S/C VX power loss at higher speeds

[Immortality]

2 faulty sensors does seem unlikely.

I would find a wiring diagram and check the earth point for the O2 sensors and go from there.

edit: I can't seem to find my wiring diagrams

I'd check over the wiring looms and see if there is any damage and clean all the wiring earth points on the engine.

 

[lout]

haven't weighed in on this post yet
my first suspect would be catalytic converter
second suspect would be fuel pump/module
the SC V6 has a two speed pump, i suspect yours may be malfunctioning

 

[Mid-life Chrysler]

Cheers Immortality........I think that's probably my logical next step.

Thanks also to Lout for taking the time to write. I have a new hi-flow cat that was fitted as part of the headers/exhaust setup so it's only a month or so old. What symptoms would I expect to get if it was stuffed? If it was the fuel pump, would I not get fault codes to show that? I'm dubious it's a fuel supply problem as it's very predictable; I can run smoothly from traffic light to traffic light without any concern. As soon as I hit 80-90 km/h, however, it loses power and responsiveness and displays the check engine light (I can power through the lag if required). I can virtually hit a stretch of road now and predict when the check engine light will appear. Mind you, I'm no guru by any means so am not disregarding your suggestions. Rest assured they're now added to the 'WTF is the answer!?' column.

 

[lout]

a blocked cat will have maximum power until the backpressure before the cat is high, then engine will have little more than idle regardless of throttle command
coasting will relieve backpressure until next time you accelerate (as you can power through will not be this)
fuel pump will not log a code but engine will log a code for running lean (O2 sensor) or something similar (sounds a small possibility)
as mentioned a CEL code 13 no signal left hand and 63 no signal right hand suggests faulty sensor or wiring, as both are affected i would suspect wiring or ECU
did you have these codes before fitting non genuine O2 sensors
if engine loses O2 sensor signal, engine will use stored fuel trim tables and richen mix up and retard timing slightly
when you power through lag does CEL then go off or stay on until next key cycle
i would hook up a scan tool and go for a drive and see what the O2 sensors are up to when you get to 80km/h etc
FYI the O2 sensors earth through the engine earth harness and also receive an earth from ECU

 

[Mid-life Chrysler]

Hi again,

Thanks for the heavily detailed reply! I'm glad you feel the cat & pump are less likely than the wiring/ECU option, if only because it keeps things heading in the general direction they already were. Nothing worse than having a handful of possibilities and trying to find the answer.

To answer your question, the codes only appeared after the after-market sensors were installed (even though the problem was present both before and after this time). The CEL will always disappear after a short while regardless of how I'm driving. Even on the motorway each day it will predictably appear then vanish within 10-15 seconds. It can do this a good 5+ times in one 30 minute journey to work or back.

Out of curiosity, is an auto-electrician the best bet for this type of diagnosis/repair? Anything electrical is not really my area of expertise (not that I really have one where cars are concerned)! :embarrass

 

[lout]

possibly an autoelec but someone with a dyno would be best bet
FYI fault 13 and 63 do not actually mean no signal as in open circuit, they mean so lean that it is outside range of O2 sensor
monitoring fuel pressure under load is much easier on a dyno

 

[Nut Kracker]

2 faulty sensors does seem unlikely.

I would find a wiring diagram and check the earth point for the O2 sensors and go from there.

edit: I can't seem to find my wiring diagrams

I'd check over the wiring looms and see if there is any damage and clean all the wiring earth points on the engine.

From what I can work out from the diagrams etc.
The earth points for the O2 sensors are here, as high lighted.
(Increase the picture size to around 150%, you'll see it in better detail).

The Black/Red wire is the earth for the O2 sensors and is the same colour back to these points.
View attachment VX Earth points 1.pdf

 

[Mid-life Chrysler]

Lout - thanks for your explanation re. the O2 sensors; makes perfect sense and correlates with the original dyno which gave the very lean results. I'm lucky that the local dyno guy is also an auto-electrician by trade so it's a perfect match for this situation. I spoke to him this morning and he wants to run it at those troublesome higher speeds to get an exact reading. I hope to get to him within a week or so and will keep you posted.

Nut Kracker - cheers for the diagrams which are now saved to my PC. I appreciate your assistance.

Thanks again and talk soon.

 

[Hrd455]

So did u end up finding the problem

 

[Mid-life Chrysler]

So did u end up finding the problem

Hi all, I just realised I never left a final update which was rude (and unintentional) on my part. This is the first time in a long time I've logged back on so wanted to finally provide an update.

Long story short, after fitting the PEC o2 sensors and with the problem continuing, I was at a loss. The dyno/auto electrical guy ended up removing the sensors and replacing them with Bosch ones which, at the time, annoyed me as I thought he was milking me for extra dollars. Until I drove the car, that is. It ran like a dream and the problem was gone in an instant. The o2 sensors were the issue all along and had unknowingly been replaced with faulty/incompatible ones. Replacing them with the Bosch set was all it took.

Again, a belated and sincere thanks to all those who helped me at the time.