CIS pressure test, question

[npresley]

I just did 2 tests with the gauge hooked up between the fuel distributor and the WUR. The valve was on the WUR side. Everything was cold. It had been sitting for a day or 2 in the garage. I disconnected the WUR electrical plug. With the valve closed Friday evening, ambient around 85°, I read 1.9 bar. I opened the valve, WUR still unplugged, and the pressure jumped to 4.5 bar. I plugged the WUR and no change in pressure. I came back about an hour later and the pressure read about 1 bar, with the pump not running. I checked it again Saturday morning, ambient around 83°. With the WUR unplugged and the valve closed, I read 1.5 bar this time, and 4.5 bar with the valve open and the WUR not electrically connected.
1.5 bar seems low and the pressure jump without plugging in the WUR sounds odd too. What do you think my issue is?

Thanks for the help,
Nathan

[timmy2]

Valve closed pump running pressure is what? (system pressure)
Valve open pump running pressure, wur unplugged pressure is?(cold control pressure)
Valve open pump running wur plugged in pressure?(warm control pressure)
Valve open after warm pressure check, turn off car and residual pressure reading immediately and after 30, 60, 120 seconds and then 15 and 30 minutes?

[ossiblue]

Originally Posted by npresley

I just did 2 tests with the gauge hooked up between the fuel distributor and the WUR. The valve was on the WUR side. Everything was cold. It had been sitting for a day or 2 in the garage. I disconnected the WUR electrical plug. With the valve closed Friday evening, ambient around 85°, I read 1.9 bar. I opened the valve, WUR still unplugged, and the pressure jumped to 4.5 bar. I plugged the WUR and no change in pressure. I came back about an hour later and the pressure read about 1 bar, with the pump not running. I checked it again Saturday morning, ambient around 83°. With the WUR unplugged and the valve closed, I read 1.5 bar this time, and 4.5 bar with the valve open and the WUR not electrically connected.
1.5 bar seems low and the pressure jump without plugging in the WUR sounds odd too. What do you think my issue is?

Thanks for the help,
Nathan

Why did you run the tests to begin with--where you having problems of some kind? If so, what?

Sounds like you've got things backward. Valve open should mean the fuel is flowing through the connecting hose of the gauge set to the wur and back to the tank (control pressure)--the pressure would be lower. Valve closed means you shut off the flow through the wur and the gas is going only as far as the gauge--the pressure will be higher (system pressure.)

If you have simply misunderstood the "open/closed" position of the valve, then your readings seem to be within spec. You have pressure differentials between open/closed which tells you fuel is properly flowing through the wur. It is not possible that the pressure will rise when the valve is open.

Test again, understanding the "open/closed" valve positions. 1.9 bar may be a bit low for cold pressure with an ambient of 85 degrees (don't have a chart handy or know your wur model) but from what you've posted so far it's not really clear if there's an issue or not.

[npresley]

yes, that's right. Valve open lower pressure, valve closed higher pressure. I have been having a little hot start issue, and a slight idle issue, which may be a rich/lean adjustment. I have also noticed that when shifting up or down, the rpms dive. Sometimes the engine dies, sometimes it revs itself and stays running. The car is a '77. With the WUR unplugged, and closing the valve, everything cold, should the pressure automatically jump to 4.5 bar. When the WUR is plugged, should valve be open or closed?

[timmy2]

Brief due to using phone.
Answer each of my questions with a measured pressure value, testing as described, and we can help based on your numbers.

[npresley]

87°F ambient, motor was not started during testing,

Valve closed pump running pressure is what? (system pressure) 4.5 bar

Valve open pump running pressure, wur unplugged pressure is?(cold control pressure) 1.6 bar

Valve open pump running wur plugged in pressure?(warm control pressure) took like 5 minutes to get there, but 2.3 bar

Valve open after warm pressure check, turn off car and residual pressure reading immediately and after 30, 60, 120 seconds and then 15 and 30 minutes? 1.4 bar immediately, 1 bar @ 30 secs, 1 bar @ 60 secs, .05 bar 120 secs, 0 bar @ 15 min, & 0 bar @ 30 min

[timmy2]

Ok, looks like you have found your hot start issue!
The residual pressure is dropping way too fast.

It should drop to about 2 bar right away then slowly drop to 1.5 bar after about 10-15 minutes and slowly drop to about 1 bar in a 1/2 hour.
All numbers approximate. but you need good residual pressure for a hot start otherwise the fuel vaporises and will not burn correctly.

I'm not sure if your car has a return line check valve, but you should replace it if it does, and then test again.
That is the cheap fix compared to the alternate or additional solution to your problem which means Replace your Fuel Accumulator.

Future tip: Warm running pressure can be found quickly by actually running the car!

Post back your results.

[NeedSpace]

Timmy2, I am still pretty new to this, but I don't think the 1977 came with a return check valve. Could be an accumulator problem?

