1967 230SL Fuel injection frustration

[Marchor]

I can't believe it has been over 2 years since I last posted...

Patient is a 1967 230SL. I have pretty much ruled out electrical solutions to the problem, I can detail what I've done electrically to solve the problem (none of it affected the miss at all) if it will help. To say the least, none of the things I have replaced/tested have helped with the problem at all.

There is an intermittent miss that occurs at all rpms (while at idle all the way to redline), a miss so dramatic that at idle the miss will kill the engine, and at speed the miss will cause the car to shudder and stall for an instant. Many times it will happen as I sit at a stop light, and to get it restarted I have to hold the gas feed to the floor and crank. A few times while she was sitting in the driveway and I was closing the garage door I have noticed that when the miss occurs a puff of dark smoke comes out the exhaust pipe.

There are days when she runs like the proverbial top for as long as I am driving, but most days the miss will occur at random times throughout the drive.

I have also noticed that she is getting harder to start the first time each day, usually requiring me to end up holding the gas pedal to the floor before she will start -- just like a flooded carburetor engine. The miss has occurred in the dead of winter, and the hottest days of summer and every temperature in between.

I installed a new fuel pump 5 years ago, not in response to this problem, the old one started leaking. The miss did not start until 2 or 3 years after installing the new fuel pump.

For me the tell-tale puff of dark smoke indicates a fuel injection problem, but then again I may be way off base.

I have built all my own engines and cars and raced in SCCA off and on since 1968 so my mechanical skills are a little above average, but this one has stumped me.

Thanks for any help,

Bob

[jameshoward]

Bob,

Your final sentence suggests that I can tell you nothing you didn't already know and had forgotten, but I'll tell you what I found when I had a similar problem. My car had an occassional miss; random; any RPM; no reason to it.

A few years before I had stripped down my distributor completely and rebuilt it. When reassembling I had to 'make' the insulating washer that sits on the dissy body where the small wire from the capacitor goes to the bolt and into the body. Having discussed the miss with another learned member, I convinced myself that my miss was a short of some kind. He kindly gave me the correct washer and I took the dissy out and replaced the washer. There was definately a short here somewhere, but whether or not this was the problem I don't know. The miss has now gone. So, not sure what's causing your problem, but since you aren't either it may be worth looking at an electrical problem, like an iffy connection such as mine, that could be causing the problem.

I doubt that helps, but that was how my random miss was fixed.

JH

[ja17]

Hello Bob,

Does your injection pump have two solenoids on the rear or one.  Sometimes the " fuel shut off solenoid" activates when it should not. Only some pumps have this. If your main fuel filter gets dirt or rust in it, you should check the gas tank drain screen and the electric fuel pump intake screen. Also see if the car runs better with a nearlly full fuel tank. A clogged "flower pot" intake opening will cause fuel starvation at half tank of fuel or less.  A fuel pressure and volume test could help diagnose some these issues.

As mentioned don't rule out an ignition problem. Bad ignition coils can be very hard to diagnose and can be very irratic.

Keep us up to date.

[JimVillers]

Bob .... One other thought would be a bad injector that would not hold pressure.  It would not provide a consistent fuel charge and would leak fuel when the engine was off, causing a flooded starting condition.  It is not as easy to check as the ignition but is easier than pulling the injection pump.

[Marchor]

Thanks for your suggestions, my thoughts follow...

Good thought on the distributor, that was the first thing I thought about as well and replaced points, rotor and cap, making certain I used the correct fiber washer. The problem continued exactly as described.

I also thought of the coil and replaced it with a new spare from my racing collection - to no avail.

Looking at the back of the injection pump there is only one solenoid. Is that the fuel shut-off solenoid, or does it mean there is no fuel shut-off solenoid since there is only one?

Concerning a bad injector that may not hold pressure, that would explain the flooded starting, but would it also explain the intermittent miss?

I have already checked the fuel filter screen in the canister on the driver's side of the engine, is there another? The problem persists whether or not the fuel tank is full or 1/2 or even less. Fuel pressure test confirms that the new fuel pump is at spec and the line is not clogged.

My real struggle is that in an unfortunate accident involving much-beloved GRANDchildren I do not have a factory manual. The only factory manual I have is for a 1969 280SE that I formerly owned, and it doesn't discuss the fuel injection system as that car had dual carbs. I'm afraid a retired professor's retirement from a small private college does not afford luxuries such as a new manual just now. Can anyone point me to a manual on the internet?

