Can somebody ID this new idle quirk?, starts & runs well -- until warm Options

[r_towle]

look in the classics forum here for Cap'n crusty's valve adjustment process...its simple and works every time.

Rich

[Prospectfarms]

Unplug and cap all vacuum lines at the plenum.
the only line that should be plugged into the plenum is the MPS vacuum.

How is the idle then?
Set valves, dwell, and timing.
How is the idle?

If its still bad, and it still shows signs of dropping off after its hot...check your CHT for the proper Ohm readings for your ECU.
Anders site has the correct readings for your ECU and your CHT...
Each year is a bit different.

If that fails...there is are three more things that affect idle.
Failed MPS...runs to rich and stalls
Failed Cold Start Injector , always open, runs rich and stalls
Poorly adjusted TPS...runs rich and stalls.

You really need to ensure your ignition system is set properly before any FI diagnostics...you will chase your tail if the valves are adjusted wrong, or your dwell and timing are off....even just a little bit.

Djet is very sensitive to proper dwell and timing for the idle speed.

Djet and Ljet are both early systems and are both a guess at best for the proper A/F settings.
Both systems suck.

When the LH jet was introduced...that has the O2 sensor and the feedback made the system self adjust...then they had a decent system.

Rich

Rich, I appreciate your thoughtfully honest comments, that info is gold, e.g., now I'll be able to set the timing.

"When the LH jet was introduced...that has the O2 sensor and the feedback made the system self adjust...then they had a decent system."

Does that describe what some call an "open loop" system?

Have you used this information to customize fuel delivery on your car(s)?

Despite the continuos frustrations, I really enjoyed learning carburetor theory a few years ago, now I'm loving "Fi 101."

[Prospectfarms]

PS: Ill go through those procedures, set valve clearance and report back

[r_towle]

Unplug and cap all vacuum lines at the plenum.
the only line that should be plugged into the plenum is the MPS vacuum.

How is the idle then?
Set valves, dwell, and timing.
How is the idle?

If its still bad, and it still shows signs of dropping off after its hot...check your CHT for the proper Ohm readings for your ECU.
Anders site has the correct readings for your ECU and your CHT...
Each year is a bit different.

If that fails...there is are three more things that affect idle.
Failed MPS...runs to rich and stalls
Failed Cold Start Injector , always open, runs rich and stalls
Poorly adjusted TPS...runs rich and stalls.

You really need to ensure your ignition system is set properly before any FI diagnostics...you will chase your tail if the valves are adjusted wrong, or your dwell and timing are off....even just a little bit.

Djet is very sensitive to proper dwell and timing for the idle speed.

Djet and Ljet are both early systems and are both a guess at best for the proper A/F settings.
Both systems suck.

When the LH jet was introduced...that has the O2 sensor and the feedback made the system self adjust...then they had a decent system.

Rich

Rich, I appreciate your thoughtfully honest comments, that info is gold, e.g., now I'll be able to set the timing.

"When the LH jet was introduced...that has the O2 sensor and the feedback made the system self adjust...then they had a decent system."

Does that describe what some call an "open loop" system?

Have you used this information to customize fuel delivery on your car(s)?

Despite the continuos frustrations, I really enjoyed learning carburetor theory a few years ago, now I'm loving "Fi 101."

FI is simple.
You are still measuring air flow.
ALL EFI systems measure air flow.
Based upon air flow, fuel is metered out to match the airflow.

There are two schools of thought on measuring air flow
Manifold pressure, and air flow volume.
Both measure air.
Both still exist in one form or another.

With the introduction of an O2 sensor, the computer can see if it guessed properly and do slight tuning based upon the exhaust gas mixture...

Heat sensors, specifically head temp sensors, tell the computer if the car is to hot, and it adds fuel to cool the motor.

The rest of the sensors are for even more fine tuning.

Rich

[benalishhero]

Open loop in modern EFI systems refers to the engine running with no feedback from the O2 sensors(and other components) while it warms up. Once the operating temp is achieved the system enters closed loop mode which uses the various EFI components to obtain the maxium F/A ratio. The vehicle will also enter open loop at idle warm or when the engine is not under load.

