MatraSport Forum

Each model => Espace => Topic started by: renaultbiler on July 19, 2008, 06:47:53 pm

Title: Espace V6 L7X 3.0 spark plugs
Post by: renaultbiler on July 19, 2008, 06:47:53 pm
I have been struggelig with the L7X for a while as it have been slightly misfiring on low revs and high torque, and only occaisonally. Not really a problem but still annoying.

First thing was i replaced the coil.
- No improvement.

Then i replaced the spark plugs, since Renault original is expencive and the manual says NGK (also expencive) i went for the Bosch platinum option as it was very accessible at the time.
- No improvement. (old ones on it was NGK)

Then i replaced the HT leads
(very expencive here so it was out of reach when replacing spark plugs at the time, cost from Volvo was over 3000 NOK !!!!! thats roughly 350 euros, from Germany i got them for like 80 euros).
- No improvement.

Then i replaced the cat, it was noisy anyways after 120k - scrambling occaisonally
- No improvement

No fault codes on it at any time other than the lambda warning for unburned fuel (richness regulation). The auto box has no faults either, it have crossed my mind that a problem on the auto box could easily affect the engine performance.

After some searching on various forums, from time to time measuring and searching on the car without results, i found that there seemed to be the BERU UXF79P (ULTRA-X platin) spark plugs to be preferred by some other owners both on price and reliability, its a fairly cheap alternative -so i took a few hours and changed from Bosch to BERU -as a last resort kinda thing...

The car now seems OK and have been so for the last couple of days  :) (cross fingers)

Anyone with similar experiences ?
Anyone that have a printout of ok and live values when the car is running ?

Only thing that is still bothering me is that the positive readout (diagnostics) of the feed to the autobox computer is around 11v while the ecu says 13.5v. When measuring actual voltage while engine running with multimeter on the auto computer it gets the full 13.5v (diagnostics say 11v at the same time). So it might still be a problem there, either with computer or wiring causing this funny voltage state. Whether or not this has anything to do with the misfiring issue.... well - a "test" autobox computer is not on every corner around here.

Title: Re: Espace V6 L7X 3.0 spark plugs
Post by: Anders Dinsen on July 19, 2008, 09:00:42 pm
Hei Tom

My experiences with running problems and our wonderfuld V6 engines are the following:

- Running problems and stalling in idle and while warming up: Defective coolant temperature sensor
- Misfires during slight acceleration: Rusty coils, i.e. weak spart. Replacing the coils cured the problem.

I don't know which spark plugs I run, except that it's the ones Renault recommended in 2004, when they were changed last time.

About the 11V vs the 13.5V - I think you may have a problem there. The voltage is used as a correction coefficient to increase the timing on the injectors to compensate for the slower opening when the voltage is lower. So if the ECU thinks the battery voltage is lower than it actually is, then it may mean that the engine actually runs a slight bit too rich. The oxygen sensor will correct it, but it may still give prolems when the oxygens sensor isn't used: Full load and acceleration.

- Anders

Title: Re: Espace V6 L7X 3.0 spark plugs
Post by: renaultbiler on July 19, 2008, 09:31:17 pm
The 11v is on the auto box computer, engine computer is fine. Still they talk together with different subjects than weather and hello so it could be something. Like a 94 Laguna non starter i fixed here the other day, ECU supply showed 16v on CLIP and temp sensors flimmering up and down and a mess of readings on the throttle signal -while the actual battery voltage was 11.8v. All this was caused by the 5v on throttle pot cable was gently and "invisible" melted onto the exhaust manifoil heading shield. So some faults really gives weird readouts on diagnostics and does not point out what the actual problem component is. AND the computer messes up several parameters even if they are not the problem.

I was once crossing a path in my mind that wispered to try yet another new coil to see if i was given a "weak" one when i replaced it, but they are a bit too expencive to have fun with too.

Lets see if the problem remains history after the spark plugs trick. ::)

Title: Re: Espace V6 L7X 3.0 spark plugs
Post by: Anders Dinsen on July 19, 2008, 10:25:31 pm
Sorry, apparantly I didn't read your post, Tom :) I thought it was the ECU. I don't know what the auto box computer would need to know the voltage for, but it's odd that it thinks it's only 11V. Tt's probably not important, then...

I have come to beleive that spark means a lot on this engine, but I'm not sure why - I know the ECU retards the ignition on request from the auto box when it's about to change gears and do other things where it's beneficial to have a lower torque coming from the engine, and I know it also advances it as much as possible (before pinking) to get the most torque when you press the throttle.

Being an oversquare design (as all V-engines tend to be), ignition timing means a lot, and I guess (but I'm only speculating) that if you have a lot of carbon deposits in the combustion chamber, so it pinks more easily, the ECU isn't able to advance the igntiion far enough to produce torque.

Fact is that after replacing the coils, I have found our car much more responsive - same way as it acted before, when I ran it on on 98 octane petrol. After I replaced the coils, there's no noticable difference between 95 and 98, so guess what I'm buying ;)

I'm a bit confused, but my wife is happy: I've fixed her car with a new set of coils... ;D

- Anders 8)

Title: Re: Espace V6 L7X 3.0 spark plugs
Post by: renaultbiler on July 19, 2008, 11:51:28 pm
im also running 95 since i cannot find any better performance running 98.

The engine computer and auto computer are connected to each other by 4 wires:

6     ---   39      Engine Torque Information from ECU
31   ---   38      Trottle Position Information from ECU
42   ---   51      Torque Reduction signal from AUTO -> ECU
43   ---   40      Engine Speed Information from ECU (rpm)

Communication is with pulses on all of these, so any difference in supply voltage between the computers would not affect the signal handling imo.

So they talk about how to handle torque all day long  ;D

Title: Re: Espace V6 L7X 3.0 spark plugs
Post by: renaultbiler on July 20, 2008, 09:42:20 pm
Just confirming the BERU choice - had a 400km trip with it today and no misfire at all and its running smooth like a cozy cat again :) In the nearby area i had a few places where the engine misfired every time (downhill, uphill, speed and trottle conditions) and now it is history after several testruns over the past days.

So i will stick to the BERU spark plugs next time for sure!

The problem seems to be a general weak coil spec on the Espace version of this engine, resulting in it being very selective about the spark plugs in order to fire properly each time.

Adding the link to pictures of howto replace the spark plugs without lowering the engine:

Title: Re: Espace V6 L7X 3.0 spark plugs
Post by: Anders Dinsen on July 23, 2008, 05:29:49 pm
Great to hear that you've fixed the problem, Tom!

- Anders