OK, my car is being a pain in the ***. Car is non-sequential, stock twins, PowerFC, full 3" exhaust with resonated midpipe.

One day out of nowhere the car started idling lumpy and vacuum dropped dramatically from -17mm to -12mm and at times all the way down to -5mm. After messing with the car I found a vacuum hose ripped and replaced it. Checked all other lines, sprayed the bay with carb cleaner to find leaks and could not find any. Had other people come through and we checked compression numbers and all was fine. Changed the spark plugs and wires, and the car was hitting -17mm again but only after the car was warmed up and idle was still slightly lumpy. I know I have an exhaust leak so I'm assuming thats what the lumpy idle is. While warming up the car does not go to -17 vacuum but stays around -14mm until the PowerFC transitions at 61ºC water temp. When the computer hits 61ºC+ vacuum hits -17mm.

The car runs perfect, drives hard, boosts properly and I could drive it no problem from NYC to LA if I wanted to, unless I turn the car off. And that is the problem.

The car struggles slightly but does start everytime when its cold but once I turn the car off and the water temps on the PowerFC are above 52ºC the car will not start again. It cranks strong but never turns over. Once the temp goes below 53ºC the car will start up like nothing is wrong. Its really annoying because I DD this car and can't take any quick trips anywhere because the car will not start again for about an hour and fifteen minutes once its fully warm and I turn it off.

Does anyone have any idea what could be causing this? Any suggestions or past experience anyone has had like this would be greatly appreciated. Car season is back and I cant take this car anywhere unless I'm planning on staying there for awhile.

 

Check out these threads, they may be of some help. Corner seals can cause hot start problems. I know that you said you did a compression test prior to this issue but IMO you should do another one

https://www.rx7club.com/showthread.p...start+problems

https://www.rx7club.com/showthread.p...start+problems

https://www.rx7club.com/showthread.p...start+problems

 

We did the compression test twice with different people AFTER the problem came up. Results were the same.

Funny thing is when I mess with the idle screw and the PowerFC starts going crazy looking to get the idle back to normal the cars vacuum also jumps up and down drastically with the revs.

 

Vacuum has a direct (inverse) correlation with rpm so that makes sense.

Have you checked the settings in the PFC to see if anything was changed? Definitely look at the fuel vs water temp menu.

I'd also take a peak at the ignition coils, esp the leading one.

 

It might be an ignition switch problem. On my FD I had to rewire a relay for the starter to get it to start up.

Is the starter itself spinning the engine but it's not starting, or is it not spinning the engine at all?

 

You never had any hot start difficulties before the vac leak? Have you adjusted anything on the throttle body? Given that you have already done a compression test with good results I would initialize the pfc and do the idle learn procedure again as long as you have the means to re load your current map. Also verify that your isc valve is working properly, if its dirty it could be sticking and not allowing extra air during hot starts. Adjusting the cranking fuel and timing can help alot but if the car used to start fine on the current values then I wouldn't start there.

 

I actually forgot to mention that I removed and checked the coils and they were good. Everything was exactly to Mazda specs that are in the service manual.

I also did reset the computer and the problem got slightly better but not much. I'm going to check out those hot start settings in the PFC that are in the first link that Montego posted up. Hopefully they help.

And no I never had any hot start problems before. I have daily drove this car for more than 4 years without a problem. Now out of nowhere I get this happening.

 

Sounds like slightly leaky injector.

 

I've heard this mentioned before while doing searches. I'll have to check that out.

Quick question, why would a leaky injector stop the car from starting up when its hot and not when its cold?? I'm curious why it varies depending on temperature.

Thanks.

 

have u pulled off your UIM to see if everything is where it needs to be?

 

Sí, I even had Roan out at my house messing with it too. He can't figure out what could be wrong with it either.

 

please verify if you have the correct fuel flow/min / fuel pressure in this hotstart situation.

I've got a car (not a rx7, it was a BMW) which had the same issues... Came out that the bearings in the pump had bind up when the pump was hot... after a shutdown, the power of the motor was not enough do get it working again!

 

Did u pull the plugs to check if it's flooding as soon as this problem happens?
Do u have a wideband?
What fuel temps read on PFC?

 

he found the problem, PFC has been getting wet causing corrosion and pins to rot off and are stuck in the harness. YUP not good.

 

i remember telling al about something to do with his harness through PM. glad to know he found the problem.

 

How did the PFC get wet? Wet shoes?

 

Well he has the feed CF hood and since he uses the car as his only daily I am thinking over time the rain+wind going through the hood + running down his fire wall through the harness and down his PFC. U can tell because everything else in the engine bay looks like it would when a motor is exposed to the elements lolol.

 

Hahaha thanks Jason. I'm going to take everything out of the bay soon and re-do it all pretty.

 

That's crazy, good thing you found out what it is tho.

 

I'm hoping thats what it is. Hopefully I can take it somewhere to get repaired.

 

Hopefully you didn't damage the pfc, and please tell me you're not selling her after the fix

 

I'm most likely not selling her but man am I tempted.

 

Once youre a rotarded, will always be rotarded thank god you thought about not letting her go, it would be a big mistake coz youre just gonna buy another FD lol