You should slow down a little. It almost seems like perhaps not enough fuel or fuel pressure is available in the base of the injection pump. You have to make positive that it is there.

As for the injector test in the air. There will be no spray until the air in the hard line has been eliminated. It also sounds like you have a marginal batttery for testing with.

As soon as I saw that the first two elements where not producing shots of fuel a couple of things came to mind. It was very unlikely that two elements would stop producing output by failing at the same time.

Also to me it was signifigant that it seemed to be just the first two elements on the injection pump that where doing this. The general thrust of my post is you may be working past where the problem is.

Not being there I of course cannot be sure of this.It just a suspicion.

thanks, aside from the tank strainer, where else would you look?
How do you test fuel pressure?

Any idea on the repeated nss failure?

Did you bleed the air out of the hardline (you'd need to repeat that 5 times- for each delivery valve) ? To do that, you'd need help or a foot operated remote starter switch if you do not have help. I am assuming you know how to bleed air so will not go into it here.

Yes hook up the 1/8" braided return line and the end cap.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

First see that there is fuel coming out the fuel return fitting on the injection pump when cranking the engine. If there is close that line off temporarily to verify a weak relief spring is not an issue. It is highly unlikley that a weak relief valve spring would suddenly occur. Although getting some gunk in the relief valve is a possibility somehow holding it open. That is even unusual as well.


Generally though if fuel is coming out the return fitting though most times you will have fuel and at least some fuel pressure in the base of the injection pump. No fuel at all coming out the relief valve and there is a problem. This problem may or may not be the cause of your current issues. This is where I would start probably if it were my car.

As for reading the fuel pressure in the base of the injection pump. This requires a harbour freight 10.00 liquid dampened 0-30 pound gauge. It is too premature to consider it's use at this time.

All you really want to find out is if there is fuel present in enough quantity in that injection pump and it has some pressure. If it is not there change out the secondary fuel filter as it may have almost totally obstructed. This is also a wise thing to do when any form of improper fueling seems present.

You can get a load of dirty fuel at any time. Or a filter just calls it a day. For example I try to only buy diesel fuel at large volume outlets. Things may have improved but I have had my share of issues over the years buying from low volume diesel fuel sales outlets.

If your battery is fundementaly weak you will have to proceed cautiously with the tests. Finding what is the issue is best done with testing rather than guessing is a better way. Many members on site will be here to help.

Another simple test. When you pump your fuel primer pump. Does the effort get harder with pumping? Are you eventually hearing a kind of squeel when the relief valve on the injection pump opens? This has to occur or again something is wrong. Just keep posting the results of the simple tests for help in interpretation of what they may indicate if things are not happening as they should be.

Again in a situation like yours you may save a lot of grief just by changing that secondary fuel filter out as well. Again I may be totally wrong but to me there is a pretty solid indication that you may not have enough fuel available in the injection pump to service the elements properly. Kind of a first things first approach to your problem if nothing else.

Hi, wanted to update here.

Replaced IP Bypass Valve with older 2 bolt model from Pick-n-Pull. (cleaned and pulled spring out to 27mm).

Bent the hardline up on #2 to check spray. after a some white smoke from the #2 injector hole while cranking, it started up and sprayed firm straight healthy looking sprays up in the air.


The #2 cylinder is not firing and the knock seems to be coming from the #2 valves area. it sounds as if a lobe/rocker is smacking against the valve cover though there is no visible scoring and is probably deeper. quiets down a bit at higher rpms...


a few questions:

-by "fuel return fitting on the injection pump" do you mean the banjo bolt connection on the port side of the ip that goes to the front side connection on the secondary filter? or is one of the other two

-my ip primer pump is the older white screw loose type. when I go to pump it it pumps quite a bit of fuel out the sides and not that much back into the ip. is this a failure?

given it doesnt seem like a fuel pressure problem:

-is there a valve part that is known to go, causing a dead cylinder and an upper engine metal "smacking" sound? given the good compression, good injector spray, correct valve/rocker adjustment spacing, this is where my ear is telling me to look.

Well things are not great. Make sure the number two injector is spraying well. Not just constantly streaming. The worse thing with the leaky lift pump is the possibility of air entering as well.

