79 Bus Cold Idle Issue

[mross]

Hi all,

I recently replaced the engine in my bus (79 automatic westfalia; federal model). It ran well until very recently. I am now dealing with cold start problem that cropped up about a week ago. It's not a daily driver, so I parked it to perform tests on the fuel injection system, but am having trouble tracking the problem down. The EGR system is plugged at the valve in the plenum, and I am using a muffler from a 412 car (no catalyst). The Bus is otherwise bone stock.

I did the following checks / parts replacements to the fuel injection system while the engine was removed
- checked fuel injection wiring harness with multimeter to make sure that all wires were still good (no opens)
- replaced Thermo-Time Switch because it failed the Bentley tests, and somebody had connected the cold start valve directly to terminal 50 on the starter
- checked cold start valve for continuity - checked good (was still working when engine removed; as too much cranking would flood the engine)
- removed crummy previous owner wiring job and connected TTS and CSV as shown in the Bentley wiring diagrams
- replaced injector seals
- replaced vacuum lines (all except for molded hose between S-boot and decel valve; patched with RTV after cleaning with soap and water)
- replaced rubber hoses between intake plenum and intake runners
- cleaned intake runners and plenum (and engine compartment, etc...)
- replaced rubber fuel lines with Gates high pressure hose (100 PSI and rated for modern ethanol fuels)
- replaced hose clamps with the solid band type (and threw away any worm drive ones that I found)
- replaced temperature sensor 2 (misplaced during disassembly)
- replaced fuel pump (stock pump leaked between housing and end cap after reassembly)
- cleaned and inspected fuel injection grounds
- installed 3 rebuilt and 1 new fuel injector (1 failed the tests for rebuilding)
- replaced phenolic spacers under intake manifold runners
- had the fuel tank acid - dipped and lined
- replaced steel fuel lines between tank and filter and between FPR and tank with steel brake line, bent to shape with a tubing bender (old lines rusty)
- replaced fuel filter
- replaced 90 degree hose from AAR to S-boot
- replaced rubber seals on brake booster one - way valve and reinstalled clamps
- cleaned the S-boot and checked it thoroughly for cracks (still good!)
- replaced all 2-wire connectors on fuel injection wiring harness and labelled them (age was causing them to start crumbling)
- checked wiring harness a second time with multimeter to verify correctness.
- injector resistor block cleaned, checked, and reinstalled
- auxillary air regulator cleaned and reinstalled
- decel valve cleaned and reinstalled
- distributor cleaned, felt wick oiled, rubbing block greased lightly, and reinstalled
- I'm sure there's something else that I'm forgetting that I replaced.

Anyway, after all of that, it ran well until the most recent hiccup as outlined above. I have performed the following tests:

Auxillary Air Regulator per Bentley shop manual
- When removed with the engine cold, the valve was open.
- When the valve was heated in the oven (on the lowest setting) for a few minutes it was closed upon removal
- Putting the valve in the freezer afterwards showed that it was closed again.
- The valve measures 30 ohms between the two terminals on the connector
- Connecting a noid light to the harness plug shows that the valve gets power when the engine is running.
- I have not changed the position of the valve inside of the AAR (nut still sealed with factory paint).

Thermo - Time Switch per Bentley
- Testing showed that a noid light plugged into the CSV connector did not light when the engine was cranking. Further checking revealed a bad connection on the body side of the double relay harness. After repairing the harness plug, I received the following results:
- A noid light plugged into the CSV connector will light up for 10 seconds and then go out when the starter is cranking the engine (wire from points to coil removed).

Fuel Pressure
- With the key on and the engine off, the fuel pressure reads 30 PSI with the pump running and the pressure gauge connected at the test port (moved vane in AFM to run pump).
- With the engine running, the fuel pressure flutters rapidly between 25 and 30 PSI. If you stop the engine during this test, the gauge reads 28 PSI.
- With the engine running and the vacuum line to the FPR removed and plugged, the fuel pressure flutters rapidly between 30 and 35 PSI.
- If you leave the gauge on the test port after running the engine, the gauge does not drop. I assume this means that none of the injectors or the CSV are leaking.

