79 Bus Cold Idle Issue

[mross]

SlowLane,

What is the I.D. of the brake line tubing you used?

5/16", IIRC I took the stock lines with me and matched up the inside diameters with what was on the rack. I would have reused the stock ones, but they were so rusty i could hold them in my fist and snap them in half with pressure from only my thumb (scary!). Anyway, the brake line solution is working out so far (I'd think that it would run poorly on the freeway if the lines were too small) and even fits in the little clips on the underside of the body.

Steel brake line is usually pretty skinny

Yeah, it usually is, but the place I got it from (a national chain) had a rack in the back with sizes up to 3/8".

IFBWax,

My green bus has to get to 200 CHT before I can let go of the throttle. Takes about 3 mins to warm up.

Are you running the stock fuel injection? What all did you have a look at in attempting to solve it? Is your bus manual or automatic?

I still wonder about the fluttering of the fuel pressure gauge needle when testing. Is this normal with the engine running?
My only other thought at the moment is that maybe something is causing a drag on the engine. However, the alternator spun freely when it was off, and I can't see a problem with the trans (same problem in neutral, park, or any forward gear).

[SlowLane]

SlowLane,

What is the I.D. of the brake line tubing you used?

5/16",

Given your attention to detail, I didn't honestly expect that you had used skinny pipe. Was just crossing t's and dotting i's.

I still wonder about the fluttering of the fuel pressure gauge needle when testing. Is this normal with the engine running?

Mine doesn't flutter, if that's of any value to you. Flutter could be induced by the regulator getting an equally fluttery vacuum signal, or maybe by a bad injector. Do you have a vacuum gauge you can put on the intake manifold?

My only other thought at the moment is that maybe something is causing a drag on the engine. However, the alternator spun freely when it was off, and I can't see a problem with the trans (same problem in neutral, park, or any forward gear).

Here's a long shot. Temporarily block the passage from the decel valve to either the plenum or the S-boot. See if cold idle improves.

[mross]

I didn't honestly expect that you had used skinny pipe. Was just crossing t's and dotting i's

Do you think I ought to pull it and install something different? What do you guys use? Thinking about it again, my recollection could be incorrect (I installed the fuel tank while the engine was still being built.). Unfortunately, I looked through my shoebox of receipts and did not find the one with the brake line on it.

Mine doesn't flutter, if that's of any value to you. Flutter could be induced by the regulator getting an equally fluttery vacuum signal, or maybe by a bad injector. Do you have a vacuum gauge you can put on the intake manifold?

I don't at the moment, but I can get one. If I get off work before the stores close tomorrow, I will pick one up and post the results.

Temporarily block the passage from the decel valve to either the plenum or the S-boot. See if cold idle improves

I just ran out and gave this a shot. Unfortunately, I got the same 500 RPM idle and same flutter on the fuel pressure gauge.

Edit: Hang on, please disregard the final sentence above. I will do the proper check in a moment.

Edit 2: I blocked the hose between the decel valve and the S-boot (at the decel valve), with no change. For grins, I also tried plugging the vacuum tee where the brake booster hose connects to the intake plenum in case the booster diaphragm has a hole in it or the check valve is not working. The booster works fine (stops easily with light pedal pressure), but I figured that it was one more thing to eliminate from the list of possible problems.

[Amskeptic]

I don't know if it has anything to do with the cam profile? Colin?

Yes it does. Breathing ability further up is achieved by keeping the exhausts open a little longer, and opening the intakes a little sooner, which makes idle vacuum drop.
Colin

[SlowLane]

I didn't honestly expect that you had used skinny pipe. Was just crossing t's and dotting i's

Do you think I ought to pull it and install something different? What do you guys use? Thinking about it again, my recollection could be incorrect (I installed the fuel tank while the engine was still being built.). Unfortunately, I looked through my shoebox of receipts and did not find the one with the brake line on it.

No, I think the 5/16 line is perfectly fine. Overkill even, as that's larger than 7mm. Me, I haven't had to replace rusted-out fuel line.

Temporarily block the passage from the decel valve to either the plenum or the S-boot. See if cold idle improves

I just ran out and gave this a shot. Unfortunately, I got the same 500 RPM idle and same flutter on the fuel pressure gauge.

Like I said, it was a long shot.

[SlowLane]

Mine doesn't flutter, if that's of any value to you. Flutter could be induced by the regulator getting an equally fluttery vacuum signal, or maybe by a bad injector. Do you have a vacuum gauge you can put on the intake manifold?

I don't at the moment, but I can get one. If I get off work before the stores close tomorrow, I will pick one up and post the results.

Actually, ignore what I said. I just re-read your initial post and noticed this:

- With the engine running and the vacuum line to the FPR removed and plugged, the fuel pressure flutters rapidly between 30 and 35 PSI.

... so that eliminates fluttery vacuum as the source of your fluttery fuel pressure.

