questions about l-jet EFI/leaky pushrod seals

howdy

I recently acquired a '78 van in the proverbial "cup half full or cup half empty" shape... it was free, but without title. The body is fairly rusty, and the very very rear of the frame is starting to disintigrate. The engine runs strong intermittently, with even compression all the way around. Currently I'm having a few issues that I -think- are related to the FI, but I haven't yet ruled out the hydralic lifters to my satisfaction.

Anyhow, when the car is 'slightly' cold, ie, not been run at speed for 5-10 minutes, the thing idles =rough= a good percentage of the time. The cylinder head temperature sensor seems to check out okay, the resistor bank is fine. I figure I probably have an intake leak -somewhere-, but have yet to find it. I've been searching the google usenet archive, and tonight came across an oddity. A few people mentioned that leaky pushrod seals can cause intake leaks. (!?) I have for sure some dead pushrod seals, judging by the little drippies on the garage floor, and the slight mess under the clylinder heads. However, this just sounds dubious to me. Could leaky pushrod seals or valve covers really cause a rough idle?? Is that just voodoo BS, or reality?

talk to me!

-Matt

'75 FXE '78 VW Bus

Reply to
matthew j henschel
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Yes. Your leak, if you actually have one, is likely one of the pre-formed hoses. There are a couple hidden almost under the air plenum on the right side - to the air bypass valve for cold start. Take each hose off and inspect for flared and cracked ends, hardness, cracks, etc. The big "S" hose that goes from the air cleaner/airflow meter to the throttle body is a common culprit with almost invisible cracks. Where the hoses attach to the "S" hose is a problem. The decel valve is sometimes a problem (if removed from system the deceleration will be much more snappy, but exhaust backfiring will increase.)

When you did your compression check, was the engine hot or cold? It starts okay but idles rough until warm... Sure sounds like headtemp sensor. Any airleaks of any appreciable size and the engine flat won't run! headtemp sensor should have about 2400 ohms resistance at about 70 degrees F. It gets lower as it heats up. You can add a variable resistor in-line and increase the resistance, or you can use one to test by replacing the headtemp sensor with the variable resistor - start engine and turn the adjuster to see if engine runs better. Easy for me to say cuz I've got 'em laying around!

The coldstart injector only works for a few seconds. The air bypass valve might be sticking but should only increase speed - not change mixture because it uses "counted" air. If it has a leak, the engine should die. Maybe a small leak in the air bypass valve circuit?

Is the fuel pressure regulator vacuum line hooked up? No vacuum would cause overly rich condition.

I'll think on it some more. Meanwhile, pop the oil filler cap off when it's running and see if it gets a whole lot worse. That should give you an idea of the amount of influence that pushrod tube O-rings and valve cover gaskets will make. Please post updates. -BH

full or cup half

is fairly rusty,

disintigrate. The engine

way around.

related to the FI, but

satisfaction.

at speed for 5-10

time. The

the resistor bank

leak -somewhere-, but have yet

archive, and tonight came

pushrod seals can cause

seals, judging by the

under the clylinder

leaky pushrod seals

voodoo BS, or

Reply to
Busahaulic

Already tried pulling the decel, checking all the hoses, using the rubber hose stethescope, etc. Found no leaks, but cleaned up every damn hose fitting anyway, just for posterity. Still no good.

I did the compression check both warm and cold. Had a problem orginally with the #3 exhaust hydro lifter sticking open, but adjusted it to 1/2 turn past zero lash and compression is right even with the rest of em now.

Air Bypass Valve Circuit?? pretell

Yup, it's hooked up. Don't have a fuel pressure gauge, so I couldn't tell you what the reading is.

Tried that as well already ;-) Doesn't make one iota of difference.

Thanks for the ideas though! Lemme know if something else pops into your mind.... I definitely have leaky pushrod seals, but I don't feel that's the issue either. It's mostly a hot start problem. It idles moderetely evenly when cold and when it's been running for a bit, but after a 10-50 minute nap after a 10-15 minute run, it is damn tricky to start and idles AWFUL.

I started another thread with a different, more specific subject, so I guess we should probably abandon this one.

Thanks again...

-Matt

'78 VW Van (new to the family) '75 Harley Davidson Superglide (seriously jealous of it's new aircooled brother)

Reply to
matthew j henschel

You're quite right to be suspicious, because this sounds unlikely, but it's true.

L-Jetronic engines measure airflow from the air cleaner thru an airbox, but air from the crankcase enters the airflow AFTER the airbox. A normal amount of gas from teh crankcase is compensated for in the L-Jet setup, but once the pushrod seals start to leak you will get way too much air and this will make the engine run lean.

The situation is worst at idle, because that's when the manifold vacuum is the max, meaning that's when you get the max leakage of unmetered air and the metered air is at a minimum.

The pushrod seals are rather easy to replace on the type 4 engine. You can replace as much as you want, but after a few such engines I quickly decided that the only parts that were actually bad were the O-rings on the head end of the pushrod tubes. The O-rings on the case end don't get nearly as hot and are generally fine.

When you replace the seals, you'll just need 8 outboard seals. (There are 2 versions, so get the right ones for YOUR engine.) Remove everything and clean up the old parts. Clean up the sealing areas on the case and head and smear all of them with clean engine oil. Install the new outboard O-rings on the pushrod tubes and oil both O-rings. Push the new/used parts back into place. You'll probably need to use a sparkplug socket to lightly tap the tight new assemblies back into place.

-

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Reply to
Jim Adney
[snip]
[snip]

Heya Jim! You are, in fact, the inspiration for my questioning. The only person I've ever read or heard saying that pushrods leaked vacuum was you ;-) They definitely leak oil, so when I have some time, I plan on replacing them. My issue seems to be 'heat-soak' related somehow, that is, it only idles rough after a short stop; once I hit the highway for a few minutes, it idles great again. In fact, I can sometimes get the problem if I kill the ignition just for 15 seconds or so. Check out my new thread on this perplexing problem.

FWIW, I do have a cracked exhaust manifolds.... I'm sure it's not helping the issue. The right one is worse and pushes a good bit of air, and it's replacement is on the way. However, I can't locate a left one anywhere. Anyone got an extra? ;-)

Thanks again...

-Matt

Reply to
matthew j henschel

They'll leak oil out when parked, and air in when running. The oil drips on either side are classic signs that you need new seals. The first time I came across this was after someone with an L-Jet 1.8 914 had already explained it to me. I really hadn't understood him until I got into this poorly running bus and then it all started to make sense.

The other poster who suggested that you check your hoses was correct. I haven't seen bad hoses as the problem with these engines, but I don't work on many of them. It's certainly true that an air leak ANYWHERE that admits air after the airbox, will cause a problem.

Sorry, that doesn't ring any kind of bell with me. It could be air bubbles in the gas line, but that would go away after a minute or so.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Reply to
Jim Adney

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