: weak fuel pump question



closs2sx
11-22-08, 02:54 PM
can a weak fuel pump cause a no crank no start condition on some occassions (lack up pressure or not turning on which may not trigger a relay?) and when it does start an up and down idle between 1200 and 500 rpm. car is a 2002 cadillac deville dhs and the crank sensors were just replaced

Ranger
11-22-08, 05:38 PM
No. It will crank with no fuel pressure. The surging idle sounds suspiciously like a ripped plenum, creating a vacuum leak. The plenum on the 2000+ Northstars is the rubber coupler between the TB and the manifold. Usually rips on the bottom where it can't be seen. Spray some Brakleeen there and see if the idle RPM increases.

closs2sx
11-23-08, 08:02 PM
well I tried the brake and carb cleaner and no change. I unplugged the vacum line to what I think is the fuel pressure regulator on the fuel rail and my fuel pressure went up from 39 to 46 at idle and seemed to smooth the idle any ideas this thing is turning into a nightmare. thanks for your help ranger

Ranger
11-23-08, 09:23 PM
No fuel leaking from the FPR nipple I assume?

If it won't crank, it's not a fuel problem. It's in the cranking (starter) circuit. Have you pulled the DTC's? Checked the battery and cable condition?

closs2sx
11-24-08, 11:54 AM
battery and cables are fine after a few key cycles the car will start. but when it does the idle strugles to stay running. I changed the fuel filter and the 1st attempt to start the car there was nothing. after a few key cycles the car started. but again the car does not want to idle and dies now and then. as the car struggles to idle the fuel pressure follows the idle up and down from 39-35 psi

Ranger
11-24-08, 12:08 PM
It almost sounds like 2 separate problems. No crank is electrical. The idle problem might be a dirty TB. If it is all carboned up, the IAC circuit may be clogged. Have you ever cleaned it?

closs2sx
11-24-08, 02:10 PM
I have taken the tb off and cleaned both sides well. where is the iac so I can check that and clean it if need be and could it be the ignition switch for the no crank. also the idle could that be bad plugs and wires? the car has 140k on it

closs2sx
11-24-08, 02:58 PM
ok I think I have the idle resolved I turned the screw on the tb ever so slightly until when the car is warm it idles at 650-750. I dont know if after I cleaned the tb it allowed it to close up and choke the car out or what but it idles fine now. Now I just need to find out what would cause an intermitent no crank condition that after a few cycles when it decides it will crank. the no crank condition may not happen for 50-100 starts and then bam no crank cycle the key until it decides to crank and then shes fine

Ranger
11-24-08, 03:23 PM
:hmm: What screw on the TB? The idle is controlled by the IAC (Idle Air Control) valve on the side of the TB. It is electronic.