Diagnosing WUR correctly?

[dreiermann]

I think that my Warm-Up Regulator may be bad, but maybe I am missing something.

The symptom is that on cold start, the engine would start and run for two to four seconds, then die. Same thing for several key-turns in a row. I left the car sit for several days, tried it again, it ran fine. A few days later, back to the four-seconds-and-then die.

So I tested the fuel pressures, I have a system pressure of 68 psi (good) and also a cold control pressure of 68 psi (supposed to be 10). In case it was a clogged return line, I put a spare piece of hose on the return side of the WUR and ran it to a gas can. The test result was the same, 68 psi. So it sure seems like the regulator.

If it is the regulator, since new ones are very expensive, I was planning to open it up and clean it to see if it can be brought back. I know that the service manual says to not do that, but if it is bad now I have nothing to lose. If anyone has tips on what to look for when the unit is opened up, please let me know. I have seen several DIY procedures on the internet (one was on a Volvo site, didn't find any here) and will be using those as a guide.

Thanks in advance!

[epmedia]

Supposedly there's a fiber filter under the metal mesh screen on the big inlet side of the WUR. You can try back-flushing it, or directly spraying it several times with spray-can carburetor cleaner. (don't use brake parts cleaner)

[Somjuan]

They're in the FAQ thread near the top of the forum thread list. Click here for what to expect inside the WUR/control pressure regulator

JR Cook has a thread somewhere about making it adjustable, it's a simple procedure that got mine running

[GDAus]

Hi ... As for write ups ... Steve Shauer from here has a very good one on his site

http://www.jtresto.com/e21info.htm

this also has the Electrical Trouble Shooting manuals (E.T.M.s, aka wiring diagrams) for the North American models as well.

As to the high control pressure, as Robert (epmedia) has indicated, it's almost certain the the filter screen in the input to the WUR is blocked. I had a similar problem ... hard starts cold and warm .... and traced it to a control pressure only about 5 psi less than the system pressure hot or cold. Mine also had some sort of fibrous material above the metal filter screen ... but I had all ready found some similar material in my fuel tank, so I put it down to random crud.

The problem with mine was a hard shiny glaze blocking most of the mesh filter screen.It wasn't obvious until I looked at it under a 30X hand magnifier.

It didn't want to dissolve with any of the solvents I was prepared to use ..there is an O ring inside ... so in the end I resorted to mechanical means. I used a fine darning needle held in medical forceps as a needle pusher ... and broke up the glaze in each of the holes in the filter screen with gentle pressure.
Yes very tedious ... but it worked, had to use the magnifier to see what I was doing of course. Managed to tap the debris out of the hole fairly easily and what was left flushed through the WUR without any problems ever since.

Hopefully you wont have to reset anything to get the control pressures back to what they should be ...but it is possible the adjust the WUR without having to modify it. Again it is a little tedious ... but you only have to do it once unless you are planning to do a lot of mods to the motor.

Cheers

[epmedia]

^ Oh yes - those darn dust bunnies. I found a huge dust bunny on the inlet side of my external fuel pump. It was an after-market fuel pump with a tiny metal mesh filter on the pump inlet. I later disposed of that tiny metal mesh filter.

[320iAman]

On mine unplugged,cold control pressure is 20 psi-WUR unplugged, WUR plugged in,warm control pressure is 47 psi, with the first high reading your startup is too lean, cars startup cold rich.

Randy

[GDAus]

The Cold Control pressure varies depending on the ambient temperature of the engine when it is being started from cold. This allows the WUR to vary the amount of enrichment for starting under varying conditions. So quoting a particular pressure is only relevant for the temperature at that time.

You have to use the relevant pressure vs temperature chart to find the checking/setting pressure tolerance range for whatever temperature it is on the day.

Cheers

[320iAman]

Ambient temperature is air temperature surrounding the WUR. In terms of thermodynamics its the surroundings temperature not the system temperature.


