Limited Throttle

[shaggy240sx]

Ok...So my SR powered 240sx has been sitting for about a year now, and I am finally getting around to working on it. My biggest problem right now has me pretty well stumped (not that that takes much).

First off the engine will not build more than about 4psi of boost. Not really a shocker since it has a FMIC, so boost pressure can be expected to drop a few psi, but I am pretty sure that it is not really making 4 psi because it seems way to slow. Also, there doesnt seem to be any difference in acceleration from 1/2 throttle to full throttle. No matter how hard I floor it, it always feels like it is at 1/2 throttle.

It does have an upgraded fuel pump (bbk 255lph if memory serves), but it is still using the stock 240 exhaust.

Any ideas/suggestions?

[Ritz S14]

Boost leak?

[shaggy240sx]

Boost leak?
That would make since, but I am not sure that makes since. If it is really making 4psi it should be faster than it is, so I am not sure that is the cause. My Pickup is faster than my 240 right now...and my pickup is as slow as they come. There very well could be a boost leak, but I am thinking there has to be something else going on to make it as slow as it is.

[timmybgood]

check your throttle body and throttle cable and pedal to make sure nothing is sticking that wouldn't allow the butterfly to open fully

and boost leak is the only other thing i can think of, because i can build over 6lbs at 1/2 throttle

[shaggy240sx]

check your throttle body and throttle cable and pedal to make sure nothing is sticking that wouldn't allow the butterfly to open fully
Ok...pretend I have the intellegence of a 5 year old and tell me that again please. :D

[ultraDorksGarage]

normally a boost leak that big on MAF equiped cars wouldnt run. would miss like crazy. like above posters i'd agree to check throttlebody for 100% opening first....then diagnose from there.

[shaggy240sx]

like above posters i'd agree to check throttlebody for 100% opening first....then diagnose from there.I appreciate the advice, but that doesn't really help me out without a little bit more information. I am a dumbass when it comes to working on cars (I can do oil, and brakes). :confused:

[fliprayzin240sx]

Stuck wastegate actuator. Try another actuator, and that should bring u up to 7 psi.

[s14 blacktop]

go to a mechanic! if you dont know anything....

[shaggy240sx]

If I could afford to have someone else work on it I would...but since money is tight I need to figure out how to fix it on my own (or not fix it at all).

I dont think it is the wastegate actuator because it moves freely when I move it by hand (although my car knowledge is limited). I suppose I could disconect the hose that goes to the actuator to see if it builds more than 4psi. I just need to be careful not to over do it.

I will see if one of my buddies knows how to check the throttle body. Thanks for the help so far.

[Jdotsturn]

Did you put your engine in yourself? Or did u have someone do it for you?

[shaggy240sx]

Had a shop do it for me. Turns out they werent exactly competent...screwed me over on the swap and then went out of business (for dealing drugs, or something like that). Thats why I have no money, and a bunch of problems to fix.

[shaggy240sx]

Ok, So I just tested the throttle body and Actuator and neither appears to be the reason.

The Butterfly opens all the way, and it still wont build more than 4 or 5 psi even with no hose on the Actuator.

I am starting to think it might have to be a boost leak like most of you have been saying, I cant think of much else. Do you think it might be possible that the stock exhaust is to constrictive to allow it to build more boost?

[fliprayzin240sx]

If I could afford to have someone else work on it I would...but since money is tight I need to figure out how to fix it on my own (or not fix it at all).

I dont think it is the wastegate actuator because it moves freely when I move it by hand (although my car knowledge is limited). I suppose I could disconect the hose that goes to the actuator to see if it builds more than 4psi. I just need to be careful not to over do it.

I will see if one of my buddies knows how to check the throttle body. Thanks for the help so far.


Umm...actuators not supposed to move....still think its a stuck actuator so swap it. You said it yourself, you dont know wut ur doing, were giving u ideas, just frickin try it. If the actuator is stuck patially open all the time, that mean your turbo is not spooling pass 4 psi. Tap the actuator vacuum line to one of the top 2 nipples on your throttle body and dont T off anything else off it.

[shaggy240sx]

Umm...actuators not supposed to move....still think its a stuck actuator so swap it. You said it yourself, you dont know wut ur doing, were giving u ideas, just frickin try it. If the actuator is stuck patially open all the time, that mean your turbo is not spooling pass 4 psi. Tap the actuator vacuum line to one of the top 2 nipples on your throttle body and dont T off anything else off it.
A new actuator is around $80...and I cant afford to spend that if it turns out that isnt the problem. Is there a way to test the actuator, so I know if it is worth spending the money? Also, the actuator doesnt move...its the arm that comes out of it that moves (it doesnt move freely like I originally said, but I can move the arm by hand if I try hard enough). I took it for a test drive with no hose on the actuator...which from what I have read should have allowed the turbo to build psi until it blew, and I still did not get more than 4 or 5 psi. Also, the actuator is connected directly to a nipple on the piping itself. I can move it to the throttle body if you guys think that would be benefitial.

I will test whether the Turbo Wheel (or whatever it is called) spins freely, and try to fix the timing (seems to be a bit off) and see where that gets me. Thanks again for all the advice everyone. I appreciate it.