P38A 4.0hse won't rev

OK, new MAF, plugs, leads (bitch), air filter and an oil change.
It's definitely better now than it was. Still not convinced it's quite right though.
Still feels a bit lazy between 3k and 4k then its off like a stung horse.
Any suggestions what to look at next??
(got new cats on order, and new back boxes. Centre box is already new so that might improve it)
What are the O2 sensors like to get out? Will I be looking at a new pair when I change the cats?

Wazzajnr said:

OK, new MAF, plugs, leads (bitch), air filter and an oil change.
It's definitely better now than it was. Still not convinced it's quite right though.
Still feels a bit lazy between 3k and 4k then its off like a stung horse.
Any suggestions what to look at next??
(got new cats on order, and new back boxes. Centre box is already new so that might improve it)
What are the O2 sensors like to get out? Will I be looking at a new pair when I change the cats?

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Utter bar-steward from what some people have described on here. Never done it myself.

Grrrrrr said:

Utter bar-steward from what some people have described on here. Never done it myself.

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Think I'll order a pair of new ones then! Saves the hassle and being stuck without the car till I get them. It could even be the O2 sensors not working properly that's causing it not to run perfectly so might as well bite the bullet!

Wazzajnr said:

Think I'll order a pair of new ones then! Saves the hassle and being stuck without the car till I get them. It could even be the O2 sensors not working properly that's causing it not to run perfectly so might as well bite the bullet!

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If you've got gas and can heat them up I am guessing they might come out easier.

No gas axe here. I have a blowtorch somewhere but not sure if it's enough. I'll just buy the new ones. One less thing to worry about then. (just got an order for a nice job this morning so I can justify a bit more money on it!!)
Got to order new airbags, shocks, discs and pads as well. Oh and a brake accumulator......... Oh and a brake pedal switch to get the CC working....... Oh and a.......... Repeat ad infinitum.......

Cruise is normally the rubber vacuum hose. Brake switch rarely fails.

Grrrrrr said:

Cruise is normally the rubber vacuum hose. Brake switch rarely fails.

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Switch is definitely not working. I managed to make it work for a while by glueing a small block of plastic to the top as it wasn't touching the pedal. Not sure if the bracket is bent or not. Might need to sort the vacuum hoses too but until the switch is right there's no point going any further.

Wazzajnr said:

Switch is definitely not working. I managed to make it work for a while by glueing a small block of plastic to the top as it wasn't touching the pedal. Not sure if the bracket is bent or not. Might need to sort the vacuum hoses too but until the switch is right there's no point going any further.

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Stop lamp switch is easy to reset. Remove it, pull plunger out depress pedal and refit switch. Return pedal to set switch. There MUST be a make and break action on the two circuits in brake switch. For cruise you need both brake switch and vac release to be working on petrol models.

The brake switch has to be set for height iirc you push the pedal down pull the plunger out then let the pedal back up to set it.
bugger to slow again

OK, I'll check it. On Nanocom, it shows the stop light switch changing when I press the pedal but the brake switch (not sure exactly what they're called) doesn't change state even if I press the switch by hand.
Was late last night when I was looking so I need to have a closer look.

Wazzajnr said:

OK, I'll check it. On Nanocom, it shows the stop light switch changing when I press the pedal but the brake switch (not sure exactly what they're called) doesn't change state even if I press the switch by hand.
Was late last night when I was looking so I need to have a closer look.

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Fit a new switch then. They must change state as pedal is pressed. As pedal is pressed the then made one activates the brake lamps the break one switches the cruise off.

wammers said:

Fit a new switch then. They must change state as pedal is pressed. As pedal is pressed the then made one activates the brake lamps the break one switches the cruise off.

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Cheers wammers, I seem to remember that both contacts were in one switch but I might be mistaken, it's a while since I last looked at it.

Wazzajnr said:

Cheers wammers, I seem to remember that both contacts were in one switch but I might be mistaken, it's a while since I last looked at it.

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Yes the brake switch has two modes. They must switch sense when brake is pressed. Also on the petrol there is a vacuum release switch on the brake pedal. As pedal is pressed the vacuum release switch disengages the cruise vacuum and the made brake switch is broken to switch cruise off, the other brake switch circuit is made to apply stop lamps. If the cars speed has not dropped below 28 MPH pressing resume on the steering wheel will return the cruise to the previously set speed.

