74 CIS “Yoggi Berra” fork in the road, should I take it?

[jsottile]

Been chasing a few CIS issues, most recent, the non-vacuum WUR is bad, residual press < 90 sec to 0 Bar

Currently running;
FD = 438-100-004
WUR = Non-vacuum XXX-129 (replacement for 438-140-001)
Throttle Position Regulator (TPR) = 438-160-001

The question is;
Should I ditch the two regulator system WUR / TPR and install a later vacuum assisted WUR?
What vacuum assisted WUR model would be appropriate?
Anybody done this upgrade? Maybe there is a thread I overlooked.
Or, just replace the bad WUR with like kind or variant?

Spec numbers for reference on this CIS are:
Warm control 2.85 – 3.0 BAR
½ Throttle 3.4 – 3.8
Full Throttle 2.7 – 3.0
Cold pressure varies by ambient ~1.0 – 2.0

Thanks for your consideration. Rennsport or bust!

J

[boyt911sc]

J,

I’ve done a successful conversion a few years ago for a PP member. PM me your email and will forward Steve’s (‘74 car owner) email address/phone. The conversion is very simple.

Tony

[jsottile]

Thanks Tony. PM sent

[pmax]

Originally Posted by jsottile

Been chasing a few CIS issues, most recent, the non-vacuum WUR is bad, residual press < 90 sec to 0 Bar

What are the running issues which make you suspect a bad 129 WUR ?

Should I ditch the two regulator system WUR / TPR and install a later vacuum assisted WUR?

The "newer" CIS systems are no stranger to running issues either so I wouldn't just for that. These are all old, most of which are NLA, parts at this point so not surprising they might have some.

[jsottile]

Pmax, the running issue has been sporadic for a while and a bit illusive. The short answer is, on long drives, at steady state speed, the engine would just start running rich. Noticeable change in engine note, very obvious. On pressure testing, the numbers all seemed to check out, until recently. The Throttle Pressure Regulator (TPR) consistently showed below spec pressures at ½ throttle input. Like 0.4 to 0.8 BARS low, which would make things rich. The TPR is 45 years old and I can’t complain. The concept of TPR is sound, simple and pretty much bullet proof as well as easily adjustable. Be interesting to determine failure. Fatigued diaphragm or fatigued follower spring??

Residual pressure is not an issue with 74, as the fuel pump activates with “key on” positon. However, while checking the CIS pressures, I did time a residual at only 90seconds to 0 BAR. Awful. I’m not sure why the WUR would have spec numbers from cold to warm and **** the bed on residual, but numbers don’t lie.

So here we are. It seems I need to replace both regulators. I’m not opposed to the two regulator set-up, just curious if there are any advantages, other than the obvious, by updating to the later vacuum WUR? More HP, lighter weight, better parking at RRVI? Sounds like Pmax votes no real advantage.

[pmax]

Originally Posted by jsottile

Pmax, the running issue has been sporadic for a while and a bit illusive. The short answer is, on long drives, at steady state speed, the engine would just start running rich. Noticeable change in engine note, very obvious. On pressure testing, the numbers all seemed to check out, until recently. The Throttle Pressure Regulator (TPR) consistently showed below spec pressures at ½ throttle input. Like 0.4 to 0.8 BARS low, which would make things rich. The TPR is 45 years old and I can’t complain. The concept of TPR is sound, simple and pretty much bullet proof as well as easily adjustable. Be interesting to determine failure. Fatigued diaphragm or fatigued follower spring??

The TPR looks like it's a more direct device in that it doesn't rely on vacuum. I like that. BTW A vacuum WUR also has a diaphragm and a spring which can also fatigue if that's a concern. Personally, I'll take the non vacuum operated device anytime.

Originally Posted by jsottile

Residual pressure is not an issue with 74, as the fuel pump activates with “key on” positon. However, while checking the CIS pressures, I did time a residual at only 90seconds to 0 BAR. Awful. I’m not sure why the WUR would have spec numbers from cold to warm and **** the bed on residual, but numbers don’t lie.

The reason I ask about the WUR is that the inability to hold RFP doesn't mean the WUR is bad. It could be your accumulator, check valve etc.

I'm not sure why the CIS experts here, who have far more experience than I have, hasn't pointed that out.

So here we are. It seems I need to replace both regulators. I’m not opposed to the two regulator set-up, just curious if there are any advantages, other than the obvious, by updating to the later vacuum WUR? More HP, lighter weight, better parking at RRVI? Sounds like Pmax votes no real advantage.

Definitely not an expert here..... but I don't think you will get more HP with the same operating fuel pressures. Also, I speculate the more direct TPR will respond faster than vacuum operated.

I would make the decision on serviceability of the parts. There are rebuilders who post here regularly for the WUR but not sure about the TPR.

[jsottile]

Pmax, appreciate the thoughtful reply. The WUR was isolated during testing. Without the WUR in circuit, the residual pressure was at 1.5 BAR after 75 min. which is very good. This result would rule out, accumulator check valve, system pressure regulator, TPR (for leak down) and cold start valve.

The question for the experts would be, “How can the WUR work perfectly from cold thru warm and not hold residual?” Just academic, but interesting.

TPR’s are not rebuildable if it is the diaphragm. Without bench test equipment, not worth my effort to replace cam springs and see if it fixes low ½ throttle pressures.

[pmax]

Good question.

Perhaps, during operation, the fuel flow is sufficient for the WUR to hold pressure but when turned off, the leak is evident in the residual pressure loss. Just guessing here.

Another option to consider besides "upgrading" to a vacuum based CIS system is going EFI.
CIS to EFI kit

[boyt911sc]

Originally Posted by jsottile

Pmax, appreciate the thoughtful reply. The WUR was isolated during testing. Without the WUR in circuit, the residual pressure was at 1.5 BAR after 75 min. which is very good. This result would rule out, accumulator check valve, system pressure regulator, TPR (for leak down) and cold start valve.

The question for the experts would be, “How can the WUR work perfectly from cold thru warm and not hold residual?” Just academic, but interesting.

TPR’s are not rebuildable if it is the diaphragm. Without bench test equipment, not worth my effort to replace cam springs and see if it fixes low ½ throttle pressures.

J,

Test and confirm that the WUR is working correctly. Unless you confirm it’s operation, you are hoping it is OK. Unfortunately, you can not rely on luck all the time for diagnosing your CIS problem. Since your mechanic was able to isolate the WUR for your residual pressure test, perform a separate test for the WUR.

If you want to improve your CIS performance, get rid of the TPR and go for the vacuum assisted WUR. Unless you are in concourse restoration, using the later CIS components would be to your advantage.

Tony