rb25 random hard start

[evolution23]

EDIT: Turned out to be the pump.

1994 series 1 GTS-25T

Stock ecu and tune
Stock MAF
Apexi pod filter
Splitfire coilpack
new plugs gapped at .8mm
.7 bar boost
sard adjustable fpr 36psi idle
new fuel filter
HKS SSQV BOV
3" exhaust
turbo timer

Anyways, i keep getting this random hard start issue, it happens after i drive somewhere then let the car sit for 20 mins or so. (car wash, lunch, grocery shopping, etc..)

I am also having a WOT hesitation, whether this is related or not is beyond me. Car boost fine if i slowly increase rpm's but if i go WOT the car feels like it isnt even boosting but i can hear the turbo spooled up and its showing me .5 bar, does not sound like its misfiring, just seems like its hesitating or just not boosting. if i back off the throttle a bit the car boost hard and shows .7 bar.

Figured out a better way to word this part. When my engine and everything is cold my BOV hardly works. The turbo will spool and pressurize up to .5 - .7 bar but all i get is compressor surge. Short video at bottom of this post. I am going to refit my stock recirculation and see if that clears up anything. HKS bov works great though after the engines already up to temp and i start the car. I replaced the vacuum line going to the bov but that did not fix this. BOV is functioning though just not when the engine is cold.. I will try blocking the vacuum source i was using off the intake and run it to a different one and see if that makes a difference, if not the stock recirc will be back on tomorrow..

Last bit of info, i installed a FPR and have it set at 36psi right now, if i remove the vac line it rises to 40psi, i cannot increase or decrease it beyond 40psi with the vac line disconnected.

Put in new NGK BKR7E plugs today, gapped at .8mm. Hopefully thats all it is but i will have to wait until the roads dry up to put the car under a load at WOT. But im thinking my fuel pump may also be on its way out which could be causing the hesitation at WOT cause thats when the pump has to work the hardest so maybe it just isn't up to par anymore. Doesnt seem like its misfiring since i put in the splitfires so i dont think its an ignition problem.

Am i on the right track here? Thanks!

[BrianV8]

I have a s1 in my car I use to have that problem also. I made it better by fluke. I was trying to solve another issue so I made a grounding kit for my coil packs after that fires so much better. Give that a try

[evolution23]

I have a s1 in my car I use to have that problem also. I made it better by fluke. I was trying to solve another issue so I made a grounding kit for my coil packs after that fires so much better. Give that a try

i was actually just wondering about my coilpack harness ground, so after reading that i will definitely clean up the ground and even run a jumper ground just to see. Hopefully its that simple.

[BrianV8]

Ya like i have yellow jacket coils the works but ya decided just for kicks to build the grounding kit and ya started way better ever since. I was kind of shocked but works for me haha

[evolution23]

Ya like i have yellow jacket coils the works but ya decided just for kicks to build the grounding kit and ya started way better ever since. I was kind of shocked but works for me haha

Well ill give it a shot in a couple days, have to send the car back to the shop to get the paint fixed.. it got parked outside in the rain before the paint was fully dried so now it has some pretty noticeable water marks all over it...

[Skym]

Faulty igniton module can make engine stall after roughly 10 minutes of driving and take another 10 minutes or so before engine can be restarted (when ignition module has cooled down).

If engine cools down enough (coolant temps drop) stock ECU can be on the part of startup tables which makes it hard to start. What happens is when cranking engine stock ECU uses a fairly lean startup table, then when let go of key it switches to a richer startup table which makes engine stumble. If crank engine for longer to get pistons pumping, sucking more air into cylinders, then engine starts normally. Pushing accelerator pedal a little bit to open throttlebody at same time is another way to get more air into engine.

Other things that can make it worse are faulty CAS (when hot or cold), oil is too thick for engine which makes it harder for engine to start, idle smoothly and lose response. Factory use a 7.5w30 oil. I found 10w40 made engine start better when compared to w50 or w60 which were way too thick. TPS not set correctly or is faulty. Intake airleaks. Dirty AACV, IACV valves (if turbo has failed on compressor side in the past and sent excessive oil into them or due to blowby oil that's built up over time).

Also running dry cell battery is better. It's lighter, engine starts better, battery doesn't fail on racetrack (main reason behind why you fit a dry cell battery on a racecar).

[evolution23]

Faulty igniton module can make engine stall after roughly 10 minutes of driving and take another 10 minutes or so before engine can be restarted (when ignition module has cooled down).

If engine cools down enough (coolant temps drop) stock ECU can be on the part of startup tables which makes it hard to start. What happens is when cranking engine stock ECU uses a fairly lean startup table, then when let go of key it switches to a richer startup table which makes engine stumble. If crank engine for longer to get pistons pumping, sucking more air into cylinders, then engine starts normally. Pushing accelerator pedal a little bit to open throttlebody at same time is another way to get more air into engine.

