rb25 random hard start

[evolution23]

Fuel pressure should increase 7.1psi or so when vacuum hose is disconnected to FPR at idle.

Looks like the fuel filter I had in my car that looked like it was never changed. Your meant to replace fuelfilter every 20,000kms or so and fuelpump, sock filter every 100,000km as part of routine maintenance. I would do a full service, replace all fluids in engine, gearbox, powersteering, etc. That's if you don't know the service history of the car.

Try removing the HKS BOV and fit a stock BOV (with new gasket as is a use once only type of gasket), stock BOV recirculation piping to rubber intake pipe infront of turbo. Probably find out that it drives better with stock BOV.

yeah i just installed the HKS bov less than a month ago, the car boosted a tiny bit better, hardly even noticeable. Im not having idle issues, idle dropping, etc.. so i figured id leave the HKS one on. i had to rebuild it once because the plastic piece in the middle of the diaphragm popped out and was holding it shut but we smoke tested and everything and its not leaking. i was planning on increasing fuel pressure by 2psi or so with the sard rising rate fpr since i have increased the boost, and im going to double check that my plugs are gapped at .8, i also have a fmic that will be installed shortly. then new oil and coolant forsure, other fluids will come later when i have some more spare cash. definitely want to the ecu tuned, i think thats part of my problems. Also have a wideband gauge and test pipe that will be going in shortly so that should help diagnose anything.

Also, when i got the car it had the stock bov and then it had an atmospheric bov on my stock i/c piping. both were functioning. So i was thinking of going that route with the hks one or would that not help?

EDIT: good news/bad news. Car did its hard start again, but it fired up a little quicker than usual when it gets hard to start and when it did fire, it barely stumbled. so it seems that it has improved quite a bit but hasnt fully gone away. so maybe it is the pump starting to go, i will try to quickly test the pressure in a couple hours if the shop not busy.

[Skym]

I think some do that dual BOV mod to get the dual GTR BOV sound or to remove all of the gas in intake piping that might reverse direction and go back towards turbo and slow it down. Recirculating BOV is best with MAF. With MAP sensor (Link, ViPEC ECU, etc) you can vent to atmosphere or recirculate BOV. On some racecars they remove BOV, put a custom blanking plate, gasket where BOV was.

[evolution23]

I think some do that dual BOV mod to get the dual GTR BOV sound or to remove all of the gas in intake piping that might reverse direction and go back towards turbo and slow it down. Recirculating BOV is best with MAF. With MAP sensor (Link, ViPEC ECU, etc) you can vent to atmosphere or recirculate BOV. On some racecars they remove BOV, put a custom blanking plate, gasket where BOV was.

ohh alright. well anyways, just got back from the shop. 36 at idle with fpr connected, 43 when we disconnect it. My sard rising rate fpr also just arrived so i will be putting that in soon, maybe even tonight. the shop says, intake is solid, ignition system is solid, Has to be fuel related. AACV and IACV got cleaned and are functioning properly, compression is all good. So they said either the pump might be on its way out or something with the wiring, or the said the stock fpr sometimes leaks pressure or fuel or something. so ill see what happens with the sard fpr, if the problem still persists then ill see if the new oil changes anything. Once all new parts are in if the problems still around ill start looking at the fuel pump/wiring. and im not sure whats going on with the boost. I usually dont boost it but on the way back from the shop i decided to give it some gas here and there and it was boosting great so maybe that fuel filter was restricting some fuel under load or something.. not sure.

[cooke24]

Have you tried resetting ecu?

Disconnect battery, pump brakes for 30 secs. Reconnect.

Not sure the tuning capabilities of a stock ecu, don't think you can do anything with the rb25 ecu. Nistune only with modded z32 ecu.

I've been wanting a powerfc for my series 2 but they are about $1500 because apexi discontinued them.

[evolution23]

The shop looked online the other day and a tuning chip for the rb25 ecu was finally released (they were surprised). I can get the site and everything if you need. and yeah iv reset the ecu a few times with no luck. Going to install the FPR tonight and set it, i believe 42.6psi is the sweet spot so ill try for that and see how things are. I think this has to do with the pump or ecu though, more likely the pump.

[cooke24]

Please send me that link. I'm pretty much at the point where the car needs a tune if I decide to keep her.

[evolution23]

PM'd ^^

On another note, Installed the FPR today, its currently set at 36psi at idle, but when i remove the vacuum hose its only rising to 40psi instead of 43. I tried to adjust it beyond 40psi but it wont go any higher (adjusts fine with the vacuum line connected). Not sure if its the fpr or something like the pump starting to die? under WOT the car really hesitates and get jerky with the boost. doesnt seem like its running properly under boost could possibly be the pump as well? (yesterday the shop said the pressure went up to about 43psi with the vacuum line disconnected but the brand new gauge i put on the FPR is saying differently..)

When engine is cold, the BOV only flutters as well until i shut the car off, then when i start it back up and the engines already warm the BOV works great... and if i go WOT the car hesitates and feels like it isnt boosting but if i back off the throttle a bit the car pulls very hard... another sign the pump is failing? or maybe blowing out the spark? Doesnt seem like its misfiring though, just seems like under WOT the turbo spools up but doesnt work, but as soon as i back off the throttle a bit the turbo works great.

