94 850 turbo with intermittant starting/missing.

calbrit01 · Post by **calbrit01** » 30 Jan 2008, 13:40

ok new plugs make a difference to it running, no missing or surging. Still starts no good though, unless I pump the gas a couple of times. Loud fast ticking noise from under the hood, which I thought was the fuel pump, but apparently its located in the tank. Code p0326 came back after a few weeks post seafom treatment, which is knock sensor - running out of things to try to fix that knock sensor error - vacuum lines, MAF, plugs, filter air & fuel - any other ideas?

SAL

Post by **Ozark Lee** » 30 Jan 2008, 14:56

I read back through the post and didn't see it but the problem may be the fuel pump check valve. The type of behaviour you describe is consistant with the check valve being bad.

To test:

1) Put a fuel pressure gauge on the car.

2) Start it and verify the pressure.

3) Turn it off and watch the pressure. It should hold. If it falls off then the check valve is bad.

The bad news is that the check valve is built into the fuel pump housing and it usually means a whole new fuel pump, replacing the guts with a Walbro won't fix the problem. I have heard that there are aftermarket inline check valves available but I have not been able to source them.

...Lee

calbrit01 · Post by **calbrit01** » 30 Jan 2008, 15:23

Great thanks for the suggestion Lee, I'll give it a go. has this been known to cause the bad starting AND/OR the Knock sensor code do you know?

SAL

Post by **Ozark Lee** » 30 Jan 2008, 15:28

The knock sensor code got thrown with the seafoam treatment, just clear it. I doubt it will come back.

The bad check valve does cause the hard starting problem.

...Lee

calbrit01 · Post by **calbrit01** » 30 Jan 2008, 16:48

Unfortunately the Knock sensor code has been plaguing me for several months, the Seafoam treatment was one of the things suggested I tried. It cleared the code for about 2 weeks, and I was ecstatic until it came back. I cleared the code a couple of times, but 100 miles or so and its back. I think I have tried most of the low hanging fruit fixes. I did read somewhere you can use a multimeter to check output from the knock sensor - not sure what level of output would indicate a good sensor, although the consensus of opinion I see is that this is highly unlikely to be the sensor itself, more likely a vacuum hose, bad plugs, etc. Anyone got a full list of the things to try?

Thanks

Simon

Post by **MadeInJapan** » 30 Jan 2008, 20:45

Are you using high octane gas? Sometimes, depending on the gas you buy in the winter time there are additive mixed in that really does a number on gas quality. If you're not using 91 or better octane gas, try switching to it and resetting your codes and see if this takes car of it.

calbrit01 · Post by **calbrit01** » 31 Jan 2008, 12:43

Yes 91, just changed to Shell though from more generic brands, so see what happens once I have been through a couple of tanks. I did find a note from BillofDurham which has pointed me to the problem noted in the manual posted on this site. seems to suggest that the cam position or sensor itself will cause this code. May try the contact cleaning first on the sensor and then the cam position adjustment or PCV/fuel pump check depending on which is the easiest.

Regs

SAL