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Discussion Starter #1 (Edited)
Hi, unfortunately I've got a strange one today. I'm experiencing a cylinder 3 misfire on my 2004 GT 2.0 JTS. This usually happens after a cold start. The idle is rough, car is choking - no throttle response, the sound coming out of the exhaust reminds me of a cannon - classic symptoms of engine running on 3 cylinders IMO. Also when there is around 5°C outside I can hear a squeaking noise coming out of the engine bay after start and it gets better as the car heats up. The V-belt is not at fault here tho. I'm not an expert but I can smell a strong gasoline odour from the exhaust as if the mixture was too rich. When I try to drive the car a flashing engine light comes up. OBD showed me a cylinder 3 misfire. All the symptoms dissapear after the car heats up a bit. Sometimes it takes a minute, sometimes a lot more. The engine light sometimes comes up even when the engine is already on operating temperature but that doesn't happen so often and the engine is running considerably smoother.

What I've tried to no avail
  • I fitted brand new NKG spark plugs and a new coil on the 3rd cylinder
  • I tried starting and driving the car with MAF unplugged
  • I cleaned all the coil,oxygen sensor and MAF connectors
  • I also tried putting in many different brands of petrol and even petrol with additives
I hope some of you might know what's wrong with the car.
Thank you for all the responses in advance.
 

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Discussion Starter #2
So I did some diagnosis today and the results were shocking. My pre-cat o2 sensors are Reading around 3.5V! From what I've read that's way off from a normal reading even for a faulty sensor. Do you have any experience with this? I don't wanna replace them for no reason since they are quite expensive. Do you reckon they are faulty or that there is some sort of a different problem?
 

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As you have a misfire you need to resolve that first as that will throw lambda off. You say plug and coil have been changed so you need to check it is actually getting signal to spark,fuel and compression.
 

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If all symptoms disappear then compression is probably ok but worth checking anyway.

Sensor voltage is utterly meaningless without data precisely outlining conditions, temperature, throttle opening, MAF reading, engine speed etc etc. If that was a natural idle voltage with warm engine then it should be around 1.25v for precat O2 sensors. If it is high voltage, it is not connectors. It signifies a rich mixture. For that then you need to look at fuel trim data for an idea why.

In conclusion, with the limited information I'd suspect non OE parts for ECU compensation for poor injector spray but that is a fairly wild guess.
 

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Discussion Starter #5
So I've learned that the lambda sensors are wideband so the readings are in norm just signaling a rich mixture. The readings don't change even when the engine is on 90° when the choke should be disengaged. That's fairly strange since the conditions in the engine change thus the engine is running fine but there is no diference in the readings. But maybe I'm just dumb..
 

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If O2 sensor readings don't change, sensors are clogged or defective. First thing then is remove them and clean with a wire brush. If no improvement, get new ones.
 

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Discussion Starter #7
That's what I have planned for today. But thank you. Now I don't feel that I'm about to do something useless
 

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Discussion Starter #8
Lambda cleaning didn't seem to help at all. I'm just wondering how can the ecu recognise a misfire on a certain cylinder? I thought it can only recognise that the coil didn't give any electricity to the glow plug. Or maybe it also knows if the injector injected. But if the mixture is wrong or something but injector and coil did their job the engine has no way of knowing the misfire happened on the 3rd cylinder or am I wrong?
 

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Discussion Starter #10
Oh.. That makes me little bit less worried since the injectors are a pain in the ass to remove. Thanks :)
 

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The description of the fault code and the code itself helps. If it was really bad, diagnosis would show open circuit but in this case, it never happened.

Have a look at the terminals for no.3 ignition coil multi plug. Ensure no terminals look oxidised or burnt and still have a good spring. I have tried tracking down ignition coil terminal repair kits but I cannot find any, unfortunately. If anyone has access to EPR and finds something, this would be a good time to chime in.

