Poor running help

[C2dweller]

Any chance of some more ideas? It still seems very jumpy when decelerating under low rpm. Tickover is a bit lumpy.

Work to date:
cleaned the ISV & MAF
Tightened the hoses
Replaced the O2 sensor (with a Bosch type)
Replaced dizzy caps
Checked eng temp sensor
Checked air temp sensor

I did a test of running it off the different distributors - one seemed a bit worse than the other but nothing major.

When I drove it in the rain it seemed quite flat - is this a clue? After speaking with a mechanic, he thought this was a definite ignition problem worsened by the additional the moisture level in the air.

I've got some spark plugs and a feeler guage, so this is this weeks work. Doubtful as car had a major service at Porsche a few thousand miles ago (although cat pipe bolts had not been removed for some time!!! making me wary)

Cheers, Lee

 

[Steve Brookes]

Poor running in the wet is often a sign of bad plug leads....unfortunately they are very expensive!

 

[AVI_8]

Start your car up in the dark and have a good look around all of the plug leads, if there's any tracking it will be obvious.

You said you replaced the dizzy caps, how were the rotors? My tickover was a bit lumpy but since my engine service it's transformed the car, I replaced my rotors and caps, comparing the new to old rotors there was a difference, other than that I'd do a google search on the rennlist forum or pelican parts forum stating 964 rough running, I'm sure you'll get a lot useful info for other things to check

 

[C2dweller]

Cheers Steve / AVI_8.

When I first inspected the dizzy caps & rotors I cleaned up the rotors and they looked fine (whereas the caps were definitely passed their best).

I've spent many long hours looking on rennlist and 911uk and nothing quite hits the spot. I do keep going back with new search terms.

I may try and measure the resistance of the ignition leads, to see if this throws up an anomally. 3 spark plugs when in last night and my feeler gauges arrived today. AVI_8 - I'll be using your engine service post for reference!

Lee

 

[Alexander_Drobik]

could not help notice this one - apologies if this has been said before - but are you sure the air flap is working correctly? I am not sure this is ignition, sounds like a fuel/filter/air flow measure issue. Did you check to see if it is running rich?

If it is leads/plugs - it should have been spotted by now.

Hope it gets sorted quickly. Good luck.

 

[AVI_8]

Lee, If you want any advice on the job send me a PM and I'll give you my number, think I covered most points but if there's anything you're not sure about once you've started feel free to call

 

[C2dweller]

One side of the engine done now, so I'll start it up tomorrow to make sure I haven't completely messed up the valve clearances. I'm a bit worried that all (both inlet & exhaust) needed 1 hour of extra gap (best way of describing it).

Some of the plug gaps also looked noticeably tighter than the 0.7mm gap recommended for the Beru plugs. Nothing too alarming with the condition of the plugs though - more grey than brown but OK IMO. Some very light blistering on some. They should have been changed a few thousand miles ago when it had a major service at Porsche, but I'm not convinced.

 

[AVI_8]

Must admit that I find that a little strange Lee, I've adjusted the valve clearences on many dozens of engines over the years and have never had to adjust more than a few of the valves on a particular engine. I presume that you are finding the gaps too large?

I think possibly that my idea of normal (a very slight drag on the feeler guage) maybe you're idea of a bit loose, buy hey as long as the feeler guage moves without force it'll be fine, just remember it's better to be a bit loose than too tight and if you have to forcibly pull the blade out it's a bit too tight, I used one blade whilst doing my adjustment and didn't damage it, if you're having to replace the blades possibly you're adjusting them a bit too tight, hope that makes sense.

Logan

 

[C2dweller]

No the opposite - too tight. In hindsight I should have tried the other method as a check - where you close down the gap and adjust out a set number of degrees to achieve the 0.1mm gap.

All will become clear when I start it up tonight. []

 

[AVI_8]

Might seem like a silly question but you are checking the adjustment at the correct end of the rocker ie, at the top of the valve stem and not at the camshaft end?

If you were checking the gaps at the camshaft end it would give the results you're seeing.

 

[C2dweller]

Can ran fine - well as fine as it does. It didn't sound noisier, so I'm sure all is OK.

AVI_8 - I did pause when I read your post, but pretty sure I got the right end. Cheers for comment though.

I've moved onto the near side now. I'd be amazed if the cat or the engine tin had been off in the last 10 years - good old main dealers...

 

[C2dweller]

I think changing the plugs and setting the valve clearances might have done the trick. The decelleration lumpiness has gone.

I am concerned about how tight all the valve clearances were - I undid a lot of them by as much as a 12th of a turn, when it should only take a 10th from fully closed!

I'm going to reset them again using the 9m angle method (see rennlist) - Gunson actually sell a tool which helps called the click adjust. This will also take account of any wear between the rocker and the valve.

Cheers for all your advice & help.