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Misfire/Coolant Issues R400K


duncs_c7

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Hi All,

 

Some of you may have seen this on FB already, but I'm not a big fan of FB so this is probably a better platform for advice for me.

 

My R400K (RBTBs/dry sump) has developed a problem whereby at around 3000rpm it just loses all power and jiggles down the road popping and spluttering.  You seem to be able to get through this 3000rpm ceiling by holding a very very light throttle until it slowly judders past it.  However, at speed sometimes the power will just drain away and it will fall back to the 3000rpm ceiling.


The issue has occasionally re-occurred at other revs both above and below 3000, but it's more intermittent.  It only happens under load, revs as normal when not under load.

 

At the same time I've found that I'm losing coolant, there was splatters around the engine bay and it was dripping when stationary, so it seemed like the hoses (replaced at the last service) were perhaps loose, but having tightened them up it's still losing it and still got splatters around the engine bay.

 

I don't know if the two are related, and I haven't had the chance to do a more thorough investigation on exactly where it's coming from since it happened.

 

The other thing of note is that somehow some water got into my garage during the big storms not long before so I don't know if any got into the car or not, but it could be a cause of one or other of the issues.  When checking for water under the HT leads one of the metal contacts in the head of the lead stayed stuck to the top of the spark plug, it re-inserted but obviously shouldn't do that.  The car ran the same both before and after that.

 

So far, theories I've heard include: the dodgy HT lead, throttle position sensor, airflow sensor, HGF, broken CAT in the exhaust, injector wiring.

 

I have to say that although I am keen to learn, I'm pretty clueless when it comes to working on cars, changing brake discs/pads is about the limit of my skills, so whatever the advice is will need to be spelled out! *wobble*

 

Your collective knowledge is most welcome, I essentially want to get a list together of everything someone with limited skills / knowledge can do to order everything I need.  If it's beyond me, then advice on a knowledgeable and good garage in the Herts area would be a useful alternative (and actually just be useful to know fullstop)!

 

Thanks in advance. *bow*

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Have you got a lambda sensor in the exhaust system ? .... if so, unplug the connector to it and see if the car drives normally. If it does ... unscrew the sensor and read the number on it and order a new one on line .... a lot cheaper than CC.
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I had similar symptoms ... traced to head gasket failure

my mechanical skills stop with the polishing cloth! ... and as these are at a reasonable limit of tune I would trust to a specialist

... however hope it is something less expensive

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Obviously I'm hoping it's not HGF.  Is there any checks I can do to verify that either way?  The oil doesn't look 'milky' which is one symptom I've heard of.

 

The car is 2004, but only about 16k miles... but I suppose it could have been abused in that time.

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I'd try to work out if the coolant and misfire symptoms are one problem or two. Each one could just be a massive red herring for diagnosis of the other if you get it into your head that they are related and they are not.

First of all, it should be easy enough to fins where the coolant is going if it spattering around the engine bay rather than being somehow consumed internally. Give everything a really good clean and dry in the engine bay so you can tell the difference between new and old spatter. If necessary, wrap bits of clean dry kitchen towel round the hose joints with a bit of tape and see which ones get wet or stained after a run. To be honest, you can usually find a wet joint just feeling round with your finger.

Once you know where the coolant is going you will have a pretty good idea whether it could be causing the misfire. My guess on the misfire would be an ignition issue. You've already found that at least one of the HT leads is damaged. I've seen a couple of cars (not Caterhams) with weak coil packs that have shown exactly that kind of misfire, low to mid RPM under load and it just breaks down and won't fire until you get the RPM up or back off the throttle. Cylinder pressures, mixture and ignition timing all affect the breakdown voltage at the spark gap; as the require voltage rises it exposes weaknesses, i.e. the spark will start to find an alternative path to earth through damaged insulation somewhere.

Given that you know your ignition leads are not healthy I'd change them for a start. Even if it doesn't fix this problem, running them like that it will only let you down at some point. Have a look at the spark plugs, check that the gaps look sensible and they're not fouled up, either with dry deposits or oil (or event coolant).

In short, fix what you know to be wrong first and then see where it leaves you.

Have you checked the TPS and lambda sensor yet? Lambda sensor is easy is Ian says. Just unplug it and see what happens, won't do any harm just to try it and if that's the problem you'll get an immediate improvement; then replace it a.s.a.p.

