bucking when going into boost

[spools420a]

Hey all I finished up a 2871r/550cc/z32 maf/enthalpy ecu/

The car runs great till It goes into boost then it just cuts off and bucks real hard.First thought was boost leak,tested and holds pressure great.It was running great before the 2871r swap so it must be somthing in the area.

the first day my afr at idle were normalish around 14ish yet today they are extremely lean at idle at 17 afr.

My prime suspect is MAF wiring at this point.Zilvia is allowing attachments so ill have to send links and explain

testing the maf with car running and backprobing the (B) 0.5v signal i get 1.40v and more as rpm climbs,(c) is on chassis ground and tested good for continuity, (D) is ecu ground and also has good continuity.(e) has battery voltage tested good.



heres the wiring diagram I followed.(if link doesnt work its the JWT sr20det to z32 maf wiring diagram.

https://imgv2-2-f.scribdassets.com/img/document/16717656/original/d69d96a85e/1548985680?v%5C%5C%5C%5C%5C%5C%5C%5C%5C%5C%5C%5C%5 C%5C%5C%5C%5C%5C%5C%5C%5C%5C%5C%5C%5C%5C%5C%5C%5C% 5C%5C%5Cu003d1



The only difference is (b) is chassis ground,I will combine (B) and (C) today to ECU ground and see if that does it.along with voltage drop testing the ground wire

I'm sure someone here has had this issue so please let me know your opinions.

again car ran fine before installing 2871r/z32 maf/550cc/enthalpy.

[spools420a]

Went and changed some wires around on the maf and didnt fix the issue but I did find some clues...

right when it bogged out the afr read 10:0.1 and there is almost no BOV sounds.I did do a boost leak test on the intake side and it holds the 15 psi I will be running BUT I didnt check the exhaust side.Because Im not hearing the BOV while passing the boost leak test Im thinking maybe a massive leak around the manifold before the turbo?

I do have a smoke tester so That will be my nest step but wont be till tomarrow,any other thoughts?


UPDATE!
went to check spark plugs and gap at 0.28" and found two of the coils have split cracks in them.I ordered 1995 maxima coil packs as I read they are a cheaper alternative but wont arrive for 4 days
Does the cracks sound like the cause?

[Silv1401]

What engine and chassis are we working on?

And is your car bucking or is it bogging when boost hits? Big difference here, and tells you where to look. If its bucking like violently and abruptly engine braking, then your issue is fuel, as in abruptly not getting enough of it. Either injectors are too small, your tuning map is crap, or your pump is not pushing enough volume. Bucking is typically attributed to fuel cut, if you've ever experienced that before. Side note, water in the intake can cause this too.. ask me how I know.

If you're bogging, that could be any number of things from faulty MAF, boost leaks, weak spark, *broken coils*, fouled plugs, bad tune, etc. This is usually attributed to running way overly rich. Typically if your MAF isn't running right or isn't giving a signal, then your car will fire up and immediately die, but if you keep pumping the gas you can keep the car alive by bouncing the revs.

Sent from my SM-N986U1 using Tapatalk

[Kingtal0n]

you need to pay attention to the wideband and watch the behavior. These engines are simple they need spark fuel air and it goes ecu -> maf -> injectors so pretty basic if there is an a/f problem its one of those. And obv it needs spark so yeah you need to make sure it can spark. And air is just compression test.

[spools420a]

What engine and chassis are we working on?

And is your car bucking or is it bogging when boost hits? Big difference here, and tells you where to look. If its bucking like violently and abruptly engine braking, then your issue is fuel, as in abruptly not getting enough of it. Either injectors are too small, your tuning map is crap, or your pump is not pushing enough volume. Bucking is typically attributed to fuel cut, if you've ever experienced that before. Side note, water in the intake can cause this too.. ask me how I know.

If you're bogging, that could be any number of things from faulty MAF, boost leaks, weak spark, *broken coils*, fouled plugs, bad tune, etc. This is usually attributed to running way overly rich. Typically if your MAF isn't running right or isn't giving a signal, then your car will fire up and immediately die, but if you keep pumping the gas you can keep the car alive by bouncing the revs.

