Studdering and No Vaccum

[Mike1992]

Fresh motor less than 15 miles. Vaccum reads about 3 psi at idle with web 452/228 combo. I hit about 5 psi of boost and it just studders like crazy and throws a cel. Boost leak check reveals air escaping threw the seal behind the tps, but mostly through the port on the valve cover. Any idea's?

 

[Mike1992]

I pulled the code to find my o2 is dead would tht cause any of my symptoms?

 

[iiiwildfireiii]

I'm going to go out on a limb here and say "YES!" When your o2 sensor is dead, the ECU goes into "safe mode" and starts dumping tons of fuel into your engine. Replace the sensor from oxygensensorsDOTcom. They're cheap and you have to do it anyway. FIX THOSE BOOST LEAKS! No point in having a performace car if you know there is a problem and don't fix it!

 

[Mike1992]

Well, I posted on a local forum and two very knowledgable people stated that its the cams causing the lack of vaccum. I have a good used o2 sensor lined up to pick up tomorrow and I'm gonna take a gander at my cam timing. Thanks

 

[Mike1992]

Cam timing appeared to be dead on. Im lost and in need of some help. Anyone?

 

[iiiwildfireiii]

Did you get your bad o2 sensor replaced? Do you have a logger? I didn't see one in your profile. Did you use one to pull the codes or did you go to Autozone or somewhere? What are your fuel trims? Have you fixed your boostleaks yet??

 

[Mike1992]

I got a replacement and I'm gonna try it out tomorrow

I'm also gonna switch the plastic tubing on my boost gauge to the copper stuff autometer sells for mechanical oil pressure gauges. It doesn't kink or bend nearly as bad. I'm hoping my tubing is just pinched WTF

 

[Talesin]

No, even running stupidly over-aggressive cams will not cause only 3in/Hg. You have a vacuum leak.

Fix your boost leak, then open the throttle plate and (assuming you don't have any valve overlap at the time) you should be able to clearly hear where the vac leak is. Failing that, start it up and leave it idling, then take a can of carb cleaner and spray it near the intake manifold gasket. If the revs go up, double check that the intake manifold bolts are torqued correctly. Then check your vacuum lines with the carb cleaner. My guess is going to be mis-torqued intake manifold bolts though, with a leak that big..

The bad O2 sensor is going to cause crappy gas mileage and bad running, but won't bring you down to 3 in/Hg. Should never be that low at idle.

 

[Mike1992]

Boost leak check only shows the seal behind the tps is leaking along with air coming out of my valve cover port. It holds well and slowly drops.

Compression reads 120-110-105-105 Keep in mind this motor has approx. 15 miles on it. I blame the cams WTF

I redid my boost gauge with copper hardline and get the same crap. I can rev the car and when I let off it hits nearly 20inhg but quickly settles down around 4inhg.

Sigh.... I guess I'll be cam shopping. This is my best bet right?

 

[Talesin]

Okay, is that the blowby port, or the PCV valve?

The rings need to seat if the engine is freshly built. I really don't think the numbers should be THAT low though, even on brand spanking new rings. And I really, really doubt that it's the cams bringing it down that far, even with how lumpy the idle is on a 274-degree cam set.

 

[Mike1992]

Blowby Port

I'm buying a set of HKS 272's friday in hopes to remedy the situation.

 

[95FlamingTalon]

My car had the same symptoms you're seeing when I had a decent size boost leak from a bad fuel injector insulator. The gauge would show 20in/hg at startup and drop to 10in/hg or lower shortly after. You should try fixing the leaks first before spending the money for parts in hopes of them solving your problem.
A dead o2 sensor won't cause a lack of boost. I was seeing 18 psi with a dead o2.

 

[vintagemuscle]

i would bet it is not your cams.
you have excessive blowby due to the rings not seating and i would also bet you have boost/vacuum leaks.
i run 272's and see no more than 14in. hg at idle which i think is a little low but acceptable.
i would recommend putting a few more miles on the engine and see if that helps the rings seat.
what compression ratio pistons are you running?

 

[Mike1992]

i would bet it is not your cams.
you have excessive blowby due to the rings not seating and i would also bet you have boost/vacuum leaks.
i run 272's and see no more than 14in. hg at idle which i think is a little low but acceptable.
i would recommend putting a few more miles on the engine and see if that helps the rings seat.
what compression ratio pistons are you running?

Vaccum was around 20inhg before I swapped in the cams. I'm running the stock pistons with sealed power rings. Like I said before I have one small boost leak in the throttle body behind the tps. The cams are for sale and I'm gonna get my stockers back from a friend to rule out a fubored motor. After theyre installed I'll post compression results.

 

[Mike1992]

Yesterday I pulled the TPS off and changed out the o-ring and sealed it up good. Let it dry overnight and started it up. Boost leak check still reveals pressure still coming through the crankcase. Vaccum is the same but I decided to take it for a drive anyways. The studdering is gone and I was able to put a few miles on it. Stock boost (10 psi) she starts pulling really hard near 4k. However I ran out of gas pulling into my driveway so I'm guess Im done for the night.

I got the cams listed on ebay and I'm gonna be picking up a set of HKS 272's this weekend.

Yay me!!!

 

[joe]

I dont know if you checked this already but it sounds like your exhaust cam could be off a notch

 

[Mike1992]

I dont know if you checked this already but it sounds like your exhaust cam could be off a notch

The best I could tell it was all dead on. I think the centerline of the cams is to blame for my symptom's. That's why I'm selling these (ebay) and buying a set of HKS 272's.

The new o2 sensor fixed the cel also : )