Why is motor (still) unhappy, occassionally!

[DC242]

The car in question is a 1988 944S manual.

Ok. Yesterday morning I took the car out and drove around happily with the windows down, the music was playing and all was right with the world.

In the afternoon, I went out and needed to turn the a/c on and after getting on the freeway, at 100kph the car began to feel like it was "missing" or "surging" ever so slightly. It was enough for me to notice but my passenger was not aware so it gives you some idea of how slight the issue was. The other thing was that when coming to a stop or slowing at a round about the motor was reluctant to idle properly. I've considered the compressor turning on an off would cause some fluctuation but it wouldn't be so frequent.

Whilst trying to work through the possible cause, what I was wondering is when you turn the a/c on, does the ecu see the request and adjust the ICV and turn the fans on etc or is the a/c operation independent. In my last car, I had a Megasquirt which controlled everything.

 

[Dreamr]

I'm not 100% on your particular car but generally when you turn on the air conditioning, an "idle up" circuit kicks in and ups the idle to compensate for the extra load from the compressor ... possibly a faulty circuit ....

[DC242]

Thanks. Yep I thought it might have something but some cars incorporate the ecu in the loop to handle it.

Anyway, putting this question on hold for the present. Went to try and fault find tonight and car would start but not run unless I kept my foot on the throttle. So, my fault finding took a different turn. Checked leads first but nothing definitive was confirmed. Decided to check the rotor cap and discovered cap is cracked and worn and so was the rotor button so before I progress I'll replace those and see what happens next.

[Peter M]

Also suggest you check for vacuum leaks in the intake.  A misplaced vacuum hose will give the same symptoms at idle too.

[TINGY]

2 hours ago, DC242 said:

Thanks. Yep I thought it might have something but some cars incorporate the ecu in the loop to handle it.

Anyway, putting this question on hold for the present. Went to try and fault find tonight and car would start but not run unless I kept my foot on the throttle. So, my fault finding took a different turn. Checked leads first but nothing definitive was confirmed. Decided to check the rotor cap and discovered cap is cracked and worn and so was the rotor button so before I progress I'll replace those and see what happens next.

May as well do the leads also.

[Harvs11]

One step at a time...  eliminate each individual fault possibility before moving to the next.  Multiple changes will make trouble shooting pretty difficult. 

Good luck. 

[DC242]

Have ordered cap and rotor today. Will also check plugs tonight. Hopefully this gets car running then I can see if a/c is still an issue.

[DC242]

So, pulled the plugs after buying the correct socket and discovered they were NGK Iridium and black as the ace of spades. Fully carbonised. Thinking now something is causing over fueling so will have to search further.

Question: Do these cars a an O2 sensor that the ecu listens too or is air/fuel regulated by the AFM?

I'm also thinking my title needs to be changed!

[Peter M]

Are they the correct heat range?

If they are, I suggest the next step is an Italian Tune Up after you replace the cracked distributor cap.

If that doesn't fix it at least it gives a firm basis to start a detailed diagnosis!   

[jakroo]

On 12/15/2017 at 3:40 PM, DC242 said:

So, pulled the plugs after buying the correct socket and discovered they were NGK Iridium and black as the ace of spades. Fully carbonised. Thinking now something is causing over fueling so will have to search further.....

Don't forget that a cracked distributor cap will cause mis-firing and this will show up on the plugs (and in the combustion chamber) as fuel ends up as not burnt as properly as expected it should be (ie looks like over fueling).

Get the new DC installed and take it for a good fang

[DC242]

So after a month of being stuffed around by various suppliers, I finally got all my goodies together and had a couple of days to play. List of works as follows.

Cracked distributor cap, worn rotor, spark plugs and original ignition coil all replaced. Leads appear newish so have left in place for the time being.

New K&N air filter fitted as old one fell apart when inspected.

Ran new brake fluid thru system with home made pressurising system.

Changed oil and filter.

Drained and replaced coolant.

Oh, and fitted new bluetooth radio.

Took out for a spin to discover the real car that was hiding behind all the old, worn out components. Happy days.

[DC242]

Following on from the complete once over, the cars been as happy as anything (like myself). So yesterday went for a 250km trip around the bay.

