A bizarre misfire and breakdown problem about 20 minutes in to driving

[dgsmiler]

My first post here....it really is a great site.  I was going to ask you experts, as after alot of research and fiddling I'm now at a loss and need some help.  I have the M130 280 engine...idles great (after alot of tinkering and using advice from here).  It does indeed run beautifully for about 20 mins ...temperature stable after warm up....so I'm running around with temperature stable - 20 mins of beautiful sometimes speedy driving....I've then at this stage stopped and pulled the spark plugs - and they're a wonderful light tan on all cylinders.... at this stage too I've felt the tank fuel pump (at the back) and it's whirring and nice and cold.   I then drive for another approx 10 mins and it starts missing - then back fires and gets worse and worse and until I'm stranded at side of road.   If I leave her to cool completely it starts the cycle again...starts fine runs for 20mins and then gets bad.  I've replaced coil, fuel filter to no effect...points seem fine.  My amateur pov is it's fuel starvation....but I'm stumped ...does fuel evaporation happen....can the FIP overheat?...what could get cumulative worse even after the engine warmed up and has been running nicely... thanks in anticipation...David (UK)

[Ed Riefstahl]

Hi David,

You mentioned the points are ok. My first thought is to make sure you don't have any side play in the distributor shaft. It's pretty common on this engine and can cause the engine to do some pretty strange things, especially after it warms up. Mine would just not start after shutting it off and restarting warm. The dwell / gap would be all over the place. turned out to have a little play in the shaft.

After considerable investigating on what to do. I replaced the points with electronic pickup. That was 15 years / 30,000 miles ago. I couldn't be happier.

Just a thought and easy check.

Ed Riefstahl

1966 230SL (Ms Magoo)
1970 280S (Miss Daisy)
1989 300SE (Majestic)
1999 BMW Z3 5 speed
1991 BMW 318I 5 Speed
1997 Toyota Paseo Convertible - Red 5 speed (have you ever seen one?)
1997 Ford Ranger step side (Mater)
2023 Mazda CX 5

[rwmastel]

If I leave her to cool completely it starts the cycle again...starts fine runs for 20mins and then gets bad.

David,
Welcome to the group!  If you let it cool, it starts fine.  What is the warm start experience like?  Can you get it to go at all?

[Cees Klumper]

Sounds like dirt in the fuel tank, recommend doing a search on past discussions on that issue, and take a look at the tech manual for fuel system issues.

[mdsalemi]

Hello David,

I did have similar experiences, though not quite identical. Unfortunately it was several overlapping problems.

First, the fuel TANK. I had the original fuel tank and after suffering some maladies I took it to a mechanic well experienced with the Pagodas. He said change the fuel tank, it's rusting internally with microscopic rust particles. So I "bit the bullet" and changed the fuel tank and many problems disappeared...for a while.

Then, I had some issues like yours, and sure enough, the distributor shaft was worn. I had that rebuilt and installed a Pertronix Ignitor system with a FlameThrower II coil. That solved the ignition problem, until it didn't.

Then I turned my focus on the fuel system, and changed the fuel pump. Lo and behold the problem was NOT the fuel pump itself, but no integrity to the wiring to the fuel pump. The mechanic on the restoration had cut the wires to the fuel pump before removing it instead of removing the wires AT the fuel pump. OK. But he used crimp connectors and this place under the car where the fuel pump lives is most inhospitable. They eventually corroded. My fix was to re-wire it with NO splices, taking the splice back up into the boot.

So, you may have multiple problems plaguing you...

[450sl]

The 20-30 minutes time span let to believe the possible fault factor might be the coil.

Regards
Mark

[Mike Hughes]

The 20-30 minutes time span let to believe the possible fault factor might be the coil.

Regards
Mark

If the coil is connected up backwards it will work, but it will fail to deliver proper spark when it gets hot enough.

[teahead]

99% of the time, issues like this is electrical.

Check the points/gap/dwell again.

Check if the coil is working right.  Replace it.

I put a 123 plus Bosch blue coil (bypassing the ballast resistor) distributor in it and it helped a lot I think.

[dgsmiler]

Thanks so much all for the feedback.  I've got plenty to check now....unfortunately the joys of employment mean I won't get under the bonnet until the weekend but plenty to get going on.  I changed the coil to a new one...but will check again the terminals...the warm start immediately after this 'shed collapse' happens is similarly perplexing as idle seems fine...but as I pull away all goes bang pop and I'm at side of road again.   Will report back when I've investigated these pointers.  Thanks again.

[Paul & Dolly]

Welcome to the group.

Check the fuel return line from the engine to the tank is operational.

Good luck
Paul

[dgsmiler]

All, thank you for all your assistance and apologies for the delay in responding - I've been out of action for a couple of weeks.  As suggested I rechecked fuel lines, fuel pump and tank and then started on the electrics...whilst checking the play in the distributor shaft I noticed a small piece of broken plastic - which after some investigation I realised was the internal seating tooth for the rotor arm. I ordered another, which I've now fitted and wonderful news the problem is solved...I guess when things got warm the rotor arm was able to move sufficiently on the shaft to put the timing out and then foul things up.  Thanks again for all the great suggestions.