mikey k

i'm sorry if the answer to this is elsewhere on the forum but i don't have time to look right now.
i just bought a 93 rx7 with 35,000 miles on it. the car has been moderately race preped (scca). the drive home was great but the next day something went wrong. the guy who sold it to me says it sounds like a vac line popped off but who knows where. he suggested asking you fine and knowledgeable people so here goes:
no smoke on startup, idle gives steady 750rpm but the car shakes badly, very low power and shaking if i try to drive it, oil pressure looks normal but boost is 11-13 vac. at idle and the needle vibrates between the two.
let me know if anyone has any idea where to look. right now i'm going outside to start looking.
thanks.

rynberg

Check the MAP sensor hose. The MAP sensor is a small box mounted on the firewall by the master cylinder (behind the intake elbow). There should be a vacuum line running from the intake manifold to the bottom of the sensor. Check to make sure that both ends are connected.

If it turns out that this is the problem, you should reset the engine ecu. Do this by removing the neg battery cable and holding the brake pedal for 30 seconds.

Good luck.

RX7SpiritR

iTrader: (1)

mikey k

thanks for the reply. i'll go check.

mikey k

it wasn't the map sensor. i feel like i've looked at all of the hoses twice already. i can't find anything.

rynberg

Hmm...that doesn't sound good.

Please list all of the mods that the car has, what boost you were running, and describe anything you may have noticed (noises, other behavior) when you lost power.

Does the car drive normally at higher rpm (above 2000 rpm)? Can you still go WOT with boost?

Trexthe3rd

I hate to say this but.....
Fluctuating vacuum readings at idle is indicative of a bad apex seal (sealing, not sealing etc. hence the unstable vacuum readings). Get a vacuum test done pronto.

mikey k

like i said, the car is a '93 with 35,000 miles on it. it has mostly suspension stuff done to it but for power mods it has:
m2 downpipe
greddy catback
some kind of midpipe (no cat installed)
k&n filter in factor box
greddy pulleys

not a lot done, but it did have a apex power fc. i couldn't come up with the asking price so he took out the power fc and dropped the price. i know it's not a good idea to go free flow exhaust on a stock ecu but i figured i wouldn't drive it much until i could afford to upgrade.
oh, and yesterday i started it up and it was smoking, not an outragous amount but more than it should. i've heard of smoking being related to apex seal damage but i've heard that was usually darkish smoke. this is light in color.
with my luck, it probably is an apex seal. my wife is going to kill me. hey, at least i got to drive it for a day and a half before it broke.
it was one of the best day and a halfs of my life.

rynberg

I'm afraid that your last post answered my question. You most likely blew your motor. Running the stock ecu is a huge no-no with a midpipe and no boost controller. Sorry man, but you should have ponied up the money for the PFC (although I am surprised the guy sold it to you that way without warning you).

Read up on how to do the compression test and take it to a Mazda dealer and make sure they test it right. Although, even if they do it wrong, you'll be able to spot a blown seal.

Snook

iTrader: (12)

DAmmit that sucks

Sorry man

SWAT81

iTrader: (14)

oh my what a irresponisble guy who ever sold you that FD without the Power FC!

volley1

Did you floor it on your drive home? Guys, if he stayed under the stock 10 psi I don't think he would have blown his engine, right?

rynberg

I'm always amazed when I see statements like this. The stock twins spool instantly in 5th gear, like on the highway. If I'm cruising in 5th at 80 mph or so (3000 rpm), I can just nudge the throttle to accelerate and I'm instantly past 10 psi.

It's true you can use throttle manipulation in the lower 3 gears to maintain a certain level of boost but that's not very easy in 4th or 5th. Besides, if you had just bought the car, would YOU be able to keep it under 10 psi?

I'm thinking that if the previous owner didn't really warn this guy, he deserves to be strung up.

RX7SpiritR

iTrader: (1)

damn man, that sux. The reason I had that post earlier with the gasp smily's is because I was already thinking it. But I didn't want to say anything to scare you. But it does sound like you blew 1 or more apex seals. Sounds like you blew one though if its not too bad. That sux man. Sorry to hear about your motor.

ROTORHP

Couldn't the smoke on startup just be from seeping oil injectors? Is it possible that a sensor screwed up causing the rough idle? Does it smooth out after it is warm?... Trying to be an optimist... feel for you man if it isn't just a sensor...

mikey k

the guy who sold it told me it was "rev happy" and that it's easy to over rev it. when it happened, though, it was on a second to third gear shift (if that makes any difference). i used a conventional compresion gauge because my friend had one handy, and the front one registered compression and the rear one didn't. looks like it sucks to be me. thanks for all you're help, i'm going to go kill myself now.