Drive went like this:

Waverley to Dromana, stopping for fuel - everything ok

Dromana to Sorrento - everything ok

On and off ferry - everything ok

After lunch - car started ok, drove down road approx 500m and car felt lazy, wouldn't idle, "stutted" when driving at constant throttle. Drive from Queenscliffe to Geelong has a lot of lights. Because we were still over 100km from home, stopping to see what was happening could have been disastrous if car didn't start again, also I had no tools. At traffic lights and rail crossing I had to play the throttle to keep engine running.

Once on the Geelong freeway to Waverley, problem cleared up, pulled in 5th gear, sat on 100kmh, idled at first set of lights and when back in garage. Problem gone.

This morning I checked the spark plugs and they all showed signs of carbon build up around the edges but the electrode and tip were clean, obviously from it clearing the fault. All leads still intact, no loose wires, cap or rotor. Car started up easily after drive and again this morning and idled happily.

So, where to from here. Thinking out loud. A faulty fuel pump wouldn't be a cause of rich running. For all spark plugs to show carbon deposits, possibly a faulty ignition coil to distributor lead, but how would it come good. Could a faulty alternator be a cause. Volt meter on dash not accurate at all so no help.

This is very frustrating as the problem occurred without warning and disappeared again so trying to recreate it could be difficult.

[DC242]

So after a day of checking and re-checking things, a test drive with a multi meter plugged into the cigarette lighter revealed a sluggish electrical system. At rest, with no load, the battery was at 12.7v. When started, the voltage would go to 13.1v but no higher. Even when driving the voltage sat around 13.02v, but would drop to 12.88v and as far down as 12.7v with no added load on the system.

At one stage, the voltage dropped down to 12.4v and the car stalled when stopping at lights. On re-start, things went back to the 13-12.7v range and didn't look like stalling.

On arriving home, a test directly on the battery showed 12.7v after an hour of sitting, and when started, the voltage only went to 13.2v. With load (headlights and heater fan) the voltage dropped to 12.88v and never recovered.

So my guess is the ecu needs to have good voltage to keep things operating or it cannot send enough power to the ignition and injectors. My previous car ran an after market ecu and it was susceptible to low volt hiccups also. 

Looks like a test of the battery and alternator are next on the list.

Anyone got any recommendations if a new battery is required?

[StevepGT3]

voltage regulator can also cause these symptoms

[Redracn]

Air flow meter or air leak into inlet manifold like a pipe/hose not fitted properly or cracked. Could also be any other sensor. Unlikely to be voltage as the ECU should be fine down to 8V or you would not be able to start the engine. Problem could be with any number of electrical connectors so cleaning them could help and is a good to do to any older car. How good is your multi meter as they are not all equal. If excessively rich you would see black smoke comming out the back. Based on plugs I would not assume rich so not rule out the Fuel pump or fuel pressure regulator. 

Intermittent problems are the toughest to find so best to be prepared to do some diagnostics when it is happening. 

[TINGY]

3 hours ago, StevepGT3 said:

voltage regulator can also cause these symptoms

What Steve said, coil to dizzy cap lead also and or all the leads.

[Redracn]

Most ignition faults result in misfires. They start at peak torque when cylinder pressure is highest as this is when the highest voltage is required and slowly get worse. This is the case for a coil with internal winding shorts and for ignition leads both for internal breaks and insulation breakdown. Based on the description I doubt ignition is the issue. As far as fuel goes being rich up to the point of missfire makes some but but not a significant reduction in torque. On the other hand lean mixtures result in a significant reduction in torque before misfire. The description of putting the foot down and having no power best fits a lean mixture unless there is significant misfire or very significant black smoke from the exhaust. It is best to keep an open mind as I have seen many many people focus on the wrong area.

[DC242]

Chasing a fault like this is difficult because when it happens, the car will not run/idle.

After my last post yesterday, another drive to go out into the evening was cancelled because of an immediate re-occurance of the problem. Again going by the multi meter, turning the key volts went from 12.7 to 10.3 and back to 12.5. The voltage fluctuated a bit but never got over 12.7v. By 500m down the road, the volts were down to 12.48 and at the first set of lights 12.4v and the fire went out. Car restarted but volts stayed at 12.4. So with black smoke evident in the mirror and playing the throttle we returned home, at which time the volts jumped to 13.05v and the car ran like new, happily idling and revving.

