1.7 16V Pinking a lot - Alfa Romeo Forum
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(Post Link) post #1 of 11 Old 02-10-16 Thread Starter
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1.7 16V Pinking a lot

Hi
As some of you know, some time ago I repaired the engine of my 33 1.7 16V.
I had some problems about starting the engine the first time, but since it started the first time, I didnīt have a problem starting it.
Since it started, I took the car to the portuguese inspection and it passed without a problem.
I have drove the car and noticed it is not working the way it should.
The main problem is that it "pinks" a lot.
If I start the car and drive, it works fine until it reachs 40 degres.
If I put the accelerator down it goes fine, like a 16V should go.
But after 40-50š of engine temp it starts pinking a lot more them it should, and the more the engine temp goes high the more it pinks.
At 80š of temp it pinks a lot, if I drive normal on a strait or down it is almost fine, but if I drive up the hill it pinks a lot.
Also if I drive on a strait and try to put the hammer down in 3š gear at 3000rpm it pinks a lot.
I also noticed that when the engine is hot (80š) the engine seams rough.
It looks that the ignition is advanced... but as it is controled by the ECU, what can be causing this?
I idles fine, when stoped it revs nicelly in cold and hot.
It has a brand new radiator and temp sensor (the blue).
Changed the spark plugs, the distribuctor cap and rotor, HT leads by others I had for spares.
I checked for air leaks and didnīt find anythig.
I notice another strange thing.
When the engine is hot, the idle speed is difficult to go down of 1100-1000rpm. If I move a little the throtle switch the RMP goes down to 900 like it should, but about half a minute later the RPM goes up again... so it is the ECU that raises it!
But then again... what is telling the ECU to raise the idle speed?
It is not "type of fuel" related, I tested with 95 and 98 Ron.

Thanks
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Hi,

The mixture is too rich.
It could be wiring fault between the blue temperature sender and the ECU connector,
or incorrect setting of the AirFlow Meter CO screw, incorrect setting of the AFM flap
spring preload, defefective AFM, injector leak, or wear of the camshaft lobes.
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(Post Link) post #3 of 11 Old 03-10-16 Thread Starter
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Quote:
Originally Posted by LoneWolf33 View Post
The mixture is too rich.
I dont think so...
On the inspection it passed with 2.50 CO... normal since by portuguese law it can be up to 3.5. And a lot of years ago the car was out of tune and failed the inspection with 7 of CO and driving it you wouldnīt notice anything wrong.
By the way check the pic I attach of the spark plugs I removed from the engine when I replaced last week.


Quote:
It could be wiring fault between the blue temperature sender and the ECU connector,
Dont think so.
The sender is connected to the main wiring by a small cable.
Today I took the car to my job and when I arrived with the engine running I disconnected the main wiring from the small cable (that is connected to the sender) and the engine started to strugle, rpm going up and down... I reconnected it and it idled normal. The same thing happends when I disconnect the Idle speed actuator.


Quote:
or incorrect setting of the AirFlow Meter CO screw
Dont think so...
As I said it passed inspection with 2,5 CO... and the voltage on pin 1 of the AFM was set by me to 2.00 volts


Quote:
incorrect setting of the AFM flap spring preload, defefective AFM,
That I dont know...
The AFM is not the original and was replaced with a new unit (same model) and when I broke the engine it was working fine. I has about 20.000Km from new.
It was never touched inside... never opened.


Quote:
injector leak
That I also dont know... but check the pic I attached.


Quote:
or wear of the camshaft lobes.
No...
The engine was repaired and I did max 500Km from repair.
All camshafts were perfect.

Today before starting the car to came to my job I turned the AFM screw clockwise (to close gas) and noticed the performance of the car was cut. The car doesnt pull the same way (normal) but when it reached full temp, the pinking was there... maybe a little bit less but stiil there, and the idle speed doing the same, difficult to be down from 1000 rpm.

Edit: my car is non cat version.
Attached Images
File Type: jpg Velas 16V.jpg (50.7 KB, 2 views)

Last edited by gralalfafan; 03-10-16 at 08:51.
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Well, according to the service manual the maximum CO percentage
for fuel injected engines should be lower than 1.7%
(with catalytic converter even less, measured upstream).

