Control Pressure Problem

[DMC5738KC]

CIS experts - Odd problem with my CPR (or WUR) I have control pressure at 70psi from cold up to warm conditions. At one point I had it set at about 55psi and recently it went up. I tried to adjust it by pulling up on the adjustment screw with the screw and nut/washers method and there was no change. I drilled the brass cover on the bottom and was able to adjust it down to 60 psi by backing that allen screw out as far as it would go before hitting the brass cover. There is definitely vacuum going to the CPR as there is an obvious leak from drilling that hole. The CPR is fairly new (within the last 6 months) so what do I need to check next? Take it easy on me - I've done some searches and haven't read anything exactly like this problem with adjusting the pressure.
Thanks in advance = novice level CIS owner

[Bitsyncmaster]

If your inlet screen on the CPR gets plugged, your will get that 70 PSI all the time. I don't know anything about adjusting the CPR so can't comment on what you did.

[DMC5738KC]

I'll definitely have to check that next. Thanks for the suggestion.

Your RPM relay is working great - best money I've spent in awhile


If your inlet screen on the CPR gets plugged, your will get that 70 PSI all the time. I don't know anything about adjusting the CPR so can't comment on what you did.

[PJ Grady Inc.]

If your inlet screen on the CPR gets plugged, your will get that 70 PSI all the time. I don't know anything about adjusting the CPR so can't comment on what you did.

Generally if the screen is plugged up the problem is deeper and the CPR will need rebuilding. That PSI reading is typical in a failed CPR. Calling your favorite vendor for an exchange unit would be the easiest/fastest fix.
Rob

[DMC5738KC]

I'm assuming that you are saying that the screen filter would be clogged by something internal that melted down, or is it possible that the debris is from the inlet side? I'll open the fuel fittings tonight and see if I can tell if the filter is clogged or not. Thanks


Generally if the screen is plugged up the problem is deeper and the CPR will need rebuilding. That PSI reading is typical in a failed CPR. Calling your favorite vendor for an exchange unit would be the easiest/fastest fix.
Rob

[Bitsyncmaster]

Generally if the screen is plugged up the problem is deeper and the CPR will need rebuilding. That PSI reading is typical in a failed CPR. Calling your favorite vendor for an exchange unit would be the easiest/fastest fix.
Rob

When I made my fuel pressure tester, my shutoff valve for the tester was not rated for high pressure fuel. Hence my CPR screen plugged with black partials from the failed shutoff valve. Live and learn:wrenchin:

[DMC5738KC]

Update. There may have been some particles in the brass filter when I took the lines off and dumped out the gas. Put it all back together and drove the adjuster in and got the pressure right at 50psi when warm. It's running much better. Thanks for the advice.

Does anyone know what the adjustment Allen screw on the bottom of the CPR actually does?







When I made my fuel pressure tester, my shutoff valve for the tester was not rated for high pressure fuel. Hence my CPR screen plugged with black partials from the failed shutoff valve. Live and learn:wrenchin:

[David T]

Update. There may have been some particles in the brass filter when I took the lines off and dumped out the gas. Put it all back together and drove the adjuster in and got the pressure right at 50psi when warm. It's running much better. Thanks for the advice.

Does anyone know what the adjustment Allen screw on the bottom of the CPR actually does?

The adjustment is to move the curve up and down meaning how fast it warms up and gets the control pressure up. Difficult to calibrate without a test bench set-up so you should not touch it. If cleaning the screen fixed you up that's fine but you have to worry how that junk got there. The filter should have caught it. You should inspect the fuel tank for dirt.

[DMC5738KC]

Expensive lesson learned. After talking to John Hervey and Rob Grady I learned that drilling the brass plug on the bottom of the WUR is the worst thing you could do as it voids any warranty that you might have had on a rebuilt unit and may make the it un-repairable. Best advice - DON'T DRILL OR ATTEMPT TO REPAIR A WUR (control pressure regulator). I hope anyone reading this doesn't make the same mistake I did by reading other forums and Internet blogs. This is a precision calibrated part and should not be tinkered with. I can usually fix most things, but this time curiosity killed the cat!

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[FABombjoy]

I wouldn't call it a precision part, the book spec for warm has an acceptable variance of .4 bar.

OTOH if you don't understand how it works then I agree you shouldn't mess with it. Many guides online only cover adjusting the basic version and not the super fancy one we have. For some owners the hardest part might be access to cold enough weather to ensure the lowest pressure settings are accurate... I dialed mine in on a 20F day, one of the few advantages of a Michigan winter :D

Even Volvo grew weary of the complex and expensive vacuum enrichment WUR and changed to electronic enrichment in '82. FWIW that system (or one like it) is fully compatible with our cars.

[DMC5738KC]

I'd love to get out of my self inflicted predicament for low dough, but it's not sounding like it will be less than $200 to $300. My problem with it now is that the the only way I can get any adjustment out of it now is through the lower (brass plug hole) adjustment which appears to put direct pressure on the diaphragm. I can get a good +/- 10psi out of that allen screw when warm, but there is no cold (low) pressure anymore - it just holds steady all the time at whatever I set it at (50psi). I wish there was more documentation on how this thing works

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[FABombjoy]

I tried to adjust it by pulling up on the adjustment screw with the screw and nut/washers method and there was no change.
This is why the cold pressure is out of adjustment. You'll need to reset the heater & bimetallic arm back to stock position or a lower position and then adjust the plug upwards until CP matches the book spec. There was also a trick where you drill a hole and install a roll pin so the assembly doesn't rotate when you're adjusting it up and down. It's been quite a while since I've had mine open and can't recall how likely it is to rotate using the screw & nut method to adjust it upward. It may take several warmup cycles to get everything spot on. With the heater disconnected you can delay the onset of warming to give you a longer window of cold pressure adjustment.

[DMC5738KC]

I did get the plug adjusted back up to where it is level with the top of the casting, but saw no change in the pressure. I haven't dug into the inside of the unit to figure out how to reset the bimettalic arm - I sure you are right, but how would I know what the stock position is? that is what needs to happen so that part works again.

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[Bitsyncmaster]

You really need to know what you are doing to make any adjustments or even take the thing apart to clean it. I tried to clean mine when I first got the my car and it would not work at all after that. Lucky I did not drill anything and it was usable as a core for a rebuilt unit.

There is an electronic unit but the cost is > $500 and don't think it buys you much since a working stock unit only affects warmup running.

[FABombjoy]

There is an electronic unit but the cost is > $500 and don't think it buys you much since a working stock unit only affects warmup running.
The UTCIS and variants don't emulate the vacuum enrichment by default either. I was working with them to get it added but then they stopped responding to emails for a month, leading me to implement the Volvo electronic enrichment system instead.

I got a deal on my UTCIS-PT, but if I were in the market for an electronic WUR/CPR I'd probably use the FrankenCIS (http://www.frankencis.com) instead. For the DeLorean neither of these are truly a drop in replacement.

I've had my stock WUR apart before but I didn't touch the disc assembly. Other than accidentally rupturing the diaphragm I think removing that disc would be where you're most likely to cause problems, and unless it's leaking or shows other signs of being cracked I wouldn't disassemble it.

This image shows why the control pressure is now constant:
http://s25.photobucket.com/user/jrcook320/media/Tech/stdWUR.jpg.html

With the heater & arm assembly raised it's no longer contacting the spring & pin assembly (for lack of better term). It will have to be lowered and then raised incrementally until the pressures are back in spec. If your warm pressure is good you shouldn't have to make any adjustments to the bottom screw.