So todays task is to check all connections and make sure the alternator exciter wire is operating and establish the voltage at the alternator.

Question. Why does the alternator have a cover on the back with an air hose. Do they run hot or is the hose for venting? Not seen this on any other car.

[Stew F]

http://www.clarks-garage.com/shop-manual/elect-22.htm

Here's a link to some info you might find useful.  

And this from 944 Online.

WHEN YOUR 944 - 944s 944 turbo/951 944s2 - WAS BRAND NEW THERE WAS ON THE BACK OF THE ALTERNATOR A PLASTIC DUCT THAT SERVED TWO PURPOSES - 

# 1 IT PROTECTED THE BACK OF THE ALTERNATOR FROM THE ELEMENTS , ROAD CRAP, DIRT AND OTHER STUFF , THAT MIGHT DAMAGE IT , AND IT ALSO HAD A HOSE ATTACHED TO IT THAT ALLOWED IT TO BE COOLED FROM OUTSIDE AIR- 

On 15/12/2017 at 3:10 PM, DC242 said:

I'm also thinking my title needs to be changed!

What's it mean?

[DC242]

Thanks everyone for their input. I've changed the topic name to better indicate what the issues are.

Well, what a morning. Multi meters on alternator and from cigarette lighter. Both within .01v of each other at rest. Close enough.

Igniter wire checked and confirmed to be connected and working. When car first started this morning alternator was showing 13.5v, steady.

After 1km with no load, alternator showing 12.9v up to 13.2v.

After 5km, I had 13.18v down to 12.9v.

After 10km, I had 14.5v and rising whilst stopped at lights so pulled over and as soon as I did I had 13.18v again. All this without load.

So shut things down for 20min or so and started off again, this time with a/c on ( was getting real hot in the car)

Within 1km, alternator was showing 12.9v and dropping slowly even at cruise. At lights, this went to 12.5v and wanting to stall.

By the time I returned home, the alternator was really under stress and car would stall as soon as the clutch was engaged.

Will be visiting auto electrician in next couple of days to get expert opinion.

As for the rear ducting, I've never seen this before and as there's not hose from the rear shroud to the next piece of ducting I'm not sure if it works as intended.

 

[TINGY]

4 hours ago, DC242 said:

 

Will be visiting auto electrician in next couple of days to get expert opinion.

As for the rear ducting, I've never seen this before and as there's not hose from the rear shroud to the next piece of ducting I'm not sure if it works as intended.

 

Good luck with the Auto eleco, I hope you get someone good, from my experience these cars a like an enigma to them.

Re, the alternator ducting,  from what i have been told and also read, if it's not fitted, re-fit it.

[Buchanan Automotive]

Get a new alternator ( exchange etc from Pelican / Paragon etc  ) do not try to fix it , if its 30 years old ( may well be ) , do not throw money at an alternator that old & at the same time replace the earth cable/s between the engine & body & the battery and body , then go from there 

[DC242]

Earth straps are a given ( been there with previous car). I would also hope an alternator rebuild is the same no matter what the brand ( I hope).

Will check out exchange units if overhaul cost is ridiculous (could well be).

 As for the rear air shroud, how many cars have this? With and without during my test drives showed no obvious difference in operation. I'm guessing, the purist would like to see it fitted as original but from a functionality point of view, does it really serve any performance purpose?

[TINGY]

13 hours ago, DC242 said:

Earth straps are a given ( been there with previous car). I would also hope an alternator rebuild is the same no matter what the brand ( I hope).

Will check out exchange units if overhaul cost is ridiculous (could well be).

 As for the rear air shroud, how many cars have this? With and without during my test drives showed no obvious difference in operation. I'm guessing, the purist would like to see it fitted as original but from a functionality point of view, does it really serve any performance purpose?

I guess if it didn't do anything it wouldn't be there

[DC242]

Ok. Shroud is because of units type of construction resulting in  heat not being able to escape properly (especially in turbo cars). Will need to find an intermediate hose piece to make sure rebuilt alternator survives.