serge said:
I don't believe this to be a problem with fuel supply -- I can reliably have the Jeep running by pulling the vacuum line off the MAP Sensor. I've adjusted the TPS using the Renix manual (did it on the tranny connector). As a verification, checked the output on the ECU - now have a perfect .80 on terminal C (was .51 before). This is with key in Run and engine off. When I start the engine, it will shutdown again. Now here is the interesting part, when I pull the vacuum line off the MAP sensor and make the engine run, the voltage on the TPS ECU connector terminal C jumps to .91. The throttle is still closed. When I shut the engine off, voltage returns to .8 volts. Is this how it is supposed to work? Is the ECU going mad?
Langer1 was posting while I was writing, we are thinking along the same lines.
I never finished tracing the TPS and MAP circuit, but did notice they share some wiring.
Have you blown through the MAP vacuum feed line with it still hooked to the TB?
You may just be defaulting into open loop, by pulling the MAP vacuum line. I know pulling the electrical plug does this.
It's possible to have good pump pressure at start up, but have it fall almost too low to run the motor after the starter is released. Pulling the MAP vacuum line, could be widening the pulse enough to run the motor. Could be it just throws the system into open loop. Open loop operation, requires fewer sensors.
The fuel pump and the power for the injectors goes through the pump relay. Mentioned in another thread, is a low voltage condition to the pump, from a sorry splice at the fuel pump relay feed (which is bypassed during start). I'd leave a fuel pressure tester on there and keep an eye on it anytime I got it running.
I'm just guessing here, but do a feed voltage test on the MAP and a function check. The TPS and the MAP work together. I saw one MAP that had a 12 volt feed, that sure enough messed up everything.
If your IAC is stuck closed (or faulty for whatever reason) it will (might) start and die. It might start and die if the EGR is hung open. It might start and die if the fuel pump is starved for amperage. Volts X AMPS = watts, Watts is what you need for the pump to supply enough fuel. Voltage tests will fool you. Put a volt meter in the fuel supply circuit, watch the volts, while starting and again while you release the starter. Your fuel pump, could be working, but working poorly.
Make sure you are getting a steady supply of fuel during start and while running.
Make sure you are getting a steady supply of voltage to the pump and injector circuit from the pump relay.
Make sure you are getting enough air during/after start.
Make sure the EGR isn't dumping exhaust gas into your intake at/or near idle. If you can work the throttle and baby it till you get above 1500 RPM or so and the motor smooths out, the EGR won't affect things much. If the wire is disconnected from the EGR solenoid, the EGR my open at idle and cause a stall.
Next step is to check most all of the sensors.
Next step is to figure out which sensor is screwing up the works.
Did you ever try to start it with a vacuum line (or two) disconnected just to see if some extra air helped the whole process?