Mattman928

It's didn't come in to play in my situation. Most of the folks I talked to, indicated it was a likely suspect.

MBMB

Update:

Fuel pressure is 50-55 psi.

WOT switch is functioning correctly (actually, it's closing at about 90% throttle instead of 3/4).

Temp II behaves suspiciously -- resistance is a little high (maybe 100 ohms), but not off by an order of magnitude. I'm replacing the Temp2 Thursday, not because I think it's far enough off to cause my trouble but because I want to positively eliminate it as a cause.

If the problem recurs with a new TempII (spelling it 3 different ways so the search engine finds it :-) ) I'll plug in a friend's LH brain and see what happens.

Jim @ EuroWerks

Stock at idle is supposed nto be about 48 psi, that does'nt sound like your problem. When John ck'ed our LH he found that the WOT switch was tripped inside the control unit.

MBMB

Since all sensors (except TII, which I'll replace) seem to test right, I've borrowed an LH brain locally. My plan is to run the car with my brain until it starts running too rich, then shut down, swap brains, and try to start up again. Any problem with this plan?

As to the TII sensor (AKA NTC 2), a question for the EEs in the crowd: is it possible that a component like the TII sensor will test fine with an ohmeter, but will actually read wrong (more resistance) when the ECU sends more current through it?

SharkSkin

Mark, this is highly likely. There are several feet of wire between the ECU and the sensor. What this means is not that the Temp II would necessarily read different, but that it would be seen incorrectly by the ECU. To see if this is the problem, the first thing is to disconnect the ECU and Temp II and check between the Temp II pin on the connector to the ECU and the connector to the Temp II. There should be essentially no resistance. Now check between that wire and ground. Should be infinite resistance. Does the Temp II have a ground connector? check that too, should be no resistance.

Another possibility is the ECU may not be sending the correct reference voltage... swapping it should identify that eventuality.

worf928

That's an interesting FP value.

Is that an idle value or a 'blip' reading?

At idle the FP should be around 48 psi.

With a throttle blip the FP should jump to 52 - 58 psi.

Maybe you already checked this, but, I re-scanned this thread and did not see if you checked whether or not you are getting vacuum to your FP dampers and regulator. With no vacuum the FP will be higher than 48 psi.

MBMB

Dave A -- wiring to Temp II sensor checks out OK. I'm doing all sensor measurements at the LH ECU connector now.

Dave C -- this is an idle FP value. How should I best check for vacuum to damper and regulator?

worf928

Disconnect the vacuum connections to the dampers and regulator. If the FP jumps by 5+ psi then you had vacuum. If it doesn't you don't. You should also hear a change in idle speed for a second or so (the idle loop will compensate for the FP change quickly.)

While you're doing that - if you have a hand vacuum pump - you can see if all the lines are ok. Vacuum lines can collapse and not flow. (BTDT)

Also, with an inspection mirror (or really long skinny fingers) you can check the main vacuum connection to the dampers. It connects to the underside of the throttle body then to a five-way connector, and then to the dampers and regulator (one end's plugged.) If the line to the throttle body becomes disconnected your FP will jump to 55 psi. (BTDT)

MBMB

Okay. Disconnect regulator vacuum, FP jumps by about 5 psi (from 49 at idle when just warmed up). Reconnect it. Disconnecting rear damper, FP jumps by about 2 psi. Reconnect it. Disconnect front damper, no change -- FP remains at ~49 (vibration in needle makes it hard to tell exactly). Hook the mityvac up to the front damper vacuum line. 16in Hg (not a real tight connection to the mityvac, so the actual vacuum may be a bit higher). Hook the mityvac up to the front damper and draw a vacuum. No change in FP.

???

worf928

Good news is that is sounds like you do not have vacuum problems.
I will defer to the opinions of others more-knowledgeable than I - but, since the front damper is supplied from the fuel pump itself the behavior you describe seems interesting. When you disconnected the vacuum to the front FP damper did you hear any idle change at all?

With everything re-connected, when you blip the throttle linkage from idle do you see the pressure rise into the 52+ range?

worf928

Wait, you posted, earlier, that your idle FP was 50-55.
Now it's 49.

???

Did the idle pressure really change?

MBMB

50-55 at idle after running for a while and failing. Things that make you go "hmmmm"? I'll double check.

I'll also try the other things you suggest . . . tomorrow (my 9-month-old son has the room next to the garage).

worf928

Yup. Perhaps redo that vacuum check when you see the FP at 55.

It shouldn't do that. The LH computer and O2 loop are convinced that the operating pressure is 48psi. The no-vacuum activated pressure 'bump' exists to provide a bit of extra fuel due to transient demand during throttle opening. If it is always at 55 then you might ummm... run rich. Except when you get on it - in which case you might be a tad lean.

MBMB

From the beginning, people were saying, "it's the LH ECU." But I figured that the mode of failure meant it was something under the hood. Finally, after eliminating every possible culprit under the hood, I borrowed a brain and swapped it out. Guess what? Problem solved; it ran like a dream.

Like an engineer friend of mine said, "it's non-linear. These cars have personalities."

Yes, I am a doofus, but at least I'm a doofus who now knows his car really really well.

worf928

Great! I'm glad you found the problem.
And you know if anything else is busted!

Did you redo the FP pressure check?