Rough Idle = charging system?

I have an 81 GTSi and I have been having a problem for years now with my left bank running rough at idle. The problem clears up around 1800 rpms. The right bank runs great at any speed. I have tried everything everybody suggested to no avail. Even the professionals could not find the problem.

Last wekend I charged the battery since it has been sitting for a while. My charger has a 14.4 VDC charge option, so I decided to try that overnite. the next morning when I started it, the idle problem was gone. I ran it for a few days and it returned to the normal problem. Now I am thinking that the ignition system somehow needs more that 12 volts to run smoothly, at least on the left bank. Normally the power at the coils and the computers is a steady 12 volts at all rpms. This made me think that maybe this power is comming from the battery, not the alternator, and the alternator is not charging to battery to 14 volts because it is not producing 14 volts, or the voltage regulator limits the output to 12 volts.

To test this theory, I am thinking about using a smaller pully on the alternator, so it is turning fast enough to produce power at the 1200 rpm idle speed.

If that doen't work then maybe the larger alternator would help.
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What do you think? Has this rough idle finally driven me mental, or is this worth a try. I literally have done everything else, and the battery with a 14V charge is the only thing that got it running right, if only for a short time.

 

You should see around 12V with the ignition off - if you don't then you have a bad battery.

Even at idle you should be seeing around 14-14.5V if you put a meter across the battery.

If you are not seeing 14+V at idle then you either have a bad connection or a bad alternator/voltage regulator (which will be built into the back of the Alternator - at least it is on my 328). The first thing I would do would be to clean every contact you can find between the alternator and the battery & then all the ground connections from the engine to the chassis & also from the battery to the chassis.

if that doesn't do it & the reading at the battery is still low then I'd have the alternator out of there & get it rebuilt.

If you have 14+V at the battery at idle & its still rough then

Try swapping the coils over & if you do does the problem move ? You need to swap all the wiring to try this, not just the HT leads. While you are at that you could try swapping the rotor arms, distributor caps & lead sets & see if that tells you anything. If you take the lead sets off the car then check each plug lead for continuity as well. Depending on which extenders you have , test them for resistance & make sure they are all the same.

I wouldn't even contemplate messing with the pulleys - the car left the factory idling cleanly & with a working charging system, it needs fixing, not redesigning!

 

From a charging system point-of-view, I don't see why one bank would rough idle and another be fine; this separate performance seems related more to valve timing and fuel/ignition than charging.

However, Ian's coil swap is a neat idea for a quick check.

BTW, I would clean all the charging system connectors and insulate well when re-installing. Also, remove the alternator and clean it up...it has connectors, etc that can have age-related resistance.

Check the alternator's pulley for smoothness. Clean it well. Clean the pulley on the crank well; dry both so no slipping (I use rubbing alcohol to dry stuff near rubber...recall your WP belt is nearby; acetone can be used but keep away from other belts). Dirty and clean alternator pics are shown.

Re-install the alternator with a new belt and be sure the belt is tight and all alternator points properly torqued (there is a tighness spec on the belts). Below is a pic:
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The only thing I could think of there Rob is if one coil is much more marginal than the other in terms of performance & was being more adversly affected by the reduced voltage - but I'm guessing with that one!

 

RJ,

Sorry about your problems. If you find your alternator is not charging fully, I can provide an original remanufactured Bosch unit for less than the price of a rebuild. No core charge. I currently have two. Please PM me if interested.

Phanks...Jim

 

Thanks everyone for advice. I have been dealing with this rough idle problem for years. Believe me when I tell you that I have tried everything anyone ever suggested at least three times to no avail. That's why I was excited about the charging system idea, but the consensus seem to be that it cannot be causing my problem.

I have been meaning to buy a wiring diagram for a long time, but still don't have one. From what I can see the output from the alternator goes to the battery cable at the starter, and from there directly to the positive pole of the battery. The negative pole is of course grounded to the chassis.

If I am correct about this, then the fact that I am only getting 12volts across the battery running or not must be a problem with the alternator and/or the built in voltage regulator, since there is no other contact in between the alternator and the battery except for the chassis ground which I have cleaned several times.

The problem is that I have swapped out the alternator in the past and gotten the same results. That is why I thought maybe it has the wrong size pulley installed, and so is turning at too low a speed when the engine is at idle. When I am driving the battery charges fine, so I am suspecting a voltage drop at low rpm.

Anyway, I was just wondering what people thought about this. I'll try a smaller diameter pulley when I get a chance and see what the outcome is. That is really the only way to know.

 

You are right of course. Like I said I am grasping at straws because I have gone over all that several times to no avail. Every part of every system has be switched over and/or replaced repeatedly, but the problem never resolves. I'm more that a little frustrated.

