cis-e operation with going/bad o2 sensor

[amalventano at sc.rr.com (Allyn)]

after more investigation:
coolant temp sensor - good
airflow sensor plate potentiometer - good

now for the weird:

i noticed every time i went to start the fuel pump would spin *quick* and 
promptly spin down to normal speed before cutting off. basically the pump 
had to build up fuel pressure over and over again every time i went to 
start. i found it takes no more than one minute for pressure to bleed down 
fully. normally i would suspect the pump discharge check valve, but somehow 
this thing is getting near-flooded during startup, combined with fuel smell 
during idle, leading me to believe the fuel is bleeding into a cylinder (or 
all cylinders). i checked the cold start valve, no leakage. this leaves 
either one of the injectors or something in the fuel dizzy (unless im 
missing something - which is why im posting here).

Al


----- Original Message ----- 
From: "Allyn" <amalventano@sc.rr.com>
To: "scirocco list" <scirocco-l@scirocco.org>
Sent: Thursday, July 01, 2004 4:30 PM
Subject: cis-e operation with going/bad o2 sensor


> this is on the passat, but its still the same cis-e so it applies to 
> basically all of us with 16vs.
>
> just wanted to bounce this off of the list to make sure im not off on my 
> diagnosis.
>
> symptoms:
> - low power while driving (no misses, just not as much power as there 
> should be)
> - at idle:
> -- idle speed constant, but engine stumbles slightly every 4-5 seconds, 
> then recovers
> -- noticable smell of fuel
> -- dpr current fluctuating at ~6mA +/- 1mA (fluctuations follow stumbling)
> -- o2 sensor voltage fluctuating between 0.2 to 0.8 VDC (also follows 
> stumbling, and fluctuates more than i normally see)
> -- manual adjustments of sensor plate, bringing DPR to various readings 
> (3mA, 10mA, 15mA), all yield the same symptoms (stumbles, fuel smell), 
> once DPR stabilizes.
> -- manual adjustment of sensor plate beyond the DPR range (adjusted 1/2 
> turn beyond hitting the stop at ~16.5mA) yields smooth idle and no fuel 
> smell. (for those not DPR savy, this action forces the management to run a 
> tad leaner than it wants to based on o2 sensor feedback alone).
>
> i think its the o2 sensor. while its still functioning, it appears that 
> the voltage is lagging behind what is actually going on with the exhaust 
> gasses, causing the management to hunt excessively.
>
> have i missed anything obvious here? any other checks i should do before 
> ordering a replacement o2 sensor?
>
> thx in advance for assist.
> Al
>
> Allyn Malventano, ETC(SS), USN
> 87 Rieger Scirocco GTO 2.0 16v (daily driver, 200k, rocco #6)
> 86 Kamei Twin 16V Turbo Scirocco GTX (33.3% complete, rocco #7)
> 86.5 Occo 16v Trailer (rocco #8)
> 90 Passat GL 16V (the wifes new daily, 200k)
>
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