Trouble hot starting the car
 

Hi all,
New FD owner and just took delivery of it yesterday.
After my first drive in the car I tried to get gas and the car wouldn't hot start. As a former rx-8 owner my heart sank thinking the engine has poor compression.
Everything in the engine bay is bone stock and hasn't been molested. Car has 55,000 miles on it.
The car is a RHD 1992 Type R and the importer claims to have done a compression test on it which yielded the following results in PSI:
99/96/97 - 92/92/94

The car came up to normal operating temp, and I used the typical rotary shutoff procedure to prevent flooding: rev to 3000, turn key, throttle to the floor.
After filling the car with gas, the car would not start back up hot. I tried cranking in 4 second bursts 3 times.
I then tried to start the car with partial throttle, and it seemed to get closer to starting.
Finally, I tried WOT while cranking, and the car started up and idled with no issues.

Can someone that is experienced with this car please diagnose this hot start issue? Is it likely a compression issue?
I did some reading and saw a few threads that mentioned that a faulty FPR or FPR solenoid could cause this kind of hot start issue. Could someone give some guidance regarding that?
Thanks in advance.

There are usually 2 main causes for hot start issues:
1. Low compression.
2. Leaky fuel injectors.

Good luck,
Vince

Is it not also possible that the problem could lie earlier than the injectors in the fueling system? Such as the FPR, FPR solenoid (I think it's called PRC?), fuel filter, and fuel pump?
What is the proper course of action to pinpoint the exact cause? Should the first thing I do be to take it for a compression test to see if the dealer lied? We are currently on lockdown in NY and most places are not open.

A FPR can't leak into the engine. It could have a torn diaphragm and leak to the vacuum hose connected to it. But typically they sit so long that fuel deposits on the injector pointless allow them to leak.

If you want to confirm or deny it is the injector leaking, remove the fuel pump relay while it is running and let it die from lack of fuel. Then wait a while, reinstall the relay and see if it starts.

Vince

All those things you listed should typically show symptoms hot or cold.

Drive the car some more. If you dont have proof of it being done, do the basic tune up items. Plugs, fuel filter etc. if you have continuous hot starting issues then have a compression test done and go from there.

You have no idea how much I appreciate the advice.
Was on the verge of a panic attack as all the rx-8 low compression flashbacks came rushing back and inhibited my ability to think rationally about what the best approach to this problem should be.
I will go ahead and change plugs and fuel filter. Are there any other recommended tune up items I should address?
Are there also any other potential causes of hot start issues other than what project88 mentioned?

An unrelated issue is also that my throttle response seems to be kind of slow, do you think my throttle cable needs an adjustment?
This is my first time owning a vehicle with a manual throttle.

I'm also curious whether it might mean anything that the car was able to start once I applied WOT.

Thank you for this tip I will try this tomorrow and post my results. Just so I make sure I understand right, the car is SUPPOSED to start after carrying out this procedure?

As a side note, the inside of the exhaust tip is absolutely caked with black soot, and the car also smells like it runs quite rich all of the time, so I'm guessing this is a possible symptom of a leaky injectors?

If the injectors are leaking, performing my suggested test, it SHOULD start. If it still has trouble starting then do a compression test.

Vince

I understand now, leaking injectors means it is flowing too much fuel into the combustion chamber and causing rich/flood conditions, so the purpose of this procedure is to start with empty fuel lines to mitigate that?
If that is the case, I'm also assuming that this should be performed on a hot engine, is that correct?

For some reason I interpreted leaky injectors as leaky injector seals and thought that the procedure was to confirm it wasn't supplying enough fuel to start. Upon rethinking, I realized it wouldn't make any sense that applying WOT like I did would fix a lean AFR situation.
Thank you very much!!

By leaking I mean that the pintle in the injector likely has deposits on it preventing it from fully closing. So when you shut off the car, the residual fuel pressure drains part this into the engine flooding it.

Second scenario. The injectors are all side-feed stock, the lower o-ring could be damaged and that would have the same result.

As far as why it would start at WOT, that's the built in de-flood mode. Cranking + Full throttle=
= no fuel delivery.

If you haven't already try to check out the FAQS at the top of this section, there are years of good information compiled into easy to read segments.

Vince

I'm betting on this. Injectors can stick open or closed if they have sat a long time w/o use. And if you had low compression, holding the throttle wide open would not likely have helped you get it started.

BTW, if it was caused by fuel deposits (varnish), running for a while (with or without injector cleaner in the gas) may clean it up.

The stock ECU will not inject fuel if you crank with the gas pedal to the floor - this is a built-in de-flooding procedure. Sounds like that's how you got it to start up.

I would definitely start with new plugs. Weak plugs can be the cause of a LOT of problems and RX-7's go through plugs fairly quickly. Fuel filter is worth doing but I seriously doubt it's the cause of this issue. Really, any time you get a new car with an unknown maintenance history I'd do most everything on it - plugs, oil and coolant change, fuel filter, etc.

Also there's no need to rev it to 3000 when you shut off the car. The only time that can be helpful is if you are doing a cold start and have to immediately shut it down - that can help prevent flooding in that case. General driving around town there's absolutely no reason to do so.

Dale

You may want to rule out (or in) compression before you start chasing gremlins.

Just did the test procedure recommended by Turbo88 twice, here is exactly how I carried it out and my results:
Attempt 1:

• Turned on the car while the engine was at operating temperature
• Removed the fuel pump relay while the car is running, car dies out in about 2-3 seconds
• Removed key from ignition
• Placed fuel pump relay back into the relay box
• Wait 5 minutes
• Attempted to start the car, turning the key to crank in one swift motion without allowing the fuel pumps to prime
• Car started after 3 pulses of the starter with no throttle (took somewhere between 1/3 and 1/2 a second to start)

Attempt 2 same procedure and result as attempt 1.
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I'm guessing this means that my injectors are faulty and it's not the compression.

What is the recommended action to address this?
I have ordered some techron injector cleaner. I'm guessing if that does not successfully fix the issue I'll have to replace the injectors?

Also, I noticed the car smells rich, idles slightly low, has some hesitation and jerkiness at low RPMs, and sometimes idle hunts between 200-300 rpms when I stop at a light.
These all seem like symptoms of bad injectors to me, is that assumption correct?

The recommended action is sending out the injectors for a professional cleaning. There are few good places that you can choose from. The one i used few years ago was "RC fuel injection" in SoCal

Thanks for the recommendation I will be sending my injectors to them.

Does anyone have any feedback regarding these symptoms?
Car smells rich, idles slightly low, has some hesitation/jerkiness at low RPMs, and sometimes idle hunts between 500-900 rpms when I stop at a light. Car still seems to be making good power.
Are these likely to be side effects of faulty injectors or should there be some other tests that i perform?
Common sense tells me yes if it was a piston engine, but I've learned to stop making blind assumptions when it comes to rotaries.

You got my recommendation. If it were me, first thing i'd do is get a compression test. Does it have other problems, probably, but you want to know the health of your internals before you start attacking other stuff.

As for the other stuff, bad injectors possibly, poor tune possibly (is the ECU stock or aftermarket), bad fuel control system, maybe.

If it's the stock ECU, it may be throwing codes. You can check for that.

I would do a compression test if it were possible.
We're in total lockdown right now in NY, in addition to this car not being registered, insured, titled because the DMV is closed indefinitely.

I don't have a mazda compression tester and my experience with regular compression testers from autozone has been that they're not accurate on rotaries for some reason.
Furthermore it's very hard for one person to test the compression with the regular testers because you have to crank and look at or record the gauge at the same time.

In short: I can't drive the car to a rotary shop to compression test and I can't compression test it myself.

Once this shitshow is over you bet your ass I'll go and get this compression tested for peace of mind, although the dealer that sold this does have a very solid reputation of selling good imports and I don't see it as being likely that he lied about the compression test that he claims he performed at operating temperature with a mazda tester.
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Fuel Injector Cleaning
 

I've used this one for my racecar injectors. They are very conscientious and responsive. Link:

Barry Mumm's AutoStuff Fuel Injector Service

How modified is the car? Stock ECU or PowerFC?

Does the car have an air pump? Does the air pump engage/disengage when you rev the engine?

Dale

From what I can see with my eyes in the engine bay, it looks completely bone stock besides the exhaust.
It does have a single loose fuse (yellow next to the fuse box) that I'm guessing is for the aftermarket stereo..not entirely sure.
I haven't actually checked with my own eyes yet but if I had to guess, it's the factory ECU. I will be checking it later today.

I'm not entirely sure about the air pump. I'll have to do some research about where that's located and how to tell if I have it.

It also has a cusco 1.5 way LSD and aftermarket suspension components.
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​​​​​​​Thanks I really appreciate the recommendation but I've found someone much closer that seems to have a good reputation on the forums here.
They're called Injector-Rehab AKA KGparts. I'll be sending my injectors to them as the turnaround will be much quicker.

Glad to hear the results. KGParts is pretty good at what they do on the east coast.

As far as the rich smell and hesitation is all symptoms of injectors issues. The cleaning should solve all of that.

Good luck!
Vince