It's probable that this is a red herring, though, in trying to solve your idle problem. I'm not certain if my experience with the Vanagon pressure readings translate well to a bus's pressure readings, as the fuel flow in the two systems is different. If the pressure tap is in the same location (between cylinders 3 & 4), then the bus has three injectors downstream of the tap, whereas the Vanagon just has one injector between the tap and the FPR, which might translate to a more steady pressure reading. I dunno, just speculating here. I could very well be blowing smoke.

Regardless of all that, a vacuum gauge is a nice diagnostic tool to have handy.

[mross]

so that eliminates fluttery vacuum as the source of your fluttery fuel pressure

I guess it's time to pull the injectors and cold start valve and check the spray pattern.

If the pressure tap is in the same location (between cylinders 3 & 4), then the bus has three injectors downstream of the tap, whereas the Vanagon just has one injector between the tap and the FPR, which might translate to a more steady pressure reading

Yup, the pressure tap is on the driver's side between the injectors for the #3 and #4 cylinders. You would think that the fuel pressure would change everywhere in the entire system regardless of the location of the tap; but I could be wrong.

I think I'm going to check the injectors for flow and spray pattern per the Bentley. If they check good, I'm leaning toward replacing the fuel pressure regulator.

[SlowLane]

so that eliminates fluttery vacuum as the source of your fluttery fuel pressure

I guess it's time to pull the injectors and cold start valve and check the spray pattern.

Well, that can't hurt (unless you smoke or make sparks while doing so).

If the pressure tap is in the same location (between cylinders 3 & 4), then the bus has three injectors downstream of the tap, whereas the Vanagon just has one injector between the tap and the FPR, which might translate to a more steady pressure reading

Yup, the pressure tap is on the driver's side between the injectors for the #3 and #4 cylinders. You would think that the fuel pressure would change everywhere in the entire system regardless of the location of the tap; but I could be wrong.

I'm not at all certain about that, which is why I threw in the caveat about the differences between Vanagons and buses. You really ought to get feedback from someone else who has put a fuel pressure gauge on a bus setup to know for sure whether your flutter is normal.

Think of the inlet to the FPR as the point where fuel pressure will be the most stable, because that is where the control point is. The farther back upstream you go from that point, the more likely there will be variations due to flow constriction, turbulence, injectors switching on and off. My point was that on the Vanagon, the test port is about six inches away from the FPR inlet, with just the #4 injector between the two. On the bus, the test port is more like four feet away from the FPR, with three injectors in between them. The injectors switching on and off generate pressure waves that propagate back along the fuel flowing through the ring, which are then seen as flutter on your gauge. I'm speculating here, so what I'm trying to say is get a second opinion.

I think I'm going to check the injectors for flow and spray pattern per the Bentley. If they check good, I'm leaning toward replacing the fuel pressure regulator

Your earlier tests appear to verify that the FPR is working within specification.

[mross]

Well, that can't hurt (unless you smoke or make sparks while doing so).

LOL, I will try to avoid that !

Moving on from the fuel pressure regulator; this evening I made the following checks:

Noid Light on Fuel Injection Harness:
Light flashes while cranking engine at all four injector plugs and the cold start valve (for 10s) while cranking.

Fuel Injector Test:
I observed conical spray from all four injectors and the cold start valve. It is a fine mist and I did not see any drops of fuel come out.

Fuel Pump:
Fuel pump pumps 50oz. of fuel in 30 seconds and is whisper quiet.

At this point, it looks like the next step is to test the air temp sensor in the AFM to make sure that it still works.
Other than that I'm running out of ideas for things to check. I think the only parts of the system that I have left to check are the air temperature sensor (poor running and stalling at cold idle does not change with AFM unplugged) and the computer. However, I don't suspect the computer; as all of the other cars I've seen that had a bad ECU would not run or ran extremely poorly at any point (cold, warm, etc).

Could this be an ignition issue? Is anything different when the distributor is cold? Could the coil be getting weak (I'm still running the stock black coil as shipped from the factory)? The condenser has been recently replaced, as have the points. I know the ECU uses the points to generate the injector pulse, and as a result bad or maladjusted points can cause poor running. However, experience suggests that bad or incorrectly set points run poorly all of the time. Furthermore, dwell was at 48 the last time I checked it (2 days ago).

Slowlane, I can't tell you how much I appreciate your help. If you're ever in St. Louis, I'll buy you a beer.

[SlowLane]

Well, you've done a more thorough job of performing all the Bentley checks than anyone I've seen, here or on The Samba.

Given that your engine runs sweetly for every condition but cold idle, I'm not surprised that every check you've done has come up positive. I'll bet dollars to doughnuts that your air temp sensor will check out fine too.

All your symptoms point to the AAR function. So let's get back to basics: with the AAR cold, can you take the AAR-to-S-boot hose off at the s-boot and blow through it into the plenum? Can you plug the other end of the AAR-to-plenum hose and check that you can no longer blow through it?

