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Discussion Starter #1
Hello everyone,

So, first thing to get out of the way, I have been having a problem with the v6 since I bought it and it seems it is getting worse. The issue is that it sometime had a slight missfire on idle and it misses a beat when blipping the throttle on idle but is fine up the rev range, car always had good power. I think it could be a bad coil.

Now, about the main issues that started 2 day ago. I was driving on the highway going to work, it was **** pouring rain and I was going pretty fast. I hit a very shard transition on the road (not a pothole but a transition where the asphalt is connecting). It was not super hard like suspension bottoming but it gave the car a rough shake. Immediately after hitting the said, car lost all throttle, 0% response, it did not feel like the engine stalled because when I put it in neutral then throttle responded but ultra lazy. I tried to push the accelerator a couple of times and throttle came back normally and I continued my journey because it was not convenient to stop. Shortly after I went over some rough road patch on the asphalt and again throttle quit, I had no response and after pushing it a couple of time car started pulling again. I stopped at the gas station to get cover from the rain and inspected the car. It had very rough idle, and lumpy rpm going up and down. Nothing obvious under the hood although MAF sensor plug was wet from the rain. I scanned for codes on AlfaOBD with my bluetooth dongle thingy, no faults present, scanned some live data, nothing obvious. I got off the highway and driving in the city when coming to a stop light in neutral engine wants to die off, rpms falling down to 100-200 then coming back up, not on every stop light but often does. It even died once and I had to restart the car, it shakes when giving throttle sometimes. On full throttle and up the rev range engine has very good power like always did.

I came home from work and decided to check some data again. Since the throttle was acting up (at least i think so) I decided to remove the glove box and disconnect and connect the little white connector that should be for the throttle. I secured it a little better with some insulating tape so that it does not wobble around (NOTE: The next day I went to my work again and throttle did not quit anymore going over the rough patches of the road but the idle issues remained). Although my bluetooth scanned is very slow and unresponsive it gives some indication. Lambda sensor does not move from 200-300 mV. It just stays there indicating lean condition or the sensor is bad. MAF sensor on full acceleration 2nd, 3rd and 4th gears seems to work properly showing values over 500. I took some videos and logs and will upload them shortly.
NOTE: Not long ago I installed new NGK plugs.
Can someone give any idea on what is happening? Bad throttle body, or the crappy connection behind the glove box? Bad lambda? Bad MAF? Bad ignition coils? Maybe the lambda connector got water intrusion on heavy rain driving?


Lambda is mostly staying at 200-300 mV, it is either lean or a bad sensor. What bugs me is that usually a lambda would not make the engine stall and drop rpms to 200.

 

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How long have you owned the car?

Chance that the cam timing was not set right since the last cambelt change. I don't know much about that, but it is a discussion point on the forums every now and then. Especially if you have had issue with idle for entire ownership.

When you changed the spark plugs did you install the correct ones? Did you make sure that no wires from the coils were pinched or damage during re-fitment of the plenum chamber for the rear bank of spark plugs. There are also two grommets that sit on the rear banks valve cover which the plenum fits into. Are both of those still in place?

From my experience with a bad coil, you only feel it when the car is warmed up, or under load (going up a incline).

Even one bad coil should not cause revs to drop that much. I had a four cylinder car with 2 plugs per coil. Even with 1 coil malfunctioning the car still ran (on 2 cylinders) and could tackle an incline. Not recommended however.

Must be some connection between the bump from the road surface and idle problem.
 

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Discussion Starter #3
How long have you owned the car?

Chance that the cam timing was not set right since the last cambelt change. I don't know much about that, but it is a discussion point on the forums every now and then. Especially if you have had issue with idle for entire ownership.

When you changed the spark plugs did you install the correct ones? Did you make sure that no wires from the coils were pinched or damage during re-fitment of the plenum chamber for the rear bank of spark plugs. There are also two grommets that sit on the rear banks valve cover which the plenum fits into. Are both of those still in place?

From my experience with a bad coil, you only feel it when the car is warmed up, or under load (going up a incline).

Even one bad coil should not cause revs to drop that much. I had a four cylinder car with 2 plugs per coil. Even with 1 coil malfunctioning the car still ran (on 2 cylinders) and could tackle an incline. Not recommended however.

Must be some connection between the bump from the road surface and idle problem.
I only had problems with throttle response from idle and very very slight rpm fluctuation. Mostly when the car warms up. EDIT: I own the car now about two and a half years.

I had the cambelt done by a good garage that used camlocks and that often does these v6 engines. The mechanic said that the timing was ever so slightly off when the took it apart and that he set it correctly. I saw 0% change on idle and my idle throttle response before and after the change.

I changed the spark plugs 6 months or so ago, original fittment NGK PFR6B plugs were installed. Saw no change to idle and throttle response then. I am not 100% sure on wires pinching on the rear bank, front bank is good. Rubber mounts for the plenum are in place.

