Hi All,

I'm getting a Hesitation on my forged 2.1. Don't notice it when the engine is cold, once fully warmed up is where I notice it.

Basically the issue happens with a quick change of throttle position, so cruising along at 40mph or so, give the throttle a stab, you get a stutter, hear a pop then it pulls fine and cleanly. Coming off and onto the throttle does the same thing. It doesn't do it all the time.

You can recreate it revving it at idle too, blipping the throttle to hold 2500rpm or so.

Any ideas?

O2 Sensor is less than 6 months old and Denso. MAF is original to the car (2003) and has been cleaned within the last 4 months.

Cheers,

Scott

 

Also plugs are brand new.

 

Air filter clogged?

 

No, fairly clean K&N Panel filter in the OEM box.

 

Could be the maf. It is 12 years old after all

 

Throttle body dirty ? ic valve dirty?

 

TB is clean, or was when I built the engine. Not checked the ICV. Just seems odd how it only really happens when the car is fully warmed up.

I might run some logs on it to check the injector timings and AFR's when it happens. I think its lean, like the injectors haven't caught on that you want to get moving, then they catch up.

 

Are the injectors maxing out on duty?

 

No, 550's running 340 Bhp. It pulls fine after the initial hesitation. Its just the split second you get on the throttle it does it.

 

Check that all plug leads are fitted firmly, that none are damaged and look for cracks on the coilpack.

I had a genuine Scoob mechanic damage a plug lead during a service, felt just like that.

 

Its Newage so coil on plug. I'll pull the plugs out this weekend and have a look at them. They are only a few weeks old, NGK BKR7EIX.

If feels like fueling though as it hesitates / Bogs, then pulls fine.

Another thing I wanted to do was check my fuel pressure.

 

is the fuel filter ok?

 

Should be, replaced that within the last 8 months too with OEM.

I think its one of the following:

Air / Vac leak
MAF
MAP Sensor
TPS
Injector timing

But why it only happens when the car is nice and hot I have no idea. If you drive it hard and get it nice and warm it starts doing it. Then go easy for a few miles and let things cool off and it gets a lot better again.

 

Which is why I STILL think it's coilpack related...get it hot, the gap has opened, the spark is poor.......

 

has the car been mapped? I've seen this behaviour when the tip in values aren't right and you either swing too rich or too lean you get a splutter/stutter then takes off.

 

It is mapped yes, by Duncan.

I did think it could be the tip in enrichment but then I'd expect that to be an issue the whole time?

 

I understand what you're saying, I will check the gaps on the plugs again, they were 0.028" out of the box.

It would be handy if it threw a misfire code though, but i'm getting no CEL at all.

 

You say its better when cold and only happens when hot? when you say hot .is that after a good drive , or just after the car has warmed up?

 

After giving it some stick and getting it hot. Not just normal warm up, hotter you get it the worse it gets.

 

Couple of other things I've noticed, cruising along at say 30mph at constant throttle, the car feels like its pulsing, like you're very slightly pumping the throttle up and down.

The idle is slightly off, you can hear it change rpm very slightly like the load on the engine is changing. Needle doesn't move though.

And when it bogs / hesitates you can hear induction noise quite loudly like an N/A car which is then followed by a pop and forward thrust (Happens very quickly though)!

 

Does wet or damp weather make any difference?

 

Checked the operation and condition of the boost solenoib valve and associated pipework ?

 

Solenoid soz

 

Yeah I cleaned that out a while ago. The engine has only been in since September last year. Also it doesn't seem to matter what RPM you're at it either.

Weather makes no difference either. I'm going to tear it to pieces at the weekend, pull the plugs, check the coilpacks, compression test it etc etc.

 

Just ordered a new IACV gasket so I can give that a clean out and rule that out.

 

Is the car equiped with avcs? A faulty nps can cause all kinds of troubles like this.

If its happening at higher temps my money is on ignition, even though its got newage coilpacks they are getting old and the one near the up pipe has had a hard life.

As a test befor you pull it apart you could pipe the wastegate actuater up directly so it only boosts to half and rule out the spark being blown out.

 

No AVCS, its a 2.0 SCDB, 2.5 nitrated crank with forged rods and 2.1 stroker pistons with Newage WRX heads.