'99 996 cab tip: misfire & stalling - *valve problem!*

[slknv]

So a month ago, my 996 died while on the way home, managed to limp into the garage. Wonder if there's anyone smart out there to help me get it running again!

Codes pulled for misfire on 6. When trying to start, it catches OK (starter and crankshaft position sensor OK) but idles really low, sounds like starved of fuel, dies within seconds - unless I hold the throttle to 1000rpm. Codes sometimes reads 5 & 6 misfires. Kept a little diary at www.dtmtune.com 

So far, I've

• replaced spark plug tube, coilpack and spark plug on cylinder 6
• Dropped oil, changed oil filter
• New oil pressure relief spring and piston (997)
• Cleaned MAF - tried starting with MAF disconnected and same issue
• Cleaned throttle body
• Cleaned sticky IACV - was all gunked up
• Tested fuel output - got 850ml in 30 seconds from the return fuel line as per factory spec
• Tried starting while bypassing fuel pump relay with a fused wire, same problem

Any and all suggestions welcome... been driving my cayenne while the 996 is offline, and of course it throws a low coolant warning and had it towed home a week ago!

[Zelrik911]

That is a good blog diary - I will look through it tonight.

Lucky you have a Nissan for when the P cars go on strike !!! 😀

[911CSR]

Sounds like it might be an injector, fuel pressue regulator not operating unde rload/pressure or fuel rail issue...Can you check the fuel pressure while running or under load??

If the pressure drops under load it may be a bad reg. if 5 & 6 are at the end of the fuel rail before return etc.

It could also be the injectors themselves or the rail or lines are gummed up enough to slow fuel flow under load. 

[slknv]

On 08/03/2021 at 13:06, 911CSR said:

Sounds like it might be an injector, fuel pressue regulator not operating unde rload/pressure or fuel rail issue...Can you check the fuel pressure while running or under load??

If the pressure drops under load it may be a bad reg. if 5 & 6 are at the end of the fuel rail before return etc.

It could also be the injectors themselves or the rail or lines are gummed up enough to slow fuel flow under load. 

Mmm... didn't realise 5 & 6 were last injectors to get fuel, does make sense. I've got an oil pressure gauge which I reckon will do to check fuel pressure too. Will try it this weekend when I get a free moment. Fuel pump seems to be a relatively cheap non-OEM part, unsure on how much a regulator costs.

On 08/03/2021 at 09:48, Zelrik911 said:

That is a good blog diary - I will look through it tonight.

Lucky you have a Nissan for when the P cars go on strike !!! 😀

Can't drive the S15 anywhere, as they tend to get stolen the moment you're not looking at it! Fixed the cayenne on the weekend at least, easy cheap coolant expansion tank swap and it seems to be running fine with no leaks, no change in coolant level, no overheating 😊

[Zelrik911]

On 09/03/2021 at 19:10, slknv said:

. Fuel pump seems to be a relatively cheap non-OEM part, unsure on how much a regulator costs.

 

I think you could get any 3.8 bar FPR that fits - from a local Holden? -  for not much money' to use as a test tool. This assumes that its easy to get to on your 996 but if its difficult to change over then get a OEM one & be done.

Have you tested Fuel tank venting?

[slknv]

On 11/03/2021 at 09:30, Zelrik911 said:

I think you could get any 3.8 bar FPR that fits - from a local Holden? -  for not much money' to use as a test tool. This assumes that its easy to get to on your 996 but if its difficult to change over then get a OEM one & be done.

Have you tested Fuel tank venting?

So, while picking up some parts from doncaster branch today, enquired about price on a FPR - $254 and 2 weeks from Germany. If I can get a generic 3.8 FPR that'll work for $50, I'll grab one and chuck it in! Put a new IACV gasket and recleaned throttle body, visually checked for vacuum leaks (though really need to make a DIY smoke machine for testing) and still starts up, splutters, stalls and dies within 20 seconds.

[slknv]

Still open to suggestions...slowly diagnosing why my '99 996 stalls on startup. Just changed the fuel pressure regulator for a Bosch 3.8 (the old one did have some fuel leaking out the vacuium port), yet still getting horrible idle and stalling.

 

https://youtu.be/A1X6tq596VE

 

If I jump the fuel pump relay (engine off), I get a steady 3.8bar, which drops to 3.2 without fuel pump running, but doesn't drop to zero.

 

However, starting the car (as in this video) we get 3.8bar of fuel pressure, but when the car stalls it goes straight to zero.