[Prospectfarms]

Thanks benalishhero, So the word "open" as used in open loop, signifies the something similar to "open circuit," i.e., "unconnected?"

[Prospectfarms]

Unplug and cap all vacuum lines at the plenum.
the only line that should be plugged into the plenum is the MPS vacuum.

How is the idle then?
Set valves, dwell, and timing.
How is the idle?

If its still bad, and it still shows signs of dropping off after its hot...check your CHT for the proper Ohm readings for your ECU.
Anders site has the correct readings for your ECU and your CHT...
Each year is a bit different.

If that fails...there is are three more things that affect idle.
Failed MPS...runs to rich and stalls
Failed Cold Start Injector , always open, runs rich and stalls
Poorly adjusted TPS...runs rich and stalls.

You really need to ensure your ignition system is set properly before any FI diagnostics...you will chase your tail if the valves are adjusted wrong, or your dwell and timing are off....even just a little bit.

Djet is very sensitive to proper dwell and timing for the idle speed.

Djet and Ljet are both early systems and are both a guess at best for the proper A/F settings.
Both systems suck.

When the LH jet was introduced...that has the O2 sensor and the feedback made the system self adjust...then they had a decent system.

Rich

Here's what I am presently dealing with:

-1.7 D-jet

-Good compression all 4

-Tune-up, dwell, timing and valves set to specifications per Haynes.

-No obvious vacuum hoses leak (air/idle screw adjustment now affects idle speed.)

-Starts at 900 RPM, after 5 minutes it rises to 1500 RPM. Idle is steady and smooth.

-Clamping the AAR hose on supply side bring idle back down to 900.

-Disconnecting and plugging manifold connections has no significant effect.

-At 15 minutes run time, the engine begins to miss and then stalls after about 2 minutes. Reving motor and/or unclamping AAR doesn't prevent stall.

-Exhaust smells rich when engine stalls--assume flooding.

Per Haynes FI trouble shooting section: "engine starts cold then stalls:" = MAPS or CHT.

This is consistent with the opinions of several members here.

Tomorrow, I will:

-Check CHT resistance value

-Go through diagnostic procedure on MPS.

Anything else?

Where will I find a serviceable MPS if mine's kaput?

[ThinAir]

Besides, starting with the basics, the other thing you'll often hear is that you should check everything else first before you look at the brain because "they never go bad". Well... almost never.

Your symptom of smelling fuel when it dies sounds alot like what happened with my son's 1.7L at RRC 2 years ago. We went around a corner, the engine suddenly died and it was obvious that it was flooded. After we got it home we went through the entire system methodically like you are doing. Because we had known good parts that we could swap we changed out AAR, MPS, etc. Finally, there was only one part left - the brain. Sure enough, after changing out that the problem went away and has never returned.

If you can lay your hands on a brain that is compatible with the rest of your system, it may be worth swapping it to see if it makes a difference. It's sounding a bit to me like a solder point or circuit board that is breaking a circuit once it heats up.

[Prospectfarms]

It's sounding a bit to me like a solder point or circuit board that is breaking a circuit once it heats up.

Thanks, ThinAir:

Those fit the symptoms. At any rate, something specific happens when the engine reaches a certain temperature. There's a clear transition and whatever the problem, it causes the engine to stall within a few minutes.

Not knowing much about FI, I hoped someone who did could ID these symptoms as indicating failure in a particular system. I now understand why it would rarely be that clear-cut.

Lessons learned by anyone who, like ThinAir, has experienced something similar and is willing to share might help me avoid a lot of unnecessary work and expense, as I attempt to source replacements for those expensive components that may be bad. (IMG:style_emoticons/default/hissyfit.gif)

[Prospectfarms]

Update:

Pulled ECU and tested resistance of CHT and MAP at pin harness per Anders.

CHT resistance 2.54K (within a few OHM's of spec.) MAP was right on spec.

My brother suggested an unseen leak at throttle body or manifold that would expand with engine temperature.

