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

[Prospectfarms]

(IMG:style_emoticons/default/beer3.gif) (IMG:style_emoticons/default/beer3.gif) (IMG:style_emoticons/default/beer3.gif)

O.K., I'm better now... D-jet is driving me to drink.

The 1.7 starts and runs well until it warms up. After 10 min. idling smoothly @ 900 it hesitates two or three times and stops idling at all, which means I can't keep it running long enough to set the timing. I can keep it going by feathering the throttle, but my nice smooth idle is gone. I reproduced the symptom three times in a row today.

By clamping off the Vac hoses one-by-one it appears the FI components seem to be doing what they're supposed to. No other vacuum or capacitance probs. found so far. Haven't checked the injectors.

This started after I repaired the ground strap on my distributor -- must have bumped something else. CHT?

I have the FI diagnostic checklists and am working on them. If this was a carburetor I'd say it was running with a clogged idle jet (IMG:style_emoticons/default/wacko.gif) . These symptoms seem specific and uncommon. At least I've not seen others posts that describe the same thing. Did I miss one?

[Mike Bellis]

Try this...

L Jet Manual

[SirAndy]

CHT?

Could be. I have seen this exact behavior when the CHT had been disconnected ...


Does it smell rich after warmup? A disconnected CHT will dump lots of fuel into the cylinders when warm.
(IMG:style_emoticons/default/idea.gif)

[Prospectfarms]

Try this...

L Jet Manual

Thnkz Mike,
Although "my" ECU monitors mainly manifold pressure (its a dog, not a lamb) I've been looking for the L-jet document you linked. IMHO, to take best advantage of the resources offered from 914 enthusiasts U've got to be able to parse suggestions and checklists that might represent "blended" experience from the two FI management system. So I've enjoyed reading the book.

As an aside I note that in the AC VW world there's a consensus that "D-jet, bad, L-jet," good." Not so with "Teeners," as far as I can see. In fact it's somewhat the opposite. Interesting, no? (IMG:style_emoticons/default/chowtime.gif)

Best wishes.

[Prospectfarms]

CHT?

Could be. I have seen this exact behavior when the CHT had been disconnected ...


Does it smell rich after warmup? A disconnected CHT will dump lots of fuel into the cylinders when warm.
:idea:

Dear Sir,

I appreciated your post 'cause after reviewing Anders I'd become over excited about the ignition timing. I once worked on a car where the dizzy simply shut down when the engine reached a certain temp, and that took forever to diagnose, but I don't think that is my issue here.

Your comment reminds me that, if the hypothesis is a fuel delivery issue the only conditions relevant to that analysis are "lean" or "rich." Engine stall because of either can offer identical symptoms (besides smell). I need to determine which it is.

I wondered / hoped whether that might be CHT, but I'm working in the breeze so I can't remember whether exhaust smelled rich. I'll repeat and pull a plug right after it stalls.

Another thought was that some failure of primary injectors meant that engine would "lean out" after cold start valve shuts off; however, further reading tells me that CSV shuts down much sooner that the 10-15 minutes of idling I observe prior to the engine stall.

I check the exhaust smell and CHT continuity this AM and report back.

Thanks again!

[TheCabinetmaker]

The cold start valve does not come on till the air temp hits about 40F.

The Auxiliary air regulator however, will open up on a 60 degree morning to give extra rpms during warm up. after about 10 minutes it should close and the idle come back to 900 (or wherever its is set). You may just have the idle set to low, or the throttle position switch may need to be reset. A mis adjusted tps will render the idle mixture knob on the ecu useless.

[Prospectfarms]

The cold start valve does not come on till the air temp hits about 40F.

The Auxiliary air regulator however, will open up on a 60 degree morning to give extra rpms during warm up. after about 10 minutes it should close and the idle come back to 900 (or wherever its is set). You may just have the idle set to low, or the throttle position switch may need to be reset. A mis adjusted tps will render the idle mixture knob on the ecu useless.

Great info! thanks. Assumed incorrectly that without extra fuel delivery, an open AAR would over lean the idle mixture -- ECU must adjust for proper mixture some other way.

My cold engine idle is first 800, then rises to 900 in a discrete stage. The third stage is stall. Are you suggesting thesel RPM values may be too low? I.e., if the TBP is mispositioned and the idle set too low, discontinuation of the AAR function would bring it down to a stall condition.

I'm going to check Throttle position sensor and re-check AAR and report.

[Bartlett 914]

The cold start valve does not come on till the air temp hits about 40F.

The CSV does not come on unless the air temperature is Below 40 maybe even colder. Unless it is leaking, it should not be a problem here.

[Prospectfarms]

The cold start valve does not come on till the air temp hits about 40F.

The CSV does not come on unless the air temperature is Below 40 maybe even colder. Unless it is leaking, it should not be a problem here.

Great minds think alike. Needed to know that. Thanks.

[underthetire]

Yep, i'll bet AAR myself. Should idle about 1500+ for 5 minutes or so, then come down. Base idle is too low.

