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'79 CA FI idles at 900rpm drops to 700 every 10 seconds w/hiss
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thebayfromak
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PostPosted: Mon Jun 18, 2018 10:39 pm    Post subject: '79 CA FI idles at 900rpm drops to 700 every 10 seconds w/hiss Reply with quote

Hello All!

I have a '74 Bus with a '79 CA FI system on it. I just installed the FI system on it recently and are having some running problems. I replaced all the rubber bits.

I got the AFM with the air adj. screw all of out whack along with the idle screw. Basically they are so far screwed in/out that I had to slightly adjust the air screw meticulously until I could start it.

Here's the symptoms:

-Cranks for a long period of time before it'll start, but once started idles at normal speed
-If I step on the gas while idling, upon taking my foot off, RPMs will drop below idle speed and engine will die
-Will idle at ~900RPM but drop down to ~700s every 10 seconds for a few seconds (Video 1)
-Eventually these dips in the idle (at the lowest RPM point closer to 400-600) would create a slight 'hiss' and the engine would want to stall out. Almost looked like something 'caught' but still popped back up to ~800 rpm (Video 2)
-I removed the heater booster fan and tubes and I noticed (with the engine warmed up, while idling) hot air coming out of the passenger tube from the exchanger and cool/ambient temp heat coming out of the driver exchanger. Both flappers were closed.
-Sounds like a constant hiss during running, not quite like a vacuum leak. I think it may potentially be the CSV constantly spraying. I unplugged it and the Bus wouldn't start.
-Adjusting the dizzy for timing one way will cause a positive vacuum and blow off the hose to the plenum from the brake booster, rotating the other direction will cause loud backfire. I can't really do much with the timing but it doesn't make much difference when I have at this point.

Video 1:

Link


Video 2:

Link


I'm still learning about FI and have combed through the AFC manual and Bentley to learning and understand better so please bear with me with all of this.

Thanks for the help and any info is greatly appreciated!

Joe


Last edited by thebayfromak on Tue Jun 19, 2018 4:30 am; edited 2 times in total
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timvw7476
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PostPosted: Tue Jun 19, 2018 12:46 am    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

Your distributor seems to have the vacuum retard can on it,
the spigot facing the distributor cap, that was used up to '74 for
emissions purpose, idle speed, timing set to 7.5 degrees After Top dead center.
Most fuel injection buses run a distributor with vacuum advance, no retard
function, that spigot should be facing away from the distributor body, can't
see it in your running vid but I'm sure it's there, you want that one hooked up
to your intake vacuum port on the engine. The buses with fuel injection
also run 7.5 degrees BEFORE Top Dead Center, not AFTER, Big Difference.
I have no idea if the CA. '79 emissions bus runs that '74 dual vacuum can
distributor, never owned a FI '79 CA special, but pretty sure it didn't.
The good news is you can just disconnect the retard spigot, hook up to
advance only spigot on the current distributor & time it, 7.5 Before TDC
at idle, look for 28 degrees Before TDC at 3,000 rpm, vacuum advance hose
disconnected from distributor & plugged. Reattach advance hose & test drive.
Plus once you've done this, you will be turning your idle screw again, 850rpm.
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thebayfromak
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PostPosted: Tue Jun 19, 2018 4:28 am    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

timvw7476 wrote:
Your distributor seems to have the vacuum retard can on it, .


So you're right but it's the DVDA dustributor that came stock with the '79 CA Buses with the electronic ignition system!

At this point I can time it to 7.5deg BTDC but everything else is too rough for me to try and time at 3000 rpm.
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Wildthings
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PostPosted: Tue Jun 19, 2018 4:32 am    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

Why does it appear that your timing light isn't flashing consistently?

I agree that you do not want the retard side of your vacuum can hooked up, and to time your engine to 28° BTDC @3500+ rpms with the hose(s) removed and plugged.
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thebayfromak
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PostPosted: Tue Jun 19, 2018 8:11 am    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

Wildthings wrote:
Why does it appear that your timing light isn't flashing consistently?

I agree that you do not want the retard side of your vacuum can hooked up, and to time your engine to 28° BTDC @3500+ rpms with the hose(s) removed and plugged.


I didn't notice that... I'm going to look at the other videos I took that day and see if it's persistent.

