System/Control Pressure test for dummies?
 

I'm about to perform a system/control pressure check on my CIS car, and want to make sure I'm getting this right. I've read over the factory manual, but got more confused after reading it. Based on previous posts I've read, here's what I beleive to be true. Please correct me where I'm off.


Cold Test (requires a cold car):

1. Hook up gauge between WUR and Fuel distributor.
2. Disconnect electrical plug to WUR
3. Jumper fuel pump so it runs
4. Observe readings on pressure gauge and compare against chart for proper values.


Warm Test:
1. Leave gauge in place as it was for cold test
2. Connect electrical plug to WUR
3. Jumper fuel pum so it runs
4. Turn on ignition (so there's power to the WUR)
5. Watch pressure raise once power is applied to the WUR
6. Observe final warm value

System Test:
1. Leave gauge in place as connected above.
2. Close valve on outbound/WUR side of gauge setup.
3. Jumper fuel pum so it runs
4. Observe system pressure

Approximate values for '76 WUR:

Cold values:
50 deg 18-23psi
70 deg 25-32 psi
90 deg 34-39 psi

Warm pressure = 40-45psi

System pressure = 65 - 75psi

All above tests are done with the car off/not running. There are some other tests for under partial and full load, and with the vacuum pressure, but how critical are these other tests?

Thanks all.

Chris

See my comments..additions:

Cold Test (requires a cold car):

1. Hook up gauge between WUR and Fuel distributor.
2. Disconnect electrical plug to WUR [not really necessary. From cold, you can watch the pressure climb w/ or w/o the engine running]
3. Jumper fuel pump so it runs [see #2]
4. Observe readings on pressure gauge and compare against chart for proper values.


Warm Test:
1. Leave gauge in place as it was for cold test
2. Connect electrical plug to WUR
3. Jumper fuel pum so it runs [not necessary..see #4]
4. Turn on ignition (so there's power to the WUR) [and engine, as the WUR warm up is element and engine heat dependent]
5. Watch pressure rise once power is applied to the WUR
6. Observe final warm value

System Test:
1. Leave gauge in place as connected above.
2. Close valve on outbound/WUR side of gauge setup.
3. Jumper fuel pump so it runs
4. Observe system pressure

Approximate values for '76 WUR:

Cold values:
50 deg 18-23psi
70 deg 25-32 psi
90 deg 34-39 psi

Warm pressure = 40-45psi

System pressure = 65 - 75psi

[Don't forget the residual pressure: leave gauge in line with the dist-wur and shut the engine off...watch it drop, then com e back 10-20 minutes later]

One follow up question. Does drawing vacuum through the WUR increase the pressure -- thereby leaning out the mixture, or vic-versa?

Just a quick tip on what I did different. Instead of jumping the fuel relay, I disconnected the electrical connector from the air sensor behind the fuel distributor and the fuel pump runs with the ignition is turned on. I backdated my heat, so you might not be able to reach it as easy with the stock heat setup.

Scott -- thanks for the tip.

Anybody have info on the vacuum assisted WURs? I've heard of John Walker disconnecting the vacuum line on a Turbo car, to keep the mixture consistent. Why is this?

I was going to check last night, but couldn’t so I’ll try and go from memory. It has been years since I had my 2.7 running in running state. But! I recall that the vacuum port was on the underside of the WUR’s rubber diaphragm. So vacuum will decrease control pressure, so it will richen.

I don’t have the vacuum connected on my 78 engine, but I think the 2.7 WUR is the reverse of the 78-79 WUR in the way vacuum affects it. But like I said, I haven’t messed with the WUR on a 2.7.

Crap you dummy ( :) ), why not just put a hose on that thing and suck on the other end. You’ll create enough vacuum to affect it, and then just watch the gauge.

I'll try to alter the vacuum when testing. Tell me though, when do you typically see high vacuum? You get high vacuum at idle, and when you lift off the throttle right? Most other conditions, especially WOT, you have very little vacuum -- right?

i do it differently:

hook up gauge btwn WUR and FD. valve on WUR side of gauge.
disconnect wire @ WUR. jump FP (term 87a and 30). valve open note cold control pressure.

shut valve, and note system press.

hook up wire at WUR, remove jumper at FP term, and START the car. oh, valve on gauge needs to be open. let the car idle and warm up. you will see the pressure move up. after about 5 min, the pressure stabilizes and note your warm control pressure.

then shut off the car, and your pressure will immediatly drop. after about 20 to 30 mins, it should stop. this is your at rest pressure.

(from memory, so PM me and i can fax you directions from my home. but i think i am right)
make sure all hoses and various accoutrements are out of the way of moving parts.