R400D Spluttering engine & bouncing speedo

[Tomiam]

I'll try and keep this concise so the information is presented clearly.

Driving to a track day:-
All good starting and driving for first hour.
Went up the motorway and stopped in service station.  Slight grounding out on the speed bump at low speed but nothing major.  Got food.  Restarted fine.
Drove out of the service station, onto the slip road (this took about 2 mins) and gave it a blast.  3/4 to full throttle.
Went perfectly fine.
Joined traffic and lifted off and the engine started spluttering.  Just like if you had a duff lambda sensor and the engine runs too rich.
Kept going on low to medium throttle and it was just about detectable but nothing bad.
Within 2 mins, all perfectly fine.
I do notice that at about 2.5k rpm the engine is a little 'bumpy' but its very very minor.  

Two and a half hours later into the trip and I give it another blast for about 15 seconds.
Lift off and the same as above.
We stop for fuel, station has 95 octane only so that goes in.

We spent the night in a hotel.  No rain.
Got up in the morning, car starts fine no issues. I give a medium squeeze of throttle on the way to the track day, no issues.

First session on track
Anything over about 4k rpm and SPLUTTER SPLUTTER SPLUTTER.  Very bad. Massively down on power.

Had a look over the car and nothing obvious.  All seems ok.
Spark plugs look a little lean. Quite light brown / grey.
Someone suggests reseting the ECU as the 95 octane might be causing an issue.
After reset it runs terrible so I take it a fuel station and put super unleaded in.  
This doesnt change anything. (NOTE: On the trip home we practically ran her out of fuel and then put 97 octane in.  No difference)

A few more sessions on track for a couple of laps each time and its getting slightly worse.  
Pulling away, its spluttering and nearly stallling.  Give it a ton of revs and it will pull away , just.
90mph is a push to achieve and the engine is spluttering like mad.

We call it a day and decide to drive home (4hr journey..)
Engine is progressively getting worse and its spluttering all the time on the trip back.  Hugely down on power  and feels a bit like its hesitating when the throttle is pressed and then spluttering / rarely surging forward.

I notice on the motorway that the speedo is very minorly fluctuating about 2 - 3 mph over / below the speed we're doing. As if the needle is bouncing.

We come off the motorway and onto the 3 miles of normal road to my home.  Speedo is bouncing all over the place about 10 mph over / below where it should be.    
Not sure if this is getting worse because of lower speed or because the problem is getting worse.

Made it home.  

I have the cable to connect her to a laptop.
I have limited mechanical / electrical knowledge but Im getting there.
I would welcome thoughts as to what area I should be looking at please as Im not sure if the speedo bouncing is connected or not.

My own thoughts on the spluttering are:
Fuel pump dying?  
TPS?
Injectors?

Any help very gratefully received as Im meant to be sprinting next weekend! :)


 

[Jonathan Kay]

Can you replicate the splutter etc with it in the garage?

What sort of speedometer?

Jonathan

[SM25T]

This sounds like you have a speedo sensor on the rear wheel. The cable to the sensor is known to fray and cause shorts .... sometimes killing engine completely. The power seems to be shared with the ecu or something vital. Unplug the sensor and see how it runs ... albeit with no speedo.

[SM25T]

Not sure where the plug connector is .... but in other cases it has solved the issue.

[Jonathan Kay]

Have you got a wiring diagram or do you want one?

Interesting suggestion from Ian... you need to disconnect the feed as upstream as possible to test that.

Jonathan

PS: Do you have a multimeter to hand?

[Tomiam]

Cheers for the info folks. Been away for two days and wife has determined I need to take her to Costa. .

Sneaking in a relay whilst she is getting coffee again..

I have a wiring diagram and multimeter. Will give more info once home.

Thank you very much for assistance!! :)

[Tomiam]

Unplugged speedo sensor by disconnecting plug at rear right wheel.

Started car. Same issues even with it stationary. Can hear it spluttering.

Tested lambda sensor. With diagnostic cable connected I can see the lambda flicking above / below 1.00 so I'm ruling out fuel / air leak.

Have a electronics diagram.. have multi meter..

Working out where to go next.

 

 

[Jonathan Kay]

If the known problem with the speedometer is a short higher up the feed than that (does anyone know?) you may need to disconnect somewhere else instead to see if that's the problem.

Which fuse does it run off?

Jonathan

[SM25T]

I have asked Mike Clark .... as it was his car that died with this fault on the IOM ..... but he is marshalling at Brands today.

[SM25T]

If the cable is damaged where the surplus length is cable tied to the chassis at the rear .... you will need to disconnect the cable a lot further forward.

