So here's the deal. I just rebuilt a friends NA Rx-7. I street ported it and we are running the stock ECU. When we get it starting properly we with toss a AFC Neo on to do a little tuning. Now before the car was torn apart to rebuild, the owner had to have a fuel pressure bleed off line. This consisted of a 'T' in the Fuel Feed Line that connected to a 'T' in the Fuel Return Line. The line between the two 'T's was bent over to block some flow of fuel. This would seem to reduce the fuel pressure by bypassing the stock pressure regulator. The pressure could be adjusted by how sharp of a bend was in the 'T' Line.

I did not re-install the Bleed Line after the rebuild and the car usually has a difficult time starting. You can clamp off the fuel feed line and start it, then remove the clamp and it runs fine. Now lately the problem is intermittent.... some times you can go out and cold or hot start it without clamping the fuel line... other times your have to clamp it or it doesn't even begins to start.

This leads me to believe there is either a problem with the pressure regulator or the cranking injector duty cycle from the stock ecu.

What do you think the problem is? From the symptoms i would like to think that it is the wiring to the coolant temp sensor. An intermittent short could cause the temp reading to change abruptly and could cause the ecu to increase the injector duty cycle if it sees a "cold" engine..

I would like to explore as many ideas as possible before hand because I have limited access to the car to work on it.

 

also....

The engine made 75 psi of compression prior to even the first start.

And if anyone has heard of this fuel line mod, i'm looking for some information on it.. in particular, why was it ever necessary?

 

Good move removing the ghetto fuel line mod.

The thermo sensor is a start, leaking injectors is another, but what comes to mind the most is......... its a freshly rebuilt motor! It's going to flood for a while, it's building compression. Install a fuel kill switch, smile and move on.

 

So the injectors were freshly cleaned by rc engineering prior... I just have a hard time blaming it on the fresh rebuild. Im getting close to a dozen rebuilds now and never had this problem... It could be the fact that this is the first stock ecu car I've built, but it would seem that the car had flooding issues prior to the rebuild also

 

It probably had flooding issues prior to the rebuild for the same reason it is having flooding issues now.... low compression.

 

A lack of a signal from the water thermosensor would result in a lesser duty cycle during START cycle. Less fuel.........less chance of flooding and also not enough fuel during Start cycle.

Think you have a intermittent short? Backprobe the water thermosensor input at the ECU plug with the key ON and shake the harness or look at it while cranking the engine over. You'd see it if there was a problem. All plugs connected to the ECU when doing so.

Lack of a waterthermo sensor input usually results in a difficult cold engine start but then the car will start just fine once warmed up. There's a caveat to that though. If you live in Florida where it's warm most all the time you might not notice this as much as someone living in Ohio.

On a car prone to flooding during START...........the lack of a water thermosensor input will result in a non flooding condition..........'cause less fuel is delivered during START cycle. ECU defaults the signal to 178*F if the signal is missing which results in less fuel during Start.

I've disconnected the signal during cool weather and the result is a lot more cranking to get it started and once started will run kinda crummy until the engine gets up to operating temps.....then all's well.

 

Good info hailers. I will check the sensor for intermittent shorts and for correct readings...

I think my next step is to check the fuel pressure, I'm not convinced that the regulator is functioning as it should.

You know more about how the stock ECU operates than I do, do you know if the stock ecu adjust the cranking duty cycle from the MAF reading? I asked because if I have to have a bandaid to make the car start properly, I would rather use the AFC Neo rather than a pump kill switch.

Im just not sure if the Neo can effect the cranking duty cycle or not, really depends on how the ECU controls fuel at cranking.