Next on list is to test TPS and inspect throttle body for unseen leaks.

I'll keep digging. (IMG:style_emoticons/default/confused24.gif)

[Prospectfarms]

Update:

Here's what I am presently dealing with:

-1.7 D-jet

-Good compression all 4

-Tune-up, dwell, timing and valves set to specifications per Haynes.

-No obvious vacuum hoses leak (air/idle screw adjustment now affects idle speed.)

-Starts at 900 RPM, after 5 minutes it rises to 1500 RPM. Idle is steady and smooth.

-Clamping the AAR hose on supply side bring idle back down to 900.

-Disconnecting and plugging manifold connections has no significant effect.

-At 15 minutes run time, the engine begins to miss and then stalls after about 2 minutes. Reving motor and/or unclamping AAR doesn't prevent stall.

-Exhaust smells rich when engine stalls--assume flooding.

Per Haynes FI trouble shooting section: "engine starts cold then stalls:" = MAPS or CHT.

This is consistent with the opinions of several members here.

Tomorrow, I will:

-Check CHT resistance value

-Go through diagnostic procedure on MPS.

Anything else?

Where will I find a serviceable MPS if mine's kaput?

Pulled ECU and tested resistance of CHT and MAP at pin harness per Anders.

CHT resistance 2.54K (within a few OHM's of spec.) MAP was right on spec.

My brother suggested an unseen leak at throttle body or manifold that would expand with engine temperature.

Next on list is to test TPS and inspect throttle body for unseen leaks.

I'll keep digging. (IMG:style_emoticons/default/confused24.gif)

All these static tests leave me wondering...

To recap, I'm looking for the condition that causes my 1.7 FI to stall out at a certain operating temperature. The idle is good for about 15 minutes and then it starts hunting, the RPM's drop and it stalls. After checking the plugs, and smelling the exhaust, I believe it is a flooding condition. The functions and behaviors of the FI components (the "likely suspects") also argue that any massive failure of this kind would result in flooding.

The possibilities are almost limitless and I wont discount any of them, but I feel it is one of three: 1. CHT thermistor never warms up. 2. ECU issue. or 3. TBS is doing something I don't understand.

As I said, the static testing only gets me a spec at room temp, and especially for the CHT, this is not sufficient. If it is not decreasing resistance as the engine approaches warm, the mix could conceivably become too rich to run -- I guess.

Its the sudden onset of the problem that really confuses me. it would seem that any falure of a FI component brought on by heat, would show some progression. This problem comes on all at once.

I'm considering splicing a pigtail to the CHT wire and grounding that when the engine is about to stall. Grounding the CHT would essentially render it invisible to the ECU. Good / bad idea?

[Tom]

You should measure the value of the CHT when it is warm.
Tom

[Prospectfarms]

You should measure the value of the CHT when it is warm.
Tom

Thanks, Tom

my last "idea" (IMG:style_emoticons/default/screwy.gif) -- to ground the CHT when the engine was about to stall-- was a round-a-bout way of checking it warm. Your note brought me back to reality .

Unconsciously, I think I was trying to avoid the trouble of removing the ECU when it was hot. (IMG:style_emoticons/default/rolleyes.gif) (I've so far done my resistance checks at the ECU 24 pin harness)

I'll check the warm CHT at the ECU pin and also check the warm MAP values at the same time. (IMG:style_emoticons/default/idea.gif)

I'm going to do this now and report back later.

Appreciate the help!

[Prospectfarms]

You should measure the value of the CHT when it is warm.
Tom

Thanks, Tom

my last "idea" (IMG:style_emoticons/default/screwy.gif) -- to ground the CHT when the engine was about to stall-- was a round-a-bout way of checking it warm. Your note brought me back to reality .

Unconsciously, I think I was trying to avoid the trouble of removing the ECU when it was hot. (IMG:style_emoticons/default/rolleyes.gif) (I've so far done my resistance checks at the ECU 24 pin harness)

I'll check the warm CHT at the ECU pin and also check the warm MAP values at the same time. (IMG:style_emoticons/default/idea.gif)

I'm going to do this now and report back later.

