Bad mis-fire. Need help quick. Racing Saturday

[RallyRS]

Ok.

Did some mods to get more power and now it runs like a bag of s##t.

My car is a 1989 Legacy RS. Before I did the mods explained below it already had a WRX inlet manifold and high flow exhaust. Pretty standard. Oh, but it is a rally car, so has a 36mm turbo restrictor with the standard VF8 turbo (turbo is next mod).

Anyway. I put in a 500Hp walbro pump, sti yellow top injectors, conversion to parellel fuel rails into one RRFPR with two inputs and one output to tank. RRFPR set to 35psi on idle with vaccum. Brought a PossumLink ECU and got car tuned my a mate (not professional tuner). Problem didn't happen while tuning with all the different bolt-on sensors on the car logging on a laptop.

Car had a alot more power and quicker turbo reponse, but under full acceleration would get a bad miss. I have a LambaLINK and it said it was leaning out when missing, so thought it would be a tuning problem. But replaced PossumLINK with old ecu and same problem. Note: LambaLINK connected to factory narrow band O2 sensor so probably not very useful information.

So must be fuel or spark. I replaced coil packs and regaped plugs to 7.5mm or 0.28". Same problem!

Must be fuel? or vaccum leak? This is as far as I have got.

Boost guage in car shows around 23psi of vaccum when off the power, which should be OK. Boost pressure spikes to around 18psi but normally at 15psi.

I'm sure its fuel. But I don't have a fuel pressure guage in the car. I'm getting a electronic/digital guage tonight, so that may show something???

I only help doing work on my car, as my brother is a mechanic and loves to help, but hates me doing too much (coz do it wrong). But I'm sure there are others like me out there. Anyway I have another idea what could be causing the problem, but my brother doesn't agree.

My idea:

My brother removed the carbon cansister when we did the conversion to parallel fuel rails. But when doing this blocked off the vaccum/breather line to the fuel tank. I beleive this line being blocked could cause the problem. My idea is that at full acceleration less fuel is returning to the tank, this missing fuel must be replaced by air or would cause vaccum in fuel tank. This makes the fuel pumps job harder and we lose fuel pressure. My understanding is that this would be like tipping fuel out of a hand held fuel tank without opening the air value at the top of the tank, no fuel come out. Is this a possible problem or am I nuts? is air required to replace missing fuel? Are there other areas/lines where the tank can get air to replace missing fuel?

I hope someone can help!

I'm leading my class (any 4WD turbo car) for the championship and need to race this weekend to keep in front.

Cheers
Hayden

[BAC5.2]

Misfire under WOT?

You need to check fuel pressure at high load. If fuel pressure is dropping, it could be a lot of different things. Some people overlook the little things, like the fuel filter. A clogged fuel filter can cause similar problems.

He shouldn't have blocked the breather line from the tank to the canister. There was a thread on this board about how to remove the canister and how to route the lines appropriately. Gas mileage suffers a lot though, but that's not an issue on a race car. Blocking the line can cause problems, I'd imagine.

[sammydafish]

You should get a good wideband on there and see what's really goin on. There's a good chance your probelm is fuel. Some of these cars have ground problems near the fuel pump. Your pump might not be putting out enough because of wiring issues. Check that first as it could be the issue and could also cause a fire wince your new pump will draw more current.


As far as the vent to the tank goes, just get a vented gas cap and you'll be fine. Without one, there will be to much pressure in the tank (mostly from expansion of heated fuel). This is not only dangerous but it can affect the pump performance. Vented caps are illegal on road cars equped with an evaporative emissions system (at least here in the US), which is most cars since the mid 80's so sometimes they are hard to find one that fits.

[RallyRS]

Wow. Thanks for your replys!

OK. Misfire happens over full throttle, full boost and between 4500-7000 rpm.

A new fuel filter was fit when fuel system changes made.

I have un-blocked the fuel breather and car is going better but still got problems. Before unblocking the fuel breather when the misfire happened the engine would basically stop. Now when it misfires it gives out a little backfire and keeps reving to redline.

Not sure of problem. I go the sensors log from when it was being tuned. Air-Fuel-Ratio is 11-12 thoughout entire mappable area. Alittle ruch, but best to be on the safe side.

I will try to get a breathable fuel cap. Sounds like a good idea.

I have some WRX white top coils, which I should be able to make fit. Will try this tonight. I think it is spark related, but not sure?

Might also check voltages to fuel pump.

Could increase fuel pressure, if it is a lean misfire.

I think LINK ecu's have earthing issues on old cars too???

So many variables.

If any of this indicates a problem that you understand, please let me know.

Thanks for your help so far.

Cheers
Hayden

[RallyRS]

Another late night last night, but problem fixed and car running sweet.

I fitted the WRX white top coils and made new earth/ground wires for the LINK ecu.

Not really sure what the problem was put it runs great now!

Heaps of power. I have driven many WRXs and EVOs, my legacy would now keep up with any of them. Pulls off the clock (180kph) very quickly and a monster amount of torque.

Should be good to race. I'm looking forward to the weekend.

Thanks again for your help.

I hope this threads helps someone else.

Cheers
Hayden

[RallyRS]

Just a quick catch-up if anyone interested???

Turned up at rally and car was running great. Alot more torque, great to drive in taller gears. Was a slippery day tho and struggled to get the power to the ground, as have LSD rear but open front.

Run 5 of the day. Came round a quick left too quick couldn't slow for next corner and slid off the side of a hill, knocking down a tree and rolling on to the roof. Bugger!

All that work now its stuffed!

I have a donor car and 3 weeks until the next event so might have enough time???

[sammydafish]

post up some photos of the car.... you should get some video too

[RallyRS]

Not sure how to load photos into reply? I do have video from in the car as it went off as well.[/img]

[sammydafish]

post the video on youtube, it's the easiest way... images need to be hosted somewhere else, this board doesn't have file hosting

[RallyRS]

Hi. I have created a profile on myspace.com to hold some pictures and video of car. If you are interesting in having a look, check out:

www.myspace.com/teamfanging

As yet only pictures. I have some video and have uploaded but haven't appeared yet.

Cheers
Hayden

[Bheinen74]

good thing for the roll cage. that car looked good in fresh paint, but you really smashed it up. are you okay.

[RallyRS]

Yip. I'm fine and the co-driver. It is actually looking pretty good again already. I have welded on a new roof and getting the chassis straightened today. New glass in tomorrow. Racing in 10 days, ready to do it again. Stupid sport!