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

[Karl Middlebrooks]

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?
>>
>