Hi, I'm new to this forum. I have a 1990 CQ and I have been experiencing problems. I have a code 2341.

The car was running great, then one day it went into limp-mode. Found out the fuel pressure supply line was leaking, so I fixed it. The car started running awful, so I did a tuneup, replaced the cap and rotor, all new spark plugs, and a new bosch fuel filter. Still had an issue, so I traced it to a bad fuel injector. Next I replaced all the injectors with the 034 motorsports fuel injector upgrade. Following that I still had a CEL.

So now, I am stuck. I still get a 2341 code (translated to 02 sensor control limit exceeded). I experience slightly longer starting time, somewhat fuel odor, and limp-home mode. The fuel pressure gauge I installed recently shows a residual 40psi which eventually drops to zero. At idle the pressure is 43-44 with vacuum, and without vacuum the pressure goes at most 54-55psi.

Does anyone have any ideas? I am automotive graduate, but brand new to Audi, let alone the rare 90' CQ.

 

I have a '90 coupe with a similar injector kit.

Your chassis production date is post March 1990?

- Perhaps the engine isn't warming up, or the car doesn't know it's engine has warmed up?
- When does the CEL occur?
- What does your water temp gauge indicate?
- How much vacuum does it pull at warm idle?

When I got it, approx. 5 years ago, my engine had numerous vacuum leaks, from the big black Elbow between the MAF and throttle-body, to several small vacuum fittings and hoses at the rear of the Intake-manifold. These may be found by visual inspection, the manifold vacuum can be read with a Mityvac. Another suspect, the crankcase vent-tube which connects to the above elbow was updated in a factory bulletin.

The O2 sensor can be metered in use, for function and condition.

Please come back and post your results.

 

Check the CTS(Coolant Temperature Sensor) How much of resistance do you see when engine warmed up(600 ~ 900? ohm if my memory right) and check power at connector. some time loose connector makes problem too.

 

* It is pre- March 1990 production.
* The CEL occurs when the car reaches a particular temperature, and typically noticed when at hot idle. On 100 degree plus ambient temperature days it will reach the temp and CEL much faster. (see attached picture)
+I am able to make most one way trips without limp-mode but if I run errands, I end up stranded or "limping" home with my warning lights on.
*The vacuum pulls 18Hg at hot idle.
*****When I last checked the residual fuel pressure today, it was approx. 50psi.
I dont know how hot it is getting under the hood but its getting to be pretty dang hot.



Thanks in advance.

 

I agree check or just replace the coolant temp switch. It's white and will go in one of the metal coolant tubes. The switch is around $31 online.
0280130040

With 240K and no idea when it was changed there is a chance it just plain wore out.

This sensor will as it states not be able to determine the coolant temp so it will stay in a warm up phase and you will run rich.

I had the same thing happen on my 88' and that was the exact cause. Replacement instantly fixed the issue.

 

The reason I was asking about the build date was because of a note I saw regarding your particular DTC (which said that this one applied to late build cars only?), which I thought was strange. I also have an early build.

Perhaps that the CEL occurs "when the car reaches a particular temperature" is key. It may be that normal enrichment is taking place and the ECU is waiting for the engine to reach normal op. temp. However, at a certain point it <i>knows</i> this should have happened, it times out on the clock, and lights the CEL.

Your 1st photo may be showing what peak temp. the engine coolant reaches on a 100° F day, correct? If so, I think that your T-stat may have failed <i>open</i>. The two heavier bars (@ 11:30 & 01:00) on the gauge face indicate the normal temp. range, which you haven't got up to yet, but should have on such a day.

My only caveat to the above is how the H2O gauge, and separately the ECU; are fed. But IIRC, the ECU gets it's signal separately from the signal sent to the temp gauge, so one may be just confirming the other. I'll have to do some reading, perhaps someone else here can point me towards a reference?

Your 2nd photo shows oil temp. is also low for a 100° F day? How long had the engine run when these photos where taken?

Perhaps you don't get a great deal of heat out of your heater (except that ambient air is 100° F!). A better check may be of both rad. hoses, are they really hot?

All your fuel pressure behaviour sounds fine.

Besides the CEL, which other warning lights come on?

18Hg vacuum at hot idle sounds reasonable enough, this may also be pointing away from vacuum leaks as possible causes for limp mode in the check-list.

 

As for the build date, the door jamb and diag. connectors say my Audi is an early build date. I noticed the firewall has what looks like a VIN number across it, but the digits don't match the window and door tags.I could be mistaken. This vehicle has quite a number of previous owners from my knowledge, so it could be a "Franken-Audi".



In regards the coolant temperature sensor, I intend to replace it this week as soon as I can. I normally would test before part replacement, but its cheap enough and it gets pretty hot under the hood.


The picture was taken after a "spin" taking the car up the highway several miles, to raise the temperature. Then another several miles back home, and after leaving the car to idle, the light comes on. The ambient temperature that day was mid-high 90's, so the coolant and oil should have been heated enough.

The water temp gauge has never really gone up high towards the marks since my ownership. Like you said, there has to be a separate sensor reporting to the cluster, unless the cluster is out of spec. For the oil temp, I haven't seen it go very high either, but under the hood the car gets pretty hot. If the gauges work fine, then the sensors need changing.

I'll report back when I change the sensor. When I get the chance during the day I'll try measure the temperatures of the radiator hoses to see how the t-stat checks out.

T.I.A.

 

No updates yet, but I was on ALLDATA and I found out that the computer uses the coolant temp. sensor, and the gauge supposedly uses the electronic thermoswitch aka MTFS water temp sensor. This was confusing at first but the thermoswitch looks a little different and coincidently also has 2 pin connector.

 

Oops...didnt know how to edit my post. *MFTS* multi-function-temp-sensor

 

The brown 3/4 pin multi relays the temp to the gauge in the dash and also upon very high temps your warning light.
The white two pin does most of the work when it comes to the motronics and running rich or running in a loop if it no longer functions.

I replaced my brown switch recently, you dash temp will be dead if this sensor dies otherwise you can drive without issue.

The white no so much.

As they say start simple and work your way up. Replace the white temp and use OE Bosch, all the other off brands might create and issue.

If this does not cure the problem you eliminated one potential and work your way up.

Last item would be the "brain" as they cost a fortune and generally don't go down.

If you have no record of when the thermostat was replaced and you think it has been 60k+ miles for the $14 or so it would certainly not hurt to replace it.

Go OE on this one which is usually Wahler but sometimes Behr.