was driving down the highway, accelerated a little and noticed the boost guage fluctuating quickly up and down while building boost. I pulled off and while it was idling, the boost guage continued fluctuating up and down. however the revs remained at a steady 900. I am pretty sure this is a blown engine. am I wrong?

also as a note. there was no overheat or temp rise.

 

Does not sound like a "blown engine" to me. Believe me...you WILL know when you have blown your engine, as it WON'T idle, will be extremely difficult to keep running at all, and will have not power whatsoever, usually accompanied by all sorts of dreadful noises and visual effects....
I mean...all you describe is a boost GUAGE fluctuation? What was the power delivery like? You could simply have a solenoid malfunctioning or even just a problem with your gauge or the line to the gauge.

 

I ran off boost until I pulled off for fear of making things worse. I justed started the car back up and it seemed to start regularly, as the idle dropped to 900 the hg decreased while fluctuating

 

So it starts and idles fine? Pop the hood and give her a little revving and see if you can hear anything unusual, like a boost leak or something.

It really doesn't sound to me, from what you describe, that you have any engine damage...I mean, you didn't do anything to precipitate blowing the engine, you know? These things just don't grenade without either something being seriously wrong with fuel delivery and leaning out, or severely overboosting...which it doesn't sound like you did.

How long have you had this car?

 

a lil mis info. u def can blow a motor and it still idle and make power depending on the severity of the broken seal crack/chip vs completely blown seal

 

Yup, 'tis why I said "usually".....

 

ok, I'm going to go start it up and rev it a bit with the hood up.

 

You really don't have much to lose. I mean, if it IS blown, it is not like you can hurt it much worse...'bout all that can happen is additional rotor or housing damage.

Just go give it hell....lol! And have a tow vehicle handy.

 

lol,

ok It took a lot more to start it up this time. It's been sitting for over an hour since I stopped it initially. It is a little rough idling and I still have the vaccum flucuation. As I stepped on the gas and began revving, I could hair a faint...click click click. It also semeed to rev a bit slower.

So this could be caused by a chipped seal?

 

So what is your overall vacuum reading at idle? It should be somewhere around 16 - 18 inches of mercury for a healthy engine.

 

fluctuating between 12-14 flcikering. I'm now positive it's blown. I am just wondering if it is bad to try to drive it to a shop when the time comes.

 

Your next step should be to have it TOWED to a rotary specialty shop for a compression test. But you may indeed be fuxored.
Sorry.

 

How about a compression test?

 

Sorry to hear bro. Look at the bright side, opportunity to upgrade (port, etc)
A little off topic:
I have never seen 18 inches of vaccuum in my life at idle and I've had many Rx-7s.
I know they can and are supposed to pull strong vaccuum, but I normally see 14 maybe 15 if I'm lucky. For instance my current car gets no more than 12, which I know is sorry *** vaccuum but it's a brand new 3mm motor with 100 miles. Could that be the cause? Or a little porting? What kind of normal things can cause shitty vaccuum on a good engine? Thanks. And good luck with your car.

 

Porting will lower your vacuum.

As for the original poster: It sounds like a chipped or cracked side seal.

 

I did a search for "vacuum" .. found this thread:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/measuring-engine-health-vaccuum-285556/

 

Ya, what is wrong with people

 

Thanks guys. Hope all is well DF, nice to hear from you. This motor does sound a tiny bit more aggressive than my last one that had more vaccuum. Makes sense, overlap. How about the 3mm, they don't seal as well as the 2 right? That can affect it also?

From the other thread Mr. Nizzles posted:

So if the engine builds compression as it breaks in, it could have crap vaccuum with barely any miles right?
And porting affects timing, so right on.

According to this, my 12 inHG is ok. Still, it's weird watching the needle right below 10 inHG on a fully warmed up engine at idle. Well thanks anyway, back on topic I guess. Sorry for the hijack.

 

I have 0 compression on one face and this is what it sounded like before and after to give you some reference:

Before-
http://videos.streetfire.net/video/f...d700dd3d45.htm

After-
http://videos.streetfire.net/video/5...e800ca28b9.htm
It's a little more rough, I'm sure other blown motors with two or more faces without compression is much more rough and may not hold idle.

 

my pfs pms motor eater reads 21 at idle 1100rpms and my defi d gauge reads 19 at idle running to front nipple on uim

 

LOL yeah I get 20 at 1100 rpms also. I idle at 750. Surely you have a stout motor there though.

 

Sounds like a chipped apex seal. This exact thing happened to my friend at the track, still idled and boosted fine, but it sounded a bit 'throatier'. And FWIW I pull ~17.5-18" of vacuum at idle with my streetported FD. My housings were absolutely immaculate and I used RA apex seals on stock springs. Try renting a piston compression tester from Autozone and see how strong each face is, or pull off the leading plug (and coil pack harness & fuel pump relay), put your hand next to the hole, and have a friend crank the engine for you. You should be able to feel an inconsistency in pressure if one of the faces is blown, unless it's really, really subtle...

Torque South-- Put a few hundred more miles on your engine, your vacuum should increase.

 

Yeah, I have a pretty aggressive streetport also and I easily pull 18 inches at idle.

 

It just makes sense that if you have a street port, which increases the volume of air in the intake and exhaust, that would mean higher vacuum readings from the extra air... right? maybe not, I only had physics in High School.

 

Sounds good drew, we'll see.