Other things that can make it worse are faulty CAS (when hot or cold), oil is too thick for engine which makes it harder for engine to start, idle smoothly and lose response. Factory use a 7.5w30 oil. I found 10w40 made engine start better when compared to w50 or w60 which were way too thick. TPS not set correctly or is faulty. Intake airleaks. Dirty AACV, IACV valves (if turbo has failed on compressor side in the past and sent excessive oil into them or due to blowby oil that's built up over time).

Also running dry cell battery is better. It's lighter, engine starts better, battery doesn't fail on racetrack (main reason behind why you fit a dry cell battery on a racecar).

the turbo is good, no air leaks, CAS was replaced 2 weeks ago with a known working one but i am doing an oil change when i find a sandwich plate so that will eliminate the oil as i was going to use 10w40 synthetic. Im not sure about the TPS, would i have idle or revving issues if the TPS was out? cause the car revs up nicely and idles right at a constant 700. As for the AACV and IACV i will give them a good cleaning and see if that solves the issue. everything else on the car seems great, its just this random hard start issue. it seems it happens after i go for a short drive then stop somewhere for 10 - 30 mins (wash the car, grocery shopping, etc..) and actually last week when it was really nice down here somewhere around +9 and sunny it was doing this more often then when it was like +2 and chilly out.

Also i have been thinking about changing the battery because the one thats in it doesnt look all that good, maybe that has something to do with this.

[Skym]

With AACV you'll need a new gasket (paper gasket?) from Nissan.

TPS helps ECU prevent engine going lean (going lean makes engine hesitate before accelerating) when suddenly pressing throttle (transient fuel enrichment). If TPS is not set correctly on idle contact, stock ECU doesn't switch to idle tables and engine can stumble, stall if put under load. If you put aircon, light's, etc on (put engine under load) and drive car forward on flat ground, then back off throttle or drive up a hill to load engine up, then back off throttle, engine can just about stall (TPS isn't set correctly).

The 10-30 minutes, cold conditions sounds like the startup tables on ECU which is a common problem after fitting exhaust which affects ECU tune (ECU needs to be retuned) or CAS is not set correctly. With CAS, check ECU for CAS error code (clear it and see if it comes back after driving, starting engine), check position of CAS via timing light. Have you replaced the stock narrowband o2 sensor (often overlooked or never replaced and would be another sensor that could cause running too rich problems after 10-30 minutes)??? The o2 sensor is usually checked every 40-60,000kms and replaced. When faulty the o2 sensor voltage tends to be very sluggish (slow to switch between lean, rich and ECU can make engine stay rich too long which creates popping sound / flames from exhaust).

[evolution23]

With AACV you'll need a new gasket (paper gasket?) from Nissan.

TPS helps ECU prevent engine going lean (going lean makes engine hesitate before accelerating) when suddenly pressing throttle (transient fuel enrichment). If TPS is not set correctly on idle contact, stock ECU doesn't switch to idle tables and engine can stumble, stall if put under load. If you put aircon, light's, etc on (put engine under load) and drive car forward on flat ground, then back off throttle or drive up a hill to load engine up, then back off throttle, engine can just about stall (TPS isn't set correctly).

The 10-30 minutes, cold conditions sounds like the startup tables on ECU which is a common problem after fitting exhaust which affects ECU tune (ECU needs to be retuned) or CAS is not set correctly. With CAS, check ECU for CAS error code (clear it and see if it comes back after driving, starting engine), check position of CAS via timing light. Have you replaced the stock narrowband o2 sensor (often overlooked or never replaced and would be another sensor that could cause running too rich problems after 10-30 minutes)??? The o2 sensor is usually checked every 40-60,000kms and replaced. When faulty the o2 sensor voltage tends to be very sluggish (slow to switch between lean, rich and ECU can make engine stay rich too long which creates popping sound / flames from exhaust).

i definitely do get a pop from the exhaust usually if i boost the turbo but dont really go hard. like shift at 4500 so the turbo just spools up. But no i have no checked the o2. As for the TPS i will try the load tests you suggested and see what happens, i havent noticed any throttle response delay but i will pay attention today. and the CAS was replaced with a known working one and i had set it to the middle, then took it to the shop and put a timing light on it and they said i was only off by maybe 1 deg. (there was a CAS code before, cleared it, hasnt come back in 2 - 3 weeks)

[evolution23]

Alright so for the load test, the idle drops to about 1000, then a second or 2 later down to 700 like it always does. I tried the throttle response, it responds immediately but used to have a very tiny turbo lag (at stock boost) now i installed a boost gauge and am running about 10psi and the lag got a lot worse but i believe thats common so that wouldnt mean anything about this random hard start. Its only doing this when i let the car sit for a couple minutes. before the meet on saturday i stopped and grabbed a burger, went to start the car and it was hard to start. Ill get around to cleaning the valves and see if that does anything. i think its because of the exhaust, the ecu just needs re-tuned is all.

[Skym]

It's called transient response. A dyno can measure transient hp (tuning transient hp / response). There's engine response (from what I understand lighter internals help to increase this), boost response (turbo size / A/R, size of exhaust housing, dumppipe diameter, boost controller affects this), transient response (I think cam specs, etc affects this). Mines R34GTR has all of these in one engine.

