Another rough Idle

[FineOlBenz]

300 Turbo
Am I ready for new injector nozzles or could there be a problem with the injector pump??

Here are the symtoms and history:

1) Receipt in the glovebox shows that someone adjusted injector pump timing years ago at approx 15K miles to cure idling problem (Errr!!!!!).

2) Car had been setting for about 8 years. Fuel, filters, hoses and so on were changes out before I started it.

3) Valves have been adjusted. None found tight.

4) Diesel Purge two cans. No change. Should I try Bio?

5) When first fired up idle was good and smooth. After running a while (15, 20 minutes) a slight miss. Miss is only at idle and not obove 900 RPM. This rough idle stays day after day unless the car is left parked for a week or so. After a week it will start and idle smooth for a few minutes and back to the rough idle.

6) Each injector has been taken appart and cleaned out. Same symtoms.

7) Clear plastic lines at the injector pump show slight bubbling of air. I tryed purging numerous times, no change.

8) I've noted some of the roughness is coming from cylinder #2. Injector was replaces and then it seemed like cylinder #4. That injector was replaced and the miss is still there. Each time new heat shields were installed.

9) I say roughness at idle, not a dead miss. Cracking open injector #2 miss is greater, upon tightening slowly it will smooth out for about 2 seconds and proceed to miss slightly. This same symtom noted on cylinder #2 was there before I took out each injector and cleaned them out. What are the chances I put the same injector back in #2???

Am I ready to try new Bosio nozzels before another injector pump? Or is there a check valve in the pump that may need attention?


Help I'm drowning in used heat shields!!!!!!!!!!!

[running-snail]

Can't help but I'm impressed with your methodology!

[FineOlBenz]

I put int the new nozzles and no change. Any other great ideas?? I could sure use one.

[Wallknight]

When you run the purge, or whatever other fluid, from a jar, bypassing the fuel lines and tank, does it run smoother, or no change?

[Wallknight]

OOOOh OOOh Ohhh! new thought-- if its ok for a few minutes after sitting for a few days, could this have something to do with compression? After a few days, all the oil would be thoroughly drained down and out of the cylinders. After a few minutes it'd be back in there. Would those rings being dry, Help?

I have more thoughts on this, if you think its possible I'll share them. But it might seem silly otherwise!

[barry123400]

Okay you could consider going with the milli volt method to possibly determine exactly what is the cause. But it is tedious and basically does work by direct comparison of cylinder to cylinder. Also no shortcuts at all if you use it. From your description I might do it eventually if all else fails. Milli volt application threads will be in the archives. Engine runs smooth for two minutes and roughens up at idle after sitting for awhile has a disturbing component to me. I doubt the injection pump can be that selective. I suggest getting rid of all the air bubbles you are seeing before doing anything else first. That may be why the problem at times seems to jump cylinders. Plus the two minute onset or delay somehow. Perhaps just enough time for the entrained air in the system to have some effect. It should not be there. I might be wrong of course. Not the first or last time either unfortunatly. Humour us by posting what it does turn out to be.

[FineOlBenz]

When I ran the purge there was no change. The fuel filter is about half full at idle and decreases on acceleration. The problem is not dead miss but a steady one as if there is still a bad injector spray pattern on one cylinder. The car runs strong, in fact very strong. I removed the fuel filler cap and there seamed to be some improvement but I think that's my imagination running wild. When I ran the diesel purge it was out of a can and no change there either. I hate to pull the injectors from the wrecked 300D cause that engine is to good to be parting on. I was going to do a compression test but the gauge had a bad seal at the coupler.. Compression is not the issue. Cranking it sounds even on all cylinders. Above idle is is very smooth. I did notice that by putting my hand on injectors, 4 & 5 seamed to be hotter than 1 & 2. Or was that my hand just getting cooked longer???????????????

By the way Diesel Giant sent one defective or miss stamped heat shield. Watch out for those.

[Wallknight]

The fact that it's smooth after sitting for many days seems to me to be the big clue.

