Engine hesitation at high revs under a full load

Had the same issue, but also by lower rpm. After changing spark plugs everything is fine.

 

@CeriCopen That seems like exactly what mine is doing. Engine cuts our for a fraction of a second under hard acceleration. I thought it might be a fuel filter, but I'm told it doesn't have one. Welz said to change the spark plugs. I've been dithering around trying to decide which are the best ones to get. Iridium, I suppose, but there are variations I don't understand.

So, have you found what the problem was? I'm a bit worried I'll change the plugs and still have the symptoms.

 

IRF6J11 are the right plugs, NKG Laser Irridium. You could use inferior plugs, but these are rated to last 80-100k miles, worth a little extra for something that lasts that long. By all accounts they generally last longer. You'll also need a slim, long spark plug wrench to reach them.

Can't say if they'll fix the problem though sorry.

 

had to change my set of new plugs irf6j11 after reached only 20000 kms. The engine hesitates at high revs.
Middle left in photo 2 and middle right in photo 1 gone bad..now driving with super plus petrol only..everthing fine until now..

 

My poor car, in June due to overheating the engine blew, so replaced the engine, ...........and this month due to freezing weather the water pump and water system froze solid. !!!............

can't understand this silly things, sorry..poor water in engine in summer ..and in new one no antifrost in winter..e

maybe and old oil too..

i have a tiny car with a 120Hp Dx HKS loader and blowoff and exaust . often goes to 110 degrees.. normal temp sensor cut engine at 120 celsius..

 

https://www.ebay.co.uk/itm/Daihatsu-Copen-0-66-Roadster-/232504336375?hash=item3622569ff7

@CeriCopen ...your car? shiny...

 

Well, I've had the spark plugs, but I didn't have a socket that could reach them. Bought one on eBay, took ages to arrive. Got it this morning, went out and put the new plugs in. Took her for a spin; imagine my face when I find that the problem remains unchanged.

@CeriCopen did you ever find the trouble? @welz have you got any more ideas? I was quite sure the spark plugs would fix the problem, now I'm mystified. It's dangerous, because if you need to get a move on, it just doesn't happen. Starts bucking like a bronco.

 

I'd be surprised if it wasn't the coils on yours mate. Have a look at your old spark plugs and see if one or more looks like it's a different colour to the rest. That's usually a telltale sign.

The only other potential thing I can think of is that maybe it's hitting boost cut. When I set the boost on that turbo after I installed it, I set it close to the boost cut in order to maximize the benefits of the upgraded turbo without it hitting boost cut itself, so there's every possibility it just needs readjusting to get it back to where it needs to be.

Those HKS DX30's are manually adjusted using the nuts on the threaded wastegate actuator.

 

There's a few things it could be:
- The wrong coolant or just running water without coolant mix
- Air bubble in the cooling system
- Faulty water pump
- Coolant leak
- Wrong spark plugs (yep, this can actually be a cause of overheating)

I had the HKS turbo on my first Copen (which freddyzdead now owns) and never had any issues with overheating despite the bigger turbo.

 

CeriCopen, the boost fix won't apply to your Copen as I'm assuming you're still using the stock turbo. His turbo is a HKS one with wastegate adjustment.

 

@gotboost? Thanks for that. I will have a look tomorrow. Since I don't know which direction to turn it, I'll have to pick one and see if it got better or worse.

There wasn't anything too unusual about the look of the spark plugs, but some of the coil pack insulators were a bit gungy on the outside. I wiped them clean before I put them back. But I didn't clean the insides, which maybe I should have done. I'll probably take them out again and do that. It occurred to me after I'd put it all back together that I should have cleaned the insides more than the outsides. That's where the high voltage is.

 

If you've got a boost gauge fitted, you'll be able to tell.
Otherwise, consider it this way: as you wind the adjustment nuts to push the wastegate flap further open, you're letting more air escape down through the exhaust rather than into the engine, so that's going to mean you're lowering the boost. Turning the adjustment nuts in a way that closes the wastegate flap will have the opposite effect; it provides more boost.

If it was me, I'd be lowering the boost to see if that helps. I do think it's possibly the coils, though.

 

@gotboost ..changed boost from 1,2 to 1 bar.wrong petrol used by my wife E10..

Now have change the cooling fluid again..

 

I had a tinker with the wastegate adjustment; didn't seem to make any difference. I found 4 coil packs on ebay, reasonable price, so I ordered them, should be here in a few days. If it isn't that, I don't know what to think. I'm taking the car to my mechanic friend next Thursday for 100,000 service. He's never seen a Copen before, so I don't know how much help he'll be.