BauerR

Got the 044 pump installed and wired up as well as the 928 Motorsports overflow tank that replaced the stock leaking one.

Fired the car up after getting the pump all wired up and let it run to check for leaks.
After about 5 mins of running from a cold start the car will stall. However, it will fire right back up. (mind you, 5 mins is the longest the car has run since ive owned it. I bought it knowing it had issues but trailered home)
After the car is fired back up it will run but for less time. Despite holding the throttle open, it will still lose all power and shut off. Again, will fire right back up and run and Rev fine...but only a minute or two.

Cold starts seem to net the longest running times.

any thoughts?

Ps, after the car stalls I can still hear the 044 pump run for a second or two, so I feel were good on the pump end

FredR

Sounds as though you might need to prove the LH computer is working OK. Any owner local to you with an S4/GT/GTS that can try to run you unit to see if the problem migrates?

Friend of mine had a similar sounding problem with his S4 a few years ago and my spare LH cured the problem immediately. Not saying this is the problem but ...?

Rgds

Fred

GUMBALL

First try replacing the EZK relay (8th from the left, top row)

Also, consider the Mass Airflow Sensor.

jcorenman

My vote is O2 sensor.

When the engine is first started the LH determines fuel by the maps alone-- fuel map plus warmup. The O2 sensor is initially disabled.

Once the engine temp reaches approx 130F then the LH enables the O2 sensor and begins to adjust the fueling in response to the O2 sensor input. This takes around 5 mins from a cold-start, depending on temperature. If the engine is already warm then the O2-sensor is disabled for only 20 sec or so.

So if it goes sour after 5 mins from a cold-start, and less with a warm-start, then that might be the point where the O2-sensor is enabled. But if the sensor is broken or hopelessly worn out, then the LH will be adjusting fuel based on a bogus reading.

First, disconnect the O2-sensor-- rubber 3-pin connector near the CE panel. If the LH detects no O2 sensor then it continues to run without it-- what messes things up is a bad sensor that is still connected. If the engine then runs sort-of-OK, then replace the sensor-- Bosch 13048. The LH needs it to be able to do the fuel mixture adaptation.

BauerR

The chart that's under tthe dash says the 8th relay over (counting from driver side to passengers) is the electronic ignition system.XVI. XXV is LH on my map.

BauerR

I was going to replace the O2s anyway. I'm assuming they are original and anything on the car that's nearly 30 years old either needs to be replaced or should be.

however, these are the ones I w a s going to order from Pelican. Are they different than the ones you posted?

BauerR

http://www.pelicanparts.com/More_Inf...orter=date_new



sorry, forgot the link

jcorenman

Except maybe the owner...

Yes. That one comes with a DIY connector assembly and the wrong connector, other than that it looks like the correct sensor. It will work but you will need to splice the old connector.

I've used the Bosch 13048, comes with the correct connector and firewall seal, around $70 from Amazon and elsewhere. Factory part is 928-606-128-01, MSRP is $195 (yikes). Also check your favorite 928 parts purveyors.

BauerR

Thanks for the info! I'll order the 13048.


I tested the relay that came out of the LH spot and it seems to be in order, although it had some discoloration on the pins. I replaced it with a brand new one just to be safe. I'll fire up the car in the morning and see if that had any effect.

Mrmerlin

I would suggest that you order the correct O2 sensor not the cut the old plug and play version,
unless you want to do the job twice,

get the part number and do a search for it.

OR get it from Roger he seems to have the best prices

BauerR

The Bosch 13048 seems like the right one.

stupid question, does the 928 only have 1 O2 sensor?

jcorenman

Discoloration could just be age, or it could be heat from a poor contact. Check the female connections in the socket, anything looking toasty there? De-oxit is recommended to keep things clean and shiny.

Yes, just the one, pre-cat.

BauerR

Everything looks good on the board. No luck with the relay swap, though. Car still stalls.

O2 sensor is ordered. I have a friend local who has a 1990 S4 so I'm hoping to try his MAF and LH

ammonman

Be sure to put your LH into his car and see if the symptoms are repeated in his car. Putting his LH into your car risks something wrong in your car like a wiring short damaging his known good LH unit.

Mike

jcorenman

Did you disconnect the O2 sensor? The LH will detect the unplgged sensor, and continue to run using the maps alone-- no adjustment. If it runs OK with the O2 sensor disconnected, but stalls after a minute or five with it plugged in, then the O2-sensor is clearly at fault.

MAF, LH, O2-sensor and temp-II sensor are all part of the "fuel equation", but subject to different failure modes.

MAFs age (hot-wire erodes), which typically causes the engine to run progressively more lean. This is compensated for by the LH and O2-sensor, until the LH runs out of adjustment range. The symptom of an aged MAF is that the car runs poorly after the battery has been disconnected, until the engine warms up and the LH re-adapts: 10-20 minutes of driving, depending. MAFs can also fail completely (broken hot-wire) in which case the engine barely runs (if at all), and only with a part-throttle "limp-home" mode (fixed injector pulse-width).

An LH failure is typically total: engine won't start, just sits there with clicking injectors flooding the engine-- or no injector pulse at all. But there are many sensors and other failure modes. As Mike points out, trying your LH in a known-good car is safer, for example a shorted injector harness will fry the injector-driver transistors.

The O2-sensor is how the LH adjusts fueling to compensate for aging MAFs, engine wear and tolerances, etc. However it is not part of the picture until the engine warms up. And if disconnected then the LH happily does its own thing based on maps alone.

The temp-II sensor also comes into play, the LH adds fuel when the engine is cold, and also uses engine temp to enable the O2 sensor. The sensor rarely fails, but harness problems are not rare.

Try the O2 sensor first, if that resolves it then the LH is fine. (You may still want to get the LH rebuilt just for long-term reliability but that is a separate issue).

And if the engine starts and runs OK after a battery disconnect, and doesn't improve markedly after driving a while (i.e. after the LH does its adaptation thing) then the MAF is probably fine. Your best guide here is mileage, they are pretty much done by 80K or so depending on type of driving-- it is start-stop cycles as much as miles that ages them (burn-off cycles).