Fuel injection pump timing and hesitation

[wwheeler]

On the first test drive after some work on the engine, I noticed some hesitation almost bordering on missing when I am entering the ramp onto the freeway (2000-3000 RPM @ 50-60MPH). It runs great at lower speeds, good at idle but stumbles a bit on the highway during acceleration. Starting is also a bit longer.

I replaced the timing chain because I did not know its age and was doing a lot of work on the front of the engine anyway. During the replacement, I am pretty sure the distributor/IP drive gear slipped one tooth on the chain. Because I had the distributor housing off, I could see the gear and was able to correct the mistake (so I thought). After the chain replacement, I matched up the cam and crankshaft marks and reinstalled the distributor EXACTLY the way I took it out. Something didn't look right because the mark on the distributor body did not line up with #1. I went ahead and checked the ignition timing anyway and it was 40-60 ATDC or very late! The engine wouldn't start of course until I moved the distributor drive gear one tooth and adjusted the body clamp. Now it is 30 BTDC @ 3000 RPM. Because I had to move the distributor drive gear one tooth for it to be correct, I am thinking the IP pump timing is off.

If the timing is indeed off (late) by a tooth or two on the drive gear, would that cause the symptoms I have descibed above? The spark plug color looks ok and the ignition timing is right on. I also did time the valves with a dial indicator and they are only off by two degrees. BTW, I have a 123 distributor that was working well before the work. I also had the injection pump off a few years ago, so I know it was in time before the work began. The fuel mixtures seem to be OK when I split the linkage at idle, 2000 and 3000 RPM.

Before I go to the trouble of removing the pump to check the timing, I wanted to get some expert advice and see if the timing could cause the symptoms. Seems like if the pump timing is late, the engine would run lean and therefore the hesitation. How far off can the timing be before you start noticing problems?

Thanks for the help!!!   
   

[280SE Guy]

Wallace,

Glad to hear that your back up and running. First thought that came to my mind is how old is the fuel in your tank? Have you checked your fuel filter(s) lately?

These might not be your problem but is something else to consider.

Regards,

280SE Guy

[Benz Dr.]

If the pump was out by 20 degrees you would notice a difference. I once told this guy to tie the pump 20 degrees ATDC and he timed it 20BTDC. The engine ran very rich but I would expect that being 40 degrees out of time.

 I run 36 degrees BTDC at 3,000 RPM on my 250SE engine. The 280SE would have used the same 051 distributor so maybe you need to bump the timing up a bit. 3 degrees BDTC at idle really isn't enough to give you full power. It shouldn't hesitate but some engines will if they lack ignition advance.

[ja17]

Hello Wallace,

The IP timing can be off quite a bit and the car will still run ok but just not quite  right. I have a way you can do a rough check of the IP timing without taking the IP off.

 Remove the injection line #4, (third from the back) and remove the fitting and the check valve in the IP. Turn the engine until it is at 12 degrees after TDC of #1 engine (compression stroke #1 cylinder, both cam lobes upward). At this point,  the #4 plunger (piston) in the IP is at the top of it's stroke.

This should tell you if you are radically out of time.

Be sure the 19mm fitting is torqued to 20 ft. lbs during re-installation

[wwheeler]

All good thoughts. The fuel is only about 6 months old and I use Stabil religiously and the filter was changed about a year ago.

When I first test drove, the timing was at at 32 and then I backed down to 30 and there really wasn't mauch of a difference.
The engine used to be exceptionally smooth on the highway, now its not so good. Even on the city streets it seems to be not quite right as Joe descibed. Doing the rough check isn't a problem because I would have to take the fuel lines off anyway. I am assuming you need to take the first three fittings off first to get to the #4 fitting. If it is at the top of its stroke, then I will have to find something else to blame. If it is below the top, I guess it is rotate the engine to 20 ATDC and off with the pump. I am I thinking correctly?

I guess the next question then is how far off does it have to be to warrant pump removal?

