Odd tickover behaviour when hot...

[morebeanz]

Looking for some input on engine behaviour (2000 4.5 Cerb) when hot/very hot. If standing at tickover (traffic queues for example), the engine at some point will start hunting with tickover going up to 1200 revs and then dipping with, often, an ultimate stall.

100 amp fuse, coil packs and leads all replaced not so long ago, and the battery is in good shape.

I have noticed that the oil pressure flickers around the same time, but I can't tell if this is the driver of the issue or the consequence.

Any thoughts out there as to what I could check? Recently oil level checks all done too.

[high52kojak]

I had the same issue on mine shortly before the ECU gave up, it was cutting power to the fuel pump.
The oil pressure will be dropping and rising as the engine revs go up and down

[morebeanz]

That sounds expensive!

If I have a re-map chip from Joo, will that rescue it, or are there a whole bunch of chips in the box?!

[Steve_T]

Dodgy earth to the ECU perhaps Ian?

[morebeanz]

Steve_T said:

Dodgy earth to the ECU perhaps Ian?

I seem to recall there's a list of earth connections somewhere in a previous thread...

>pullsoutsearchweapon<

I'll check it out, thanks.

[morebeanz]

Steve_T said:

Dodgy earth to the ECU perhaps Ian?

I seem to recall there's a list of earth connections somewhere in a previous thread...

>pullsoutsearchweapon<

I'll check it out, thanks.

[morebeanz]

I noticed one thread referring to the tacho pick up, and how a dirty one was impacting the ECU and hence the running of the engine.

Is this accurate?

[Tanguero]

I had very similar symptoms and eventually traced it down to a plugged carbon canister preventing the fuel tank from venting properly.

[morebeanz]

Tanguero said:

I had very similar symptoms and eventually traced it down to a plugged carbon canister preventing the fuel tank from venting properly.

Wouldn't that affect the engine at all revs, though?

[Tanguero]

You would like to think so wouldn't you, however my symptoms were very specificaly at idle and when the engine was thoroughly warm. When it next happens in a safe place, let the engine stall then nip round and undo the fuel cap. On mine there was a big "woosh" as pressure was equalised.

I have had no reoccurence since changing the carbon canister. It may just be worth checking your tank when it next happens.

[morebeanz]

Tanguero said:

You would like to think so wouldn't you, however my symptoms were very specificaly at idle and when the engine was thoroughly warm. When it next happens in a safe place, let the engine stall then nip round and undo the fuel cap. On mine there was a big "woosh" as pressure was equalised.

I have had no reoccurence since changing the carbon canister. It may just be worth checking your tank when it next happens.

Good idea, thanks, I shall investigate that too...

[assynt road]

Had a similar problem when the engine was hot, I was stuck in a jam and the engine was running ragged and stalling if I didn't keep some revs on the throtle. Problem was cured by changing the lambada sensors, never had anymore trouble.

[morebeanz]

Lambda sensors do seem to be a weak spot on these cars, although I suspect that's a consequence of having to put up with the emissions from an AJP rather than anything else. I probably have mine replaced every other year or so, and I had them done late last year, so I hope that's not the issue!

Edited by morebeanz on Wednesday 12th May 08:52

[Tafford]

Can anyone help please with the earth points list mentioned in the above - I know I've seen it recently in a thread but I can't find it....

[vroom]

morebeanz said:

Looking for some input on engine behaviour (2000 4.5 Cerb) when hot/very hot. If standing at tickover (traffic queues for example), the engine at some point will start hunting with tickover going up to 1200 revs and then dipping with, often, an ultimate stall.

100 amp fuse, coil packs and leads all replaced not so long ago, and the battery is in good shape.

I have noticed that the oil pressure flickers around the same time, but I can't tell if this is the driver of the issue or the consequence.

Any thoughts out there as to what I could check? Recently oil level checks all done too.

Have you checked for any spurious D throttles on the ECU s/w?

Any noise pick up due to worn throttle pot carbon track can give unwanted spurious fuel enrichment on idle that plays havoc with the tickover