Hi

Can anybody help, i have a 96 Impreza Turbo with mods of full de-cat exhaust system, hks foam air filter, baileys dumpvalve and re-map done by scooby clinic.

The problem i have is when first started up whether cold or warm car is hesitating off boost, feels like the car is bogging down.

Also when first started their is a slight mis-firing happening when stood still, but once you get going this dis-appears.

Also when off throttle at about 2500-3500 rpm their is violent popping / banging from the exhaust, sounds like a firework is going off.

Once car is warm approx 5-10 mins, all hesitating disappears but still have fairly loud popping in exhaust.

Can anybody please help

Cheers
Dan

 

Running rough when cold and fine when warm is usually down to a faulty coolant temperature sensor.

Normally pops and bangs on lift off usually means the engine is running generally lean if you're still using a recirculating air bypass valve however the fact that you have a VTA dumpvalve tells me on lift-off you're getting a rich state in between gearchanges or overrun, so instead of intercooler air recirculating back into the turbo inlet after the MAF sensor it's been dumped straight out to atmosphere.

The MAF has already metered the air that went in and the ECU is expecting it to be recirculated back round from the intercooler therefore fuels accordingly. Now that chunk of air is missing your air fuel mix on lift-off is rich. Although your injectors switch off on lift-off there is still fuel left in them which also goes into the cylinder. That excess injector fuel mixes with your already rich state air fuel mix which instead of being burned in the cylinder it's now being dumped out through the exhaust ports and straight into a hot inlet manifold. The excess fuel ignites in the manifold and you get pops and bangs.

Get rid of the VTA and put the original factory recirculating valve back on, that should help get rid of the pops and bangs. If you're still getting pops and bangs after that get the car back to ScoobyClinic and get them to another look at the mapping as that would then suggest lean running unless they mapped the pops and bangs in.

I take it your ECU has had an ESL board fitted and then been mapped.

 

have you ever replaced the coilpacks.. sounds like coilpacks to me.

coolant temp sensor issue would give a cel and rad fan running

you never seen overrun stratgy? removes all fuel.. or you keep it in for some pops and bangs.. vta dump valve does NOT cause rich on over run.. the ecu is not monitoring the MAF sensor and fuelling on it on overrun.. it uses the overrun fuelling stratgy...

Simon

 

Does anyone know what ECU the OP is using?

 

Not 100% sure which ECU i have, whats the best way to find out

 

The ecu is in the passenger footwell, under the carpet....

You may have to unplug the ecu and undo the top cover of the box and take some pics of the internals. As majority of aftermarket ECUs use standard cases.

This way you can be on the safe side of it being identified and you having to do the whole identification thing again.

 

Thanks for the reply, will check the ECU out tonight.

Had a look around the forum and from what info i have gathered i think it is either the coilpack or plugs that are causing the problems.

Would i be right in assuming this??