1987 Fuel Selector valve help

[Iowa Fox]

I'm gonna throw one up for the experts here.

I have a 1987 V1500 GMC 305 TB fuel inj that developed fuel system issues. The fuel gage on the right tank stared reading way past full. While driving down the road I flipped the dash switch back and forth a few times to check it. When I flipped it to the right tank it quit running. I flipped it to the left tank and it started. If you flip it to the right tank it dies immediately. Been trying to troubleshoot it with the service manual. With the engine not running I can hear the selector valve make a pretty good clunk when I switch to the left tank. When I flip it to the right I can't hear anything and thats the side the truck won't run from. When I flip it back to the left I hear a nice clunk. Should I hear a nice clunk when I flip the dash switch both ways and can a bad valve keep a fuel pump from running? The trucks got about 80K on it, always garaged, and doesn't even get driven in the rain unless I get caught. I have had it since it was almost new. Any advice would be much appreciated guys.

 

[chengny]

Let me ask:

Is your select switch a momentary type (springs back to the middle position) or does it stay in place when toggled towards one tank or the other?

With TBI, I am going to guess it stays where you toggle it to.

 

[Iowa Fox]

It stays in place. Its just a simple rocker switch on the 1987 with TB and pumps in the tank.

 

[chengny]

Yeah that's what I figured. With the momentary type switch the valve stays where it was last switched to (it is actuated by a little step motor). With a TBI equipped truck (and systems earlier than 1981), the valve is shuttled by a solenoid. That is the clunk sound that you hear. The valve will default to the production tank unless the switch is in the auxiliary position (RH) and the circuit has power.

There isn't any way to diagnose this without opening something up. I guess the easiest thing to do would be to pull the switch out of the dash and exchange the leads that go to the valve actuator (i.e. the light green and dark green).

If, after switching the leads, you find that you can then run on the RH tank but not the left - the problem is in the switch.

If it still runs only on the left and not the right - you either have a broken/disconnected wire to the RH tank (light green) or the Pollak valve is shot.

 

[rich weyand]

You have two symptoms:

1) reading way past full on RH tank.

2) does not run on RH tank.

Way past full reading means the sender wire from that tank is broken (which means it is broken between the tank and the valve, since the other gauge works), or you lost the ground connection on the RH sender unit. I think this is also the ground wire for the fuel pump in the tank (you have a pump in each tank with TBI, right?).

So first thing to check to me is that you have an intact ground on the sender unit of the RH tank. A break in that connection will cause both symptoms you are seeing. I'm not sure what else could.

 

[Iowa Fox]

Any idea what usually happens to the pollak valves when they take a dump? For a small plastic part they're sure pricey. Thats why I want to be sure before I change it out, plus it looks like a heck of a job.

 

[chengny]

When the select switch is moved to the RH tank, power is supplied to the actuator and the valve to that tank opens and the valve to the LH tank closes. Since you have a TBI system the return lines also switch over.

For tank level indication, one common pink wire is lead from the dash gauge to the switching valve. Two wires come out of the valve and are lead to each tank. There is a set of contacts that move along with the valves. When the tanks are switched so does the circuit that indicates the level of the tank.

As far as what causes these valves to fail, I think usually they get hung up in mid-stroke by some little piece of debris. But since your valve seems to have failed in a static condition, I doubt that is your problem.

I would take a good look at the switch on the dash and the wiring before tearing the Pollak valve out.

 

[Iowa Fox]

Should I be able to hear the valve click when I switch the tanks on the dash with that switch? I think this particular set up was only used for one year (1987). I'm wondering if ethanol could have swelled the o rings in the selector valve since it happened after the very first time I put some in the RH tank.

 

[rich weyand]

Have you checked the ground wire connection on the RH tank?

 

[Iowa Fox]

That was the very first thing I did was to take the grond wires off the frame for both tanks and clean and reassemble them. Next I'm going to clean the ground at the buss bar just to be sure. Didn't have time to even look at it today. I also pulled the plug on the selector valve when I cleaned the grounds and its clean.

 

[chengny]

Yeah, but you were on the RH tank and then, without you changing anything, the actuator apparently shifted the valves/gauge contacts away from the full RH tank position. And now, for whatever reason it is unable to switch over to the RH tank at all.

Here is some detail on description of operation of both types of Pollak tank select valves:

Pollak Motorized Valves

Pollak fuel selector valves are 6 or 3 port valves which switch the fuel feed and return lines simultaneously. They operate by using an electric motor to drive the valves into position. Being motor driven, they have high closing pressures (65 psi) and are suitable for applications with in-tank fuel pumps. The valves are stable in either position, only drawing current for a fraction of a second while the position is transferred. They manage the switching of both the supply and return of fuel from the selected tank along with the fuel gauge switching if required.

Solenoid Valves

Solenoid valves are electromagnetic 3 port selector valves that are used to switch between two fuel lines. They are driven such that the valve selects from one port when energized and from the other port when de-energized. Typically, they are rated to a lower fuel line pressure than the motorized valves and they only come in the three port version so 2 valves are required to manage the feed and return flows.


