Cold Fuel Pressure Results ... Next Step?

mca · 09-10-2007, 04:18 PM

I am having cold start issues on my 82 SC - see Cold Start Issue - Video. In a nutshell, she starts right up with immediate revs and then drops off just as fast ... and dies.

I have no warm start issues. No hunting idle. Fuel mixture checks out. Timing checks out. O2 sensor not hooked up. No cold drive-off hesitation. Runs great warm or cold.

FWIW ... I can keep her running on the first try if I keep the rmps above 1k using the throttle.

I just completed a cold fuel pressure test. The reading was 69 psi which is within system specs (65-75 psi). Test done on cold engine with fuel pump running.

What is my next step? AAR test?

Mysterytrain · 06:03 PM

mca,
You need to think of the AAR as an automatic hand throttle. Jim's website explains its function pretty well. The device 'regulates' the amount of air that is bypassing the throttle housing and thus increases rpm's. Early CIS cars had a hand throttle between the seats to accomplish this task. The device has a bimetal strip that has a heating coil wraped around it. As the bimetal strip heats up it closes off the air flow and the rpm's drop. To do this, it needs 12 volts and engine heat to close completely. The AAR can also be tested in place. You can remove the outer hose and then use a mirror and flashlight to look into the opening. On a cold engine the opening should look like a cresent moon. The colder the ambient temperature the larger the cresent shaped opening. The heating coil can be tested at the electrical connector it should measure 15 to 20ish ohms.
If the AAR is stuck closed then cold starts will suffer..but once warmed up the engine will run perfectly.
AAR Revisited

boyt911sc · boyt911sc's Garage

MCA,

Since you measured the system pressure (cold) at 69 psi, what was your cold control pressure? It is important to know your cold system and control fuel pressures when troubleshooting for cold start problem. This will be your baseline data, then proceed investigating other CIS components. Remember that individual CIS components like WUR, AAR, CSV, etc. could be bench tested and replace only as needed.

Tony

mca · 09-11-2007, 05:26 AM

Quote:

Originally Posted by boyt911sc

Since you measured the system pressure (cold) at 69 psi, what was your cold control pressure?

I thought that was the cold control pressure

Would the cold control pressure be the pressure with the engine running while below normal operating temps?

If so, I assume the pressure gauge connects in the same place - between the center of the fuel dist and the wur.

Paulporsche · 09-11-2007, 02:23 PM

If you search jim williams or get the Bentley manual you will be able to see the testing procedure. The fuel pressure you got is in the acceptable range (65-70psi) and
it remains static.

The control pressures vary depending on engine and ambient temps. An 82SC should have a ccp of about 2 to 2.4 bar @ 20C w/ the engine cold and running and the heating element of the WUR disconnected, and a wcp of 3.4 to 3.8 bar w/ the engine warm and running. A lower control pressure allows for a richer mixture and vice versa.

You should also have a residual fuel pressure of at least 1.3 bar after 10 min and 1.1 bar after 30 min once th e engine is off.

Paulporsche · 09-30-2007, 09:08 AM

Any update on this thread?

mca · 09-30-2007, 12:43 PM

Paul -

All of my pressures are right where they should be.

Recently she has been starting great. Maybe b/c the temps aren't in the 100s anymore?

Anyhow, I just replied to one of your threads ... pertains to decel vavle. I replaced the vacuum hose to the decel and hooked it up ... haven't had any issues since.

So to answer your question ... I still don't know what exactly is going on but I am happy with how she is currently running.