So a while back I had a persistent detonation issue in my 899 swapped Robin, eventually tracked it down to 0.5 bar fuel pressure and turning it up to 1.2 sorted it, until I popped a ring last year. Got a new engine in with new throttle body and issue is back. I say new tb, just the top half with reg and injector.<br />
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Tested yesterday and pressure was down at about 0.75 bar, adjusted up to 1.2 as previously but this time it's still knocking. When engine is cold it starts at around 3000 RPM, it'll rev higher when it's hot but under light load, or trying to hold over about 65 mph it knocks like a Jehovah's witness.<br />
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Any ideas? Kind of hit a bit of a dead end this time. I'll try to check fuel pressure while driving later on if parts arrive from Amazon in time.

Any unmetered air entering the engine?

I'm pretty sure there's no air leaks. I swapped the ECU for a 1.1 with McKritch chip and it ran fine if a bit rich when hot (except for high rpm full load, it was pinging again) but when cold its way overfuelling.

May look at filter and fuel pump and possibly putting the old reg/injector assembly on it again.

My 1.2 spi 8v pings a little at high rpm at full load. Probably didn't help that the head is skimmed a little too much so My compression is a bit high!

Is it knocking or just Pinging? Knock sounds more like a bottom end issue???

Pretty sure it's just pinging. 2 engines have done the same. First one I cured it by increasing fuel pressure, this second one does the same but higher pressure hasn't changed a thing. It also does it at very light throttle, the point just before coming completely off.

With the 1.1 ECU it runs a bit cooler, so I'm sure it's running lean for some reason. Just have no idea why. I still need a fuel pressure reading while driving, maybe my pump is going a bit kaputt.

Have you watched the fuel pressure as you rev it? It could be that it can hold pressure on idle but as soon as you give it some throttle it gives up.

Definitely worth looking at the fuel filter and pump to start with. Maybe worth checking your ignition components too to make sure you are getting a good spark.

Just standing it holds pressure fine, but not tested under load yet, need to make some long hoses for my tester.

I fired the parts cannon at it last year so most of it is new. Going to change filter when I get a chance, then pump.

Worth a look. I changed my pump and tank about 5 years ago. I changed it again recently and found quite a bit of sandy stuff in the pump housing. Didn't seem to affect how it performed, but it could have caused issue over time

Checked pressure while driving last night. Full throttle in 1st, dropped half a bar about the same time it started detonating.

Think I've found the culprit.

If you increase the base fuel pressure on idle to half a bar higher, does the issue go away or does the fuel pressure always drop to the same point again under load?

It's already set to 1.5 bar, the reg doesn't go much higher happily. It just rockets up.

Something doesn't sound right then. My reg will go higher than 1.5 bar no problem. Definitely sounds like it could well be pump related, or a blocked fuel filter

Changed filter at last, slight improvement but next morning it was pingy again. Tried resetting fuel trim through iawscan which failed, but it's ran fine ever since.

have you had the pump out and changed that? or checked the connections and that you are getting full voltage to the pump?

Duty cycle on the injector going high enough to drop pressure? Or sticking open?

I've finally picked up a seicento to do a fi conversion on my robin, might keep the 899 engine to mock up onto one of my spare gearboxes.

Mine is a citymatic donor car, I was a little confused when I first saw it I expected an auto but it had been converted to full manual, it was original semi auto with an electronically operated hydraulic clutch.

Some minor differences in wiring to the throttle body and ECU because the semi auto had two outputs on a Bosch throttle position sensor that uses a rectangular plug and a second ECU to control the clutch, the butterfly shaft is longer with a different angle on the locating peg preventing you just fitting the Marelli tps

It seems the standard Marelli unit is electrically compatible though which is good news, I've already tried a 32mm Punto throttle body on the car,

I'm hoping ECU loom was modded correctly when converting back to manual clutch as I can't find much info on what mods would have been required.

I changed the pump and filter, it still knocks when cold but is fine when hot, so I'll take that.

Tbh if you have a complete car I'd do the 899 engine swap and not make the mistakes I did, and then sell the reliant lump to someone who will happily pay 500 quid for it because it runs.

There is always the chance the hydraulic lifters are going noisy, mine tap at idle for a few seconds when cold until i give it a rev.

Is the map sensor piped up to the right stub? They have size different holes for the evap canister, oil breather and map sensor.

My engine isn't the best, it is reliable doesn't overheat but smokes a bit.

120k on the clock, recently had a new oil pump/drive gear/shaft and bushes, low mileage crank, cam, followers and pistons from an engine with a cracked block, I didn't have time to swap the liners as I needed to get the car back on the road.

The original cam bevel gear and oil pump drive failed damaging the crank and small ends.

It's definitely not the lifters, they make their own noise. I'll check the map but it does the same without it connected.

You'd definitely do well putting that 899 lump in it. I can share the 3d model of the adaptor plate, although I am looking at getting a couple machined unless I do the MX-5 gearbox swap first

My dad said the same thing when I told him why I'd bought the fiat.

The engine in the seicento has the map sensor take off on the intake spacer, the earlier Cinquecento one has it on the lower part of the throttle body the left hand one of the three.

The other two take off points are for the evap canister and the oil breather pipe, i mixed them up when I test fitted a 32mm the throttle body.

Having the oil breather on the larger pipe caused the tick over to go from 860 right up to about 12-1300 and it took longer for the revs to settle back to idle.

The map sensor would have been seeing a lower than expected vacuum too.

I dont have an oil breather to the intake, mine goes to the airbox. There's 3 vac points on it, one is brake booster, evap which now goes to pneumatic control valves and the map. Booster is blanked off.