Hesitation under light load?

[93_jdm_fd]

I've been having this issue for a while now and can't figure it out. I have no problem under full load in any gear with and hesitation, choking, stuttering, etc. When I cruise in 3rd around 60km/h and step on it boost is great then go shift into 4th and try and maintain the boost it feels like it hits a wall but then takes right off.

I can get it to do everytime in pretty much every gear when I boost and let of then boost again it stumbles and pops and starts flying like a rocket.

My brother also has a gtr that has a engine getting rebuilt so I swapped his Maf's first thing, no change, swapped his ignitor no change, I have replaced the plugs and gapped all plugs from 0.6 to 1.1mm at different times and found no difference. Fuel filter is new, timing is dead on, made up a boost leak tester and found no leaks even with a evap smoke machine.

So fuel delivery problem, misfire under light load or what?

[RixR32]

ECU codes?

Check MAF wiring and connectors also. Check connectors for corrosion and wiggle the wiring see if it changes.
Check TPS voltages and set if necc. Should be .48v at idle and around 4v at WOT
Check coilpack HARNESS & coils as well. Swap for known good ones if u can from the other car.

Doesn't sound like fuel pump, fuel pump would start to give out under high demand/load first I would think...
Boost leak....same thing. Should be worse under high demand...
Possibly injector leaking maybe? How does it start/idle?

Make sure to let us know what fixes it!

[93_jdm_fd]

I did have a few injectors leaking and replaced all the top o-rings and bottom seals. No leaks anymore, I have also set the tps to like .48 and 4.5 wide open. My idle is perfect at about 950rpm and so smooth. I am going to swap out the coils and harness tonight and see if that changes anything. I also have an hks evc 3 to install and set to standard boost to rule out the stock solenoid causing any problems.

I will update as I go because this problem seems to be very common some have fixed the issue but no real definate answer as to what it was.

[RixR32]

Mine was coils/harness.
Sometimes coils test ok for OHM's but are still weak or fail due to heat,..etc.

[Skym]

Hesitation before accelerating = engine running suddenly lean. Can be ECU tune related. Idle contact is around 0.44v when TPS is new, so could be running a tad rich.

Also sometimes it can be BOV related (some people modify them which causes this problem), or gasket on BOV's are leaking if have been removed, refitted without replacing gaskets (use once only). If rounded raised ridge seal on inner part of gasket is crushed, gasket is stuffed.

On my car it was the modified stock BOV. Doesn't hesitate anymore with Synapse BOV, car just accelerates.

[93_jdm_fd]

I removed the stock BOV's to but didn't remove them from the elbow, I replaced both vacuum lines going to them. The gasket could still be leaking though. Gonna try coils and a harness tonight and see if that helps.

[93_jdm_fd]

I didn't get a chance to swap over coils tonight so tomorrow I'll do it. This issue I've been dealing with since last summer, parked the car for the winter and now it's time to deal with this problem and maybe solve it.

I think I have another common problem that a lot of us gtr drivers deal with is the cold start hesitation and I think if I find out one it will fix the other. So I start it and always bring the revs up to around 2000rpm, wait until a few minutes without moving my foot from the gas pedal the rpm drops.

This means to me that the coolant temp is up enough for ecm to lower the rpm or come out of start mode, I guess. I even notice now with the coolant temp gauge starting to come up, I can't even bring 1st gear past 3000rpm without it stumbling and then sling shot through the rest of the rpm range. To me this is not normal. I park in a heated underground parking stall and I don't think Nissan would make a vehicle that would cause a accident pulling out into an intersection.

Anyone else have this cold start issue and fixed it? My cold start and light load boost issue are the exact same stumble, hesitation symptom.

[krystalized_jdm]

Had similar issue, was my TPS.

[Skym]

Probably a combination of things (TPS, lack of functioning BOV's, etc).

Hesitation can happen without BOV's or with atmosphere vented BOV's. The recirculated stock BOV's help to keep turbo's spooled at a higher rpm inbetween gearchanges thus reduce lag when get back on throttle (can measure this with dyno). Without BOV's the turbo's can slow down too much, thus have to get back up to speed again causing the lag. Also when the turbo's slow down too much, can get reversion (air reversing direction) that heads towards MAF's and causes A/F ratio problems (usually with atmosphere vented BOV's) that can cause hesitation, stalling, etc.

HKS made this device to solve the hesitation, stallings, etc problems -

http://www.hkseurope.com/electronics/sld.asp#eids

Also if engine has mods, start up, warmup tables, etc need to be retuned and above problem could be tuned out by running a blow through MAF setup.

[93_jdm_fd]

I will swap the coils and then tps for fun but it's problably not going to fix anything unless I get a nistune set up. I have apexi filters, full exhaust so right away running the stock ecu it probably has no clue what's going on when cold and when warm under load. The stock ecu is for running the car in japan at sea level and on a stock car, not for my car at almost 3000 feet above sea level with mods.

Nistune is in the future and from hours of reading up on it last night seem this will solve a lot of problems for people running stock ecu's with just simple bolt on mods. My car runs perfect and smooth but cold and under light boost has issues.

[93_jdm_fd]

So for an update, I didn't end up swapping coils or the harness out for my brothers. I ended up swapping out his mines tuned ecu that has been chipped for intake, exhaust, rev limint delete and 1bar boost. I figured I would try this first and see what happens. I swapped the ecu and did the idle learn. Drove it home and did my usual run in 3rd, boost, shift and boost again in 4th and had no hesitation. Went out the next day and just kept it in 3rd boosted, let off, came into it again without changing gears and still had no hesitation at all.

Still not 100% convinced but will try this ecu for a few more days and see how it goes, so far so good. I think it's just adding after market exhaust and intakes will definately mess up a factory tuned ecu.

[Skym]

If at altitude, engine is probably running rich (less air at higher altitudes). There's probably a leaner tune with Mines ECU.

[93_jdm_fd]

Maybe but with this ecu it smells likes it's running rich, either way I don't really trust any chipped ecu's. At least I know it runs and acts much better with a different tune so Nistune is going to be the route I take. Gonna try this ecu out for the next day or so and see if I can get the boost to act up.

[Skym]

Thinking about it more, engine running richer should eliminate the hesitation (not running suddenly lean). I always think leaner, as engine runs into 10's at factory and usually intake, exhaust mods lean the tune out. So engine running richer makes sense.