The saga continues (was T44TQ MC2 stumbling)

[Ameer Antar]

About the air temp sensor, the readings you got sound strange. Actually,
the sensor reading while plugged in should be 400-700 ohms (I assume at
shop temp). Also the second and third test (28.38 in Bentley) just test
that the wires from the ECU to the sensor are clean. If you got 143 ohms
from one pin on the ECU and the sensor, what was the reading from the same
pin on the ECU to the other lead of the sensor? If it was higher, then you
have bad wiring. If it's in the 400-700 ohm range, yer ok, as long as
swapping the other ECU pin does the opposite. If this is confusing, follow
the 3 steps in the Bentley exactly and you should be able to diagnose it.

Although this seems like a sensor issue, have you checked the air-flow
meter flap for sticking? This could also be a sticky fuel dist. plunger, as
that might reduce the amount of fuel metered, esp under accel. There are
many sensors that affect the CIS and ignition systems. If all of attempts
lead to uncertainty, following all the Bentley test procedures might be
worthwhile. It would take quite a while, and you might not be able to do
all of them. But hey you never know what you might find out of spec, even
though it may seem OK...

If you're thinking there is trouble w/ the cold start system, you should
just pull the CSV on a cold day, aim into a glass jar and start it up. This
is pretty easy to do. There's a graph in the Bentley that shows you how
long the CSV should squirt according to temp. Problems in the CSV could be
the valve itself, bad thermo-time switch, bad coolant sensors (there are
actually more than the multi-temp sensor), wiring of the sensors, or even
fuel not getting to the CSV. If the CSV system is OK, I'd also check the
system and control pressure. It's important to watch the pressure rise, cuz
something might be stuck inside the warm-up regulator. In diagnosing you
should be sure you can prove a part is working correctly. If your not sure,
and you find something else wrong, don't just drop the first part, unless
you can prove it. Sometimes, there are actually a few different problems
acting up at the same time, which leaves you more frustrated, even though
you may have replaced a broken part...

good luck.

-ameer

At 07:40 PM 10/6/2002, you wrote:

>To: QSHIPQ at aol.com, sjmauto at attbi.com, t44tq at mindspring.com,
>         quattro at audifans.com
>Date: Sun, 6 Oct 2002 18:59:46 -0400
>Subject: Re: The saga continues (was T44TQ MC2 stumbling)
>From: Larry C Leung <l.leung at juno.com>
>
>This message is in MIME format.  Since your mail reader does not understand
>this format, some or all of this message may not be legible.
>--
>[ Picked text/plain from multipart/alternative ]
>At the moment, I believe that the air temp sensor in the IC
>is possibly suspect. The main question is, can the air
>temp sensor affect cold starts? If so, how? Does a sensor
>that acts as if the air is warm prevent the cold start valve
>from firing? What end of the resistance range is considered
>cool? Hot? From the Bentley, all I can figure out is that the
>range of resistances that are acceptable are from 0 to 700 ohms
>with the sensor plugged into the circuit. Measured resistance
>of the lines from the sensor to ECU is about 143 ohms.
>
>Symptoms:
>
>Car stumbles on acceleration under load, or struggles under
>load intermittently.
>
>Acts like it's either retarded or starved for fuel, SOMETIMES
>recovers when backing off of the gas and re-applying, though
>this doesn't always help.
>
>Worse at part throttle under boost, though sometimes goes totally
>flat even at full throttle.
>
>Worse when the car or air is warm
>
>BUT, won't start when it's cold without pumping the gas, even then
>sometimes won't start totally cold if it's cool out.
>
>Gets full boost, and then some, wastegate is shimmed. Stock ECU,
>never have hit fuel pump shut-off. ECU can reach a sustained 1.5
>bar with an occasional blip of 1.6 on the dash gage.
>
>
>Background of repari attempts:
>
>So far, have eliminated vacuum leaks as the problem. Used Ether
>based starting fluid and even manipulated the rubber parts while
>spraying, no effect.
>
>Passes weakly the dipstick test, (stumbles but doesn't stall, stalls
>when oil filler cap is lifted.)
>
>Cleaned ISV and Crankcase breather.
>
>1 month old Multifunction sensor, and plug wires.
>
>1 - 2 year old cap, rotor, plugs, visually check well.
>
>New Fuel filter
>
>Freshly cleaned air filter (K&N)
>
>Clean and checked air temp sensor (engine cold) 407 ohms,
>
>                       550 ohms at the ECU
>
>Codes: First two codes - Bad OXY sensor, over-rev
>                                                 reset -
>
>                                                 Run car after new fuel
>filter
>
>                                                 Air temp sensor
>
>                                                 reset
>
>                                                 Air temp sensor
>
>Rechecked the air sensor - 550 at the sensor.
>
>So, is the sensor showing enough heat to warrant a ignition retard
>or not? looks like if seems to respond to longer runs under boost
>with more stumbling, however, traffic doesn't allow a real test of
>this.
>
>Any ideas?
>
>Thanks for all of your help.
>
>LL - NY befuddled
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>
>
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