Randy

[Tom D]

"ambient" temperature is a little missed used here and GDAus eluded to that when he said the "engine" temperature. the operation of the WUR is dependent on two different outside forces, the "ambient" temperature of the bi-metal spring within the WUR and the amount of time that electricity is supplied to it.

if you study the chart that GDAus posted above you can see that as the ambient temperatures rise so does the fuel pressure and a higher pressure creates a leaner mixture. however this ambient temperature is not the outside air temperature, but rather the temperature of the inside of the WUR.

for example: the out of doors air temp is 10ºC when you first start your car in the morning. since the WUR, the insides of the WUR and the engine are all probably 10ºC then the cold pressure will less then 1 bar. you then drive the car to the store bringing it to operating temperature. you go inside for 2 hours and then come out and start the car again. the "ambient" outside air temperature is still 10ºC, but because the temperature of the WUR and more importantly the bi-metal spring inside it has retained residual heat from the engine's block and the cold pressure will be greater then 1 bar.

the 2nd influence is electricity. as soon as you turn the key a current is passed to the bimetal spring and it is this spring that controls the valve that controls how much fuel pressure is bleed off. in this case if you were to go out to the car, the cold engine temperature is 10ºC, but instead of starting the car you turn the key to the 'on' position and listen to the whether report on the radio and then start the car. the cold pressure would be greater then 1 bar because the bimetal spring had a chance to heat up, closing the WUR fuel pressure relief valve.

this is why it is very important that you test the WUR in a very systematic manner. once you start the engine you can not get the same results until you let the engine completely cool down, nor can you get the same results if you test it again after switching the ignition on and back off even if you didn't start the engine.

[epmedia]

*regulator valve

Just messing around

Glad to see you posting, Tom!

[jrcook320]

Looks like the good ole boys have you on the right track. It's not hard to clean, worst case you may need to separate the small internal diaphragm valve assembly. I've done this many times and often find varnish buildup. Doing this will allow you to remove the o-ring and soak the inlet screen and valve body in carb cleaner without risk of damage to the o ring. You may need to use a pic to scrape - think like a dentist removing plaque.

With cold control pressure equal to system pressure you have complete blockage somewhere. While wur is most likely, you may want to also check for a clogged feed line between fuel distributor and wur.

Once things are clean I would remeasure both cold and warm control pressure. You can adjust warm control pressure back in to spec by moving the valve body out of the aluminum wur housing, reducing spring pressure on the diaphragm. If it needs adjusted this should be done first. Final adjustment is made by tapping the body back in to raise pressure to proper spec while measuring. It's imprecise and requires disassembly of you go too far which is why I drilled and tapped holes to pull the valve body back out.

Once warm pressure is set you can dial cold pressure back in (as Tom pointed out- only after complete cool down) by tapping the bimetallic spring post in to reduce primary spring pressure which will reduce control pressure.

Of course, cold control pressure must be set relative to measured ambient temp referencing the correct spec. Early and late e21's are different. The assumption is that the wur has cooled completely to match ambient temp.

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[dreiermann]

Thanks for all the input, everyone! I hope to get the WUR removed and opened up tonight. Because of the intermittent nature of the starting issue, and the fact that the cold pressure is equal to the system pressure, I am kind of expecting to find a loose chunk of varnish in there somewhere. Before I checked the cold pressure, I did remove the power to the WUR, and the garage was at 10 degrees C, so the high control pressure was not caused by heat inside the WUR. When I get the cold pressure to the point where I can reliably start the car, I will check the warm pressure.

[jrcook320]

Just be aware that changing warm control pressure will also change cold control pressure.

