Badly running 3.2 Carrera

[88targa32]

Hi all,

My first post here so hopefully you guys can help me out.

I have a 3.2 Carrera (1988) that has been running fantastically for ages now. Last week I changed out the distributor cap & rotor arm as part of general maintenance & now it runs terribly. The symptoms are as follows:

It starts first time & idles at 880 but there is an unburned fuel smell. It has a slight hesitation in the throttle so it is not as smooth or as linear as it was previously. Almost like it is not firing on all cylinders. Once warmed up at around 10/15 minutes, there is a massive flat spot like no spark or no fuel. It then kicks & bucks for a bit. Engine stays on, it never stalls, just no power. A minute or so later, away she goes. Hesitation is still there & the flat spot kicks in randomly. It has gone from a car that you would trust pulling out of junction to a car that you need to think about before you make the move. Again, it ran beautifully before this.

I have reverted back to my old distributor cap & rotor arm but strangely, the issue is still there!

I have also changed the fuel filter, plugs twice, plug leads twice, DME relay, 2 caps & arms, even swapped out the air flow meter to one that is only 2 months old & working perfectly in another Carrera but no change. I have cleaned & sanded all earth/ground points. Plugs are all a nice tan colour.

It has 95,000 miles with a fully documented Porsche History. Top end rebuild 2 years ago. Vacuum leak check all clear. Leads all in the correct orientation.

Has anyone experienced anything like this from their 3.2 & if so, can you shed any light on a possible solution??

Thank you all in advance.

Alan

[SilverWT]

My feeling on reading your description is fuel delivery.

Maybe the fuel pump is playing up, or sucking crud from the tank.

Or possibly the fuel pressure regulator, or pressure damper.

 

Mark

 

[88targa32]

Thank you Mark,

Would the pump not act up all of the time if it was on its way out? Are there any tests that can be done on the regulator or damper? It was driving absolutely perfectly up to the distributor cap/rotor arm change. The unburned fuel smell in the engine bay tells me that it is getting fuel. 

I have just pulled the plugs again & for the first time, they look a little bit sooty. They were a nice even light brown/tan recently. Now, I only had it running in the garage & not really driving on the road so maybe that i sthe reason here. 

I have had people say it is the air flow meter, the cylinder head temperature sensor, the ecu & a number of other things. If I go at chaning every part on it, I will never know what has actually fixed it & I would be seriously out of pocket too.  I am just too comfortable with this shotgun approach. I am hoping someone here has experienced a similar issue & hopefully can help me out. 

Thank you again Mark, I am definitley going to check the fuel pump to rule that out (or in).

Alan

[sopor]

Can you double/triple check that all the plug leads are in the correct sequence? Easy mistake to make.

[Ian Comerford]

7 hours ago, sopor said:

Can you double/triple check that all the plug leads are in the correct sequence? Easy mistake to make.

And fully seated

[88targa32]

Hi guys, yes that would appear to be the most obvious mistake & solution but I have refitted the leads probably 10 times now to just to make sure. I have even numbered them in bright colours to make sure they are all in the correct order, both on the cap & on each plug 🧐

Thy all "click" nicely into place at both ends too.

I have a new coil & main earth strap to fit today. They can't hurt. (Main earth strap from engine/transmission to chassis was a bit tired looking)

I have been all around the rear of the engine with a camera to check each pipe, connection, cable etc. All appear to be in good condition with nothing loose & nothing cracked or leaking.

Keep sending suggestions 👍

[sopor]

Longer shot yet… dizzy rotation direction on a 3.2 is clockwise. Firing order is 1,6,2,4,3,5. Ignore any numbering that might be on the cap.

Confirm Cylinder 1 location on the cap by lining up the timing mark on the crank pulley with the engine case pointerand having rotor point to notch inside dizzy.

Looking into the engine compartment:
Left side, from the rear of car forwards - 1,2,3
Right side, from the rear of car forwards - 4,5,6

 

[88targa32]

Thanks Sopor,

Good shout, I have naturally looked at the numbers on the cap for the order but maybe these are not in the correct sequence. However, each cylinder fires & there is a decent spark at each plug but it does feel like its only running on 4/5 cylinders. None of it makes any sense to me at the moment.

Alan

[Type911]

You have this sticker on the slam panel?

[sopor]

Is my memory correct - the SC is the odd man out where the dizzy rotates ACW whereas all the other aircooled engines have dizzies that rotate CW? Not that we’re talking about an SC here.

And maybe it’s just me but that sticker can create confusion because the wider section of the engine is meant to be the flywheel end but it could be misunderstood as being the fan. The arrow should help but…

Every time you try to make something idiot proof a smarter/dumber idiot comes along.

Edited June 15, 2024 by sopor

[88targa32]

Type911 - Yes I have this label on the slam panel - I have it imprinted on my brain at this stage 🤣

Sopor - How true is that. I also presume the layout of the plug wire harness will help to dictate where the leads go too. But yes, I will 100% check these again later today. As mentioned, everything sparks but it just feels like it is not firing on all cylinders when under load. It is so frustrating 😕. The fuel smell also tells me that there is a lot of unburned fuel & no spark to ignite it. I will go back at it with a clear head later today.

Cheers guys & keep the suggestions coming. I will post the solution here when I/we get there so hopefully it will help other owners with a similar issue.

