Hey everyone..

So after 4 years of relatively trouble-free RX-7 ownership, I've finally encountered my first big dilemma.

I was driving on the freeway tonight, so I decided to do a couple of WOT pulls for fun. During my first pull, the boost warning limiter on my Profec B Spec 2 went off for a second. I checked my PFC peak readout and it was about 1.15bar - no real cause for concern (I usually run at 1.10bar). Injectory duty was around 83% and there was no knock.

I dialed down the boost controller by 5% and stepped on the gas again. After the pull, my stomach began to sink. The car felt a little bit different - I stepped on the gas and the car felt extremely sluggish. I started talking like they do in the movies after they realize their spouse/best friend/child was dead - "no.. please.. no no.. please..".

I exited the freeway and pulled up to the stoplight. My car sounded like a ******* WRX - it had the really throaty gurgle of a boxer engine, and it idled rough. My boost gauge showed ~12" vacuum (down from 15-16) and I limped the car the whole way home. It took me three tries to get the car into the garage, because I stalled it twice trying to creep into the garage.

So now I don't know what to do. This car has been built up perfectly, and I can't even make a guess yet as to why the engine blew. I'm scheduled to drive back to college in 3 days - I guess I'll have to leave the car at home and figure it out later. I just installed a set of Tein Flex coilovers - they have less than 200 miles on them, and I just had my '99 front-end fitted. Selling the car is almost out of the question, but this sure is a slap in the face when I've taken so much care of the car and building it up properly.

Augh.

 

Sounds exactly like my current engine. Blown but not out. Get a comp. tester and check it. Sounds like bad news to me.

 

(1) The PFC gives boost in Kg/Ccm^2, not Bar.

(2) 1.1 Kg/Ccm^2 = 15.6 psi , 1.15 = 16.4 psi.
But we all know that the PFC is inaccurate, and it worsens the higher the boost
goes. By my calibration of my stock map sensor to the PFC and other pressure
measuring devices, 1.1 Kg/Ccm^2 is really 17psi boost.
Your 1.15 /Ccm^2 by my calibration is 18psi boost.

(3) If you are running a stock map sensor with the stock PFC setting for it, and on
normal premium gas without water/alky injection, you have been living on the
edge for a long time and were lucky to last this long.

 

get a GM 3 Bar map sensor after your rebiuld the engine. a little bit of tuning and it should be back to being pretty reliable.

 

Does this mean the optional boost control kit sux as well?

 

I like my Blitz boost controller because it has over-boost protection.
Set a maximum boost setting and it will actually reduce boost when it hits that point to either keep that maximum or even go lower.

Nothing wrong with the optional boost controller. The inaccurracy is due to the map sensor setup parameters within the PFC. These you can change but only with the DATALOGIT.

If a owner ever compared the PFC boost reading to the boost gauge or boost controller boost display (if it has one), it is obvious that the two don't match up.
This has been mentioned since 1999 when we original owners installed the first PFCs. When the DL came out , I calibrated mine.

 

Chuck, you hit the nail on the head. I blew two (!) motors as a result of the stock map sensor and too much boost many years ago before this knowledge was prevalent.

Wompa, do you have a stock or 3 bar map sensor?

 

I have the stock map sensor.

I guess you learn something new every day. I had no idea that the stock map sensor was considered so inaccurate.

 

Just wondering, did you check the vac line that goes to the map sensor. If this pops off, it can give you symptoms of a blown motor.

 

Yeah, I checked it. I ziptied it back when I first got the car, because I'd read about problems with it popping off.

 

It's not. The stock sensor is very accurate, up to it's 2-bar+ limit (~16-17 psi actually). The Commander displays boost slightly lower than the actual boost level. This is a known problem for years.

You were running 16+ psi on pump gas and only hitting 83% injector duty with 550/1300s? It sounds like your fuel map was VERY lean to me. What AFRs were you tuned to? Timing?

 

My AFRs were tuned to low-mid 11s. The tuning was all done by Steve Kan.

I know the Mazda MAP sensor is considered a 2-bar sensor. What I've never understood is that 2bar = ~29psi, so why would it have trouble reading above 17psi?

 

you are forgetting vacuum is part of that 2 bar.

