WRX101

I had my Imprezas engine rebuilt after it lost compression which was caused by a faulty MAF (Mass Air Flow) sensor. It was mapped with a dump valve on etc. before however when the engine went, it also seized up my HKS dump valve.
I run the 'new' engine in and everything went fine, however now I feel the car is overboosting due to it having no dump valve and it was mapped with one.

Should I have the car re-mapped or put a new dump valve back on in the hope that this will sort out the overboost?
My worry is that dump valves aggravate MAF sensors but if the car is mapped to have a dump valve, is it unlikely to cause the MAF to fail?

Hope I've made myself clear and you guys can give me some advice.
Thanks

Curtis450

Dump valve simply lets off the excess boost when the throttle is closed. Doesn't affect boost levels. Although not sure how it 'seized' when your engine went... or how you lost compression due to the MAF?

edit - the d.v will make it run slightely rich yes, with the MAF, and if its tuned to not do that, then its best to wack a d.v back on yes, any will do, doesn't ACTUALLY matter, but a good make like Forge would be good

WRX101

I believe the MAF went shortly after I had bought the car. I put a dump valve on without getting it mapped. I drove it around as normal for over a year unaware the MAF had gone causing it to run lean and detonating. It was only when I went for a full re-map that I was told the problem wasn't due to the modifications, it was because the MAF had gone and they were suprised my engine had lasted that long after hearing it 'pinging' through headphones. I got about 4 months with a new MAF and being correctly mapped for the mods, before the engine finally went.

f4la k

iTrader: (1)

Just use the standard bov. its far better than many of the aftermarket chav whisles..

Jolly Green Monster

iTrader: (4)

you should get it checked / tweaked when then engine change was done really to ensure the issue that caused the engine to fail, most likely maf as suggested is now resolved and that the first map was not on a failing maf..

The dumpvalve if not leaking shouldn't effect the map and you should be able to swap between etc.. however it sounds like one was possible leaking / faulty possibly when it was mapped.

Get it checked / tweaked to be safe.

Simon

WRX101

They swapped the MAF sensor when it was mapped. I have since bought a brand new MAF to be safe as well.
Do you think then that by putting another dump valve on will fix the problem? or should I have it 'tweaked'?
In your experience do dump valves cause the MAF sensor to go more frequently even if they are mapped with one correctly?

WRX101

Thanks for your updated message Curtis.
Why do you rate Forge? Any particular model?
I was thinking about another HKS SSQV as they sound very good I think!

The safest thing is probably to get it re-mapped again but I don't see why putting a dump valve back on again should damage it, if it was mapped with one in the first place.

Curtis450

Won't damage it all no, it simply reads the air flow going in and tells the ecu how much fuel to add. The dump valve kind of defeats this. But just get a new one, put it on, and get the map tweaked as said. Piece of mind then you know when you are giving it some that its 100% safe and wont go bang again.

Forge are just good solid design and dont open up at silly low revs and low boost.

WRX101

Interesting. The HKS did release air at quite low revs, I didn't know this was bad though.
Dump valve and a re-map you say?? In an ideal world yes I'd agree with you but I'm low on funds at the moment so was thinking:
1. Either get it re-mapped 'without' a dump valve.
OR
2. Buy a new DV and this should sort it out like you said earlier.

Id rather not spend £200+ on a dump valve to find out after that it still needs re-mapping you see..

Jolly Green Monster

iTrader: (4)

If I am reasding correct you are saying it was mapped on the previous engine, therefore must be checked and tweaked if required

Curtis450

200 on a dump valve???!!!! Look on ebay, or on here.. probably around 40 quid. If its one or tova- a map obviously.

WRX101

Thank you for replying.
I had the engine 'rebuilt' but its the same engine. You see, once I'd run it in and could put my foot down again, the performance of the engine didn't feel quite right, I assumed it was because I had to take the dump valve off and put the standard recirculating thing on, therefore it's recirculating the air which the ECU thinks is being blown off. You're saying I should get it re-mapped again then? You don't think putting a dv back on will solve the problem?
Cheers

Jolly Green Monster

iTrader: (4)

the dumpvalve only (or should only) dump air on lift off.. it has no effect on performance when you put your foot down. It is possible to tune the pick up on gearchange with differing dumpvalves etc but if it is not leaking be it dump to atmosphere or recirculate it should have no effect on the map or performance.

the fact you are saying the dump valve is effectying it would indicate one or other of the dumpvalves is leaking or it was mapped with a leaking dump valve etc.

Simon