CIS Testing with fused jumper wire

[kaskander]

Hi All,

My 1981 SC began starting hard warm. Cold starts are great. I followed the procedures laid out in the post below:

CIS Troubleshooting for Dummies

I also read the Bentley manual. I will admit that at first things did not make sense, but after reading and rereading the forum, watching some youtube videos, making a fused jumper wire, I took the plunge.

My results are as follows:

System Pressure: 5bar
tested by doing the following
ignition to on position, 30/87a jumped, WUR unplugged, engine off, pump running, valve closed

Control Pressure Cold: 2.4-2.5bar @72f for bosch WUR ending #090
ignition to on position, 30/87a jumped, WUR unplugged, engine off, pump running, valve open.

QUESTION 1: Bentley says Engine Cold and Running. Is this just simulated by ignition on + 30/87a jumped + WUR unplugged? Otherwise what's the point of the jumper wire

Control Pressure Warm:
Didn't really test (see below question)

QUESTION 2: Bentley says Engine Warm and Running. Is this just simulated by ignition on + 30/87a jumped + valve open + WUR plugged in and waiting 3/5 min for WUR to warm up? Or do I need to start the engine, and let run for 3/5 minutes for the plugged in WUR to warm up?*** Update just had to plug it in!



Residual Pressure: 10min 2.2bar 30min 1.75bar 3hrs 1.5bar
Tested as follows:
ignition to on position, 30/87a jumped, WUR unplugged, engine off, pump running, valve closed to get to system pressure of 5 bar. Then removed 30/87a jump and switched off ignition. Opened valve, recorded above measurements after time intervals

QUESTION 3: Bentley mentions running engine again after getting to system pressure. Is this just simulated by ignition on + 30/87a jumped? or do I need to run engine.


QUESTION 4: Bentley does not mention opening valve... did I do this wrong?



I just want to make sure I am running the tests correctly as there is conflicting information on the site. I didn't want to run the engine today as I spilled a little fuel during setup despite letting car sit over night, so decided to ask and try again in the AM.

Ideally I run the tests again based on my questions above getting answered, test power to WUR, test WUR resistance, and test spark, before trying to diagnose futher.

Thanks in advance. Good posts on this forum have been instrumental to getting me this far.. really want to close the loop!

[MarkWard]

Hello, I’m not familiar with the troubleshooting in the manual, but have a fair understanding of CIS. The engine starts fine at ambient most likely because the cold start valve is priming the intake. The valve is electronic but temp controlled. When the engine is warmed up you don’t have that added fuel. It is depending on air flow lifting the sensor plate and spraying the injectors.

There are 2 pressure readings with CIS. System pressure and control pressure. Control pressure is on top of the piston in the fuel distributor. It balances the airflow plate movement. Higher system pressure makes it more difficult for the sensor plate to move up which leans the mixture. Lower control pressure let’s the sensor plate move up easier richening the mixture.

The warm up regulator adjusts control pressure. It has an elec element that increases control pressure. It also is affected by surrounding temp. It’s acting like a choke. Lower control pressure for starting. Higher control pressure for at temp running.

Next is system pressure. System pressure is set by a relief valve in the fuel distributor. The higher the system pressure the more fuel is available at the injectors. Problem is if you increase system pressure you also increase control pressure. Both pressures are checked between the top center outlet of the fuel distributor and the inlet to the warm up regulator. The manual valve open reads control pressure. Closed you read system pressure.

Starting the engine cold the control pressure is low. As the engine warms up pressure will increase. It should not increase to match system pressure. Example. System pressure valve closed should be say 80 psi. Control pressure might be 36 psi cold and 58 psi hot. You can do this with the engine running and not worry about jumping relays or disconnecting connectors. My numbers are an example. The factory manual lists the specs.

So to your problem. Hard start hot has plagued CIS since the beginning. Fuel pressure check valves may be letting fuel pressure bleed off too soon. Injectors may leak down and without the cold start prime, take a lot of cranking to bleed the fuel system. Pump really only runs when the sensor plate lifts by air flow.

