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Misfire at >3500 rpm


NedeSquare

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Hello everyone,

I am new to Caterhams, and in need of a little help. I have owned a 2009 Supperlight with the 150HP Sigma for the past 6 months. The car has only done 6000km and been running well. 

When out for a Blat today, the car would stutter and pop when traveling between 60 and 70 MpH in 6th gear, (Approx 3500 - 4000rpm). Very noticeable to the point where the car 'kangaroo hopped' at speed. On slowing down and reducing revs, no issues to note. Once back up to similar speeds, the issue repeated itself.

Any ideas on where I should start to look at problems, All HT leads are secure, the fuel is 98 RON, the oil recently changed, no issues on gauges.

Any advice greatly apreciated.

PS - I am in New Zealand, so not many Caterhams here.

Cheers Nede. :-) 

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Do you get the problem when you rev the engine with the car static?  Perhaps as a next step take out the plugs and see if there are any clues in terms of condition, gaps, and discolouration.  If the plugs are the original Ford plugs, gap settings above 1.0mm have an association with premature failure of the coil pack.

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Will the car accelerate through the misfire and does the misfire clear at higher rpm / lower gear or is it only at constant speed on level road?

There is an engine vibration period at about those revs which can show up any bad connections. Check ALL engine bay plugs and connections especially earths, including battery.

As Jim said plug gaps should be 0.9mm....standard Ford gap has caused problem?

Is the air filter reasonably clean?

Lots of other possibles including poor fuel quality

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Thanks for the replies.

When I change down a gear, the misfire clears, (I think from memory). It really seems to be on a level road at constant speed (approx 65mph in 6th gear). The Plugs are NGK platinum plugs, not sure how old, but fitted by prior owner. I'll check the issue again this weekend, pull the plugs out, check all earths and plugs and see if the isssue occurs when reving and static.

Air filter new and fuel only 3 to 4 weeks old. (Unless water has gotten into it, as the car has been outside for a few weeks while I renovate my garrage.

Update to follow.

Carl

 

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The 150 Sigma in its final UK spec left the MAP sensor open to the atmosphere with the hole facing upwards.   I am not sure a direct hit with water from standing outside would be good for it, but only Easymap could tell you if its working or not.

It you have a 150 Sigma and the MAP sensor is open to the atmosphere with the hole facing upwards, do yourself a favor and fit a small piece of rubber hose and bend it over to face the ground, to prevent water/rain damage. 

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Some 150 sigmas had a problem with the Ford TPS failing and the two throttle bodies can go out of sync.They are a bit of a pig to set up without the right gear. The lambda sensor is also a bit suspect but that usually gives idle/low speed problems and high fuel consumption but can be checked/eliminated by disconnecting it (under drivers footwell).

Sorry to hear of the recent events in Christchurch...so sad.

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  • 1 month later...

Hi Folks, 

Sorry to bring this up again, but I have been flatchat at work and only now got to checking items out. The misfire has progresively beocome worse, so here are deatils of what I have done / observed.

When cold, you could almost say everything is normal. Once warmed up, the running has progressively got rougher, and now, holding any constant speed results in lots of pops, and the car bunny hopping / running rough. The exhaust is very sooty when idling and does not pick up smoothly when revved (Bogs down). Accelerating through the gears does not show the problem, but the overall power is significantly down on usual.

Here is what I have done.

Checked Spark Plugs - Seem OK

Checked and cleaned all earths - Seem OK

Removed Lamda sensor (Very sooty, Cleaned up all contacts and reinserted) - Running without the Lamda sensor connected the car ran really rough, so Not sure if that eliminates it as a problem, or confirms it. 

Checked and cleaned MAP sensor and ECU connections.

I'm not sure how to use EasyMap, so I will google that today and see what to do there. What should I be looking for on Easymap to see if the Lamda sensor or MAP sensor is stuffed?

Thanks in advance for advice.

Carl

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Just a simple check...take the air filter off and look down the throttle bodies at full throttle. Are all the throttles open the same?

(should be fully open and exactly the same) It needs vacuum gauge/flowmeter to balance them and easymap to set the TPS

The throttle potentiometer (Ford part) is also unreliable 

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Does the Sigma have coolant and inlet air temperature sensors? If so they are worth checking. Easimap should let you see the temperatures they are reporting, make sure they seem sensible. For example, if the coolant temperature sensor has a bad connection it will appear to the ECU to have a high resistance which corresponds to a low temperature; if the ECU thinks the engine is still cold once it is hot it will over-enrich the mixture, resulting in the engine running OK when cold but showing all the signs of a rich mixture when hot, which is what you are seeing.
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  • 1 month later...

Hi everyone.Thanks for all the advice. Finally got round to doing some work on the cat and found the following

Checked TB's - Visual check all OK (Need to find out where to get a device to measure the airflow)

TPS out - 1.01 - Adjustyed to 1.04

Spark Plugs fouled - Changed to ones ordered from Caterham (presuming correct gap set by Caterham)

Changed MAP sensor.

Pleased to report the car is now running smoooth as, and I have a buig smile on my dial.

The idle is now a little high, ~1000, and I presume that the idle adjustment is the screw on the throttle cable attachment to the Throttle bodies. I altered this screw, but the effect did not seem noticable after one turn each way.

Cheers Nede

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