Fuel system woes

[floatingboy]

I'm a new full member but have been lurking for quite some time.  I've gotten a lot of great info from previous posts but I've come to the point where I'd like to get some input on my specific problem.  I'll be as detailed as possible (it'll be a long one!), so that you don't have to ask too many follow ups, hopefully.

1966 230SL.  In the last 2 years since I've worked on it, the car has always had hard starts.  All ignition components are new (except distributor), and dwell is spot on, distributor doesn't short.  Spark in general checks out.  Once the car starts, which it always does after some cranking, things are--or were--just fine. 

Finally took it on a longer trip over a year ago and about an hour into it, it started bogging down/misfiring under heavy load.  Mainly up hills and such.  But the drive was almost over so I didn't become an issue.  Same thing happened on the return drive.  Thought maybe the flower pot wasn't refilling quite quickly enough and was starting to get a bit fuel-starved after driving for a while.  But as most trips are shorter, it wasn't really an issue.

Fast forward to last month. Decided to take it to a car show a couple of hours away.  Half hour into the trip, it starts bogging down over 3k RPMs.  The engine is in need of a rebuild, so I figured that maybe plugs were getting fouled.  Found a parts store, got new plugs, popped 'em in.  Old plugs actually looked good, though.  Thing is, I was stopped for the better part of an hour.  Got back on the road, and I swear the thing ran better.  No misfiring either…for a little while.  Another hour though, and the problem was back.  Limped it there at 55 MPH and then had the same problem, although more pronounced on the way back the next day.  Decided to take a look at the fuel filter.  Seemed pretty dirty, so (don't yell at me), I left it out for the rest of the trip home.  Immediately the car was happy again…for another hour.  Then same problem.  But I could stop, shut it off for a few minutes, then restart and be ok. 

I decided that the tank fuel strainer should be changed and the tank checked out for normal operation.  I ran the car one more time to burn a little extra fuel and it decided to actually DIE on me several times, rather than just misfiring.  Tank was quite low on fuel.  But each time, I could restart after less than one minute and drive for another couple of minutes before the same issue would recur, always restarting immediately. 

Pulled tank, and of course there's crap in it.  Rust, sediment.  Strainer doesn't look all that bad though.  Flushed the tank as good as I could and got 90% of the junk out.  There was actually flaky rust in the lowest part of the tank below the strainer where it feeds into the fuel line.  I thought for sure that was the problem.  Put in new strainer and reinstalled.  Installed fuel fitter, too.  Won't start.  Then maybe starts, but dies again.  Then won't start.  Then starts and runs a little, dies again.  Fuel tank has about 2 gallons in it at this point.  Enough to run, but not much gravity pressure to feed the fuel pump perhaps?

Electric pump moves a liter every 10 seconds  at 12-13 psi right after the pump (perhaps a little low on the pressure).  On the bench it was performing beautifully.  Oddly, even though pump always spins, I don't always see fuel circulating when I look into the tank from the sending unit hole.  This was the case yesterday, so I pulled the outlet hose from the pump and suddenly it was back in business.  So I blew out the line between tank and injector pump.  Still no start.  Put 5 more gallons of fuel in.  Pulled the WRD and made sure plunger was moving freely, then started car with WRD removed.  Fired right up, although ran too rich, and was sucking too much air, so i reinstalled WRD and it calmed down and ran.  And didn't die!  (Question is, was it because of more fuel in tank or because of freeing the WRD perhaps?)  So I drove it around the neighborhood, great power, chirping tires,  trying to get it to die, but it was doing great.  Pushed it hard (4k RPMs in 3rd) and that made it mad.  Died and wouldn't restart.  Towed it home, and it fired up in the driveway (of course).  Perhaps because it had cooled down some.

Pulled WRD and all seems to be functioning properly.  Thermostat opens 2 mm in hot water.  Lower stage of WRD pulls air when all the way up, and shuts off air when depressed about 2 mm, so it seems to be perfectly adjusted in relation to the thermostat.  CSV and TTS are functioning properly (good resistance values on the TTS).  The starting solenoid has stopped working, so I think that might account for the bad cold starts, but not for the dying once warmed up.  Seems like that if it failed in the pushed out position, that would make the car run super rich, which it doesn't.  Also, injection pump doesn't have a lower fuel cut-off solenoid.