Schematic view of the Pollak 6 port valve:

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And a picture of what must be the actuating assembly of a solenoid type:

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Problem is, I can't figure out which type you have. By all accounts, an 87 (with TBI) should have a solenoid type ( a single wire control circuit) but the schematics show a 5 wire control circuit, which would indicate a motorized actuator. Here read this thread, the subject is discussed at length:

http://www.gmsquarebody.com/forum/showthread.php?t=9052&page=2&highlight=pollak

Schematic etc from the 1987 service manual:

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[Iowa Fox]

Chengny, Thanks a million for all that information, I know you have put some serious thought into this. I've been staring at it until my eyes are going crossed. I have the 5 wire 6 port system. I think GM put them out both ways in 87. I hope their troubleshooting tree applies to both systems. In the Fuel Injected supplement for the 1987 service manual they have this wiring diagram.

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Looks like there are only the grounds at the tanks and the buss bar. The rear lamp wiring in the TB wiring diagram really has me wondering. Take a look at it and let me know what you think. I'm starting to wonder if their service information for this one year system is correct.

Thanks

 

[chengny]

Okay, it does make sense - when one realizes that with a TBI equipped vehicle the tank select system actually has 3 functions instead of just the normal two. I completely forgot that, in addition to switching tank feed/returns and level indication, the dash switch also energizes/switches the associated fuel pumps.

Since the power supply to the fuel pump must continue - even after the plumbing and level indication have been changed over - the momentary switch/motorized actuator set up used from 81-86 was not an option (apparently the same wiring harness was to be used in model year 1987).

A solenoid operated actuator operated by a rocker switch (the pre-81 design) was also not a viable option because solenoids only use an O/I type signal - they move in one direction when power is applied and only move back due to spring pressure when power is secured. The fuel pumps each needed their own power supply - that was switched on and stayed on - when it's tank was selected.

So, both pumps needed power even after the tanks were switched over. But a solenoid set-up was only on/off not left/right and a standard motorized actuator would burn up if power was left on for any considerable length of time.

In the end, it appears that Pollak developed an actuator that was specifically for the 1987 model year. It is a motorized actuator with a rocker switch that killed the power only to the motor windings (and continued to supply the pumps) after the valve had shuttled. That allowed GM to use the same wire that moved the valve to supply power to the fuel pumps.


Here read this - it explains it much better than I am:

The information I have is the 87-91 carbureted & TBI trucks used a 4
terminal dual pole dual throw rocker switch (D7089C - #15599081) and a motor
type switch-over valve (not solenoid operated) that included a fuel level sender
switching circuit and switch-over current control (#15548879). This system
was very similar to the previous carbureted trucks with the exceptions of
the rocker switch no longer is a momentary type switch and once the
switch-over valve is in commanded position, the unnecessary current flow is
ended by an switch and diode circuit within the switch-over valve itself.
The left & right fuel level circuit switching is handled internally by the
switch-over valve.

Link to the forum that info came from:

http://lists.diy-efi.org/pipermail/gmecm/2006-February/028002.html


1987 tank select diagram:

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81- 86 wiring:

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Now that we've learned all that useless information - you still can't run on your auxiliary tank. With the dash switch in the RH tank position, check for power on the gray wire that leads to the RH tank. That lead splits off from the common gray wire before it enters the Pollak valve.

So, if you have power to the pump on the gray wire - the dash switch is operating correctly. The Pollak valve has an internal problem.

But if the switch is in the RH position and the gray wire to the fuel pump is dead - the switch is bad.

 

[Iowa Fox]

Thanks chengny, With your coaching this is starting to make sense. Check my thinking- if I split the connector at the firewall I should be able to check the power on the gray and tan leads. If I have power at the respective dash mounted switch position the dash switch is OK. What is the pink wire #30? Could it be backfeeding in anyway causing problems.

Now I do not have a working fuel gage for either tank both just peg way past full.

 

[chengny]

Check my thinking- if I split the connector at the firewall I should be able to check the power on the gray and tan leads. If I have power at the respective dash mounted switch position the dash switch is OK.

Yes, in a schematic sense, that is what I meant when I said:

With the dash switch in the RH tank position, check for power on the gray wire that leads to the RH tank. That lead splits off from the common gray wire before it enters the Pollak valve.

I would have probably just left the wiring intact and poked through the insulation on the gray wire with my meter probe.

The pink wires are part of the tank level indication system - and are an entirely different circuit. The contacts - that switch to show the level in the active tank - are only mechanically interfaced within the tank switch actuator. They (the contacts) are somehow "piggy backed" on to the linkage that moves when the tank switch valves shuttle.

But, while the tank level indication circuit does not play a part in the plumbing switchover (or the fuel pump power supply switchover), they do provide a good indication of proper valve actuator operation.

Since the tank level contact set is mechanically coupled to the valve linkage, an abnormal tank level reading at the dash is a good indication that the actuator is not fully cycling.

The gas gauge is controlled by a variable resistance which is driven by the float in the tank. The sensing leg from the gauge is attached to one side of the variable resistance. The other side is lead out through the sender head and is grounded to the frame.

The greater the resistance, the higher the gas gauge reads. So, if the ground connection from the sender head is lost, the gauge pegs high. For the same reason, if the contact set cannot fully switch over, continuity from the sensing leg to ground is lost - and the gauge goes full high.