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[dreiermann]

OK, I opened up the WUR and it was VERY clean inside - it was still 1977 in there. The steel diaphragm looked new. I could not figure out how to remove the pressed-in 1" diameter piece that has the two fuel-line connections, but the screen at the inlet appeared to be clean and clear. With the steel diaphragm and O-ring out, I sprayed some carb-cleaner in both the inlet and outlet, just for good measure. Once re-assembled, I blew air into the inlet (just by mouth, not air-compressor) and some air did come out of the outlet, but with noticeable resistance. I checked the two lines to the fuel distributor, those were both clear. Not sure what could be keeping the cold control pressure so high. I will re-install it, re-test the pressures, and see what happens.

[epmedia]

OK, I opened up the WUR and it was VERY clean inside - it was still 1977 in there. The steel diaphragm looked new. I could not figure out how to remove the pressed-in 1" diameter piece that has the two fuel-line connections, but the screen at the inlet appeared to be clean and clear. With the steel diaphragm and O-ring out, I sprayed some carb-cleaner in both the inlet and outlet, just for good measure. Once re-assembled, I blew air into the inlet (just by mouth, not air-compressor) and some air did come out of the outlet, but with noticeable resistance. I checked the two lines to the fuel distributor, those were both clear. Not sure what could be keeping the cold control pressure so high. I will re-install it, re-test the pressures, and see what happens.

Before going further, I must ask if the symptoms have been the same since your ownership of the car.

Based on what Josh says (jrcook320), regarding 'moving' the valve body, maybe someone 'blindly' banged on the WUR valve body.

Or the inlet filter is still dirty. Remember there's probably a 'felt' filter under the metal mesh screen on the inlet. I've seen pictures of these felt filters in another thread here, but I cannot find it. it was a 2 or 3 stage felt filter.

fyi: just because there is fuel flowing through return side of the WUR, does not mean that proper amount of fuel is being allowed to flow.

Maybe Josh can elaborate better than I on this, he is the master on this subject.

Glad to see you posting, Josh.

If I can find my '78 spare WUR pieces, I may try to dissect it, regarding those felt filters under the metal screen.

[dreiermann]

Before going further, I must ask if the symptoms have been the same since your ownership of the car.

No, the troubles I had when I first got the car were due to vacuum line routing and a throttle stop that would not allow the throttle to close enough to idle. Since then, the car has been great and was my daily driver all summer. Then one morning in the fall, the non-cold-start issue (engine started, ran for about 3 seconds, then died - consistently over multiple tries to start) cropped up. The car sat for a few days, and when I tried it again it fired right up. The next time I tried it, it would not start. So I have not driven it since then, and just now gotten around to checking the fuel pressures. The only other known issue I have with the car is that the idle has been slightly rough, and when I try to set the ignition timing the OT mark and the Z-ball are very jumpy.
So back to the non-cold-start issue - because the engine would run for a few seconds, I interpreted that is the cold start injector getting fuel, but not the main injectors. I guessed that cold control pressure would be high, and it turned out to be very high (68 psi, same as the system pressure). That is why I was looking at the WUR as a source of the problem - I figured on finding a complete blockage since both the system pressure and the cold control pressure were the same.
The inlet filter screen - it would be good to remove that and check/clean that part of the WUR, but I can't figure out how to get it out of there without breaking the plastic housing.

[cgifool]

regarding the jumpy OT mark and Z-ball, you might possibly try removing the rotor and putting a drop of fine-grade oil on the pad under it to lube the advance mechanism, in case its getting a little stickety.

[Tom D]

...the screen at the inlet appeared to be clean and clear....

the varnish from old gas is not something you can see by eye, but its there. try soaking it in carb cleaner for a few days.

[dreiermann]

the varnish from old gas is not something you can see by eye, but its there. try soaking it in carb cleaner for a few days.

That is a good idea - there are a lot of other 'projects' on the car that I can take care of while it is soaking. I will dis-assemble it again to get the O-ring out of there prior to soaking - is there anything else remaining in that part of the regulator that the carb cleaner might damage?

[jrcook320]

That is a good idea - there are a lot of other 'projects' on the car that I can take care of while it is soaking. I will dis-assemble it again to get the O-ring out of there prior to soaking - is there anything else remaining in that part of the regulator that the carb cleaner might damage?

