Odd poor run issue 280SL

[MichaelB.]

Ok gents. I have  tough one. I have been working on it now for a few months. Here is what I have.

1970 280SL. Good driver quality. I have put good miles on it with one nagging issue. I can drive this car enjoying each mile for about 15 minutes... Then something is a-miss. Car is original & low miles (50k) with only a Crane ignition module upgrade that has been on there for 16 years.

The car runs just as expected. No temp issues, no odd sounds. But at the 15 minute mark (nearly every time) it starts to misfire, cough, sputter. I can keep it running, but at even full throttle the car will eventually coast to the curb. It will do this with a full tank, half, even a quarter. Now here is the rub... I will cycle the key after pulling over - and once I restart - it runs without flaw again. And I mean perfect.

It will then tool down the road for just about equal time (10 minutes?) then do it all over again. Cycle the key... And I am back to full strength & running like new. 

So... What have I done? 1. I started with a spark plug check. All good. Replaced them anyway. 2. I replaced the spark plug wires. No change. 3. I checked the fuel flow out of the tank fuel lines. It checked good. 4. I replaced the engine mounted fuel filter. No change. 5. I checked inside the tank for blockage or debris. Nothing. 6. I checked for return line flow, confirmed good. 7. I replaced the distributor with a 123ignition. It seemed to be an improvement... But... Still does it. 8. So I replaced the coil tonight, and my youngest Son & I took it for a long drive. At 25 minutes I thought I had it... But then bingo. It did it again. Sputter sputter. And guess what? As I was still rolling I quickly cycled the key - and of course it was back to 100% again as soon as it restarted. I had only rolled maybe 100 yards. Drove us home like a champ after the restart.

What the heck? This car is not computer operated. How can re-booting it make mechanical things work again?

My thoughts? Could the ballast resistor be an issue? I know with the 123ignition using the ballast resistor is not necessary. Is that ballast somehow a timed item? Its still there and connected. Fuel pump? I am under the impression that the fuel pump is just a fuel delivery part not a pressure provider with this system. I can't imagine I am missing something there.

I am going to attach a fuel pressure gauge next & drive with it giving me a report until it fails. Maybe I will see some pressure irregularities. Anything else to think of from the group?

[Benz Dr.]

Possible bad ignition switch? Turning it on and off makes a new connection for a while? I would also check the head light switch - all power goes through it first.

 This may an odd problem but not unheard of.

[Cees Klumper]

I'm also thinking electrical. While you dealt with the usual suspects, perhaps it's a bad engine ground, battery cables, the wiring going to the distributor; so as Dan suggests elsewhere in the electrical / ignition system.

[MichaelB.]

Thank you both. My lead tech had mentioned that he wanted me to "wiggle" the ignition key next time that this happened to see if that did anything positive. He had previously asked if I had a lot of key chains or keys along with my ignition key. I will try that without hesitation. As for the headlight circuit... I did not know that but will investigate! The car sat a lot (4000 miles in 20 years) so I can comb over the grounds & cables.

[mdsalemi]

Michael,

Open up the distributor cap, and check the wiring of the Crane module.

I had a very similar problem (before ditching the Crane some years back) and here is what was happening: the wiring of the Crane, which runs along 50% of the inside circumference of the distributor (mine was an -050 FWIW) had suddenly decided to come a bit loose. It made contact with the shutter wheel, and when it did it had issues you describe. As soon as you pulled over for a restart, all worked well again.

I only found this out when examining the wire closely; it has a pvc cover on it, and it was obvious that something was rubbing on it. The only thing that moved was the shaft with the shutter wheel on it.

[MichaelB.]

Thank you fine sir! I thought of the Crane module & its possibilities which is why I converted to the 123ignitions set up. That was an overall improvement ~ but alas the condition persists! 

My next step is testing electrical zones like that ignition & headlight switch.

[Shvegel]

I have seen something similar caused by an overly dirty gas tank or fuel filter.  As you are running the dirt clogs the filter or screen in the tank, the car dies, the dirt falls off the screen or filter and you restart and so on.  Remove the screen in the tank(Under the recessed hex plug on the bottom of the tank) and the fuel filter and check them.  Be sure to drain the tank before removing the plug.

If that isn't it I would hook a test light to the positive coil teminal and ground and go for a drive and see if the ignition switch is dropping power. If the light goes off when the car dies that is probably your problem but the even timing of what you describe puts my money on the fuel.

[mdsalemi]

I have seen something similar caused by an overly dirty gas tank or fuel filter. 