[Tomiam]

Righto... I think (well tbh.. Im bloody sure) Ive found the fault.

Despite checking the spark plugs / wires etc , one of the wires had a break in it.  Once Id pulled back the tape covering it, it was nearly sheared off!  I guess the engine vibration had caused this.

Speedo is still disconnected and Im 30 mins late for my sisters birthday party.... so ive got to dash but will take her out for a drive tomorrow.  Pretty confident given the massive improvement in engine tone that the spluttering is fixed though.

Speedo cable.. I will investigate tomorrow.

Worrying though.. as one wire has snapped.. whats to stop the others going? Is it worth me replacing them?

 

THANK YOU! again to everyone for their help and advice.  It IS very much appreciated. :)
and.... Im gaining knowledge! :)

 

 

[Jonathan Kay]

Well done.

Worrying though.. as one wire has snapped.. whats to stop the others going? Is it worth me replacing them?

Good thinking. I suppose it depends on the cause of the failure. Was the run of cable nice? How old are they? Can you add a photo?

Does anyone know if there's a reported problem?

Jonathan

[john aston]

You won't be as daft as I was but anyway......I had precisely the same symptoms in my R400D a few years ago. I blush to admit that some idiot had failed to tighten the battery terminals properly. Intermittent for a week or two and then worse and worse. .

[ScottR400D]

Which wire was at fault?

[John Vine]

Pleased to hear you may have diagnosed the fault.

There are two well-known problems with R400D (and R300D) engine wiring: TPS and coil-on-plug (COP).  IME, they are both caused by high-frequency vibration. 

When you say "one of the wires had a break in it", do you mean one of the pair of wires that feeds one of the COPs?  And, in particular, where the wires enter the COP connector?  If so, that's exactly the problem I encountered (on #1 cylinder).

The solution (TPS and COP) is to replace the original wiring with upgraded race looms incorporating silicone-sheathed cabling.  For the COP wiring loom, you need the flexi-loom.  Note that you may need to do some loom splicing.  For info, there are some photos here of my repair.

JV

 

[Tomiam]

Fantastic info. Thank you. :)

 

The break sounds in exactly the same place as yours John.

The break in the wiring was just before the clip which connects to the COP. As in .. about 2 mm before. The cylinder was the furthest one from the drivers seat (don't know what number that is sorry.)

 

I shall look into that race loom.

 

[Tomiam]

When I say 'look into' I mean... I just ordered one. :)

For reference : my r400 was registered in 2008. Has done 15.5k miles and has been garaged since I got her last year.

All wiring is secured in place with cable ties and loom tape. Ie. Very little movement apart from at the point where wires connect to the coil on plugs. Wires at this point are not tight.

 

Hope this info helps someone :)

[SM25T]

No. 1 cylinder at the front of the car.

[Jonathan Kay]

... looking forward to hearing if fixing the ignition fixes the speedometer problem...

Jonathan

[Tomiam]

45 min test drive complete.

Speedo working as normal.

Engine behaving 99% as normal, the odd splutter when I'm in 5th or 6th, 2k rpm and I put my foot down. Doesn't do it if I'm in correct gear. Happened twice on the trip and last about 4 seconds.

The odd 'miss' coming from the engine at 2.5k rpm in 5th or 6th but it's so infrequent that it's not an issue and was there prior to fault as reported above.

 

Will replace existing COP loom with race flexible loom and see if those minor niggles go. At worst it's future proofing it, at best I may have a minor break starting to happen and I'm avoiding being stranded.

 

[Jonathan Kay]

:-)

Jonathan

PS: "... stranded" :-)

[Tomiam]

Took me a while to get it :)

[John Vine]

A thought.... do you have a cat fitted? 

If you were suffering from a persistent misfire, it would be worth checking the internal matrix (at the front where the collector feeds in), as misfiring over a long period can seriously damage the cat's health.  (Horror pics here.)

JV
 

[Tomiam]

Good.point John. I will check.later.

Flexi loom is due here Wed ( tomorrow ). Anything tricky about it or is it simply a case of plugging it in with a minor bit of work?

[John Vine]

If your car already has the 6-way male Econoseal fitted in the engine loom (mine didn't), it's plug 'n' play.  If not, you'll need to cut the COP wires (eight in all) near where they enter the loom, and fit the 6-way male connector.  IIRC, CC include this connector, plus terminals and seals, with the flexi-loom.  You'll need a crimping tool too.  The connections are described in WN515.   If you don't have this, I can send you a copy.  More info here.

JV