Loss of power at low revs

[Guest]

So I'm driving along the M25 this very chilly morning on the way to work, on the road for about an hour and hurtling along at about 15-20mph, when the car suddenly and temporarily loses power. I can only describe it by saying that it felt like I'd stabbed the brake, mishandled the clutch, hit a rev limiter, etc. It only lasted about half a second, if that, and the engine was still running so I continued driving, with a hint of a kangaroo effect for the next mile or so before calming down again. The CD and the heater fan cut out at the point of the power loss, then restarted a second or so later.

Two other new things accompanied the return of power: a faint fast-tick sound, kind of like the sound of rapid static, which seems to be coming from behind the dash in the approximate area of the radio/heater; flickering headlights, very slight but noticeable. I don't know if these two things give a clue to something? It seems odd that they arrived at the point of the power loss but beyond that I'm bereft of ideas.

As I'm a mechanical and electrical novice, I don't know where to start. Has anyone else had a similar thing happen, or can help advise me where to start investigating?

Cheers,
John

 

[Guest]

Mine is in the garage as we speak for a very similar problem. Update from garage confirms it is not air flow meter, DMU chip, ht leads, or spark plugs. They are still trying to work it out (using a rolling road and connecting it up to some computer thing) but this is proving difficult as the problem only occurs occasionally.

I'll let you know what the outcome is when i know. Although I have a fair idea the outcome will involve me going bankrupt paying for all the investigative man hours used trying to locate the problem!

Richard

 

[Guest]

Oh dear............. Well, I suppose from a positive perspective, if they're looking into things so deeply to find the cause then they will find anything else that needs to be done, fixed, replaced, as they go along. Oh, hang on a minute, sounds like an even bigger hole in the wallet.....

In that case, good luck and I'll take a deep breath before I read your post regarding the findings! [&:]

John

 

[Guest]

First impressions are that the fault was a major electrical cut-out, on the basis that the engine/CD/lights etc. all cut at the same time. Could the battery, or the main earth/power connections, or the ignition switch have become disconnected - difficult to prove, apart from generally playing with the main wiring around the battery/ignition switch.
The static noise could be something shorting/burning, or just arcing around a possible loose conection on the ignition switch - no smell, obviously.

 

[Guest]

Hi John,

Thanks for your feedback already. My gut feeling today while thinking about it at work and then noticing some specific additional symptoms in the dark on the way home, is that there is an electrical fault. Just my luck that I was intending to learn about these things so that I could one day troubleshoot when the problems happen - instead I've got a problem already and know nothing about circuits yet. [8|]

With the benefit of thinking about it all day and now having made the drive home I can recount better detail of what happened this morning, plus share the additional things I've noticed on the way back tonight.

This morning:

1. 15-20mph travelling speed (1st gear)
2. CD and lights were on
3. Turned the between-seat control to 10 (it doesn't work at any other setting)
4. Second or so later the engine/lights/CD cut out (fan NOT kicked in yet)
5. Second or so on from that, everything apparently back to normal, fan THEN kicked in
6. Kangaroo wobble effect, fairly mild, fairly high-paced wobble
7. Possible faintest smell of burning, though not sure if it was my imagination
8. The shorting/arcing/static sound seeming to come from behind centre part of dash
9. When arriving at work, noticed flicker in headlights

On way home, noticed this as well:

1. No flicker in lights as I started the journey
2. Applying brakes made headlights dim momentarily
3. Signalling made headlights dim momentarily
4. CD volume dropped momentarily at start of braking or start of signalling but not for duration of it
5. Turning between-seats control to 10 dipped headlights as it kicked in but lights returned to normal when fan was running
6. Fan is now running at irregular speed (so left it off when I realised things are obviously not well)
7. Kangaroo wobble present below around 30ish mph, whether in 1st or 2nd gear
8. Engine idling irregularly when car is stationary
9. Headlamp flicker still there when idling but apparently not when driving - also, I'm pretty sure that the flicker is in sync with the irregular dips in the engine idle speed
9. On turning the engine off having arrived home, the interior light came on, there were a couple of dull clicks as if some electrical switch was operating, and the alarm armed itself.

Does it seem likely (as I'm presuming from a novice standpoint) that the current pull of the fan coming on this morning caused the failure somewhere? Everything still seems to work but the symptoms indicate that something major is seriously amiss. And that's as far as I can guess.

I can look at the battery wiring at the point of where it meets the battery, but I'm sorry to say I'd have no idea how to investigate the ignition or wiring - partly because I don't know how to get to it and mainly because I wouldn't know what I'm looking at (good or bad).

I'm still intending to drive the car to work and back - or is that a foolish thing to do.

HELP!!!

John (hopelessly worried.....) [&:]

 

[Guest]

John

Car electrical circuits I understand, so just ask if you need to.
The idea that turning on one circuit causes another to go dim, and that the alrm came on when the engine was turned off, seems a clear indication of either a bad contact in the primary electrical power circuit, or a battery with an internal problem.

The primary electrical circuit consists of the earth strap from the battery to the car's chassis, and the main cable from the battery to the ignition switch. First thing to do would be to remove these cables from the battery (earth wire FIRST, so that the positive lead has nothing to short out against), generally clean/check, and then re-attach tightly to the battery teminal (in this case, positive FIRST, if both are removed at the same time). The battery terminals might be lose, the lead corroded, etc.