...and that was my next suggestion, Michael. (thanks, Shvegel) I fought a series of runnability issues starting about 5 years after the car was restored. Sadly there was not one problem, but several all intertwined:

1. broken/weak power connection to rear fuel feed pump; bad crimp connection.
2. Crane wiring issue inside distributor
3. rust and corrosion inside fuel tank

Can you imagine what runnability issues can be when you have all of those happening at the same time? Yeah, not fun. Made life miserable for some years.

The solutions are so obvious once you know the problems.

1. Replace the wiring to fuel feed pump and avoid crimp connections; use solder. NO connections outside of car body!
2. Replace Crane with Pertronix
3. Replace fuel tank

Been humming along ever since...

[BaronYoungman]

I think it is the fuel pump.  When the pumps get older the armature starts to go and when it heats up will cause it to run slower or just stop altogether.  check the pump 1 liter for every 15 seconds from the output going to the injection pump.  Bob

[MichaelB.]

Alright gents. I am on it. I will not leave us hanging either. A full report with solution is emanate.

[Cees Klumper]

The reason I think it is electrical rather than fuel delivery is because of the instantaneous nature of the fix: turn key off, then on again and the car runs like it should. I don't think pollution in the fuel system, or a deteriorating pump, can respond that quickly. But let's see how it pans out.

[MichaelB.]

Great points.

I did pull the lower screen in the tank & found it to be without flaw. Then I pulled the fuel gauge sending unit and scoped the insides of the tank looking for any debris. The tank has zero contamination within (that is when I checked for return fuel flow).

I too had thought that the screen could be building up debris / & then perhaps it fell away once I restarted. But no evidence of that could be found.

I have considered having the fuel pump rebuilt - again I assume it to just be a transfer pump to the injection pump. It seems to be doing that job. It getting hot and starting to fail does make some sense to me. My previous thoughts of attaching a fuel pressure gauge would help with that diagnosis. So I may do that tomorrow as a preliminary measure.

[MikeL43]

Try putting the old points back in.  I had a similar problem with a Pertronix unit and there was some type of electronic breakdown in the integrated circuit that only showed up after the ignition got hot.

[MichaelB.]

Very good. I did change out the whole distributor & went with a digital 123ignition system. I have found it to the the best on the market on several attempts with my other cars. So the Crane is out of the loop now.

Anyhow this is what i found today:

I looked for a fuel port to plug my old school pressure gauge into. I configured a connection & checked the spec in the book. I started the car & the fuel pressure at rest was right within spec (about 1 bar). Then off I went.

The 1st photo shows my trip in the 1st several minutes.
Then off to the highway.
Second photo is at 10 minutes plus - highway driving right before I cycled the key.
Third photo is one second or so after I cycled the key without stopping.
Forth photo is 2 minutes after the key cycle.

[MichaelB.]

Clearly I have found what seems to be a problem.

At its lowest (photo attached) the car was still running today, but I was gentle with it & did not need it to go all the way dead anyhow. But... What does it mean? Do I just assume the inner workings of the fuel transfer pump need rebuild? Do I look for a relay fault? By-pass in injection pump? Something clogging? Harness? The possibilities may be endless.

So I will start with the most logical & go I guess.

As a side note. The stuff I have done to date have made the car run (while it IS actually running) fantastically. 

[BaronYoungman]

Michael, if you want to pop up to Downers Grove Illinois, I can loan you one of my rebuilt fuel pumps and you can see if that solves your issues. Bob (630) 903-9877
I always have parts and a few rebuilt ones about

[mdsalemi]

Harness? The possibilities may be endless.

I'm sure you've checked this, but the pump must have full voltage in order to function properly. In order to maintain full voltage, you need "wiring integrity" for lack of a better term. It was only when I threw in the towel and got a new pump did I understand what the real problem was, and that was the harness.

The integrity of wiring means all the connections must be 100%. Start at the pump itself, and verify the integrity of the connector terminations--I believe they are ring connectors. If they are loose or corrosion present (remember this is a harsh environment under the car!) that may be an issue. Trace the wires back through that long rubber grommet thingy back into the trunk, where they connect to the harness in there. Make sure you have good solid voltage at the harness; if you don't have it there you surely won't have it at the pump.

What had happened to me, Michael is that the restorer (bless his heart must have been one of the workers...) removed the fuel pump by cutting the wires rather than removing the connections at the pump, and snaking them back into the trunk. When it came time for reassembly, they used crimp connections which were great--for 5 years.

My solution was new wiring from the pump back up to the harness--and the connections were all soldered.

[MichaelB.]

Yes Michael & (Bob) Baron. I think you are both on the right track. So... I will 1st check the connections electrically, then Baron, I will opt for your offer if Michael's suggestion does not net the preferred results.

