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Lumpy delivery of low down power

2K views 20 replies 6 participants last post by  unsavoury 
#1 ·
Drove a mile to work, all was fine.

Drove 10 miles to a friends after work, roof down, all was fine.

Left there and drove 10 miles home in the rain and all the way home the power delivery was lumpy low down. Below 3000 revs if the throttle moved at all the power delivery went all over the place from nothing to getting thumped in the kidneys.

Also got a squeak from some sort of belt (I think) every time I changed gear.


So, a spot of googling says it's a MAF or a coil pack.

Does that sound right and is this a colossal pain in the arse or a smile fix?


Thanks all (again)
 
#2 ·
Sounds like a misfire and your alternator drive belt needs tightening slightly.

Have you scanned for and error codes yet? That may help determining the cause of the misfire. If you don't have a code reader, then dampness caused by the rain will most likely have been a factor. Start by having a spray around with WD (water displacement) 40 and checking all ignition components for signs of damage, wear or just being lose/badly connected. If its dark, you can sometimes even seen stray sparks in the engine bay, pointing to the cause of the misfire. You might even be able to hear the slight crackle of sparks going to earth too.

The alternator belt should be a simple fix, or it may need replacing if obviously worn or deteriorated. If in doubt, replace it - if that belt gives way, its not uncommon to take your cambelt with it resulting in a wrecked engine.

Be methodical and don't assume anything. Good luck.
 
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#3 ·
Thanks for this, very comprehensive and very helpful!

I don't have a code reader unfortunately, I know a bloke with a generic one though, does that work? I think the ZT needed a specific reader.

I thought it was probably something to do with the rain, I also am very aware that this car hasn't had any TLC its whole life and as such needs a lot of grease and WD40 etc. smeared in all sorts of places, being not too technically minded though I worry about spring it in the wrong places. Any tips on what and what not to spray once I'm in there?

It was serviced a week ago and I think they did the spark plugs then, could they have done something wrong?

More googling says I should be checking my HT leads while I'm there?

Sorry for all the questions, I am a real novice but keen to learn.

Thanks
 
#4 ·
Sounds like, as you suggest, it's the rain. The alternator belt on mine isn't quite tight enough and can squeal a bit in the rain. I has very bad misfiring a while back which came and went and eventually got really bad. Changed the plugs, HT leads (not the coil packs though, as they're expensive - I wanted to see if other things worked before I changed them) and cleaned out the IACV (idle air control valve) and everything was alright. Probably it was the HT leads. WD40 might be a temporary fix, spray on your leads, but be wary of it bursting into flame if you have corona/sparks from your HT leads ;0)
 
#6 ·
It's near the inlet manifold at the rear of the engine hatch (you need to remove the hatch to get at it, but then, you need to do that to get at the HT leads anyway). I recall it's on the rear engine compartment bulkhead, midway along, near the top. It's a pain to get at it though - there are two screws that are fouled by the inlet manifold. I can't recall exactly, but I think I tried a cranked screwdriver and gave up, then did it with a 1/4" wobbly stubby ratchet with a posidrive insert.

I'd search the forum for 'IACV' if you want detail. Try the HT leads first.

As for your alternator belt, it's never a bad idea to change it, but it's a bad sign if when you inspect it it has crosswise cracking. That would be a belt well past its sell by date. The trouble with the alternator belt (well, one of them) is that often the belt tightening adjuster screw is seized. It may snap off. Then you have to tighten the belt manually, levering the alternator with some tool in an appropriate place to get the belt tight, then tightening the bolts. Rule of thumb is that it should be tight enough so you can deflect it 1/2" either way at mid span with a bit of force, or twist it through 90 degrees at mid span.

Also, I changed my alternator belt from the driver's side wheel arch, but the bolts are stiff and I needed to be resourceful with impromptu levers against the wishbone and crankshaft pulley to get enough force on the bolts to break them free. I also needed a 15mm deep ended (cranked) ring spanner for one of the bolts. You would attack it from the hatch, which I hear is easier, but I'm not sire if you still need a 15mm cranked ring spanner still from that angle.
 
