you tried using propane to find the vacuum leak? the stuff works wonders. ive been able to find cracked manifolds at work. hairline cracks that arent visible to the eye. just need a bottle w some sort of regulator and just barely leak the propane out through a small hose.

 

For some reason that sounds a bit dangerous. What happens when/if it ignites? What kind of response are you looking for?

 

Using propane like that is an old school method of finding a vacuum leak. With a carb'd engine, a vacuum leak results in a lean mixture. Propane, if present around the leak, is sucked into the engine richening the mixture and thereby changing engine speed/sound. Typically engine speed increases. With a speed-density efi setup like we are running with MS, vacuum leaks should have little effect on fuel mixture. A leak in our system would result in a high idle speed, but if VE table is tuned properly, mixture should be fine. In that case, the propane trick may not work as effectively either, although perhaps the over-rich condition could be used as an indicator.

An alternative to propane is to squirt carb cleaner around the joints in hopes it will be sucked into the leak with a similar engine response. Some obvious safety issues also exist using propane for this purpose, but it is a common shop practice. I suspect propane is a safer alternative than soaking a running engine down with car cleaner.

 

when propane hits a vauum leak it will get sucked in and respond like your adding fuel. when you have a vacuum leak on a map based system, it will respond by adding fuel, so rpm goes up. with the added propane, it will see it as too rich and drop rpm. your using a very small amount of propane. its easier than unsing carb clean, beause you can pin point a area to check. if you have something sparking in the engine bay that would ignite propane, i think that is a more serious problem there.

 

Ok, I think I got the vaccum leak figured out. :p
When I got the engine from my friend it didnt have the long bolt that goes through the upper intake manifold.. I just never worried about it. Well, I took off the upper intake manifold again, and on the side facing the TB there was alittle black stuff and some gas accumulated on the gasket.

 

RG had the bolt for the UIM, so thats fixed. But now..... yeah more problems
Before it would start pretty easily, but it idled high even with the tb closed as far as it could go. The rpms didnt like to go down at all, it would just bog and die.
Ok, now on to today. It wouldnt start at all, the settings didnt change, didnt mess with anything. We pulled it around the block several times, nothing. (well except the most rediculously loud backfire ever :p)
The theory right now is that a injector got stuck open, it must have worked some what just a few days before when it would start though.

This weekend I am going to put some n/a injectors back in the primary slot and see if that helps any.

Does anybody want a s5 turbo swapped 86 base??? lol jk

 

This car is frustrating! The backfire we had was nothing short of impressive! I honestly thought it blew a hole in the exhaust system it was so loud. I can only imagine what the neighbors were thinking!

My current feeling is that a primary injector may be stuck open. I'll give you what I know so far and see if anyone agrees with this diagnosis. Of course I won't know for sure until I actually test it.

The car has run before with these injectors. Keep in mind they've got somewhere over 170,000 miles on them so an injector issue is probably pretty likely. They do need to be rebuilt either way you look at it. We got the car to start a few days ago. It's idle was high as mentioned before. It has been running very rich. I've tried dialing fuel out and once it gets leaner than about 11.5-12:1, it stalls. That makes no sense. It tries to run very rich. Timing is set at a point where it should at least run. That's always the goal before tuning for performance.

Trying to crank it today, nothing happens. It just spins over. We pulled it down the street with the fuel cutoff to clear it out. I could watch the wideband so I knew there was no fuel going in. I'd turn on the fuel pump kill switch that we installed and suddenly the a/f would jump to the low 9's. The settings are assuming we have a 2.6L, 4 cylinder engine using 550 cc injectors set at 14.7 afr. That gives us an 8 ms injector opening. It shouldn't show up in the low 9's afr wise. We can also smell fuel pretty bad and the insanely explosive backfire is proof we've definitely got fuel. Yes spark has been checked.

I have a hunch that one of the primary injectors is sticking open. Maybe not all the way, but at least partly. I suspect we are getting a really rich rotor and a lean one. Since there is only 1 O2 sensor, it is getting the average of both of them. This could explain why it only runs rich and why after it gets learner near 12:1 afr, it dies. It could be that I am pulling fuel out of them but really only affecting one rotor. The other rotor's injector could be sticking causing too much fuel to get in. This would explain the rich readings on the O2 sensor and explain why the engine dies even though it appears rich. One rotor could be getting so lean that it doesn't want to run anymore. That's the hunch anyways.

What does anyone else think about that being a possiblity?

 

Ken, here's the RX-8 trigger wheel info you asked for. Sorry to put it here. It was just the easiest thing to do.

 

It definitely sounds to me like you could have a stuck injector. It's a shame the primaries are such a pain to get to on these engines, as it'd be pretty easy to tell what's going on if you pulled a primary out.

thanks for the rx8 wheel diagram. James got that wheel to sync last night on the bench, and was just waiting for angular data.

Ken

 

heh, you might say that...





Looks like im in the market for exhaust

 

wow thats awesome!!

 

Yea i bet that was a good one

 

Impressive young skywalker ...

 

Now THAT must've been a backfire!

 

Check out how restrictive they are!



The exhaust has to come out of those little holes in the pipe at the bottom, then come back towards the front and go out the other pipe.

Im just going to try to beat it back into shape as much as I can, then use it untill I can get a replacement.

 

Holy crap we did blow a hole in the exhaust! WOW!!! That's a first for me!

 

As a little bit of an update, Brad pulled the primaries and installed his old n/a primaries back in their place. He pulled out the plugs and cleaned them and then cranked the engine over with the plugs out to help dry out the chambers. After reinstalling the plugs he tried to fire it up and it does start. It won't stay running as the injectors are 460 cc and the MS is set up for 550's but at least the ability to start initially over and over again lends credence to the theory of a stuck injector. The a/f gauge doesn't fall down to 9:1 afr at startup anymore either. That at least seems like good news. If I reset the injector sizing in MS, hopefully it'll let me tune it now. Of course a blown out muffler on a rotary is by no mean quiet so that may be a PITA to deal with. It's always something on this car!

 

It will stay running if I push the pedal in some, probably just needs the idle screw readjusted. It is a little rich (11:1) but thats easy to fix.

Dont need to worry about the noise either, I tried hammering the muffler back and it would probably help. But, I called a friend and he has 2 stock mufflers for me... and he delivering them here soon.

 

Very nice hole! I saved that one to my pics file lol!

See ya in a bit with your new mufflers Bman.

 

Got the mufflers, no flanges on them though
I just put the old one back on for now, hammered it closed. Helps some, but its still kinda loud.

elnots- man, after riding in your fc I want mine running so bad! lol