911sc warm running issue

[twaldron]

Originally Posted by boyt911sc

Thomas,

If you disable the TTV by unplugging the electrical plug, the cold motor would start and run a bit longer but would stall later(?). With the CIS pressure gauge installed, observe at what control pressure the motor would stop running. Keep us posted. Thanks.
NOTE:
You should not have a cold control pressure spike during this test.

Tony

Well you’re right about the lack of a fuel pressure spike with the TTV unplugged.

Ambient temperature 93°. It warmed up decently smoothly from 2.1 bar to 2.7 until about 1:15 in and it began its stumble to death. Highest pressure I achieved with this test was 2.75 where it stopped climbing. It never reached the 3.5. I made a video of the gauge face with sound. Video length 2 mins, from START to DEATH.

[boyt911sc]

Originally Posted by twaldron

Well you’re right about the lack of a fuel pressure spike with the TTV unplugged.

Ambient temperature 93°. It warmed up decently smoothly from 2.1 bar to 2.7 until about 1:15 in and it began its stumble to death. Highest pressure I achieved with this test was 2.75 where it stopped climbing. It never reached the 3.5. I made a video of the gauge face with sound. Video length 2 mins, from START to DEATH.

Thomas,

The motor stalled @ 2.70 bar (39 psi.). Theoretically, this motor should be idling @ 3.6 bar (52.0 psi.). So it means that the mixture is LEAN. There are two ways to interpret this condition:

• LEAN because less fuel.
• LEAN because too much air.

I would bet my money on the second scenario. LEAN due to air leaks or unmetered air. You need to locate the sources of these air leaks and fix them. The good news, a smoke generator could easily identify where these leak sources in your CIS.

You could buy or borrow or build a smoke generator. If you build yourself a smoke generator, you are are not saving much $$ considering the time and effort you will spend making one. But some people enjoy building things. Keep us posted.

Tony

[twaldron]

Originally Posted by boyt911sc

Thomas,

The motor stalled @ 2.70 bar (39 psi.). Theoretically, this motor should be idling @ 3.6 bar (52.0 psi.). So it means that the mixture is LEAN. There are two ways to interpret this condition:

• LEAN because less fuel.
• LEAN because too much air.

I would bet my money on the second scenario. LEAN due to air leaks or unmetered air. You need to locate the sources of these air leaks and fix them. The good news, a smoke generator could easily identify where these leak sources in your CIS.

You could buy or borrow or build a smoke generator. If you build yourself a smoke generator, you are are not saving much $$ considering the time and effort you will spend making one. But some people enjoy building things. Keep us posted.

Tony

Sounds logical. For the sake of my edification, in the test above, the gauge actually stopped climbing at 2.7 bar, before the car really began stumbling. It didn’t die while the gauge was still climbing to 3.5. Why is that?

Also, when the TTV was plugged in, gauge showed 3.5, but it died similarly. Trying to wrap my head around this stuff.

Also, any suggestions on a good, cheap smoke kit?

[boyt911sc]

Originally Posted by twaldron

Sounds logical. For the sake of my edification, in the test above, the gauge actually stopped climbing at 2.7 bar, before the car really began stumbling. It didn’t die while the gauge was still climbing to 3.5. Why is that?

Also, when the TTV was plugged in, gauge showed 3.5, but it died similarly. Trying to wrap my head around this stuff.

Also, any suggestions on a good, cheap smoke kit?

Thomas,

Repeat the test experiments you just conducted:

• The TTV plugged “IN”.
• The TTV plug disconnected.

NOTE:
Both tests should be done with the engine cold (at least 2 hours rest). Record the total time from start to stall time. Start the first test (TTV disconnected) and allow the motor to sit for 2~3 hours. Then do the second test (TTV plugged IN).

We will discuss the test results (total running time) for both tests. Do not forget to monitor the control fuel pressure versus time. A 30-sec intervals would be great.

There are two (2) EVAP Leak Testers that caught my attention namely:
Auto Tool for $77
Romodes SM601 for $80

They look impressive than my home-made 1-gallon paint can contraption. But my smoke generator has been very effective and proven over the years.