SOOOOOO, is my fuel pump dying, even though it checks out on the bench?  Is there an explanation for the fact that it ALWAYS spins but doesn't always make fuel circulate in the tank?  It draws 1.5A or so at idle but I haven't been able to check that under load.  Basically, I keep coming back to a failing pump, but don't want to spend the $$ only to find out that it wasn't the problem!  I am also partly worried that sediment got into the injection pump, although I was able to blow air through it, and also verified that all fuel lines are clear.

If you've made it this far, I thank you for your perseverance! 

Rob
Potomac, MD

[Jordan]

Rob, it certainly sounds like a fuel starvation problem.  I had somewhat similar problems, after driving for awhile the car would stutter and jerk before dying, usually going uphill.  I eventually replaced the fuel tank as I too found about an inch of crud on the bottom of the tank.  While you say you cleaned the tank did you also make sure the hole in the side of the flower pot at the bottom of the tank was unplugged?  When the fuel level in the tank drops below the top of the flower pot the fuel enters the flower pot from a hole in the side at the bottom of the tank.  Mine was completely plugged and when the fuel level dropped low enough the pump would drain the fuel in the flower pot and then starve and the engine would die, even though I had gas in the tank.  If I waited the fuel would eventually work through the plug and I could again start the car. 

Have you checked and cleaned all the fuel filters, one in the tank, one in the electric fuel pump and the main filter up at the engine?  If they are dirty then you still have crud in your tank.  Have you checked the fuel flow rate of the return line at the fuel tank?  Are you still getting a litre every 10 seconds?  Some things to check.  I'm sure others will add there own thoughts.  Good luck.

[Bonnyboy]

I think it sounds like the fuel pump isn't working the greatest.  What is the pressure after the fuel leaves the Injection pump on its way back to the tank.    My pump gave me the volume but not the pressure after the injection pump and when I replaced my fuel pump the problems went away.  I'n not a mechanic or expert but the volume travelling through the Injection pump seems to be fairly important for the proper running.   My car ran great on the highway but intown driving made it stop - especially up a hill.

I was able to check the pressure with a water guage from a water sprinkler setup - it was enough to tell me I had a problem with the fuel entering the tank.

[ja17]

Hello Rob,

Take the time to hook up a pressure gauge to the metal line going to the CSV. You can temprarily leave the gauge on under the hood. Read the fuel pressure when the engine is acting up and when running good. I still think you have a fuel supply problem. Did you clean the intake fitting screen in the electric fuel pump?

[stickandrudderman]

Firstly, well done on a systematic and methodical approach.
I second JA17's advice. Install a fuel pressure gauge, although I would run it into the car. This will tell you categorically if you have a fuel problem the moment you start to experience the symptoms. Personally I always insist on the tank being properly cleaned/overhauled by a specialist at the slightest sign of contamination.
One other possibility is a blocked ventilation system causing vacuum in the tank. Does the tank have a dent in it anywhere?

[floatingboy]

Thanks all for taking time to reply.  I actually first installed the pressure gauge at the outlet of the injection pump and got basically zero PSI.  I thought perhaps the gauge was bad (brand new gauge), so I blew high PSI air into it and then hooked it up to the outlet of the electric pump.  That's when I got the readings of about 12-13 psi.  I will reconnect it to the outlet of the IP and see what the reading looks like.  The reason I thought the gauge wasn't working was because the hose that I used to plumb the gauge into the IP outlet would visibly tense up as soon as I activated the electric pump.  Maybe blowing air into the new gauge shocked it into working.  It's a cheapie, so I don't doubt it.  I'll try it again at that point and also at the CSV line.

As far as the tank goes, I have visually verified that the small hole on the side of the flower pot is clear and allowing fuel to enter.  I helped out any possible clogs by means of a bent wire hanger.  The tank appears undamaged.  When I removed it for cleaning, I blew air into all fittings, including vents.  I thought maybe venting was an issue, but opening the filler cap or removing the sending unit makes no difference.

