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R400 D - Electrical problem.. i think


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I would be VERY appreciative of some advice please.
Scenario:  Had car since June.  Bought 2nd hand.  Was fine when I bought it.   Sent it away to get it the geo / flat floor set up done.  On the way back, it rained incredably hard.  Car started running VERY rough.   Since then its been an issue and its been away at a garage for the last month trying to fix it.  I dont think this garage has a lot of Caterham experience though.
My mechanical knowledge is very low, but increasing quickly.

Description of my Seven & problem:

  • Caterham R400 Duratec with roller barrel throttle bodies (minister) and dry sump.
  • Problem: Engine runs very rough at less than 4k rpm when it's being driven.  Spluttering and losing power.  Almost like its flooding itself. This is the main problem & its near undriveable when its like this.  
  • If starting from cold, (most of the time) driving it'll be fine for a few to 10 minutes but will splutter for 0.5 seconds and then a minute later, it will do it again. Then 30 seconds or so later it'll splutter like mad, losing power.
  • As soon as the revs go over 4k rpm, it clears up and away we go!  Its not running perfectly at this point though and you can hear it in the engine noise but its much much better.
  • At idle its a little rough.
  • Once the engine is up to temp, the engine will die when you pull up to a set of traffic lights after 3 or 4 seconds.  Starting it after this is a bit tricky and will require 2 or 3 attempts with some throttle pumping.
  • Spluttering and losing power appears to happen only when the engine is up to temp. 
  • Rain may be a contributing factor. It appears to run rougher in the rain.
  • Engine is a bit 'iffy' to start. Always requires a little bit of throttle to start it. Never starts just on the button.


Whats been done thus far:

  • All electrical connections checked.  Two corroded ones found , pins replaced and electrical contact cleaner used to ensure all is clean.
  • Garage found alternator was on way out.  This has been replaced but didnt fix it the spluttering.
  • Lambda sensor has been replaced.
  • Throttle position sensor has been replaced.
  • Throttle bodies have been checked and rebalanced.
  • Spark plugs replaced with gaps of 0.8mm on all.

I went to pick it up from the garage yesterday believing it should be fixed.  Got about 10 mins away from them and it started playing up again.   After someone pulling out on me on the way home and me missing them by about 20mm...  Im starting to think things are not destined to go right.. ;)
Id rather not take it back to the garage straight away.  About time I wrapped me head about doing this myself (with assistance).

I spoke to Caterham yesterday who were very helpful and pointed me towards checking the Manifold Air Pressure Sensor and its wiring.  Which seemed easy enough when they explained it over the phone.  
I have also acquired a wiring diagram for the R400.  http://www.lotus7.club/sites/default/files/images/Docs/Guides/guide.pdf

Couple of questions, and please excuse if these are a bit obvious but:-
1) How do I check the MAF wiring for breaks?
I understand that I can put the + terminal of a multimeter on a wire at the MAF connector plug end and put the - terminal of the multimeter on the other end but... would I be right in saying that I need disconnect the ecu plug and put a paper clip down the corresponding pin and test off that?
i.e The wiring diagram for the MAP shows a code of UN45 for one wire, which corresponds to pin 21.   Is it that simple?

2) Anyone had experience of something like this happening before?  

ANY assistance / advice / information very greatly appreciated at this point.   



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Sorry to hear your troubles.

Always difficult when it's intermittent. How long would you need it to run to think it was fixed or not?

Don't know about the MAP sensor and lead. Can you add some photos? How difficult would it be to swap the sensor and local wiring? That might be the best diagnostic route, and if you're lucky someone might offer one for the purpose.

In general unless you know exactly what are you doing then to test continuity it's usually desirable to disconnect both ends from anything. Then set your multimeter to resistance and measure. With your fault you also need to wiggle the wiring while you test. Is the connector big enough to get small crocodile clips on the pins?


PS: This sort of sensor?


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Hi Jonathan, 

Thank you very much for your speedy reply!

Thats the sensor.  It's fitted on the top of the carbon fibre bit for the air filter cover over the throttle bodies, so that the sensor is inside.   I can get some photos done later for sure.  at the moment im at work.

The fault has gone from intermittent to being very evident everytime I've driven it in the last 3 weeks.
I would suggest that if the fault doesnt appear for 2 hours of driving, then thats going to give me a lot of confidence that its fixed.

Its a piece of cake to replace the MAP sensor. Would take about 3 or 4 minutes max.
In terms of replacing the wiring, Im not sure.  The wiring disappears into the loom which is wrapped in what appears to be black insulation tape.

I can put a paper clip in and then croc clip to that, or I could get someone else to help hold them in place whilst I wiggle the wire.

Does the MAP talk to the ECU from cold or is it only working once up to temperature?

I will try and get some video of the fault in action too.  


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Can't help with specifics I'm afraid, but when you take any connectors apart, check very carefully that none of the pins are recessed slightly. 

