Cis stumble on start.

[theiceman]

Hey boys..
My engine has always started flawlessly..I rebuilt due to a broken head stud a few years ago.. and since then I have had a small stumble on cold starts.
I never did anything about it for two years as it only stalls out one of 100 times..but the stumble makes me nervous that it could backfire one day . It never has.
I did not touch cis during rebuild..just unbolted it. Then bolted it back on..
It's odd as it starts immediately. So makes me think CSV is working..then sounds like she is kicking in and holding it steady.so makes me think wur is working. ( 78sc 26.2 ohms )
I do have gauges so will run through all the tests. Just wondered if anyone has had these symptoms.
If I stop and restart it warm start is perfect.

Thanks..

Video below


https://youtu.be/3bzMfFcnorM

[2jmotorsports]

That does sound like the teeniest tiniest of poppity pops from a ever so slightly lean mixture. I would try a smoke test for vacuum leaks. It might be a leak small enough to lean it out a tad and not big enough to prevent it from starting.

I was going to suggest checking the fuse and wiring to the OXS relay but you dont have a lambda circuit...

[theiceman]

okay then i guess my first step is tracking down a smoke machine and checking for vac leaks.
thanks for the tip.

correct no lambda.

[boyt911sc]

When you started the cold motor in the video, were you touching the gas pedal? It seems you were assisting to get it to start(?). The problem will be more obvious if you keep your feet away from the gas pedal.

It is a good practice to check your fuel pressures (CCP, WCP, & SP). Check for air leaks and finally, test your fuel injectors for spray patterns. The fuel injector/s flow test is one of the most commonly neglected inspection people do to their CIS until the problem becomes noticeable.

I would not worry too much if it happens only @ 1% incident. I will take it anytime specially for a 40 plus year-old car. Parts age and deteriorate. So don’t expect it to be perfect. Could you try again starting it unassisted? Thanks.

Tony

[theiceman]

Originally Posted by boyt911sc

When you started the cold motor in the video, were you touching the gas pedal? It seems you were assisting to get it to start(?). The problem will be more obvious if you keep your feet away from the gas pedal.

It is a good practice to check your fuel pressures (CCP, WCP, & SP). Check for air leaks and finally, test your fuel injectors for spray patterns. The fuel injector/s flow test is one of the most commonly neglected inspection people do to their CIS until the problem becomes noticeable.

I would not worry too much if it happens only @ 1% incident. I will take it anytime specially for a 40 plus year-old car. Parts age and deteriorate. So don’t expect it to be perfect. Could you try again starting it unassisted? Thanks.

Tony

No Tony. That is completely on its own. I have touched the gas on starting in 5 years. That's what makes me think the wur is good as I think it can grab and hold idle once it gets passed the stumble

[theiceman]

Tony I did a second sample. So you can see what I'm talking about.
I thought you might have me run the numbers so i will get the gauges on tomorrow.. I also have a baseline from before my top end work so will be usefully.to compare.

https://youtu.be/WRU-k5zsz68

I have some nylon fuel lines with fittings so I might develope an injector spray pump for cleaning and testing.

[theiceman]

hey guys .... i may have "stumbled" onto a clue.. but more on that in a minute.

first the numbers.
wur (045)
system pressure 70 psi ( 4.8 bar ) took less than 2 seconds to get there
cold control pressure at 25c (1.8 bar ) slightly low but right on the edge.
2.6 bar 2 minutes after plugging heating element in..

10 minute residual 1.6 bar
30 minute residual 1.3 bar

now the interesting part.....
at no point did i ever start the car.. but the bentley said checks should be done with car running. so i removed my jumper and started the car. i expected it to stumble as it was the first time i had started it that day .
it fired up and for the first time in two years since my rebuild it started like it did before my build and as soon as it fired it lept to hi idle like i would expect when it is working .

all i really did was cycle the fuel pump and prime the system.
if it had been a vacuum leak or injector i would have expected it to stumble.

so i need to repeat some tests. but i'm starting to have a few other ideas now as to where the problem could be.
i'm sure if i bypass the safety switch so it runs the pump as soon as ignition comes on it will fix it if i am correct, but where is the joy in that

the other thing i found interesting was when i went to connect the gauges this morning, not even a dribble came out of the connection at the top of the wur. i mean nothing. i wonder if i am simply losing prime and it takes a second for the pump to prime the lines.

stay tuned

[pmax]

Originally Posted by theiceman

wur (045)
system pressure 70 psi ( 4.8 bar ) took less than 2 seconds to get there
cold control pressure at 25c (1.8 bar ) slightly low but right on the edge.
2.6 bar 2 minutes after plugging heating element in..
...
but the bentley said checks should be done with car running.

That's because the 045 WUR has a vacuum control. Use a hand pump.



