Fuel System Woes
Posted: Wed Nov 03, 2010 9:20 pm
Hi everyone! I thought I would fill you all in on my latest Astro Anomaly:
Lately my van won't hold an idle when it's cold outside and the engine is also cold. I mean, cold for southern California, like mid sixties. I start it in the morning and it fires right up and then after about 7 seconds it starts to sputter and will die if I don't rescue it with my foot on the pedal. If I open the throttle the idle raises but it won't stay there, it still comes back down and dies. The only way I can keep it running is to constantly "goose" the gas pedal, if you know what I mean. Maybe this will help: If it was carbureted, it would be like it was only getting fuel out of the accelerator pump.
I have to do this for several minutes until the engine is warm enough to take care of itself, but then if I put it in gear it stalls. So I let it warm up some more. Total time from a cold start until I can actually drive it is anywhere from 7-15 minutes depending on the ambient temperature.
I wasn't sure if it was loosing spark or fuel so I used my timing light to verify that I was getting a spark in all six plug wires when it stalled. I am, so I deemed the ignition system to be okie-dokie.
Moving to the fuel system, I tried a small squirt of brake spray in the TBI as it was about to stall and whattaya know? It came back to life! So, it's running out of gas. I looked for a vacuum leak but found none.
Then I thought maybe the coolant temperature sensor was failing and the ECM didn't know the engine was cold. But, I checked that with my laptop and WINALDL and the sensor reading agrees with the current weather, and I can see the coolant temp drop at exactly the rated temperature of my thermostat. So I think the sensor's OK. I also noticed that the voltage from the O2 sensor was staying really, really low for several seconds at a time which also indicates a lean condition.
Next I figured it was a good time to check fuel pressure. I hooked up my gauge and turned the key. I heard the fuel pump run for 2 seconds but the gauge reads zero? I started the engine and still 0psi. Well it's a cheapy gauge from Autozone so maybe I can't trust it. But then, after running for a minute or so I look at the FP gauge and it's now reading 4psi. As the engine warms up the pressure rises, and finally settles at around 10psi, at which point the engine runs normally.
I know the TBI FP spec is 9-13, so ZERO would explain my problem, right?
I needed to find out if the fault is in the regulator or the pump. I understand that if I block the return line, the fuel pressure should rise. If it does go up, the pump is good and the problem is the regulator. If it stays low then the pump is at fault. Correct?
With the return line blocked, the gauge should read maximum pressure from the fuel pump, which should be around 16psi right? When I blocked the return line it only went up to 12psi.
So it went up, which says regulator, but not as high as it should, which says pump. Now I'm a little confused. But, my next step will be to check voltage at the fuel pump. Also, I will retest the fuel pressure with a higher quality gauge to verify that step of the diagnosis.
Any questions, comments, suggestions?
Lately my van won't hold an idle when it's cold outside and the engine is also cold. I mean, cold for southern California, like mid sixties. I start it in the morning and it fires right up and then after about 7 seconds it starts to sputter and will die if I don't rescue it with my foot on the pedal. If I open the throttle the idle raises but it won't stay there, it still comes back down and dies. The only way I can keep it running is to constantly "goose" the gas pedal, if you know what I mean. Maybe this will help: If it was carbureted, it would be like it was only getting fuel out of the accelerator pump.
I have to do this for several minutes until the engine is warm enough to take care of itself, but then if I put it in gear it stalls. So I let it warm up some more. Total time from a cold start until I can actually drive it is anywhere from 7-15 minutes depending on the ambient temperature.
I wasn't sure if it was loosing spark or fuel so I used my timing light to verify that I was getting a spark in all six plug wires when it stalled. I am, so I deemed the ignition system to be okie-dokie.
Moving to the fuel system, I tried a small squirt of brake spray in the TBI as it was about to stall and whattaya know? It came back to life! So, it's running out of gas. I looked for a vacuum leak but found none.
Then I thought maybe the coolant temperature sensor was failing and the ECM didn't know the engine was cold. But, I checked that with my laptop and WINALDL and the sensor reading agrees with the current weather, and I can see the coolant temp drop at exactly the rated temperature of my thermostat. So I think the sensor's OK. I also noticed that the voltage from the O2 sensor was staying really, really low for several seconds at a time which also indicates a lean condition.
Next I figured it was a good time to check fuel pressure. I hooked up my gauge and turned the key. I heard the fuel pump run for 2 seconds but the gauge reads zero? I started the engine and still 0psi. Well it's a cheapy gauge from Autozone so maybe I can't trust it. But then, after running for a minute or so I look at the FP gauge and it's now reading 4psi. As the engine warms up the pressure rises, and finally settles at around 10psi, at which point the engine runs normally.
I know the TBI FP spec is 9-13, so ZERO would explain my problem, right?
I needed to find out if the fault is in the regulator or the pump. I understand that if I block the return line, the fuel pressure should rise. If it does go up, the pump is good and the problem is the regulator. If it stays low then the pump is at fault. Correct?
With the return line blocked, the gauge should read maximum pressure from the fuel pump, which should be around 16psi right? When I blocked the return line it only went up to 12psi.
So it went up, which says regulator, but not as high as it should, which says pump. Now I'm a little confused. But, my next step will be to check voltage at the fuel pump. Also, I will retest the fuel pressure with a higher quality gauge to verify that step of the diagnosis.
Any questions, comments, suggestions?
