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Modus 1.4 limp or not?

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limp modus
3K views 13 replies 3 participants last post by  Zxdan 
#1 ·
Hello expert Elf's.

After doing some research I have discovered similar posts, but not the same.

I start the vehicle in the morning and drive for about half an hour on open road with not much traffic no problems power acceleration all good.
I come to a bottleneck on the freeway where you are forced to standstill.
Watching the rev counter, it suddenly drops by 200rpm within 15 seconds.
When trying to accelerate again the vehicle coughs, splutters and backfires when changing gears.
When traffic has resolved and the vehicle is still in this state once the accelerator pedal is pushed flat against the floor all the power comes back and that is the only drive-able position on the accelerator.
I you carry on for 5min or so it clears and the idling revs come up by 200rpm and the whole accelerator pedal is available again.

In a nutshell, if you keep the vehicle above 1500rpm it will never go into this mode, but if you start to idle then within 20sec it comes back.

What be the thoughts on this one, is this limp mode or not?

Many thanks
Cheers

Zedd
 
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#3 ·
Thanks, I already did that, it was very dirty. Sprayed it out with carburetor cleaner.
I have a 2l Scenic, on that vehicle I took throttle body out and even opened it up where it is is factory sealed and found the mechanism on the inside was also very dirty, just have no idea how the dirt gets into the sealed unit.
Maybe I should open up this one as well.
 
#4 ·
Hello again Elf's

I wish to update my progress.
After finding the alternator fault, the battery charge fault has never returned. However vehicle will start perfectly and idle at about 1000 rpm if left to idle within a minute the revs drop to 800 rpm, if you try to drive now the vehicle feels like its running on two pistons.
If you are persistent and keep foot flat on accelerator it coughs and backfires and eventually takes off. Once you let it idle again the fault returns, but if you get onto a main road without any stops it clears completely until you get back to stopping, then it faulty condition all over.
Found a fuel filter that was completely blocked and somehow the vehicle still managed to run. (replaced)
I have two alarms
Airbag and steering, I don't know the reason for the steering because the steering works just fine.

I have already replaced the:
injectors
coils
spark plugs
key set ecu and fuse box
all the sensors except crank sensor, which I cleaned
throttle body

Its been taking me weeks to sort out and I don't seem to be getting any closer

Any ideas anyone?
 
#5 ·
Hello everyone,

I would like to update progress, went to buy new inlet manifold seals from Renault, were I fount a workshop manager and he told the vehicle will never go into limp mode if the engine light is not shining. So that ends all my speculation on limp mode.
I then told him what the car does with the spluttering on idle and in the meantime I also discovered that when pushed hard on uphill it seams to suffer from fuel starvation.
He said I should check pump pressure and should not be below 3.5 kpa.
My test showed 3.3 kpa, so I blocked off the return flow and pressure went up to 4kpa.
I just reconnected the engine injector rail and spluttering disappeared, so I'm off to buy a new pump.

I would never have thought of this myself because logic tells me that if a fuel pressure problem exists, it should only affect the vehicle at a higher speed and not at idle.

Anyway hopefully some can learn from my experience, I will complete the repairs and write a final post if successful.

Cheers Zedd.
 
#7 ·
Hi thanks for the comment,

The return flow is just after the external fuel filter by the tank, guess that is how they regulate the pressure.
If I measure pressure right at output of fuel pump, there is no return flow and is about 6 kpa, by the time fuel is in the front by the injector rail its at 4 kpa with return fuel line blocked.What I deduce from this is that its one of 3 things.
1) Pipe from pump to injector rail restricted.
2) Fuel pump pressure too low.
3) Return flow circuit too open, (too much flow)

I wish someone here on the forum knew exactly what the pressure specs are.

What are the opinions?
 
#8 ·
Where are you measuring fuel pressure,.
fuel pressure is measured off fuel rail,...
Is it a genuine fuel filter,, some after market fuel filters restrict.
What happens driving up a steep bank, does the car hold back, usually it does if not enough fuel pressure.
+- 0.6 BAR is the tolerance,,, it is 3.5 bar,
Now how accurate is your pressure gauge..????
Could have a lazy fuel pump, but does not normally show on tickover, more when being pushed hard...
(not much fuel needed, or pressure under NO-LOAD conditions)


What about connection to the accelerator pedal,, has this been checked
 
#9 ·
Hi ours 2012

Thank you for your input.

I used a compression tester, with a BAR scale, seems accurate enough. I have a vacuum gauge as well that has a PSI scale for fuel pressure, but I found this to be worthless, I think because it is not intended to work with fuel injection but carb pumps which are very low pressure.
I disconnected the fuel line directly from the pump and output from pump is 6 BAR, reconnected the line and disconnected plug from injector rail, measured on the fuel connector, the one that connects to the injector rail and get about 3.3 BAR there.
I bought a new pump, they are relatively cheap (after market) not genuine. and also replaced the fuel regulator on the return flow in the fuel pump housing. There is no change, only once I block off the return flow the pressure at the injector rail goes up to just under 4 BAR and the car runs fine, no missing no spluttering.

Would the fuel pump deliver a constant pressure or is it variably controlled as you drive by computer?
Where should I be taking a reading on the injector rail because I'm only taking readings with the engine not running?
I also already replaced the accelerator pedal, also no change.

I now have so many spares that I think I'll get me a non runner real cheap and see if I can get it to run and sell it.:smile2:

Many thanks for your help so far.

Cheers Zedd
 
#12 ·
Hi friends

I just remembered, I might have left an important detail out. When I bought the car, it wasn't great and first thing that went was the catalytic converter, totally blocked the exhaust so much so that it burst the braided wire flexible coupling in the front by the manifold, I decided to take it in to a exhaust specialist that put in a free flow exhaust and removed the cat. (legal in this country)
Question, would the oxygen sensors not be giving the wrong readings to ecu if exhaust was incorrect? That might affect the injector, pressure or injection time?
Does the fuel pump pump have the same pressure all round or does it increase pressure with more fuel consumption

regards

Zedd
 
#13 ·
Dunno if you can sort any real time readouts while driving ?
Trim values, throttle, Air, whatever.
And see if anything seems out when you get the issue.
May be able to work back from that?

Or the old fashioned.

Run it for ten minutes when all okay.
Stop, pull the plugs, check colour, take photos, make sure you know what pot they come out of.

Cause the problem, stop.
Pull the plugs....see what differences?
Wet/black would infer too much fuel or not enough air.
White, too little fuel/too much air.
And are they all the same ?
 
#14 ·
Hello, final update all sorted.


Took three different lower lambda censors and an original exhaust in order to get fixed, now I have a performance open free flow spare exhaust lying around and not getting used. Took the Renault garage about a week to fix.
Something they told me that doesn't make sense to me is, that the free flow exhaust seemed to cause the lambda failure.


Cheers


Zedd
 
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