On another note, I have never understood the function of the red air hose to the alternator cover. I guess it is supposed to supply cooling? It seems to mainly blow oil under the cover. Is it even necessary? And that cable has always seemed soft to me. I have never found a crack and the resistance has always been zero ohms, but it always has made me suspicious. I have never seen anything like it on another car. I guess it must contain a fusible link somewhere.

 

My uneducated guess is that your battery is weak and not holding a charge. It's simple to take it to just about any auto parts store and they can put it on a load tester and tell you immediately whether it's good or bad. If it's bad, simply buy a new one and you're done.

In addition, look at the ground/negative cable, and in particular where it attaches to the chassis. Old cars tend to get corrosion on the negative cables, particularly at that connection point or in a cut-off switch, if you have one. Consider replacing the ground cable, cleaning the connection point and making sure you have a good ground from battery to chassis. Corrosion can cause enough of a drop in voltage that it will interfere with the ignition. Worth cleaning ground wires in the entire system, if possible.

 

I would recommend replacing the chassis ground cable.

I had a Porsche, where I replaced the alternator, battery, belts battery connectors... and still had low voltage. The original ground cable looked great, but I replaced it with a brand new one and suddenly everything was better. The whole project started because the car seemed to be running hot all the time, but it was just that the temperature gauge was seeing an artificially low voltage due to the bad ground.

Oh, and in the case I'm describing, it was the engine-to-frame ground, not the battery ground cable.

 

Totally concur with looking at cable connections/wiring, especially grounds.

The system worked correctly when it was new - it didn't need a smaller alt pulley then and it doesn't need one now. Something is causing the reduced voltage - it COULD be the alternator but if it is, it's not due to the pulley.

With any sort of electrical issue, the connections are the first thing to look at and grounds are the first connections to look at. Break all related connections, shoot them with DeOxit or something like that, coat them with dielectric grease and remake them.

 

308 GTS1 Ground cable:

http://www.trutlands.com/product_info.php?products_id=3943

supercedes to:

http://www.trutlands.com/product_info.php?products_id=7968


The quickconnect cables are more expensive:

Front ground:

http://www.trutlands.com/product_info.php?products_id=3942

Battery quickconnect to ground:

http://www.trutlands.com/product_info.php?products_id=3941


Cable from battery to starter (OEM has quickconnect under engine bay; I can't tell if this does; this is for the QV):

http://www.trutlands.com/product_info.php?products_id=4649

 

How about another way? Remove the alternator belt. If your alternator belt also drives the water pump I'd do it with the engine cold, but you can run the engine for 15-30 seconds with no water pump for an experiment. With the belt removed does the idle still studder and smooth out at higher RPM? If so, it's not the alternator. And then you can move on to something else.

 

Pro Ferrari Tech guy responding: How do you know this? Short of pulling a coil wire and disabling a bank, one would not be able to tell (due to roughness) which side was running rough. Was this done, or are we/someone speculating on what they think is happening? Please clarify.

 

the alternator is the same then the Golf only to change the pully ond the front housing

 

The alternator for the all 308 is the same then the Golf only to change the pully ond the front housing

 

Yes, that's exactly what I did. BTW, the battery is a brand new optima. I checked the battery ground cable, but have not checked the alternator to starter cable yet.

 

Wow this problem is still there?

There seems to be two issues, the slightly low battery voltage while running and the ignition problem on one bank.
The alternator to starter cable wont affect any of this.
The only paths are:
Ground:
Alternator to engine, to ground strap, to chassis, to battery ground strap via the red connector.
Positive:
Alternator to battery via red connector under car.
There would be a remote possibility that something is loading the battery when running but this seems unlikely. For example when the headlights are on full beam, the battery voltage when running would be no more than 12 usually.

Regarding the ignition problem this seems like some kind of contact problem which is creating a resistance meaning it only works when unusually high voltage is present.
Have you tried swapping over the two ignition boxes? Also check the vac pipes to both boxes.
Check low tension leads to both coils.
The engine crank sensors might be another area to check. These are simply coils and produce a relatively low voltage output so any resistance in the connections would cause problems. There is one TDC sensor per ignition box so these would be bank-specific. It would be worth checking all the connectors for this and maybe even try replacing or swapping them over.

 

Thanks, but I did all that two or three times. New wires and extensions too.

 

Alternator slip ring worn. Good idea to replace on a 308 alternator rebuild.

This was the problem with my GT4 alternator having intermittent charging symptoms.

Auto Lectrics in Campbell, California did an "above and beyond" rebuild by replacing and soldering a new slip ring along with the usual bearings, regulator, etc.

Great company to deal with in the bay area.
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