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Discussion Starter #1
This is on my 3.0 Verde.

If I try putting a load on the engine – accelerating from low speed in a 4th or 5th gear – there is an intermittent but noticeable jerk from the engine at low RPM until above tach gets over 2K. Feels like a mis-fire but it only happens at low speeds in a higher gear; never in 1st or 2nd. Something must have changed as I could always pull from 1K RPM in any tall gear without an issue.:eek:

Questions:

Is there a load sensor anywhere I’m unaware of?

What exactly is the function of the throttle position sensor and what happens when they go bad?

Ignition?

Any help would be great. Thanks.
 

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Is the Throttle Position Switch the same as the later models of the GTV6? If so it is simply a 3 position switch. It tells the computer if the throttle is at idle, not at idle or wide open. If it is actually a Throttle Position Sensor then I don't know anything about it.
 

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But Mad North-Northwest
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Bad tank of gas knocking due to you lugging it?

Regardless, you're *really* not doing the engine any good by lugging it like that.
 

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Look to your AFM. Get some Deoxit-5 or Radio Shack's equivalent, remove the black plastic cover and clean the rheostat.
 

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Check the ignition system too, could be a bad wire or plug.
 

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Discussion Starter #8
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Bad tank of gas knocking due to you lugging it?

Regardless, you're *really* not doing the engine any good by lugging it like that.
Funny you mentioned that ... I seem to recall this began soon after a bad bit of gas from a rinky-dink station in the sticks. I've since flushed thru clean fresh stuff but still it is there.

You are definately right about the lugging (Duly noted Eric!):D

Look to your AFM. Get some Deoxit-5 or Radio Shack's equivalent, remove the black plastic cover and clean the rheostat.
Good point and probably worthwhile maint.


Check the ignition system too, could be a bad wire or plug.
Where to begin? Is it fine to unplug each wire while the engine is running? I've ruled out cap & rotor as the look good. This could not be advance related?

Thanks all.
 

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I've ruled out cap & rotor as they look good.
You especially should know looks don't count. Verify.

Is it fine to unplug each wire while the engine is running?
Sure. Stand barefoot in a puddle and hold one hand against a good ground, too... :eek:

OK, actually it is advised to not do that as it might adversely affect the electronic ignition somehow. But I've done it with both our L-jet Spider and GTV6 to pin down a problem and didn't fry anything.

Another fun thing to try is to open the hood with the engine running on a dark, moonless night. Once your eyes have adjusted to the dark if you have really bad ignition wires you can see them glowing blueish &/or sparking to ground.
 

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It seems that the easiest, best starting point is to get out your timing light and see if your advance is set properly, AND see if the advance "jumps around" under your timing light. If no, then your ignition system is likely healthy. If yes, better start checking from rotor onward.

It sounds like ignition ping and it's possible that in the lower gears the RPMS are allowed to rise quickly enough that it won't ping.
 

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But Mad North-Northwest
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Funny you mentioned that ... I seem to recall this began soon after a bad bit of gas from a rinky-dink station in the sticks. I've since flushed thru clean fresh stuff but still it is there.
Hmmm. Well, carbon build up will cause higher compression. And higher compression can cause detonation. Maybe your bad gas resulted in carbon build up on the pistons?

I realize I'm reaching here, but I'm trying to link to something you know went bad and it seems more likely than your timing suddenly changing on you. In any case, bottle of Techron (or preferably BG44K, or maybe Seafoam if you're feeling ambitious) couldn't hurt anything.

Incidentally, if it *is* detonating it can cause damage, so don't do things that cause it to detonate.
 

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1966-2013
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Trying to accelerate in 4th or 5th from the sub 2000rpm range?
Do you pull away from a dead stop in 3rd?

Has the tach been confirmed as accurate as I can't make myself believe that you could pull from as low as 1000rpm in a high gear without issue prior to this. If that were truly the case, you'd only ever need 2 gears: 5th and reverse.
 

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iv just set up with megasquirt, and im having the same sort of problem at the moment, a minor sort of missing while accell'ing from about 1300 up to about 2, then its gone after 2. WB02 jumps leaner for a split second and back. worst happens in 4th at about 1800rpm. iv got new plugs too.
 

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Discussion Starter #15
Replies ...