[barry123400]

If the air was not in the return lines when you ran with the purge? But engine was still rough you can discount the air. Depends how much air you are seeing in your clear return lines as well. In reality you should have none. As a general principal anytime I detect air I find the source as the injection system is not really designed to cope with air well. It is compressable for starters where fuel is not. If you can pin the slight miss down to one cylinder like number two I would start with a compression check after swapping the single injector with a known good one. If the injector and compression check out welll.Then the milli volt method to determine how the number two pump element is deficient and if it is correctable by you. Some are and some are not. It just depends on the voltage readings you get and you ability to think the results of the tests through. At that point you are beyond guesswork. Many have made it work well enough for them to improve their situation a lot. Has actually avoided the need for the removal of the injection pump to the shop or it's replacement. When it turned out to be the source of the problem by tests that is.

[FineOlBenz]

Sitting for a few days has given me no clues.

[barry123400]

My thought about the sitting for days was the air dispersed in the fuel in the pump slowly floated to a high point and made a large bubble in the pump. Somehow because of that you got good fuel with no bubbles for a couple of minutes in the pistons of the pump. A wild guess but about all I could think of when you mentioned the presence of air in the system. I cannot see compression improving on one cylinder from the engine sitting around for a few days for example. Or an injector changing in any way. Nor an injection pump element for that matter. I still would get rid of the air problem before going on just in case. It would be a shame to go to a lot of effort only to find later it was the air and it should not be there anyways. Wherever it is coming from will probably get worse over time as well. I already suspect #2 pump element might be a little weaker than the others. The introduction of air is to every pump piston but the number two piston may not be strong enough to pump up to release pressure at idle with some air introduced where the other four pump pistons are tighter and able to cope better. Add too much air and all the pistons will not deliver fuel. You might also have gotten a simular indication on number four perhaps to a lesser extent. Just some random thoughs that are provable by tests if required. With no air I suspect it has already been proven that #2 element can reach full release pressure and that pump is usable for quite a time yet. Thats the two minute good idle. My thoughts may be wrong but maybe worth thinking about. Also if you do pull the number two injector again have a look in the pre chamber to make sure the ball is there and chamber seems ok. Really do not expect a problem there but never hurts to check. It also does not suprise me that engine is strong. As revs pickup probably the effective compression on #2 element is high enough to overcome any air present. Less piston leakdown. Number two cylinder fires normally. Again try to find and get rid of the source of air in the fuel first. Perhaps someone else has better ideals?

[FineOlBenz]

I just tryed to blead the air again. Here's how. I removed the plugged return line and added a length of hose into a jar. By pumping the primer pump there is lot's of air bubbles on the return side and it would not blead out clean. So I started the motor. Good presure at high RPM and no flow at idle. Sounds backwards to me? I also just replaced the O ring and copper washer on the secondary filter thinking it was back flowing there, but no change. I posted on another thread where someone had high engine temps after going to Bosio nozzles. He corrected his high temp problem by getting the injectors ballanced. My question to him was did it also cure the rough idle. I'll run a resistance reading on the glow plugs in the morning after I get a new battery for the ohm meter. Is that how you check them, by resistance readings?

[barry123400]

I can be too long winded trying to get my point across. Forget reading the plugs for now. Concentrate on the air. I really do not like the sound of the amount of air you seem to have by description. You are aware that the prime pump on these cars can be a serious source of air entrance to the system itself on some occasions. Is it leaking fuel when you pump? One other thing I do myself is watch the prefilter. I am never overconcerned with the size of the bubble in there changing. What I do not want to see is a stream of bubbles leaving it and going up the line everytime I stroke the pump. Also I am not an expert and always try to keep an open mind.

[barry123400]

If you submerged your return tube in fluid and are getting constant air bubbles in the fuel being expelled from the pump you most likely have found the cause of all your problems. Once you get clean air free fuel out of the return with no bubbles I really expect your problems to dissapear. If you do not see any bubble stream leaving the prefilter You should probably replace the primer pump assembly. It just screws off the pump and is pretty east to change. I really dislike changing parts without absolute proof they are really bad. It is late at night here and I am pretty tired so cannot think of a quick test but ithat part is highly suspect. If they leak fuel at all when pumped I always change them out. I preffer the newer version that you do not have to unscrew to pump by the way.

[Ara T.]

Do you have the old white plastic style primer pump or the newer, smaller black primer pump? Perhaps your old pump is too far gone and leaks too much. Before I changed mine i would get diesel everywhere leaking from that pump when I bled the system. But it still bled so... I dunno. It's worth a try though, you will have to change it eventually anyway.