If one hasn't been 'clicked' fully into it's shell it will be pushed back into the shell when you plug them together, making contact initially. However, when things warm up and move around with the vibrations the contact will become intermittant or break altogether.

When the plug is apart, a firm (not excessive) press on each pin will show up any that are not engaged in the shell properly and prone to sliding back into the housing.

Edited to add, this is most likely on multipin connectors (eg ECU) rather than the sensor itself 9but still worth a pros though).

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Cheers for the info Ian.   I shall get a look at them tomorrow.  :)

Jonathan.  Photo of the sensor (in positiion) Im talking about re: checking the wiring for it.

Just tweaked my back at work  taking a plastic bag down off a shelf... hopefully will be ok to work on the car tomorrow.  What was it saying about stuff happening to stop this fault being fixed...


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What Ian says... intermittent faults are much more likely to be caused by problems in or between connections than in a run of wire. (But a counter-example to that rule of thumb cost me a lot of time recently.)


PS: Do you want help with diagnosing your back problem? No multimeter content... :-)

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Anyone had experience of something like this happening before?  

You mentioned that your car began to run very roughly after heavy rain.  Something very similar happened to me a couple of years ago after an annual service at Millwood's.  While I was settling the bill, an enthusiatic fellow outside gave my car (R400D, but with standard plenum then) a VERY thorough power-wash.  Water got in everywhere through the bonnet. 

The car ran like a bag of old tin cans all the way home (100 miles or so).  The problem turned out to be water in and around the ECU.  I unplugged it and carefully dried everything out over a couple of days.  Result?  Magic!  The car ran as sweetly as ever.  

I'm not saying this is what happened to you, but I do think the ECU and connectors are set in a very vulnerable spot (especially with RBs like you have -- and like I have now).

Failing all else, can you borrow an ECU from someone to do a swap test? 

If you fancy bringing the car down to Dorset, I'll happily let you try my ECU.  BlatMail me if you feel that's worth pursuing.  



From your photo, it looks as though you have the standard coil-on-plug loom.  Have you examined very closely the wiring inside the connectors?  (By inside, I mean beyond the weather seals.)  IME, the standard wiring can fracture -- caused, I believe, by high-frequency vibration -- and can produce some of the symptoms you describe.   Details here.  Photos here.



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Cheers for posting John.

I've had to resort to booking an auto electrician to come out as I my back has decided it's time to play up.

I will defiantly get him to check those points you listed.

Unfortunately it's not possible for me to drive it down to you. It really is rough as anything below 4k rpm.

Thank you for the offer though.


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Your MAP sensor could be the problem, but it should cause issues at all revs, not just below 4000RPM. You can test to see if the MAP is sending a reasonable signal to the ECU by holding the revs at somewhere between idle and 3000RPM while the car is stationary, then unplug the electrical connector on the MAP sensor, the engine should then just die if it had previously been sending a plausible signal.

I would really encourage you to get the MBE cable and the Easimap software, you and any mechanic without it are really very much in the dark without being able to see all the sensor outputs at the same time to diagnose the problems. I would offer a loan of mine, but the return courier charges between Western Canada and the UK would cost about the same as the cable is worth (Easimap is free to use and can be installed on any Windows PC). You need the MBE-MAP-KIT-3-CAN, which is £120 inc VAT from SBD Motorsports:


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Sounds like a very good idea.  The auto electrican I've spoken to give me the impression he has the necessary cables / software (I did explain its a Caterham R400) but even so... for the money it will definately help either now (if he doesnt have them) or in the future.

Will give them a call tomorrow.   Thank you! :)

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Unless the auto electrician deals with MBE ECUs (certain TVRs, Nobles and Caterhams being the main vehicles using them), he is probably thinking a generic OBD2 analysis system would work. The generic system cable would certainly fit as Caterham has fitted a compatible connector, but they don't use OBD2 messages, only very basic CANbus messages that have to be interpreted by the MBE Easimap software, which a generic system would not be designed to do.

If you get the cable, you will be able to drive the car around while the problem is occurring and log the data from the sensors (I usually put the laptop on the passenger seat and hold it in place with the harness over the screen). If you can't interpret the results yourself, there are probably ten people or more on Blatchat who have enough experience to have a look at your data and see what should be checked. We would be looking for things such as the lambda sensor warming up correctly then oscillating at the correct voltage levels, sudden changes in sensor or fuel injector values while the engine revs and throttle position is steady, etc.

SBD should be able to help you confirm over the phone or via email that there is no issue with cable compatibility and that you already have the CAN-H and CAN-L wires in place in your car that will be used by the MBE cable and adapter to connect to a USB port on your laptop.

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Thank you once again. :) I've taken a photo of the ecu and the diagnostic port and sent them off to sbd in an email so that when I call they can make sure that the right connection is on the lead. :) When I spoke to the auto electrician he asked what ecu I had on the Caterham and when I said MBE he said it would be fine and would DL the software over the weekend. You're probably right though.. and even if he does have the right kit, I think it's still worth me getting a lead myself.