Sent from my SM-N986U1 using Tapatalk

sr20det redtop s13.

car idles and revs fine and only does this when getting to around 4-5k rpm
it feels like hitting a rev limit and just cuts out,doesnt feel like bogging or spark related really it feels like the ecu is making it cut out.Ill pull some codes in a bit/check the exhaust side for leaks and test fuel pressure

since it was running just fine before the turbo install/550cc/enthalpy/z32 Im gonna focus on these areasThank you for the reply.

[spools420a]

you need to pay attention to the wideband and watch the behavior. These engines are simple they need spark fuel air and it goes ecu -> maf -> injectors so pretty basic if there is an a/f problem its one of those. And obv it needs spark so yeah you need to make sure it can spark. And air is just compression test.

yes agreed,ive only ran the car twice since this has been going on and last time it was lean at idle and pig rich when it cut out seeing 10:0.1 afr.The way the turbo responds and sounds feels like a boost leak but smoke tested the entire system with throttle open and it holds boost.

However I did reuse the exhaust manifold gasket and wondering if I have a severe leak at the manifold which would explain the lean idle/slow resonse and possably the o2 sensor is making it jerk under boost?So today im smoke testing that exhaust side as well.
Thanks for the input and I will try and record the next time.

[spools420a]

UPDATE:

I tested the fuel pressure and here are the results...

With no vaccume line removed it at 43 PSI Fuel Pressure

Revving the engine the psi jumps to 50 psi

removing the vacuum line we see 53-56 psi

adding 10 psi of air pressure we are at 66 psi of fuel.

Pretty sure i'm on the right track to the fix now.My first thought was replae the FPR but giving it some thought Im wondering if a partially clogged fuel filter may be the issue since its on the return line side this would increase fuel pressure and reduce fuel volume correct?

anyways i ordered a z32 fuel filter and a walbro 255lph pump just because the old pump is 15 years old and cant even hear iit anymore when i drive like i used to hear it.

if this doesnt fix issue i will replace the fpr though it didnt seem like the diaphram was torn or anything.also ill look for slight kinks in the lines.

[Kingtal0n]

yes agreed,ive only ran the car twice since this has been going on and last time it was lean at idle and pig rich when it cut out seeing 10:0.1 afr.The way the turbo responds and sounds feels like a boost leak but smoke tested the entire system with throttle open and it holds boost.

However I did reuse the exhaust manifold gasket and wondering if I have a severe leak at the manifold which would explain the lean idle/slow resonse and possably the o2 sensor is making it jerk under boost?So today im smoke testing that exhaust side as well.
Thanks for the input and I will try and record the next time.

1. O2 is not used during boost. I recommend you disconnect O2 sensor until you fix the issues. It is useless for diagnostics.

2. Wideband telling you 10:1 is super rich. It means you have a boost leak or a maf related issue. Wideband needs to read between 11 and 12 (11.2 to 11.5 is ideal) for pump fuel 93 octane gasoline to run the engine properly at WOT.

3. Smoke test is not a boost leak test. You need to fill the compressor -> engine with 20psi of 'boost' pressure using an air compressor.
make sure to disconnect the crankcase vent tube before doing this. DO NOT PRESSURIZE the crankcase. Recommend pulling out dipstick just in case.

My bet is you have a giant boost leak that does not show up until the plumbing hits 5psi+ of pressure. Or you have a spark blowout issue.
Once you test with actual pressure in the plumbing to 20~ psi and rule out boost leaks, you verify the coils are good, spark plugs are gapped properly 0.032" to 0.028" is fine. DO not go lower than .027" or higher than .035". Make sure you are using the correct plugs NGK copper BKR7ES iirc.

From there it is simple maf -> Ecu -> injectors relationship. The maf placement is important, no closer than 5 to 7" to the turbo. Use a large tube for 300zx sensor. avoid reducers that are not smooth. Look at GReddy Z32 maf tube for sr20det for example. The maf should have a few inches of straight tube on both sides.
The other issue is blow-off valves screw with maf sensors, depending on the type of blow off it may be an issue. Push style BOV are designed to leak near idle from variety of manufacturers and this will cause major issues if you've removed the recirculation tubing.

