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?

[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?