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General Information => Troubleshooting => Topic started by: derekp on October 03, 2008, 11:22:09 am
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I've a 92 eco diesel with 165k miles on it, recently purchased. I've been getting 38-40 mpg (which I consider poor) so I put new nozzles in. they are 308's from kerma. A shop poptested and set pressures to 155-160 bar and confirmed pressures, nice spray and no leakage.
My mileage on first load of fuel since then dropped to 36.
I do notice a little more smoke on cold start (Its 50 deg. F in morning where I live)
The timing belt is supposed to have been done 20k Miles ago (before I bought it)
I run my tires 30 fr/32 rear and I use a k&n filter that is clean.
I have a set of glow plugs that I'll be putting in cause the engine runs ratty on first start up (since I bought it). Compression is 420-500 (400 being wear limit - yes, I did the comp. myself)
Any great ideas on why the mileage drop off? My driving style and commutes are pretty constant.
Are the 308 nozzles "too big" (I got a small power boost since nozzle)
I havent checked for air in lines yet, and I'm on the verge of checking/setting inj timing myself (a new adventure for me)
any helpful thoughts appreciated
Thanks!
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308 are little big? 261 prolly would of been a better choice?
your pump may need some tweaking or just replace with a tru TD pump to go with the 308 nozzels?
tires my self i run at 35psi! if you have any bad bearings or out of allignment that would lower your milage
what is your timing set at?
Duane
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Sometimes installing larger nozzles will make weaknesses in your pump more apparent.
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I dont know what the timing is - the car is a recent purchase (owned it about 4 months now) and I'm still trying to fix all the little nags it has.
I run the tires at 32/34.
I just (this weekend) replaced glows (thinking cold start smoke and rough idle when cold meant a bad glow)
3 of the 4 were good - the 4th one I couldnt test as the top ripped off of it while trying to unscrew the bus bar bolted to it - the nut was hard rusted to the glow. I havent started the car since doing that as I'm repairing the shifter linkage and the cars not back on the ground yet.
Why would "pump problems" after a nozzle change cause a drop in mileage?
I'll probably try checking the timing if nothing else plays out - but even before me messing with nozzles, I only got 38-40 and still thing thats on the low side for this car???
Thanks!
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In my state there is no emissions inspection on diesels (yet) the previous owner had someone remove the cat (in a very kludgy manner) so there is no cat on the car to clog up.
The exhaust is very unrestricted as the car has the oem style center muffler and a glass pack in place of the fat muffler at the rear of the car.
Also, to restate, the mileage droped with the install of the injectors.
thanks!
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Since you had the pop pressure of the injectors reset after the new nozzles were installed and you haven't reset the timing of the engine I think you may have caused the timing to be retarded on your engine. When the pop pressure goes up it takes longer for the injectors to build up pressure as compared to the old pop pressure, this causes the engine to rotate farther before the injectors fire which retards the timing. You should have the timing set to the factory settings (most people go to the advanced end of the allowable range) and also consider resetting your internal IP pressure. The internal IP pressure controls the dynamic advance mechanism on the IP and with the switch over to ULSD it seems that this is causing the IP internal pressure to be reduced due to a lower viscosity of the fuel. Combine everything together and you are probably running slightly retarded on IP timing and this could be the reason you saw a drop in fuel mileage.
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Ok, I understand the part about resetting the timing - I dont understand resetting the internal IP pressure though - and I dont recall seeing anything about it in the bently manual
Ive never done pump timing but have the tools to do so (not afraid to do so either)
Can you explain the IP pressure thing to me or point me to a ref about it?
Thanks!
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Here you go, about a quarter of the way down is a link to a more in depth page.
http://vwdiesel.net/phpBB/viewtopic.php?t=16372&highlight=internal+pump+pressure
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Are there the sounds of marbles bouncing on a plate at idle?
actually my car kind of makes that sound at a slow idle , all most sounds like a bad throw out bearing , but i swear it's coming from the injection pump .
it goes away with the cold start lever pulled out , or the idle set higher .
what is it ???
