Intermittent Misfire | Appears fine, suddenly starts misfiring, then snaps out, repeat

[James28]

I am getting an intermittent misfire whilst driving. Car will appear to be driving fine, but then all of a sudden will start misfiring, and I don't mean just running lumpy, it will lose the majority of power for say ten/twenty seconds, before seemingly snapping out of it and working fine. Repeat multiple times.

When I say intermittent, it's to the point where it's not driveable. Pretty much can't go above 70mph without it happening, and it also happens at lower speed too.

For the most part there's no warning lights on the dash or anything, but then the other day the emission light came on so plugged in and it threw up fault codes for the emission sensor and misfire detected on cylinder 2. It was due a oil/plug change and I already had the bits so quickly did that today and cleared the fault codes. First drive and it's still there, started happening again on my way back from petrol station. No warning lights on dash and no fault codes though so can't really diagnose.

Probably a bit of a stab in the dark, but anyone experienced a similiar issue? The car was sat around for a while (3 months ish) so I'm a bit concerned it's fuel filter/pump related due to the fuel having sat around. Other possibilities I can think of are injectors?

 

[Rojer]

Sounds similar to issues i had, turned out to be TDC sensor. If you give the wires to the sensor a little wiggle and the car cuts out then thats the issue.

 

[Greeny.]

Had exactly the same thing on my old 172 a few years back, it was intermittent on and off for months but then and suddenly stopped firing all together, ended up being a injector issue.

 

[Rojer]

Seems more likely to be an injector especially as you had a fault for misfire.

 

[cmcquitty]

Another vote for injector no.2. Does it misfire on idle when it's bad? If it does, you could unplug it on idle to confirm.

 

[R3k1355]

Misfire sounds like the injector, but if you're getting O2 sensor fault as well you might also be looking at the 1st lambda sensor too.

 

[Darren S]

Have you rinsed/steam-washed your engine recently? Been there - done that, with exactly the same symptoms. Those spark plug pots are like the perfectly shaped champagne flutes for holding and trapping water.

That said, it did sound good to be a Scooby for a short while.....

 

[Iain C]

I'd say injector

 

[pete_rawli]

Injectors?

 

[James28]

Cheers guys.
1. Is there any way of testing injectors?
2. Do I need to replace all at same time or is it fine to just replace one
3. Best place to source replacements / best brands to go for?

 

[R3k1355]

Code reader should tell you which injector is at fault.
You can just replace the one, but don't be surprised if another one starts giving you grief soon after.

Genuine Magneti Marelli injectors are best, part number 805001446001 I think, Renault number is
8200207049.
You can usually find a set online cheaper than from Renault.

 

[jamesycc]

Injector most likely. You'll only get a code if its a failed injector and the eml flashes up.

Mine was intermittent so had to wait until it misfired whilst driving and leave the obd reader plugged in.

As soon as the eml flashed I ran a scan until I got a code telling me which cylinder it was.

Was a pain.

 

[James28]

So I replaced injector on cylinder 2 and issue is still there.

It's weird. When it happens it's also as if the throttle pedal just stops doing anything at all, it'll start misfiring and the throttle will be unresponsive to me pushing it. Then all of a sudden it'll snap out of it, run fine and throttle will kick in again. I'm talking like ten second intervals