why is it that rotaries always have trouble with hot-starting. for instance my car starts right up in the mornings but is near impossible to start after i go for a 20 minute drive and shut it off...

i've always known about the hot start problem but i've never known exactly why it happens..

 

Its usually because of minor flooding thats caused by either low compression or leaky/dirty injectors.

 

BUT... the question is, why only when the engine is hot and not cold?

 

Cars will have more compression when they are cold, less when they are hot. Thats your answer right there. Your motor was recently rebuilt so low compression shouldn't really be an issue...try replacing the injectors with a new set or known quality used set. They may be leaking.

 

The man speaks the truth! Metals expand when heated. That means your compression is lower then the engine heats up. I learned this is true with my TII's engine. Cold it had 120 and 115 psi on front and rear rotors. Warm it went down to 105 and 95ish. :o


Santiago

 

The stock ecu's cranking maps suck thats about it.

 

Oh damn, you said a mouthful right there!

 

mine would flood like that too. then i double checked the vacuum lines and found i had 2 of em crossed, after that it started better hot than cold.

3 things:

1) the vacuum diagram isnt detailed enough, you need to physically trace each line to its solenoid, for the acv anyways.

2) the leaky injector thing is bs, ive seen 1 leaky injector in 10years

3) they will not tolerate ANY vacuum leaks

 

really, maybe i need to do a bone-cold compression test then.. i was always wondering why my results were worse when the car was totally warmed up

 

Nope, the stock ECU is probably the best you'll ever get to start the car. Try doing a full standalone on the car and getting it to start as easily in all conditions as the stock ECU. That's the time consuming stuff on a standalone unit (starting, idle, sensors). WOT is the easy part.

That's not the problem though, it's either a compression issue (not likely on a rebuild w/ the miles he has) or a fuel problem. Check injectors first, then fuel filter then pump.

 

i have no solenoids and i have 4 vacuum lines (boost gauge, fpr, boost sensor, bov). everything is blocked off and the vacuum rack is gone. could this be part of the reason for the hard starting?

 

Compression tests are to be done when the car is warm, it's just that the car will MAKE more compression when it's cold which is why you have a hot start problem, not a cold one. Check the injectors...

Compression must be checked and compared on the same gauge, gauges do vary so keep that a constant rather than a variable.

 

well, when the engine is hot the compression numbers are in the low 80's. when the engine is cold the numbers are in the mid 90's

 

its prolly not helping, but it shouldnt be a deal breaker either.

you still might have another leak somewhere, theres been a couple of threds about presurizing the intake to look for leaks, this way works really well!

 

with the reverse vacuum thing?

i just got new LIM/UIM gaskets from mazda and rechecked all the caps the other day so i SHOULDNT have any leaks (you know how that goes though)

the gaskets i got from mazda were actually really high quality. not the crappy old regular paper ones like i had on my old TII

 

I see you have never owned a standalone.

One of my previous engines had 60-60-60 on both rotors. Haltech e6k equipped it started perfect everytime, at every temperature. One of my other t2s had a hot starting issue on a fresh rebuild on the stock efi. Haltech e6k equipped, perfect start everytime. Just rebuilt another t2 a couple weeks ago, perfect start right up with haltech.

I agree with j9, I've never seen a leaking injector, and I've tested and have had many lets leak tested by shops.

 

Dont you need the primary injector bleed socket?

 

I have been fighting this problem on my FC for a couple years now.......so far I have been loosing. I have had the injectors repaired at RCEngineering, Compression is good, and no vac leaks. Only thing I havent replaced on the car is the ECU (NextOnList)

 

Double Post

 

Thats not what I was trying to say but I guess what I wrote came out wrong The flexibility of a standalone is best and you can change most variables to suit the engine in question. But, in my experience, stock ECU's are very very well suited to stock cars. To me, getting the right variables for things like idle, starting, decel etc... are the hard parts of tuning a standalone. WOT under load is easy

 

the what?

i didnt know such a thing existed..

 

Did no one notice he said low 80's? Isn't that bad? That doesn't sound good to me....

 

Well that's one problem! DUH!

You removed the HOTSTART solenoid!

It changes the FPR's Vacuum source to a static rate to help with hotstarts!

That is the ONLY solenoid I kept lol because I have a rebuild.

80psi isn't totally bad. That is border line going low compression.

My rebuild righht now is doing 65psi on all rotors and 90 total in each housing(build up psi)

 

here is my setup. I just put the hotstart here.(orange plug)

 

**** man, time to go dig up the other wiring harness.. can you provide any more details about this? since i just CUT the entire solenoid plug section off of my wiring harness i'd have to unwrap that section, connect the solenoid, the plug, and run vac lines. can i get some explanation of where to run the lines to and which solenoid goes with the orange plug?