'87 TBI No Start.....HELP

[Jims86]

OK, I energized the red wire @ relay. I've got 12V @ the tan w/white stripe wire @ selector switch, but no voltage @ either fuel pump wires (tan or gray)
Figured the switch must be bad, so I check continuity between blk to gray, and tan to tan w/stripe with switch toggled to feed left pump. Then checked blk. to tan, and gray to tan w/stripe with switch toggled to feed right tank...switch seemed to check OK.

I figured the next thing to try would be to use jumper wires to replace the switch......so I jumped tan w/stripe to tan, and black to gray.......I was surprised to see no voltage @ tan wire.....jumped it to the opposite way, and had no voltage @ gray wire. Just for the hell of it, I removed the jumpers and verified that I still had 12V @ tan w/stripe wire. I found that as soon as I connected tan w/stripe to tan, voltage @ tan w/stripe was lost???

I'm a little confused by this....what am I missing/doing wrong?

Dave

wow...ummm.
there is the fuel tank selector switch, then theres a selector valve, and fuel level sender switch down below...I wonder if there is a ground problem down there.

try this link:
http://67-72chevytrucks.com/vboard/attachment.php?attachmentid=804988&d=1316879958
The terminated wire you wer telling me about, is on that diagram.

 

[hotrod1442]

Jim, I can't get that link to work?

 

[Jims86]

try dis...scroll down, and you should see the diagram in the post.
http://67-72chevytrucks.com/vboard/showthread.php?t=485168

 

[hotrod1442]

Did some more testing;
-I got a new Fuel Tank Selector Valve (so at least I'd have a known good component).....I didn't see any grounding @ the valve assembly, and it's mounting screws are formed into the plastic housing, so I don't think they have any ability to ground the unit. All wires going to the unit looked good.
-I disconnected it (old unit) to run some tests......no changes in the results.
-I plugged in the new unit and retested.....no changes in results.
-I looked a little harder and found the drivers side weatherpak connector feeding the dr. side pump & sender (still not sure I got my head around what that pink w/white & tan connector that has the tan terminated is all about.....) anyway the left pump runs.
-To further test the pumps, I applied 12V to the pumps @ the weatherpak conn. coming out of the firewall in the engine compartment......pumps started.
-I retested powering up the red wire at the fuel pump relay, and checked the fuel selector switch....again, I have 12V present @ tan w/white stripe wire until I plug in the switch, or use jumper wires to do the switching. What do you think is going on with this issue?
-I also confirmed that the Grounding Bus Bar under the dash that the
ground from the tank selector switch is ground to was good.

What is the relay or ?, that is mounted on the firewall beside the fuel pump relay, and what is it's purpose?

Any thoughts on where to go from here

Thanks, Dave

 

[89Suburban]

Excellent diagnosing guys instead of blowing money and throwing parts at it blindly.

 

[Jims86]

Did some more testing;
-I got a new Fuel Tank Selector Valve (so at least I'd have a known good component).....I didn't see any grounding @ the valve assembly, and it's mounting screws are formed into the plastic housing, so I don't think they have any ability to ground the unit. All wires going to the unit looked good.
-I disconnected it (old unit) to run some tests......no changes in the results.
-I plugged in the new unit and retested.....no changes in results.
-I looked a little harder and found the drivers side weatherpak connector feeding the dr. side pump & sender (still not sure I got my head around what that pink w/white & tan connector that has the tan terminated is all about.....) anyway the left pump runs.
-To further test the pumps, I applied 12V to the pumps @ the weatherpak conn. coming out of the firewall in the engine compartment......pumps started.
-I retested powering up the red wire at the fuel pump relay, and checked the fuel selector switch....again, I have 12V present @ tan w/white stripe wire until I plug in the switch, or use jumper wires to do the switching. What do you think is going on with this issue?
-I also confirmed that the Grounding Bus Bar under the dash that the
ground from the tank selector switch is ground to was good.

What is the relay or ?, that is mounted on the firewall beside the fuel pump relay, and what is it's purpose?