Appreciate the help!

Started engine, ran well for 15 minutes, hesitated and stalled as usual.

MAP and CHT resistances are within spec at "warm" (=/- 200 F). These values are from the ECU connection pins. I couldn't detach the CHT sensor wire from the harness. There is a terminal block but the spade would not pull out with moderate force and I was afraid of breaking the plastic cover.

Don't have a vacuum tool, so I can't test MAP "leak down."

Next check is the throttle/air distribution manifold assembly looking for something out of order (like a big a-s hole) underneath. Also the cold cold start valve for leakage.

[Tom]

I have heard of cracked plenums causing a vacuum leak. Going to be a hard one to check. Maybe someone on here will give you a good way to check the plenum for vacuum leaks.
Tom

[Prospectfarms]

I have heard of cracked plenums causing a vacuum leak. Going to be a hard one to check. Maybe someone on here will give you a good way to check the plenum for vacuum leaks.
Tom

Indeed. I've not seen a lot of info on how the plenum/throttle assembly goes together or, more to the point, comes apart.

[Prospectfarms]

ThinAir, did you do more work on your son's 914 since this post?

http://www.914world.com/bbs2/index.php?s=&...t&p=1129848

It indicates that a problem with the MAPS electrical connection caused the car to suddenly flood-out.

Did you later determine an ECU fault? Per:

Besides, starting with the basics, the other thing you'll often hear is that you should check everything else first before you look at the brain because "they never go bad". Well... almost never.

Your symptom of smelling fuel when it dies sounds alot like what happened with my son's 1.7L at RRC 2 years ago. We went around a corner, the engine suddenly died and it was obvious that it was flooded. After we got it home we went through the entire system methodically like you are doing. Because we had known good parts that we could swap we changed out AAR, MPS, etc. Finally, there was only one part left - the brain. Sure enough, after changing out that the problem went away and has never returned.

If you can lay your hands on a brain that is compatible with the rest of your system, it may be worth swapping it to see if it makes a difference. It's sounding a bit to me like a solder point or circuit board that is breaking a circuit once it heats up.

Thanks a lot!

[ThinAir]

This actually all started with this: http://www.914world.com/bbs2/index.php?sho...c=80367&hl=

I thought I had posted my solution, but I can't find it.

Yes, I solved the ultimate problem by replacing the ECU. The car would randomly flood and die immediately. We took the approach that the ECU "never goes bad" because they hardly ever have a problem, but in our case it was the only component that we hadn't changed for a known-good unit so there was little choice left. Since we had one available, it was worth a shot. Problem has never returned and the car made a very successful trip to RRC last Fall with nary a hint of a problem.

[Prospectfarms]

This actually all started with this: http://www.914world.com/bbs2/index.php?sho...c=80367&hl=

I thought I had posted my solution, but I can't find it.

Yes, I solved the ultimate problem by replacing the ECU. The car would randomly flood and die immediately. We took the approach that the ECU "never goes bad" because they hardly ever have a problem, but in our case it was the only component that we hadn't changed for a known-good unit so there was little choice left. Since we had one available, it was worth a shot. Problem has never returned and the car made a very successful trip to RRC last Fall with nary a hint of a problem.

ThinAir, Thanks for the update. Reading about your experience helps a lot. Sorry you had to go to so much trouble back then. Great work sticking with it to fix the car. Helps me consider my issue from a more positive perspective. Stuart

[Prospectfarms]

look in the classics forum here for Cap'n crusty's valve adjustment process...its simple and works every time.

Rich

Rich, I forgot to thank you for the reference to Cap'n crusty's valve adjustment process. Heard of such, but never before in sufficient detail to be useful.

Found it the thread and it worked well for me.

As I was underneath the car, it struck me that the different methods for setting lash seem to represent a spectrum of "automechanica" that starts with a standard Haynes approach. In the middle of the spectrum is the modified method found in "How to Keep Your Volkswagen Alive." and at the end is Cap'n crusty's way, which is the most logical, but requires visualization of the operation of the motor's top and bottom end.