Hot Start Issue / Flooding

[ROT8TOR]

My first post because I've owned RX7's for over 20 years and I've never had this issue...

I have a '9o vert that's been the perfect car of the 3 I've owned, but now this...

As of late, after driving the car a few miles and it gets up to temp and then I cut it off, it won't restart. Acts flooded. If it does by chance fire, it runs like it's got half power. I'll give it a little gas for 20 or so seconds and then something "pops" and the motor runs fine all the way home. After it cools waaaay down, it'll fire right up like nothing was wrong.

I ran it, stationary, in my driveway until it got up to normal temperature. Periodically I put in gear and went back and forth up the drive. Put it in park and let it idle, periodically reving rpm's to 2000 - 2500... not much...

After I knew it was hot enough, I got out the car to look under the hood for leaks of ANY sort... (everything is dry on motor, no vac leaks) and suddenly, the car just dies.

10-15 minutes was all it was on. It gives NO sign of cutting off and when it does, it cuts off clean with no aftergurgle or anything. NO engine light comes on to read the codes, either.

When the car is cold it starts up and drives perfect.

I have spare parts, so I changed plugs, then coils, then Crank angle sensor... all to no avail.

Everything I use is OEM and car is totally stock.

I think the question may be...

"Is the car being told it's cold when it is really hot and not letting it start?"

Thanks for your help,
R8R

[Pete_89T2]

That "running on 1/2 power" symptom sounds like you may have a sticky seal or two. First thing I'd do is a compression test. How is this car normally driven? Daily, once in a while?

[RETed]

Flooding is a part of life with these cars.
Even the newer RX-8's do it.
It's due to "bad programming" in the stock ECU - nothing you can do about it unless you remove / replace it.
Low(er) compression and / or low voltage problems makes this worse.

That "half power" is probably due to one set of spark plugs on one rotor being fouled so bad from flooding that it doesn't fire anymore.
Basically, it's running on one rotor, so you're right about "half" power...literally.
Once all that gasoline is burned off the fouled spark plug, the engine will run like nothing happened.


-Ted

[FRED]

During the start process the ECU does not use the afm for fuel delivery. It uses an internal fuel map that determines how much fuel is delivered during start and uses the water temperture to decide how much is used during the start procedure.

There is no way for you to fix this fuel map other than buy a RTEK.20 or aftermarket ECU. There are ways to TRICK the ECU to use the afm for fuel delivery during the start process and that will result in less fuel being delivered with a hot engine and thereby a better start of the car. Unfortunatley if you trick the ECU to use the afm instead of the internal start fuel map........cold starts will be more difficult. Cold meaning water temps under ??? 120* on the whole.

This Trick is nothing more than NOT letting the ECU see the Start signal when you hold the key to Start. It more or less consists of depinning the wire on the ECU that sends that start signal to the ECU.

That or build a fuel cut switch I guess. I don't know what your abilities are when talking about depinning a wire from a ECU plug. I'd never cut a wire. No need to do that.

[ROT8TOR]

So, do you want me to replace the N351 unit under the passenger floorboard?

Could this malfunction be caused from mixing positive & negative on the battery when jump started? AAA came out after I killed the battery trying to start it and beknownced to me... he had em momentarily crossed. ???

I really don't think this is the issue, just because I felt it was a more fuel than electrical issue, like a leaking injector.

It may not be the case, but I swear I smell BAD gas coming from the car.

[FRED]

Nope, don't recommend replacing the ECU. Suggesting flooding RX are what RETED mentioned in his post above. Also low compression RX will flood easily when hot for the same reason I mentioned in my post above.

During START there is a preprogrammed fuel map dependent on the water temp, rpm and seeing the Start signal. This fuel map is too rich for a car with low compression when the engine is hot.

I was suggesting keeping the ECU from seeing this Start fuel map and doing that by eliminating the Start signal that goes to the ECU from the start elect circuit. And you'd do this by depinning one wire at the ECU plug.

A more common fix is to just make a fuel cut switch and toggeling it on/off to cut the fuel during the start of the car...............to keep too much fuel being delivered during......start.

Attached is a page out of a old training manual that is online, and this page explains better than I tried to, how fuel is delivered during START of the car.

Not using the internal start fuel map means the afm is used for fuel amount during Start and that amount is much, much, much less than what the internal fuel map delivers during Start.

[ROT8TOR]

So...

Do I change the water thermo sensor or the solenoid resistor?

Another thing I've noticed...

The electric fan is on an awefull lot. After cutting the car off and you go turn back up the key to get power... The fan will stay on forever. 15-20 minutes easy, then it'll cut off or kill the battery... whichever comes first.

I've got double or tripple extra parts and a running '91 Vert to swap whatever I (We) need.

