Funky Sr problem...

[daryl337]

Hello all, I am sort of new to the SR20DET world, and after doing some investigation through your searches I had not found anyone describe the same symptoms I would like you to figure out with me. So you know, I have a Redtop SR20 which I transferred over to my '90 240SX keeping the stock SMIC.

Starting up my car, the little kitten idles fine, perhaps 50 rpm's too low which is easily changed with the idle set screw. Here is my problem. T.T Note that this does not happen 100% of the time but it happens quite often and can be counted on to occur again.

Opening up my butterfly from the engine bay (considering I cannot be two places at once) I get an incredible popping sound (Which sounds alot like a loud paintball gun) that originates from my compressor intake tube. At the same time that this happens a puff of exhaust gasses comes out the turbine side of the turbo. From the drivers seat, applying throttle to the gas you can hear it... and then I also notice while looking at the tach that the engine seems to rev slower than my KA, that is, it does not seem to climb though rev's in an instant, instead it provides a slower steady climb which takes about 5 seconds to get to redline.I had test driven it before I fixed the boost leak, and I am about to describe what occurred hoping that the answer coming back to me isnt just "boost leak you idiot."Starting out in first gear, you can crawl at a moderate speed as long as you dont throw the pedal to the floor, but second gear is where things started to act funny. Shifting into second, you let out the clutch and for what seems like a millisecond the car seems to act just like it did in first, but the second you hear the turbo spooling a large powerloss is apparent followed by a violent attempt by the engine to shut down.Could this be the ever so common (Or so I have read) MAFS wiring problem? My only reason for not thinking it is so is that standing still... I can rev the engine to 7,000 rpm's and not feel anything wrong with the engine other than the popping noise which starts in the low RPM's and disappears after about 3,000 Rpms. I have checked to see if my wastegate is stuck which I would associate with a spooling problem as well as a compressor surge (Perhaps that popping sound is air coming back up through the intake system?) , and quickly grabbing the actuating rod and moving it I found that it is not. At first I thought the problem was severe boost leak (which there was at the time) But I had fixed that and now I have this problem remaining. Here is the incredibly sad part... which makes me feel like a jack @#%... I am not 100% sure that my vacuum hoses are in their correct locations. I am going to list the hoses I have connected and what they are connected to... and I would like you to correct me if you see a problem in my vacuum diagram (verbally expressed)..

-Starting at the BOV located at the SMIC, the vacuum hose coming up T's to the large nipple on the throttle body, and the horizontal nipple on the selenoid with the green top (located on top of the power transistor)-If I am correct about my selenoids.. located under the power transistor is the Pressure regulator control solenoid(Which I will call the PRCS now since I am lazy) which has 2 hoses... the one located furthest forward in the engine bay T's off to the wastegate actuator valve and the intercooler piping (plugged onto the little nipple/ that is coming from the piping and is located near the carbon canister). The hose from the rear side of the PRCS plugs into the bung located on the compressor intake tube via a female->Male adapter piece.-The other upper vacuum line located on the throttle body goes to my fuel pressure regulator, while the lower one goes to the carbon canister.

I have hypothesized a few answers to my problem but am not sure if they are it. To further describe the popping noise, think of it as a backfire which resonates sound through the intake tube.

A) Perhaps my PRCS has gone bad and is preventing my wastegate actuator from doing its thing? B) It could be a MAFS problem but it seems funny that it would discharge air like it is (Or atleast like I think it is), I would usually associate it more with the slow rev's, although it can rev up to 7,000 rpm's as long as I take it up there slower than normal. C) I am a retard and should check over my vacuum hoses for the 1 billionth time to make sure that they are secure and without cracks.

I am sure that this problem is not unique and might be something that is stumbled upon quite often, however I have never heard of people describing these symptoms to me. So I thought I would ask here. So please... release that infinate knowledge about SR's onto me so that I may become a troubleshooting guru.

I did the wiring myself, using my SR's interior harness (from the clip) to extend the necessary wires.My timing is set at 15 degrees, I know this because I had timed it a couple days ago... and yes I have taken off the crank angle sensor plug to allow my oil pump to prime and circulate. My dash light concerning oil pressure is off like normal.

It feels as if the throttle positioning sensor is messed up, however I dont think that is the case. So if you have any other suggestions please tell me what may be the problem and what a solution is to fix it (Without pulling my engine back out. xD)

Sucking on the vacuum nipple to the bov... I was able to get the valve to open and close... and then blowing on the inlet and outlet hoses the valve seemed to be sealing up rather nicely. So I think that throws it out of the problem area. The hose to the wastegate actuator is actually still attached... so there went that idea as well... however throwing open the throttle and closing it at high RPM does not seem to show any signs that the wastegate is actually opening (Watching the rod... it does not look like it moves)I took it for another test drive (hoping that I some how miraculously fixed it... but that was not the case)Taking detailed mental notes... I found that at 3,000 rpm's (almost on the dot) the popping noises stopped... however acelleration was still completely sluggish. Tomorrow morning I have to investigate further (Its been 3 days of tweaking and trouble shooting and I have still not come up with a solution)

[Blown240sx]

Almost sounds like compressor surge... Im not toally sure but Ive seen those symptoms with that case. It had something to do with the BOV setup. I belive it was on this forum or that dead forum and they told how to fix that problem.

[daryl337]

Fudge.. I searched around but I dont think I found a sure way to fix it. T.T

[Luke]

Make sure the timing is correct. Adjust your TPS to .455v on the center pin. (you can un-screw the 8mm bolts and rotate it to adjust it). Then make sure you're BOV isn't leaking and your intercooler couplers are secure and not leaking.

One thing I can assure you is that you do NOT need the solenoids for the boost (green knob). Take the 2 things off the ignitor chip plate and toss em!

The vacuum lines are simple: 3 lines start at the throttle body. The bottom one goes to the canister, block it off unless you are using the canister. The larger one on top runs to the bypass valve (BOV). The smaller top line tees to the fuel pressure regulator, and runs across the front of the engine to your boost gauge and/or the boost pressure port on your boost controller.

[ItzGenX]

Ahh yes, slow revs in neutral indicate very low ignition timing.

[daryl337]

Thank you all, we have traced it back to a faulty CAS which was sending crappy signals in lower RPM's.....

That is fixed and now I just have a stutter pre-boost... however during boost I run fine. I am thinking it is the BOV leaking or something.. and then closing up afterward. However the car is drivable as long as I dont throw my pedal to the floor before I am boosting.

[Luke]

Thank you all, we have traced it back to a faulty CAS which was sending crappy signals in lower RPM's.....

That is fixed and now I just have a stutter pre-boost... however during boost I run fine. I am thinking it is the BOV leaking or something.. and then closing up afterward. However the car is drivable as long as I dont throw my pedal to the floor before I am boosting.

Faulty CAS, what did you do... replace it?