has anyone with a 89-90 truck had an issue with there single board engine controlers? my FSM shows it but I cant find it .I think its the black box under the bulkhead connection? I seem to have a no start issue going on > I have replaced the IGN. switch start/run relay but still have the issue I have tripple checked my gauges and grounds , what happens is everything goes dead on the instument cluster and the volt gauge reads dead but if i turn the key several times it will read and the truck will start . have power through the IGN. swicth and the relay and can get the truck to crank by jumping but not start un less I power up the VE solenoid , and it will start every morning first thing but when its warn nothing , also noticed that if I leave the key on for a lenght of time with out moving a thing the volt meter will all of a sudden pop up to center with out a sound one,no click, nothing and then truck will start.
its getting to me if its cold it starts or if I leave it for 15-30 min. it starts. this truck has never given me any problems till this year .

 

Oh man....electric gremlins suck!!!! As far as i know, the bulkhead connection is our black box, i have an early 91. I've been thru most of the truck and i haven't seen anything else.

 

I think the black box on the firewall ( drivers side ) is the control box for the grids on non i/c trucks. I don't know if it has anything to do with actual crank and power to the switch. I wonder if your ignition switch is tired or has a bad connection.

 

its got a new switch and a good connection

 

Have you opened the bulkhead connector? Check to make sure all the connections are good and clean with no melted connections.

Also have you replaced your starter relay? I was having starting problems a lot like yours and I finally replaced the starter relay and all is good again.

 

new srarter relay too and everything in the bulk head connection looked good. everytime I open a connection I put dielectric grease on them.too

 

I just tried disconnecting the grid heater relay, the black box under the bulk head connector. There are two connectors, I unhooked each one individually and tried starting the truck...started fine. Then disconnected both connectors..again started with no problem. So the grid heater relay should not affect your starting.

I have gotten "bad" starter relays right out of the box. Maybe try another "new" one...or grab a couple from the wreckers...they are the same as gasser units.

 

Only gas engines have sbec. If you have an auto trans, you may have a bad neutral safety switch.

 

well my fsm says it has one . and I have already replaced the NSS

 

You need to accept the fact that your truck doesn't have an sbec. If you have a fsm, it will also tell you how to install a distributor. That doesn't mean you have one, it just means the manual covers all the trucks for that particular model year.
My factory service manual has wiring diagrams. It makes simple problems like this very easy to diagnose when used properly.