Any thoughts on where to go from here

Thanks, Dave

I think your switch may be jacked. Canthe switch be opened up? maybe clean the contacts? Or you could throw a new one on. Everything is checking out at this point.
can you snap a pic of this other relay? maybe rattle off the wire colors? May be the blower fan control.
The terminated wire I think, is there for a single tank setup....they save money by using one harness for everything, and just add the options later.
Can you keep that pump running and at least see if it will run?

 

[hotrod1442]

I was kinda thinking the switch might be bad as well.......but that is why I decided to use jumper wires to see if I would get the same affect as when the switch was in place. I jumped the connector both ways, blk.(ground) to gray, tan to tan w/white stripe.......then went tan to blk., gray to tan w/white stripe. Either way, as soon as I made the +12V side connection, current was lost?

I'll try jumping a 12V feed to one of the pumps tomorrow and see if it will start/run.

Thanks, Dave

 

[hotrod1442]

I applied 12V directly from batt. to both left/right pump feeds at the switch plug, and again both pumps would start. So I decided to apply 12V directly to the tan w/white stripe wire terminal @ the switch plug and retry pumps........both pumps worked, and I could toggle back and forth from one side to the other, as well as both senders worked properly..........YAH!!!!! Oh, and truck fired right up, toggled back and forth, from side to side, worked fine.....YES!!!!!

I figured it had to be the fuel pump relay (even though it seemed to check OK in previous testing) So I replaced the relay, but unfortunately that wasn't the cure

I'm back to wondering what function that other relay (located beside the fuel pump relay) has?
It has the following wires going to it; orange, tan w/blk. stripe, & pink w/blk. stripe.....3" from the relay, the pink w/blk. is spliced with another darker pink w/blk. wire going to a separate terminal on the relay.

Any ideas on what this relay is for, as well as what direction to go from here?

Thanks, Dave

 

[Jims86]

I applied 12V directly from batt. to both left/right pump feeds at the switch plug, and again both pumps would start. So I decided to apply 12V directly to the tan w/white stripe wire terminal @ the switch plug and retry pumps........both pumps worked, and I could toggle back and forth from one side to the other, as well as both senders worked properly..........YAH!!!!! Oh, and truck fired right up, toggled back and forth, from side to side, worked fine.....YES!!!!!

I figured it had to be the fuel pump relay (even though it seemed to check OK in previous testing) So I replaced the relay, but unfortunately that wasn't the cure

I'm back to wondering what function that other relay (located beside the fuel pump relay) has?
It has the following wires going to it; orange, tan w/blk. stripe, & pink w/blk. stripe.....3" from the relay, the pink w/blk. is spliced with another darker pink w/blk. wire going to a separate terminal on the relay.

Any ideas on what this relay is for, as well as what direction to go from here?

Thanks, Dave

Can you snap a pic of it?
will your old fuel pump relay plug into it?
The dual tank stuff is something that i have not dealt with much.

 

[hotrod1442]

I haven't got a camera handy to take a pic.......but the relay is mounted right beside the fuel pump relay, attached to the same bracket on the firewall. The two relays look identical to each other.

I seem to have misplaced the old fuel pump relay, so if it doesn't turn up, I'll get another new one to try.

 

[foamypirate]

I haven't got a camera handy to take a pic.......but the relay is mounted right beside the fuel pump relay, attached to the same bracket on the firewall. The two relays look identical to each other.

I seem to have misplaced the old fuel pump relay, so if it doesn't turn up, I'll get another new one to try.

That other relay is usually the kickdown switch relay for a TH400 equipped TBI truck, seems odd that a 1/2 ton would have it.

 

[hotrod1442]

Yes, it has a TH400 transmission. That explains what the second relay is for.

Anybody have any ideas what's going on?

Dave

 

[Jims86]

Yes, it has a TH400 transmission. That explains what the second relay is for.

Anybody have any ideas what's going on?

Dave

at this point, I am thinking of corroded connections somewhere, maybe on some plugs, wher the wire goes through the firewall, or a bad plug up top in the relay receptical.
I have experienced a lot of that in other cars lately. like when you have a dirty batt post, and you turn the key and "Snap!" all the lights on the dash go out, and no power to anything.
also got a 2 volt difference between the battery post, and the positive cable clamp while running...12.3 volts at the batt post, and 14.6 to the very tightly clamped cable terminal. Scraped it clean with a knife, and bwamo, problem solved!