1995 Chevy G20 Van Wont Idle

[Wopper]

OK, I am new to this forum, I have just completed a head gasket replacement on my 1995 Chevrolet G20 Beauville van with a 400 SBC, Edelbrock performer manifold, JBA shorty headers.
Impco Model E Vaporiser, and a Model 300A mixer.
I had some broken and disconnected vacuum lines at front of the TBI base when I disassembled for head gasket replacement.
Seems there was a tee connection from front of TBI vacuum and the charcoal canister was disconnected.

Problem is now after assembly, the engine wouldn't start, i got it running last nite, had to purge air from the electric shutoff solenoid.

But running it seems to die if not higher rpm, it will restart and run but only high rpm.

Where do the vacuum lines go from the thermostat housing electric whatever it is??

[C3H8]

Welcome to the forum. Unfortunately I could not enlarge your pictures to see the vacuum lines. Your description would indicate a fairly simple correction though. You probably had some vacuum leaks at your throttle body gasket. The mixer mixture screw was likely set quite rich to compensate for this. Repairing the gasket or hoses has likely resulted in a pretty rich mixture since you don't have vacuum leaks anymore. You need to get the engine running again and keep it at about 2000 RPM if possible. You then need to turn your mixture screw in to lean the mixtures out. As you do this the RPM will increase and the engine will smooth out. As the RPM increases slowly take your foot off the gas and keep adjusting the engine to maintain the highest RPM. Let the RPM drop lower and lower as you do this until the engine reaches idle and keeps running.

The mixture adjustment is under the hex plug on top of the vapour fitting on top of the engine. It will have a slot in the top of the screw for a flat bladed screw driver. The plug is a 1/2" wrench. Use a light screwdriver for this and do not push down on the screw driver while adjusting. Adjust in fairly small increments as the mixtures change dramatically on this mixer with very minor turn. 1/4 to 1/2 turns make a fairly big change.

The next consideration. You have a 5920 controller on there. This controller maintains the correct mixtures once the mixture screw is reasonably close to the correct setting. It does this by applying vacuum to the top of the propane regulator through an electric control valve. The 5920 uses the O2 sensor and changes the vacuum being applied to the regulator. This may be the lines you tried to show in the picture. We need a clearer picture of the lines. The electric control solenoid will run continuously when the mixtures are correct. Its normal cycling rate is 10 times per second with the on off frequency varied to control the vacuum. Instructions with schematics for the 5920 can be found at www.dualcurve.com.

[Wopper]

Thanks for the quick reply, I switched around some of the vacuum lines, I have now got it to idle , now it has a hesitation when you try to accelerate, even when in neutral.

The van ran fine before head gasket blew.

I know it is just a matter of the Vacuum lines, as one of the tees was broken when I disassembled ( Duh, I forgot to take a photo when I took this apart….)

Can you give me a schematic of where the vacuum lines are supposed to connect??

This van also has cruise control, and the large vacuum reservoir mounted under hood.

I will send some pics later when I get a chance….its pouring rain out right now…..

[Wopper]

OK, here is a cartoon of my current vacuum hose schematic, I know the 5920 vacuum solenoid is not connected to any vacuum right now, so what line is this supposed to connect to?
Engine starts, runs and idles good right now…….

[C3H8]

Your missing a vacuum line from what I can see in the picture. You show a solenoid attached to the regulator and going to what appears to be the vent on the lid. If this is a vacuum line the solenoid is likely a 3 port solenoid and should be controlled by the 5920. The solenoid varies vacuum to the top of the secondary diaphragm controlling the mixtures. Question? Is this a three port solenoid you drew in the picture? If it is disconnect the vacuum line from the lid of the reg and the hesitation will go away. If the hesitation goes away look at the 5920 instructions I referred to previously so you can connect it properly.

If it is not a three port post a picture so I/we can figure out what it is.

[Wopper]

Ok, I do not have any hesitation with the way this is connected in the schematic. Actually seems to run perfect right now, I just know this is not the way it was originally connected because the solenoid has always made a"ticking" sound at idle and had a vacuum line to lower port.

However, the Solenoid controlled by the 5920 is NOT currently connected to any vacuum line.

The top port on the solenoid has always been open, the hose side port went to top of regulator, and lower port went to Vacuum on the TBI somewhere??, with a small one way vacuum tee ( this is where I am not sure what it was connected to ???? ) Now one way tee is at the vacuum ball and Cruise control and the Top port had the little foam filter on it, that dissolved about 10 years ago ( I have owned this vehicle for 16 years….

I did find the installation instructions for the 5920 online and printed a copy.

PS, Much thanks for your help here!!

[C3H8]

Good. The vacuum line at the bottom of the solenoid is supposed to be connected to a mixer vacuum source. It picks up vacuum just below the mixer but above the throttle plates. Any other vacuum is too strong and will cause hesitation problems. There is a vacuum opening on the bottom of the mixer marked VAC that is perfect for this. Other then that drill and tap a hole into the adaptor holding the mixer on the TB. Your correct the solenoid originally clicked all the time at a frequency of 10 htz. It varies its off and on time to control the vacuum. You can check out if you are too lean by measuring the voltage across the two terminals on the solenoid. If the voltage is zero you need to richen the mixtures by turning the adjustment screw CC. If it is 13 volts or bat voltage it is too rich and you need to lean the mixtures by turning the mixture screw clockwise. Keep in mind that your O2 sensor is now 20 years old and depending on voltage may not be functioning properly. If the mixture is set right and the O2 is operating correctly the solenoid will click continuously. Set the mixtures to a voltage range of 3 to 7 volts.

