1964 230SL Hard Starting...When Cold

[mistertj]

Had this issue a year plus ago. The engine just cranks and cranks and eventually starts to fire and eventually catches. Last time it turned out to be the cold start valve. Just wasn't getting voltage. Turned out to be a dirty fuse and was fixed by turning (rotating) each fuse to make better connections.
Did not use the car all summer and up until now. The symptoms are back...engine just cranks and cranks. I have a lamp connected to the cold start solenoid...it lights and I can hear it "click". Disconnected the fuel line from the cold start valve and aimed it into a plastic bag tie wrapped to the line. It gets fuel but I'm thinking maybe just not enough for a good spray. Is there an easy way to check the fuel pressure? Where and how would this be accomplished? The fuel pump runs and puts out enough fuel to support the engine running once it gets started but I'm wondering if there is enough pressure for the cold start nozzle to spray nicely? Suggestions?

[BobH]

Hello, maybe the actual valve, filter or the nozzles are blocked, it describes on here how to clean the CSV and test it

https://www.sl113.org/wiki/Engine/ColdStartValve

[rwmastel]

Is there an easy way to check the fuel pressure? Where and how would this be accomplished? The fuel pump runs and puts out enough fuel to support the engine running once it gets started but I'm wondering if there is enough pressure for the cold start nozzle to spray nicely?

If you have the connectors/adaptors, I believe the best place to measure fuel pressure is at the port on top of the main fuel filter canister.  Others my have better suggestions.

The best place to measure fuel flow rate is at the return line to the tank - measures full fuel circuit.  Do not under estimate flow rate, it is as important, or probably more important, than pressure.  This is per Baron Youngman, a member here who has rebuilt a few hundred fuel pumps.

[mistertj]

Sorry for the delay but finally got to check the fuel pressure coming from the pump. Screwed a pressure gauge into the top The larger fitting) of the engine fuel filter holder. The photo says it all. Just a tad over 1 psi. So, before I just change the pump...will drain the fuel from the tank and then change the tank filter. While I am in that area, change the small filter that I have in the line between the tank and the pump and at the same time, check the input filter to the pump itself. If none of those show clogging/restrictions...then I'll pull the pump and put in the spare that has been rebuilt. While I'm all messy with that, will put in a new fuel filter at the engine. Will let you know what the results of all that are.

[Pawel66]

If I may...

Perhaps others will have another explanation and suggestions for such a low pressure. I am assuming you checked the pump is working...

But if you are getting to filters, I would do the tank filter last. If you have additional in-line filter - do it first. If the gauge shows pressure after the main filter, I would do it next.  Then the screen in the pump (you may need to hit it with the impact gun, the nut may be difficult to move and it is difficult to hold the pump on its hanger if you do not want to remove it).

Reason I am suggesting to check the tank filter last is because it may be very difficult to unscrew it... I would do the easier ones first.

[mistertj]

Hi Paul - Thank you for the input. I screwed the gauge into the top of the filter where the larger nut is. Don't know if that is before or after filtering. With your input though, since it's been years since I last changed the main filter, will start with that first and work backwards toward the tank. Next would be the filter at the pump inlet. I'll pinch off the fuel hose and do that. Yes...an impact wrench on that fitting, otherwise might damage the pump mounts and still not get it loose. Again...thanks for the input.
Tom

[rwmastel]

MisterTJ,

Good job, you're on to it!  You know all the filters and as Pawel said, start with the easy ones!  My fuel tank screen came out easy the first time I did it, but every car is different.  The first time I changed my main filter, a couple weeks after buying the car, the canister was 1/3 full of rust!!  Clearly, I had fuel tank issues and the previous owner had maintenance work issues.

I can't wait to hear your findings.  Best of luck.

[Pawel66]

I do not want to take it too far not to side-track you in the wrong direction, but there may be other topics - clogged lines, e.g. tank-pump or return line or you may have the flower pot issue, in which case the fuel supply will be fine until low fuel level, when fuel does not get to the flower pot from above but through a narrow passage near the tank floor.

So, again, there may be other issues for this low pressure than filters, I am not sure where is the best to start.

P.S. I spent half a day on my fuel tank filter. I had to finally drill it through and cut the threads from inside the hole to loosen it. I was very scared - working with drill and saw blade practically inside the fuel tank...