And while you're at it, get rid of the elevator chime before the stripper jumping out of the cake !

[SkiVT]

Your ccp w/o vacuum applied should have been approx .6 bar lower than the graph. As stated, need to test it with vacuum applied. Other thing to check is the vacuum line connection from wur to thermo valve. It needs to connect on the outer nub of the thermo valve. The center nub connection on the thermo goes to the decel. When connected properly and when thermo valve is working, it holds off vacuum in those first 30 or so seconds at startup keeping your mixture on the rich side.

[boyt911sc]

Originally Posted by theiceman

hey guys .... i may have "stumbled" onto a clue.. but more on that in a minute.

first the numbers.
wur (045)
system pressure 70 psi ( 4.8 bar ) took less than 2 seconds to get there
cold control pressure at 25c (1.8 bar ) slightly low but right on the edge.
2.6 bar 2 minutes after plugging heating element in..

10 minute residual 1.6 bar
30 minute residual 1.3 bar

now the interesting part.....
at no point did i ever start the car.. but the bentley said checks should be done with car running. so i removed my jumper and started the car. i expected it to stumble as it was the first time i had started it that day .
it fired up and for the first time in two years since my rebuild it started like it did before my build and as soon as it fired it lept to hi idle like i would expect when it is working .

all i really did was cycle the fuel pump and prime the system.
if it had been a vacuum leak or injector i would have expected it to stumble.

so i need to repeat some tests. but i'm starting to have a few other ideas now as to where the problem could be.
i'm sure if i bypass the safety switch so it runs the pump as soon as ignition comes on it will fix it if i am correct, but where is the joy in that

the other thing i found interesting was when i went to connect the gauges this morning, not even a dribble came out of the connection at the top of the wur. i mean nothing. i wonder if i am simply losing prime and it takes a second for the pump to prime the lines.

stay tuned

Were you aware that you had pre-heated the WUR, AAR, & TV including priming the system before starting the engine? Running the fuel pump to measure the control fuel pressure for your test (engine not running) also made the the other CIS components got energized because they all get power from terminal #30. Unless you unplugged them before the test.

With the motor is still cold, the CSV will come into action with the other CIS components pre-heated with the system primed already. This is the reason why you got the motor to run with ease.

Tony

[theiceman]

i was wonder how long i would slide by without the stripper comment .. i mean what are the odds !!!!

well that is all good news.... as i was on the low side.. if i add .6 bar due to the none acting vacuum that puts me right in the middle of the range for my wur and ambient.

i rechecked this morning and at 23c I am at 1.6 bar. with the engine not running.

if i add .6 to that i am right in the correct zone i am supposed to be in. I suspected initially that i had no problem with the wur as once it gets past the stumble, cold running and warm running are fine. i dont have a vac pump but maybe i iwll rig one up if i have to come back to this.

when i started it initially it was the same reading. but it did move up rather quickly ( i imagine due to the wur element warming up. )

re: thermo valve , all vacuum connections and hoses are new and correct but it does give me something else to check. But it s simply a shut off switch . it blocks off vacuum flow, i cant see which port it being on making a difference, but it is correct.

[theiceman]

Originally Posted by boyt911sc

Were you aware that you had pre-heated the WUR, AAR, & TV including priming the system before starting the engine? Running the fuel pump to measure the control fuel pressure for your test (engine not running) also made the the other CIS components got energized because they all get power from terminal #30. Unless you unplugged them before the test.

With the motor is still cold, the CSV will come into action with the other CIS components pre-heated with the system primed already. This is the reason why you got the motor to run with ease.

Tony

does make sense Tony Thanks. i was aware of the WUR and left it unplugged for a while but did not think about the other two.. but as i said its a clue. something for me to ponder.

[theiceman]

I do have another WUR which made the car run like crap ... i mght rebuild thst one and see if i can get it working. checks out at 25 ohms but the CCP was 2.9 on that one so definitely something wrong with it.
if i can get it working just might give me something to play around with . I have seen double vacuum wur rebuild kits on the net so i will rebuild this one without messing with mine.
right after i build my injector crack pressure testing and cleaning device

[SkiVT]

The thermo absolutely matters which port is connected to the wur. It allows immediate vacuum if connected center port to wur which makes you lean for the first 30 or so seconds after starting instead of rich. Tony has a really good testing thread on the subject from a couple years ago. The part doesnt fail often but worth a test to eliminate as your cause. My ccp was a bit high in this video, which I later fixed, but watch the jump when the thermo opens around 30 sec. If connected incorrectly that “jump” happens immediately.

https://youtu.be/x3HXhqlwFMM

[theiceman]

Thanks skiVT i will follow up ...

incidentally the bentley talks about warm running with vacuum connected and disconnected... is it talking about BOTH vacuum sources ? ? the VVT and the port up top ??