1990 240SX KA24E idle problems after swap - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

sil80drifter · 04-19-2006, 10:59 AM

Here is the situation:
I have swapped an SOHC into my 90 240SX, as my other engine blew.
The only thing I've changed were the head and block (long block some would call it). The intake manifold remains the same. All of the sensors/equipment that were on the intake manifold remained there from the other engine, and before their setting allowed the car to run. I am running 460cc injectors with and SAFC, and the settings there also didn't change, as the car ran fine and idled before. The car is turboed, but the wastegate is left open, and this exact configuration ran fine before with the old engine.
I've done the timing chain on this swapped in engine, and as far as I know the engine is in decent condition, and has 70k miles on it.

So when everything was connected I've tried to start up the car. It has a hard time starting, and when it does, it idles at 2000 rpm, and bounces between 2000 and 2400 rpm and backfires crazily. The timing light shows timing around 15btdc (stock) then. It is not very responsive to throttle, and I cannot get it to revv higher than 4k. When I turn down the timing to around 0 BTDC, the engine idles more regularly, still around 2000rpm, and there is less backfire.
But, when the car is set at around 0 BTDC, it won't start at all, I guess the timing is too retarded.

I cannot figure it out. All the things are just the same. Could this be a timing chain issue (a tooth off)? I've done the chain quite a few times before, so it's not a likely thing to happen, but I guess not impossible.

The oddest thing about this idle is that my vacuum/boost gauge shows around 0 when this idle is going on. So this leads me to believe that something is really wrong. I just can't figure out what. I've pulled the water temp sensor plug and the idle got worse, as expected. All sparkplugs are firing and injectors are injecting, I've pulled them all in order and saw a definite difference. The only thing I didn't check was compression, but that doesn't seem to be a likely culprit.

Any help/advice is appreciated.
Thank you,

sil80

s15iv · 04-19-2006, 02:06 PM

sounds like you might have an air leak somewhere around the intake manifold. Check gaskets for air leaks, make sure vaccum lines are connected properly and also look for pin holes in vaccum lines.

NIK90s13 · 04-19-2006, 02:15 PM

+1 on the intake leak, spray carb cleaner on intake/ vacume lines ect. see if that changes the idle.

sil80drifter · 04-20-2006, 01:16 PM

One more thing that I thought of, since the car idles without any vacuum, maybe the timing is so messed up that it spools my turbo while idling, and that's the cause of the 0 vacuum. I'll try to run it N/A by connecting the MAF straight to the intake manifold, but if you guys have any other suggestions, let me know.
sil80

04-19-2006, 10:59 AM	#1
sil80drifter Leaky Injector Join Date: Jul 2002 Posts: 54 Trader Rating: (1) Feedback Score: 1 reviews	1990 240SX KA24E idle problems after swap Here is the situation: I have swapped an SOHC into my 90 240SX, as my other engine blew. The only thing I've changed were the head and block (long block some would call it). The intake manifold remains the same. All of the sensors/equipment that were on the intake manifold remained there from the other engine, and before their setting allowed the car to run. I am running 460cc injectors with and SAFC, and the settings there also didn't change, as the car ran fine and idled before. The car is turboed, but the wastegate is left open, and this exact configuration ran fine before with the old engine. I've done the timing chain on this swapped in engine, and as far as I know the engine is in decent condition, and has 70k miles on it. So when everything was connected I've tried to start up the car. It has a hard time starting, and when it does, it idles at 2000 rpm, and bounces between 2000 and 2400 rpm and backfires crazily. The timing light shows timing around 15btdc (stock) then. It is not very responsive to throttle, and I cannot get it to revv higher than 4k. When I turn down the timing to around 0 BTDC, the engine idles more regularly, still around 2000rpm, and there is less backfire. But, when the car is set at around 0 BTDC, it won't start at all, I guess the timing is too retarded. I cannot figure it out. All the things are just the same. Could this be a timing chain issue (a tooth off)? I've done the chain quite a few times before, so it's not a likely thing to happen, but I guess not impossible. The oddest thing about this idle is that my vacuum/boost gauge shows around 0 when this idle is going on. So this leads me to believe that something is really wrong. I just can't figure out what. I've pulled the water temp sensor plug and the idle got worse, as expected. All sparkplugs are firing and injectors are injecting, I've pulled them all in order and saw a definite difference. The only thing I didn't check was compression, but that doesn't seem to be a likely culprit. Any help/advice is appreciated. Thank you, sil80

04-19-2006, 02:06 PM	#2
s15iv Join Date: Apr 2006 Location: Santa monica Ca. Posts: 47 Trader Rating: (2) Feedback Score: 2 reviews	sounds like you might have an air leak somewhere around the intake manifold. Check gaskets for air leaks, make sure vaccum lines are connected properly and also look for pin holes in vaccum lines.

04-19-2006, 02:15 PM	#3
NIK90s13 Zilvia Junkie Join Date: Jan 2006 Location: texas Age: 58 Posts: 471 Trader Rating: (0) Feedback Score: 0 reviews	+1 on the intake leak, spray carb cleaner on intake/ vacume lines ect. see if that changes the idle.

04-20-2006, 01:16 PM	#4
sil80drifter Leaky Injector Join Date: Jul 2002 Posts: 54 Trader Rating: (1) Feedback Score: 1 reviews	One more thing that I thought of, since the car idles without any vacuum, maybe the timing is so messed up that it spools my turbo while idling, and that's the cause of the 0 vacuum. I'll try to run it N/A by connecting the MAF straight to the intake manifold, but if you guys have any other suggestions, let me know. sil80