Fuel Pressure Priming

[velorider]

I'm working on a long crank issue. I hooked up the fuel pressure gauge today after the car sat for a week. The pressure was 0psi as expected. I turned the key to position II and the gauge climb to 20psi, turn the key back to position I and then to II again and the pressure climbed to 40psi. Then turn the key to position III and the gauge jumped to about 55psi and started normally. After about an hour the pressure dropped back to 0psi. I repeated the same process with the same results.

So here is what I'm thinking. After an hour the pressure drops to 0psi, when I turn the key to position II the pump primes the line to 20psi and might jump to about 40psi when I turn the key to position III. So I think when I experience a long crank it's because the starting pressure is around 40psi.

My questions are:

This behavior normal?

Why does the pump only prime about 20psi, shouldn't it prime to 40psi regardless of the initial pressure?

Thanks
John

*Edited to clearify crank issue

[jimmy57]

The pump runs for a set period (1.5 seconds) when you cycle ignition on. It is normal for it to only go from 0 to 20 and then 20 to 40 as you describe. The pressure should be held after you shut it off after running to 25 or more psi for at least 20 minutes or it will have hot restart problems. If it goes to 0 overnight that is ok but if it drains back to tank completely then cold cranking will go longer. If it drained completely it would not get to 20 psi on that first short pump run.
The 55 psi initial pressure when started is normal too. That is a vapor lock clearing process to run pressure up to a higher amount and then settle back to 42-44 psi after 40-50 seconds.

[abscate]

Are you trying to fix a slow crank or a hard start issue ?

[velorider]

I guess it would be called a hard start issue. It's seems to crank fine, just take longer to start then it should.

I did replace the fuel filter as part of regular maintenance about 3 months ago.


Thanks
John

[velorider]

Reviving this thread because I finally fixed the issue. Months and months of it happening more frequently and finally last week it cranked for a long time and kind of slow. So I ran over to AutoZone and got the battery and charging system tested.

The battery passed but was at 78% charge and the charge system was putting out 13.3 volts. It also reported diode failure.

So I replaced just the alternator's voltage regulator for $40 to see if that would resolve the problem. For the last week the starts have been much faster and the starter seems a tad faster.

I tested for A/C voltage but detected none so I think the diodes are fine. The system tested fine when I first got the car, and this starting issue has been since I got it. My thoughts are the system was at the edge of ok but enough to cause long starts occasionally.

One of the brushes on the old regulator was significantly shorter than the other so I think it was barely making contact.

My last Volvo had alternator issues about 100K also, I wonder if the brushes just wear out around that point. On my previous car I replaced the complete alternator $$$. I wonder if the $40 voltage regulator would have fixed it.