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A thought...

The finger has been pointed at the sensor in your photo.  This is, I'm reliably informed, a combined air-temperature / barometric-pressure sensor.  It can't be a MAP (Manifold Absolute Pressure) sensor as it sits on the open-to-air side of the rollerbarrels.  So what happens if you disconnect it altogether? 


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Cheers John.
I've been out to double check and it looks like you are correct.  I believed it to be called a MAP sensor as thats what CC had told me it was and described its location as being there.  Unless Ive misunderstood... entirely possible...
There are four wires coming out of it.

Cable from SBD Motorsports has arrived.  Tbh.. its not much more than a printer cable and an adapter but hey.. if it works.   I've booked Friday off work as auto-chap is coming over then.
The adapter connects to a black diagnostic connector underneath the dash, where the steering wheel is.  Cable supplied looks to be long enought that it'll connect to a lap top on the passenger seat.

When I first started trying to find the cause of this problem, I disconnected the lambda sensor. Which appeared to solve it.  However, after replacing the lambda (with a new one) and cleaning up the connector pins the problem still remains.    
I will try unplugging it, but Im not 100% convinced that it will be an indicator of something given my experience with the lambda sensor.
Doesnt the ECU drop into a 'safe mode' when it detects a sensor is offline or am I talking out of my rear?...    ie: If the fault is sensor A and I disconnect sensor B, the ECU will drop into a safe mode because its not getting info from sensor B, which makes it look like sensor B is the fault one.

Here's to Friday and hopefully a productive day...

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The typical behaviour when the lambda sensor is disconnected is to drop to open loop mode due to an implausible lambda value (not in the range of 0.5 to 1.5), the values for fuel would then be based on engine load, coolant and air temps, etc, as is the case during engine warm up.

A few tips from my experience, when using the cable and Easimap (please ignore anything which is SBO - Stating the Bleeding Obvious!):

- follow the install instructions carefully

- be careful getting in and out of the car while the adapter is connected under the dash, it is rather in the way of your knee. Use some Velcro or tape to keep the cable out of the way of your legs or car controls

- make sure you easily have enough battery run time in the PC to capture a whole session, PC shutdown during logging will lose all data

- save logged data to a file before switching screens using the page up / down function

- don't use an inverter powered from the car's battery or power from the 12V socket in the car to power the laptop (this is a tip for any vehicle), as there is a high risk that a ground loop would be created through the mapping cable to the laptop with a risk of signal noise or even damage to the electronics

- don't try to add too many panels (sensor displays) to a screen, 30 seems to be a good number (I tried to log every conceivable sensor at the same time, it didn't seem to work very well and many values that can be logged are useless or just a different processed value of the raw sensor anyway. From what I remember there are 3 default install pages, the second page is the best starting point for default sensor panels.

- have a driving strategy for collecting data and plan a suitable route before starting the logging, don't be tempted to view the data while driving (take a passenger to do that if you want to correlate poor running while viewing parameters in real time)

- monitor all the way from engine start to engine stop through warm up to avoid losing any useful info

- it is sometimes worthwhile checking all the idle values while the car is parked, but running - is any value fluctuating strangely, is the TPS value correct, are the temperature sensors giving expected values, etc?

Once you have a data log, we can go through how to filter and review the results to home in on the problem, if it isn't immediately obvious to you or your mechanic.

Good luck!

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Thats absolutely 'flippin' brilliant information! 
I was thinking of using an inverter Id used to power a PS3 in the family car, so thats a mistake avoided there!   Good idea about planning a route too, hadn't even thought about that.

I've asked the auto electrican to bring his own laptop whilst I'll be providing the cable & software (installation notes duly acknowledged).

I shall be making a donation to Nuke the Luke after this.   You've all been very helpful and , with nothing in it for yourselves, have gone out of your way to assist.   

Very much appreciated. :)


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You know... I didnt think of that.   I'm sure he would appreciate a bunch of folks in Sevens turning up with various differing medical opinions... :)

Tension.. Ive long gone past the point where Im surprised with these things happening.  Lol.  Its almost comical (in a basil fawlty way) as Ive only posted the main crux of whats happened thus far to get in the way, as I didnt want to waste peoples time with irrelevant info.
Im hoping for a phone call later today and will see if I can arrange for him to pop out this weekend.
I have a busy work week next week. A busy work week at the start of Dec is unheard of in the last 13 years Ive worked here, but ya know.. it makes it awkward to get time off to fix my car.. so perhaps I should've expected it!

I have a lap top so could do a logging session on my own but its only got about 10 mins battery life in it...  I'll see what happens after the phone call.  

Tune in same time, same place, next week/month/year for more exciting adventure!!! ;)




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