73.5 911T CIS Pressure Test

muddy · 07-07-2003, 10:30 AM

73.5 911T with cold start and warm start problems (but once started, it runs great!).

I'm getting ready to do a CIS pressure test. I have my gages (from JC Whitney) and I've read through plenty of other threads on the subject as well as my Bosch FI Mgt book.

1st problem is that I'm not sure how to bridge/jump the fuel pump relay circuit. I'm not the best at reading the wiring diagrams, and I'm not even sure if I have a dedicated fuel pump relay?!? I've read various places to bridge 30 & 87 on the relay, but where the heck is it? Looking at the wiring diagram (Part 2) for the 73 with CIS (Page 227 in the Haynes manual), it appears that there is no relay. Does this mean I perform this bridge at Fuse Box I?

Secondly, I've noticed air in the fuel lines at the plastic see-through Tee in the engine compartment. I'm assuming that this is not a good thing and is most likely contributing to some of my problems.

A little more background that may help:
Cold start problem just recently surfaced, after I removed/checked/reinstalled the microswitch. PO (actually I think it was the PO's mechanic) left the connections to the microswitch barely hangin' on (most likely not connected). Looking at the wiring diagram, if this was not connected, then it would bypass the cold start valve. Well, now that they are back in the mix, it takes 3-5 cranks before it starts, then the RPMs slowly (10 - 15 sec or so) raise from 200 to around 3000 (with throttle up). It seems to kind of stick there until I tap on the accel pedal once, after which it drops back down to about 1000.

Also the left front screw on the air box (under the microswitch) was loose. Must have had air leaks as well.

It's possible that the PO put a bandaid on the CIS system by disconnecting the cold start system, then adjusted other components to compensate. My plan is to put it back it it's original condition if possible.

Any guidance is appreciated.
Chris

Jim Sims · 07-07-2003, 11:34 AM

There is not a fuel pump relay in the OEM 1973.5 CIS system; the pump should run with the ignition key in the run or on position. Nor is there an air flow switch on the air metering plate arm. These safety systems did no appear until later models. The cold start circuit only works while the starter is turning and if the microswitch on the throttle body is closed (and connected into the circuit) when the the throttle lever (small lever on the left between the seats) is pulled up fully. Check to see that the microswitch is closing when the throttle lever is pulled up. If not, there may be a problem with the small plastic arm (in the tunnel) through which the throttle lever moves the throttle linkage. The sticking throttle sounds like the the hand throttle or worn bushings or loose or broken springs in the throttle linkage. The warm up except for the low RPM's at the beginning seems almost nominal if the the hand throttle is holding the throttle body open (as it should). Jim

muddy · 07-07-2003, 01:00 PM

Jim-Thanks for your response.
Microswitch closes properly when the throttle lever is pulled up. Throttle linkage springs do seem a little loose. I'll replace those.

Without a fuel pump relay, can I just have a second person turn on/off the ignition key while I perform the pressure test? I'd rather run a bridge with a switch in it so I can control it from the engine compartment, but I'm not sure where to wire the bridge to. From the wiring diagram I discussed earlier, should I run a bridge (long enough to reach the engine compartment, with a pushbutton switch and inline 15amp fuse) from Fuse Box I #1 to #7?
Chris

Sunroof · 07-07-2003, 01:03 PM

If the hand throttle "claw" is not functioning it is not hard to replace; HOWEVER, it needs to be replaced!

The plastic piece is indeed a claw like fitting that is pushed on over the throttle cable under the hand brake unit. The best thing to do is at least the drivers seat for easy access. With both seats out, it was much easier to access everything. I believe two bolts hold down the brake handle plate. Once those are removed just lift the handbrake and throttle unit carefully. It won't go far because their is not much play in both these cables, but just enough so you can move the unit over abit. This will expose both the brake and throttle cable. The throttle cable is the closest to the drivers seat. If you look under the cable into the well you may find old pieces of the claw that broke apart over the years from getting too brittle. It took a needle nose pliars to retrieve these.
Remove any remaining pieces from the cable. On the cable as well is a barrel shaped, wire stop held on by a set screw.

When you get the claw (I believe its a dealer item only) you will see from its shape how it fits over the cable and works with the wire stop. You can adjust the throttle positioning by moving it back and forth and adjusting the wire stop with the set screw. Are you with me? The little piece is literally pushed and pulled by the throttle lever against the wire stop. Its basically just a connector to control the cable movement. Be patient, use a lot of light working in that tight space and have someone help by holding the brake unit up or slightly over to allow access to this replacement piece. It easier then you think.

Once you get this on, you can make adjustments to the mixture setting and warm up regulator. As mentioned earlier, the first CIS was a straight forward system. Not much to really adjust, but you would be surprised what the right mixture setting does as well as point gap and clean fuel.

Several years ago, I appealed on this board for help in installing this piece because warm up was a bear without it. I recall the gentlemen signing off with these words..................."life is wonderful with a throttle lever"...............believe me nothing truer was ever said about the 73.5.

Good luck...........

