when my alturnator was dying. Bad Earth turned out to be the problem.
  Skoda Fabia vRS

Koivis, how are you checking the codes ?

afaik no one makes a fault code reader for Renaults...........

Nick, sounds like ignition problems... might be worth checking the r****d unit as this could cause the problems..

will be a nightmare to diagnose though unless you can make it happen more often...

it was me who had it, but never found the problem, hasnt happened for a while now though.
  BMW 320d Sport

Well its not done it today either. I did think of the ignition coil mods that Ive got but by my thinking, theyve been on for a couple of months now and not a single glitch, so it cant really be them. then suddenly yesterday after a long cruise down the A1, it was cutting occasionally. It was always at very gentle throttle positions and speeds so the engine under hardly any pressure at all. All the coil connections look ok and it cant be the plugs or leads cos otherwise theyd do it all the time. Ill break out the XR 25 and see what it says.

If only the 16v actually *had* a throttle position sensor, Id have a look at it! Im suspecting the alternator/battery though. Over the summer its had a bad habit of lighting up the battery light when on the motorway (high revs) at night in the rain, when you wind the window up to the top. Someone else had that problem as well didnt they?
  Skoda Fabia vRS

i think i might be havin alternator trouble now

and Joe, Halfords dont sell a Renault code reader, if you can prove me wrong i will gladly buy one NOW, ive wanted one for ages trust me ive looked

Nick: what yearmodel is your car? In my -91 there is a throttle position sensor. I doubt it has changed. Just go look at the butterfly housing and you can see it at the radiator side of the throttle axle. I had just the same symptoms, jerking at part throttle, mostly at steady speeds.

F7P engine RENIX ECU has MAP sensor, inlet air temperature sensor and tp-sensor instead of airflow meter (or airmass meter). If it had only MAP-sensor, throttle response would be slow, because plenum pressure doesnt change instantly according to throttle position. Thats why there is a tp-sensor, giving ECU chance of reacting fast to throttle changes.


me and arron had this ages ago and ive never traced the problem but being a reno it could actually be anything causing this to happen,

mine use to do say cruing at a constant 80-90 on the motorways and never did it round town or while accelerating on the M-ways.

ive had a new alternator, new starter and new fuel filter, but ur car is sound mechanically as its almost all new so u can try the fuel filter. its only a 10 anyway or it could be dirty fuel. . other then this its like what ive been thorugh and expensive trial and error mate, your gonna be running round in circles and its especially hard to fing as it only does it now and again not always.

  Skoda Fabia vRS

how did you fix yours Paul

and ATTN KOIVIS could you please tell me how you have read the fault codes stored in the ECU, as i wasnt aware there was a home reader available
  BMW 320d Sport

looks like lots of answers here then. Ill get it up in the air at the weekend and check all the earth straps, see if thats the problem. It hasnt done it at all today either.

BTW Koivis, I was pretty sure the ECU runs the fuel/ignition map by a combination of MAP reading, inlet temperature and engine speed. Ill check again.

Hi Nick, the ecu maintains stoich until WOT occurs.. it then has ti switch to the WOT table,,, (thats triggered by the wot microswitch or signal)

Map and rpm are 2 axis of the table, coolant or inlet tem is purely a scalar.. it adds a predesignated formula to the mass calculation

the primary sensors are MAP, RPM and WOT..

all the rest are simply scale factors.

here a tip m8.. to test for a bad earth.... dont.......... just add another giid earth strap.. if it help, its inducative of a strap problem...

sorry, yes to add. the tp is also monitored as well as WOT.. the RATE of change is signaled to the ecu to apply rate enrichment (to combat lag)..

there is even a table for degrees per sec enrichment in there
  Skoda Fabia vRS

Joe, do you know how much it is, if its reasonably priced ill be goin very soon to buy it

ill try an remember to ring them tomorrow