I guess my next steps will be to check the injectors if I can figure how to remove them with any damage being done. I will also double-check my work on the points/rotor/capacitor. Then I will await any other suggestions that might be forthcoming.

Thanks again for all your advice.

[KevinC]

If it helps, I have a manual that I am not using. If you want to send me an email seperately with your address, I can send it to you. Use it as long as you would like and then ship it back when you are done.

[wbain]

Take the car to an emissions testing station and let them check. It may be running rich caused by a leaking cold start valve. There is a small bolt by the csv that can be unscrewed. If there is fuel leaking, the mechanism needs to be cleaned. Check the wiki, that's where I found this info.

[ja17]

Hello,

If your injection pump has one solenoid then it is most likely a starting device. We can get into that after you find the miss. If you have ever had an issue with dirt or rust in the main fuel filter canisister, then you should check the other two screens.  The first one is attached to the main gas tank drain on the bottom (22mm allen !).  As Dan C. related to us, the back end of many spark plug sockets is a perfect fit.  You can use this to remove the drain plug by using a extention and ratchet handle. The other screen is in the intake fitting of the electric fuel pump. This can be checked by unhooking  the line from the tank and then remove the fitting on the electric fuel pump.

Unless you actually do a fuel pressure check when the problem is occuring, you cannot be sure that you do not have an intermitant restriction in the fuel supply.

[Marchor]

Thanks again for the many suggestions, as I mentioned I will be looking at several things and will add the two filter screens mentioned. Grandchildren -- and their parents -- are in town, so work will resume Saturday. As always, I took her out again today and she ran perfectly for more than an hour in town and in the country. I mean, literally perfect. Ahhh, frustrations...

Bob

[julianmaba]

Marchor - since it is puffing out black smoke when the miss occurs (too much fuel), perhaps the cold start valve in intermittently (randomly) engaging — due to an electrical short, or faulty cold start relay (if it has one). As a test to isolate this — try temporarily unhooking the wires to the cold start valve and see if the problem goes away (might be best to do this on an already warm engine since your cold start valve will not operate for a cold start).

[Sirasila]

Just curious... Is it possible to modify it to use a more modern electronic fuel injection pump? Would it help the car run better and easier to maintain? I know it's not original and many would deem it unfit to modify anything. I'm just trying to explore options for a people who can't access a fuel injection pump in good order without breaking the bank.

[wbain]

Just curious... Is it possible to modify it to use a more modern electronic fuel injection pump? Would it help the car run better and easier to maintain? I know it's not original and many would deem it unfit to modify anything. I'm just trying to explore options for a people who can't access a fuel injection pump in good order without breaking the bank.

The Fuel injection pump is a high pressure pump and can be considered an analog computer.

[twistedtree]

From what you describe, it sounds like the whole engine dies momentarily, as opposed to just one cylinder?  If so, then the issue is likely in components common to the whole engine, not just a specific cylinder.  Things like a bad injector, plugs, plug wires between dist and plugs are unlikely to be the cause.  The cold start valve test mentioned sounds like an easy one to try and will rule that out.  If what you are experiencing is a total cut-out of the engine, then I'd be looking at ignition things.  You didn't mention plug wires.  Have those been replaced, especially the one from the coil to the distributor?  What about the ballast resistor?  Could it be shorting or otherwise failing?

On the other hand, if you are having a reduction in power or stumbling, but it doesn't seem like total engine shut-down, then you could just be losing one cylinder or be experiencing general fuel starvation.  I have limited experience with Pagodas specifically, but in general I've found fuel problems tend to reduce/impede operation (typically under load), but not momentarily kill an engine completely, then recover.  If a fuel problem is bad enough to kill the engine, chances are you aren't calling a tow truck.

[JimVillers]

One more testing thought.  After running the engine for a while, feel the temperature of the coil and the ballast resistor.  A bad or incorrect ballast resistor might cause symptoms like you describe (the ballast resistor must match the coil).

[julianmaba]

Marchor - did you try isolating the cold start circuit in case this is intermittently dumping fuel to the intake manifold? It's a simple, quick test.

[nadeem]

it is an electric problem related to ignition system. the ignition system cutoff due to any reason check your point coil rotor and distributer cap.if every thing ok then you must check your ignition switch.if the contacts are loose in the ignition switch it will cutoff while in jerk or points heatup. by pass the ignition switch give direct positive current to ignition coil and drive for while and check if you get the same problem

[Benz Dr.]

A bad head light switch with also do this. Not common and more of a problem on 190SL's but I've seen it on 113's too. All power goes through the head light switch.