Jump to content
Sign in to follow this  
finnystew

944s Cold start ignition issues

Recommended Posts

Bad news.

Misfiring is happening again. But intermediately. Sometime on a cold start it just takes about 5 mins of running to get it to clear up and it'll run perfectly. Other times it just misfires a little but (Drivable). Then today it was misfiring so badly that I drove home after a test drive with several stalls and a huge amount of unburnt fuel coming out the back. 

Something I've also noticed is that if the engine starts to misfire, I can change the calibration for the AFM to make it run leaner and it sometimes magically comes good!

Also in the last couple days it has developed a problem that was there when I first got the car, but seemed to have gone away. This is that after the driving the car for 5-10 minutes it will start shuddering back and forth violently. Particularly on acceleration. It does this until it cant take it and the engine dies. However if shuffle through the gears I can stave off the engine dying (switching back and forth between 3rd and 4th)

To update, i've replaced recently: Spark plugs, Leads, injectors seals, filter baskets and hats (which seemed to solve the issue but alas). I also have the injectors a DIY clean and tested the spray which looked perfect. 

Share this post


Link to post
Share on other sites
2 hours ago, tazzieman said:

Are you sure you haven't got a split vacuum hose somewhere?

Cant be sure no. Ill look into doing a bubble spray test tomorrow. Is this characteristic of this behaviour?

Seems like it could explain the intermittent nature of the problem. (sometimes sealed, sometimes not, sometimes sorta)

Thanks 

Share this post


Link to post
Share on other sites

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

How did you get on with the, TPS? have you tried running without it, if the TPS WOT switch (or it's wiring) was shorted it would bring in a different (richer) map, and ultimately I reckon that's what's causing your issues, over fuelling causing fouled plugs, check your (DME) coolant  temp sender as well, 

with these tests it's best if you test at the DME plug, so you test the wiring as well.

List of things which effect  (over) fuelling

Engine temp.

AFM, inc. air temp

TPS

Fuel regulator

injectors

Have you checked you FQS on the DME? https://www.google.com/search?q=PORSCHE+968+FQS&source=lnms&tbm=isch&sa=X&ved=0ahUKEwis_4y-x5LhAhXCAnIKHWcaAKsQ_AUIDigB&biw=1215&bih=666#imgrc=TIi78SqLe-SnFM:

I know how frustrating and demoralising it can be when you have engine issues but you'll get there

Share this post


Link to post
Share on other sites

After the vac line checks which you need to do anyway (splits can be hard to diagnose , sometimes wiggling/pushing on each hose can affect the idle by opening up a split). There are some awkward to get at spots.
Fuel pressure regulator?
What about your ECU? Intermittent problems are often electrical. The soldered joints get brittle after all these years + vibrations. They can be reflowed. Easy to pull and inspect the board for obvious  burns etc. Can you borrow an ECU - quick efficient way to test if your is faulty?
Bloody annoying all of this , but at the end of the day you will have a fine car that runs as nature intended.

Share this post


Link to post
Share on other sites
15 hours ago, 944s2cab said:

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

How did you get on with the, TPS? have you tried running without it, if the TPS WOT switch (or it's wiring) was shorted it would bring in a different (richer) map, and ultimately I reckon that's what's causing your issues, over fuelling causing fouled plugs, check your (DME) coolant  temp sender as well, 

with these tests it's best if you test at the DME plug, so you test the wiring as well.

I didnt end up looking at the sensors since my mechanic said those are 'trimming devices' and thus wouldnt be causing the misfiring. However, the TPS diagnostic page on clarks garage seems to fit my issue almost perfectly.

  • Poor idle - particularly a high idle condition
  • Engine cuts out to an idle condition during acceleration
  • Poor power at various RPMs (various throttle positions)
  • Surging idle
  • Misfire
  • Stumble during acceleration

So i've got the DME out and my multimeter. Only seem to be reading OL for it all though. Im probably missing something obvious. 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

PFA [Porsche Forum Australia]

This is an online platform for like-minded Porsche fans/fanatics/tragics to come together to read, chat and share.

It is also a platform to arrange and participate in off-line social meet-ups, events and drives.

×
×
  • Create New...