Also... why no engine codes to read?

There's only 66,ooo miles on this motor and it runs great, so I'm hoping it's not on it's way out.

Thnx, R8R

[FRED]

Why would one change the water thermo sensor????????? IF a water thermosensor fails the ECU defaults to a hot temperature which is 178* if memory serves. Makes no sense to change it.

ECU codes cannot detect a low compression engine. Theres no reason to suggest the water thermo sensor is bad code or no code. Easy to check out though. On a normal car the sensor outputs approx .5 or a half volt at the ECU with a hot engine. No reason to think it's bad though.

Reread what RETED wrote about RX and flooding.

There's no solenoid resistor on series five car or series four built after the middle of 1987. NOT a player anyway.

I've been thru this in the past and viewed it with a meter. I got a engine up to full temp and turned it off. Then disconnected the START signal to the ECU. Then started the car and viewed the pulse width of the primary injectors on a meter while cranking the engine over (ignition disabled so it would not start up). The pulse width was 5.96 ms.

Then put the wire back on the ECU and cranked the engine over. The pulse width of the injectors was 17.62 ms.

Now which case above would be the least likely to flood an engine? The 5.96 ms of course. The AFM is being used for fuel in this case and the internal fuel map is being used when the wire was back on the ECU and the pulse width was 17.62 ms.

Just my way of showing what happens if the ECU never sees the Start signal. Virtually no chance of the engine flooding when hot. None imho.

I can see you want to just change parts to fix this problem. Ain't a gonna happen but have at it. I through here. Done my part. Gone. Last suggestion is to build a fuel cut switch to make a temp fix. Usually works every time once you get the hang of it.

[Pete_89T2]

Another thing that causes flooding, especially if the car isn't driven frequently enough, is leaky injectors. What happens is over time fuel deposits/varnish will cause the injectors to stick open a bit. Since the fuel lines are still under pressure for a short time after you shut down, some of that pressurized fuel leaks down into the engine. This is more likely to happen with the secondaries, since they only open above 3500 RPMs or so, and they will be "exercised" much less than the primaries under normal street driving conditions.

Have the fuel injectors in this car ever been removed for cleaning/flow test service? 60K miles on a 21 year old FC tells me this guy's car hasn't been driven on a regular basis, so the odds that the injectors are gummed up are pretty good - I'd consider this a preventive maintenance item.

[ROT8TOR]

Ok, ok... relax...

Why would you send me the diagram then? I assumed one of those components was the issue.

I'm "throwing parts" at it, because I have them and no other funds to go deeper.

It's easy to say, "It's done and you're finished with it."

But, let's try the little things first before you suggest a rebuild.

I'll check compression tomorrow after I check out the possibilty of a leaky injector and I'll get back to you all.

[RETed]

What most of us do is install a fuel pump cut-out switch.
Once the engine floods, kill the switch.
Crank engine over for a few seconds.
Turn on switch to turn on fuel pump.
Viola, engine fires as if nothing happened.
Cheap, simple solution for a big headache...


-Ted

[GoopyPerformance]

2Nd Gen cars are famous for flooding...
I always check compression on 2nd gen cars pryor to any other work.

[FRED]

The page out of the training manual tells one how fuel is delivered during START. It is not a list of things that might go bad. That was posted by me so you could understand what is going on. You don't seem to follow that idea.

TOO much fuel is being delivered by the internal fuel map in the ECU and that map cannot be changed unless you spend bucks on a RTEK2.0 or install an aftermarket ECU like a Wolf, Haltech whatever. On those outfits you set the amount of fuel being delivered during START and that is why even a pig low compression RX can start each and every time using an aftermarket ECU i.e the Mazda fuel map exists no 'mo, no how.

In two posts of mine I suggested two different ways to prevent flooding during START. Either a fuel cut switch or arranging it where the ECU never sees the Start signal and therefore never uses the Start fuel map (gotta be the fourth time I've written that, just gotta).

Go buy new injectors, new sparkplugs, change the oil and oil filter.........send out the brand new injectors to be cleaned by some online shop............and that pig will still flood during hot starts. Bye. Gone before I have a hissy fit and get pissed off and get thrown off another forum.

[ROT8TOR]

Wow... For some one who is so adimate about it being right, you're wrong.

I fixed it.

It was a poor positive connection on the battery.

Here's what happened...

The car had enough power to send fuel from the pump, but didn't have enough starting power to spark the plugs. The plugs, with no spark, are now flooded for when I tried to restart the car.

Oh, and Fred, maybe you should take some time off the computer and seek anger mngmnt. You know you want to.

[RETed]

Originally Posted by RETed

...and / or low voltage problems makes this worse.

Oh well...


-Ted