Snook

iTrader: (12)

Don't get too upset. If you go to the Midwest/Mountain RX-7 Forum maybe you can find some guys to help you take out the engine and put a new one in. Sure this sucks, and it's happened to a lot of us including myself so don't feel so bad man. This could end up being a weekend fix and you can learn a lot about your car in the process. However I think at the cheapest you are going to need a reman 2000 dollars, set of used turbos 500, and an ecu so this doesn't happen again Used pettit ecu's go for 400 or so. 3000 bucks is a lot but then you shouldn't ever have a problem with the car again and you'll have a warranty on that new motor if you choose to get it.

If you were in the area I would volunteer to help out. I'm selling my car now and I would never sell it without the ecu because I know it's dangerous. Even a warning to the buyer isn't enough because it's hard to stay off the throttle when you get the 7 you are excited.

good luck with everything
Snook

mikey k

oh, and i can't blame anything on the guy who sold it to me. he has been very helpful and supportive this week and if he had any idea this was going to happen, i don't think he would have sold it without the power fc.

mikey k

i work on an air force base and we have an auto hobby shop available to use. they have a whole bunch of tools and equipment there (probably not many special tools like i'm sure this would require). is there any way some friends and i could tear it down and replace the seals ourselves or would we be way above our heads? the guy who sold it to me included two shop manuals. one big mazda shop manual in a three ring binder and one similar, slightly smaller one.

mikey k

also, my friend found some engines on www.revolutionrotary.com and www.rx7store.net. there is one on revolutionrotary with 3mm apex seals, 3mm corner seals, hd corner springs, high vol oil pump, and street ported for $2,850. does anyone have any first hand experience with something like this? how did it work out?

volley1

rynberg: I understand that the stock twins spool instantly in fourth and fifth. I just did a boost test in fourth yesterday. I am just saying maybe he was careful on the way home with the car. I got my car in Kansas and drove it back to Colorado and grannied it the whole way because I had never driven an fd and didn't want to blow anything. Looks like he did floor it though so it is a moot point. I see you post a lot and know a lot more than I do about fds and I respect that. Just don't try to make me look like an idiot when I was asking a simple question. And it is true if he would have stayed below the stock boost levels he wouldn't have blown his engine with those mods. Anyway, sorry about the car man that sucks. Good luck.

Snook

iTrader: (12)

mikey k: The cheapest route is to get a reman, a used set of turbos if needed, and an ecu. There are many questionable engine rebuilders out there and I just wouldn't take another chance. If you have enough money get a pettit motor you can't go wrong there. And I think it would be VERY hard for you to take apart the engine and rebuild it. Taking the engine out and putting the new one back is very doable with minimal tools. You can't just replace the stuff that went bad because then you may have a high variance in compression between the 2 rotors which means one will have to "carry" the other. Plus there will be other damaged parts inside the motor, most likely a rotor and housing will need to be replaced. The side housings are generally not a problem. Make sure you do it right do it once or the car will never run right for you and you'll be broke and hate it.

either way, a rotary isn't that easy to blow up guys. You can overboost it in certain situations and nothing will happen. The guys that blow motors are hitting too high of boost than their car can handle in the right rpm range in the right gear and holding that through 1 or 2 gears at least. You don't blow a motor on the highway in 5th getting 14psi on the stock ecu and quickly letting off.

Take these comments with a grain of salt. I'm just trying to illustrate how blown engines occur MOST of the time. A strong rule to follow is don't go anything over 10psi on the stock ecu at any time and nothing above 12psi with upgraded ecu and stock injectors and fuel pump.

Snook
(giving lots of advise)

rynberg

I wasn't trying to make you look like an idiot. My point was that on the highway, it is nearly impossible to not hit 10+psi, even in normal driving. It does not take going to full throttle. And yes, if he would have been able to keep the car below 10 psi, he probably would have had no problems.

mikey k

the car does not have a boost controller, so if the boost was high it was because of pressure drop across the turbos due to the high flow exhaust. this was not a case of "turn up the boost for instant gratification".

cpa7man

iTrader: (2)

I agree. He should have never sold it to you with the stock ecu.

Rynberg is right! Today I forgot what gear I was in, and I hit 10 pounds of boost at 2500 rpm. On the Hwy I see boost on most small inclines.

Also is there no boost gauge in the car??