Very Slight Partial Throttle Miss, 2000-3000rpm

[Rezlo]

RB25DET S1,

All the usuals:

PFC

Q45 MAF

Q45 TB

750cc

good pump at stock fuel press

Splitfires

ectr

Start up is ok, could be a little smoother, WOT is perfect ectr ectr,

My A/F's are spot on threw the whole map, timing is decent,

Only thing that is irritating me is between 2000 and 3000rpm at light throttle loads, maybe 20% at about 2.2v Maf and about 35-40deg timing, zero knock, I get a very slight stutter, if i just tip in on the throttle its gone, and if i let off slightly its gone,

Changed my BCPR7EIX to BCPR7ES coppers last weekend in a hope the EIX's were a touch fouled but no change gapped at .030" or .76mm.

If I remember right my Q45 TPS shut voltage is about .5v, all other sensors are running smooth, no glitches or anything like that, only that one little stutter.

Ive done the remove 2-3 deg of timing and add some timing, no change, ive also added some fuel and removed some, no change, maf is clean, all seems good.

Any Ideas? Im a bit nervous going to a bigger plug gap because I run 1.4bar on my GT3076R with meth injection, but ive got a sneeky feeling they are a touch tight.

Thanks guys!

[h2k]

RB25DET S1,

All the usuals:

PFC

Q45 MAF

Q45 TB

750cc

good pump at stock fuel press

Splitfires

ectr

Start up is ok, could be a little smoother, WOT is perfect ectr ectr,

My A/F's are spot on threw the whole map, timing is decent,

Only thing that is irritating me is between 2000 and 3000rpm at light throttle loads, maybe 20% at about 2.2v Maf and about 35-40deg timing, zero knock, I get a very slight stutter, if i just tip in on the throttle its gone, and if i let off slightly its gone,

Changed my BCPR7EIX to BCPR7ES coppers last weekend in a hope the EIX's were a touch fouled but no change gapped at .030" or .76mm.

If I remember right my Q45 TPS shut voltage is about .5v, all other sensors are running smooth, no glitches or anything like that, only that one little stutter.

Ive done the remove 2-3 deg of timing and add some timing, no change, ive also added some fuel and removed some, no change, maf is clean, all seems good.

Any Ideas? Im a bit nervous going to a bigger plug gap because I run 1.4bar on my GT3076R with meth injection, but ive got a sneeky feeling they are a touch tight.

Thanks guys!

I have almost the exaxt same setup and I also have the same problem! I have q45 maf and tb, garrett gt4088r turbo running 1.5 bar, 800cc inj and running NGK BCPR7ES plugs gapped at 0.6mm to survive the boost. But at low loads in low rpm range it stutters, but if I accelerate or decellerate it runs smooth as a kitten. But cruising in low speeds its terrible! I turned the ignition table pretty high and it got slightly better but it's just a compensation for something else that is wrong. My theory is that the q45 tb is so large and with only 5% opening it lets in to much air because the powerfc still thinks it has a regular 2.5" throttle body and doesnt leave idle mode. Or it doesnt like the q45 tps, I'm trying to get a regular R33 gts25t tps sensor, it looks the same and it has similar voltage values but it does have a different nissan part nr.

[Rezlo]

I might try fit my RB25 TPS back onto the Q45TB, or maybe try adjust it up a touch, it is rather irritating, must be a fix for it.

[The Dan]

It's your o2 sensor

[Rezlo]

I run a PLX wide band and my PFC gets the 1v output, wideband has had its LSU4 replaced in the last few weeks, no change,

does it with the feedback turned off as well....

[Rezlo]

Adjusted my TPS yesterday, was at .450v, set it to .600, hesitation is near gone, I can just hear it, but cant feel it

[h2k]

Adjusted my TPS yesterday, was at .450v, set it to .600, hesitation is near gone, I can just hear it, but cant feel it

I just checked, my TPS is also set to .450v. I'll try .600 tomorrow and see if it helps me to!

[Guilt-Toy]

tune!!!

[Rezlo]

tune!!!

As I said, everything is set just right, A/F is spot on, even changed the WB o2 sensor, does it with o2 comp on and off, ive dropped the AF down a point, braught it back up a point, moved the timing down and up, nothing changes it.