[mistertj]

Hi Paweł - Had the "flower pot" issue years ago with the original fuel tank. So much rust flakes that it would block fuel getting to the filter. I replaced the tank to fix. What I am going to start with is the filter since it's long overdue for a change. Then I may pull some hoses to check on the fuel flow before I go back and mess with the pump input. Oh...on the tank filter, I made a crude tool to unscrew that filter. I've only used it once though. (See photo)

Tom

[rwmastel]

Then I may pull some hoses to check on the fuel flow before I go back and mess with the pump input.

Check the flow rate at the return line at the fuel tank.  That checks the whole system.  If there's a restriction, work your way backwards through the lines/system.

[mistertj]

I'm looking at the fuel filter canister. Looks like I can do everything from inside the engine bay...no? It's been so long but I seem to remember having to do a lot from above before dropping the canister cup into a container below.

[ja17]

Temporarily plug off the fuel return line to see if pressure increases. Reason; if the return check valve is stuck open, it will casuse a severe fuel pressure loss.

[mistertj]

Joe - Thank you. Where is the check valve anyway?

Tom

[rwmastel]

Mechanical Fuel Injection pump.  Do some searches for it, you'll find threads discussing it.  I'm not sure what's in the tech manual about it, but worth a look.

[Pawel66]

Injection pump outlet fitting. First check if you have this valve. I do the fuel line and look inside the fitting. There is or there is not a small hole. Its presence or lack of it indicates if the valve is there, but kill me, I do not remember if the hole means valve is there or vice-versa, you have to look up. It is connected with the presence of the T connector presence at the return line near the fuel pump.

[mistertj]

OK...today's activity. Pinched off the fuel return line...no change in pressure. Still read about 2psi, which is 1 psi more than yesterday. Then proceeded to change the fuel filter. Did it from up top but put what I call an absorbent diaper....one of those white things. Oh, the remaining fuel in the filter canister was kinds dirty but one might expect that. From there proceed to the fuel pump input filter. Think that's a 28mm and with a very small torque driver, it undid. Not too dirty but flushed with some spray carb cleaner. Put it all back together and checked the pressure...kinda down to nothing now. As a just in case, added a couple gallons of fuel. Tried again and still no fuel pressure. Next I pulled the fuel line coming from the injector pump and stuck the hose into a pint container. Flicked the key on and watch the fuel flowing out...maybe a pint in about 5 seconds. Anyway, will put in a different fuel pump next. Not sure if I'll have time tomorrow but whenever I do, will let you know the results. Cheers 

[rwmastel]

Next I pulled the fuel line coming from the injector pump and stuck the hose into a pint container. Flicked the key on and watch the fuel flowing out...maybe a pint in about 5 seconds.

I believe the proper flow rate is 1 liter / 15 seconds.  Flow rate is very important and not always related to pressure.  Keep at it!

[Pawel66]

A pint in 5 seconds sounds about right. Let the pump warm up a bit, then measure - maybe more precisely. You need above 0,6L in 15 seconds (poor result but may work), 0,8L would be ok, 1,0L is good. So a pint in 5 seconds may be ok.

But you need it at the end of the return line.

[mistertj]

Thought about it early this morning...really early. How can I have that much fuel flow and so little pressure? Checked pressure this morning with a different pressure gauge. The pressure is there....hmmmmm! So will order a replacement gauge but in the meantime, back to checking the cold start components. 

[ja17]

Yes, your pressure is good! Also, with an 230SL engine most check valves are built into the large banjo type fitting at the return line connection of the injection pump.

[mistertj]

Thank you Joe.
Put it all back together and tried to start. After what seemed like forever, it finally started to fire on 1 cylinder, then a couple more kicked in but the others never did. Pulled spark plugs and they were all black. Put in new plugs but still only finally got it to fire on a few cylinders. Checked exhaust tubes temps and cylinders 2, 3 & 4 were much lower than other three so I replaced the injectors in those cylinders with known good ones. Filled injectors with gasoline and tightened all connections. Again, cranked forever and finally caught on a few but the others never caught. I'm at a loss as to what might be going on so gonna take a break.

[Pawel66]

Then maybe you are experiencing the spark issue on those dead cylinders. I would perform my favourite exercise of watching blue lightenings around plug connectors in a dark garage when engine is running.

[mistertj]

Taking a break but will give that a try when I return.
Thanks

[ja17]

Try cracking loose the injector lines at the injector one at a time while the engine is running. You will hear each cylinder kick off or kick in, when tightened, if fuel is being delivered.