I just recently got finished swapping a turbo S5 engine into an existing turbo S4 RX7. The S5 engine that went in to replace the blown S4 was a low mileage rebuild with solid compression . (Around 110). The swap used all S4 electronics and harness on the S5 block. Everything started up as usual the first time and I fixed any small issues. Now I've ran into an issue I can't seem to get past. When the car is cold keeping the car running is very difficult. I crank it, it starts right away and then it dies out. Input from the gas pedal does nothing to keep it running. It starts right up and then dies about 10 times before I can finally use the gas pedal to hold the idle. Once I get a chance to hold idle it runs fine. (Car has a full emissions delete). After 20 seconds or so it idles on its one. Once its to this point I can turn it off and start it back up with no issues. Even a couple hours after with it sitting, the car will still fire up and run without an issue. The car has no vaccumm leaks so that isn't an issue. My next though was the TPS, it was indeed bad and I replaced it with a unit from Atkins. I put that in and set the TPS, its runs better but I still have the cold start issue. Next I assumed ignition timining. This is the part I am working with how. The pulley has two lines. A leading and trailing line. My timing gun has the option to set timing anywhere between 0-60 degrees. What do I want timing to be on the red mark and what do I want it to be on the yellow mark? If you have any other suggestions to my issue other than timing please let me know. Thank you.

 

The timing has been set properly and the TPS sensor replaced and adjusted. I am still having the same issue with keeping the car running. Any help would be greatly appreciated.

 

Timing set procedures are in the FSM.

The engine speed must be below 1000 RPM to set the timing.

Pull CAS, make sure it is not inserted one tooth off. It helps to remove the CAS cover and hold the rotor in place while you stab it.

Set your timing light for 0. Clamp onto one of the leading leads. Adjust CAS until the pointer lines up with the first mark (leading, yellow).

That said, how long have things been sitting?

If longer than a few months, I'd highly suggest having the injectors cleaned and tested.

Also, is the ECT connect? If that coolant temp isn't being read by the ECU it will default to 80 degrees C (as I recall) which will make it hard starting cold.

 

Relevant but somewhat irrelevant Aaron, but I have a question.

My car starts fine regardless of temperature but when it is freezing outside (yeah, it freezes down here sometimes) my engine sounds vastly retarded or either trailing ignition is switch off. If I let it run for a few second (takes longer the colder it is) the idle will suddenly jump up like the ignition timing advanced some or the trailing spark came on.

It doesn't cause any driveability issues, but it does pique my curiosity. My car has done it ever since I have owned it. I have had 2 engines so it isn't a mechanical thing.

 

To the OP. It sounds like you may have a failed coolant temperature sensor, ( the one on the back of the water pump).

If this is failed the engine will think it is warm and not run fuel enrichment. Then is makes sense that as you warm it up it becomes easier to start.

A vac/ boost leak could cause the same issue being that it would be leaner than it needs to be to start. Sounds like you already checked for this but maybe it is worth checking again. I had a leaky blow off valve cause this once, took a long time to figure out.

 

Just re-read your post that it starts right up. Probably not a vac leak then. I'm putting my money on coolant temp sensor. You can test it with a multimeter and hot water, check out the FSM.

 

Can I assume that your second post is in regards to me?

 

Nope, that was for the OP.

I'm not sure whats up with your car, but it might be worth taking off you BAC, cleaning it and testing it.

 

I'm going to test the coolant temp sensor now as we speak, thanks for pointing that out. I have tested vac/boost and AFR. All seem to be reading well. I also realized I don't have a BAC valve installed right now? Is there a good chance that's my issue right there?

 

Issue Resolved, I replaced the sensor with one I had off a spare motor and it started right up and idled first try in 5 degree weather. Thank you so much, this was driving me crazy.

 

No problem buddy. Glad I could Help.

 

Temp switch at bottom of rad jumped instead of connected?

 

I don't have a temp switch on the bottom of my rad.

 

They are distinctive to S4's and not S5's. You might want to focus on the water thermosensor.