The color of the spark plug electrodes seems OK, but it doesn't tells you how's the
AFR at medium or heavy engine loads.

So the temp sender and it's connection can be ruled out.

Ignition advance at running engine is based on RPM signal and corrected by the AFM
signal (and engine temperature).
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Quote:
Originally Posted by LoneWolf33 View Post
The color of the spark plug electrodes seems OK, but it doesn't tells you how's the AFR at medium or heavy engine loads.
I can not check the AFR... dont have the tools to do that.


What would you recomend me to do?
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(Post Link) post #6 of 11 Old 03-10-16 Thread Starter
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The small cable that connects the temp sender to the main wiring is just a bypass cable, isnīt it?
Or does it have some resistor inside?

I ask that because the pinking seams to be temp related...
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Quote:
Originally Posted by gralalfafan View Post
I can not check the AFR... dont have the tools to do that.


What would you recomend me to do?
A roller bench test combined with exhaust emission test is a safe way to determine
what's happening with the AFR during acceleration.
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Quote:
Originally Posted by gralalfafan View Post
The small cable that connects the temp sender to the main wiring is just a bypass cable, isnīt it?
Or does it have some resistor inside?

I ask that because the pinking seams to be temp related...
Someone may correct me, but as I recall there shouldn't be a bypass or anything else inserted
between the loom and the sender, the loom should be long enough to reach the sender directly.

Check that extra piece of cable with an ohmmeter, maybe something odd will be found.
I've forgot to mention that, the failure of the air temperature sensor inside of the AFM
also could cause similar symptoms. The blue coolant sensor is used as base and the air
temperature sensor used as a correction in the injection system.

The engine requires more fuel when cold, so that's usually prevents pinking,
but if the rich condition persists at hot engine, the extra fuel in the cylinder will
rather explode than burn fast, even with correct ignition advance.
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(Post Link) post #9 of 11 Old 03-10-16 Thread Starter
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Quote:
Originally Posted by LoneWolf33 View Post
Someone may correct me, but as I recall there shouldn't be a bypass or anything else inserted between the loom and the sender, the loom should be long enough to reach the sender directly.
Left hand drive versions all have that extension... about 20 cm...
Iīve checked that small cable and it is an extension (zero ohms)


Quote:
I've forgot to mention that, the failure of the air temperature sensor inside of the AFM
also could cause similar symptoms.
If that is the problem, is it possible to solve that without replacing the AFM?
Is it possible to repair that sensor?
What you said make sense... (100%)


From the start I assume that the AFM is fine, the way it was... the car was left alone for 7 years, so the part should be the way it was... (perfect "almost new", 20.000Km)

Is there a way to check on some pin of the AFM if the internal sensor is faulty?
Is there a value in volts or ohms that I can check on some pin?

Last edited by gralalfafan; 03-10-16 at 13:07.
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Yes, it's possible to replace the air temperature sensor. It requires to open up
the top of the AFM, and desoldering the pins of the NTC element.

But before you do that I'd recommend to check the sensor resistance on the ECU side connector,
between pin#22 and pin#6. It it's infinite, you've found the problem.
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(Post Link) post #11 of 11 Old 04-10-16 Thread Starter
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But before you do that I'd recommend to check the sensor resistance on the ECU side connector, between pin#22 and pin#6. It it's infinite, you've found the problem.
Yesterday night checked some things and you dont need to check pin 22 and 6 from the ECU connector.
You can do it on the AFM.

You have to put the tester on "ohms" on the 20.000K scale.

- Measure between pin 2 and 3 and move the flap - resistence starts at about 55 ohms and as you move the flap it goes up.

- Measure between pin 4 and 5 and you have the resistence of the sensor. Mine was 1500 ohms was I arrived home (7.30 PM), 2000 ohms 1 hour later, and 2900 ohms at mid night (15š outside temp).

This is ok, I have to other AFM but from 75 TS (0280202202) that I almost certain that are the same as the 33 16V, and measured bouth with similar numbers.
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