 

Getting conflicting results as the fuel pump does correct volume, correct pressure (both engine off and on), so maybe it's not fuel related as I was thinking?

Getting different codes too, mainly relating to misfires on cyl 6 (sometimes 5 as well), P1514 (IACV which I've removed, cleaned, tested working with a 9V battery). Still determined to get this sorted on my own!

 

[Costas]

I could be off track - But there seems to be a lot of mechanical noise (ticking/clicking) present (maybe misfire is contributing to this on the mic pick up) but I would have thought that the engine would have been a lot quieter if it was just a simple fuel starvation problem...?

[slknv]

On 21/03/2021 at 22:43, Costas said:

I could be off track - But there seems to be a lot of mechanical noise (ticking/clicking) present (maybe misfire is contributing to this on the mic pick up) but I would have thought that the engine would have been a lot quieter if it was just a simple fuel starvation problem...?

Yeah sounds terrible. However have made a bit of promising progress - after changing the fuel pump with no improvement, I disconnected the belt and ran the engine - started and idled perfectly! And of course, as soon I replaced the serpentine belt, went back to backfiring and misfiring, then stalling. At least I know know the engine can run perfectly, so now just need to troubleshoot and replace/repair the defective component!

 

[firstone]

Wow, how strange. 

Serpentine belt eliminates water pump, not electrical or fuel so unlikely unless it's a water leak into a cylinder. 

Air conditioning pump, you can electrically disconnect it to eliminate that.

Alternator you can test also. I'm thinking it's this, but you can eliminate the others first.

Do the bearings in the idler pulleys while you're there. One of mine siezed and broke off losing it. Bolt had to be extracted which was no big deal but I had to get a guy in to do it. Not mushroom in there.

[slknv]

23 hours ago, firstone said:

Alternator you can test also. I'm thinking it's this, but you can eliminate the others first.

Yep the alternator / electrical system is definitely the problem!

Today I removed the plugs at the back of the alternator and ran it - car runs perfectly (eliminates water pump, power steering pump and aircon compressor and belt tensioners as suspects). Also means the MAF, IACV, fuel system etc are good. Obviously not a longterm solution to have a disconnected alternator.

Put a replacement alternator regulator in, reconnected it, and once again bad idles, backfires & misfires.

Now that I've narrowed it down to an alternator/electrical issue, where do I go from here?
I replaced the Y cable a couple of years back.
Not a starter motor or crank position sensor problem (it starts no problem, just idles bad, stalls then dies).
Battery tests good and ran the car perfectly fine without alternator connected.

Luckily this isn't my daily driver but I'm getting a little fed up with it!

[st3ve]

Good work with the diagnosis, sounds like you're getting close!
The alternator has a freewheel clutch on it I believe, maybe a problem with that?  Or else a dead short or something otherwise weird going on inside the alternator which causes it to have a much higher load on the engine at idle than it is set up to handle?  As simple as bad bearings in the alt?  Does it sound fine when you spin it or does the pulley clutch prevent that simple test?
I might be tempted to remove the alternator and take it to an auto electrician for testing?

[Stephen Tinker]

Replace the alternator - you have a faulty field winding which is compromising the supply voltage to the ignition system .

If you have a good multimeter, check the static battery voltage with the engine off - it should be 12.6v fully charged, 12.4v @ 50% charged..

Start the engine and you should see 13.6 - 14.5v @ idle @ the battery terminals depending on the battery condition.

 I suspect that the faulty alternator is dragging the voltage down enough to cause the ignition problems you describe....

 

[firstone]

Seems like it to me too.

Other than that I'd check the wiring to it.

[slknv]

Put a new bosch alternator 0 124 515 042 this evening, no improvement - still stalls at idle.

Going to pull it out next weekend and trace back wiring from alternator. Might as well change the starter while I'm elbows deep. At least with Melbourne weather I'm not missing any sunny days with the roof off! Was thinking of selling this car once it's fixed, but I know as soon as I take it for a proper drive I'll appreciate it again!

 

 

[slknv]

This rabbit hole gets deeper - from a totally cold start, starts no problem and idles at 1000rpm for 3 minutes PERFECTLY. Then it starts backfiring, vibrating, dropping idle and almost stalling. Usually stalls after 4 minutes. Restarting immediately after this causes same issues.

Thought I'd swap in a new starter motor while checking the Y cable (which I replaced in 2018) and checking vacuum lines. So, removed airbox, dropped drive belt, removed alternator, throttle body and plenum.
After pulling the plenum, found a bit of oil in bank 2 (right side) while bank 1 was clean. Looks a bit more orange then most oils I've ever used, a little concerned there might be a bit of coolant mixed in there! Researching further, maybe I have a weird AOS problem? I kinda hope so, as it's a lot easier/cheaper than a cracked head problem...