The hose that goes from the S-boot to the AAR elbow has a metal sleeve that slides into the elbow. Make sure the sleeve isn't sliding too far into the elbow and blocking flow.

Really starting to run out of ideas here.

[mross]

Well, you've done a more thorough job of performing all the Bentley checks than anyone I've seen, here or on The Samba.

Thanks man! Also, thank you again for being patient and helping me step through the troubleshooting process . This bus has been a long project, but I'm starting to see the light at the end of the tunnel.

Also, I checked the air temperature sensor in the AFM tonight and got 1750 Ohms at 75 degrees Fahrenheit, so it looks like you're right on that front for sure.

The hose that goes from the S-boot to the AAR elbow has a metal sleeve that slides into the elbow. Make sure the sleeve isn't sliding too far into the elbow and blocking flow.

Ooh, good idea! That may very well be the culprit. The stock AAR elbow was glued or cast onto the metal sleeve, so I used a sleeve that I had leftover from an early Vanagon from years ago that didn't have the boot cast / glued onto it.

I'll have a look at the AAR stuff again tomorrow night; as I'm a bit tired this evening (up after midnight every night this week troubleshooting this monster). That, and I have to go get another little fuel injection hose clamp. I dropped one into the phantom zone last night and realized that my spares are a size too small. Where does that stuff go? I even ran my magnet under the intake plenum.

Really starting to run out of ideas here.

Hahhahahah, yeah me too. At this point it has to be something simple that I overlooked.

Thanks again,
Mike

[SlowLane]

The hose that goes from the S-boot to the AAR elbow has a metal sleeve that slides into the elbow. Make sure the sleeve isn't sliding too far into the elbow and blocking flow.

Ooh, good idea! That may very well be the culprit. The stock AAR elbow was glued or cast onto the metal sleeve, so I used a sleeve that I had leftover from an early Vanagon from years ago that didn't have the boot cast / glued onto it.

Here's the solution I finally settled on after having one too many AAR elbows fail on me: http://www.boostcontroller.com/index.php?category=377
The 1/2" version fits snugly on the AAR spigots. It's got 10" legs, so there's plenty left over for other short connections like AAR-to-plenum.

[mross]

Here's the solution I finally settled on after having one too many AAR elbows fail on me: http://www.boostcontroller.com/index.php?category=377

Good idea! I've been looking for a better one for a while.

I put the stock AAR elbow back on today and clamped it with a hose clamp to make sure that the metal sleeve doesn't slide too far down into it. I blew through the AAR to S-boot tube and can blow air into the plenum no problem. I then clamped the hose between the plenum and the AAR closed and tried to blow air through it and was unable to. So, it seems that there are no leaks here. I also took the steel EGR tube between the engine tin and the EGR valve off and made sure that it was still blocked (steel sheet cut to shape with no hole in it between upper EGR tube and EGR valve, but looks factory in case of inspection headaches). The EGR is blocked at the muffler end with a rectangular steel plate. The EGR tube between the exhaust and the upper EGR tube (between EGR valve and engine tin) is removed. I made the gasket between the engine tin and the upper EGR valve with no hole in it. I made new gaskets and reinstalled them with a light amount of RTV.

Also, I put some clamps on the vacuum tee that connects the brake booster and decel valve to the intake plenum, in the interest of eliminating any vacuum leaks from this source also.

Trying again, I get the same 500 RPM cold idle, but it doesn't seem to stall as often. However, that could also be due to the temperature; as it is about 90 degrees today vs. 55 - 75 degrees when i was doing the rest of the tests.

[SlowLane]

Wow, this is really getting to be a puzzle.

I do note that all of your efforts have been targeted at the FI system components. Can I safely assume that you've made sure the basic tune-up items have been taken care of? ie. valves adjusted, ignition timing, ignition dwell (if you still have points), good rotor and distributor cap, clean air filter, etc.

Exhaust leaks can also have an insidious effect. If you (very briefly!) block the exhaust pipe while the engine is running, can your hear any ffftt-ffftt-ffftt sounds?

[mross]

Can I safely assume that you've made sure the basic tune-up items have been taken care of? ie. valves adjusted, ignition timing, ignition dwell (if you still have points), good rotor and distributor cap, clean air filter, etc.

The distributor cap, rotor, plugs, and wires were new with the engine rebuild. The air filter was still clean (had about 1000 miles on it), so i reused it also. The points and condenser were reused because they only had about 200 miles on them when the engine was pulled. Dwell is at 48 degrees per my meter. The timing was set per the book at 7.5 degrees at idle with a stroboscopic timing light. I painted the little notch in the fan pulley to assist in timing it.

I'll have a look for exhaust leaks in a moment.

Edit: I ran out real quick and blocked the exhaust with the engine running. The engine stalled almost immediately, and I didn't hear anything like an exhaust leak.

Also, this engine has hydraulic lifters, and the valves are non - adjustable.