Anything from 15% throttle on to 350kw im making is 100% spot on, its only very light cruize that it does it, TPS was sitting on .850v when it was doing it,, due the the Q45 TB being JUST cracked open.

Since setting the TPS up it cleared up perfectly, now a few days later is doing the same thing again, will look at it again tonight.

[Guilt-Toy]

can you take a few pics of your engine bay please? can you take a few of the air filter setup and AFM position ? I need to see how its setup.

What afr are you running when your getting this miss ?

Take pics of the location of your AFM from the mouth of the turbo and post em up then PM me once done so i can check it out.

As I said, everything is set just right, A/F is spot on, even changed the WB o2 sensor, does it with o2 comp on and off, ive dropped the AF down a point, braught it back up a point, moved the timing down and up, nothing changes it.

Anything from 15% throttle on to 350kw im making is 100% spot on, its only very light cruize that it does it, TPS was sitting on .850v when it was doing it,, due the the Q45 TB being JUST cracked open.

Since setting the TPS up it cleared up perfectly, now a few days later is doing the same thing again, will look at it again tonight.

[Rezlo]

It runs right on 14.3 to 14.5, at light throttle when it happens.

Ive richened it down to 13.2 and up to 15.5 (in small incremints obviously) with no change, today I went up a degree at a time 10 degrees in total, and back to norm, then down 10 degree's. Stuff all difference.

Out of shear desperation I even changed the MAF to a BRAND NEW Q45 unit, still nada,

TPS voltage looks smooth, grounding on the motor is all good, and my previous intake setup was near identical with no problems, and ive run hundreds of MAF'd SR20's with longer and shorter intakes with no change.

This one has got be stummed, almost at that stage of saving my pfc map, initialising and doing some basic settings just to see if its not somthing else ive fubared, but honestly, it doesnt look that way.

As ive said, 0-5% throttle its mint, and 10% + its mint, but just that TINY region its mucking about.

[The Dan]

Have you considered possibly cleaning your injectors. Or even possibly retuning. Also compression test all cylinders while engine is hot to determine if there may be an issue. You could have some buildup on a valve that is not noticeable on WOT but on cruise it's evident. It's not always a sensor or tune issue. Just a thought.

[The Dan]

Also try checking voltage to pump when it is doing it and fuel pressure in the rail also.

[Guilt-Toy]

get some plumbing pvc piping and move the afm further down inside the gaurd - also make sure there is no direct air flow getting to the AFM - so just tape some cardboard infront of it.

if you have to leave your Air filter off just for the test then do so - the aim is to get the AFM as far away from the turbo housing as possible. my AFM sits right in the front gaurd and i have a plate that stops direct air flow (mucks with AFM voltages / readings)

try that and let me know what happens... will only cost $5 and if it fixes it then you know what path you have to take.

oh also try a different AFM. it could have a issue

cheers

It runs right on 14.3 to 14.5, at light throttle when it happens.

Ive richened it down to 13.2 and up to 15.5 (in small incremints obviously) with no change, today I went up a degree at a time 10 degrees in total, and back to norm, then down 10 degree's. Stuff all difference.

Out of shear desperation I even changed the MAF to a BRAND NEW Q45 unit, still nada,

TPS voltage looks smooth, grounding on the motor is all good, and my previous intake setup was near identical with no problems, and ive run hundreds of MAF'd SR20's with longer and shorter intakes with no change.

This one has got be stummed, almost at that stage of saving my pfc map, initialising and doing some basic settings just to see if its not somthing else ive fubared, but honestly, it doesnt look that way.

As ive said, 0-5% throttle its mint, and 10% + its mint, but just that TINY region its mucking about.

Edited September 10, 2007 by Guilt-Toy

[Rezlo]

This is what makes it interesting,

Have you considered possibly cleaning your injectors. Or even possibly retuning. Also compression test all cylinders while engine is hot to determine if there may be an issue. You could have some buildup on a valve that is not noticeable on WOT but on cruise it's evident. It's not always a sensor or tune issue. Just a thought.

My injectors are about 5000km old, I did how ever run a bottle of pretty serious cleaner threw them 2 tanks ago, no change, also checked their ohm's, all good. I also run water/meth, keeps the motor pretty shiney inside.

Also try checking voltage to pump when it is doing it and fuel pressure in the rail also.