I still think the pre-cat O2 sensors show too high a voltage but although I don't think it is wiring, it would still be a good time to check the common terminals between the ECU and pre-cat wideband O2 sensors.
 

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May sound simple but have you tried swaping both spark and coil pack from cylinder 3 with cylinder 1 spark and coil pack ... I had a brand new dud premium coil pack once ..

If you swap them, recheck with obd reader if it moves the fault to cylinder 1 .. your on to a winner if not will eliminate they two item.
 

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The description of the fault code and the code itself helps. If it was really bad, diagnosis would show open circuit but in this case, it never happened.

Have a look at the terminals for no.3 ignition coil multi plug. Ensure no terminals look oxidised or burnt and still have a good spring. I have tried tracking down ignition coil terminal repair kits but I cannot find any, unfortunately. If anyone has access to EPR and finds something, this would be a good time to chime in.

I still think the pre-cat O2 sensors show too high a voltage but although I don't think it is wiring, it would still be a good time to check the common terminals between the ECU and pre-cat wideband O2 sensors.
There is no thermal repair kit the plugs are captive need to buy full loom from Alfa .. Alfa didn't do a reapair kit and neither do Bosch automotive.

I bought a second hand loom off ebay with the plugs. As a few of the plug lock latches on mine were broke when I bought mine. Then cut and soldered them in to my original loom.
 

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Discussion Starter #14
I already tried swapping plugs and coils with a different cylinder, then replaced them and swapped again. I'm planning to clean the connectors again but I don't think that's the problem since engine temperature seems to have impact on the engine condition plus resistance raises with temp. Worth trying tho. Anyway I'm very glad that you try to resolve the problem with me :)
 

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You could have a go with a set of needle pliers and have a gentle pull/wiggle at the terminals associated with the fault you're seeing. The actual problem youre seeing I have little experience with....connectors and stuff I do though and sometimes a pin can break at the base, inside the plastic. It'll still stay in there though and provide conductivity but not as it should and also give a high resistance point. Its painstaking to do but free.
It also seems you've been very thorough to this point and it might well be the injectors that are the problem?
You can have them checked/serviced and see what state they're in. Fruity had his done a while back. He was pleasantly surprised with the condition they were in but yours might need some work
 

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Yes, as stated, I have looked around for the terminals in the coil multi plugs and cannot find the terminals (which should be able to be changed) but I cannot find a repair kit or even the terminals separately. If anyone ever finds a source for these terminals, I'll give it a go. As it was, I didn't want to try too hard on my own JTS as it has good terminals in the plastic housings. My conduit for these wires was a complete mess so I fitted new wire binding for now but I still plan a thorough overhaul if and when I find the correct terminals. Unfortunately even Kojaycat could not help. I have once again begun contacting specialist suppliers of Bosch Automotive to see if I can track down these things.

After looking at the multi plug terminals for the coils, a regular 6.3mm male spade terminal could be inserted into the multi plug terminals so see if there is a secure fitting. If not the spring has become weak and a good electrical connection cannot be assured.
 

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Thanks, I'll see what I make of that but due to lock down, I don't have the with with me. At least they do butt connectors which is the correct way to join wires these days. It is how wiring harnesses are made.

I'm not criticising anyone for solder joints as it is how I used to do things but I found out the recommended way is now butt joints and heat shrink.
 

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Discussion Starter #19
So today I disassembled the terminal, cleaned it with a contact cleaner and pushed the pins in to ensure a better contact. Didn't help but what I've discovered is very interesting. There is a wire soldered to one of the wires on the terminal
936268

It leads through several wiring looms somewhere into the ecu I guess. I think it's just a replacement wire for the original one but why would someone leave the old wire connected? I'll probably try to cut the wires and try what the engine behaves like with only one of them connected at the time and redo the solder.
 

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Someone prob found a fault in that wire....decided it was broken somewhere along its length and decided to bypass it with a new wire for a quick fix. If its happened to one it has maybe happened to others.....
 
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