sr20det boost/vac issues???

[redninja450]

I'm new to this site so here it goes; when I turn the car on and let it warm up; the rpms starts to surg badly and when I take the car out and put it in load, the boost stops at 5psi and then the car starts to buck and shake very hard. It bucks in 1st gear every now and then, but in every other gear it always bucks. I would hear a very loud bang coming out of the exhaust like its got a serious case of backfire. What should I start looking for to fix this problem? Every advice I can get will be helpful; please reply back!

[SpeedRacer1]

Look for a loose intercooler hose. It sounds like a vac leak where the air is just being released around 5 psi instead of going into the engine. The reason it might happen less in 1st is because the engine has less load in first and thus cannot build as much boost. Also check the settings on the BOV if you have one.

[redninja450]

Does the vac leak also cause the car to buck and shake? Also my vac on the boost gauge reads 14-15 in.Hg; is this where it needs to be around?
Modified by redninja450 at 1:42 PM 7/5/2008

[mistamacadamian]

yea 15-20 is average vaccum. get a fitting for your intake and boost leak test. its easy.

[redninja450]

I'll get on it right away with the fitting, thanks for the advice.

[SpeedRacer1]

A vac leak can cause issues because you are losing air that has been measured by the MAFS. So the engine is trying to burn air that is no longer there. This will cause plenty of problems from the bucking to the backfiring.

[redninja450]

I did an intercooler piping leak test with the bov on it and discovered that there was too much pressure with 30 psi so I reduced it to 15 because that's how much I'm boosting on the turbo, but left the vac line that goes on the bov off; am I suppose to leave it connected to the bov? I took the intercooler and the pipings off to see if there's any damage to the pipes or couplers, but couldn't find any. Is there any way to test the wastegate to see if it's sticking open?

[mycleans13]

hey i am having the same exact problem caint figure it out for the life of me did you ever find out what it was

[Sr20S13Det]

Have you guys checked your MAF sensor. I went to test drive my first 240 and it started bucking and wouldnt make alot of boost. the guy that had it before broke the clip off the sensor and it fell off while i was driving. Sounds alot like what you guys are having problems with. Thought i broke the damn thing lol .

[snake240]

ill bet on boost/vac leak. keep the vac line hooked up. just set your regulator to like 10 psi, get a bottle of soapy water and start spraying everything. for instance if you bought a cheap intercooler kit, the aluminum pipes can be porous and have pinholes. spray all connections and look for bubbles. good luck.

[mycleans13]

maf checks out as far as unplugging it while the car is idling and it makes a difference and i did the some water thing and found a few tiny @$$ leaks but nothing that made a difference checked coils, injectors, fuel pump, ignitor chip, maf, leaks, new plugs, new fuel filter, sprayed the maf with maf cleaner, swapped ecus, i dunno wtf else to do im stuck the only other thing i can think of is the cas but the car runs to good on the vac side of things and at idle but as soon as i get into boost its f***ed

[katinkid]

im having same exact problem!!!! 89 240sx coupe sr20det blacktop fmic. car boosted fine just gets heat soaked every once in a while...

last night on way home from work, droped it down to 4th gear, went to boost and as soon as i hit 0psi started bogging out and kind of popping.

i do have a blown d/p gasket but have had the for the last 2months no problem. when i got home popped the hood and noticed air filter k&n off of the intake. "hopefully it wasnt like that and didnt suck anything in" put the filter back on and same problem.

car sits runs perfect right now at idle and in vacuum. drove to work:) but if i start to put a load on it it boggs out right at 0-1psi

not meaing to thread jack but it seems a few of us are having this problem would be nice to find the answer:)

[katinkid]

ummm... is it me or has this forum not moved in like 2days... no new posts or bumps or anything????

[90_240sxx]

i have the same problem i changed out spark plugs and it helped out a lot

[nzmoman]

maf checks out as far as unplugging it while the car is idling and it makes a difference and i did the some water thing and found a few tiny @$$ leaks but nothing that made a difference checked coils, injectors, fuel pump, ignitor chip, maf, leaks, new plugs, new fuel filter, sprayed the maf with maf cleaner, swapped ecus, i dunno wtf else to do im stuck the only other thing i can think of is the cas but the car runs to good on the vac side of things and at idle but as soon as i get into boost its f***ed

If the problem is really bad then I always recommend going through and pulling all of your piping and reinstalling it.

don't forget to check your boost gauge, boost controller, or any other device that you have hooked up to the vacuum/boost system. I have pinched hoses and tubing before which caused this problem. Make sure your BOV is not stuck open. Check all your couplers and make sure they are not torn. Check your throttle and make sure that there are no open vacuum ports that should be capped off. What you are describing, if it is vacuum related, should be traceable between your MAF and the intake manifold. There really shouldn't be too many places that you need to check.