[timmy2]

Needspace,
Me too, but I highlighted my words in my last post for ya in red.
Now go back and tune your car bud... J/K

[boyt911sc]

Ty, Dennis, Larry, and others......

You guys are doing a great job helping other CIS owners get their problem/s resolve. I'm on vacation some where away from my home base but not too far away from a computer. If I may add something to erase some myth about CIS troubleshooting is VAPOR LOCK. Low pressure system like carburators are easily affected but not Ketronic Injection system!!!!! Even if you intentionally filled the fuel lines with pressurized gas, the gasoline (fuel) is an incompressible liquid and would readily displace any existing gas or vapor in the fuel lines. This is another myth.

This is also similar to replacing fuel filter in the CIS system. Air entrapped in the fuel line/s will not cause starting problem. Some people blame their problem/s to something they have not proven or tested to be the culprit.

Tony

[T77911S]

Originally Posted by boyt911sc

Ty, Dennis, Larry, and others......

You guys are doing a great job helping other CIS owners get their problem/s resolve. I'm on vacation some where away from my home base but not too far away from a computer. If I may add something to erase some myth about CIS troubleshooting is VAPOR LOCK. Low pressure system like carburators are easily affected but not Ketronic Injection system!!!!! Even if you intentionally filled the fuel lines with pressurized gas, the gasoline (fuel) is an incompressible liquid and would readily displace any existing gas or vapor in the fuel lines. This is another myth.

This is also similar to replacing fuel filter in the CIS system. Air entrapped in the fuel line/s will not cause starting problem. Some people blame their problem/s to something they have not proven or tested to be the culprit.

Tony

not to get off topic, but i question that.
when my car will not start hot, about 20-45 minutes after shutting it off, even though my FP runs with the key on, i can "prime" the system for a minute or so and it still will not start. BUT! i have figured out if i press the gas pedal to the floor, if it will fire in the first 2-3 seconds of turning over, it will start. it runs VERY bad, only on a few cylinders, but it runs. it then clears up after about 20-30 seconds of running.
if it does not fire in the forst 2-3 seconds, i have to lift the sensor plate to get it to start.

[T77911S]

i was going to say that 1.5 seems low for cold, but you have the vacuum controlled WUR, which drops the pressure even more. ihave seen .8 bar with mine, and my WUR is fairly new.

i dont have all my pressure results here, so some is from memory.

you should see about 2.8 warm, without vacuum and about 3.4 with vacuum.
you should also see a jump if CCP after about 20 seconds, with engine running and everything connected, due to the thermo time valve (TTV) opening.
you can also remove the vac to the WUR with the engine running and you should see the pressures drop.
if you dont, the TTV is bad. this will make your car run rich, causing it to surge at idle and possiblely stall when you let off the gas and the RPM's drop.

dont know for sure, but 4.5 system sounds a little low.

i would go back and recheck you procedures for checking pressures.
you mentioned the WUR being plugged. not sure if you are talking aout the electrical connector or a fuel line.
no fuel lines should be plugged. remove the connector for CCP and connected for warm. ignition needs to be on so power is getting to the WUR. check voltage just to make sure.


with the valve open, you are seeing control pressure.with it closed, that is system pressure.

[timmy2]

Hot start problem with no residual fuel pressure. Classic accumulator symptoms. Lets not send him chasing everything in the system until the main problem is fixed.

[ossiblue]

Originally Posted by timmy2

Hot start problem with no residual fuel pressure. Classic accumulator symptoms. Lets not send him chasing everything in the system until the main problem is fixed.

Agree. However, he needs to retest his check valve first, as you mentioned earlier. If he doesn't have an in-line valve, there is one in the fuel pump inlet. Regardless, he needs to test residual pressure in line before the accumulator to see if it is the check valve. As you say, a much easier and cheaper fix than an accumulator.

[NeedSpace]

Originally Posted by T77911S

not to get off topic, but i question that.
when my car will not start hot, about 20-45 minutes after shutting it off, even though my FP runs with the key on, i can "prime" the system for a minute or so and it still will not start. BUT! i have figured out if i press the gas pedal to the floor, if it will fire in the first 2-3 seconds of turning over, it will start. it runs VERY bad, only on a few cylinders, but it runs. it then clears up after about 20-30 seconds of running.
if it does not fire in the forst 2-3 seconds, i have to lift the sensor plate to get it to start.

I have experienced vapor lock on both a carbed 1.9 liter 1957 mercedes and a 1978 carbed cessna 152 with lycoming 110 HP engine. The one thing about your "fix" is isn't this exactly what you could do for a flooded engine. Is it possible that it was a flood situation rather than vapor lock? Specifically in the MB, the fuel would vaporize before getting to the carb disabling my ability to get fuel down there and not starting. I am not sure how or where this would happen in a FI engine.

npresely. The fuel check valve is easy to get to, remove the skid plate under the front of the car (4 bolts) and it is attached to the fuel pump. Not sure which fuel pump you have but should be fairly easy to replace. Have a lot of towel handy and be sure to clamp off the fuel line before the pump. (still my money is on the accumulator, but at $250 replace the check valve just in case).