#9 ·
Try the plugs - examine them for colour and gap/erosion. Also, for similarity of colour between all four.

Have you got an OBD reader for any fault codes - or one of the better ones for live data?

May be a process of elimination needed here, replacing stuff, pain in the backside but often it's the only practical way.
 
#10 ·
I don't have an OBD reader no, I shall do a spot of googling and see if I can get one if it will be helpful.

The car was serviced a month ago and the plugs changed then so I can't imagine they are the problem.

I think it's running a bit rich and its idling quite high, that combined with today's overheating is making me think maybe thermostat?
 
#11 ·
Is your fuel pump priming properly?
You should hear it whir for less than 3 seconds when you turn the ignition on.
I understand that a misbehaving fuel pump can cause loss of power on accceleration and
lumpy engine behavior.
Easily replaced if this is your problem.
 
#16 · (Edited)
and you should not, for any reason , put wd40 on your plug leads, the plugs, insulators, coil packs, terminals or any other part of it.

its an oil based lubricant using an evaporating penetrant to get the oil in the same place as the penetrant.. which then evaporates leaving the oil behind..

its not good for plug leads because oil is an insulator.. so any defect.. or flaw in the lead is now insulated.. if its got an oil film on it.. its also not going away.. because the oil protects it from changing.. its like covering the flaw in paint and pretending its not there. a tracking fault or insulation flaw in the lead is now hidden... but still there just because you put wd40 on it, it hasnt gone... its still there.

being an insulator - oil is not something you put your brand new spark plugs in before you put them in the engine... is it? so why spray them with a penetrant containing oil - ever?

why change the properties of an insulator by adding something like oil and penetrant fluid to it.. without knowing for certain what you are doing? some oils degrade insulators for example..

coil packs were never made covered in oil, its not in their spec.. its not part of their service requirement.... so why are you doing that?

a terminal relies on contact.. and oil is an insulator... so it stops contact.. it insulates... so oil on the terminal.. no contact.

:)
 
#18 ·
and you should not, for any reason , put wd40 on your plug leads, the plugs, insulators, coil packs, terminals or any other part of it.
Well it's got me going a few times when I've had tracking on damp leads, granted the leads may well have been past there best. It's also a cracking water dispersal when you need to get a soaking wet electric meter and diss board back in service pronto.
 
#17 ·
WD40 is an oil-based substance, but is not really a lubricant. It was developed to achieve water dispersal, hence the 'WD' in the name. The '40' bit came about because it was the 40th formula the chemist who invented it tried. It is also an insulator, but electrical contact between metal surfaces is achieved through high pressure point to point contact (micro cold welding) between high spots and WD40 cannot form a film which can prevent that.

The utility of WD40 is that it really does displace water and moisture quite well, so if the OP suspected he had a problem with surface tracking of his spark through a moist conductive surface layer, WD40 can test for it. Good as a test, if not necessarily a permanent solution.

This is why after steam cleaning of an engine they go through the spark electrics spraying everything with WD40 to try and eliminate the inevitable moisture which seeps in. Well, that's what they did last time I had an engine steam-cleaned, years ago mind you.

The only worry I have with the stuff is whether it affects rubber/silicone rubber on a long term basis - I have no idea - but as an aid to diagnosis as to whether you have HT tracking problems, it is very useful IMO (although, it is as well to wait a few minutes before starting the ignition as it gives off some volatile vapours and I did actually once succeed in lighting it as my spark leads were tracking to earth so badly ;0)
 
#20 ·
If you don't have the engine cover off it will be faint. It suggests the pump is working but unfortunately they can have intermittent faults.

Have you changed your fuel filter recently? Always a good idea even as a service item.
What car do you have? If its a vvc, with the coils mounted at the bottom of the engine, the ht leads have to be kept away from the
crank position sensor or they will interfere with the signal causing some 'interesting' effects.
 
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