So, that gives you some things to think about and check. CIS parts have gotten rare, so if the only problem is the hot start. VW had a recall to add a pulse relay to the cold start valve. It pulsed the cold start valve while cranking. That fuel ignited quickly and then bled the air out. It would be reasonable to add a momentary switch to manually operate the cold start valve before starting. Similar to pumping the pedal on a carb engine. I am a big fan of CIS and it works well on my 80. No reason to spend money for another fuel system at this point.

Hopefully this helps. I’m posting from my phone from memory. Happy hunting and I apologize for the long reply since I didn’t really answer your specific questions.

[kaskander]

UPDATE:
Ran tests again after leaving car sit and fuel evaporated

System 5 bar
CCP @70f 2.2bar
CCW 4bar (I just plugged in the WUR and let it warm up without starting the engine and a jumped 30/87a)

I attempted to run engine but it would not start. Back to work

[MarkWard]

So I don’t have to do the conversions. Does your gauge read PSI? If so, post those please. My suggestion would be to leave the pressure gauge installed over night and have a helper start the engine in the am. Note the control pressure as it idles to temp. The jumping recommendations are more for when you don’t have time for the engine to fully cool off.

When you close the manual valve you are putting full system pressure on top of the fuel distributor piston. That is making it difficult to start. You can close the valve on a well running engine as a test long enough to read system pressure, but the engine will likely lean out and stall. Since you know the system pressure, you don’t really need to measure it again. It’s more important to know the control pressure during warm up and at temp.

After you start the engine in the am, you’ve lost your chance for another cold test. If it runs 5 mins, it will take at least an hour to be considered cold. You should also pay attention to the fuel pressure when you shut the engine off. You’d close the manual valve as you shut the engine off. It should hold pressure for quite a while. If it drops to zero quickly you will need to address that.

[kaskander]

System 5bar - 73PSI
Cold CP @70f for bosch #090 2.2bar - 32PSI
Warm CP 4bar - 58PSI
Residual 10min 2.2bar 32PSI, 30min 1.8bar - 26PSI

[MarkWard]

From memory those numbers look good. Have you verified the ignition timing and the fuel mixture? Does this engine have an oxygen sensor? Have you visually checked the airflow sensor plate height?

When you crank the hot engine. The sensor plate needs to lift for the injectors to start spraying. If the plate is out of adjustment or you have a vacuum leak, that will allow unmetered air past the sensor plate. The hot engine will not start till the injectors are spraying fuel.

It’s not easy to get the boot off the sensor to check the plate. A smoke test will reveal vacuum leaks.

If it were mine and it ran fine after it started, I’d richen the mixture slightly maybe a 1/4 turn or add a momentary switch to activate the cold start valve. You could pull the injectors, a bit of a pain and compare spray patterns and see that they don’t drip or leak down. Plan on new injector seals if you are planning to pop the injectors out unless the seals are newer.

[kaskander]

Thanks.. The warm CP may be a little high. Unfortunately my engine wont start at all now. I have not removed the pressure gauge but I doubt that would cause an issue. I did measure power to the WUR and the WUR resistance with a multimeter. Could I have messed anything up there?

[MarkWard]

It’s hard for me to know why it won’t start at this point. If the system pressure is being “held” on top of the fuel distributor, that would make it very hard to start. Remove the air filter and with everything off, verify the sensor plate lifts easily from below. The warm up regulator will work even if it has no power, so I wouldn’t worry about possibly damaging it. Perhaps something was accidentally disturbed. Engines need spark at the correct time and the correct amount of metered fuel. A timing light is easy to check for spark. Also, make sure the fuel pump relay is seated properly. After all these years the contacts are worn.

[kaskander]

Thanks Mark, I may have shorted something with the multimeter, or disturbed something, although I didn't shift anything. I have to do some more checking, part of the learning experience!

