Fuel pressure and FV anomalies

[RDM]

OK, so I set out to check my fuel pressures for the first time today. Now that I have the right WUR (The right WUR?), I am continuing to pursue a high load miss/buck/light jerk. By high load I mean 2000-4000 RPMs heavy throttle, or uphill.

A (perhaps) second problem: I find if I put the throttle down all the way, there is a drop in power. Simply backing off of the throttle will restore acceleration, but the miss / buck / jerk remains.

Engine speed drops noticeably when oil filler cap is removed, so vacuum leakage is in the acceptable range.

1980 SC Targa, US model, ~58,000 miles, sitting overnight in the garage

11AM, ambient temperature 52 F / 11C, light rain.

WUR 072, cold reading 26.1 ohms, newly rebuilt.

Fuel pressure gauge connected on WUR end of FD-WUR fuel line



With fuel pump relay jumpered and key on
System pressure 71 PSI / 4.9 bar, in spec

Cold control pressure (heating element disconnected) 23 PSI / 1.6 bar, in spec

Residual pressure taken with valve to WUR open and key off (repetitive intermediate measurements omitted)
0 min 28 PSI /1.9 bar
.5 min 25 PSI / 1.7 bar
5 min 24 PSI /1.65 bar
10 min 23 PSI / 1.6 bar
30 min 20 PSI / 1.4 bar in spec



Now here's where things go incomprehensible. Without changing any hose connections or valve orientations, I turned the key back on to run the fuel pump and reconnected the WUR wires.

Warm control pressure taken with valve to WUR open and key on (repetitive intermediate 30-second measurements omitted) There was no delay between connecting the WUR wire and taking the first measurement.
0 min 47 PSI 3.2 bar (?!)
3 min 46 PSI 3.15 bar
6 min 46 PSI 3.15 bar

What just happened? What did I miss? The pressure is immediately much higher than it was before, rather than increasing over time. Did doing the residual pressure first mess this up, or is something else going on?

Frequency Valve

Ground wire to engine mount bolt, green wire to green/white wire in test port. Unlike Bob K, my Sears dwell meter only has two wires. I guess I didn't pony up for the deluxe model back in the eighties.

Startup (cold engine) Gauge read on 8 cylinder (45 degree) scale
0 min 20 degrees / 44%
2.5 min dithering @ ~ 1Hz between 23-25 degrees / 53%, idle oscillating slightly with the dithering.
3 min 25-27 degrees / 58%, no idle oscillation.
3.5 min and after 26-29 degrees / 61%, no idle oscillation



So, according to the experts I've read (Tony, Bob, Jim, tirwin, Bentley) I should see 85% at cold startup and 50% at warm idle. Too rich, if my CIS understanding is correct.

So the next step is to adjust the dreaded 3mm allen head screw, or...?

[psalt]

I should see 85% at cold startup and 50% at warm idle. Too rich, if my CIS understanding is correct.

Dru,

No, if the system is in closed loop, the duty cycle reading is the correction factor. If you are reading 61% in closed loop, the basic mixture is too lean and the system is increasing duty cycle to compensate. Are you saying that the duty cycle reading is dithering at hot idle , but the idle speed becomes constant ? If so, I would be checking the throttle switch. These cars generally run best with the hot closed loop duty cycle set to 30-40 % and the vacuum retard disconnected. This gives a richer open loop AFR under WOT. Have you checked your high speed ignition advance ?

[Bob Kontak]

+1 on psalt description of the duty cycle.

61% duty is lean when warm. psalt set me straight on this several years ago. I was thinking backwards. You are not sniffing exhaust (with the dwell meter) you are "sniffing" the Lambda system's reaction to the exhaust - via O2 output.

Also - check warm pressure rise from stone cold - including electronic warm up of bi-metallic strip.

[RDM]

Originally Posted by psalt

I should see 85% at cold startup and 50% at warm idle. Too rich, if my CIS understanding is correct.

Dru,

No, if the system is in closed loop, the duty cycle reading is the correction factor. If you are reading 61% in closed loop, the basic mixture is too lean and the system is increasing duty cycle to compensate. Are you saying that the duty cycle reading is dithering at hot idle , but the idle speed becomes constant ? If so, I would be checking the throttle switch. These cars generally run best with the hot closed loop duty cycle set to 30-40 % and the vacuum retard disconnected. This gives a richer open loop AFR under WOT. Have you checked your high speed ignition advance ?

Right, right right. The FV dumps more fuel to lower the pressure and richen the mixture.

So how do I get there? Is the solution behind screw number 3 (mm, allen type)?

Originally Posted by Bob Kontak

+1 on psalt description of the duty cycle.

Also - check warm pressure rise from stone cold - including electronic warm up of bi-metallic strip.

Bob, I thought I was, but got results that surprised me. I didn't expect the pressure to go up until I connected the wires to the WUR, but it did. I will repeat this test tomorrow (without the residual pressure test in the middle) to see if I get different results.

The car has been professionally set up to work with the -011 WUR that was on the car when I purchased it, so several rounds of adjustment may need to be made.

[psalt]

Dru,

If your CIS lambda system is showing a too lean, closed loop, duty cycle, I would take C Probst advice and first check for vacuum leaks at the injectors, gaskets and rubber boots. This only takes a few minutes with an unlit propane torch, listen for a drop or increase in idle speed (depending on mixture strength). If the injector sleeves are original and you can wiggle the injectors, there are probably leaks. The exterior sleeve O ring is the weak spot, it bakes much sooner than the interior donuts. If you have no leaks, and are sure that the temperature and throttle switches are working correctly, and the system has gone into closed loop on a warm engine, start by making a 1/8 turn clockwise adjustment to the mixture screw. Remove the tool, rev the engine and verify that the duty cycle reading has dropped. Once you set the mixture to 30-40 duty cycle, disconnect and plug the two vacuum lines to the distributor and reset the idle speed with the large thumb screw to 850 rpm. Set the ignition timing to 5 BTDC, then rev the engine past 3000 rpm and verify you are getting advance up to 25 BTDC. Reconnect the advance hose (front, orange) and leave the retard hose (grey, rear) disconnected and plugged. Go for a test drive.