[V8] Do bad/dirty sensors always throw codes?

[Tony and Lillie]

The coolant sensor wiring ends up plugging into the ECU. I'd recommend 
replacing that plug and wiring, you can get a repair kit from autohausaz.com

Tony

----- Original Message ----- 
From: "Karl Middlebrooks" <benzeenprophet at hotmail.com>
To: "Tony and Lillie" <tonyandlillie1 at earthlink.net>; "Audi V8Q Mailing 
list" <v8 at audifans.com>
Sent: Wednesday, February 18, 2009 4:02 PM
Subject: Re: [V8] Do bad/dirty sensors always throw codes?


> Ah, OK. Thanks for the info. I feel a little bit better now.
>
> I just pulled the MAF, and while I don't have a multimeter with me here in 
> Oregon, the only thing I could see that might have been a problem was a 
> little bit of corrosion on one of the terminals, which I cleaned up.
>
> I went to pull the coolant temp sensor, and I can find where it connects 
> to the back of the passenger side cylinder head, but from there, where 
> does it wind up? It the other end of it the connector that's on the bottom 
> of the coolant reservoir? I pulled the connector that's on the back of the 
> back of the cylinder head and it seemed to be seated well, with no 
> corrosion, but the hard plastic that's mounted to the cylinder head is 
> cracked, so that the wires are exposed; the wires are intact, though, so 
> I'm not sure what I should do.
>
> --------------------------------------------------
> From: "Tony and Lillie" <tonyandlillie1 at earthlink.net>
> Sent: Wednesday, February 18, 2009 1:19 PM
> To: "Karl Middlebrooks" <benzeenprophet at hotmail.com>; "Audi V8Q Mailing 
> list" <v8 at audifans.com>
> Subject: Re: [V8] Do bad/dirty sensors always throw codes?
>
>> I have a little btidbit of BTDT on mine.
>>
>> First a background. I bought my V8Q (1991 3.6 auto) in 2003, with 253k on 
>> it. One of the things stated as wrong with it was that it took two or 
>> three times to start the car from cold. When I picked the car up, I 
>> didn't know how bad the problem really was, because it was already 
>> running.
>>
>> After MUCH troubleshooting, I found the ECU was bad. I put a 1990 ECU 
>> from a parts car in there, and the car has started right up when cold 
>> from then on.
>>
>> Now, when the car had the problem at first, I would occasionally use 
>> starting fluid to start the car. Well, when I say "I", I really mean 
>> Lillie, as it was her car. One morning, I got a call that the car 
>> wouldn't start, even with the ether. So, I came home,and it started right 
>> up. Well, what I didn't realize is that the car backfired when she was 
>> trying to start, and burned the pool of ether that was in the intake. In 
>> the process, it badly burned both the intake temp sensor, and the MAF. 
>> There were no indications that this had happened. However, over the next 
>> several months (years) milage slowly dropped from 25 hwy to about 21 hwy, 
>> and power was a bit down. As it got worse (eventually about 15mpg hwy) 
>> the car would billow black smoke and had a noticable power decrease. I 
>> had a 4-wire that had been replaced several times, and new 
>> caps/rotors/plugs. New FPR also. Well, long story short, I pulled it one 
>> day as a reference for a project, and noticed how burned it had become. 
>> Put another on there, and the problems I was having were gone.
>>
>> In this time, I pulled codes at least 10 times, the only code I ever got 
>> was something along the lines of "Idle control rexceeded maximum 
>> specification". So, long story short, yes, sensors can go bad without 
>> throwing codes.
>>
>> This is one significant difference between newer cars, and the pre-obd2 
>> cars. Now, they compare a # of variables, and if one component doesn't 
>> read correctly, it throws that code. On my car, only unplugging the MAF 
>> threw a MAF code, despite the fact that the readings were WAY off.
>>
>> Tony Hoffman
>>
>>
>> ----- Original Message ----- 
>> Subject: [V8] Do bad/dirty sensors always throw codes?
>>
>>
>>> On V8 #2, my starting point was a car that got 10mpg, was as loud as a 
>>> Harley, little power on acceleration, and it just feels like the engine 
>>> is missing.
>>>
>>> After working on the exhaust (replaced clogged cats and rusty exhaust 
>>> pipe), swapping out the FPR, and disconnecting the OXS, among other 
>>> things, the car now gets 14.3mpg in town and has more power, but it's 
>>> still not right. Still lopes a little and feels like it's missing on 
>>> acceleration, though appears to run smoothly once up to speed.
>>>
>>> Only code I've ever gotten is 2341. After disconnecting the OXS, I get 
>>> 2342 (which sounds like what I should expect with the OXS disconnected).
>>>
>>> Other folks with similar performance problems have replaced/cleaned the 
>>> MAF and coolant temp sensors, according to the archives. However, I'm 
>>> not getting codes for either of these. Is it possible that the sensors 
>>> are contributing to the problem, but not enough to result in a code?
>>>
>>