HELP: 1st gear + clutch + brake = stalling out

[muibubbles]

read a few of the stalling threads non had the symptoms i have...
here are my known symptoms, they may not all be related...

car takes a few seconds to crank before it catches- hot and cold starts
if im in neutral and slam the brakes car is still fine
if i clutch in and im in 1st gear and brake, the car stalls out
idles at 1000rpm (was having previous stalling issure so raised the idle)
vacuum on the commander reads ~ -36xmmgh at idle (i believe it should be near -47x mmgh car has a mild street port)
boost gauge reads around 12 vacuum ( i believe i pay more attention to the pfc)
volts are reading hight 13.x-14.1

any suggestions what could be the problem?
-benny

[Whizbang]

generally speaking, depressing the clutch lowers the running speed of the engine. At least this has been my experience with the Rx-7.

There could be several issues. What shape is the carb in? Rebuilt anytime recently? Is your fuel pressure correct? Was the car changed from a low altitude to a high altitude?

[muibubbles]

carb? the fds have carbs? sorry not very car literate lol
rebuild within the last year
fuel pressure should be stock at about 40psi
it was changed from low then to high alt i believe.. tuned in nj and has stalling issues and when i got to deals rich tweaked some settings

[David Jerome]

No carb on a fd. I said on the other forum, compression test it.

[Whizbang]

wow...totally thought i was in the 1st gen forum.

[Brent]

To add a few things to what has been said above:

Vacuum on a street port is generally a little lower than on a stock engine. When you check compression, the Mazda compression tolerances are based off engine RPM's being 250.

If compression checks out, I would look into your throttle body and components. As for your symptom where it stalls when you pull in the clutch while in 1st gear, check out your dash pot on your throttle body. They are known to go bad and cause this problem. Do you run a PFC? If you do, I can give you some pointers to help with this problem. As for your idle being high, I would also ensure everything is set correctly on your throttle body, not just your idle adjustment screw. Street ports tend to need to idle a little higher to smooth out opposed to a stock engine though, so that might be normal.

[muibubbles]

compression- yeah my friends told me i should vacuum lower with a street port but it seems like everyone over looked that detail

as per throttle body idler screw some people mentioned, i prefer not to mess with that as it has never been touched and it was running well before with the current setting

what exactly am i looking for on the dash pot?

i am running a pfc, last time rich tweaked it at DGRR, and im back in nj now.. idk if the altitude makes a difference?

when my car was running perfect i would idle around 850-900 rpms.. i believe its idling higher as i had to add tension to the throttle cable in order to drive the car home from dgrr

thanks for the input, my friend should be bringing over a compression tester today
-benny

[Brent]

There is alot more to adjusting the idle on the throttle body aside from the idle adjustment screw. There are actually a couple of "idle adjustment screws". Also take into account that your TPS might be out of adjustment, butterfly inside throttle body may be sticking etc... which will all give you issues with your idle.

Also, even though you have a street port, the normal vacuum numbers are based off the FD idling at 750rpm's. So having 12 at 1000 seems on the low side to me.

The dashpot is what allows the plates to ease back and maintain the idle when your RPM's would normally drop drastically(ie pulling in the clutch). If your compression turns out to be good, I would guess your dash pot is seized. There are some settings on the PFC that can band aide the problem until you can get another dash pot. If it turns out to be that, let me know and I'll let you know what settings.

Hope compressions tests out strong today.

[SPICcnmFD]

Vaccum is weird to me especially after alot of upgrades, hard to tell a lot about engine health unless it just drops alot over time. When I added 850cc primaries it dropped alot, from like 17-18 to 14-15, and I know of others that have had this happen as well. And with a brand new Streetport rebuilt engine, that I know is better than the old one, only pulls about 14-15 at 1k rpms just like the old stock port I had. A compression test really the only good way to tell IMO.

I'd say the dashpot is either bad or needs adjusting, or if you have a PFC, there are some things to do. Does it do it when it cold or warm or both?

[muibubbles]

so me and my friend just did a compression test after warming up the engine.. dont know if the tester was working correctly or not but the front rotor was reading 60psi on all 3 faces and the rear rotor read 60-30-60 or 60-30-30 pretty sure its the first one...

soo what are your diagnostics? what should the compression be reading on a mild street ported engine?
once again the vacuum is reading of -36x mmhg on the commander

[muibubbles]

ok just tightened all the spark plugs.. idk if that helped i cant tell if it sounds better but the exhaust pulse still doesnt sound just right...

after i tightened the plugs when i would touch the gas it would kind of hesitate drop down 100rpms? then catch? after a few times it did that it went away... was that signs of a stuck seal?

OH I FORGOT to mention we seafoamed the car after the compression test

[Brent]

60-30-60 do not give you anywhere close to a healthy engine. A good healthy engine should easily have 100+psi. It will still start and run at 60psi, but your engine is extremely weak. The 60psi is bad enough, but you have one uneven pulse, which most likely means you have internal damage(maybe a chipped apex seal?) There are a couple of things that might cause the low compression, but chances are your engine is toast. Has your car been smoking lately?

[muibubbles]

thats what i thought.. what is the proper compression for a streetported engine?

thats why i question the compression tester.. front rotor 60-60-60 rear rotor 60-30-60? is that even possible to have an engine with that much suckage? if those numbers were true, would the car just be "slower" or SLOW?

the car feels slower, but i havent been on it so i wouldnt know fully, but it deffinately still moves pretty quick......

[Brent]

Steet ported engine compression should still be 100+psi. It will be down on power with 60psi, but still be "fast". I drove one of my FD's with around 60-70psi all weekend at the track without issue a while back. 60psi is a big concern as that is way below spec, but even bigger is the 60-30-60 number which indicates engine damage. I'm sure some of the engine builders will chime in here with their thoughts, but it sounds like you most likely need a rebuild. since it's not 0 compression on one face, I'm going to guess a chipped apex seal, but once again... there are plenty more knowledgeable guys on here as far as engine internals go.

[David Jerome]

Originally Posted by Brent

60-30-60 do not give you anywhere close to a healthy engine. A good healthy engine should easily have 100+psi. It will still start and run at 60psi, but your engine is extremely weak. The 60psi is bad enough, but you have one uneven pulse, which most likely means you have internal damage(maybe a chipped apex seal?) There are a couple of things that might cause the low compression, but chances are your engine is toast. Has your car been smoking lately?

He was using a piston compression tester with no schrader valve. I dont think he actually only has 60psi, that is a pretty common psi bounce when using a piston tester. He would need the valve installed to let the overall compression build up to get a decent idea of the actual engine compression.

However, he definitely has an issue on one/two of the faces with the result he got.