When we went to do the oxy sensors on George, they were in tighter than an Aberdonian's pocket!

We heated them and eventually they came out, but at cost...they stripped the threads on the pipe, but luckily we were able to re-thread both sides and insert new ones.

The cats also didn't want to play, snapping the studs and stripping one thread. Again, we were able to re-thread and insert bolts.

Use the OE stuff if you can.



Ended up cutting in half and using a socket to remove the knackered ones...



As you can see, the blackened mess of soot was caused by mice! Little blighters chewed through 3 of the leads.



Cat's didn't look that old and there were no obvious noises or damage so we re-installed them



George is a happy bunny for the most part, but I have noticed she hesitates and sometimes gives a pop upon sudden acceleration like at a roundabout,so my first port of call will be the MAF and give it a dose of electrical contact cleaner.

However, if your cat(s) have fallen apart I would say your oxy sensors died a while back and have been murdered by large amounts of fuel. The lack of power and hesitation is usually caused by the ECU enriching the mix and keeping it that way to compensate for the lack of signals from the sensors. New cats, sensors and boxes if you can. If they broke up the bits will be clogging up the system somewhere and if the exhaust gasses cant get out,power will be down.

OK folks. Full new exhaust (apart from centre section which was new anyway) and cats and O2 sensors and once again it's a bit better but I'm still not 100% convinced it's absolutely right.
Is there anyone in the northwest with a V8 petrol that would be happy to take me for a spin in theirs so I can see how it compares to mine.
I'm just not sure if I'm being harsh on the poor girl or if she really is suffering.
That said, she's just driven 1000 miles in the last 2 days so I'm currently very happy with her.

just time your accelerations between various speeds such as 30-50, 30-60, etc. Then anyone can compare.

But remember it's a 2 ton RR not a race car.

pwood999 said:

just time your accelerations between various speeds such as 30-50, 30-60, etc. Then anyone can compare.

But remember it's a 2 ton RR not a race car.

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Yeah, it's not so much a lack of speed that I'm bothered about, I'm not expecting it to be super quick.
It's just that there seems to be a dead zone in the middle to high end of the rev range on full throttle.
In other words, let's say I'm cruising along at 60mph and then hit a long hill, it starts to slow down so push the pedal down. At first, it's OK, keeps the speed, but anything from about half throttle seems to make little change. Eventually it will kick down one gear, but then doesn't sound so smooth and still not much "go". Eventually it'll kick down another gear and above 4.5k revs upwards on full throttle it goes OK but still doesn't sound quite as smooth as I expect.
Now, it might just be that that's how the torque curve is and I just have to accept a bit of caning it up long steep hills. (there's lots of them in Czech)
That's why I would like to see what other V8's drive like so I can decide if I have a fault or if that's just the way they are.

I'm starting to wonder if your Cruise Surging and Midrange Revving issues are related ?? They both require speed inputs, so maybe the ECU's are getting different info to the speedo ?

pwood999 said:

just time your accelerations between various speeds such as 30-50, 30-60, etc. Then anyone can compare.

But remember it's a 2 ton RR not a race car.

Click to expand...

Yeah, it's not so much a lack of speed that I'm bothered about, I'm not expecting it to be super quick.
It's just that there seems to be a dead zone in the middle to high end of the rev range on full throttle.
In other words, let's say I'm cruising along at 60mph and then hit a long hill, it starts to slow down so push the pedal down. At first, it's OK, keeps the speed, but anything from about half throttle seems to make little change. Eventually it will kick down one gear, but then doesn't sound so smooth and still not much "go". Eventually it'll kick down another gear and above 4.5k revs upwards on full throttle it goes OK but still doesn't sound quite as smooth as I expect.
Now, it might just be that that's how the torque curve is and I just have to accept a bit of caning it up long steep hills. (there's lots of them in Czech)
That's why I would like to see what other V8's drive like so I can decide if I have a fault or if that's just the way they are.

pwood999 said:

I'm starting to wonder if your Cruise Surging and Midrange Revving issues are related ?? They both require speed inputs, so maybe the ECU's are getting different info to the speedo ?

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Now, there's a thought. I never thought that there could be two signals and one of them wasn't good.
Someone did suggest doing some data logging so I'll have a look into that.
Never done it before. I did put an SD card in the nanocom in anticipation of trying data logging but never got round to it!