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starts, runs and a minute later it dies


jon L

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starts, runs and a minute later it dies. restarts right away and repeats.

At times it will run fine for 1-2 minutes then all of a sudden it dies.

Drives great and performs great. Just the idle, which it won't do.

 I have replaced the TPS, 02 sensor, IA sensor, Maf sensor, and the AT sensor.

I also checked the idle screw position. 

What am I missing?

 

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What's the fuel pressure? And if the pressure is good how long does the pressure hold when the engine is off?

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Fuel pressure is 38 lbs at idle and it goes up as the rpm increase.

the pressure holds for about 30 minutes before slowly losing pressure.

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I am not certain about this, but I am pretty sure the engine starts and runs open loop for a short period of time, even when warm. Then the sensors come back on line and start adjusting parameters. I know it may be difficult, because it will drop out of diagnostics every time you need to restart, but you might want to observe sensors in turn to see if there is any indication of faulty operation when it wants to die. Right now, I suspect a faulty MAF, even though it may have been replaced. My sons car had a similar issue, and the MAF appeared to be operational, but it was apparently out of range just enough to cause poor idle or loss of idle at somewhat random intervals. Disconnect the MAF and see if the idle stabilizes.

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Disconnected the MAF and it ran for a few seconds and then died. At time the engine will start

with a high idle "1600RPM  The next time it will start with the correct idle. 750-850 RPM.

I also noticed that it never goes into closed loop. What about the cat, could it be plugged up?

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Could the knock sensor cause it to shut down. I have a code that tells me I have a bad knock sensor.

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I can only relate what I just went through with the grandsons car. We couldn't get the O2 sensor to work reliably and it would not go into closed loop either. After verifying the wiring to the O2 sensor was intact and the signal was present at the connector on the ECM, we finally tried a spare ECM from the donor car. The replacement of the ECM corrected the closed loop operation and the O2 sensor became active as it should be. The one thing we did notice is the car will not go closed loop just sitting and idling but must be driven a bit before it will engage. 

As for the knock sensor, I had a related issue many years ago, where I didn't get a knock indication when I should have, like hitting a bracket on the front of the engine with the engine idling. In that case I changed the ECM as well and it has been fine since. If you can get the engine to stay running, maybe a helper will be required, get the knock signal up in diagnostics and see if it is increasing just sitting and idling and if that is okay, hit one of the brackets for a front accessory and see if the numbers jump. Constant knock or intermittent will reduce spark timing but I wouldn't believe it would kill the engine.

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 have a new ECM from Rock Auto. It will go in tomorrow. The IAC voltage varies just before it shuts down.

I will report on any improvement.

I have a error code indicating the knock sensor circuit is bad.

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On 10/20/2020 at 10:48 PM, jon L said:

 have a new ECM from Rock Auto. It will go in tomorrow. The IAC voltage varies just before it shuts down.

I will report on any improvement.

I have a error code indicating the knock sensor circuit is bad.

Can we assume the ECM didn't help since we didn't get a report?

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No, The ECM did not help. No improvement whatsoever.

I have replaced all sensors and my downstream 02 sensor is reading correctly now.

The last test I ran was on the IAC. The manual has the instructions.

And guess what, the sensor itself if right on, however the plug was

not making contact with the sensor. I don't know if the plug is bad or

the wire at the plug was bad. but I replaced the plug w/ wires and you 

guessed it all is fine. The IAC was opening up, but failing to close and

cut down the idle. Evidently the IAC would open up so far that the engine

could not stay running.

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