[T77911S]

i would think if it was flooding as in a leaking injector i would get hydro lock and it would not start at all. also, if i try to start it and not run the FP for a minute or 2, then it will not start. it will slightly fire, if there is such a thing, then it just truns over.

what i think, or hope, is happening is that by running the FP, i am circulating cool fuel through the system to remove as much air as possible and by holding my foot to the floor allows for as much air as possible to raise the sensor plate to "bleed" the last air out of the injector lines.

i have no residual pressure so either my accumulator or my check valve is bad.
so far it has not failed to start by doing this. i know, just fix i dont have to do that. just lazy right now.
actually just very busy working on the house and trying to get back in shape on the bicycle. 10 years and lots of chinese buffets have done there toll.

sorry to be OT. not trying to fix my problem, just talking.

[Vereeken]

So is this being resolved?

I agree with system pressure being marginal 4.5bar should be 4.8bar ideally. But according to the specs for a 77 4.5 is still within spec (just).

Residual pressure is also bad, it drops too fast to low.

Cold start pressure is also low for 87 F. It should be Around 2.0/2.1 bar for that temp.
Now if it is a 77 with a 033 type WUR the CCP is much too low. In that case it should be around 2.8 bar without VAC at 87 F.

I guess this is not the case because OP does not complain about cold start issues.

In any case here are the specs for different WURs from Jims excellent website.

Michel

Year model System Pressure Cold pressure Warm pressure Vac conn Info Source Note
Bosch part number
0438.140.xxx @ temp (C) @ temp (C)
73.5 .001 4.5 to 5.2 1.6 @ 10 2.7 @ 35 None S.B.
74 - 75 .001 4.5 to 5.2 1.6 @ 10 2.8 @ 35 None F.M.
74 - 75 .008 4.5 to 5.2 1.3 @ 10 3.0 @ 40 None F.M.
74 - 75 .009 4.5 to 5.2 1.2 @ 10 3.0 @ 40 3.6 @ 40 F.M. 1)
75* 911, 911S .017 4.5 to 5.2 1.3 @ 10 2.7 @ 35 None S.B.
75 911S/C 4.5 to 5.2 0.6 @ 10 2.2 @ 35 3.6 @ 35 S.B.
76 - 77 911, Carrera, 911S 4.5 to 5.2 0.8 @ 10 2.4 @ 35 not spcf'd S.B.
76 - 77 .033 4.5 to 5.2 1.4 @ 10 3.2 @ 40 3.6 @ 40 F.M. 2)
78 -80 * .045 4.5 to 5.2 1.8 @ 10 3.0 @ 40 3.4 @ 40 F.M.
78 - 80 after Jan 79 * .069 4.5 to 5.2 1.4 @ 10 3.2 @ 40 3.4 @ 40 F.M.
'78 - '79 .045 4.5 to 5.2 1.8 @ 10 3.0 @ 40 3.4 @ 40 F.M.
'80 .072 4.5 to 5.2 1.8 @ 10 3.5 @ 40 None F.M.
'81 - 83* .089 4.5 to 5.2 1.2 @10 3.0 @ 40 3.6 @ 40 S.B.
'81 - '83 .090 4.5 to 5.2 1.6 @10 3.4 @ 40 None F.M.


* ROW

[T77911S]

my 77 with a new WUR, vacuum control, CCP was .8 bar. i dont remember the temp, but i am in the south so it does not get that cold.

[Vereeken]

Originally Posted by T77911S

my 77 with a new WUR, vacuum control, CCP was .8 bar. i dont remember the temp, but i am in the south so it does not get that cold.

0.8 is a spec for some 77s but at 10 degrees celcius (so about 50 F).

I am unable to get a good start with a ccp that is low but perhaps I have other issues . With too low pressure it seems to flood the engine quite easily.

Does a 77 have a hand throttle?

[T77911S]

no hand throttle. the thermo time valve is what drops the CCP even more by blocking vacuum to the WUR. another advantage to this is reduced backfiring when cold, even though it is low for only about 20-30 seconds.

i think it was maybe in the 50's when i checked mine. the TTV dropped the CCP about 1 bar i think. so the "normal" CCP was around 1.8 bar.

if you need a higher CCP, it is "acting" rich when cold. what can make it act that way is the question.
you might check your mixture when warm. also, make sure the ignition (plugs, wires, cap and rotor) are in good working order. check timing too.
too cold a plug could possiblly do it.
timing- make sure the advance is working and that it is set properly. perhaps too much advance??? do you have a vacuum advance and is it connected to the correct port.
does the motor have a lot of miles on it? perhaps it is just "tired".