M400 "stuttering" problems

[chillidog]

My M400 developed a very bad "stutter" today at Snetterton.

Basically the symptons are this

1. At idle, the idle speed is too high @1500 rpm

2. Although under no load it revs freely, under load conditions it reaches around 4000 rpm and then stutters (it's just like it's hit an electronic rev limiter). It won't rev above 4000 rpm under load.

3. I've been getting pops and small bangs on the overrun for a while now, but put it down to sticky throttle cable. However the cable has been fixed and the "backfires" are much worse; maybe this is what's causing the exhaust bracket to break so frequently.

4. When I *gently* press the throttle under no load conditions, the revs initially drop slightly and then pick up as expected. I also notice the same effect that revving the engine using the "rocker" at the engine end of the throttle cable (ie. the other end to the foot pedal) so I don't think it's the new throttle cable related.

5. When driving and depressing the clutch the revs take ages to some down; it's as if the throttle cable is sticking again but I don't think that's the cause.

6. I'm also beginning to think that even prior to today's problem the performance has been lower than it should be; I feel I really should be spanking some of the other cars at track days more often and with more ease, especially in a straight line drag race where driver skill has less effect.

7. The boost gauge seems to indicate that things are working in that department, getting to around +0.7.

So basically it's running very badly at the moment and the dealer and factory are (quite reasonably) on holiday. My pride and joy is sick so has anyone got an idea as to the problem?

--
Richard

[joust]

Sounds like a simple broken lambda sensor. I had exactly the same symptoms on my 2.5l

The annoying thing is that it's only £20 or so, but they don't seem to be very "strong".

Hope that's what it is!

J

[chillidog]

joust said:

Sounds like a simple broken lambda sensor. I had exactly the same symptoms on my 2.5l The annoying thing is that it's only £20 or so, but they don't seem to be very "strong". Hope that's what it is! J

Ta for that - hope you're right. With all the weird symptoms that could make sense.

So frustrating as it's a good weekend for a drive and Snetterton was becoming a lot of fun. Ah well, all cars break every so often.

Hope you have a good day at Mallory tomorrow.
--
Richard

[joust]

chillidog said:

Ta for that - hope you're right. With all the weird symptoms that could make sense.

So do I!

chillidog said:

Hope you have a good day at Mallory tomorrow.

Should do. Paul's racing his 2.5, and I'm hoping Lee will be along with his M400 patched up after the barging a few weekends ago a Brands.

It'll be nice to sit down and watch some people I know racing! Wouldn't get me out there though!

J

[paulcundy]

Dear Justin,
As far as we know Lee is not coming (not registered, not applied, not at pre race practice, not in listings).
I'm racing against a westfield, a bunch of motorsports Exiges/Elises, a pair of atoms and a 340 amongst others.
I'm also in the Endurance race but am doing both stints myself, so a Red Bull will be in the pit lane for driver re-fueling.

I've never driven Mallory before - its a brilliant little circuit

Steve Rubie-Todd was there on friday with his just run in M400 - I was able to keep up with him but only just, lapping at 55-56 seconds with my best being a 54.5.

Regards
Paul C

[3rtt]

Richard, sometimes the ECU has been known to through a "hissy fit" for no real reason. This may have been the cause to your simptoms.

I'm sure the factory will verify when they return after the weekend.

Cheers,
Ian.

[Matt_FP]

Lambda Sensor gone south is the most likely. However it would be hard to narrow it down without plugging the lappy in and seeing what the ECU was seeing.

Best Regards
Matt

P.S. Paul - I clocked you at a 54.10

[turnbaugh]

chilidog,

Good luck and please let us know what you find as the problem.

I would like to keep a log of these things in case someone needs to know in the future.

Dean T

[robp]

joust said:

Sounds like a simple broken lambda sensor. I had exactly the same symptoms on my 2.5l The annoying thing is that it's only £20 or so, but they don't seem to be very "strong".

Richard - I agree with Joust and others. Could be straightforward sensor malfunction, but if not you may need to get the cat converter checked out. On my 3R I had a similar problem which was only evident on the track - fine at first but after driving for 5-6 mins it appeared to hit a rev limiter and lose power to such an extent that Audi TTs were overtaking me on the straight at Donny -shock horror. Initially thought it was a fuelling issue but after much time back at the factory and out at Brunters it transpired that the cat converter had 'collapsed' internally - reducing exhaust flow and increasing exhaust temps (water temp -remained resolutely normal). With the high exhaust gas temps the lambda sensor simply shut down fuelling. Once fixed and with a spanking new map courtesy of Yellowshed - never looked back!

[honestbob]

Don't ignore the basics when things misbehave.I had misfires under heavy acceleration and after two ECU's exchanged under warranty,it turned out to be bloody spark plugs!

[chillidog]

A brief update: the faults have been fixed very promptly by my local dealer (Kerridges).

1. Loose (vacuum?) hose to turbo fixed (sorry didn't get all the technical details). This cured the high idle speed problem.

Other problems fixed by replacing the ECU. I think they pretty much checked everything before doing this including changing the plugs and checking the various sensors with the laptop.

She's now running very well, no pops or splutters on the overrun and "pulling" like it should.

Thanks to the dealer for the prompt work.

Happy again
--
Richard

[joust]

Glad you got it sorted!

J

[robp]

Yep - happy you're fettled again, Richard.
Day 4 for me was seeing mine on the back of a flat-bed truck on it's way back to the dealer. On the plus side -I now know my tracker works. Hopefully will return promptly with steering fixed and other bits sorted.