I understand what you're saying in how to time it but any thoughts on the other things I mentioned? Even if I try and accelerate to time it, it'll just die when I let of anyways. Amongst having trouble even starting, I feel like there's more going on than just the timing.
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PostPosted: Tue Jun 19, 2018 9:14 am    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

first you start with checking all the plugs for proper gap and wires to be sure there is no carbon tracking or breaks in the wire. To do this open the door at night in the dark, keeping hands/hair loose clothes away from belt & pulley, to look for halo's and sparking of the wires. Also look inside the cap for cracks or carbon tracks. The pifffst then slow then piffffst slow is either a wire cross tracking so that that engine is misfiring between wires, or it is a valve seat leaking that is causing a misfire. It can also be loose carbon in the engine. Make sure you run some water or GM upper cylinder cleaner thru it to reduce loose carbon particles. If you have a catalytic converter try running the bus with it off. Extreme back pressure will sound like that sometimes.
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PostPosted: Tue Jun 19, 2018 9:30 am    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

Yup- Make sure the ignition system is 100% first- only THEN move onto the fuel system, otherwise you are just chasing your tail.

These bus distributors always did seem to be prone to breaker plate wobble so be sure to check that out.
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PostPosted: Tue Jun 19, 2018 10:34 am    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

Is the plug firmly attached to the AFM? The engine may idle without the plug installed, but it will not rev.
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thebayfromak
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PostPosted: Tue Jun 19, 2018 2:27 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

SGKent wrote:
first you start with checking all the plugs for proper gap and wires to be sure there is no carbon tracking or breaks in the wire. To do this open the door at night in the dark, keeping hands/hair loose clothes away from belt & pulley, to look for halo's and sparking of the wires.


Being that my motor is a '74 with a '79 CA FI system, which should my plugs be gapped to? '74 or '79 CA Specs? That's all very helpful! Though living in Alaska with near 24 hour daylight doesn't help but I'll figure it out. Laughing

SGKent wrote:
The pifffst then slow then piffffst slow is either a wire cross tracking so that that engine is misfiring between wires, or it is a valve seat leaking that is causing a misfire.


By wire cross do you mean spark plug wires crossing which could send mixed signals to the plugs?

------

Also the one thing I'm still perplexed about is why would my right/passenger heat tube from the exchanger be hot, almost too hot to touch (this being inside the engine compartment, after removing the blower fan and tubes) yet the left/driver side be room/ambient temp? This is while the motor is warmed up. Could cylinders 3/4 not be producing hot exhaust which in turn wouldn't heat the air going through the exchangers? I just can't wrap my head around a reason that wouldn't involve the engine not producing hot exhaust gasses. Any input would be great!


Last edited by thebayfromak on Tue Jun 19, 2018 2:33 pm; edited 1 time in total
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PostPosted: Tue Jun 19, 2018 2:29 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

Wildthings wrote:
Is the plug firmly attached to the AFM? The engine may idle without the plug installed, but it will not rev.


Plug is firmly attached! I can rev it but not very much, maybe around 1200-1600 RPM before the engine starts wobbling quite a bit. I presume timing here...though it's at 7.5 deg. BTDC at idle, currently.
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PostPosted: Tue Jun 19, 2018 2:52 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

do you have a 1979 California ignition system with both a CA distributor and CA coil?
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PostPosted: Tue Jun 19, 2018 3:04 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

SGKent wrote:
do you have a 1979 California ignition system with both a CA distributor and CA coil?


Yes I do. It's all installed.
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PostPosted: Tue Jun 19, 2018 3:10 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

use the California 1979 gaps then.

Were two wires run side by side, and the insulation is weak or old they can induce a signal between each other, causing a spark on both wires. The pifffst sound you here is a small backfire. That can be cause by worn wires, a valve seat leaking causing hot gases from another cylinder to ignite fuel and air, or by a backed up catalytic converter.

One test that might help you is to gently remove one wire at a time on the distributor cap and see if the RPM falls or not. That may reveal which cylinder is causing the problem, and if more than one cylinder is involved.
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PostPosted: Tue Jun 19, 2018 10:14 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

Check the order of your spark plug wires one more time.
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telford dorr
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PostPosted: Tue Jun 19, 2018 11:09 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

On solid state ignition systems like on the '79, it's better to ground a plug wire than to disconnect it. Keeps the coil output voltage in check, protecting the coil driver transistor. Slide the distributor cap plug wire boots back so you can slide a grounding wire down the side of the plug wire to kill a cylinder..
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thebayfromak
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PostPosted: Thu Jun 21, 2018 6:36 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

SGKent wrote:
use the California 1979 gaps then.

Were two wires run side by side, and the insulation is weak or old they can induce a signal between each other, causing a spark on both wires. The pifffst sound you here is a small backfire. That can be cause by worn wires, a valve seat leaking causing hot gases from another cylinder to ignite fuel and air, or by a backed up catalytic converter.

One test that might help you is to gently remove one wire at a time on the distributor cap and see if the RPM falls or not. That may reveal which cylinder is causing the problem, and if more than one cylinder is involved.


