Have an S5 turbo motor with a S5 AFM and S4 ECU (long story and no it's not in an RX7). I rebuilt the engine using an Atkins seal kit, their satin black apex seals, solid corner seals and 9:7-1 rotors, due to Atkins supplying the wrong O rings for the oil side dowel pins I had to go through it again (they have not responded to my complaints but that's another story) and now that the motor is back together and leak free it runs great but is an absolute sacbusting bastard to restart when hot.

Before and after first rebuild did not experience this, but the motor ran maybe 90 minutes total before coming back out to fix the damn oil leak. Now that it's back in it has maybe another 90 minutes to 2 hours run time and runs great, it just won't start when hot.

I have been messing with rotaries for a while and learned the hard way to have a fuel pump kill switch, I typically flip the switch off and run the engine at 2500 RPM or so till it dies, never had a problem with hot restart until now. I have to pull the plugs, spin it over, wait a while then stick the plugs back in and cross my fingers. I have had to let it cool off overnight before it will start, it runs like crap for a while (maybe 3 minutes) before clearing out enough to run well.

Residual fuel pressure is great, doing the FSM test after 5 minutes it's still hanging at 35-36 PSI, spec is a minimum of 18. New spark bolts, non platinum NGK's. My homebrew checker box shows no fault codes, if I start unplugging stuff it starts flashing codes so I have to assume all the various sensors are alive and well.

Ideas?

 

as i would always say, do a compression test on the engine and be sure it is at full temp before doing the test if you have hot start problems.

if the compression is lower than 85ish psi then you will have starting issues due to many variables. diagnosing an engine that has a control system problem is wayyyyyyyy tougher than ruling out the engine first. i have a car in the shop with a fresh engine and it is having similar problems but the compression is fine, ive spent hours checking connections, pressures and swapping injectors and i know ALL the common problems to look for.

 

I'll do that. I only have a boinger motor tester so of course the results may be iffy. The more I think about it, the new apex and corner seals probably just need to get seated properly. I have an HPDE coming up next weekend, 20 minutes of flogging it that should take care of that.

But just in case: what about ether starting fluid? Help, hindrance, really dumb idea, etc?

 

I wouldn't recommend either. Starting fluid is one thing I have always been an opponent of. And at the very least, take it up to myrtle beach and back, making sure to vary your engine speed to get it good and broken in.

If you're having a hard time hot starting, it very well could be compression. From what I've read... that is. First hand experience has shown otherwise. I had an NA that would start and idle like brand new, and it had 30 psi on both rotors. That thing was WORN out.

The most likely culprit is your old *** wiring harness. Specifically the coolant temp sensor (water thermosensor). In the process of removing and reinstalling the engine, you probably damaged the brittle 25+ year-old harness or pulled wires from a connector.

 

They never responded to my complaints about shoddy craftsmanship on their 4 port intake manifold for side draft either...
I'm not really thrilled about them or most of the parts, the special tools were decent though.

Also poor starters/ignition can give off a hard start issues too.

 

I second double checking the water thermosensor. Having a connector pin pushed back, bad sensor and bad wire will definitely make for a hard hot start.

 

I will first install the correct air flow meter and go from there.

 

This one is super common by the way. Especially with the thermosensor.

 

My code box says everything's fine incl the thermosensor but it's still worth checking. When I did this swap, I went through the entire wiring harness checking for bad insulation etc. The motor in the car ran fine with this harness and had no hot restart problems but had a busted apex seal on the rear rotor, that was why it got rebuilt in the first place. The more I think about it, the more I believe it just needs run time, from what I understand the solid corner seals don't seal well at low RPM when new. And yes they are in the right way!

The car isn't even faintly street legal so a MYB round trip won't be possible, looks like I will have to use my first sessions at CMP for break in.

 

The more these engines are run the better they are.

 

Yep. Unlike some previous motors, this one took 2 sessions at 7/10ths to start running better, then I beat it like it owes me money for 4. Now it runs great, fires right up hot or cold. Oil pressure right where it needs to be, coolant temp 180-185, makes about 7.5 PSI boost and runs like a raped ape.

Off to Road Atlanta next!