...what shall I do to this engine?

[otta]

I own a very nice roadsport with the beloved rover engine and exhaust on the left... Car has been running smoothly but I have picked up some simpthoms on the engine that I cannot really figure out.

Looking for some enlighten ideas/experience! :-)

In no particular order:
- jerky on lift off sub 3k rpm, i.e. 2nd gear enganged but no throttle the car, like if you are slowing done in traffic ahead, car doesnt keep rpms and ride becomes bumpy
- minimum rpms has become a random variable, in all my other cars there is a cold min and a hot min, with the caterham sometimes it is 1k, sometimes 1.5k sometimes 1.25k, for no particular reason or not consequentially to a spirited drive or anything.
- sometimes (especially when the car decides that the minimum is 1.5k rpm) if I give a little bit of throttle in neutral and fully release it takes a while to settle back to the minimum, almost like throttle is still partially open.
- finally and this developed today there is a nasty vibration at around 6k rpm under pull, not there in neutral but definitely there in other gears... Rattle goes away after the 6k mark and from 3k to 6k rpm the engine is very smooth as always...

All gauges are fine, recently changed oil, spark plugs, tensioned throttle cable, installed an oil cooler/radiator, always runs on vpower. So cannot really see what can be wrong... Heard a lot of horror stories on these engines so if these are the symptoms of a problem in the camshaft, gasket, valves blah blah would like to try and address sooner than later...

Anyone experience something similar??

[gedG]

As a cheap and easy starter I would introduce a small amount of slack to the throttle cable and ensure the jubilee clip holding the air filter onto the throttle body is not too tight.

[downsman]

The first few symptoms made me think of the time I had a accellerator cable break, I had variable idle and jerky low speed control in the few weeks before it snapped.

The high speed vibration though. Just a thought , have you checked your engine mounts are OK. If the engine moves it can alter the engine speed. A friend discovered on a recent handling day that his engine was moving and increasing the revs due to lateral load!

[otta]

Thanks guys... Checked the tension on throttle cable with various settings, also the engine mounts seem pretty sturdy. The vibration makes me think, it appears at the same rpms irrespective of gear but not in neutral... So only under load... crankshaft got unbalanced maybe?

Spoke to a local mechanic (I have the car in Italy) and he suggest that the electrics going into the throttle body might need replacement.

I am more thinking about valves and cams having an issue... Or the injection ecu going crazy.... Is there any diagnostic that can be run on this car? Or visual evidence that cen be used?

[sfaulds]

First 3 symptoms are probably a duff idle control valve, and the last could be any number of things. Check the engine mounts, anything sitting again the engine, alternator bearings then you're into clutch plate or CRB breaking up.

[otta]

sfaulds said:

First 3 symptoms are probably a duff idle control valve, and the last could be any number of things. Check the engine mounts, anything sitting again the engine, alternator bearings then you're into clutch plate or CRB breaking up.

Thanks, I disassembled the idle control valve, cleaned it etc etc... It didn't seem broken or loose so I suspect it must be the ecu giving the wrong inputs? Do you guys know how to interface with the beast?

I stripped the car nose and checked all things close to the engine including mounts.... Everything seems pretty tight, can it be misfiring?

[otta]

Did a test drive this morning after the valve clean out... Also I killed the battery for 10 minutes to have the ecu reset, switch on the car and hot idle was 1.25k, then when it got hotter got down to 1k. So far so good...

then after the oil was hotter did some pulls with high revs, the problem resurfaced, idle at 2k blah blah... Now visual inspection of the valve did not reveal any issue, do u guys think it is definitely the culprit and need replacement? Or can it be a sensor somewhere else? I would want to try and swap it to isolate the issue but have no other caterham near by unf....

Also is the CRB an engine out kind of thing?

Thanks all for the kind replies so far... Very helpful

[WillieLocost]

CRB is engine out, yes. You should hear the noise by pressing clutch pedal in/out when in neutral and engine running, it's more of a rumble than a rattle.

For the rattle, check the crank pulley bolt is tight...they have a habit of coming loose. Also check the alloy plate along the centre of the cam cover if it's an EU2 engine. Does it sound like a vibration rattle?

The rev issue (Engine hanging onto revs with throttle lifted) is almost certainly your IACV. Even clean ones can mess about. Get it up to temperature on a run and wait for it to start misbehaving, then turn engine off, remove the rubber hose feeding the IACV and block it with your thumb while you get someone else to start the engine & rev it/allow revs to fall. Replace the hose and see if the fault re-occurrs. Personally I, and others, have just blocked the rubber hose, or removed the IACV and fitted a blanking plate.

[otta]

WillieLocost said:

CRB is engine out, yes. You should hear the noise by pressing clutch pedal in/out when in neutral and engine running, it's more of a rumble than a rattle.

For the rattle, check the crank pulley bolt is tight...they have a habit of coming loose. Also check the alloy plate along the centre of the cam cover if it's an EU2 engine. Does it sound like a vibration rattle?

The rev issue (Engine hanging onto revs with throttle lifted) is almost certainly your IACV. Even clean ones can mess about. Get it up to temperature on a run and wait for it to start misbehaving, then turn engine off, remove the rubber hose feeding the IACV and block it with your thumb while you get someone else to start the engine & rev it/allow revs to fall. Replace the hose and see if the fault re-occurrs. Personally I, and others, have just blocked the rubber hose, or removed the IACV and fitted a blanking plate.

Thanks WillieLocost... I ll kill or replace the IACV then.

For the rattle/vibration I already did disassemble the cam cover and fixed it properly, I ll check the crank pulley as well. Not sure I hear the crb rumble though... Might be something else, problem is there only under pull or in gear...

I ll try all the suggestions... Thanks a lot for the advices!

[Steve-B]

CRB failure does NOT necessarily give any warning sounds, so don't sit back and wait for that. My CRB self-destructed north of Sydney a couple years ago on a blat with no sound, until the pieces started flying about in the bell housing, of course it was too late then.

Any vibration of a soon to fail CRB would be felt in one's left foot, so I really doubt that's the issue.

[V7SLR]

otta said:

- finally and this developed today there is a nasty vibration at around 6k rpm under pull, not there in neutral but definitely there in other gears... Rattle goes away after the 6k mark and from 3k to 6k rpm the engine is very smooth as always...

recently changed oil, spark plugs, tensioned throttle cable, installed an oil cooler/radiator, always runs on vpower.

Have you definitely tightened the plug cover down properly? .... common problem!

[otta]

Definitely don't feel the problem on the left foot, vibration is there at a given rpm range (somewhere in between 5.5-6.5k) and only under pull irrespective of gear. Not there in neutral if I just rev up the engine.

The above makes me think that it is not speed driven (would only show up on a given gear), nor rpm driven (would be there in neutral), nor gearbox driven.

I took out the spark plugs cover (i.e. the red one) and re-bolted it down tightly with not much change. Checked all other things close to the engine including mounts and they seem fine/not loose. The clutch associated theory can make sense given it is under pull irrespective of gear and at or around the torque peak, having said that don't feel the sound or slippage of the clutch in any other circumstance so an engine out thing seems a little bit agressive as a start point... I also thought the engine or crank have some balancing issue?? or can it be the allegedly faulty IACV vibrating under suction from the high revving engine under pull? (would kill 2 birds with one stone )