I've been having a problem when accelerating hard. If I put my foot to the floor, its fine until sometimes 3rd but usually 4th and 5th. It feels like its cutting the fuel for a split second.

Ive done some background reading and i guess it could be overboost.

Engine mods are fully de-catted and hks SPF induction kit, also Forge Recirc valve. I had the problem before I fitted the Forge valve so surely it cant be that.

Anyone help me please?

Thanks

Bing.

 

anyone?

 

Does sound like Fuel cut...

Do you get a hard, de-excelleration type feeling...

If it is Fuel cut due to overboost the easiest and cheapest way to sort it is a manual boost controller AFAIK...

Can be had for about 20ish squid and will allow you to turn down the boost (just a little) to overcome the fuel cut...???

G.

 

If thats the cheapest option, then i should try that first i guess. If it turns out not to be that, sod it, i got a manual boost controller.

Ive read a lot of threads in which peeps were having overboost probs after decatting. Is this because the engine is breathing too freely and requiring an amount of fuel over the ECU's safety limit?

 

Good question...anyone? I've got a similar problem. After replacing the downpipe and up-pipe which were both blowing, it drives lovely - momentarily touching 15psi then dropping to around 11 and pulling cleanly. Only problem is that when you get up to autobahn speeds in 5th and put your foot down it will hit overboost/fuel cut. Not sure which because at high speed I'm watching the road not the boost gauge LOL

But it feels exactly like a fuel cut due to overboost. Any ideas why the ECU isn't controlling the overboost properly in 5th? Can fuel cut happen because knock is detected or AFR goes lean for example? Otherwise why would it only happen in 5th gear at high speed when the engine's having to work hardest?

 

Just picked up my first Impreza today (WRX, 1993) and having exactly the same problem particularly in 5th - when flooring it the car suddenly feels like it has hit a brick wall and I seem to remember it making a 'spitting' sound. Came as a bit of a shock as I was overtaking someone on an A-road at the time.

 

The fuel cutting briefly is your ECU protecting your engine from overboosting, as the previous fella said fit a manual boost controler and set it back a little.

Lee DT.

 

After a Decat , should get a Remap to help things.
Then get all the Boost pressure and that sorted.

 

How can fitting a manual boost control turn down the boost?
Bit confused here cos the car is overboosting all the time in 4th and 5th so that means that the boost is available. (possibly chipped already)
Surely if you add a manual boost controller, then on the minimum boost setting on the controller, you are still going to have that same amount of boost that is already causing the overboost situation. The controller will only allow you to add to what is already there.
If I am wrong then let me know, but it doesnt make sense.

 

If you are running an electronic boost controller, you no longer need to go through the boost control solenoid, thus meaning you can run wastegate pressure. wastegate pressure is always lower than standard (i think it's about 0.4bar), and is the spring pressure on it's own. The boost control solenoid raises the pressure to the ecu set level by bleeding off some of the boost.

 

Yeah, I understand thats what would happen with an electronic controller, but the previous post say use a manual controller which I think is the wrong thing to do.

 

If your car is "hitting a brick wall" then you are "over boosting"
I.e for some reason the ecu, boost solenoid and plumbing have failed to control the level of boost to a figure below that at which the fuel cut comes in e.g 13 psi.
The over boost only need be for a tiny moment (a spike) to trigger the fuel cut but once that saftey level has been passed the fuel cut will come in.
You are simply running too much boost than you should be. End of story.
By putting a manual boost controler on you are completly removing the control of boost from the ecu and the boost solenoid and all it plumbing. (which will probably be the cause of the problem - e.g a boost hose split or snapped off).
With a manual boost controller you simply control the boost via a ball and spring. Once it is set - its set.
With the MBC in place you can then adjust the boost down to what it should be i.e below the level of boost that triggers the fuel cut. e.g 11.7psi. Plus a MBC is a little better at reducing boost spikes.
So yes a MBC would solve the problem provided the boost level is reduced sufficiently.

Andy

 

I have a manual boost control on my car an my93. This is fitted to a pipe that runs into the boost solenoid, so the boost solenoid is still getting a feed to it. I dont think it is a dawes mbc on mine but I would imagine that all mbc fit in the same way?
Is this the case or are other mbcs fitted elsewhere?

 

My manual boost controller is a 2 port version and so does bypass the ecus boost solenoid.

I also have full decat but used my controller to up the boost. I had a little hesitation at 3500 rpm but fitting the controller helped. Just £25 armval version from ebay.

 

Not sure what type of MBC you have there. The one i used before defo bypassed the solenoid completly. Thats the whole point of it! so that control of boost is taken away from the ecu.

 

hmmmm think I may check the cpu, thinking about it I had a superchip on a nissan bluebird turbo, many many many years ago (I was 18 at the time, fastest taxi in the west). That used a bleed valve cut into the pipework. This is something similar.
Think that I will remove this to hopefully preserve my engine, from what Ive read my mbc is very primitive.

Out of interest, where do the dawes mbc plumb into? what is a 2 port mbc and how do this work?