Technical It's doing my head in...

[Jim Haseltine]

It's not often I have to ask for advice about cars but my daughter's Seicento Sporting is doing my head in. It's recently started doing the self-revving thing (revs between 1000 and 3000) all the time, it's so bad that she doesn't feel in control when driving it. I've searched the forum and changed both the temp sensor (it didn't seem right when I tested it) and the idle control. It's made a difference - most of the time it now 'idles' at over 3000 and when it doesn't, it's back to the varying revs. Not only that, it seems to be running rich, it's very difficult to restart when warm and runs on too.

This is going to sound like and episode of Fast and Loud, but I've got 3 weeks to sort it and I'd rather not resort to another gallon of unleaded and a match.

 

[lazybones51]

Sounds like an air leak from one of the vacuum pipes to me. Give them all a check, if you spray WD40 or something similar around them and the engine note changes, you will have found the area with the leak

 

[Eklipze3k]

Vacuum leak was gonna be my guess too.

 

[fingers99]

:yeahthat:

Especially common on SPI cars.

 

[blu73]

agreed... line to map sensor is first line i would check if your happy its not the idle control valve. Temp sensors tend to result in over fuelling and not erratic idling.

 

[Jim Haseltine]

I've already replaced part of that pipe (the piece between the inlet manifold and the plastic unit which I assume is either a vapour trap or a check valve), I'll do the other part.
Although I doubt this has anything to do with it, there are two thin vacuum lines fiited to a valve in the airfilter box which I'd guess control whether the intake air is cold or warmed by the manifold - does it matter which pipe goes where?
Changed the plugs as I couldn't remember that they'd ever been changed since she bought the car - the blackest sootiest plugs I've every seen. Is the #1 plug really awkward to get to or was it just me?
This car has had just about every common Seicento fault over the last 6 years, duff speedo sender, failed thermostat, leaking fuel tank and worn clutch bushings. Rev counters seem to only last about 18 months too. Timing belt tension roller lost it's bearings as well, leaving it stranded in Leeds on Xmas Eve.

 

[blu73]

I've already replaced part of that pipe (the piece between the inlet manifold and the plastic unit which I assume is either a vapour trap or a check valve), I'll do the other part.

little square thing under a metal mount near the ecu?? thats the map sensor.

Although I doubt this has anything to do with it, there are two thin vacuum lines fiited to a valve in the airfilter box which I'd guess control whether the intake air is cold or warmed by the manifold - does it matter which pipe goes where?

don't really need these ones but you could have a leak on them lines, any leak anywhere on the inlet side will cause erratic amounts of air going into the engine which is what results in erratic idle - a constant leak (for example a vac line has come off completely) means there is more air than there should be resulting in a high idle. Could try just removing these pipes and blocking them off completely to see if it makes any difference.

There is also a vac line to the charcoal cannister which is under the passenger arch behind the liner on a sei from the rear of the throttle body on both spi and mpi i think (I'm not great on mpi cars as never had one, is it spi or mpi just for the record?)

Changed the plugs as I couldn't remember that they'd ever been changed since she bought the car - the blackest sootiest plugs I've every seen. Is the #1 plug really awkward to get to or was it just me?

Black plugs is of course running rich but its a bit hard to say anything about that without knowing when you changed temp sensor and thermostat and stuff, stuck open stat results in very long warm up times (if they warm up at all) and so is on choke all the time. Similarly if temp sender is bad it can run super rich all of the time. I wouldn't expect plugs to ever cause high idle and erratic idle though but can't hurt having fresh in

 

[Jim Haseltine]

little square thing under a metal mount near the ecu?? thats the map sensor.

No, the pipe from the manifold to the map is in two pieces with a cylindrical plastic unit about an inch long and same in diameter in the middle - looks like either a check valve or vapour trap. I've changed one piece of the pipe, I'll change the other tomorrow and take a look at the other pipes too.

 

[blu73]

sounds like non-return valve on the map sensor line (well i have always assumed its a one way valve, never actually looked at on in any detail) - again that thing isn't really needed, i only ever seen a few sei's with that thing still there so you could also try replacing it with one piece from the manifold to the sensor as i guess that valve could fail as well.

 

[mrcinquecento]

yeah, i'd go for a one piece pipe too on the map. No idea why you'd want or need a valve in there on the map line,

it's a bit like on the windscreen washer pipe, they always come with a one way valve on them too, no idea why, they just fail and need removed.

Top tip, if they ever fail when you're out and about, a capri-sun straw makes a perfect on the fly replacment

My guess if there's a vacuum leak would be servo pipe, i forgot to put mine on once after a rebuild and it revved around 3.5k at idle and was surging all over the place just like that.

 

[cc1]

I think the inline valve is an arrestor to protect the sensor from being damaged by over pressure from a backfire in the intake manifold.
The ones on the washers are check valves to stop the fluid from emptying out the pipe back in the tank.

 

[blu73]

learn something new everyday.. that does make sense i suppose as i guess that cause quite a bit of pressure, i know from having turbo cars they can take a few bar of positive pressure no problem but thats not quite a backfire haha

 

[Jim Haseltine]

Right, after two weeks of having to fix other vehicles I got back to the Seicento today. Replaced the manifold to MAP hose/plastic thingy with one piece of hose and the car now idles (sort of) without the self-revving. It's still rich and when idling has a hint of a miss. Playing around a bit showed that removing #4 plug lead made no difference to the way it was idling and there are sparks tracking down the rubber of the connector so I'm going to replace the plug leads.

 

[5000Kg]

maybe low fuel pressure.
when fuel pump die slowly, injector havent close completely and always leaking.

 

[fingers99]

Unlikely -- it only has one injector -- SPI car.

 

[blu73]

well as we know there is an issue with plug 4 lets just wait and see what happens with new plugs and leads before we start hypothesizing anymore

 

[Jim Haseltine]

New plug leads - no difference.
When cold it starts on first turn of the key and idles around 1K revs with a hint of a miss. Once it's run for long enough for the fan to kick in it idles around 500rpm and if stopped won't restart unless the accelerator is hard on the floor and then I have to play with it until it settles down - again at around 500. The exhaust pops a bit too.
Tomorrow (weather permitting) I'm going back to first principles with a compression test.

 

[Jim Haseltine]

Compression test was ok - hardly any difference between cylinders either.
As for running rich, these are the plugs that I fitted 3 weeks ago. Car has only been run in the drive since then - no distance on the road.

 

[fingers99]

Swap plugs round. Does misfire swap with plug? If yes, replace plugs.
If not, swap coils round. Does misfire move? (Rare, but not impossible for coil to fail on one plug only.)

Failing that, if SPI engine, my guess is a mechanical issue. Compression test, dry and wet.

Tricky one, though.

High idle usually = inlet side air leak (all the hoses, inc. servo hose, on the inlet side, plus the inlet manifold gasket, plus the TB base gasket, possible culprits).

Failure to restart when hot may implicate coolant temp sensor.

If engine is missing on one cylinder, ignition/compression issue.

 

[Jim Haseltine]

Right, some movement. Solved the rich mixture (I think), noticed that when the system pressurised there was fuel dripping onto the throttle plate even if the injector electrics weren't connected. There was some corrosion at the bottom of the injector bowl which was letting fuel leak past the bottom sealing ring.
There's still a hint of a misfire though which by moving the coil packs and running the engine with just one connected seems to be the signal to the pack for cylinders 1&4. Both packs work ok when on 2&3 but both show the same miss (maybe once every 5 seconds or so) when running 1&4.
I'm going to take a look at the TDC sensor.