480 Turbo Auto (1991) Idle issues & plugs fouling.

[stan_deezy]

The first thing I'd ask is what were the ambient air temperatures like when the fault occurs and in comparison to when you checked the car over?

Also, was the air damp when the fault occurred and dry when you checked it over?

If the air temperatures were different then perhaps sticking a multi-meter on the coolant temperature sensor and checking the values against the known ones (would think that the 480 forum might have this info?) just to make sure it's not the sensor.

The dampness question is simply to see if it's a weakness in the HT circuit, although I'm unsure if these engines have HT leads or pencil coils?

What about the wiring from the lambda back to the ECU? (I'm also wondering if the lambda isn't actually used at idle as in some systems I'm aware of, which means it could be discounted straight away?).

I know I'd probably wait until it did the "bag of bricks" idling again and immediately switch off and check the state of the spark plugs just to see if it was a single cylinder causing the issue or all of them.

[Paul240480]

The first thing I'd ask is what were the ambient air temperatures like when the fault occurs and in comparison to when you checked the car over? Been chasing this 'fault' for over a year, it occurs all times of the tear and in all temps.

Also, was the air damp when the fault occurred and dry when you checked it over? It's been checked in various weathers, but usually soon after the fault shows - so in similar conditions. I can't stick it down to a damp weather fault I'm afraid

If the air temperatures were different then perhaps sticking a multi-meter on the coolant temperature sensor and checking the values against the known ones (would think that the 480 forum might have this info?) just to make sure it's not the sensor. Thanks, will do. The coolant temp sensor was replaced in 99 by the 'indie' I purchased it from.

The dampness question is simply to see if it's a weakness in the HT circuit, although I'm unsure if these engines have HT leads or pencil coils? It has HT leads, they are only about two months old from GSF

What about the wiring from the lambda back to the ECU? (I'm also wondering if the lambda isn't actually used at idle as in some systems I'm aware of, which means it could be discounted straight away?).

I know I'd probably wait until it did the "bag of bricks" idling again and immediately switch off and check the state of the spark plugs just to see if it was a single cylinder causing the issue or all of them. I've checked the plugs mant times when the fault happens & all four have been sooted up.

Thanks for the lengthy reply you've obviously given it a lot of thought

I've been out today & used contact cleaner on all of the leccy connectors including the ecu multi-plug. Added a smear of vaseline to for good measure.

I then tried upping the resisrance on the maf from factory setting of 386Ohms to 450. Went for a motorway spin of about 20 miles & the mpg dropped to 23.7 :cry:  So its back at 386 now!

Strangely enough, I checked the plugs again today & there was no sign of 'sootyness'. Normally after a weeks use they would have started to foul. So maybe making a step in the right direction.

I'm in contact with a chap who has a (very low miler) 460Turbo Auto & he's getting 30.8mpg.

Maybe mines at rebuild point?

Do GSF supply compression testers? Maybe one of those would tell me if the motors on it's last legs..................

Thanks again Stan

[stan_deezy]

No worries Paul, I have been scratching my head with this one  :lol:

Compression test would be a great idea. What is your oil consumption like?
(I'm also thinking here about the turbo)

If the coolant sensor is now 9/10 years old then yes, I guess it's possible it's past it's best.

I'll keep head-scratching!  :lol:

[Paul240480]

Okay, I'll get teh temp sensor checked tomo' (off out today - not in the 480 :lol: )

Oil consumption is vertually zero between oil changes, which I do every 6K

Tried to get a comp tester here the other day. Local motor factor scratched his head and said 'whats one of those?" :lol:

Most web-shops I've found so far will only deliver them in UK. Including AmazonUK & AmazonFr don't stock them. Weird!

[Paul240480]

Okay we decided not to go out due to naff weather.

So I've just tested resistance of the temp sensor. Not quite sure what the result I got says. Thinking I'm not very good at this :oops:

Haynes says "Resistance at 20c should be 2500 Ohms +/- 300".