[TheCabinetmaker]

Unplug the hose to the AAR at the air cleaner and plug it. Then try to start the engine cold. If it won't start you "may" have found the problem. open the air bleed screw on the throttle body a couple of turns, and try it again. The tps and ecu idle mixture must be set or it still won't work as it should. It'll be better, but still not 100%

[Tom]

From above;
Great info! thanks. Assumed incorrectly that without extra fuel delivery, an open AAR would over lean the idle mixture -- ECU must adjust for proper mixture some other way.
The ECU adjusts fuel mixture based on several inputs, one of which is RPM's.

I think vsg914 has a good test for you, although I would do it a little differently. Start car normally when cold, after about one min, close off the hose to the AAR from the air cleaner by pinching it with some pliers. If the engins stalls, you have the idle set too low. As others have said, with the AAR operating and open, your idle should be 1500 or so.
Tom

[charliew]

Tom, is it really Magala Red?

[Prospectfarms]

From above;

The ECU adjusts fuel mixture based on several inputs, one of which is RPM's.

I think vsg914 has a good test for you, although I would do it a little differently. Start car normally when cold, after about one min, close off the hose to the AAR from the air cleaner by pinching it with some pliers. If the engins stalls, you have the idle set too low. As others have said, with the AAR operating and open, your idle should be 1500 or so.
Tom

Tom, thanks very much for that clarification. It must seem obvious to you and now it is to me too.

Along those lines, do you know of a document that describes what the ECU "does" with the input from each pin. Manuals and checklists I've seen tend to focus on a description of what each device in the system measures with less detail about how the ECU responds to each signal in order to maintain a "stoichiometric air-fuel ratio".

The TPS must need attention. I think the idle screw is at the end of its travel for it would only turn 1/2, and as vsg914 predicted, that had little effect on idle speed. Though the engine now will continue to run after warm-up, there is little throttle response after the AAR kicks off

Synopsis:My problem was too slow idle during warm-up and then a predictable and sudden stall at 10 minutes. Plugs were fouled. CHT lead had fully or partially ground out. Fixing it (and /or changing plugs) brought the cold idle up from 900 to 1500. Even so, clamping the AAR stalled a cold engine, but a warm engine continued to run without AAR, albeit unacceptably rough and slow (4-500 RPM.) I know that the vacuum system leaks -- the hoses are 25 years old or more. I don't know why the air screw would not turn in more than 1/2. Perhaps it is at the end of its travel and per VSG914 the TPS needs work.

Thanks for all the good advice. There was a lot of it (IMG:style_emoticons/default/type.gif) It really helped.

[ThinAir]

Even though this problem started after a specific repair... when was the last time you adjusted your valves? Generally with D-Jet systems you want to start with basic, simple (and free) things first. Vacuum for the rest of the system is affected by proper valve adjustment so if your valves aren't right you'll chase your tail on a bunch of other stuff because the foundation isn't solid. Besides that, I've personally experienced that valves which are too tight will run great when cold, but produce a crappy running and stalling engine once they warm up and close up the gap.

[Prospectfarms]

Generally with D-Jet systems you want to start with basic, simple (and free) things first. .

That's true for any diagnostic procedure. Thanks for the reminder about the valves. How are things in Flag? You're lucky to live in the city of my favorite airport (free parking).

[Bartlett 914]

I think the idle screw is at the end of its travel for it would only turn 1/2, ........

I know that the vacuum system leaks -- the hoses are 25 years old or more. I don't know why the air screw would not turn in more than 1/2. Perhaps it is at the end of its travel

You must fix all vacuum leaks. The idle adjustment screw is a "controlled vacuum leak". It cannot have a proper effect if the system leaks elsewhere. Fix the leaks first! and adjust the valves.

[Tom]

The information I have is Paul Anders' stuff and Jeff Bowlsby's site at The Classic Porsche 914. He has a lot of info there and lots of wiriing diagrams. You can figure out which wire at the ECU goes to each sensor from the diagrams there, but the best description of what the ECU does is on Paul Anders site.
Tom

[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

[Prospectfarms]

The information I have is Paul Anders' stuff and Jeff Bowlsby's site at The Classic Porsche 914. He has a lot of info there and lots of wiriing diagrams. You can figure out which wire at the ECU goes to each sensor from the diagrams there, but the best description of what the ECU does is on Paul Anders site.
Tom

Thanks so much, Tom. I'll revisit Mr. Anders and Mr. Bowlsby. I appreciate everyone's input. (IMG:style_emoticons/default/type.gif)

I agree with the posts that urge dealing with vacuum leaks now. My original inquiry was inspired by a sudden change in engine performance and whether the new symptoms indicated a specific condition. Is that backwards? Anyway, I'll have to take a different approach now since I can't time it in the present running condition. (IMG:style_emoticons/default/wacko.gif)

Before I adjust the valve lash: Are the values stated by Haynes, etc. still thought to be the correct specification? For my 1.7 that would be .06/.06. I ask because at some point it's been agreed that VW type 1 (magnesium engine case) valves should be set slightly over recommended factory spec. I think I'll start a new valve adjustment thread for some questions I have on good head hygiene. (IMG:style_emoticons/default/unsure.gif)

Despite the potential vacuum problems the engine is running much better than before I started this post, so thanks again to everyone who took the time to help me. (IMG:style_emoticons/default/bye1.gif)