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?

[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?

[Prospectfarms]

Follow up and diagnosis. Ultimately it was the fuel pump...

This thread helped fix the problem of engine dying from idle when it reached a certain operating temperature. At the point of stalling, no amount of feathering the accelerator would prevent it.

After testing the FI components the important ones gave good readings. I spliced into the harness to test the resistance of the CHT and some of the others over time. While it seemed to be operating to spec, I discovered CHT would momentarily ground out -- flooding the engine, but not killing it. I repaired the skinned wiring leading to the CHT and fixed some vacuum leaks. Tune up was hard because I only had about 5 minutes to set the timing between warm-up and stall. Doing a valve adjustment gained another 5 minutes. Strange. Determined the AAR was remaining open all the time and made allowance in the throttle screw and the idle mixture knob on the ECU until the motor would start and idle appropriately.

After all that I had a much better running engine until it stalled. Every time after about 15 minutes of idle from cold. At least it wasn't running rich anymore. That turned out to be an important clue.

Brought a length of fuel line into the driver compartment and hooked up my water heater/fuel pressure gauge. Went through the ritual of starting car, allowing it to warm up and waiting for it to die. For the first time after two weeks of fooling with this issue I noticed the pressure drop in conjunction with the hesitation that preceded stall. I'd looked for this before from the engine compartment but I think all the other work prevented the engine from dying so suddenly, so this time I was able to notice some pronounced flickering of pressure right before it stopped running.

The next day I fried the ignition harness. Ironically it was not the wires I was splicing into to test resistance that failed. Ordered a nice harness from Jeff Bowlsby and rigged up a temporary connection with the starter, coil and oil pressure gauge so I could continue with the stall issue.

One problem with d-jet is you can't casually swap suspect components for known good versions to track down a problem. Its either impossible to find them quickly or they are prohibitively expensive to buy just for that purpose.

Found a $31 Bosch in-line electrical fuel pump at NAPA that specified correctly. Maybe it won't last a week but I wasn't sure whether an electrical problem was discontinuing signal to the pump, or whether the pump was failing. Now I know. Money well spent even if it prematurely fails. The old pump was failing. It showed good pressure until it didn't. The new pump works great. Engine starts easily/runs better now

Up on JS right now so no test ride but the car idled relatively smoothly for 45 minutes before I turned it off. Every once in a while I'd rev it to keep the oil flowing and the gas off the cylinder walls. Runs 50 degrees cooler at the Ch tins now. I like to think the bad pump was creating a lean mixture and heat. Big difference from when I thought it was flooding out. The ambient is 20 degrees cooler than before, so that's probably the real explanation.

The "idle quirk" problem appears solved, (IMG:style_emoticons/default/biggrin.gif) now I can go back to testing FI components, fixing vacuum leaksand dialing in the tune.

THANKS FOR YOUR HELP.