I had a look at the AOS as best I could, could see a little dried coolant leaking from the top of it, and no idea when it was last changed. So, since I just keep throwing parts at this old thing I was planning to buy a new AOS and connections and change it out.

Any suggestions or comments? http://www.dtmtune.com/2021/05/still-working-our-way-through-problems.html

 

[slknv]

Bit fed up with this car... one step forwards, 5 steps back. 

Did spark plug tubes, new bosch plugs, new Beru updated coils. Started instantly & ran brilliantly.... for about 3 minutes, then stalled. Back to the usual chunky start and stalling. Stuck in a new fuel filter cos why not. Fuel quantity and pressure is fine. Tested coil connections - no problem at all 6 with pin 2 grounded and pin 3 +12V with key in.

After letting it sit for a week... tried starting it yesterday and hearing a pretty deathly loud knock/slap 🙄

Today got the mufflers off and coils/spark plugs out - wondering why 4 & 5 are carbon fouled while the rest look fine? Literally 0km driven and maybe 10 starts out of these plugs. Possibly related to the liquid in the intake plenum in the above post.

Tomorrow is some borescoping with my $5 scope (don't know how well that will work) and a compression test. If that goes poorly, partout time and setting fire to the rest of it! 😜 If compression is good... might have to call an actual qualified mechanic in for a look as I'm reaching the limits of what I can do methinks.

 

 

[Steve996]

Sorry to hear mate. I’ve been following the thread hoping you find something simple, but don’t have any pearls of wisdom to share. If it were me I’d be getting it to a reputable shop for a look at this stage. Let us know how you get on. 

[jakroo]

1 hour ago, slknv said:

 

....Might  have to call an actual qualified mechanic in for a look as I'm reaching the limits of what I can do methinks.

That sounds like a good idea before you spend any money on a diesel and petrol mix to burn it

[Zelrik911]

2 hours ago, slknv said:

Today got the mufflers off and coils/spark plugs out - wondering why 4 & 5 are carbon fouled while the rest look fine? Literally 0km driven and maybe 10 starts out of these plugs. 

Is it easy to swap around the 4/5 injectors with - say - 1/2 to see if the black deposits move too?

[Cookster]

I would suggest you try the team at NineAuto in Highett, they have always provided me with great service.

[slknv]

Scoped the engine, there's good news and not so good.

Good - no bore scoring. Not so good - shiny spot in cylinder 6 piston head, looks like a valve is stuck! No debris visible in cylinder thankfully, was shut down instantly when I heard the noise - I even have it on video. This explains why 5 & 6 plugs were running rich, to compensate for 6.

Now need to decide what to do.

1. Do I keep the 996, eventually find the time and motivation to lower/remove the engine, pull bank 2 head off, send it for repair, then put it all back together? I reckon I could do everything but retiming the head when reassembling, would get a pro in for that.
2. Keep it on jackstands, procrastinate, sell it as a "barn find" in 10 years for $100k? 
3. Advertise it with fully disclosed issues and wait for all the timewasting snowflakes to start crying IMS!! FRIED EGGS!!! and offering me $82.50 for the car?

Anyway, going to join as a financial member here now and start selling off a bunch of other parts I'd accumulated for this car 😂

[Zelrik911]

Could this be a sticking valve / lifter issue??? Seems to be a common 996 problem - based on lots of Web info. Maybe its something you can fix yourself.

Hopefully a valve isn't bent.

 

 

[tomo]

The lifters are fairly reliable according  to those that know , Failed chain tensioners,  or bore scoring is usually  the culprit according to those in know. 

[st3ve]

Yes, perhaps tensioner blade failure (aka variocam pads, see the entertaining rebuild series on YT by 'Man in a garage') which allowed unstable cam timing initially and more recently jumped a tooth or three and bent one or more valves.  If that's all it is, and the contact was not too severe, then a minimum but quite acceptable solution could be just removing the one head and repairing the affected valve/s.  New chains and guide rails both sides (other head can stay on) and you'll be motoring again.

Of course nicer to split the case and replace pistons, rods bolts, rods, install new crank bearings and IMS chain/paddle etc etc, but that's in the mission creep department.  It's the variocam pads that seem to go way sooner than other stuff in the 3.4's.  A 15-20yr or 1xx,000km service item even?