Engine Stalling Upon Starting or Upon Throttle Application
 

So I have searched the forum for about a month now trying to resolve this on my own based on others' past experiences but unfortunately I cannot seem to find anything that matches the symptoms I am seeing. Any help on the below issue would be most appreciated. I apologize for the length but want to give as much info as possible to help detail the problem and what I have tried so far to fix it.

Car: 1993 RX-7 100% Stock, No modifications. 49,200 Miles on original engine.

Chain of Events: After a failed fuel pump about two or three years ago and due to work travel etc the car sat un-started for quite a length of time. I rarely drive it but generally start it and idle it, rev it up, change the fluids, etc every few months to keep it fresh.

A month ago I finally got some time and replaced the fuel pump, cleaned the fuel tank out, replaced the fuel filter, spark plugs, engine oil, and flushed out the radiator. After priming the fuel system and a little coaxing the engine came to life and held about a high but clean steady idle and I was able to move the car out of the garage to just let it idle awhile before pushing it in any way. It sounded and was performing as expected.

The car warmed up to operating temperature and held normal temperature for awhile. After 10 mins or so of that I felt it safe to leave the car unattended for a few minutes while I went to get some tools. When I returned less than 5 mins later the coolant alarm was sounding and the temp gauge was pegged at "H". The engine was stumbling attempting to stall and had near zero throttle response. I immediately shut it off and allowed it to completely cool down and did not attempt to re-start it for about 3 weeks.

Yesterday I replaced the thermostat, topped off the cooling system, and then started the engine. The car instantly starts, revs to around 2000 RPM and then immediately shuts off. If I ever-so-slightly touch the throttle I can sometimes get it to hold around 2500 RPM for a few additional seconds before it stumbles and stalls. If I press the throttle any farther it immediately stalls. Once the car reaches anywhere near warm temp, it stops starting at all... sounds as if it is flooded. Once it cools down a bit, it will return to starting, reving for 2 seconds then stalling.

So far I have:
- Pulled the plugs and they are fairly clean (not damp, no sign of coolant, etc), just a little soot.
- Turned over the engine with the Trailing plugs out for a quick audible compression test and have a consistent PSST PSST PSST cadence on both chambers
- Checked the engine oil for any sign of coolant... none
- Replaced the Circuit Opening Relay, Fuel Pump Relay, Ignitor, and Fuel Pump Resistor with known good / operating units off my other FD.
- Jumped the GND/TEN terminals to check the codes... nothing shows.
- Jumped the GND/FP terminals to check fuel pump operation. Sounds good....
- Reset the ECU a number of times.... no help.

I am out of ideas...... any thoughts or help would be appreciated. I realize the overheat is very bad, likely severely shortened the life of the engine, but right now I have compression, fuel, and spark. This issue seems to be somewhere with the control system. Something that would have been damaged by the higher engine / coolant temps that would cause the ECU or ignition system to go into limp mode / immediately shut off after 2 seconds or under any throttle application.

Oh the memories.......
I would start by making sure the hose to the Map sensor didn't get knocked off. Take a voltage reading on the middle wire, can't remember exactly but should read less than 1 volt at idle. Also check the plugs to the IAC and TPS, strange things happen to cars with wankels.

So far your on the right track with the testing you have done. Did you track down the reasoning for low coolant if that was the case?

My check list would be;

Vacuum leaks.
OMP.
TPS.
MAP SENSOR.

I know you side no codes showed up so the sensors listed may be fine. Also check the coolant line going to your TB for leaks, best of luck.

Chris.

Sent from my iPhone using RX7Club

Thanks for the quick responses! I have been messing with things and I am almost certain its a vacuum leak at this point and Im pretty sure its the hose going to the Boost Sensor and maybe the EGR solenoid (just based on the way its behaving). I was racking my brain trying to figure out what would have gone wrong after an overheat and Im guessing that the raised engine temp after sitting so long may have caused one of the brittle old (20 year old original) vacuum hoses to finally split or pop off.

Added to that, yesterday when I got a friend to sit in the car and turn the ignition so I could examine the engine closer and I noticed a very faint but consistent very high pitched whistle coming from under the upper intake. Immediately after the car shuts itself off that whistle persists for about 2 more seconds and raises in pitch. Its definitely sucking in air from a very small crack or hole in a line..... hopefully thats the culprit.

So, next plan is to order some silicone vacuum hoses / zipties and tackle re-doing the rats nest. Haven't done that in about 10 years since I did the job on my other FD, should be a fun walk down memory lane.

Ill update the post once I change those over and let you all know how it turns out. Thanks again!