What's technically a missfire, and what causes them please??

[nico]

Oh kay, had the cam timing checked by another pro garage, but am still getting chronic (what i would otherwise call hesitation) engine miss' fire, first thing on a morning (till I give it some juice) and it gets warmed up at idle.

Guys at Fiat reckoned ECU could be causing it, but the garages say not. Likely causes are please???

 

[Tom]

Normal: bang bang bang bang
Missfire: bang bang bang

If its just missing when its cold thats probably down to the mods you've done.

 

[KeithR]

Does it feel like its putting too much fuel in the engine, causing it to flood, then when you give it some it clears it all up???

KeithR

 

[Tom]

It WILL be putting more fuel in when its cold, otherwise it just won't run at all.

 

[KeithR]

Does it feel like its putting too much fuel in the engine???

Yeah more fuel would be ok, i asked if it was putting too much fuel in

Der



KeithR

 

[Tom]

More IS too much

Given how much he has changed it from makers spec its hard to expect a smooth cold idle.

 

[nico]

I did wonder if a bit of a dodgy start up wasn't just a minor consequence of the mods I've done.

It dosn't bang. The noise is like the whole engine holding its breath for a split second before theres then a bit of a pop from the exhaust and bit of a ding from the engine.

Mebs does it half a dozen times once every second or so for half a dozen times (till I go out an unlock it to give it some juice).

I had to give the two ECUs a few weeks to try and get along whilst the guy who mapped it was away. Eventually the ECUs stopped arguing over the idle rpm and seemed to be getting along, although I wanted it to idle nearer the 9 mak rather than the 7 that indeed it used to idle at before. He said that it was running leaner than it need to again, since the de-cat went on, and he had changed the mix last time too, so this alteration to the fuel could inevitably be the culprit I guess. Prior re-map needed no alteration though, and emissions were spot on.

 

[Tom]

The bang was to represent it firing a cylinder.

So you're using a remote start, giving it no throttle and expecting it to idle perfectly from cold. IMO its fine, ignore it, its normal. If it was missfiring under power or hot idle then its something to worry about.

You can't compare the mixture when hot with the mixture for cold startup. The ECU will add a lot more fuel, just like the choke on an old car.

 

[nico]

Cheers for the re-assurance Tom

I've no complaints about the running once warmed up. It runs like a dream now. Quiet once warmend up, and quiet at speed cruising (more so since the first mod when the exhaust went on beleive it or not!) but give it some juice and the roar it gives out is awesome
I've sworn never to tamper with the engine tuning ever again though!

 

[Ash]

ive had a couple of cars with sports cams and they all ran lumpy when they were cold its just a side effect unfortunatly

a normal cam is compramised becaue it is setup to let the engine run smooth throughout the rev range with any driving style where as a sports cam is set to give u the best power when ur giving it some so the low end idle is compramised. i think its isnt a bad trade off really

Im Driven to Earn, and I Earn to Drive......

 

[Ash]

forgot to say it does improve a little bit once the cam is a bit more worn in (usually )

Im Driven to Earn, and I Earn to Drive......

 

[Tom]

You hope the cam never wears

There are ways to make lumpy cams idle nicely but cold idle is always a problem. Fiat would have spent AGES making it cold idle just fine.

 

[Anonymous]

MAF Sensor

Mine een doing the same thing. Judderey first thing in the morning and if I booted it started misfiring.

Took it to garage tobe hooked up. Air sensor problem (MAF sensor)

Get it hooked up and checked mate

 

[Tom]

Anon, read everything again carefully please.

He says it missfires UNTIL he boots it and runs fine when warm.

 

[Anonymous]

TOM

I know!!

MINE DOES THE SAME.

MISFIRES TIL THE ENGINE IS WARM THEN RUNS FINE. BEEN DOING IT FOR 3-4 WEEKS. HAVING THE MAF REPLACED TOMORROW

I CAN READ TOM!!!

 

[Tom]

"and if I booted it started misfiring."

Make up your mind on the symptoms please

Given that nico didn't complain about this before and between then and now he has had a few 'things' done to the engine including several rolling road setups I would have hoped a dodgey MAF would have been spotted.

 

[Anonymous]

Mine went on the rollin road 2day. It came up with no errors to the engine. The only reason he realised it was the maf is because the machine was hooked upto it and the voltage was far lower than it should be.

SO No, it might not show as an error.

 

[Tom]

If the voltage was much lower than it should be, why was it not missfiring or running badly when warm? Makes no sense now does it.

A faulty MAF on a JTD screws the power no matter what the temp is.

 

[Ash]

mr annon tom is normally right most of the time (like 99% ) and agian hes right if a maf dont work the car just looses all its power all the time. i have driven 2 jtd's with faulty maf's and both when they have been fixed and booth had a hugue hugue difference in power!

Im Driven to Earn, and I Earn to Drive......

 

[Anonymous]

am no expert in ecu's a crap like that.

It misfires badly first when the engine is cold, but doesnt when warm. The cars performance was really poor whether cold or hot.

All I can think of is that when cold the engine is running to rich because more fuel is being pumped through. so it misfires.

When it was on the rolling road he could only get the engine to 80BHP and it would only goto 6000rpm.

Its a 155 HGT so should have about 145BHP to the wheels and should go all the way to 6,600 before it reaches the limiter.

I will let you know 2morra when it is all fitted.