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Its a diesel.... That's how they sound. :lol: :lol:
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This (http://www.vwdieselparts.com/forum/viewtopic.php?t=4868&highlight=pump+pressure) link over at the VWDieselParts.com forums will explain how the internal pressure controls the dynamic advancement mechanism of the IP along with a bunch of other stuff and this (http://www.vwdieselparts.com/forum/viewtopic.php?t=5936&highlight=internal+pressure) topic over there is a discussion on how to accurately measure the internal pressure of the IP during operation. There is a ton of information over on that forum also that has to deal more with stock VW diesel motors and how to maintain them.
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I'm pushing my way thru the 109 (web)pages of hagar talk - Has anyone done any kind of summary across all that ?
It seesms that using ultra low sulfur fuel means one should adj IP pressure though its not a trivial task ("tap on it and try again" seems to be the method)
Have many people done the "time by ear with engine running"
thanks! I finally found a forum where useable useful info exists!! Great Stuff
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Have many people done the "time by ear with engine running"
thanks! I finally found a forum where useable useful info exists!! Great Stuff
That's how I ended up doing it.
I set it with a dial as usual then started it up and thought I was gonna toss a piston it was so loud!!
Well my injectors were set @ 139 when new so I'll bet they are closer to 135 at best now, suppose to be 155 so I had to retard it.
I just loosened the pump and set it by ear "Red Neck Style".
No idea where it is but it runs great!
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thanks! I finally found a forum where useable useful info exists!! Great Stuff
Not to be snide or nasty but this information has been quoted on here quite a few times. Using the search would probably bring it up.
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My luck - tried the by-ear method of timing - might have done some good - might not. Put things back together and start car up - look ma! Air bubbles in the fuel feed line to injector pump!
Ok, I examined with 4 eyes, the lines (feeds and returns) and I dont see any cracked lines. The returns on the injectors are new too.
Is there any reasonable way to find source of air bubbles?
Not seeing any bad lines/fittings my only thoughts would be to disconnect feed line from tank and pull a vacuum on it up at the fuel filter inlet and work my way forward from the back of the car sealing off whatever part of the line I open up.
But it bugs me that I DONT see any fuel leakage - I would expect leakage when the engine is off.
Is it possible that the water separator is letting air in? Is that common?
any one have any other good ideas on how to deal with this issue?
Also, I have the so-called heated fuel filter - could air be coming in at that pinned connector to the filter?
thanks...
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Because the feed side is under suction, you will almost never see it leak, but it will draw in air
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Air bubbles in the fuel are usually caused by a restriction in the fuel system.
The vacuum caused by the pump pulling against the restriction will expand any air in the fuel. Doesn't mean there is a leak.
It means your filter is clogged or somethiing.
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Well, it drives better, the cold start smoke is tremendously diminished too.
Too early to tell what my advance-by-ear did to fuel mileage.
What are the signs of "too much advanced" IP?
Also I now see that I've got air bubbles in feed and return lines at idle (the bubbles diminish if I rev the engine up) , so I'm trying to plod my way thru air leaks or line restrictions.
Consensus seems to be if the water separator is a problem, remove it.
I guess that would be ok to do as I just discovered theres a drain on the fuel filter - though it may be a bit messy to drain that given its location.
Outside of air leaks or restricted lines, is there anything else that could cause air in both feed and return lines? I'd only recently noticed the air, yet I'd replaced some of the soft returns on the injectors. visuals of existing lines dont show any cracking either. I've got clear line ordered to replace the stuff I cant see thru, not quite sure what to do beyond visuals and the vacuum gauge test.
Thanks for the tip on IP being retarded with replacement of nozzles!
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The check valve after the water separator was causing 5 inches of vaccuum at the IP. A 6 month old fuel filter was good for another 1/2 inch of vaccum.
Are there fuel filters of the mesh type (instead of the bosch paper type) that would be less restrictive?
Whats the purpose of that check valve - is it for a federal safety standard or is it to prevent line drainback when car shuts off
Also, why the heck do I see air bubbles in filter to ip line when I shut car off?
thanks again all for the info on IP timing and air leaks
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Just a side note, i hope this isn't off topic, but how much can a clogged cat drop your milage?
That sparked my interest
I made a post where people listed signs of too far advance IP timing. Use the search and tick the box "include all words" i wish that was set as the default