No you should be fine to soak it if the o ring is out. Not sure what plastic piece you're referring to, the only plastic components in the wur are the electrical plug and the vent cap.

You may have blockage downstream from the wur, make sure the return line is clear.

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[dreiermann]

Not sure what plastic piece you're referring to

After the WUR is opened up and the spring, bimetallic lever, etc., the four screws, backing disk, metal diaphragm, and o-ring are removed, I am looking at (what appears to be) a gray plastic piece with a groove in it for the o-ring. I don't know how to remove that without damaging it. If I could get that out, I could probably remove the inlet screen which would make it easier to clean.
Blockage downstream of the WUR - I did test the cold control pressure with the return line disconnected, and it did not affect the result.

[epmedia]

I was just thinking...

If the 'primary' fuel filter (next to the fuel pump) is very dirty (happens sometimes with 'winter' fuel), the filter element may have a tear in it, making a mess of the fuel system. I suggest getting a new primary fuel filter and then later continue with your t-shooting efforts. Also drain the fuel filter 'inlet' to a clean container to get an idea of the fuel tank(s) condition... While you're down there; if the 3 pieces of fuel hose on the suction side of the primary fuel pump are the original cloth braided hoses; they need to be replaced, because sucking air bubbles and possibly seeping fuel.

In the mean time (just a suggestion):
*Wear eye protection.
1) reassemble the WUR (don't install yet).
2) rig something on the return side of the WUR to accept the tube of a 'spray can' carb cleaner.
3) back-flush the inlet filter several times, allowing a few minutes between each time.
*monitor results between each back-flush.

Edit: this may not work, unless the valve is held open somehow. I forget what the inside of the WUR even looks like. May be able to rig something to back-flush with that 4 screw cover/diaphragm removed.

[dreiermann]

The primary fuel filter is one that I installed this spring, I did cut open the old one as I did not know how long it had been there - it didn't look too bad.

Dropping the tanks for inspection/cleaning is on my to-do list for this winter, mainly because I want to replace the vent lines and that will be the ideal time to check out the tanks. Also on my list is re-plumbing the fuel pump and filter, and removing the secondary fuel pump (I posted some questions about that over the summer). But before I do that, I would like to get the car running without any further changes so that I can verify that the pressures are still within spec when the second fuel pump is removed.

I did open the WUR and plugged up the inlet side, and have it upside-down so that I can backflow carb-cleaner through it, and let it soak. When I take out the plug (a bolt), I should be able to see anything that leave the screen/filter.

Thanks so much for all the info, everyone!

[dreiermann]

Update on 'progress' - I soaked the inlet side of the WUR in carb-cleaner for over 40 hours with a slow drip backflowing through the inlet screen, then rinsed it with more carb-cleaner and blew it out (from the inside) with compressed air. It must be very clean, the air flowed through it quite easily. I reassembled it, re-installed it, and then checked the pressures. The cold control pressure was still at 62 psi. Frustrated, I decided to re-connect the power to the WUR and to the fifth injector and see if it would start. It did start!

Now I am doubting if I am reading the pressure correctly. I hooked everything up as shown in "How to Tune and Modify Bosch Fuel Injection" and followed those procedures, and also checked them against what appears to be the factory sequence reprinted in the Walloth and Nesch catalog. I can't figure out what I might be doing wrong but I also can't figure out why I am able to start the car with such a high control pressure. Beyond that, I am still wondering what the original issue was that caused the intermittent non-starting. When the issue first happened, I did check the air meter flap, and it was moving freely. I can't think of anything else that would cause the engine to run for several seconds and then die.

[mjweimer]

Is the cold start injector working properly? Does not explain the strange control pressure issues or the intermittent nature of the issue but it is easy to check.

FYI- my car started and died when cold and I traced it to a inop cold start injector. Started fine when the car was warm which led me to pull it, place it in a glass jar and watch for spray on the next cold start.