944s Cold start ignition issues

[finnystew]

Hi all,

I bought myself a 1988 944s a couple weeks ago. It’s been going great except it has some issues with cold starts.

The car struggles to idle and drops down to 800rpm while sputtering until I give it some revs for a couple minutes and then it’ll stabilise for the most part. It seems quick to stall and sputter at low revs while driving also.

The engine seems to be running too rich as I burnt fuel is going out the exhaust and upon inspection the spark plugs were black with carbon build up. I replaced the spark plugs with NPK titatium tips that were replaced and provided by the previous owner along with the ignition coil.

The issue seems to have exacerbated after I took it for a spirited drive during which I smelt unburnt fuel after some acceleration.

Next I’ll probably check cracks in the vacuum lines and distributor.

Any suggestions/ Theories?

Thanks

[Buchanan Automotive]

Hi Finnystew,

There could be a lot of issues going on, may be a good idea to check past maintenance and see what has been replaced in the last few years. They are now at the age where the factory wiring harnesses are getting on and in most cases deteriorating. check for cracked connector boots. Particularly in your case around the throttle position sensor, idle stabiliser valve, NTCII sensor(coolant temp) and speed reference sensors. While you are at it also have a good look at the injector plugs. they may seem OK but because of their design previous repairers will grab at the wire harness to remove the plug instead of disconnecting the clips. in almost all cases you will find the wires inside the connecters to be frayed. 

Being an S the throttle position sensor is in a difficult position. I would want to check for operation of the sensor at the ECU first before trying to get access to it. Basically its inlet manifold off to get at it. It was also common for tuners to remove the air mass meter and adjust the spring inside to add or subtract fuel as needed. this will be evident if there is silicon holding the black cap on the air mass meter. It may also be an air mass meter issue. They are very long lived but nothing lasts forever

Regards

Sean

[TINGY]

Could be as simple as plug leads, dizzy cap or rotor button, these three items combined caused a failure to proceed on an '86 car that i had.

[tazzieman]

Those vac lines are very pesky and many have never been replaced. Cracks are sometimes subtle and hidden. Like under the manifold.
A good time to "ground zero" everything rubber if it's the least bit hard , crunchy and well, suss. 

[finnystew]

So... 

Upon reading up on the previous owners notes I know that he was experiencing the same issue.

’hunting’ ‘sounds like it’s running on 3 cylinders’

He replaced the dist rotor cap which was cracked and the rotor button which was worn,

spark plugs, ignition coil, an alternator rebuild which had been putting out low voltages and is what he claims fixed the issue. 

However here we are... So my main suspect now is the spark plug leads as @TINGY996 suggested. Running the car with the 1st cylinder’s lead out has no change. It also shocks me if I touch parts of it while the car is running. So perhaps it’s loosing charge on its way.

Just tested the lead by pulling it out and holding it against the metal of the manifold in the dark. Sparks are showing all the way across the rod that meets the spark plug. But also on the lead. Which is why I was being zapped.

anyone know where to get a set of leads??

[Buchanan Automotive]

good find, make sure you buy the correct beru leads. Bob whymms or autohaus should stock them. there are aftermarket versions but in all honesty they are absolute rubbish. Stay away from any carbon leads. 

Regards

Sean

[TINGY]

On 08/02/2019 at 08:22, Buchanan Automotive said:

good find, make sure you buy the correct beru leads. Bob whymms or autohaus should stock them. there are aftermarket versions but in all honesty they are absolute rubbish. Stay away from any carbon leads. 

Regards

Sean

Absolutely what Sean said, go Beru leads.

I had spark at every plug and lead just not enough to make it fire, it really threw me, after new plugs, leads, dizzy cap and rotor it fired up straight away.

[finnystew]

Okay so Beru leads finally arrived. Plugged them in... no go. Still sounds like cylinder is not firing for the most part and unburt fuel coming out the back. No sparks coming out of the lead now though so atleast that’s something.

 

I really thought that was the issue. Thoughts? Might have to make a trip down to the local Porsche specialist

[Buchanan Automotive]

So now there is no spark coming out of 1 lead or all of them? work backwards to the coil. did you remove the cap and inspect both he cap and rotor. 

Make sure the leads are in the correct positions on the cap

Regards

Sean

[finnystew]

Removed the cap again and inspected both. Showing signs of some wear but looks good. 

The car came with a different lead arrangement to that shown on the cap. So with the new leads i tried the way shown on the cap- wouldn't start.

Switched it back- wouldn't start. 

The coil was changed recently.

[finnystew]

okay so. I did a compression test today which came up all good.

then after installing all the plugs and leads again the engine fired up and is now doing much better. 

However, it’s still behaving similar to when I started. Hunting to idle and stalling very easily especially on cold starts

Also noticeably misfiring but less than before.

It also bucks and shudders in low gears when I let off the gas but also sometimes with the gas.

I will be investigating the idle control valve and a couple sensors mentioned earlier in this thread.