It seems that the easiest, best starting point is to get out your timing light and see if your advance is set properly, AND see if the advance "jumps around" under your timing light. If no, then your ignition system is likely healthy. If yes, better start checking from rotor onward.

It sounds like ignition ping and it's possible that in the lower gears the RPMS are allowed to rise quickly enough that it won't ping.
Light is on loan right now but I will get it back this week. I'll check both with and w/o vacuum.


Hmmm. Well, carbon build up will cause higher compression. And higher compression can cause detonation. Maybe your bad gas resulted in carbon build up on the pistons?

I realize I'm reaching here, but I'm trying to link to something you know went bad and it seems more likely than your timing suddenly changing on you. In any case, bottle of Techron (or preferably BG44K, or maybe Seafoam if you're feeling ambitious) couldn't hurt anything.

Incidentally, if it *is* detonating it can cause damage, so don't do things that cause it to detonate.
I'm only now reaching 30K on a complete rebuild (new pistons, valves etc.) so I'm hoping carbon buildup would not be too much an issue. The Techron is a good idea!


Trying to accelerate in 4th or 5th from the sub 2000rpm range?
Do you pull away from a dead stop in 3rd?

Has the tach been confirmed as accurate as I can't make myself believe that you could pull from as low as 1000rpm in a high gear without issue prior to this. If that were truly the case, you'd only ever need 2 gears: 5th and reverse.
Not from a standing stop - while in town I'll sometimes take a corner in 4th or 5th and speed up without shifting and without an issue. The majority of the time I'll downshift and run the range but when speed limited it should be fine to keep it in the higher gear. No?


02 sensor?
Also relatively new - 30K miles on it but how do I check that?


iv just set up with megasquirt, and im having the same sort of problem at the moment, a minor sort of missing while accell'ing from about 1300 up to about 2, then its gone after 2. WB02 jumps leaner for a split second and back. worst happens in 4th at about 1800rpm. iv got new plugs too.
This is exactly my range. There is no issue in 1st or 2nd gear - car pulls strong. It is only when there is a load.


Thanks for the to-do's. Keep you posted.
 

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Not trying to steal your thread but sounds similar as to what my car does.

When mine is under acceleration, it feels like a wave/surge when sweeping through the RPM range. For instance, more power at 3K, less at 4K, more at 5K.. and so on...
 

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Not trying to steal your therad but sounds similar as to what my car does.

When mine is under acceleration, it feels like a wave/surge when sweeping through the RPM range. For instance, more power at 3K, less at 4K, more at 5K.. and so on...
That sounds like a weak ignition advance module or a dirty wiper track in your AFM. Try unplugging your 02 sensor and see if it repeats.
 

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1966-2013
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while in town I'll sometimes take a corner in 4th or 5th and speed up without shifting and without an issue. The majority of the time I'll downshift and run the range but when speed limited it should be fine to keep it in the higher gear. No?
Dunno.
In town you'd never catch me even considering going above 3rd anyway unless I'm planning on cruising faster than 45 for a while, which in town is 'never unless you want a ticket'.

I like to have the ability to brake as well as accelerate for possible incident avoidance rather than limiting things to strictly 'lock em up and pray' because there's nowhere near enough grunt available to squirt through an opening or whatever :shrug:
 

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A follow-up to #17. At this stage in life - the car's, the lube in the hall-effect sensor (HES) can be expected to be 'toast' which would cause it to 'hang up' and perhaps be at fault. Upon checking your timing, if it 'suddenly' off, check the wear of the upper distributor shaft bushing. Simply grasp the rotor and see how much you can wiggle it from side to side. If it is sloppy, it is possible for the rotor to engage the cap and rotate the distributor out-of-time. To check the HES's freedom of movement, remove the distributor and the vacuum advance unit, then hook where it couples to the vacuum advance and check that it moves freely. Been there, done that, numerous times and am still in love. Sick?
 

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well, iv got new plugs, and they look perfect still, new wideband O2 sensor, with less than 1000kms, no afm. my miss is most felt in the higher gear while cruising, but sometimes while taking off from first gently.
checking the rotor cap and button, and they look fine. im going to try testing the leads with a spark tester and checking the resistance next, and also check at night for and spark leakage.

could it be a coil problem? mine would be pretty old.
 
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