Bob
73.5T

73.5blackT · 07-07-2003, 01:10 PM

I just replace the plastic piece on my hand throttleon my 73.5 last week. I did remove my seats to make it easier to get to the throttle linkage and would suggest at you do also - just a lot easier. If you need any assistance post and I'll respond

muddy · 07-07-2003, 01:23 PM

Appreciate your responses concerning the throttle & associated linkages. I'll save those for later. Throttle claw & microswitch are working OK, just slightly sticky.
I need to start with a pressure test to truly diagnose what's happening during cold and warm starts...
Chris

muddy · 07-07-2003, 02:00 PM

Can anyone help me understand these wiring diagrams?
Should I run a bridge (long enough to reach the engine compartment, with a pushbutton switch and inline 15amp fuse) from Fuse Box I #1 to #7?
Chris

Jim Sims · 07-07-2003, 02:25 PM

If in OEM condiiton the fuel pump should be hose clamped to bracket under the car on the driver's side just forward of the rear axle. Follow the wiring back from the pump and up to the shelf on the driver's side of the engine compartment. Near the electrical chassis these pump wires should lead into a two pin connector. Take this connector apart and and jumper across it; one fixed jumper and one with your hand switch closing the other side of the circuit. Jim

Jim Sims · 04:49 AM

If you want to jumper up front; you should get power to the three wire side(side with three wires connected to it) of fuse number 7. Also check to see that the cold start valve connector is well seated. Jim

muddy · 07-07-2003, 05:03 PM

Great tips, Jim. Hopefully I'll be able to investigate this tonight. Chris

muddy · 07-08-2003, 06:54 AM

Found the 2 pin connecter from the fuel pump in the engine compartment in OEM condition with proper colored wiring (just as you said, Jim). Ran my jumper/switch and it looks like I'm ready for the pressure test.

Instead of running another jumper up front to get power to the fuse #7, I'll put the key in the on position & use the pushbutton to turn on the fuel pump. See any reason why I should not do that? i.e. the on position will power something else that shouldn't be on during the test?
Thanks,
Chris
73.5 911T

Jim Sims · 07-08-2003, 02:44 PM

The only thing I can think of that might matter is the WUR; depends on the test you are doing. Engine should be cold for the cold test pressures; "cold" like it sat all day in the shade or overnight. Everything will come on, that's left on: (radio, lights, etc.) so you might want to make sure things are turned off so you don't run the batteries down. Have a fire extinguisher handy and don't do this test in a garage with an open flame (hot water heater pilot light, etc.) in case you spill gasoline while making the hookup. Wear safety goggles in case your hookup leaks and sprays gasoline. Jim

muddy · 07-11-2003, 06:13 AM

Ran the fuel delivery test last night. Tested downstream of the plastic
tee. Results were 1700 cc/min. Anyone know what the fuel pump specs should be for the 73.5T? Can't seem to find it...

One interesting point is that I ran the test twice. First with the elec connection to the WUR disconnected, and second with it connected. Same results for both tests. I read somewhere that as the elec connection warmed up the WUR, it would decrease the fuel flow/amount. By the way, test was with key on, and a jumper across the fuel pump. After reviewing the elec diagrams (ugh), I think the WUR gets it's juice from the starter solenoid. So why do the books tell you to disconnect the elec connection to the WUR if you do not even engage the starter solenoid during the tests?? Maybe the wiring is different on later models....

I will also be doing the system, control, & residual pressure tests soon...stay tuned.
Chris
73.5T

Jim Sims · 11:51 AM

850cc/30seconds so your fuel pump return rate is right at specification.

http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_1973_CIS_add.jpg

On the 73.5T's the WUR gets it's power (see above diagram) from a relay that is energized via the voltage regulator whenever the car is running. It shouldn't affect the fuel pump return flow.

muddy · 07-11-2003, 01:44 PM

Thanks Jim, you've been a great help.
Appreciate you pointing me to the wiring diagrams. I do have those, but I guess I have a problem reading them.

According to the Bosch FI book, when the bimetal arm in the WUR warms up (either by block temp OR by the elec connection), it decreases fuel return to the tank and increases control pressure. This is what got me thinking about doing 2 fuel delivery tests (WUR connected/disconnected).

I guess I'm also getting ahead of myself. Checking flow rate downstream of the tee when the WUR is warm is similar to the Warm Control Pressure check with my gauges between the fuel distributor and the WUR.

I only had the key on (car not running). But the FI books say just to reconnect the WUR (and give it 1-2 minutes to warm the arm) when doing the warm control pressure check. Car shouldn't be running during that test. Am I missing something?

Chris
73.5T

muddy · 08-20-2003, 06:34 AM

Finally got back to my pressure tests last night....

System pressure was 2.8 bar
Control pressure (cold) was 2.2 bar
It was probably about 75F or so when I ran the tests.

Didn't do warm control pressure yet...figured I'd solve system pressure problem first, then retest.
2.8 bar??? Seems way too low.
Fuel delivery is OK. Any recommendations on what I need to do to get my system pressure up?

Should shimming the system pressure regulator be first on my list?

Thanks,
Chris
73.5T