71 280SE 3.5 - engine trouble
 

I have a 1971 280SE 3.5 coupe. It is in excellent shape, however yesterday I went for a drive after having the car sit for 2-3 months and the engine died several times, prior to this it ran fine.

While driving yesterday, the engine keep dieing on me. I drove a couple of blocks from my home when it just died, it would restart after a minute or two. I then continued on and thinking it just needed to warm up so I got on the freeway and drove 10 miles and then parked. When I tried to return the engine died three more times while driving home! When trying to restart, the engine turns over, though it will not completely engage. It acts as though it is not getting gas, even though I have a full tank.

Does anyone have any suggestions as to what might be going on? I was thinking it might be a fuel relay going bad, or possibly a vacuum leak?

Any help would be appreciated.

Thanks,

Dave

Fuel pump or ignition circuit are the most likely candidates. Check for spark when it won't start. If it's got spark to the cylinders, it's fuel.

Ditto on what Tomguy said. I would check and clean the fuel pump contacts under the car first. Also check the lead from the master relay to the battery. If the battery terminal is corroded, master relay (and the ECU) may not get proper voltage and cause problems. I would get a spare fuel relay no matter what for testing because it is the same as the master relay.

And check whether the ignition coil leads are corroded/loose. If nothing works, it is more than just an ignition misfire, which means coil leads broken, distributor rotor failure (unlikely) or your points broken/not opening/not sparking.

Intermittent failures are the worst to diagnose, but usually are electrical related.

Good luck,

Bert

Off-chance, but possibility that your ignition module is overheating. It happened on my 4.5 to my parents before it died. I am pretty sure it comes from having the points closed too much (I forget if that'd be too high or low dwell).

How does Pertronix ignition module fare in these models?
Does away with points

I have Petronix in my 3.5 coupe (Ignitor I) and it works fine. I have the flamethrower coil too so it was a very simple setup, but I lost the tach function. I still need to fix that by adding a wire and resistor from coil to tach, but I have not been able to locate what and where exactly the singal wire is for the tach in my car. I may go back to MB coil set up with switchbox for tach signal.

Bert

71 280SE 3.5 trouble
 

Thanks guys!, I did go around the car and check and reconnect all of the ignition contacts that I could get to as well as check the fuel pump contacts. Also checked battery contacts, although battery is new.

Someone also suggested that it could be a fuel screen / filter issue, both in the gas tank and in the engine compartment, since they have never been changed to my knowledge - not a bad idea even if the problem turns out to be something else, so I have ordered both.

The car seems to start fine now, however I guess the only way to really test it, is to get back on the road. I just hate to go through the problem again of dieing on the road somewhere, especially on the highway!

FYI, I do have an electronic ignition system, installed years ago. always worked fine.

The only problem I had that took a long time to figure out was a faulty light switch in the car that was causing the car not to start sometimes. Very frustrating!! The switch had arched in the back, causing the ignition system to sometimes short out when trying to start the car. It was not until we researched the problem did we notice that the ignition system actually goes through the light switch! I am lucky it never started a fire, when they discovered the problem it was obvious that the switch had some serious arching going on the back of it.

Will keep you posted on if the engine dieing problem is fixed or not.

fire hazard
 

The fire issues are manifold in these models , perhaps someone can advise in detail about hose replacement and other items
Regards
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Most people are unaware that everything goes through the light switch. I had a 190SL that had the same problem and it would misfire when the head lights were on. It ran poorly all the time when it had this problem and it was very difficult to figure out. I found it by accident - burned my fingers a bit too.
I changed the head light switch and it was a totally different car after that.