Technical Engine drops above 2500 rpm

[Mauricemx]

Hi,

I'm new to this forum and I hope you can help me with the following problem of my Fiat Punto 1.2 8V (2000)
First of all I'm from the Netherlands. I'm not familiar with the technical words in English but I hope you will understand the story.

My car starts normally, but when I exceed approximately 2500 rpm (it's a guess, I don't have a rpm display) the engine stalls, until it drops beneath 2500 rpm, then it accellerates till 2500 rpm, then it stalls again and so on. The problem is the same when I accelerate in the neutral gear.

This started 2 months ago, first only incidents but it became worse.
The fiat garage examined the computer, but after resetting it, they didn't find any error codes. Head gasket is ok.

I replaced the TMAP-sensor, without any result.
The ignition coils seem to be ok, same resistance values for both of them (low and hight voltage contacts).

The car display doesn't show any engine problem, no blinking light.

Spark plugs and cables, air filter, oil filter, oil and the rear end of the exhaust have been replaced 6 months ago.

What seems weird to me is the following:
I took the cable of a spark plug.
I attached a spare plug on that cable and held it to a metal part
With the engine on I could see sparks very clearly
When I accellerated the sparks disappeared completely
I did the same with the other cables, same result.
Is this normal?

Any suggestions are welcome!

Thanks.

 

[judderbar]

Hi,

I'm new to this forum and I hope you can help me with the following problem of my Fiat Punto 1.2 8V (2000)
First of all I'm from the Netherlands. I'm not familiar with the technical words in English but I hope you will understand the story.

My car starts normally, but when I exceed approximately 2500 rpm (it's a guess, I don't have a rpm display) the engine stalls, until it drops beneath 2500 rpm, then it accellerates till 2500 rpm, then it stalls again and so on. The problem is the same when I accelerate in the neutral gear.

This started 2 months ago, first only incidents but it became worse.
The fiat garage examined the computer, but after resetting it, they didn't find any error codes. Head gasket is ok.

I replaced the TMAP-sensor, without any result.
The ignition coils seem to be ok, same resistance values for both of them (low and hight voltage contacts).

The car display doesn't show any engine problem, no blinking light.

Spark plugs and cables, air filter, oil filter, oil and the rear end of the exhaust have been replaced 6 months ago.

What seems weird to me is the following:
I took the cable of a spark plug.
I attached a spare plug on that cable and held it to a metal part
With the engine on I could see sparks very clearly
When I accellerated the sparks disappeared completely
I did the same with the other cables, same result.
Is this normal?

Any suggestions are welcome!

Thanks.

You should see sparks at higher revs.

 

[Mauricemx]

You should see sparks at higher revs.

Thanks Judderbar.

So at least I know, the ignition is not functioning properly, but what can be the cause of that?
Is there a way to check if the ignition coils get a pulse? Does it come directly from the ECU?
Can I check if the injectors (monopoint I believe) also stop working above 2500 rpm? Then it should not be just an ignition problem.

Of course I can try to replace different parts, for example the ECU or some sensors, but that could be expensive guessing. However, any suggestion is welcome!

 

[Ziggy122]

Dont go parts darts.... diagnosis is best option

Coils resistance value maybe okay
But when underload, they breakdown


Also check timing

 

[Eklipze3k]

Being the 8V, I'd say the timing is probably out by a couple of teeth. Lucky it's non-interference or you'd be looking at bent valves! Do you know when the timing belt was last changed? If not, it's probably worth doing (along with the water pump and tensioner) if only for peace of mind.

 

[Brendan W]

Timing would be my initial suspicion as well. Set the camshaft pulley at the mark on the head. The first fully engaged belt tooth on the crank pulley should be at the crank pulley mark.

 

[Italian Job]

Guys, why timing ??? even if it was out by a tooth or two the plugs would still show a spark maybe early or late but a spark will still be present.
I suspect maybe the crank sensor is breaking down

 

[Mauricemx]

Thanks for all the replies!
Ziggy122 What do you mean "when underload, they breakdown"? That both the units of the ignition coils might be broken?
Eklipze3k I don't know if the belt has ever been changed. Tomorrow I will call my brother who owned the car, a couple of years ago the head gasket was replaced, so maybe also the timing belt.
Italian Job Can I test the crank sensor or do I just have to replace it with a new one? Should't a broken crank sensor give an error message or a blinking light on the display?

I have to wait for the weekend when I can use my fathers garage, I will try to check the timing and I will keep you guys posted.

 

[Italian Job]

The crank sensor failing will not give an error message or a flashing light.
The sensor can be tested but you will have test it with the car running to produce your faut, the best person to help you test it i think would be Judderba.