I forgot to mention that on the day when I started to get these issues, before I hit a bump on the road, when I got on the highway I ran the car hard from 2nd to 5th gear up to 7000 rpm. In 2nd and 3rd gear between 5k to 7k rpm I notice that the car misfired or kind of jerked a couple of times on hard load high rpm. It did that in 2nd or 3rd gear, and that never happened again. I tried to reproduce that again but with no success.

This intermittent problems are driving me crazy. Today the idle does not drop that much and appears that everything is almost okay but yet is still feels bad. Especially at idle and when switching to neutral when coming to a stop, rpms drop too much down to 300-400 rpm them come back and it is fine.

EDIT2: On the day when issues start and throttle quit on the highway, when I got to the gas station and scanned the ECU. I remember it said throttle learn process 4.0. Now when issues seem to got a little bit better now it say throttle learn process 9.0. Dont know if this is connected in any way.

I have captured a good video of the bad throttle response on idle that has gotten much worse since the day these problems started. On 0:45 you can perfectly hear and see what I am trying to show, also you see how much the rpms dip down when I let off the accelerator and let the car settle. Here:

I also uploaded a sceenshot of the datalog that I did yesterday. Highway 6th gear 4000 rpm. Now I can see that the lambda is responding and assume that it is working correctly but on idle it shows car as dead lean.
 

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Discussion Starter #4
Today I discovered a new symptom of this issue. I cannot rev the engine below 1500 rpm, the pedal does not react no matter how slow I press it just goes to 1500, also when I drive slow in first gear through traffic below 1500 rpm the car jerks and lurks drastically and undriveably. I now am more confident that the problem is throttle related.
 

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Try giving the throttle body a clean with some throttle body cleaner. Remove the air induction hose and have a look for carbon deposits.

On the earlier engines there are a few vacuum / crankcase ventilation hoses. One runs behind the plenum chamber. Make sure that they are all intact with no damage. It's an expensive hose to buy however.

From what I have read a bad MAF can result in poor performance in the upper rev range. How is the air filter?

If you have an electronic throttle you could try the throttle reset procedure. It's somewhere on the 156/147/GT forum pages. I'm not sure if it works for earlier cable throttles though, I would think not.

If the garage you used to do the cambelt works on these cars quite a bit and they are not too far away, perhaps they would have a better idea or be able to help you out. They might have a spare MAF that you could try out perhaps.

My V6 car is a little rough when warming up, but I think that is quite normal at cold start-up.
 

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Discussion Starter #6
Try giving the throttle body a clean with some throttle body cleaner. Remove the air induction hose and have a look for carbon deposits.

On the earlier engines there are a few vacuum / crankcase ventilation hoses. One runs behind the plenum chamber. Make sure that they are all intact with no damage. It's an expensive hose to buy however.

From what I have read a bad MAF can result in poor performance in the upper rev range. How is the air filter?

If you have an electronic throttle you could try the throttle reset procedure. It's somewhere on the 156/147/GT forum pages. I'm not sure if it works for earlier cable throttles though, I would think not.

If the garage you used to do the cambelt works on these cars quite a bit and they are not too far away, perhaps they would have a better idea or be able to help you out. They might have a spare MAF that you could try out perhaps.

My V6 car is a little rough when warming up, but I think that is quite normal at cold start-up.
I clean the throttle body regularly and is probably spotless. Nevertheless, I will remove it and give it a good clean although I do not believe that is a problem. My suspicion is toward the throttle body itself, accelerator pedal or wiring.

The garage that did the cambelt is about a 2.5 hours drive from me. MAF works fine. I do not have any problems when the car is cold just when it start warming about at 50-60c it starts to give troubles.
 

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Have a look at this thread. The OP had poor running after hitting a bump too, found something in the throttle body was not quite right.

 

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Discussion Starter #8
Have a look at this thread. The OP had poor running after hitting a bump too, found something in the throttle body was not quite right.

Wow, that is incredibly helpful. Thank you very much I will give it a try.
 

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Discussion Starter #9
I have cleaned the throttle body, disassembled the motor unit of the tb and cleaner the carbon wiper tracks with cotton and alcohol and now the problem is fixed. No more funky idle, car revs up nice and clean overall i am very happy.

BUT, now the engine has low power over 3500-4000 rpm, it runs good below but as soon as it hits 4000ish rpm it falls on its nose. It can rev the whole way but feels like it leans out. Lambda now reads correctly at idle since tb clean. I notices that now the MAF reads a bit lower, it rarely goes over 500kg while before it could.
 

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Update: drove the car again this night, power was great, pulling like never before. I dont know what is happening, Alfa is probably pulling my leg a bit. Ill see if no issues come back but as of now, it seems all good.
 
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