When I pulled the tank, there absolutely was larger, chunky rust/debris in the lowest part of the tank BELOW the in-tank filter.  I blew and rinsed all of it out to my knowledge.  I tried to remove the inlet fitting to the pump in order to clean the screen but it was very stubborn.  I have learned not to really force things because they like to break, and I contented myself that it was clear because of how easily fuel flows through it (1 liter every 15 seconds).  Maybe that's faulty reasoning?

One update is that I removed two shims from below the WRD.  They totalled maybe just over a millimeter in thickness.  Even without that, I have verified that the thermostat, which itself moves a full 2mm when warm, does not completely close off the airflow.  I see that the inner plunger is adjustable, however I haven't figured out how to removed the 14mm nut on the side that is responsible for disabling the WRD.  It has to come out so that the inner plunger can come out.  I tried to get a wrench on the lock nut inside there but couldn't manage to hold it AND turn the smaller nut.  So it must come out.  How does the 14mm spring-loaded nut on the side come out?

As far as the fuel pump failing goes, I can see why it would be responsible for the car being underpowered at times or even sputtering and dying, but then why not restart immediately?  Once it dies, it often won't restart for a while.  This is in contrast to before when it would always start right back up and then run again for a while without problems.  I guess having a gauge in place during all these conditions should tell me definitively what's going on.

Last but not least, the starting solenoid is dead, so I ordered the updated one from Rock Auto.  They just got back to me saying that they have none in stock and Bosch doesn't either.  I knew Bosch didn't, but I was hoping they still had one!  Dammit.  Anyone have one?  Or can they be rebuilt?  I couldn't figure out how the dang thing comes apart.

[George Des]

The check valve on the outlet side of the fuel supply pump can also be a source of problems like this if it is sticking. As far as the solenoid goes, the last time I went to buy one I went to an MB dealership. A new solenoid would have cost about the same as a rebuilt starter that already included a new solenoid. You may want to explore this before searching further for the solenoid

[KevinC]

The check valve on the outlet side of the fuel supply pump can also be a source of problems like this if it is sticking.

I can certainly relate. Easy and low cost fix if this is the culprit!

[floatingboy]

The check valve on the outlet side of the fuel supply pump can also be a source of problems like this if it is sticking. As far as the solenoid goes, the last time I went to buy one I went to an MB dealership. A new solenoid would have cost about the same as a rebuilt starter that already included a new solenoid. You may want to explore this before searching further for the solenoid

Oh, I mean the one on the back of the injection pump.  The starting aid.

[garymand]

Rust in the tank.  I had a rusty tank once.  It would run fine until the fuel filter clogged with powdered rust.  Then it would die.  The engine would not start for about a street light.  With traffic behind me and a new green light, the car would start and get me to the middle of the intersection and die again.  The rust doesn't float.  It falls off the filter to the bottom of the housing and unclogs in about a minute.  When the engine starts the rust churns up and clogs the filter again.  Check the filter and housing bottom, you may have an ounce or two of fine rust powder hanging out there.  If so get the tank coated. 

[floatingboy]

Ok, the latest.  I really went back and forth because it did seem like a fuel supply issue, and indeed it could be if the tank was quite low, say, with less than 2 gallons in it.  But even with over 5 gallons, it was having issues.  It came down to one time it stalled right as I pulled it into the garage.  Key was still on, yet I noticed total silence.  I.e., no whirring/whining of the fuel pump.  I put my hand on it and it was still.  That sealed it, I was getting a new (well, rebuilt) pump. 

Fast forward to two days ago.  Once I got the rebuilt pump on (and enough fuel in the tank to actually travel to the pump inlet, the car was happy.  Drove it about 15 miles RT on surface streets and it was fine.  Powerful enough, not missing.  But yesterday I took it on a 40-45 mile RT on mostly freeway.  It was 95 degrees out.  It did fine, even sitting in construction traffic (engine stayed at right over 180) and had power until the last few miles of the first leg, when it started to miss a little.  Once off the freeway I could tell it wanted to probably die at a light, but I kept my foot on the accelerator enough to keep it running.  At the destination, foot off the pedal, it died.  But restarted and was able to move it to a parking spot.  It rested for an hour, then restarted normally and drove fine for the first little bit.  Then, at highway speed, it started to really bog down just like the old fuel pump was doing.  Finally I pulled over to the shoulder expecting the engine to die immediately, but it didn't.  It idled fine in park, but didn't want any load or it would miss horribly.  Shut it off for 5 minutes and restarted and drove the rest of the way with the car feeling like it was at about 85-90% of potential. 