Even though the primer pump leaks it may still seal when screwed down though. You can do a compression check on the number two cylinder and try introducing air to the cylinder if it is low.

Even though I am not there it does sound like a mechanical issue might unfortunatly be present. It is always almost hard to be sure of much at a distance.

to recap symptoms for food for thought:

dead #2 cylinder
upper engine knock
injection good
compression good
valve adjustment good

Maybe the stretched spring new overflow valve made a difference for #2 injector. Look into injector #2 hole with a flashlight and see if the balll is still in place and if clogged with carbon. If clogged, soak it with Marvel Mystery Oil to dissolve the carbon. Blow it out before installing #2 injector and try running it again. With 290 psi compression, fuel injected and air, it should fire.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I'd say time for a leak-down test to determine if the missing compression is getting out via the valves or the rings.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Since you had 290 pounds compression on testing with the number two cylinder. It should be capable of running.

I would check the valves. rockers and lobes etc on the number two cylinder very carefully with the valve cover off though. If you first verify that the number two injector is spraying seemingly normally first.

The noise of a mechanical nature made me wonder perhaps if a valve was somehow disabled .Or has some other strange issue. Unusual with these cars but not impossible either. Make sure to rotate the engine over when examining the valve situation carefully on that number two cylinder.

As this story goes, the injectors were swapped out, and the #2 worked effectively in another hole...and an injector that worked effectively doesn't solve the problem in #2. So the injectors, regardless of their actual condition, are not causing the problem.

I think another compression test is in order. The numbers from the first test aren't good, but they're admittedly produced by an inexperienced hand. They are good enough for the engine to run, perhaps, but not good enough for it to run well. So a follow up leakdown test makes the most sense if another compression test shows similar results. At that point you will at least know whether or not it is even worth it to pull the head, if the will and budget are there to delve that deeply. Otherwise, just button it up and see what happens. Your options in the real world are most likely drive it until it croaks and sell it as is or find another engine, with an outside chance that it can be economically repaired.

__________________
'79 240D

she spent a couple days at a shop. turns out to probably be a pre chamber problem aka "fuel knock" aka "piston slap" aka "nailing". any info on pre chamber failure out there so I might be able to cross reference this? what do I look for in the pre chamber to be sure its failed?

there are several threads ive found but they all end with no resolution:
http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1518233-300td-piston-slap-sound.html
Troubleshooting my engine knock (long-ish) 1982 300D
Knocking sound

this shop wants $220 just to try to diagnose the problem which doesnt seem right.

i didnt see this post before. i think youre right. so the ball is just a bb that sits at the bottom of the pre chamber? is it obvious if its out of place or clogged?


will look into this. may have the shop do it.


yeah its spraying normally. see prev post


based on what im seeing via google i think the prechamber is likely. will report back. ty

Maybe a dumb question but do I soak/ clean/ blow out the pre chamber while its in the engine? or do I have to remove the pre chamber to do this?

Fuel knock, nailing, and piston slap are not all the same thing. The info you got from the shop is essentially, "it could be any of a whole bunch of things, and we aren't going to waste our time diagnosing it for free." You have nothing new to work with.

Back in your post #66 you put up a snapshot showing what is labeled as the #2 pre-chamber. It looks fine. The ball is intact, and a clog at the bottom is a real long shot. If you got 290 lbs. coming out of it, then it isn't clogged! That's not your problem.

What you've shared already tells us that you have either a fuel delivery problem or a compression issue. You've eliminated the possibility of a bad injector, and it sounds like you've probably eliminated the possibility of a bad delivery valve. I don't think base fuel pressure is the issue. That leaves valves, rings, a broken piston (remember those chunks of iron in the oil pan?) or a faulty head or head gasket.

You didn't get a very good set of numbers on your first compression test. It is not unreasonable for your engine to run poorly if those were accurate readings. I suspect that they weren't. You should try it again. If you still see the same numbers on a second test, then the next step is going to be a leak-down test to see where the compression is going. Getting a diagnosis is a process. Unless you have much experience (which you obviously don't), or great luck, you can't skip steps. You just end up back at square one with no better idea of what the problem is than when you started.

__________________
'79 240D