Fuel pump is hard wired, Nismo regulator is set spot on 300kpa at idle w/hose disconected and 280 with it conected.

get some plumbing pvc piping and move the afm further down inside the gaurd - also make sure there is no direct air flow getting to the AFM - so just tape some cardboard infront of it.

if you have to leave your Air filter off just for the test then do so - the aim is to get the AFM as far away from the turbo housing as possible. my AFM sits right in the front gaurd and i have a plate that stops direct air flow (mucks with AFM voltages / readings)

try that and let me know what happens... will only cost $5 and if it fixes it then you know what path you have to take.

oh also try a different AFM. it could have a issue

cheers

I did try a different AFM,

I can get it to do a slight miss even in neutral standing still,

tried blocking the front of it this morning, also no change, I cant actualy move it further down, my filter hits the bottom of the fender well.

I have done a compression test, checks out good.

Next step is to remove my map and run a base map to see if I havent stuffed somthing up.

[The Dan]

What brand injectors? What happens to the fuel pressure when the miss happens? What were the compression test results?

You need to determine whether it's a programming issue, a sensor issue, or a fuel/spark issue

[h2k]

can you take a few pics of your engine bay please? can you take a few of the air filter setup and AFM position ? I need to see how its setup.

What afr are you running when your getting this miss ?

Take pics of the location of your AFM from the mouth of the turbo and post em up then PM me once done so i can check it out.

My engine bay:

Only difference since pictures is that I have a much larger air filter on now, about double the size.

[Guilt-Toy]

Guys your AFM's are tooo close to the turbo.

Thats the problem. I had this exact issue and the only way to fix is is to move the AFM away from the turbo.

Make some custom piping out of PVC pipe like i said before and put the AFM somehwere else with double the amount of pipe length if possible and test it.

I am sure this is whats going on. I have been through this and this was the best and easist fix. My air filter grabs air from the air duct right in front of the front bar (be sure the air filter does not have the air flow hitting it because this will stuff with your air flow signals as well) i put a aluminium plate in the air duct and the air goes around it to the inner gaurd where the air filter and AFM meter is.

The good thing about this setup is that the police cannot see you have a POD and they dont defect you because its enclosed.

My engine bay:

Only difference since pictures is that I have a much larger air filter on now, about double the size.

[Rezlo]

Guys your AFM's are tooo close to the turbo.

Thats the problem. I had this exact issue and the only way to fix is is to move the AFM away from the turbo.

Make some custom piping out of PVC pipe like i said before and put the AFM somehwere else with double the amount of pipe length if possible and test it.

I am sure this is whats going on. I have been through this and this was the best and easist fix. My air filter grabs air from the air duct right in front of the front bar (be sure the air filter does not have the air flow hitting it because this will stuff with your air flow signals as well) i put a aluminium plate in the air duct and the air goes around it to the inner gaurd where the air filter and AFM meter is.

The good thing about this setup is that the police cannot see you have a POD and they dont defect you because its enclosed.

I hear you, very valid point, but before i reworked my charge pipes it was far closer, and it didnt do it, now my filter is actualy on the splash guard, it can not go any longer, it is as long as it can be... unless I use a foam mushroom filter, but in SA that is not an option due to dust, also I have my RB in an S14, so i dont have as much space.

I re-set my ecu and just plugged in the basic settings, its just noticible, but still there, I am going to extend the MAF right down with the filter off and check, What I dont understand is why it would only do it at a certain flow, mainly 2.1 to 2.3v below that its fine, above that its fine, one would think that if its turbulance or air distortion it would do it more at low or high flow, not somewhere inbetween?

Either way ill give it a try Thanks for all the help so far guys!

[Rezlo]

Fitted a Q45 maf onto a customers PFC controled SR20 S14 running a GT35R last night, for a little test, i made the AFM about 10cm away from the turbo, got some funny readings especialy when slowing down, then about 15cm away and it was perfect, 20cm away, same thing, 30cm, and the longest I could get it which was about 50cm away, and still no change from where it was fine at 15cm away, all backed up to log files with my fcedit.

Ive taken my fuel pump out and stuck it in a customers car which packed out while I wait for my tomei pump, once fitted ill re-adjust everything, failing that ill change the TPS, and failing that im going to kill somthing :-)

Will keep you updated, especialy guilt-toy with the same irritating problem,

Cheers