 

[Eklipze3k]

The crank sensor failing will not give an error message or a flashing light.
The sensor can be tested but you will have test it with the car running to produce your faut, the best person to help you test it i think would be Judderba.

judderbar is in Finland, not the Netherlands, unless I'm mistaken?

 

[Italian Job]

Would you please explain the meaning of this post and also enlighten me to how a timing issue would cause no spark to be produced above 2500 RPM ??????

 

[judderbar]

Thanks Judderbar.

So at least I know, the ignition is not functioning properly, but what can be the cause of that?
Is there a way to check if the ignition coils get a pulse? Does it come directly from the ECU?
Can I check if the injectors (monopoint I believe) also stop working above 2500 rpm? Then it should not be just an ignition problem.

Of course I can try to replace different parts, for example the ECU or some sensors, but that could be expensive guessing. However, any suggestion is welcome!

Well given what the other members are saying about the crank sensor the first thing to do is unplug the sensor and plug it back in a few times to make sure the connection is good. The sensor is strongly magnetic so cleaning it might help.

To test the low voltage side of the coil circuit, you will need pins to probe the coil plug or put pins thru the wiring. I have a LED in series with a resistor for this kind of test. The ECU grounds the 12V supply to the coil to drive the coil circuit and flash the LED. I think it would be OK to use a 5w 12v bulb in place of the LED as the coil circuit consumes about 10 amps in the small instant of time the coils are grounded.

Easiest way to test injectors is with a long handled screwdriver with the blade on the injector and handle pressed to your ear. Fairly easy to recognise the injector is clicking.

 

[Mauricemx]

I tested the injectors, I could hear them very clearly with a screwdriver, but just like the ignition, they stop working at higher revs. If both the ignition and injection stop working, I think I may conclude that there isn't a problem with either of them. I was thinking about the ECU, a sensor or a wire.
I also removed the crank sensor, there was not a lot to clean. The engine simply stops running when I pull it further away from the gearing wheel. I reconnected the connector a few times with no result.
I was kind of fed up with, so I tried to disassemble the ECU, not a good move, I destroyed it while opening.
I'm gonna replace the ECU with a used one. If that doesn't solve the problem it will be the end off my 18 year old car.
Thanks for all the advice. I will let you know if another ECU solves the problem, but it may take some time to find one.

 

[judderbar]

I tested the injectors, I could hear them very clearly with a screwdriver, but just like the ignition, they stop working at higher revs. If both the ignition and injection stop working, I think I may conclude that there isn't a problem with either of them. I was thinking about the ECU, a sensor or a wire.
I also removed the crank sensor, there was not a lot to clean. The engine simply stops running when I pull it further away from the gearing wheel. I reconnected the connector a few times with no result.
I was kind of fed up with, so I tried to disassemble the ECU, not a good move, I destroyed it while opening.
I'm gonna replace the ECU with a used one. If that doesn't solve the problem it will be the end off my 18 year old car.
Thanks for all the advice. I will let you know if another ECU solves the problem, but it may take some time to find one.

Some progress in your checks which is good. A reprogrammed Punto 8V plug and play ECU is not particularly expensive.

What about the crank sensor? What kind of sensor do you have? If you have a two wire sensor check the resistance.

On my car the sensor has a resistance of 931 ohms. When you crank the engine it can produce a voltage of 3.5V. If you put a LED directly on the contacts the LED flashes on and off as you crank the starter. It could be your sensor has started breaking down and cannot manage a clear signal at higher revs.

 

[Mauricemx]

Today I finally got the ECU by mail, including ignition switch with key, fuse-box (inside car) and cockpit. After replacing the ECU and the ignition switch the code-sign was blinking and the car wouldn't start. When I also replaced the fusebox I could start the engine. But unfortunately it was not the solution to the problem, the engine didn't go beyond 2500rpm. So I destroyed the old ECU for nothing :-(
I also tried the following (didn't make sense to me but some people recommended):
- replacing the ignition coils and spark plug cables (I could borrow them)
- removing the exhaust manifold (obstruction of the exhaust?)
Both without any result.

The only thing that I can think of is replacing the crank sensor like some of you advise.
The one I have has three wires, one is ground, and between the other two I measure a resistance of 1143 Ohm, 20% more than judderbar.
I will replace it saturday.

 

[Mauricemx]

Solved: Engine drops above 2500 rpm

Car works again !

After so many attempts this was the final one I had in mind: changing the crank sensor. And it worked!

Thanks a lot to all of you, but especially to give me the advice to replace this sensor ;-)