Good to have to it running again though

[944s2cab]

can you clarify, is it misssing on one cylinder or all four, pulling individual leads off their  plug and seeing if rpm drops on every cylinder, You say the plugs were black, are any of them wet with unburnt fuel? 

KISS principle, these engines are rather simple, all you need to run is, compression, (metered) fuel and spark at the right time

Have you looked at your injectors,  one or more could be leaking, 

Wrong  injectors fitted 

here are some way out there possibilities,

Wrong DME (maybe someones fitted a 944S2 one, 

Right DME but with an aftermarket chip

if I was a betting man, I'd bet on injectors

[finnystew]

I cannot seem to isolate any particular cylinder but pulling the leads.

This arvo a mechanic dropped by to pick up another car and had a look at the 944s and gave some casual advice. He too pulled the leads to no avail.

Suggested it could be a bad lot of fuel. So i pulled the fuel sender line and inspected it. Looks fine to me, however the issue did arise soon after filling up.

Also mention adjusting the AFM since its running too rich

Injectors are the same dark green ones as stock. The plugs have been wet with unburnt fuel when I inspected them. So I will inspect the injectors next.

 

[finnystew]

So I’ve pulled off the fuel rail. Next I’ll test the resistance on the wires and test the injectors.

Unfortunately the little rubber bit on the injector came off while I was pulling for the fuel rail and it fell off into the cylinder. So now I’ve got a whole lot more work ahead of me :((

Also noticed this nick in the return line.

[tazzieman]

We've all dropped stuff into cylinders! At least it's rubber.
If they are the original fuel lines , now is the time to replace. They are almost certainly hard and brittle & may look good on the outside, however...
Your mention of the issue arising after a new tank of fuel is I think telling us something. Even thought the PO had some issues.
I'd drain the tank as well. 

[finnystew]

I’ve managed to retrieve the end bits off of the 2nd injector. Luckily the engine was turned off such that the valves were shut and I just needed to take the intake manifold off to get them.

its obvious why the nob came off upon inspection. It’s cracked. Could this potentially be causing the issue? Leaking fuel or mucking with the spray pattern?

or does it merely protect the injectors nozzle?

Yet to test all injector connections

[tazzieman]

Don't like the look of that! You can pulse 12v through an injector with some carb cleaner running through via a pipe (Ghetto bench clean)
You'll get an idea of the spray.
I've done it btw.

 

[TINGY]

Pretty sure you can buy the caps of the end and i know you can get the seals @finnystew

[finnystew]

Fixed the issue! No more hunting or misfiring.

turns out it was the injectors. The caps were old and falling off the injector and covering the nozzle, thus disrupting the fuel spray. One was an incorrect type without the bevel inside and another cracked. 

Gave them a clean with carb cleaner, replaced filter baskets, o-rings and caps from 80s falcon models. Which are compatible funnily enough. Got it all from a man who used to race Porsche’s and falcons!

Thanks for the help everyone

[firstone]

Awesome. Well done. Must nice to drive again.

[finnystew]

1 hour ago, firstone said:

Awesome. Well done. Must nice to drive again.

Definitely a good feeling

[944s2cab]

Well done, What's next on the list?

[finnystew]

On 12/03/2019 at 22:09, 944s2cab said:

Well done, What's next on the list?

Investigating a shudder at low rpm in first gear happeneing when I come off the throttle. Really annoying when driving around town.

Then replacing the headlights with LEDs (ideally warm white). It’s just too dangerous to drive at night with these dim halogens. Along with some interior lights. 

Hopfully get the shifter a bit less swampy. A tune. 

Then I want to get it set up for a trip to the snow season coming up. And I’m sure other things will come up as they always do.

[944s2cab]

12 minutes ago, finnystew said:

Investigating a shudder at low rpm in first gear happeneing when I come off the throttle. Really annoying when driving around town.

Then replacing the headlights with LEDs (ideally warm white). It’s just too dangerous to drive at night with these dim halogens. Along with some interior lights. 

Hopfully get the shifter a bit less swampy. A tune. 

Then I want to get it set up for a trip to the snow season coming up. And I’m sure other things will come up as they always do.

I got these, https://www.ebay.com.au/itm/2x-H4-CREE-LED-Headlight-Car-9003-HB2-180W-6500K-Replace-Hi-Lo-Beam-Bulb-Lamp-t/192760842518?hash=item2ce1710916:g:rFoAAOSwfgRb2Qr6, a lot better than stock, a bit blotchy on solid verticle surfaces (like a wall) up close, although probably too blue for your (and my) liking, if the shifter play is side to side, there is a mod with thrust washers and a nut and bolt, https://rennlist.com/forums/924-931-944-951-968-forum/698280-mini-project-tightening-up-shift-linkage.html, I found that the bolt/nut hit the side of the tunnel so had to clearance it,

 

[tazzieman]

3 hours ago, finnystew said:

Then replacing the headlights with LEDs (ideally warm white). It’s just too dangerous to drive at night with these dim halogens. Along with some interior lights. 

I upgraded my halogen globes on my S1 ; perfectly happy with the result for not many $. And I drive along a bush road at night ; I need to see the animals !