"stuttering" disco

What about the ignition system? Had a few bouts of this kind of crap which turned out to be ignition amp related (although a new ignition amp on its own didn't actually properly sort it). If they aren't new I'd slap a new coil, ign amp and probably plugs on it.

That said, I'd have thought ignition problems would be apparent at a certain RPM, not a certain speed.

Does it stutter on hard acceleration only, or on part throttle as well?

You can run with the fuel cap off for a bit to see if that is an issue?

The ECU may have stored a code or two.

I'm assuming it's a V8 by the way you talk casually about 90 mph...

Hi Tim,

yup she's a v8 - how did you guess???

new plugs, leads, rotor arm, dizzy cap so far

Its really noticeable when accelerating, but its still there when holding a speed.

Its defo a speed thing, which leads me to think ecu/sensors - cos all the time we were in low range yesterday (ie under 35mph) there were no problems at all, but the rpms were right up there.

I think the fuel cap thing is a red herring, but there is a definite issue brewing vacuum wise there.

Si

...and Si K spake unto the tribes of Usenet, saying...

I'd be looking at fuel delivery first, from what you say. The times when it is happening are when the demand for fuel is highest - high revs in low box are unlikely to need as much gas, whereas 70-80 on the open road you are flooring it. If you back off to 60 or so, does it go away?

Trial run with petrol cap off, check fuel filters, fuel pump pressure? Lots it could be, but that's where I'd start looking.

Had exactly this problem on a motorbike, turned out to be a blob of dried Simoniz in the breather hole in the filler cap.

On or around Sun, 4 Dec 2005 16:28:59 -0000, "Si K" enlightened us thusly:

could well be. You need to check the tank breathers - IIRC, 4 of 'em linked to a system of pipework that goes off upwards. Bet you find it's blocked.

There shouldn't be vacuum in the tank, period.

Had exactly the same problem on my range rover , spent a small fortune replacing every bit of the ignition . it would only do it at a set speed in top gear every other gear /speed was fine , felt like I was driving over a rumble strip it would splutter and slowdown drop down a gear and it would tale off no problems, back up to 55 same thing would start again ! Luckily I got talking to a bloke who was V8 mad , he said it was the airflow meter and I pointed out I had replaced that but there was still no change he told me that this was quite common as the engine was a bit old and the wiring was not as new so there may be more resistance in the electrical system so it was over fuelling just a bit , and this would only show after cruising in top gear as in lower gear the throttle position is not as constant ie in 4 you would spend more than

So how do you fix it ? well what id did was ( he said he had don this many times ! ) to take the top off the airflow meter mark up were everything was , and take the readings of the resistance of the arm across the variable resister , once this is done identify the wires that the voltage is sent to the variable resister arm .

Ok this is the bit where you have to have a bit of faith ! go to maplins and buy a 10 k varialbel pot one with a shaft on like a volume control then on the airflow meter readjust the variable resister arm so the resistance is slightly lower ( cant remember exactly how much lower I set it , but I think it was less than 10 K ohms ) Cut the wire that is connected to the wiper arm on the loom and connect the pot between the wires with enough wire to go back to the drivers seat .

Take it for a run and get it up to speed , it will be a bit rough to start but if you fiddle with the pot that you now have inside the car you will be able to get it running well , small adjustments are best and give it time to settle down between tweaks.

Once its running fine park up and using a meter read the resistance across the pot AND the airflow meter , you should now be able to remove the pot join the wires back together and set the position of the wiper arm in the air flow meter using the reading you had when the pot was in place !

got the old rangie runnig like a dream useing this method !

hope this helps

Bloody clever. Make sure the pot you get is LINEAR tracked and NOT a volume control, which are Logarithmic tracks. A Maplindroid is unlikely to know the difference.

Steve

ah interesting - it had to have the airflow meter changed to get it going after the failure last week. I've got to get a new meter, as the one on it belongs to Dakar Cars till i get a new one.

will get new meter, then try your method

cheers

Si

Sneaky but I can't help thinking it's a cure without touching the real cause of the problem, a high resistance connection somewhere.

Not relevant as you are measuring the resistance after you have empiricaly tweaked the pot under test. A log pot might make adjustment slightly trickier if it happens to be at the "wrong" end of the pots rotation. In which case swap the fixed end wire to the other end of the pot...