350se spluttering when hot. stop, restart, then runs fine for another 10 minutes

[buddahbrown]

Hi everyone, thanks for all the info exchanges on this forum, has been invaluable and good to do some dreaming.  My 350 se (aust delivery) is doing some weird stuff at the moment.  It runs beautifully until hot (say, 30 minutes) then runs incredibly rough, but doesn't stall.  I can put the car in neutral, turn it off, restart, then it runs fine for another 10 minutes and the same scenario! We have cleaned the tank, cleaned the filter and problem still persists.  Any thoughts would be valuable- getting desperate and expensive.  THANK YOU!!

[Nutz]

Year?

[Nutz]

How about the fuel filter? Did you change this?

[koan]

You say "It runs beautifully until hot", can you describe this a bit more?

Is it 10 minutes of idle and the rough running starts or 10 minutes of driving?

Tried running with the fuel cap removed?

koan

[SELfor50]

K-jet or d-jet? (Did they make k-jet 350's?)

[Nutz]

(Did they make k-jet 350's?)

Yes

[motec6.9]

First i would check breather line from tank in boot is not crimped take fuel cap of and go for a drive to see if it is vac loc i had the same problem with a falcon a few years ago

[buddahbrown]

Hi everyone, thanks for the replies.  Year, pretty sure it's a '76.  Fuel filter has been replaced. No crimp in the return pipe and no better when the cap is off the tank.  I was cruising down the freeway yesterday to force her to splutter and check what happened when she had been running for say, 10 minutes and put the boot in and whoa.... splutter, definitely a fuel supply issue..... even the mechanics are a baffled.....

[koan]

cruising down the freeway yesterday to force her to splutter and check what happened when she had been running for say, 10 minutes and put the boot in and whoa.... splutter, definitely a fuel supply issue..... even the mechanics are a baffled.....

You didn't say if it played up after idling for 10 mins. I assume it doesn't from your description.

When I first got my car it would do something similar. After a run down the freeway it would stall or almost stall on the off ramp but would start straight away.

I suspected it was the EGR system feeding too much exhaust gas back into the inlet manifold. I checked the vac plumbing to the control valve and cleaned out the pressure pickup port on the exhaust manifold which was blocked with carbon.

Can't be sure that's what fixed it but it came good about that time.

Your problem is a bit different, mine wouldn't idle, yours is with throttle open.

Does your 350 have EGR ?

EDIT: Where in the world are you?

koan

[buddahbrown]

I'm in Perth Koan.... funny thing happened today, I took it out, gave it a run and couldn't force the problem!!! Even spoken to MB Spares and they are baffled also.  Will pass on the exhaust gas idea.  Thanks!

[koan]

I'm in Perth Koan

Too far for me

Had another thought, dying alternator let battery drop to 8 Volts giving similar symptoms. Would run OK up to about 2500 RPM with not much throttle but open it up and it misfired, coughed and generally carried on.

It could be ignition related but why stopping and restarting fixes it I don't know.

Substituting the ignition module and a clean of connections might give a clue.

The fault hasn't really gone away... It's just hiding for a while.

koan

[buddahbrown]

Thanks again Koan... met the mechanic today and got him to take it for a run with me in the car- agreed it is a fuel issue as it is leaning out.... next stop- injector cleaning.  A little while ago the fuel pump was going berzerk and pumping untold amount of fuel into the system so that it was just billowing smoke and only running when the throttle was wide open- maybe it's some kind of residue from that- anyway, they haven't been properly cleaned in over 12 years so probably a good place to start.  Thanks again mate.  BB

[Big_Richard]

ive seen a w116 350 driving around osborne park before by a young fella.

I cant remember the colour or its appearance, but from memory it was quite a good one.

got a picture of yours by any chance ?

I found it astonishing at the time that a 116 driver/ enthusiast in perth wouldnt be on this forum, since there are so few here.

[TJ 450]

I've also seen a couple of 350s being driven around. It's good to see and very refreshing.

I was just thinking the other day, just how fresh W116s and 126s look, considering how old and disgusting many 1990s cars look these days.

Good on ya mate. 

Tim