I'm wondering if your car has a upgraded fuelpump (changed by previous owner) or fuelpump is on the way out. Checking fuelpressure (higher than factory) should tell you if there's a aftermarket fuelpump installed. Probably would explain the hard start when cold, hot symptoms if running excessively rich or wiring to fuelpump is faulty. But change the oil to thinner version first, then check fuelpressure. Could even be as simple as a blocked fuelfilter which fuelpressure test should pickup on.

[evolution23]

It's called transient response. A dyno can measure transient hp (tuning transient hp / response). There's engine response (from what I understand lighter internals help to increase this), boost response (turbo size / A/R, size of exhaust housing, dumppipe diameter, boost controller affects this), transient response (I think cam specs, etc affects this). Mines R34GTR has all of these in one engine.

I'm wondering if your car has a upgraded fuelpump (changed by previous owner) or fuelpump is on the way out. Checking fuelpressure (higher than factory) should tell you if there's a aftermarket fuelpump installed. Probably would explain the hard start when cold, hot symptoms if running excessively rich or wiring to fuelpump is faulty. But change the oil to thinner version first, then check fuelpressure. Could even be as simple as a blocked fuelfilter which fuelpressure test should pickup on.

Fuel pressure was checked about 2 weeks ago. I may be wrong but I think it was at 43psi then when revved went up around 45 - 47 but I may be wrong so if that sounds like way wrong numbers then I am definitely wrong. I have a sard fpr on its way from a member on here as well. I have some temp gauges on way so I will be changing the oil when I find a sandwich plate and be changing the coolant when I do water pump/timing belt and install the water temp gauge. I will pick up a filter tomorrow if I can and swap that out.

I know compression is good, intake is good (no leaks and new filter), revs great, spark is good (new plugs and splitfires), I will also ground the coil pack harness better to check that, change that fuel filter tomorrow then the oil will be changed as soon as I track down a sandwich plate (looking to find locally as I'm moving shortly so I don't want anything shipped right now). I have noticed now since the boost controller is installed, when I first start the car and go for a drive the blow off valve doesn't really work. It makes the flutter sound but won't make the psiuuu sound (HKS SSQV) but after stopping when I start the car again the bov works perfectly. so I found that slightly odd, and when I really give it gas i hear the turbo spool up and feel it pull then it kind of gets sluggish for a second or 2 and then pulls really hard. I though it was just the turbo lag but it may be something else. It feels like the car tries to boost then bogs down for a second then boost again rather than smoothly boosting. Hopefully it's not the pump going, I do occasionally notice a strong fuel smell after shutting the car off as well. Hope some of that info helps. I'll reground coilpack harness and change the fuel filter tomorrow and see what happens.

[Skym]

If aftermarket BOV is venting to atmosphere it can cause engine to stall, run rich (flames when backing off throttle), cause startup problems and is well known to cause acceleration problems if adjusted incorrectly. If is a cheap HKS copy BOV, I hear they are known to leak and I think have diaphram problems. Also the diaphram inside BOV can be affected by heat. That's why I switched to a piston type recirculated (have to recirculate BOV with a engine that has a MAF sensor) BOV (Synapse BOV) which solved alot of drivability problems I had with modified stock BOV (diaphram BOV).

Fuel pressure sounds like it's higher than normal, as RB20, RB26 at factory is around 35.5psi with vacuum hose to FPR connected and when engine is idling. I assume RB25DET wouldn't be too different, but need to 100% confirm with someone who has a R33 manual.

Can buy a R33 manual from here -

http://www.jpnz.co.nz/afawcs0131170/CATID=24/SUBID=273/page=1/products.html

[evolution23]

If aftermarket BOV is venting to atmosphere it can cause engine to stall, run rich (flames when backing off throttle), cause startup problems and is well known to cause acceleration problems if adjusted incorrectly. If is a cheap HKS copy BOV, I hear they are known to leak and I think have diaphram problems. Also the diaphram inside BOV can be affected by heat. That's why I switched to a piston type recirculated (have to recirculate BOV with a engine that has a MAF sensor) BOV (Synapse BOV) which solved alot of drivability problems I had with modified stock BOV (diaphram BOV).

Fuel pressure sounds like it's higher than normal, as RB20, RB26 at factory is around 35.5psi with vacuum hose to FPR connected and when engine is idling. I assume RB25DET wouldn't be too different, but need to 100% confirm with somone who has a R33 manual.

Can buy a R33 manual from here -

http://www.jpnz.co.nz/afawcs0131170/.../products.html

i called the shop, my pressure was around 35 when the fpr was connected, when the fpr was disconnected they said it went up to around 45psi. does that sound right? I can get it tested again if i need to but hopefully those numbers sound right this time.

edit:

OHH my. so i replaced the filter, cleaned up the ground on the coilpack harness and ran a second ground for it. i will try this and see if the problem goes away, car started the same as always but what i did find was when i ripped open the fuel filter it was filthy. filter was pure black and the fuel that was left in it was filled with contaminants. Pics below. hopefully this was my problem.

[Skym]

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.