I will be in Joliet at the race track tomorrow after more diagnosis... Maybe I will take your number along for if I can break away.  Thank you.

[hkollan]

Hi,

While you are at checking out the pump for electrical issues, I would check and clean the intake mesh on the pump.  I use A small magnet to check for rustparticles that clogg up the pump and restrain the fuel flow.

Hans

[MichaelB.]

Michael, if you want to pop up to Downers Grove Illinois, I can loan you one of my rebuilt fuel pumps and you can see if that solves your issues. Bob (630) 903-9877
I always have parts and a few rebuilt ones about

I just wanted the list to know what a valuable asset we have in the Youngman family. Both Baron & his bride greeted me with their young Son and we talked cars & parts for over an hour. It was a real pleasure and a fruitful event. They have more collectible cars in their driveway then most car shows have in attendance.

Nevertheless I now have a "test" unit to try once I confirm all of the harness suggestions from Mr. Salemi and so many others. Then maybe we will bring this thread to a close 

Great group here with all of the suggestions & real world help.

[MichaelB.]

List update.

Latest: Sat/Sun I checked every consevable electrical connection. Looked for bad grounds, bad continuity... Anything. But all looked very tidy. I removed the fuel pump shield & looked for kinked fuel lines, more poor connections, or even debris there. Nadda. In fact the current pump looked relatively fresh. But with Byron's test unit in hand I wanted to try swapping the pump. While I was at it I drained some fuel looking for issue too. Still nothing. So I placed Byron's pump in line and fired it up. It cranked & started and the (still connected) pressure gauge read pressure. So off I went for a drive.

I only got about ten minutes until it stalled and coasted. Same result. It was a valiant effort, but no joy.

So I cleaned up some of the testing work then parked it at home & pondered. I knew I had left the tank at 1/4 and I considered how that could benefit in the diagnosis. I thought about draining the tank in its entireity but could not see much gain there. Nevertheless I knew I had to get it back to my shop so I decided to just go tank up in the morning and do more research.

This morning I went to the local Shell & put $25 in. The PSI gauge was still attached & reading pressure but I did not think much of that. After a fill up I headed to the highway. As I was tooling along at an indicated 80 I started to prepare for the inevitable stumble. But as I motored along the stumble never came. So i motored some more. No stumble. More motoring... No stumbling. I circled around & back to the shop & looked over the pressure gauge (still motoring). It was holding steady. I got out & looked over the engine (in amazement) thinking about what was different. PSI gauge still healthy. Then I thought ~  there is something different! This is the 1st time I have had more than 1/2 a tank of gas - since forever!

Yes I had checked the tank for debris previously, yes I had looked at the filters, but I never really looked at the tank baffles (flower pot) to confirm if the current set up was allowing the "pot" to fill up when the fuel was lower than the top of the baffle. I now see that it seems to prefer the full tank level.

I have a theory on this... Perhaps in the past this tank was "sealed" like they did moons ago. When they implemented the sealing maybe they partially blocked the "screen" or orifice for the return to the pot when the tank is low? And while I had looked in there for debris I was not well versed enough to consider that "flow" characteristic back to the pot when the fuel was lower than the top of the pot. Sure it looked clean, but were the passages allowing it to function as designed? Perhaps not.

At this point I have a happy running car (two hours straight now!) when the tank is over 1/2. So I at least know where to focus my attention. I will get Byron's test unit back to him and know that I am closer to a resolve each day 

[Cees Klumper]

Sounds like you´ve located the cause, congratulations, lots of hard work went into that one! Now that you report this, I do recall someone had this issue before, that so long as he kept the tank reasonably filled up, he'd have no issues. Are you going to attempt to have it cleaned out or spring for a new tank?

[MichaelB.]

I am going to look inside with my new found education about the flower pot and decide. I don't mind putting a new tank in. I just did so for my 1980 MGB LTD and it was a whole $105... I bet the Pagoda tank is more 

This car is running so well now (with all the upgrades done for diagnosis) it makes this all worth it.

[BaronYoungman]

NOW, THAT IS SOME DETECTIVE WORK!  I am impressed by your logic and perseverance, you definitely thought outside of the box.  It was a pleasure meeting you and your son.
Sincerely, The Youngmans

[mdsalemi]

...I do recall someone had this issue before, that so long as he kept the tank reasonably filled up, he'd have no issues...

Um, that was me, Cees. And a new tank solved the problem. There's too much "stuff" happening with the Pagoda tank, and if it was as easy as opening a suitcase, cleaning it, and closing it, by all means that kind of cleaning and refurbishment works. However, a new tank solved a lot of problems.

MichaelB, they are not cheap. Not in MGB territory, more like 10x that price.