[V6-12v] Hesitation

[James4ihl at aol.com]

Tom --

Thanks for those suggestions, helpful as ever.

The engine is basically the same as your 93> 2.8 V6 AAH engines. It just 
appeared on the A80 in Europe, which ran from 92-95, with the A90 discontinued, I 
believe. Whereas in the US, I believe the A80 was discontinued and the 
A90/A100 ran from 93>. There are slight differences in that the Euro models didn't 
require the EGR system, due to different emissions regs, etc. But overall it's 
the same beast. A slight variation on my model is that you still have a MAF 
with a manual CO adjustment available (you set it by reading the output from the 
lambda probes) wheras on the later models this was set automatically by the 
ECU in resonse to the lambda signals).

I cleaned the MAF sensor very carefully with some isopropyl alcohol (I had 
some left over from the days when I had cassette deck heads to clean!) and a 
very fine, soft inter-dental brush (even a q-tip was too large and heavy handed 
for those very delicate wires. Although it hasn't cleared the intermittent 
hesitation problem, the car otherwise responds better under load, and feels more 
like it's raring to go rather than being coaxed. It didn't appear that dirty at 
first sight, but there must have been a slight film of grime because it shone 
a lot brighter after cleaning. Definitely worth the 10 minutes of effort.

Yeah, the fuel pump was replaced a year ago, with no change in this 
particular problem. However, I never thought of the relay. I kind of assumed that the 
relay was closed continuously as soon as the ignition is switched on, but it 
kind of makes sense that if the contacts are dirty you could get a voltage drop. 
I guess the easiest way would be to replace it and see if there's a 
difference.

I'm familiar with the second valve you mention (the Intake Manifold 
Changeover Valve - which swaps between the 'long' and 'short' air intake routes above 
4000 rpm to even out the torque curve) and have checked the function of that 
valve visually (you can clearly see it operate when you rev the car past 4000). 
However, I was not aware of the smaller valve which opens the bigger one. 
Whereabouts is that, exactly? Or are we talking about the same valve?

I had considered a sticky throttle valve, but I think the valve is directly 
connected to the throttle cable (is that correct?) so if that were true, I 
should feel the throttle peddle jam, which it doesn't...

Yeah, the first thing I checked was the air supply. All clean and a new 
filter there.

I'll definitely check out the other stuff though, thanks for the ideas!

James

In a message dated 12/2/04 6:24:03 pm, tomchr at ee.washington.edu writes:


> Was this the one where you had trouble pulling out into traffic because you
> didn't know if the car would bother to make power available?
> 
> I don't know your particular model. I'm fairly familiar with the I-5's and
> the 93-95 V6. But I haven't heard of a 92 V6... Oh, well... I assume it
> works like the 93-95 M.Y. V6.
> 
> I would suspect the fuel pump. If that has already been replaced, try the
> fuel pump relay. I'm kinda guessing in the dark here... But if the contacts
> in the relay have too high resistance, it would make sense that the voltage
> across the fuel pump drops when it tries to draw more current (under
> heavier loads).
> 
> There's a charge-over valve by the throttle body which opens up the second
> (larger) butterfly valve. You might wanna verify that it works. There's a
> vacuum operated valve on the port side of the throttle body which should
> operate when engine rpm is increased above 4000 (even without load)
> according to Bentley.
> 
> Also make sure that the engine can breathe. No dead birds in the airfilter,
> please... But I assume you've already checked it...
> 
> BTW: What did you use for cleaning the MAF?
> 
> Tom