legacycentral bbs

hi all i have again got a problem with my 91 legacy turbo.i have fitted new coils so thats out of the question,it doesn't show a cel light when the problem occurs.
what happens is at 3-4thou rpm it hesitates like a missfire then put your foot down and the car halts and backfires,when this happens the rev counter drops to about 500rpm from 5500 also the boost gauge flies up and down.
i am running an mbc and have disconnected the standard 3 port boost solenoid.
i have also changed the spark plugs,maf sensor and wastegate actuator.the mbc is put straight in the line that comes from the wastegate.
please help.
oh yeah one more thing this seems to happen at differing boost pressures anywhere from .5bar upwards.
the performance is very poor up to this point aswell.however if you just lightly press the throttle it will go to 7000rpm no problem.

Are all the leads to the coils properly connected? Make sure all of the connections are tight and try changing out your plugs, or at least regapping them.

carl i have the same problem, and what happend to me last year around this time was i blew a piston. thats why its off the road i dont want to fuck it up agian.

the last thing i did was stick ngk iridium plugs in and after that this started to happen. i havent got to change them, cuz i just took it right off the road.

i was thinking it was all sorts of things like you spoke about. try gaping the plugs.

Did you disconnect the boost solenoid completely so the ecu has no idea what boost the engine is seeing?

hi will try gapping plugs.with the boost solenoid i just unplugged the pipes the electrical connector is still connected.is this wrong should i plumb the mbc in with the solenoid.

Also, which plugs did you use?

Please don't say Boschs...

How much boost are you running?

beleive it or not the boost is restricted to .5 bar and it still fuel cuts.
it also backfires when the cut happens.the fuel pressure drops a little nothing much and the lambda locks rich.
i have also had the car cut out a few times,today whilst fiddling i found that after removing the washer bottle i started the car and the abs warning light was on and also the battery warning light.i fiddled with the wires and the lights went out.this happened a couple of times but i can't pin point the exact cause of this.

Is it a harness that you ended up jiggling to get the codes to disappear?

The same thing used to happen to my car back in the day. It would be so finicky that when it rained I would have to jiggle some more wires.

Try to trace the wires back to their respective connectors and see if the connectors are still intact. It's a b!tch and a half to do, but at least you'll know your connections are true.

Also, you never did answer my previous question. What kind plugs are you running?

The way you described it it doesnt sound like fuel cut. Fuel cut isnt a hesitation like a misfire. Fuel cut is VERY defined, like youre slamming on the brakes for a fraction of a second.

i am running ngk platinums.there was once a topic on this forum with a download for diagnostic software,would this help me and where is it.

ok getting somewhere now i gapped the plugs down turns out they were gapped too big.this sorted out the misfire and premature fuel cut.now another problem has arose when you put your foot down it hits full boost then slowly the boost backs off til it gets to .5bar where it settles.
has anyone had this before is it simply a hole in a pipe or could my mbc be causing this.

Boost spikes are sometimes caused by the MBC.

I used to spike to 18psi before settling to 15-ish.

Whoa whoa. I thought the plugs came pre-gaped from the distributor.

i thought they did too should have checked tho,my problem with boost is it spikes to around 1bar then drops to .5 bar.should i just change the mbc for a decent one the one on there now is just a bleeder from a fish tank.

I should check that in my car. I don't trust the Zex plugs that are in there.