Pulsing revs ~2k rpm

[philwaters]

Ran the Zetec for the first time this year after taking it out to fit a new clutch over the winter and having the inlet manifold matched to another cylinder head (big valve for another upgrade - coming soon).

 

Engine ran fine (after a couple of attempts due to weak battery and probably slightly tight engine) - tick over was nice and steady although I did have to tweak the stop up a small amount to get the target tickover revs (TB's have been off the engine).

 

However, when I lifted the revs to 1800 - 2000rpm and held them there, the revs started to drop away before coming back up - it would do this repeatedly if the throttle was held still - I would estimate the revs would drop to tickover over a period of about 2 secs before rising back over the same time frame. It didn't feel like the engine was miss-firing at all and I can't quite figure it out.

 

The only thing I have though of since is that I didn't re-calibrate my throttle pot after tweaking the revs up. As throttle opening just above tickover is quite critical, could this be it?

 

ECU is Emerald and running Jenvey TB's - everything on the engine is as it was last year (apart from fresh coolant and a new oil filter).

No tax on the car yet, so no chance to go for a run and see how it drive to see if it happens higher up the revs - but it blipped up to 3500rpm with no problem, but I didn't hold the revs there to try it.

 

 

Phil Waters

[Mr Locust]

Is the closed loop enabled?

 

Ian

 

Green and Silver Roadsport 😬

[philwaters]

No, shouldn't be as I took the wideband out last year and turned it all off.

 

Planning to fire up the knackered old laptop that I keep in the garage again tomorrow night and double check the map and re-do the throttle pot.

I'm just not sure what effect the throttle pot calibration would have - if it could cause the issue I was seeing.

 

Phil Waters

[philwaters]

Hmmm, idle thoughts (I thank you 😶‍🌫️) - I think it might be the throttle position setting for the idle control....

First thing I'll check tonight!

 

Phil Waters

[philwaters]

It wasn't... but it was the fuel cut-off throttle number value. Adjusted this back down and it is fine again now.

 

So - basically the behaviour (to help those in the future) was that it idled fine and was fine up to the 1700rpm that I have set as my 'don't cut fuel below' value. Because my old closed throttle position was a higher reading, once the engine hit 1700rpm it was allowed to cut the fuel and the actual throttle value was still below the threshold in the settings. So it cut the fuel, the revs dropped down and then it would start fuelling again once the revs dropped below 1700rpm and the revs would pick up - and it would repeat this loop for as long as you could hold your foot steady.

It was fine above about 2000rpm because it was then above the old closed throttle position.

 

That'll teach me for not checking through the whole map - but then it has been well over a year since I used the software.

 

Phil Waters