[280SE Guy]

Wallace,

Time to change the filter anyway so you can eliminate that part.

Regards,

280SE Guy

[ja17]

Hello Wallace,

Start by removing the rear most fitting first, slide it up the metal line then move to the next one and repeat.

 Feeling the IP piston get to TDC is sort of "vague feeling" but if it is radically off, it will be apparent.

Yes for IP removal and set up for installation, turn the engine in the correct direction until 20 degrees after TDC #! (both cam lobe upwards)

[IXLR8]

Hi--

When I freed up my stuck FIP, I put toothpicks into the holes on the fittings over each of the pistons. As you rotate the engine by hand, you can watch the toothpicks move up and down like a calliope. It will be easier to see when TDC is reached using this method.



The other Joe

[wwheeler]

I was just notified by the city that they will be tearing up my alley this week. Because I use it for access to my drive way, looks like the W111 is in dry dock for two months. I knew about this in advance and was going to rebuild the rear axle during this time. Looks like I'll be adding the removal of the IP as well. I will probably end up removing the fuel filter anyway for clearance and change the filter.

Great idea about the toothpicks. I will try that. I stated incorrectly to set the engine at 20 Btdc when it is as Joe says, 20 Atdc. That is a good example of why you shouldn't trust your memory and always refer to the spec book.

If IP timing is off, I won't know if it solved the problem until I can get back out on the road. Oh well, I have other things to do to fill my time like adding headrests and installing my newly refurbished chrome mirror. That is a snazzy piece!

[Benz Dr.]

I've never seen a plugged fuel filter on these cars. I've seen other things plug up but not the main filter. It's rather large relative to the whole ystem which makes me wonder why everyone points to something that should rarely ever be the problem.

  I would bump the ignition timing up to 36 degrees. 30 isn't enough.

[tel76]

Hello Wallace
After reading your first post above it would appear that you have the camshaft and crankshaft timed correct, but you had to alter the distributer drive shaft to obtain the correct ignition timeing,this suggests that the injection pump timeing is incorrect.
As you cannot use your car and it is not that hard to remove the pump i think you should bite the bullet,remove the pump and ckeck/reset, it is the only way you can be 100% sure.

[Shvegel]

Another thing to consider is how it is running. In my experience a hard, staccato or rough miss is usually an ignition issue and a odd feeling like you are moving the throttle pedal but you are not is usually fuel related. Any chance you removed any ignition wires and 2 were put back out of order?

[ja17]

Good thought on the plug wires Pat, it could be something simple like that.

[wwheeler]

When it misses, it is not sharp, staccato as you describe for the ignition. I have experienced that before with another car and that is a very good description BTW. It is more like that latter which I would take for being too lean. I actually never took the wires off the cap but rather laid them off to the side. And besides, it runs too well at idle and lower speeds to have the wires crossed. But I will check anyway to be sure.

The crank and cam are definitely in time as I checked that many times and also timed the valves with an indicator.

I was planning my attack last night to see what exactly I needed to do to remove the pump. Not too bad as I have done it before a few years ago. As Eric said, I know the pump is out some because the distributor setting is different, the question is it out enough to cause the problem? I think it is time for surgery. Now I just need an attractive assistant!   

[wwheeler]

I finally removed the injection pump and here is what I found. The marks are definitely off. It looks to be advanced by about 20-25 derees. Not drastic but do you think that would be enough to cause the stumbling at higher speeds under a load? I guess there is only one way to find out. I have some other items that I am going to do while the pump is out, so it may be a couple of weeks before I get it back in. The bad news is that my alley is being redone and won't be usable again for three months. So I won't really know until then.

I was going to replate the fittings on the check valves while the pump was out. Any problems just taking the fitting out, replacing the seal ring and retorquing it?

[Benz Dr.]

I can see the lines on the pump for timing but what's the extra yellow dot for?

[wwheeler]

That is a silicone plug I used to keep the oil from pouring out from the pump. That size plug just happens to be the same color as the timing marks!