 

manifold
absolute
pressure
sensor

15 psi of "boost" is 15 psi above atmospheric which is ~14.x psi which is ~ 2bar

 

sounds to me like you motor said bye bye to you...

 

Aeka and mad_7tist, that's what I figured.

Oh well, I guess I got what I deserved. Ignorance is punishable and costly in the rotary world, I guess this is my first big wakeup call. I thought I was pretty knowledgeable, but I guess that MAP sensor information slipped under my radar.

 

But if your tuner tuned for 1.1kg/cm2 using a PFC, it is not your fault. Or did you adjust boost outside the range your car was tuned for?

 

SO the solution is to get a GM 3 bar map? How does that wire up?

 

don't beat yourself up bro. I am seriously contemplating going single turbo and this bit of info also slipped under the radar for me. And I also thought I was rather knowledgeable on these cars.

 

A couple of thoughts:

(1) Because you have the stock map sensor, the highest your commander will display is 1.15. Theoretically, you could spike to 30 psi and the commander still would register only 1.15. Do you have a peak/hold boost gauge?

(2) We were both tuned by the same person, and I haven't had any problems for over a year.

(3) As already mentioned, 83% inj duty is very low for that boost level. We have similar power setups, and just to compare: I run 850s/1300s with an apexi bnr pump, which greatly outflows the supra tt/nippondenso pump above 15 psi boost. At about 1 bar boost, I see peak injectors duties in the mid 80s. With more boost and 600cc less injector, something isn't right. Are you running the supra tt pump? That may be part of the problem. Read a thread entitled 'some fuel system ramblings' for more info.

 

How did you overboost w/a boost controller? I thought the spec ii had a over boost feature that cuts boost if you go above your preset limit.

 

Although it's ported, he has a stock internal wg. That coupled with cool night air can lead to minor boost spikes/creep.

 

^ I was assuming that cool night air doesnt exist in Texas this time of year. I could see this in winter months but not now. Maybe the Vmount really drops temps but I doubt it can go from 50c to 25c during the summer even at night. Even if it does the PFC corrects for this.

Why have creep/spike now if he hasnt had a problem in the past? he said himself the car was well built/done right so it seems he would of addressed this problem had it cropped up.

sorry your engine is dead. my engine lost a coolant seal about a 3 weeks ago and it sucks not having your fd running.

 

(1) I had the exact same thoughts regarding the 1.15 readout limit. I don't have a peak/hold boost gauge, but my boost controller warning/limiter was set at 18psi and it did go off. Peak readout on my boost controller was 18.7psi which would make sense now. The only reason I didn't pay as much attention to it as I should was because the readout has always been about 2psi higher than both my PFC commander and my boost gauge, so I kind of wrote it off. The 1.15 kg/cm2 readout matched up with what I thought my 'adjusted' boost controller (16.7psi+2) readout should be, so I wasn't terribly alarmed or anything.

Now I have to figure out why the boost was creeping. I turned down the boost controller by 20% after the first pull because I wanted to be safe, but apparently it still crept way up during the second pull. My best guess is that one of my vacuum lines running to the boost controller solenoid developed a small split or something. I guess I'll find out for sure whenever I feel like touching the car.

Now I've got to develop a good course of action. Luckily I just came across $3,500, so I have room for lateral movement.

I'm not really happy with how the previous owner had this engine built. The engine has a race port (super-aggressive street port), and S5 T2 rotors were used in place of FD rotors to lower the compression as a safeguard against detonation. (didn't work LOL)

I'm thinking about picking up a reman engine so I can return to stock ports and normal FD rotors. Does anyone have any input regarding the recent quality/durability of remaned engines, and how much the usually run for?

I'm really hoping my BNR turbos didn't get a facefull of apex seal. What are my odds that I'm going to be looking at getting my BNRs rebuilt too?

Man, how expensive.

 

First sorry to hear about the motor...

Second, IMO experiencing from supercharged motor high boost with hot ambient temp would destroy head gaskets and/or pistons due to detonation. In your case high boost + high intake temp + hot weather probably destroyed the apex seal(s).

Lately temperature in Dallas at night are in the mid to low 90*.