Before you read this, I don't wanna hear any crap about "OMG WHY ARE YOU USING AN FMU ON A BUILT MOTOR?"
I'm using an FMU because it's a damn leaf blower turbo and it's a temporary setup.

With that said:

I have a T-25 KA24DET, and it's having issues. The mod list is as follows:

Engine:

-Supertech 8/6/1 Forged Pistons
-Eagle Forged Rods
-Ported/Polished Head
-Fel-Pro Headgasket
-ARP hardware
-T25 from an SR20
-Small FMIC
-Greddy Type S Knockoff BOV

My problem is that my car will not go into boost at full throttle. The perfect way to explain this is it feels like the speed limiter that happens when you top out a 240SX in it's stock form. Hopefully that makes sense. When boost kicks in at full throttle it falls on it's face, like vrooooom ---> boost kicks in ----> bwahhh bog stutter, etc.

(the car has the FMU now) It doesn't have the 6:1 FMU on it right now, and I haven't been driving it, but I still feel as if it should go into boost just fine. I've seen videos on youtube of people with KA-T T25 setups and their cars go into boost without ANY fuel management. I'm not saying that's a good thing, cause it most certainly isn't, but I'm saying that something must be wrong with my setup, not allowing it to go into boost.

Possible boost leak?! What's going on!

It does however seem to build boost at half throttle...and it also has a slight miss at idle. My spark plugs are NGK BKR6E gapped @ .028

So you are saying that when the boost should come, the engine starts to run like it's like on rev limiter ? or the engine is just dyes ? there are many causes why these could happen, i could help you with it, the best way is if you shoot a short video of it and post it so i can hear exactly.

I'm saying that while at full throttle and boost kicks in, it bogs like CRAZY. Like it doesn't even accelerate. But it doesn't die.

If you've ever topped out a stock 240sx you'll know exactly what I'm talking about. It's not like the rev limiter...it's not the bwa-bwa-bwa-bwa-bwa sound. It's like the SPEED limiter, vrooooom (speed limiter hits) bwaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa.

Not enough fuel maybe? Clogged fuel filter?

And I can make a video tomorrow, it's 3:24 AM over here in California.

Well I had to say that, cause everybody's brain explodes when I tell them I'm using an FMU. FMU's work. It's a T25, not a GT35.

Anyway, the engine also has a slight miss now...which it never had before I installed the turbo setup. Here are my ideas...?

1.) Possible clogged/dirty fuel injector, bad seal?

2.) Possible clogged fuel filter, but wasn't noticeable before, since it didn't call for as much fuel as the turbo setup?

3.) Boost leak? I'll be making a tester for this.

I have changed the cap/rotor, and I have new spark plugs, so I don't think it's a spark issue.

are u still using ur oem filter? u really need to change it to a 300zx one.. also u REALLY need a wide band to monitor ur afr's.. like kouki munster said, u could have too much fuel or not enough n that could lead to a big headache.. u got some good parts on ur motor n could ruin in it..

how much boost u running?.. r u running the stock fuel pump?

1 more thing, i may miss read ur post but what r u using to tune ur car? ecu? safc?

It wasn't really the fmu part that made me face palm, but that is beside the point.

Start with the simple/cheap stuff first, then move on to the more complicated stuff, and a wide band o2(should have it anyways since you are running an fmu) will help greatly in figuring out why it is bogging under boost.

I do plan on getting a wide band. I absolutely need it, and I'm going to get it as soon as possible. I haven't even been driving the car, cause of this problem, so no worries.

@ MixedS14, it does have a 300ZX filter on it, but I can't even remember the last time I changed it. I bought a new one today, and I will be installing it tomorrow.

@ Kouki munster, what do you think it possibly could be besides fuel? Or are you absolutely sure it's fuel related? That would even cause the miss at idle? Which means there's not enough....right? Oh and I fixed the text so you could stop face palming, LOL.

I had an issue like this once. My airfilter was one of those paper type filters. I switched to a K&N one and it went away.

How's your car at idle? If it's unstable I'd also check for vacuum leaks.

It has a cone air filter, seems fine to me..?

At idle it misses and is unstable. And when I drive it very slowly (like 5-10 MPH) it feels like I'm towing an anchor.