Alan

[angusb]

On my car, one of the clips with hold the Dizzy cap had been mullered, allowing the cap to sit at a angle. Other than that , even if the plugs are in the correct firing order, if they are connected in the wrong orientation relative to the  cap, you can knock the timing out causing the symptoms which you describe.

[Chris T]

Another simple one. Double check the rotor arm is pressed onto the distributor shaft fully, they can be stiff to go fully on. Cheap fix if you are lucky! 

[88targa32]

Well,

This morning consisted of fitting a new transmission ground strap which was a total pain in the rear! New coil fitted too. Swapped out the rotor arm as the one in it didn’t seem to fit tightly. Rerouted leads, reseated dizzy cap, confirmed leads again. She started on the button as usual, ticked over nicely & settled into a nice idle. Took her for a spin and only got 100 yards down the road. Loss of power, engine hunting wildly. 2 minutes later and it was revving normally but still hesitant under load. Totally bewildered with it now. 
 

Please keep the ideas coming. 
 

Happy Father’s Day to all the dads 😉

[angusb]

Not sure if this will help . What would suggest is to use a Ignition tester to check that all leads are indeed receiving a spark. (These are cheap as chips tool ,just held against the lead, and flash when there is a spark) . I everything is working well , move on to the plugs, and check they are gapped correctly, Its very unlikely, but check that the distributor pinch bolt is tight.

   If all is good , then the Ignition system is good, move on to the other items which may cause trouble:

   Is the Oil cap properly on ? It forms part of the vacuum system

   Under the N/S/R wheel  there are two flywheel sensors. Look at  insulation on these wires, is it in good condition ?

 You replaced the  Fuel filter, is it a OEM item ? There is a vacuum hose  on the rear of the Air Filter box, is it loose? 

 Is the fuel fresh? 

  There are various other tests which can be made, but these require diagnostic equipment, These are detailed in the Workshop manuals, download able from the Technical section.

   

  

  

  

[88targa32]

Thank you Angus,

Oil cap is good, fuel filter is good. The 2 sensors do show signs of the insulation breaking away & I have just checked the cylinder head temperature sensor, it seems to be the single cable type. A lot of comments online say this should be changed to the upgraded 2 cable type with built in earth. 
I’m just still a bit confused that this all started when a new dizzy cap/rotor arm were installed. It was perfect before this but even with the old cap and rotor arm on now, it’s still bad. 

[sopor]

Kinked fuel line at the filter?

Can you put a fuel pressure tester in place and see if the pressure remains good while the car is running poorly?

[88targa32]

Thank you Sopor, fuel lines all good. 
The car rev’s nicely while stationary. It loses its power intermittently when under load. It just bogs down and reverts to idle. I’m not sure if there is anything left to try on the spark side of things so maybe it is down to fuel and air. 
Has anyone had any experience of the the 3 sensors giving trouble? Speed & reference sensors & the one that pops up a lot on other forums I’ve cylinder head temperature sensor. 
Could be time to get it into a good Porsche Indy to sort. They will just want to throw every new part available at it. 
 

Cheers guys for the input. If anything changes, I will of course update this post. 
 

Alan

[Chris T]

10 hours ago, 88targa32 said:

Has anyone had any experience of the the 3 sensors giving trouble?

Yes! Every 3.2 owner out there has at one time or another had issues with these. As said elsewhere here 'if they are original and currently not broken, they soon will be' If the insulation is cracked change them, if they are original, change them..... CHT sensor too while you are in there! Talk to Matt, he'll sort you with some quality replacements. DIY job too with some patience. 

[sopor]

And back to fuel delivery for a moment… fuel requirement at no load is quite low regardless of engine speed. So a car that idles and revs fine when stationary but then starts to stumble under load at speed could well have a fuel delivery issue. 

[Nige]

Have you removed AFM or upset it an anyway?

 

Speed sensor issues usually give a non start.  I'd be looking at the fuel filter, or at least putting the old one back on if you still have it, just to rule it out.

[88targa32]

Thanks Chris T, yes they all look to be original to the car & the CHT has only 1 cable so I am assuming it is the older type.

Nige, yes the AFM was removed as it was a suspect with this issue. We fitted an almost new one from a known working 3.2 & it made no difference. It was only a 2 month old Porsche supplied exchange unit too. Having said all that, my original one was tested & it does show a voltage drop in the sweep but as I had swapped it out to the known good one, I have ruled that out as the issue. Would you think that could still be a factor here?

Thanks again.

Alan

[Nige]

Sounds like you've tried every option related to electrics, from my experience with speed sensors one mine they either work or don't with nothing inbetween so as it starts and idles fine I'd rule those out.  I would expect the same for the ECU, it either works or doesn't.

 

[88targa32]

Thanks Nige, I think as mentioned above, I probably need to look at fuel, pressure, pump, regulator, damper or possibly a stuck injector.

The quest continues 🙄

[88targa32]

A quick update on this.

I thought I found the problem yesterday. The centre metal piece inside the new rotor arm that connects to the distributor shaft was missing. No metal piece inside at all! I also noticed some scratch marks inside the new dizzy cap. This has to be the cause. So, off to my local Porsche Centre who had these 2 parts on the shelf. An hour later, all fitted & up she started. Drove fine for 10 minutes & then the dreaded flat spot yet again 😪

Fuel pressure test being done today so fingers crossed, this is the right direction to go 🤞

I will update the findings later.

Alan