[V8] Help Diagnosing V8 Fuel Problem...

[Gene Caldwell]

1) I was under the impression that the sequencing test only identifies 
whether the injector solenoid is getting electrical power and is not frozen.
2&3) I took the 5 injectors from my 91 200q20v to a local marine service 
shop.  They also do a lot of injector ultrasonic cleaning and testing, 
checking patterns and flow rates.  The injectors were in fairly good 
shape before the service, but the engine was still smoother afterward.
4) I had a similar sort of "constrained fuel delivery" sensation in a 
Jetta once.  It turned out to be a failing fuel pump relay.  It was 
actually a solder joint cracking from mechanical stress of weight of the 
relay mechanism.  A little resoldering and some epoxy to more firmly 
hold the parts in place cured the problem.   But that was a known issue 
with that vintage of VW, I haven't heard of anything like that for the 
V8.   But I've always been told that the constant speed stumble (surge?) 
can be a symptom of an O2 sensor issue.

-Gene

Korn, Bob wrote:

>I appear to have a similar issue with my V8.  It appears to be fuel delivery
>issue.  I have a stumble or miss, very noticeable at highway speeds when
>holding a constant speed.  You can hear the motor go flat for a few seconds,
>then clear, then flat, it seems like fuel delivery is being constrained in
>some way.
>
>I have new wires, plugs, caps and rotors, pulled plugs and all appear even
>in appearance, a little lighter brown than what I would consider normal,
>however I'm not certain I know what they should look like.  I'm used to a
>nice light chocolate brown color on a properly running motor. 
>
>Recently replaced O2 sensor within last 15K.  Checked the wire splices on
>the O2 sensor last night, great shape, I used those screw together
>connectors with the rubber boots around them, they have worked great.  Good
>test recently as we have received a couple inches of freezing rain, sleet,
>slush and snow combination the last couple days, excellent Quattro weather!
>Also put new fuel filter on, and lubed center ujoint and emergency brake
>cables while under the car. :-) 
>
>1. I understand we can sequence through the injectors and listen to them
>buzz-Will an injector buzz and still not deliver fuel, I assume a clogged
>injector will still appear to function with this test.
>2. How can I test for injector performance?  Clogged, damaged tip, etc?  
>3. Can you take the fuel rails and injectors, as an assembly, to a shop to
>have them run through a cleaning process?  Or does this require the rest of
>the car for some reason?
>4. Any other ideas?
>
>Thanks!
>
>
>Bob
>90 V8Q  134K Pearl Gray Sports
>
>  
>