Temperature Sensor 2
- The TS2 reads 2380 ohms at 55 degrees fahrenheit (cold engine).
- Moving the test lead from the body of the sensor to the cylinder head does not change the reading.
- The TS2 was installed with nothing on the threads.

The AFM was replaced a few years ago with one from fuel injection corporation because of a flat - spot issue. I have not yet checked it, but the engine idles the same whether it is plugged in or not. I have not altered the setting of the idle mixture control screw on the AFM. Neither have I altered the position of the wiper on the resistor track inside the AFM (AFM cap still sealed). I set the dwell, timing, and idle speed with the engine warm and double checked it for correctness. Changing the idle speed so that the engine doesn't stall when cold makes the idle obviously too fast when warm. I also double checked the spark plug gaps and found them to be correct per Bentley. I also double checked to make sure that the vacuum lines were installed in the correct locations. If you guys have any ideas on what I might check next, I would be greatly appreciative; as I am not quite sure where to go from here. My current theory is that the fuel pressure regulator is bad because of the slightly low pressure indicated by the gauge and the fluttering of the gauge needle. Sorry about the wall of text!

Thanks again!
- Mike Ross

[vdubyah73]

check for dis-located v/c gaskets. you could have a crankcase ventilation vacuum leak. the v/c may not even leak oil at all if the vacuum sucked the gasket in along the top. if the gasket was sucked in at the bottom it may only leak briefly at shutdown. this can be a pretty big vacuum leak, thats why you may have little to no oil leaking.

[mross]

That's a good idea! I will have a look and post results when I get home tonight.

[Amskeptic]

That's a good idea! I will have a look and post results when I get home tonight.

P.S. You must tell us how it runs when warm . . . at idle, cruise, and under full acceleration from 35-50 mph in 3rd gear. After all you have done for that car, it should be embarrassed, misbehaving at all.

[mross]

P.S. You must tell us how it runs when warm . . . at idle, cruise, and under full acceleration from 35-50 mph in 3rd gear. After all you have done for that car, it should be embarrassed, misbehaving at all

LOL, yeah this thing was pretty iffy when I bought it, but it's getting better. I'm happy to have the engine compartment cleaned out, all tins painted and repaired, and everything hooked up like the book says, though. Anyway, it runs great when it's warm. The idle is perfect, acceleration is fast (for a bus), and I have not noticed any hiccups. I have no trouble maintaining speed on the freeway. When it's warm, the engine does not hesitate or stall, or act up. It doesn't shift into 3rd until about 35 (cruising) or around 45-50 if you're accelerating hard. It seems to have plenty of power, as onramps are no trouble and cruising at 65 on the highway takes very little demand from the throttle. The engine runs well and does not stall after i drive the bus for about three blocks. The factory thermostat, cable, warm-up flaps, and even rubber grommet around the cable are installed and were checked for proper function before I ran the engine (and again while the engine was running).

I had a look at the valve cover gaskets today, and they were not sucked in or missing any notches from the cork. The valve covers do not leak. I also checked for vacuum leaks with an unlit propane torch at every place where vacuum lines connected (including fuel injectors, oil filler cap, valve covers, S-boot, CSV, PCV valve, distributor, EGR assembly blockoff, EGR valve connection to air distributor, throttle body gasket, etc) and did not find an increase in idle speed from holding the torch near any location where there could be a vacuum leak.

I also tried starting the engine (cold) and moving the AFM vane slightly to richen the mixture. This causes the engine to stall, and the exhaust to smell like unburned fuel. For this reason, I don't think that there is a vacuum leak. Could the idle mixture be too rich when cold? Also, how can I check the PCV valve for proper function (might be a moot point, since I can't find one for sale anywhere)?

[SlowLane]

Sorry, but having read through your post twice, I don't see any description of exactly what the problem you're having is. I get "Cold Idle Issue", but what sort of issue? Fast idle, slow idle (would that be an idle idle?) , loping idle, itinerant idle, just plain refuses to idle?

Given the exhaustive list of things you've already checked, I'm going to suggest maybe a throttle-shaft vacuum leak.