My theory is a bad rebuild, but I was wondering if something else like the fuel pump relay could cause this.

Thoughts??

[garymand]

You are on the right track. fuel pressure or flow.  Pull the fuel filter and syphen the gas out of the ff canister into a clear continer.  Look for powder that can settle like dirt in water, capable of blocking the filter when churned up on a bumpy ride.  The stuff in your tank is so fine it gets through to the filter.  depending on the condition of the filter and how it was changed, stuff may have gotten through or there is enough powder left in your system to partially block something.  Once you stop, the stuff starts falling out of solution.  its a fine pwder.  so measuring the flow may not help if the stuff has time to settle out.

Its not your fuse probably , but I had the FP fuse link crack and become intermittent while driving.  Very unnerving.  I was in such a noisy freeway location I couldn't hear that the FP wasn't turning.  After a tow home, It was obvious no fp whine.  Fuses looked fine.  Meter showed voltage accross it and no voltage to ground on the outside.  Turned the fuse and the pump started, but I could see the break in the metal.  Cheap fix that time.

[floatingboy]

Thanks for the reply.  There most definitely is fine powder.  However, I would think that if that were causing the big loss of power because it amasses in the filter canister, then even if it did settle in the bottom after sitting for five minutes, fuel flow would immediately stir it up causing the condition to repeat itself very, very quickly.  However, this isn't happening.  Yesterday it went from total loss of power to almost normal and stayed that way the next 20-25 minutes home.

[garymand]

This is no fun I know.  This caught my eye: "One update is that I removed two shims from below the WRD.  They totalled maybe just over a millimeter in thickness.  Even without that, I have verified that the thermostat, which itself moves a full 2mm when warm, does not completely close off the airflow.  I see that the inner plunger is adjustable, however I haven't figured out how to removed the 14mm nut on the side that is responsible for disabling the WRD.  It has to come out so that the inner plunger can come out.  I tried to get a wrench on the lock nut inside there but couldn't manage to hold it AND turn the smaller nut.  So it must come out.  How does the 14mm spring-loaded nut on the side come out?"
Should be 10 times that movement from cold to 70 F.  20mm?  Maybe 12mm?  2 is harly any movement= bad.  14mm nut? that disables the WRD? If it is on the side of the FIP, don't mess with it.  Why disable the WRD?

Let me relate my regretable experience with a rusty tank: I taught my son to work on cars by tenderly rebuilding the motor on a dark green 67 250SE with beautiful pebbled tan leather (don't remember the exact name) for my high school son's first car. It was a San Fransisco car always garaged but bad valve guides and the car wouldn't start.  It had a dead battery.  I thought it was a good investment for $2000.  He drove it to school a few times and  loaded some of his water polo buddies and headed to a meet 40 miles away.  He got 20 miles on 101 in bay area commute traffic and the car started acting up.  He and the team missed the meet.  Very sad story.  To his credit, he nursed the car most of the way back stopping, going 15 miles, and called me from a taco bell on the El Camino. This was before cell phones for kids.  When I got there, the car ran fine the rest of the way home.

4 or 5 days and a few other sad stories later, I found the red powder in the filter canister I pulled the rusted tank.  It sounded like sand on the bottom.  Got a junkyard tank and fixed it.  But my son was afraid of the car by this time.  We sold it for $4000 and he found a 944 porsche, red. 3 944's later, he gave me the 944 turbo S and drives a C55 because it is very fast AND dependable.  I guess I taught him to drive a dependable car. 

Its not the big rust, its the fine powder that your garbage disposer-like fuel pump sends down the line to the filter.  You said you cleaned "{most}" of the stuff out of your tank.  oops.  As long as you have crud in the tank, that disposer is crunching it up and sending it down the line.  Fortunately MB had a Murphy working there who put a big fine gas filter on these cars.  Hopefully the small micro inch (sub micron) sized particles act like pollishing powder when small enough to get through the filter pores.  That is if 'Murphy' knew how small the particles needed to be to go through without hurting the FIP.  I'll bet he did.

So yes, it really does sound like rust.