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Discussion Starter · #1 ·
Hello folks,

I found this forum a few weeks ago and have dropped in a few times to search your tech archives. It's been very useful and I'd like to thank you all for sharing your knowledge. Anyway, I thought I should introduce myself before wading in with the questions :)

I'm actually here on a friends behalf - he doesn't have internet access but he has owned a '95 155 1.8 8v Silverstone for a couple of years now.

He's had several years (mostly) trouble free motoring from the car, but recently when it went for it's MOT it failed on the emissions test (9%!).

He tells me the car was always hard on fuel, with 24mpg the average regardless of how he drove it. However it passed it's MOT last year no problems.

My friend is a competent old-school mechanic but has always avoided working on the alfa because it was fuel injected and had an ECU. I, on the other hand am teaching myself mechanics with a fuel injected Pug 205 so I have few qualms about a bit of sensor diagnosis.

This is getting a bit long winded so I'll try and get to the point.

The plugs indicate the car is overfueling. The coolant temp sensor and throttle position sensor are working. The 4-wire heated oxygen sensor is reading a 12v constant on the heater wires and a fluctuating reading between 0.1v and 0.458v. There are no obvious vacuum leaks and the air filter is clean.

Oh, and the ECU is outputting a 4-4-4-4 when I connect a test light to pin 8 of the ECU.

What are we missing? Why such bad fuel economy and why such a high CO2 reading? Is the lambda sensor sending the wrong signal to the ECU and causing overfueling? Would a busted CAT give such high readings?

Any help or even just a fresh approach to this would be greatly appreciated. The more my friend and I try and figure this out the more confusing it seems to get. Thanks in advance,

chief
 
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Discussion Starter · #2 ·
Hi Chief
I too have a Silverstone (1994) and find I get about 26mpg regardless of how I drive it. At the last MOT, the emissions test was repeated on my car as it failed the CO level at fast idle (2757rpm). I didn't own the car at the time.
The test read 0.48% (limit is 0.3%) for CO.
The HC test was 49ppm (limit 200)
The lambda reading was 1.03 (limit 0.97 - 1.03).
This is right on the limit, could there be a problem here ???

At the rerun, the CO content dropped to 0.18%, HC to 47ppm and the lambda to 1.01.
The CO level at tickover was 0.05% (limit 0.50%).

I would suggest that whatever part tells the ECU how much fuel is needed (or something like that) during running at revs higher than idle could be faulty.
This would account for the high fuel consumption aswell.

Let us know if you discover the problem, there are probably a few people putting up with poor fuel consumption.

Good Luck

Marlon
 
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Discussion Starter · #3 ·
This is all very technical and totally beyond me but over at the alfaowner site, there is a guy called Numan who hangs out there (excuse my phrasing). I think he's actually a mechanic from Norwich way who works in an Alfa Garage(?)He's a bit good with this densely techno stuff. There is actually a 155 section, perhaps if you posted your question there you might have a bit more luck.
BTW, hi everyone, haven't been here for a while, sold my 155 (eventually), got the 156 Selespeed, love it to bits and spend a lot of time on the aforementioned site. Miss some of the banter here though and Wrinx who swings both ways (Alfaowner and 155.com of course!) suggested I might like to visit again....hope y'all don't mind. Greetings everyone. PS if any of you think you've got problems, the brand new 147 owners over there wink are all tearing their hair out with electronics faults, bless 'em.
 
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Discussion Starter · #4 ·
Thanks for the replies guys. Marlon I'll post here again when we figure it out. Clive, thanks for the info - I'll go and check out the alfaowners site.
 
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Discussion Starter · #5 ·
Hi Chief

Welcome to the forum wink

Did the MOT tester do both emissions tests? Mine failed on the idle but passed on the fast idle. This seems usual for Alfa's as they are on the limit.

The obvious answer here is the oxygen (lambda) sensor but I dont know if the values you quoted are correct or not.

A busted cat would cause the car to fail, whats the mileage on the car? Never heard of one failing on these forums.

If I rememebr correctly, 4-4-4-4 means no fault!!

BTW, we also have our own "techy" on 155.com who has helped us out with some excellent advice.......Jimybob's the man :D

Hope you get it sorted.

wrinx
 
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Discussion Starter · #6 ·
Thanks for the welcome wrinx. It's good to find another friendly forum (I'm a 205 owner but don't hold that against me :) ).