From what you described I'm reasonably confident that the issue is related to either to much or not enough fuel, but it is hard to say what is causing it without actually being there to tinker with it.

The miss at idle can be caused by a number of things, all of witch may or may not be related to the bogging issue.



Edit: just re-read your first post, it seems to do fine at half throttle, but it bogs at WOT, that really makes me think that it is not getting enough fuel, I'd say put on the fmu and get a wide band on it quick.

Well, does a turbo car use more fuel, even at idle? If that's the case, maybe I do have clogged injectors, etc...

It's almost like it's running on 3 1/2 cylinders.

And yeah, it does build boost at half throttle, but it still feels like I'm towing an anchor.

How was the idle when it was stock?

The fuel requirements at idle will be for the most part be the same with or with out the turbo, and any fluctuations will be compensated for by the factory ecu programing.

Is it just missing at idle or is it surging up and down a few hundred rpm?

Also, do a compression test on it to make sure that you didn't hurt anything in the motor.

And just because I don't think that I've said it yet, you really need a wide band o2.

Razi wrote:How was the idle when it was stock?

The idle at stock was perfect!

kouki munster wrote:The fuel requirements at idle will be for the most part be the same with or with out the turbo, and any fluctuations will be compensated for by the factory ecu programing.

Is it just missing at idle or is it surging up and down a few hundred rpm?

Also, do a compression test on it to make sure that you didn't hurt anything in the motor.

And just because I don't think that I've said it yet, you really need a wide band o2.

It's just a miss, it doesn't surge or anything.

Hmm, I'd check for vacuum leaks then.

When I had a vacuum leak, my idle was a bit unstable.

I did a mental checklist of all vacuum related things on my car and double checked them all and found that my EGR block off plate wasn't sealed properly.

I plan on pressurizing the system tomorrow to check for boost leaks, using this:

http://www.vfaq.com/mods/ICtester.html


And I'll check my EGR block off plate as well, etc.

StryfeS13 wrote:It's just a miss, it doesn't surge or anything.

That makes me more confident that nothing is hurt in the motor, I still suggest doing the compression test just for peace of mind.

Well I'm sure nothing is hurt in the motor, it's not like I've been going around stomping on it lol. I drive it up my street, see if it goes into boost, and when it doesnt i put it in neutral and "putt" it back home.

I'll do a compression test tomorrow.

Any other thoughts?

what maf are you using?..and check to see if your knock off BOV is the issue...it may be stuck open...ive seen that before..specially with the greddy knock off's...you should pin out the injectors (ohm test) to see if all are functional...allso..when you did your build..did you plan out the injector size too..or did you leave em stock? ...last but not least....before you run the car again....get a wideband..and a ecu tune.

Stock maf, heard it's good up to 230 hp range (read this on KA-T.org) which I'm definitely no where near @ 7 psi. The BOV isn't stuck open I already checked. I'll test the injectors tomorrow.

When I get the money I plan on going with 550's and a Z32 maf, and a T3/T4. But this is just a temporary setup I'm running right now.....

Update...

-Made a boost leak tester today. Found a leak at the outlet of the turbo, and a leak on the cold pipe where it branches off to the idle-air. Fixed both.
-Removed and cleaned injectors, put new seals on them
-Tried removing the air filter as Razi said
-Changed my fuel filter
-As stated before, I fixed all boost leaks. I pressurized the system to 20+ PSI and no leaks were present.

Did NOT solve my issue whatsoever. It still won't go into boost, feels like it hits a wall when boost kicks in.

And now my car doesn't want to idle at ALL.

I'm thinking when I install the FMU it will be fine. But the idle issue.....idk.

Hows it idle with the MAF disconnected?

Hm, I haven't tried that yet. What would it mean if it idled fine?

That the MAF is malfunctioning.

The MAF worked fine before, what would cause it to malfunction now? Hope that's not it..

Dunno. But it's an idea haha.

Anything else that could possibly be wrong...? This is so freaking aggravating haha.

Possibly this...? I don't have the actual Greddy blow off valve in the picture, but mine is exactly like that and has that bottom nipple too (the angled one) What is that for? I don't have it going to anything on mine.