so i just replaced my spark plugs(local store didnt have wires), oil change, and installed a fuel cut switch connecting to my fuel pump. and STILL my car is hard to start when its fully warmed up. could it be my plug wires? and also ive read that if your car is hard to start then it could be of low compression. so if i put about oil in the housings then will this build pressure just temporarily? or will it be more towards a permanent fix??? it also could be a water thermo sensor ive read but i dont even know what that looks like or where its located. and what numbers should i be seeing when doing the compression test?

 

Plug wires don't cause hot start issues...unless they are disconnected. Leaking injectors or low compression are the more likely culprits. If you have a fuel cut switch, that should solve your problem shouldn't it?

Try this, when u turn off your car, use the fuel cut switch instead if the key, see if its still hard to start the next time. If not your injectors may be leaking fuel under the residual pursue un the fuel lines.

The water thermo sensor tells the ecu what temp it is, and the ecu uses that information to reference a startup fuel map (which us too rich stock). It is located on the back side of the warmup housing under the thermostat. Its green.

Oil I'm the housings is only a temporary fix...as in, as long as it takes for the oil to burn up.

great compression is 125+
Good compression is 100+
Decent compression is 80+
Anything lower ...

 

I smell rebuild

 

80 psi per face is not good its ****...thats when your gonna experience flooding problems.

 

k thanks for the good info. but if i use the fuel cut switch to stall out my car, isnt that a primarily bad thing?

 

its not compression ,theres thousands of 7s with low compression
and still start up when its hot
ive rebuilt engines with used housing and new housings
no differance
i used to think the same thing untill i read a few hailers threads

 

Some reading material:

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/looking-car-has-hot-start-problems-499744/
https://www.rx7club.com/rtek-forum-168/starting-fuel-map-886098/
https://www.rx7club.com/general-rotary-tech-support-11/car-keeps-flooding-when-i-crank-549190/

Low compression won't help the situation, but Mazda's start map injects more than twice the amount of fuel needed to start the engine when warm.

 

Might have been touched on in the links provided, but if pin 3B, which is the start signal, is "not" seen by the ECU when cranking the engine then the car will rely on the AFM to select how much fuel is injected when the engine is cranked and this amount is far less than what would be injected if the ECU "does" see the start signal. So one option you have is to install a simple cutoff switch between the ECU and the wire leading to pin 3B. Thus you cut the wire to pin 3B before it reaches the small plug at the ECU and install the switch. When preparing to start the car in a situation that mirrors your problem situation you would flip the switch to the off position and start the car while in a cold engine environment you would allow the "start signal" to be received by the ECU.

 

so i read that in one of the links, that one solution is to depin 3B on the ecu? so that the car will then rely on the afm, which will then shoot out enough fuel from my injectors? and if i want to cold start it just put the 3B pin back on the ecu?

 

You could do the depinning but you might find yourself having to pin, depin, pin...... on a constant basis which might be a pain in the crank case. Using the cutoff switch would make things much easier. The depinning of 3B is best suited when the climate is either constantly warm or constantly cold as opposed to a few days of cold followed by a warm day followed by a cold day and so on.

 

damn what a pain, if only i knew how to change out the fuel injectors, i would be in the clear, but since i dont know how to...this sucks. anyone know of a write up of how to change em?

 

I feel your pain. I have a fuel cut switch and a 3b switch and STILL have hotstart problems. I am thinking stand alone. seems to work for everyone else.

 

whats the stand alone????

 

Means replacing the stock ECU with an aftermarket type.

 

go standalone ,as well as the added power you will also fix the problem

 

i didnt know that they costed about 1000usd... hella much

 

megasquirt is much cheaper but also much more diy work involved to save the moneys

 

the s4 in a hot start will throw a solenoid that will deny the fuel reg the vacuum signal from the engine for a short period
( the hotstart flag is determined by the switch in the radiator and or back of water pump ,, NOT the ECU coolant sender )

the idea of this is that the extra rail pressure will compensate for changes in fuel density due to rail boiling after shut down


if the solenoid does not work,, you will not get this extra compensation required
if the switch in the radiator or back of water pump is faulty,, same
( whichever one it is cause i cant be arsed double checking )


also,, sometimes hot start compression is low on some cars with worn bearings and thin oil grades

and some internal coolant leaks ( depending on location ) may be worse when the motor is warm and thus require a plugs out , fuse out blow down before it will go

( leak-down and TK litmus test the coolant system )

 

Shutting off the FPR solenoid which cuts off vacuum to the FPR, which in turn will cause higher fuel pressure ..........will not work when starting the engine. Ain't no vacuum til the engine actually starts.....last time I looked. In other words does not apply to Starting the car 'cause the lack of vacuum at the FPR already exists. The pressure is already in the 37-39 psi range (normal idle it's 28-32psi).

The internal fuel map of the ECU is what determines the amount of fuel during start. See the attachment from the Mazda manual. It's determined by.......engine speed under 500 rpm..........the output of the water thermo sensor......and the START signal being seen at 3B of the ECU on series four cars.

A failed water thermosensor results in a ECU default signal of 176*F. Failure in this case means disconnected sensor at the back of the water pump housing or a pushed back socket in the sensors pulg.

The difference in fuel amount delivered is shown on a Palm device on page two, post 44, of this thread.....https://www.rx7club.com/showthread.p...t=graph&page=2

Or if you have a digital meter with duty cycle you can backprobe the primary injector(s) and look at the duty cycle with and without the water thermosensor connected to the ECU when the engine is hot. You'll see what is shown on the Palm device in that thread just above.

The last time I looked the water temperature sesnor in the bottom of a series four car is closed after something like 120* and has nothing to do with closing the FPR solenoid. The FPR solenoid depends on the water thermosensor for determining the closing of the FPR solenoid. for hot starts. That is for after the engine actually starts and is for ???? I forget how long the solenoid stays closed. Something like 120 seconds . It's in the 86-87 FSM.

 

The people who developed the RTEK 2.0 recognized this as the way to prevent flooding during starts.

On the palm display there is a graph just like the one shown in the above post of mine, and the owner of the RTEK 2.0 can vary the amount of fuel at different temperatures to prevent hot starts. It works very well. No pulling EGI fuses, no pulling sparkplugs, no fuel cut switch. Just set the amount with the Palm and never have to fiddle with anything else ever again.

Prior to owning a RTEK I bought a voltage switch kit from JAYCAR and installed it. http://www.jaycar.com.au/productView.asp?ID=KC5377

It was a simple to build kit and I used the water themosensors input to the ECU to trigger the relay in the kit. The relay either opened or shut the signal to 3B on the ECU's small plug. I set it so that the circuit was open at any temp over 120*F and it worked fine for me.

The RTEK 2.0 for series four cars also included the feature that the series five cars have. That would be where you HOLD you foot to the floor when starting in order to unflood a engine. Holding the pedal to the floor is seen by the ECU thru the TPS output and if the ECU also sees the START signal at the same time.........it cuts the fuel injectors off so no more fuel is injected and you can figure out the rest.

I think the series four non turbo do not have this feature, only the turbo cars. You'd have to check with Digital Tuning to be sure (their site online).

 

Part of what I said above is not quite right as you can see in the attachment. The cutting of vacuum to the FPR solenoid is determined by two things. Airintake temperature and water temperature over 149*F as seen by the water thermosensor on the back of the water pump housing.

But again, that FPR solenod shutting off has zip to do with actually STARTING the engine. It applys only after the engine starts and is now making vacuum.