So started her up temp reading on the computer said 'Cold' (obviously) ran for a while & first reading it picked up was 40 degrees.

So switched off, unpluged sensor and it gave me 1.26 (with my Hilka multi-tester set at 20k - if I set it at the next lowest setting of 2k it shows a reading of 1 which is 'overload').

So does this reading mean 1260 Ohms & therefore well below the correct spec'?

Or am I just doing it wrong. I don't think I am, as it works fine when testing resistance on the maf.

If it helps, with engine running, unplugging the sensor causes a slight rise in idle speed.
cheers.

[neo]

Have the fuel and air filters been changed yet?
Throttle body been cleaned?

[Paul240480]

Thanks, yeh fuel filter about 20k miles and 2 years ago. Air filter in July this year and about 3k miles ago tops.
Throttle body & tps within the last week, idle valve too.

Gotta be a sensor issue or some worn wiring on a sensor, but can I find the
 :shock:  thing.

[stan_deezy]

I'd change the temp sensor  


Edit: just thinking about this a bit more, if the sensor works the way the vast majority do then the trick I've used in the past is to get the engine warm, disconnect the sensor plug and bridge the two pins with a piece of wire, fooling the ECU into thinking the sensor is working and up at max temperature. If that sorts the idle issue then it's the sensor.

The one other sensor that can give you similar issues but tends to be more reliable is the air inlet temp sensor.

Oh, and I've also seen this fault occur simply due to a duff thermostat.

[Paul240480]

Thanks again Stan, good ideas there. Got quite a few things to try now.

Just gotta get SWMBO out of it for more than 5 mins :lol:  so I can have a go!

Air inlet sensor , would that be the MAF? If yes it was replaced in 02' under warranty from the 'Indie' I bought the car from.

Mmm thermostat, now that's one thing I have no record of ever being changed......... should hae done that when I got my radiator from gsf methinks :oops:

Cheers again.
Ooh, could a duff coolant temp sensor cause a reduction in MPG aas well as idle issues?

[stan_deezy]

There should an air inlet temp sensor somewhere in the system, I'm not entirely certain that the maf will do both jobs but that's based on similar systems rather than the specific one here.
The air inlet temp sensor would be somewhere on the inlet piping, possibly close to the maf, but like I said it depends which system is used in your car.

I'd still be inclined to swap out the coolant sensor as it can cause the very issues you are complaining about: poor idle, fouled plugs and poor MPG, all because it's telling the ECU that "the engine is stone cold and would it mind injecting heaps more fuel please?"  :lol:

[Paul240480]

Okay Stan, reckons you could be onto something there. I've emailed Julie at London to see if she can supply one for me.

In the meantime,

Had another look at things today. Plugs still okay. Car is running well. Pulls well etc. However still at 23.7 mpg.

Re-checked Coolant temp sensor. Engine Cold, (Tester at 20k) got reading of 8.73 (does that mean 8730? __ :shock:)

At 80Degrees got .45 (450?).

Is this acceptable?

Used the diagnostic box again Got a 1:1:1:  So no snags there then?

Now, this was funny.
Whilst in test mode with ignition on. The following happened in this order

1) C/locking, locked then unlocked itself
2) Horn blipped (nearly jumped out of my skin)
3) Drivers door went down a couple of inches
4) Front wipers did one sweep
5) Windscreen wash squirted

Bizzare.
_______________

[stan_deezy]

The readings you are getting suggest the sensor is working  

Don't know what you did to trigger all those "circus car" type faults though!  :lol:

[Paul240480]

Er, yes I do now. Following another reply on 480-europe.

When you use the diagnostic-box.
Press once & it tests out-going info from ecu
Press again & it tests info coming into ecu
Press again & it does a sequence of tests - ie: windows, wipers,washers,c/locking.

[stan_deezy]

That's clever!  :lol:

[Paul240480]

BTW, have now, sadly sold the 480 Turbo. 'He' went off to Amiens, about a 500 miler & made it with no probs :

Is now subject of a rolling resto', by someone with more 'ability' than me :lol: