hi ive owned the rx7 18 years,, has been garaged last 8 years. would like to get it all back on road for summer so i need some help been trying to fix this issue for a year,, please everyone any ideas please chime in....

Car start easily perfect from cold,, but hot is very hard to start (im gonna do a video and add to this post)
right first thing,, compression you will say,,, ive tested it twice here are the numbers,, i will conduct a 3rd test and post pictures of the results.

front rotor 80 87 83 rear rotor 94 95 90

2nd test
front rotor- 82 89 84 rear rotor- 91 94 89

this is getting the engine to 80+ degrees,, i know these numbers aren't the best but i'm lead to beleive they are in the middle and unless i get down to low 70s its not the issue.

so where am i looking,,,faulty coils,,,faulty igniter,, fuel pressure issue..vacuume leak, something in the tune??? (apexi power fc)
some one throw me some ideas,,
for info car has big battery and rx8 starter so cranks at 280rpm, injectors and coils are stock running stock boost,, but will all bolt ons.

 

Compression maybe but I would start with fuel pressure. How is your fuel pump set up?

 

fuel pump is walbro 255,, it was doing this problem before i installed pump,, i can do a fuel pressure test and check that..
my personal thoughts are compression,, as the temperature gets hotter and hotter on the engine it gets harder and harder to start.
but everything i search says should easily start with 80+ psi

 

HOW is the fuel pump set up. Did you reuse the o ring seat or did you change to a hose?

 

the pump came with a rubber hose that you attached to the metal hanger thing, whats the issue you trying to put across,, low fuel pressure?

 

Sort of a different view on fuel pressure, or injectors and fuel in general - after a hot difficult start, do you see black smoke out the exhaust? Did the engine ever flood after a hot attempt to start that failed? If so you may have an injector leak or too high start fuel pressure.

 

the rubber hose that came with the pump is not to be used. It's a set up and I have no idea why these manufacturers keep including it. That hose is not submersible and not for in tank applications. I actually don't know what it's for. That hose will swell up and rupture in the tank effectively putting a hole in your straw subsequently leaving you with low fuel pressure which would/could explain the hot start issue.

Pull your pump and inspect. Even if the hose is not ruptured, replace it because it will.

 

no smoke,, i will get video soon,, it cranks over there is a odd pop like its trying but doesnt catch if you keep trying you can get it to start but hard it doesnt flood out... I would love to hear engine builders input on the compression numbers...

FDAUTO,, i watched many videos they all used that rubber pipe,, im not saying you are incorrect but it is fuel hose. i will look into this..

 

Its fuel hose yes but its not rated for submersion. This is the discrepancy. It's inclusion with the pump would imply it's purpose but it's a set up. Those little rubber pieces are for the trash. It's a guarantee they will swell and rupture. It's just a matter of time

 

^What he said. For use submerged inside the tank, you'll need a hose with a SAE 30R10 rating/spec.

 

resolution?

 

Check if there is vacuum to the solenoid controlling the FPR, or if the solenoid has been removed, if there is vacuum directly to the FPR. If the FPR is not getting vacuum it will close and increase pressure to your injectors by, maybe, 25%.

Is your gas fresh?

It has been reported that the TPS might check out to be in spec, but then go out of spec when the engine bay gets hot. Perhaps try a different TPS (don't drop the machine screws into the engine bay).

 

Pause...... what? The fpr will what when there's no vacuum? Where did you get that from? The difference between base fuel pressure at atmospheric and under running vacuum is maybe 5psi maybe. 5psi tops. I want to say with a 43 base, your idle pressure is ~38. Where is this 25% and the fpr being "closed" coming from?

 

FSM Page F-98 Fuel line pressure test engine running (vacuum on):28-32 psi

FSM Page F-91 Fuel Line pressure test ign on not running: (no vacuum): 35.6~38.4 PSI

To assist with hot starts Mazda inserted a solenoid between the vaccum source and the FPR; the ecu tells the solenoid to close off vacuum briefly when the engine is hot to increase fuel pressure to the injectors.

See explanation on P-105~107 of FSM.

35.6 psi - 28 PSI = 7.6 PSI

7,6 PSI / 28 PSI = 27.1% ~ 25%

 

Take an FD FPR in hand. Try to blow through it. Now take a hand vacuum pump and apply vacuum. Try to blow through the FPR.

If the solenoid fails and therefore cuts off vacuum, the FPR loses vacuum assist and the spring inside the FPR closes the valve.

Likewise if the vacuum hose to the FPR fails.

If the injectors are prone to leaking, the increased pressure will increase the chance of flooding.

 

 

Due to problems with failing solenoids many shops will remove the solenoid and run vacuum directly to the FPR, which helps keep it open, always.


How they deal with the CEL, I don't know.

 

Also for the FD, Mazda increased the test level for compression to 100 psi instead of 85 psi. The initial USDM FD FSM still had the 85 psi level for the lower boost FC. They corrected the USDM FSM for the 1994 model year. But all the JDM FSM had 100 PSI starting from October 1991.

If a shop failed to catch this correction, they may have merrily continued to think 85 psi was fine, whereas Mazda clearly did not.

This difference of compression between this cars front and rear rotors at 80:95 likely is getting close to out of bounds.

 

sorry for delay haven't had much time,, do i need to rebuild engine then,, i dont wanna start throwing money at coils and stuff if if the compression is low,,, a local tunner told me low 70s are a problem area and my compression is lowish but still fine,


my FPR is connected to the manifold,,, no solenoid,, im gonna try install factory ECU and try hot start, (thinking it something in the apexi tune)

 

Go through the troubleshooting process. If you jump straight to rebuild and it turns out the issue was in the tank the whole time then you will have the same problem. If you are on a power fc then the situation with the fpr solenoid doesn't matter.

Pull the hanger and check the hose

 

Could also be leaky fuel injectors.

Does the car burn any coolant?

Dale

 

There was a guy had a similar problem, with the power FC, and it turned out to be his temperature sensor.

There is several temperature sensor, but it was the one on the block closer to the firewall.

Another guy had a similar problem and it was his TPS.

Meanwhile, what weight oil are you using?

 

I'm gonna do some testing and report back,, i'm gonna "T" into fuel line check fuel pressure and leak down test to see if injectors are leaking.

Ill triple check throttle position sensor readings, i'm 99% sure they are in spec. (im using readings off power FC rather than check at the sensor)

The temperature sensor for water is located behind thermostat housing and reads correct on power fc commander, (i have defi gauge and reads nearly exactly same).

Dale,, car doesn't appear to be burning any coolant. (i have a pressure testing kit to test coolant system,, ill dig it out and check it out.

cold start video below

 

This is commander screen,, showing battery when running water temprature,, also throttle position settings. closed and open settings,,, do they all look good??

 

this is a hottish start,,, i only got car to 82 degrees,, it gets worse when i reach 90 degrees when its hotter it cranks longer and sometimes doesn't catch i have to let off key wait and try again.