Tony

[twaldron]

Originally Posted by boyt911sc

Thomas,

Repeat the test experiments you just conducted:

• The TTV plugged “IN”.
• The TTV plug disconnected.

NOTE:
Both tests should be done with the engine cold (at least 2 hours rest). Record the total time from start to stall time. Start the first test (TTV disconnected) and allow the motor to sit for 2~3 hours. Then do the second test (TTV plugged IN).

We will discuss the test results (total running time) for both tests. Do not forget to monitor the control fuel pressure versus time. A 30-sec intervals would be great.

Tony

TTV UNPLUGGED:

Ambient temperature 94°.
Started with a CCP of 2.0 bar which moved steadily up to 2.7 and stopped.
:30 - 2.3
:60 - 2.6
:75 - 2.7 (where it stopped increasing)
At 2:15 in, it began to stumble and spiral into a hard, sputtering death at 2:34.

TTV PLUGGED IN:

Ambient temperature 86°.
Started with a CCP of 1.9 bar which moved steadily up until the needle pop at 2.3
:30 - 2.1
:60 - 3.3
:90 - 3.5 (where it stopped increasing)

AT :49 seconds in, gauge pops from 2.3 to 3.2 but continued to creep up to 3.5
At 2:20 in, it began to stumble and spiral into a hard, sputtering death at 2:55.

I PM’d you the links to videos of the two tests.

[boyt911sc]

Thomas,

You need to test and verify the absence of significant sources of unmetered air going into your CIS. Without performing this test, it is quite difficult to identify the culprit and get this motor to run.

Tony

[twaldron]

Originally Posted by boyt911sc

Thomas,

You need to test and verify the absence of significant sources of unmetered air going into your CIS. Without performing this test, it is quite difficult to identify the culprit and get this motor to run.

Tony

Will do! Thank you.

Praying for something simple, and an intact airbox

[kaskander]

I went through an issue w/ a hot start problem, that morphed into similar behaviour. Learned a lot about the CIS system through this forum and JIM's CIS site, (past posts and individuals who responded). Did all the pressure tests which was an awesome learning experience. Results were in spec (well CCP was a little low, but ok).

I was going to take it to a shop, but in looking at maintenance records, the cap/rotor were last replaced in 2004, and no record of the spark plug wires being replaced (they were berus, so were at least replaced once since 1981). Cap was pretty pitted, wires were definitely "ratty". I figured, I should replace these items, rather than have a shop replace as part of a "let's replace parts and see what happens strategy". Long story short; it's been 2k miles since I replaced the components and the issues have disappeared.

Might be something worth looking into especially if those components are old, although this should have nothing to do with the spike cp.

[twaldron]

Originally Posted by kaskander

I went through an issue w/ a hot start problem, that morphed into similar behaviour. Learned a lot about the CIS system through this forum and JIM's CIS site, (past posts and individuals who responded). Did all the pressure tests which was an awesome learning experience. Results were in spec (well CCP was a little low, but ok).

I was going to take it to a shop, but in looking at maintenance records, the cap/rotor were last replaced in 2004, and no record of the spark plug wires being replaced (they were berus, so were at least replaced once since 1981). Cap was pretty pitted, wires were definitely "ratty". I figured, I should replace these items, rather than have a shop replace as part of a "let's replace parts and see what happens strategy". Long story short; it's been 2k miles since I replaced the components and the issues have disappeared.

Might be something worth looking into especially if those components are old, although this should have nothing to do with the spike cp.

Thanks for chiming in. Probably a good idea to check those out. I know it’s been a long time and I have a brand new cap on the shelf.

Waiting on the smoke tester to show up to get back into the car.

[PeteKz]

Let me clean up something I said earlier. I didn't realize you were running the engine when the CP "snapped" up. After Tony said that was due to the TTV opening, I realized that occurred while the engine was running, which explains it. Usually, you do the CCP and WCP testing with just the fuel pump running, then attach a vacuum pump to test that the TTV is closed, then open, and that the CP rises a certain amount with a certain amount of vacuum applied. I missed that your engine was running. So once again, Tony got it right!