[roy gray]

Hey there bro.You may be barking up the wrong tree.Do you have spark?Did you mention that?If I missed it,I apologise.CIS,though antiquated is a very reliable,idiot-proof system that generally doesnt degrade in real time.It normally suffers when idiots mess with it whi don't know what the hell they're doing.Ask me how I know.Back to your problem.Remove a plug.Check for spark.If you have it,what does plug look like?If its soaking wet,you probably have no spark,and yes,fuel is not the issue.Is the plug abnormally clean?Then you may not have fuel.Is it sooty black?Then youre way too rich.It's very common for an old CD box to just give up the ghost.Fuel filter could be plugged solid,but its not likely.Hows your compression?When were the valves last adjusted?I just fixed an 80 320i with no fuel issues.It wasnt bad CIS,but electrical.Same with a 91 500sl.9 times out of 10 its not CIS.Just sayin.Dont worry about pressures so much.If your pump is working(absolute press.>80 psi,the rest of the system is probably fine.Cheers,Roy

[kaskander]

Roy. Luckily I have not fiddled with anything. Unfortunately I am out of town so all I can do is learn and start the troubleshooting. I have not checked for spark yet. It probably should have been the first thing to check to be honest. We shall see

[kaskander]

Update.

Back in town. Measured battery volts… 9.6

So all that playing around with my fuel pump plus lights on drained my battery. Used a portable starter, and it fired up. I still have all the pressure gauges hooked up, so will run the tests again tomorrow.

[porschedude996]

bookmark

Good information

[kaskander]

To close the thread.

Finally back in town after travel. Battery is shot. When cold, I can start using a jump starter, so decided to take it for a drive with the pressure gauges in, to get the car up to true operating temperature and then do the residual fuel pressure tests.
-10m 2.8bar
-20m 2.5bar
-30m 2.2bar
-1hr 1.7bar

The above are above spec....

My WUR's CCP. is a bit low to be honest, but not having a cold start issue (although cold idle is a little low)

Tried to start the car, yep same problem. Portable jump starter, wont crank engine long enough, so had to call AAA (because I am a genius and didnt just drive it home...). We have the same issue with their larger jump starter. Just to prove that my fuel pump is fine, I jumped 30/87a for a bit. Tried to jump start one more time, and car fired right up and idled perfectly. I did the "remove the fuel cap" test and idle dropped a bit, so I guess no significant unmetered air.

Next day, I replaced the battery (confirmed dead). I went from an H8 to a H6 AGM. It fits great when moving the retainer bracket. Car has been running great ever since, so i guess a dying battery was causing the issue. Well, at least i learned a ton about CIS systems.

Aside from members of the forum, the below links is amazing. Contains the full testing procedure as well.

https://jimsbasementworkshop.com/
https://cis-jetronic.com/index.php?rt=product/category&path=65_66

[MarkWard]

Congratulations. Nothing wrong with gaining experience. It will come in handy next time. I would not sweat the warm up regulator pressures. It’s more important there is a difference in values cold to hot than the actual pressure. It’s also important that it’s less than system pressure.

A faster warm up idle comes from the auxiliary air regulator. It allows air to bypass the throttle plate cold and internally closes as it warms up. It has an electric element and uses ambient heat to control the opening.

[porschedude996]

Bookmark

[boyt911sc]

Originally Posted by kaskander

System 5bar - 73PSI
Cold CP @70f for bosch #090 2.2bar - 32PSI
Warm CP 4bar - 58PSI
Residual 10min 2.2bar 32PSI, 30min 1.8bar - 26PSI

Kaskander,

The fuel pressures you provided were good except for the WCP which is out of spec. What was the WUR heater resistance value (Ohms) at room temperature? Thanks.

Tony

[kaskander]

Hey Tony!

I redid the test a few times; most time the WCP was 3.6-3.8bar. I don't really understand why it would fluctuate...

The resistance when cold was 16 Ohms.

Thank you for taking a look at my post; your posts really helped me understand the basic CIS functionality

[boyt911sc]

Originally Posted by kaskander

Hey Tony!

I redid the test a few times; most time the WCP was 3.6-3.8bar. I don't really understand why it would fluctuate...

The resistance when cold was 16 Ohms.

Thank you for taking a look at my post; your posts really helped me understand the basic CIS functionality

Kaskander,

The WCP is spot one @ 3.7 bar/53.7 psi. But it is odd for a WUR-090 to have 16 Ohms when cold. Recheck the heater resistance value. The spec when cold is between 25~26 Ohms. Keep us posted.

Tony

[kaskander]

Will check it out. I replaced the battery (confirmed dead) and hot start problems went away completely. It’s my daily and I have had no problems since.

Thanks Tony!