Checked plugs, changed wires. The vehicle runs fine while the pedal is pressed but is struggling to idle or will fluctuate idle as in the earlier video. Any thoughts?
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PostPosted: Thu Jun 21, 2018 9:55 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

Replace your TSII (temperature sensor two)
Testing is not always full proof. If yours turns out to be good, throw it in the glove box for a spare.

1979 Calif. DVDA
Image may have been reduced in size. Click image to view fullscreen.



Fuel Injection Vacuum Hoses
Thnx to mayor and ratwell
http://www.ratwell.com/technical/VacuumHoses.html

Image may have been reduced in size. Click image to view fullscreen.



Lifters Hydraulic or Solid ?

Tune up


Timing

-Cranks for a long period of time before it'll start, but once started idles at normal speed.
1. Test CSV
2. Injectors leaking flooding engine.
3. Fuel pressure to low
-If I step on the gas while idling, upon taking my foot off, RPMs will drop below idle speed and engine will die .
1. Vacuum hoses on wrong
2. Vacuum leak
-Will idle at ~900RPM but drop down to ~700s every 10 seconds for a few seconds (Video 1).
1. Vacuum leak
2. Stickey valve
-I removed the heater booster fan and tubes and I noticed (with the engine warmed up, while idling) hot air coming out of the passenger tube from the exchanger and cool/ambient temp heat coming out of the driver exchanger. Both flappers were closed.
1. Cylinder 1-2 need valve adjustment
2. Plugs fouling
3. Intake leak
-Adjusting the dizzy for timing one way will cause a positive vacuum and blow off the hose to the plenum from the brake booster, rotating the other direction will cause loud backfire.
1. Valve adjustment

Vacuum gauge


Finding vacuum leaks with smoke (smoke test, tester)

Fuel Injection Fuel Pressure Testing
Fuel Injection Leak Down Test

Good luck
Tcash
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Wildthings
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PostPosted: Thu Jun 21, 2018 10:06 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

All the bay owner's manuals show a .028" spark plug gap, while other sources show a .024" (the Bentley gives both). You are probably fine with a .032" or even a .035 gap especially if you are running some form of pointless ignition.
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PostPosted: Fri Jun 22, 2018 7:03 am    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

use a smoke generator to look for vacuum leaks if you haven't already. Block the brake booster next test unless you have already tested it for leaks.
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thebayfromak
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PostPosted: Mon Jul 16, 2018 8:24 pm    Post subject: Re: '79 CA FI Running Problems - Please advise! Reply with quote

Tcash wrote:
Replace your TSII (temperature sensor two)
Testing is not always full proof. If yours turns out to be good, throw it in the glove box for a spare.

1979 Calif. DVDA
Image may have been reduced in size. Click image to view fullscreen.



Fuel Injection Vacuum Hoses
Thnx to mayor and ratwell
http://www.ratwell.com/technical/VacuumHoses.html

Image may have been reduced in size. Click image to view fullscreen.



Lifters Hydraulic or Solid ?

Tune up


Timing

-Cranks for a long period of time before it'll start, but once started idles at normal speed.
1. Test CSV
2. Injectors leaking flooding engine.
3. Fuel pressure to low
-If I step on the gas while idling, upon taking my foot off, RPMs will drop below idle speed and engine will die .
1. Vacuum hoses on wrong
2. Vacuum leak
-Will idle at ~900RPM but drop down to ~700s every 10 seconds for a few seconds (Video 1).
1. Vacuum leak
2. Stickey valve
-I removed the heater booster fan and tubes and I noticed (with the engine warmed up, while idling) hot air coming out of the passenger tube from the exchanger and cool/ambient temp heat coming out of the driver exchanger. Both flappers were closed.
1. Cylinder 1-2 need valve adjustment
2. Plugs fouling
3. Intake leak
-Adjusting the dizzy for timing one way will cause a positive vacuum and blow off the hose to the plenum from the brake booster, rotating the other direction will cause loud backfire.
1. Valve adjustment

Vacuum gauge


Finding vacuum leaks with smoke (smoke test, tester)

Fuel Injection Fuel Pressure Testing
Fuel Injection Leak Down Test

Good luck
Tcash


TCash,

Thanks for all the info and the chart! Here's a late reply with an update.
Found and fixed a vacuum leak at the 3 way elbow at the brake booster. Replaced the spark plug wires, gapped the plugs.

Everything else has been fixed or is running well except the RPM fluctuations. It starts fine but I'm getting an idle of around 1000rpm and every 5 or so seconds it will dip to about 600 and sounds like it is choking out or about to die, then kicks right back up to 1000rpm. When I shutoff the vehicle after this happens, mild smoke comes out of the engine fan. (This didn't happen after stopping while driving short distances).

I'm hoping to find a mechanical explanation for the issue if possible to better understand whats going on. Thanks!

Joe
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