I don't know the results of the MOT fast idle test, but we did our own using a Gunsons gas analyser and CO2 did drop on part throttle but was still high.

It probably is the lambda sensor but we want to test as much as possible before we start replacing parts.

The cat's done 80k. Also, the car's been bump started which we've heard is very bad for a cat? Can anyone confirm this? Also if the cat is done could it be the sole cause for such a high emmissions reading?

Re the 4-4-4-4 ECU reading, it's supposed to mean no faults - but we disconnected the coolant temp sensor and repeated the test and it still read 4-4-4-4 so we could be doing the test wrong.

I look forward to hearing from Jimybob. In the meantime thanks for the help, keep it coming :)

chief
 
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Discussion Starter · #7 ·
could well be the lambda or the water temp sensor. 9% is very high the fast idle test is done at between 2450 and 2800rpm on most cars..one thing to point out to you all when you go for your MOT make sure its not left ticking over in the yard before the emissions test CATS can overheat and give mile high readings and they take ages to cool off there is a specific temperature at which the cat 'lights up'..on your way to the test station drive the car hard(not fast)4000rpm for a mile should do it i know it sounds crazy but it cleans out all the crap and warms up the cat just nicely
 
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Discussion Starter · #8 ·
Chief

You are not supposed to bump start cat equipped cars as it pumps unburnt fuel onto the "honeycomb" which is very bad and will destroy the cat. However, a garage (I no longer use!!!) said they bump started cars all the time with no problems!!!!

The advice from Jimybob is good, take the car for a decent run prior to the test. The test equipment shouldn't start to test until the oil is up to temperature but its not always enough for the cat. I'm told it can take about 10-12 miles for the cat to reach proper temperature (feel free to correct Jimybob!)

Still not convinced its the cat thats at fault, the apparant overfuelling seems to be the problem which points to the oxygen sensor again.

wrinx
 
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Discussion Starter · #9 ·
welcome to the forum chief... good to see new faces :D

i dunno about this sort of malarky.. just saying hello and welcome.. that's all really

enjoy!

J
 
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Discussion Starter · #10 ·
it can take ages for a cat to 'light up' but a good run will do this no problem the oil on the other hand can take twice as long to warm up to 80 deg,when sat idleing in the garage waiting for the oil to warm up the cat is either boiling away or getting too cold and getting clogged up so its for this reason that you should drive hard before the test so when you get there you can just get on with the test.
 
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Discussion Starter · #11 ·
by the way ive only changed ONE cat in ten years its very rare for a cat to be faulty....the one i changed had fallen to bits inside.
 
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Discussion Starter · #12 ·
Thanks Jimybob that's all good advice which my friend will need as the car's in for the retest on Friday.

I tested the water temp sensor resistance at various temperatures and everything checked out according to Autodata's technical data. I never tested the signal voltage with the engine running though so I'll do that to completely rule that out as the problem.

At Clive's suggestion I posted this question on AlfaOwners as well and a very helpful chap from NumanRacing has confirmed for me that the lambda sensor is operating outside the proper range. He's also suggested that the wiring may have been tampered with so the lambda sensor is looking the likely culprit at this stage.

Thanks everyone for your help. Much appreciated. I'll keep you posted...
 
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Discussion Starter · #13 ·
Jimybob

Didn't you say the water temp sensor is almost impossible to test acurately as it is continously changing values. the dealer tech I spoke to said they use an oscilloscope to test them.

wrinx
 
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Discussion Starter · #14 ·
Whoops, a few more replies sneaked in there while I was typing my msg.

You really are a friendly bunch! When my mate drags himself into the 21st century and gets a pc I'm sure he'll be a regular here. I know how addictive these discussion boards can be, especially when you're stuck in work on a Saturday night like I am wink .

Thanks again for the welcome people.

chief
 
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Discussion Starter · #15 ·
Wrinx when I started getting into car mechanics I convinced myself to buy a datalogging multimeter, which I connect to the laptop. It's not just as good as a scope, but it still lets me print out impressive looking graphs and stuff to satisfy the techno-junky in me :)
 
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Discussion Starter · #19 ·
BTW Chief, one of our number is the webmaster for the Peugeot Sport Club. Do you use their site???

wrinx
 
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Discussion Starter · #20 ·
hehehe...

well i've got a digital multi-meter... bneh neh neh neh neh... bet you're jealous... erm ok.. maybe not! :D :D :p :D :D

J
 
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