This is how to properly run a blow off valve on an MAF sr20det.
https://i.postimg.cc/nVwNh0NC/20210622-184445.jpg

Notice
1. the blow off is as close as possible to the compressor (turbo).
2. The blow off recirculates AFTER the maf, BEFORE the compressor Inlet
3. The blow off recirc is far away from the maf sensor to avoid disturbing the maf sensor

This is a 450rwhp sr20det that I helped this customer to run properly after tuning it and explaining about the maf situation.
Anyway, she's finished and you were spot on. She runs like a dream. No more stalling or hesitation. All the right wooshy noises. She's like a proper commuter now. Thank you for the guidance, I couldn't have done it on my own.

[burnsauto]

well it depends on the kind of smoke test. Some use pressure+smoke, while some just use smoke alone.

But I agree, it does sound like a boost leak. ...at least from sitting in front of my keyboard.

Double/triple check every thing related to holding pressure. Check for tears/holes in couplers, check to make sure you are using the correct size coupler (not one that's close enough), and check any smaller connections (If the BOV is leaking under pressure - if adjustable, try tightening the pressure on the spring to the point where it doesn't open, also the gasket for the BOV if one is used), and any of the hoses going to or from the intake manifold.

[silviaks2nr]

Definitely sounds like a boost leak to me too. When you wire your new fuel pump in be sure to use full copper 12 gauge wire with a 40 amp relay. Only use the factory fuel pump +12v as a trigger for the relay.

[spools420a]

Thanks for all the help,YES it even feels like a boost leak.Tested by pressuring with air/smoke at 15 psi (my max boost ill be seeing) with open throttle and it hold the pressure.
---------------------------------------------------------

Z32 MAF wiring is

A - Nothng
B - signal
C - spliced into D
D - goes to ECU negitive
E - battery power
F - Nothing

C was originally had it own ground on the chassis ground but tried wiring it into D to see if it helped.nope

B gets around 1.5v at idle and as I rev it up it smoothly goes up in voltage,seeing a max voltage of around 3.5v at around 5-6k rpm

D was tested via voltage drop test and good ground.

E - is seeing battery power

I couldnt find what the signal voltage should read at the 5-6k rpm if anyone can confirm if the signal voltage at this rpm is good please let me know.

-------------------------------------------------------------------
The fuel pressure is not right though
FSM says
36psi with vacuum line connected
43psi with vaccum line diconnected


I checked the fuel pressure.
with vacuum like hooked up to the fpr it was seeing 43 psi fuel

just revving up the motor the fuel pressure jumpped to 50 psi

vaccume line removed we see around 52-56 psi of fuel


at 10 psi added to the fpr we were at 66 psi of fuel,being a 1:1 fpr i should see 53 psi and its not even consistant as it reads slightly different each time i add pressure

we def have a fuel pressure issue,It may or may not be the issue causing the issue but its somthing that needs solving.

Again thanks a bunch for all the help guys!

[spools420a]

1. O2 is not used during boost. I recommend you disconnect O2 sensor until you fix the issues. It is useless for diagnostics.

2. Wideband telling you 10:1 is super rich. It means you have a boost leak or a maf related issue. Wideband needs to read between 11 and 12 (11.2 to 11.5 is ideal) for pump fuel 93 octane gasoline to run the engine properly at WOT.

3. Smoke test is not a boost leak test. You need to fill the compressor -> engine with 20psi of 'boost' pressure using an air compressor.
make sure to disconnect the crankcase vent tube before doing this. DO NOT PRESSURIZE the crankcase. Recommend pulling out dipstick just in case.

My bet is you have a giant boost leak that does not show up until the plumbing hits 5psi+ of pressure. Or you have a spark blowout issue.
Once you test with actual pressure in the plumbing to 20~ psi and rule out boost leaks, you verify the coils are good, spark plugs are gapped properly 0.032" to 0.028" is fine. DO not go lower than .027" or higher than .035". Make sure you are using the correct plugs NGK copper BKR7ES iirc.

From there it is simple maf -> Ecu -> injectors relationship. The maf placement is important, no closer than 5 to 7" to the turbo. Use a large tube for 300zx sensor. avoid reducers that are not smooth. Look at GReddy Z32 maf tube for sr20det for example. The maf should have a few inches of straight tube on both sides.
The other issue is blow-off valves screw with maf sensors, depending on the type of blow off it may be an issue. Push style BOV are designed to leak near idle from variety of manufacturers and this will cause major issues if you've removed the recirculation tubing.

This is how to properly run a blow off valve on an MAF sr20det.
https://i.postimg.cc/nVwNh0NC/20210622-184445.jpg

Notice
1. the blow off is as close as possible to the compressor (turbo).
2. The blow off recirculates AFTER the maf, BEFORE the compressor Inlet
3. The blow off recirc is far away from the maf sensor to avoid disturbing the maf sensor

This is a 450rwhp sr20det that I helped this customer to run properly after tuning it and explaining about the maf situation.

Thank you GREAT info!I didnt know how picky the mAF was?!?

This has me thinking as I have a very small air filter because the one I had didnt fit after installing the MAF.I'll try removing it just to see if it makes a change but wont get to that till after the new walbro pump gets installed.,Also im using the original rubber piping past the maf and it does have some nasty S bend.Also no my bov isnt recirculated,I will try removing the BOV and see if it helps and if it does I will buy a recirc one. Ill try everything you said thanks again!

PS doing the smoke test the system was pressurized with air as well at 15 psi which is a few more psi then im running.It wasnt just smoke alone.

Spark plugs are BKR7E-11 not sure if the 11 makes a difference so I ordered NGK BKR7E.

[burnsauto]

it sounds like you're on the right track looking into the fuel pump and maf. was the maf new or used? can you confirm it worked on a vehicle before? how did the car run before you upgraded the turbo and the supporting mods? are you 100 percent sure that the tune from RSE is accurate? Were the injectors new or used?

it's a shame you couldn't datalog any of this..

[Kingtal0n]

The reason you want copper plugs is because they are cheap.
The BKR7ES should be a $2/each plug
gap them down for getting your engine on the right track.

Always use new plugs when diagnosing issues so you can inspect the plugs to determine what sort of issues you are facing (oil/fuel/wet/dry/whatever)

Keep a second and third set of cheap plugs set aside brand new plugs for replacing when you fix some issues, to get a new read on the situation.


Maf voltage looks about correct. 4.5V is approx 450rwhp so 500hp or 520bhp or so at full 4.5 to 5volts which you are probably very far from so 3 to 3.5v is fine

Fuel pressure regulator is adjustable? Set to desired pressure around 43-44psi while engine is off (no line connected = engine off).
If regulator is OEM and the pressure is high,
A. replace fuel filter (use 300zx filter)
B. possible clog in return line
C. possible bad regulator (Never seen one though)
D. possible overpowering the OEM rail (are you using a walbro 450 or some huge pump?)
E. possible bad fuel pressure gauge

In any case, 50psi of pressure is not that much extra pressure over 44psi. It should not make a big difference (5% fuel adjustments?) But it IS a diagnostic concern and should be fixed.


So again, it goes
Maf -> ecu -> injectors

Thus, if there are NO boost leaks, and the maf sensor is CORRECT, and FUNCTIONAL, and placement is PROPER,

The only thing left is tuning wise (injector size & delay setting mostly, maf selection), & wiring related. The ECU must control the injectors based on what it see from the maf sensor. For ROM TUNES I always use a SAFC to dial in the exact a/f ratios as needed because ROM tunes vary from car to car. This is due to differences in the various AGED components i.e. the maf sensor on one car will be 3.2v the other will be 3.4v for example, it needs dialing in using an SAFC to achieve proper a/f ratios. Another example, 550/740/etc...cc injectors vary greatly in lag time (latency delay) and system voltages (one car is 14.4v the next is 13.8v etc) thus the injectors are ALWAYS a variable.