[Wopper]

Ok, here I am again….

Did some work as you suggested to connect the vacuum to the base of the mixer.

Problem, there was no vacuum there, removed the mixer from the adapter plate, the vacuum hole was plugged by the gasket.

Opened up the hole, reassembled, connected hose to the solenoid, and presto, the solenoid begins ticking as it was before.

Adjusted idle mixture with voltage as you recommended, I am getting 4-7 volts.

Now I seem to have some hesitation just off idle and running rough just off idle until about 2000 rpm.

I have not tried anything else, not sure where to go now….

[Wopper]

Updated Schematic…..

[Wopper]

Monday morning, ran perfect COLD until warmed up ~ 3-4 minutes, then started to hesitate and stumble off idle..............
Help!!

[C3H8]

OK. We're getting close, don't panic. I'm still concerned about that vac source. The vacuum we require is in inches of water column, not mercury. If your able to read the vacuum with a standard vacuum gauge it's way to high. it takes 27" water column to make 1 inch of mercury. The absolute best location is on the underside of the mixer marked VAC. It will be plugged with a screw with a flat head slot. It is 1/4 X 28 threads. You looked like you used a throttle plate opening and that may be too strong.

In the event that the vac is correct you need to look at the fitting at the regulator vent where your vac hose from the solenoid is attached. There should be a small hole on one face of the fitting. The other possibility is the vent opening in the solenoid (the port that had the filter on it). If this vent is plugged it would cause a hesitation.

You set the idle to 4-7 volts. That's good but what happens off idle. If the voltage drops to 0 and you have a hesitation it means the mixtures are very lean. It could indicate a strong vacuum, missing orifice on the regulator fitting or plugged solenoid vent. The orifice on the reg vent is supposed to be .073 or just around 3/64 inch drill.

[C3H8]

Two other items I forgot to mention.
Your diagram, you marked a component "what is this". It appears to be a heat controlled switch for the Charcoal canister that sends gas vapours to the engine to be burned. It will no allow this unless the engine has reached a specific temp.

Another cause of hesitation can be the EGR. If the EGR valve has failed or is leaking it may send vacuum to the EGR at Idle. This will cause an off idle hesitation. You can confirm a faulty vacuum switch by just disconnecting the vacuum hose at the EGR temporarily and plugging the vacuum hose. In BC this will have to be temporary as I believe you have yearly Aircare checks and if the EGR is not working there is no way to pass the air care test. If the solenoid is leaking replace it. The other possibility is the EGR valve itself. That would require replacing it if you suspect this is the problem after checking everything else in the previous post.

[Wopper]

OK;
Brand new EGR valve…..replaced cause I was tinkling I was going to block it off…but after reading more, it is not a good idea, I had already made the base into a cover….$$$ say goodbye to $80…
Next: I know the charcoal canister is connected to this, just was not sure what its function was or if it could have any impact on this issue.

I have not connected to any gauge for the vacuum, it is very weak, if I close with my finger when running at idle, it is not strong at all. I was actually thinking it was too weak…..
Could I connect with a slack tube?
I might be able to find a gauge for inches of water. How many inches of water are we looking for??

I have not driven with the solenoid connected to meter, I am wondering what this reading will be when cold….

I looked under the mixer for port marked Vac, I did not see anything marked, the tube that I used is above the throttle plates, at the base of the mixer body.
There is another adaptor plate there that the gasket closed the hole that I did open.

I will look again for the plugged port you are saying, will it be on the flat bottom base of the mixer between the adaptor plate??
I might be better to drill the lower adaptor block as you previously mentioned to clear the EGR valve.

I fuelled up today, horrible fuel economy 234 km to 90 L of Propane…. Has got to be way too rich!! - Was getting ~ 380 - 400 km to 80 L before, and it passed airfare no problem in September.

[Wopper]

I forgot to mention vent hole on regulator, I have not looked at any of this, orifice size is 0.071".

I will remove and blow out the hose and orifice elbow fitting.

Is there any way to clean out the top vent on the solenoid?? Can I blow out with compressed air??

The "ticking" seems to be a lot weaker than before on the solenoid, maybe from weaker vacuum source?

Should it have one way valve on this vacuum source?

[C3H8]

I am attaching pics of the vac port. It is the port just beside the brass clamp I can see in your picture. The other pic is of the top side showing the passage. Its the hump you see in the pic. If the pictures don't work I will post them again once I figure out photobucket.

The vacuum is about 5 to 8 inches wc at idle and 20 to 25 at WOT. You can suck water up a straw easier. The 3 port solenoid takes vacuum from under the mixer which is about the same as the vacuum inside the vapour hose and secondary area of the convertor. The solenoid pulses to control the vac pulling up on the secondary diaphragm and cause the mixtures to lean out. The solenoid on/off time is controlled by the 5920 monitoring your O2 sensor.

From your description it does sound like you might have a solenoid problem.

you should not have a one way valve in the vacuum line.

You need to drive it at normal speeds with the volt meter on. It should show the voltage controlling all the time except at WOT.