[Amskeptic]

I also tried starting the engine (cold) and moving the AFM vane slightly to richen the mixture. This causes the engine to stall, and the exhaust to smell like unburned fuel.

Been here, done this, got the teeshirt.

Open up the AAR valve. It is adjustable. Get your idle speed as high as possible within specs, meaning, try for a 1,050 rpm idle when warm. Your engine needs air air air air at cold idle.

The great surprise for me when I cured this issue, was that moving the wiper CCW to richen it *actually leaned the mixture*!! I have done battle on theSamba over this seeming illogic, but the ECU has a very specific program to lean out the mixture!! if the rpms drop!! to prevent flooding!!! which is worse than anything! When we move the wiper *without a corresponding increase in rpms!!!** the ECU just cranks back that injection pulse.

Your AAR has an adjustment nut that you loosen after you stick a small allen wrench inside the opening. With the nut loose, you crank that opening more open!! then tighten the locknut.

My engine immediately burst into song at 1,300 rpm for one minute, and settled down to a normal idle in four minutes, after this adjustment. Even new AARs do not know about worn valve guides, it is not about just blowing money and sticking on a new one.
Colin

[mross]

Sorry, but having read through your post twice, I don't see any description of exactly what the problem you're having is.

I looked through it again and realized that I was so preoccupied with my list of notes that I forgot to throw it in. At cold start, it idles slowly and tends to stall if i don't keep light pressure on the throttle pedal. After driving for a few blocks, it clears up and runs well without stalling. Adjusting the idle speed faster makes it idle too fast when the engine is warm.

throttle-shaft vacuum leak

That's a good idea. I looked at the throttle body while the engine was out (and cleaned it), and it seemed ok. If the bushing is worn, will I be able to see or feel it? I will check for a leak there with the unlit propane torch in a minute.

moving the wiper CCW to richen it *actually leaned the mixture*!!

Wow! I didn't realize that the ECU was that 'smart'. Good to know. I will take the AAR off and see if I can adjust it for more opening.

[SlowLane]

At cold start, it idles slowly and tends to stall if i don't keep light pressure on the throttle pedal. After driving for a few blocks, it clears up and runs well without stalling. Adjusting the idle speed faster makes it idle too fast when the engine is warm.

That does sound like an AAR problem.

throttle-shaft vacuum leak

That's a good idea. I looked at the throttle body while the engine was out (and cleaned it), and it seemed ok. If the bushing is worn, will I be able to see or feel it? I will check for a leak there with the unlit propane torch in a minute.

I just threw that out there with no information. I now think it's unlikely to be the source of your problem. Given the age of these engines, pretty much all of them will have some throttle bushing wear, but there is a seal on the shaft under the spring assembly which shoud help in that regard.
The seal does tend to get old and hard. German Supply has a picture here http://www.germansupply.com/home/custom ... 388&page=2, but they're sold out. Bus Depot has a listing for the same part number here: http://busdepot.com/details.jsp?partnumber=022133069, where they call it a "washer". I tried ordering one from BD some months back and they had none in stock and didn't know when they would get any more.

Auxillary Air Regulator per Bentley shop manual
- When removed with the engine cold, the valve was open.
- When the valve was heated in the oven (on the lowest setting) for a few minutes it was closed upon removal
- Putting the valve in the freezer afterwards showed that it was closed again.
- The valve measures 30 ohms between the two terminals on the connector

I assume you meant "open again" there.

A more functional test, if you have a source of 12VDC, is to provide 12V to the AAR terminals when at room temperature, then time how long it takes to close fully. It shouldn't take more than a few minutes. This tests both the heater element and the bi-metallic actuator and gives you an idea of how long after starting you can expect the AAR to have an effect on your engine's operation.

Then remove the voltage from the terminals and confirm that it eventually returns to fully-open (not really important to time this part, you just want to make sure it returns to the initial position).

Also, be aware that the commonly-available aftermarket AAR elbows are utter crap and can easily fail within days of you installing them. If you can find a genuine VW elbow you'll be much farther ahead.