Do you know how to check the TPS? From my limited knowledge of the RBTB setup ... don't remove it or even undo the screws unless you're confident with recalibrating it using a voltmeter and/or laptop hooked up to the ECU (which I'm guessing you're not). It's very fussy over being calibrated correctly to match the map loaded into the ECU. You can do all the checks you need to see if it's grossly misbehaving at fully throttle with a voltmeter without disturbing it.

I'd be inclined to think it's not a collapsed catalytic converter if it pulls through and settles again at higher RPM.

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  • 4 weeks later...
  • Member

Weirdly initially there was no sign of the misfire when I drove it round the block so I decided to take it a bit further. Sure enough it started appearing again so I decided to head for home. When at home, before turning it off I took the bonnet and nose cone off to look for signs of the coolant leak. The fan was on at this point.

Was it overheating while moving or did the fan only come on when stationary?

Obviously I'm hoping it's not HGF.  Is there any checks I can do to verify that either way?  The oil doesn't look 'milky' which is one symptom I've heard of.

You can test for products of combustion in the coolant, either garage or DIY.

Jonathan

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Right well after not having time to think about it for a while I thought I'd see the lie of the land today.

 

 

So coolant reservoir actually had a bit in it (when I left it before it was dry), which I thought was odd. Anyway topped it up to near the max line.

 

 

I also noticed there was some oil on the floor, it appears to be dripping from the driver's side at the bottom where the gearbox and engine join. No evidence of anywhere else in the engine bay. So anyway, I topped the oil up, ran the engine for a while (which seemed normal), checked the oil and the level seemed fine.

 

 

Took it out for a drive, expecting the misfire to be there, but at least wanting to get to the bottom of the coolant issue.

 

 

Weirdly initially there was no sign of the misfire when I drove it round the block so I decided to take it a bit further. Sure enough it started appearing again so I decided to head for home.

 

 

When at home, before turning it off I took the bonnet and nose cone off to look for signs of the coolant leak. The fan was on at this point. The coolant reservoir was now full up well over the max level. No sign of leakage. So I shut the engine off, and then all the coolant got sucked out of the reservoir and I could hear the cap squealing as it was continuing to suck. Put a little more water in which soon got swallowed up, wouldn't be surprised if it was full again later as there was nothing visible externally so I can't see that it's going anywhere.

 

 

Does any of this make sense? I do start to get the feeling misfire is related to heat levels, in which case I presume it is a doomsday HGF situation.

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Just a note of caution. I have two friends who both had similar symptoms which did turn out to be head gasket failures. Both had "sniff tests" done and both came back negative for combustion gasses. One had a second test later which came back positive. Both had the head gaskets replaced by Dave Andrews who was able to point out evidence of fire ring breaches, and both were fine afterwards. So the "sniff test" is not always conclusive. Maybe it takes time to accumulate enough combustion products to give a positive test?
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Is it possible that the coolant system wasn't bled properly when the hoses were replaced at the last service?

 

Either way, having looked up the procedure I'm guessing it's not something I could take on! Might be time to ship it to someone with some skills! *cry*

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Well I did in fact manage to bleed the coolant system, it really wasn't as difficult as I was expecting.

 

Weirdly, it seems to have fixed everything. Plan now is to fit new leads anyway, and then just keep any eye on things for a while. Might send it to someone for a once over as well.

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Just remember that driving the car with a faulty headgasket potentially damages the head.

It is not the end of the world to change it (I'll be doing it on mine this week), but try finding a decent VHPD head...

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I'm not sure what else I can do, I also don't want to replace a head gasket that's perfectly fine. If it is the early stages of HGF then no doubt the issues I've been having will return. However, given that it started just after having the hoses replaced and appears to be fine after bleeding is surely evidence that there's a good chance this was the issue?
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Well I did in fact manage to bleed the coolant system, it really wasn't as difficult as I was expecting.

Any particular tricks that made a difference on yours?

However, given that it started just after having the hoses replaced and appears to be fine after bleeding is surely evidence that there's a good chance this was the issue?

I'd get out there and drive it... and I'm sure that you'll be keeping an eye on the temperature anyway.

Jonathan

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