CIS Fuel Test Pressure Question '77 2.7

[kpfoten]

Hello,

I tested my fuel system today with my JC Whitney CIS test kit. I pulled the airflow sensor plug and turned the key on to let the fuel pump run. Is this the same as jumping the relay site?

Anyway, I got a ridiculously high Cold Control Pressure -- roughly 70-75psi. With the NM heat, I should've gotten around 40psi, I'm guessing.

System pressure, etc, seemed to be ok. (didn't check the warm control pressure--it was late and neighbors, etc.)

So, I'm thinking that the WUR or the System Pressure Regulator are bad?

Any help would be appreciated. Thanks again.

Kris

[cowtown]

I tested my fuel system today with my JC Whitney CIS test kit. I pulled the airflow sensor plug and turned the key on to let the fuel pump run. Is this the same as jumping the relay site?

Yes, it is.


Anyway, I got a ridiculously high Cold Control Pressure -- roughly 70-75psi. With the NM heat, I should've gotten around 40psi, I'm guessing.

This is with the valve on the tester open? Did you unplug the WUR cable? It heats up an element in the WUR, accelerating the control pressure increase.


System pressure, etc, seemed to be ok. (didn't check the warm control pressure--it was late and neighbors, etc.)

I bet it will be the same as your tester "cold" pressure


So, I'm thinking that the WUR or the System Pressure Regulator are bad?

I wouldn't replace anything until you get a reliable reading on cold control pressure. If the car starts OK cold, chances are there's something wrong with the measurement technique, not the WUR.

[Jim Sims]

Nominal cold control pressure values for 1977: 20 psi @ 50F, 32 psi @ 75F and 49 psi @ 100F. You indeed need to know the warm control pressure (39 to 45 psi is nominal) to analyze the cause of this high cold control pressure (if it really is high). If both the cold control pressure and the warm control pressure are high then the cause could also be a restricted fuel return line in addition to a defective WUR. One checks this by rigging up a temporary fuel return line into a gasoline can. No sources of open flame and have a fire extinguisher on hand. If the pressures become normal with the temporary fuel return line then there is a restriction in the return line. Cheers, Jim

[kpfoten]

Thanks so much guys! Yeah, the WUR cable was disconnected.

I have a bear of a time getting the dang thing started. I have to spray a puff of starting fluid in and crank her over. Even then, the thing idles low low low and I have no throttle response. When I finally get it driving, I have to feather the throttle to get it to rev up...

I'll get her started today... The whole thought of running it makes me nervous yet... There was some grease on the exhaust that ignited a few weeks ago--I didn't get it fully cleaned off...

[cowtown]

Kris, you're difinitely on the right track checking out the pressures. Once you get that straightened out, another thing to check for cold starts is you thermo-time switch circuit that sprays extra fuel into the plenum via the 7th injector.

Does the 77 have a hand throttle, or does it use an Aux. air valve to control starting idle speed? You might check this item (whichever one you have) also. But the pressures (listed by Jim above) are definitely the first step. Let us know how it turns out!

[kpfoten]

Well, first-off, something I did made it run smoother. I don't know if it was setting the magnacores onto the dizzy cap better or what... Could've been bad gas as well, the thing was stored for 2 years... Anyway, no real backfires to speak of this time around...

However, Warm control pressure is high (5.5 bar) upon running for 5-10mins. My CIS book states what Jim suggests. I'd like to test my return line from the WUR. I haven't looked yet, but which line is it? Any recommendations for test set-up? (i.e. how don't I burn my garage down?)

Thanks again

[kpfoten]

OK, the return line was an easy find. However, there are some other players in the game (aren't there always...).

Coming out of the WUR, There is a line that goes to a Thermo-Valve. Is there any way of testing this to see if it works? It goes to a T fitting that runs from the intake to the dizzy. BTW, I have very little vacuum...

The fuel line comes from the WUR to a split that goes to the Accumulator and the return line to the tank. Could the Accumulator be involved in the mix?

Thanks!

[kpfoten]

Jim, pressure does not become normal when I hook up a temp fuel-return line.

WUR?

Can I somehow clean this or is it shot?

Thanks!

[1980SC]

It is the WUR, and you can fix it yourself.



There is a thin metal disc within the WUR which acts as a diaphragm. It's stuck. Take it apart. Free it up, and your control pressure will drop down. You may need to replace the o-ring which resides near the metal diaphragm. I found one of the correct size at Lowe's hardware store.

Don't worry about the other CIS components until you get your control pressure down.

-Rob
1980sc

[Jim Sims]

You can unscrew the fitting on the WUR attached to the line that runs to the fuel distributor; check to see if there is a screen there that is clogged. Also, disconnect the banjo fitting (of the return fuel line) and look and see if there is anything clogging that hole.

But first, what is your system pressure (pressure tester line to WUR closed off)?

Jim

[kpfoten]

System Pressure was right around 75.

Thanks for the info. I appreciate it! This is like getting Aunt Nellie's blood-pressure down in the ER!

[kpfoten]

Also, I checked cold pressure by bypassing the line from the fuel distributor to the WUR altogether.

[kpfoten]

suspect clogged screen--how do I get it out?

[kpfoten]

Crap. The lower diaphram seems to work well. I was taking that thin metal plate off and it cracked. Oh well. Anyone have a sale on WUR's?

I was also wondering how you're supposed to get the circular piece that connects to the fuel lines loose?

[kpfoten]

Update:

Installed my new WUR, turned the key and the dang thing fired right up and runs like a top!!

Thanks to all that helped me trouble-shoot. Have a beer!