[mross]

I just went out and had a look at the bus again. I took off the AAR and adjusted it for more opening. Upon reinstallation, I noticed that the vacuum line from the AAR was a little too long and was a bit kinked with the valve installed. I shortened the hose so it wouldn't kink and it now seems to idle much faster when cold. Also, it doesn't need to crank as long to start. LOL, sometimes I can't see the forest for all of the trees

Slowlane, good catch on my typo; I did mean open again. Also, the AAR elbow still looks good, but I will put the stock one in the glove compartment in case i need it. Thanks for the advice.


Colin and Slowlane, thank you both for all of your help!

[Amskeptic]

vacuum line from the AAR
seems to idle much faster when cold.

Public place here, with a vast lurker readership, we do not call the AAR "supply hose" or "outlet hose" to the intake plenum a "vacuum line", which is reserved for Items That Need Vacuum To Do Their Job. Slow Lane, what would you call the incoming hose and the outgoing hose for the AAR if you had to create a parts list that was intuitively helpful??

Let's parse, "seems".
Is it idling more appropriately when cold? No stalling? Does it kick down after several minutes? Do you need to lean out the overall mixture IF you had attempted to compensate for prior cold behavior?
Colin

[SlowLane]

Slow Lane, what would you call the incoming hose and the outgoing hose for the AAR if you had to create a parts list that was intuitively helpful??

I'd avoid naming them based on their intrinsic function (ie. incoming, outgoing) because that pre-supposes knowledge of their function on the part of the user. It's far too subject to mis-interpretation. Instead, I'd name them based on what the user can see, which is what the two ends of the hose connect to. Eg. air-plenum-to-AAR hose, or AAR-to-S-Boot hose, or @#%^%%-prone-to-cracking-in-hard-to-spot-location AAR elbow (sorry, that last one might not be very helpful).

I realize those names are verbose, and not something one would wish to use repeatedly in describing a procedure, but they might be tolerable in a parts list.

Let's parse, "seems".
Is it idling more appropriately when cold? No stalling? Does it kick down after several minutes? Do you need to lean out the overall mixture IF you had attempted to compensate for prior cold behavior?
Colin

Diagnostic tach/dwell meters can be had for quite reasonable prices. Helps to take "seems" right out of the equation.

[mross]

Ok, I went ahead and hooked up my tach-dwell meter, ran the engine until it was warm; and set the idle to 925 RPM per the decklid. Then, I let it cool off and checked the idle again when cold, and had the same problem as before (tach said 500 RPM with engine cold). Sorry about the post on Saturday, I wasn't feeling my best that morning. I also re-adjusted the AAR to make sure it was open fully (rechecked work from Saturday), and made sure that the hose between the AAR and the intake plenum was not kinked (and that the hose between the AAR and S-boot was clear / not kinked.

Do you need to lean out the overall mixture IF you had attempted to compensate for prior cold behavior

I still have not adjusted the AFM for idle mixture (adjust screw on top of AFM) or overall mixture (change position of wiper on resistor track). Do you recommend I try this?

Anyway, if you guys have any other ideas; I'd be happy to hear them!

Thanks,
Mike

[IFBwax]

Westy78 or 78Westy (one of the two) and I both have newish Raby engines and we both have the same problem. My straight factory build brown bus starts right up and goes like hell. My green bus has to get to 200 CHT before I can let go of the throttle. Takes about 3 mins to warm up. I've learned to live with it. Makes me take it easy and get everything in order before I bolt out. Once it's above 200 it runs really well. I don't know if it has anything to do with the cam profile? Colin?

[SlowLane]

Mike, in looking over your original post, one thing popped out at me:

- replaced steel fuel lines between tank and filter and between FPR and tank with steel brake line, bent to shape with a tubing bender (old lines rusty)

What is the I.D. of the brake line tubing you used? It really should not be smaller than the original fuel lines. The fuel in these systems goes racing around the ring at a pretty good clip. Any extra restriction can affect delivery, especially on the low-pressure side feeding your pump inlet.

I don't for a second think that this is causing your cold idle problem, just something that made me go "whaaa?". Steel brake line is usually pretty skinny, at least on the cars I've worked on.