The ignition switch contacts unplug from the back of the switch barrel, I believe, but are awkward to get at/remove/replace, as you generally can see either the switch contacts, or the hand that is trying to remove them. Still, this might give you a chance to check for any 'oddities', but don't do it if you can't get it back on.
Famous last words.

In terms of the centre of the dashboard, all I can think of is the heater switches, or the radio. Never checked them on mine, so ......

I have the Bentley manual, which is good for electrical diagrams, so can help with questions. Email me if you want.

 

[Guest]

John, thanks for the detailed advice. [] Well, I checked the battery and all is OK there, wires were securely attached but I removed them and there's no corrosion so reattached tightly. I had a new earth strap fitted last year and I hoped I'd find it was maybe loose and be the answer but all is visbly. I didn't attempt the dismantling of the ignition as I'm not confident enough that I'd get it back on... [&:] There doesn't seem much more I can do at present... I'm thinking I'll consider dismantling the ignition at the weekend, hopefully with enough time to spend getting it back on.

Thanks agian for your advice John, it's much appreciated.

 

[Signor]

Greetings
For what its worth, it definitely sounds like an earthing fault somewhere. If you look around the fuse box area and behind the "board" that runs from left to right across the back of the dash, (held on by four 10mm nuts I think) in the front luggage compartment, you should find some common earthing posts attached to the bodywork. Maybe one of them has worked itself loose!
Sometimes a little corrosion [&o] will cause a high impedance connection and all sorts of problems accure as the electrical components try a find a better earth route,(have you ever seen someone indicating which causes the rest of the light cluster to flash out of phase!).
I believe there is also an earth strap on the gearbox which could be iffy?
Hope this is of some help
Alex Kovac (alias Signor)

 

[Guest]

Thanks Alex, I'll see if I can get a look at that. I haven't seen anything that looks bad so far but I'll investigate until the problem is located, which could be some time!

 

[Guest]

ORIGINAL: rs

Mine is in the garage as we speak for a very similar problem. Update from garage confirms it is not air flow meter, DMU chip, ht leads, or spark plugs. They are still trying to work it out (using a rolling road and connecting it up to some computer thing) but this is proving difficult as the problem only occurs occasionally.

I'll let you know what the outcome is when i know. Although I have a fair idea the outcome will involve me going bankrupt paying for all the investigative man hours used trying to locate the problem!

Richard

Well, I've not found anything that is obviously wrong, so I don't know what could have caused my initial problem. The only thing lingering since the incident is a bit of a slight lurching behaviour (as if the throttle is being gently stabbed, if that makes sense) in 1st and 2nd up to around 3500 revs.

Richard - did the garage find the cause of your problem? The symptoms seem similar to the ones I've had so I was wondering if they located something that might shed some light on what happened to mine.

John

 

[Guest]

Seems like it may be a stab in the dark but as you have mentioned a couple of times, the heater control needing to be on 10 to work and on several occasions this coincided with your fault ,do you think it could be a short in the solenoid for the automatic temp control? Maybe not enough to blow a fuse but significant enough to pull the voltage down to cause your other problems
Ian

 

[Guest]

John,

After much searching the garage found a "fractured" wire connecting power to the injectors. The fracture the reason why the sudden & total loss of power only occured periodically and for a fraction of a second. Anyway the new wire did sort out this problem.

since then (about 300 miles later) I have had further problems with a "fluttering" occuring at speed. This has been diagnosed and corrected by a reconditioned air flow meter. In the circumastances I am surpised the car was capable of moving at all two months ago, what with no current to the injectors a knacker airflow meter.

All back to normal now though.

Richard

 

[zwhitea]

This has been diagnosed and corrected by a reconditioned air flow meter.

Out of interest how much did the AFM cost you as I sure I've got a fault on mine, which I've currently corrected for its MOT by borrowing the one of my partners car.. []

 

[Guest]

Its will be about £150 for a reconditioned AFM. The garage has loaned a spare while mine is refurbished so haven't had the exact bill yet.

 

[Guest]

ORIGINAL: CTJM

Seems like it may be a stab in the dark but as you have mentioned a couple of times, the heater control needing to be on 10 to work and on several occasions this coincided with your fault ,do you think it could be a short in the solenoid for the automatic temp control? Maybe not enough to blow a fuse but significant enough to pull the voltage down to cause your other problems
Ian

Now that I've returned with a list of tools to buy after visiting Bones, I'll see if I can take something apart and have a look! [8|]

 

[Guest]

ORIGINAL: rs
since then (about 300 miles later) I have had further problems with a "fluttering" occuring at speed.

What do you mean by "fluttering" exactly? I'm experiencing a kind of mild kangaroo effect in 1st and 2nd, and a sudden lurch if I lift off the throttle, so I'm wondering if that's an air-flow problem as well. [8|]

 

[Guest]

John,

No the fluttering is only a slight traceable judder, the feeling of slowing you would get if you hit a large patch of water on the road after a down pour. The kangeroo effect you mention was (in my case anyway) electrical current failing to get to the injectors and thus the engine being momentarily starved of fuel.

Richard