New plugs and splitfire, new apexi pod filter, new fuel filter, intakes got no leaks, compression is 150 - 160 across the board, coilpack harness is also grounded nicely. So intake and ignition are both good, issue must be with fuel, im thinking the pump may be on its way out.

edited first post in thread for slightly more detailed.

[RWD_GTR]

my car was doing that with a bad tune. would only accelerate under partial throttle.

[evolution23]

my car was doing that with a bad tune. would only accelerate under partial throttle.

Still have stock ecu and stock tune, everything says that my current set up does not require a re-tune so im not really looking at that right now. since the pressure only rises to 40psi when i remove the vac line im thinking the pumps on its way out and it cant hurt to put in new plugs even tho the ones in it look pretty new but ill change them anyways.

[Skym]

As far as I know, stock FPR is a rising rate FPR (I think is 1:1 with intake manifold). I think adjustable FPR adjusts this ratio, as have control over orifice size which when smaller makes fuel pressure rise when engine is reved. Fuel pressure should rise when engine is reved, as voltage is increased to fuelpump which pumps more fuel and I think when combined with less air to FPR (pistons going up and down which sucks air into engine from plenum, FPR) it makes fuel pressure rise. Only place to test this safely is on a dyno, where A/F ratio, fuelpressure is monitored / datalogged.

The fuelpump on a factory car is not running all the time at full throttle, as it sucks power when light's, aircon, etc is on which I think puts more strain on alternator at idle. Also can heat up the fuel (need a fuel cooler) and shortens lifespan of fuelpump (brush type). If run non brush type fuelpump you supposedly can run at 100% with reliability.

If fit bigger lph fuelpump with stock FPR, the stock FPR has a small orifice to relieve the pressure inside fuelrail, so fuel pressure rises and engine runs richer at mid to high rpm where injectors are open more. To solve this rich problem requires a retune where fuel is removed via fuelmap and ignition map adjusted to suit.

Stock ECU can pull ignition timing to 0 which stops engine accelerating when on knock / low octane maps (ECU + knock sensors detecting knock). Missing at higher rpm due to wide gap on sparkplugs can make engine miss which could make ECU switch to knock maps. Even anything banging on engine (excessive noise) can make ECU switch to knock maps, as knock sensors + ECU pick it up as engine knocking. Engine running lean, knocking is another, so is running lower octane gas (sometimes it's a bad batch of fuel from service station).

[evolution23]

From what i gather, at WOT the pump is working its hardest so when i go WOT if the pumps starting to go it cant keep up the flow and is causing it to lean out and lose power. then as soon as i let off the gas a bit the pump doesnt have to work as hard to supply as much fuel and is able to supply enough fuel at 3/4 throttle so the car gets the right mixture again and regains its power. so that makes sense that that could be my problem.

The other thing iv read is that the plugs could be getting blown out but it doesnt seem like a misfire, seems like a not enough fuel or too much fuel problem. I think its either bogging down or leaning out at WOT, leaning out makes more sense to me and the pump starting to die could also be my hard start issue as it seems its doing this when the engine is warm/hot. So ill replace the plugs tomorrow anyways, and then if the problems still there im going to pick up a walbro 255lph pump as im sure it cant hurt to replace the stock one anyways, then hopefully that solves my issue. if the problems still there then im going to hold off and drive like a granny until i get my fmic and everything in and then get back to trouble shooting this. seems like the pump to me though, im about 90% sure its fuel related and everything i read points me towards the pump. plus the walbro and new plugs will come in under 100 bucks so why not, right.

Also, i should have a wideband gauge installed in about a month so if the problems still around when that goes in it should help eliminate some issues. running out of stuff it could be tho. if its not the plugs or pump, im down to ecu, injectors, ignitor, maf.. but if new plugs/pump doesnt fix the issue then after the rest of my parts in i will of replaced everything i wanted and will be sending it off to the shop to have them deal with it.

[Skym]

If hit revlimiter (fuel cut) engine can start missing.

[evolution23]

If hit revlimiter (fuel cut) engine can start missing.

no it will do it 5000 rpm+ i will try to get a video of the dash and see if i can mount my go pro down by the passenger headlight and try to get the sound, and show what my gauges are showing. Everything looks and sounds right, but it just doesnt work under WOT. to me, it seems like under WOT there isnt enough gas.

Edit:

Weather is not permitting today, its pouring rain so its hard to get the car under load cause the tires are just breaking free. Changed the plugs and gapped them to .8 but havent been able to go WOT with all this rain... uploaded video of the "compressor surge"

Stock BOV and a Walbro 255lph pump will hopefully be in tomorrow, depends if theres a break in weather or not.

[Skym]

Sparkplug gap.

[evolution23]

Sparkplug gap.

Currently at .8mm as im running .7 bar. Should i gap at 1.1mm instead? i believe .7 bar is around 11psi