Author Topic: 1987 1/2 ton pickup electrical problem  (Read 14151 times)

Offline jailbreak74

  • Newbie
  • Posts: 4
1987 1/2 ton pickup electrical problem
« on: September 11, 2006, 06:28:00 PM »
hey guys, how are ya?
i'm brand new here so if i'm not following suit somehow, let me know ok...
anyway , i have a driveway full of gm trucks, and i've been workin on em for years. sometimes you need an outside prespective to solve a problem, so here i am. i'm working on my brother in laws 1987 1/2 ton 4x4 pickup with the  305 tbi. here's  where i started, from what he told me he started the truck up the other day and it ran fine, then it just quit all of a sudden. he then continued to try to start it up , and it turns over fine but will not fire...i did all the usual simple tests first and it has spark, but didnt seem to be getting fuel. i have encountered this many times before on my chevy's, a couple times on my 89 jimmy and a couple times on my 84 pickup with no ecm. on the 84 the module would kill the spark, and on the 89 i would still get spark, but no fuel to the injector, so that is what i went by with his 87. well, to try to shorten a long story, after i changed the control module i turned it over , it fired for about 3 seconds, and then quit. i sprayed a little gas into the tbi turned it over it fired again and quit just as fast...no fuel..so now i get the rest of the story from my brother in law. the day he started it and it quit, he told me it quit when he turned the head lights on!!! so now i went on a different mission. checked both sides of the obvious fusable links, then went into the fuse block. i'm getting power to the windshield wipers, directionals, hazards, blower fan, ecm, crank, and a couple others i cant think of right now, but no power to the headlights, dashlights, brake lights, radio, and the fuel pump isnt turning on, but i cant find the fuse for it in the block....i'm now stumped, i'll bet it's something simple i'm overlooking (hopefully anyway right???) one more thing that has me wondering is, this truck has duel fuel tanks, but he hasn't touched the left hand tank in years, nor the switch. it is always on rh and he only uses the right hand tank. i think it has something to do with electrical because of the whole no power to the lights deal....any opinions ? anyone have this problem or a (reasonable facsimili thereof)??? i stole that line from the 3 stooges.....thanks for reading and your help will be greatly appreciated. sincerely JB


Offline Lt.Del

  • Andy aka:SgtDel
  • Senior Member
  • ****
  • Posts: 3864
  • DelbridgePhotography.com
    • www.delbridge.net
Re: 1987 1/2 ton pickup electrical problem
« Reply #1 on: September 11, 2006, 11:10:00 PM »
I remember somewhere that I read that the electric fuel pump will stop working under certain conditions to keep fuel from pumping (ie: a wreck, engine turns off, etc..).  I do not know if there are sensors or switches (probably both) that will kill the electric to the pump under these certain conditions.

Now the question would be, what are these conditions and what controls the circuit?  Seems youv'e checked the obvious and know what you are doing...you are probably close to solving the mystery.



 

SgtDel
aka "Andy"

www.delbridge.net

1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4


Offline VileZambonie

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 17383
Re: 1987 1/2 ton pickup electrical problem
« Reply #2 on: September 12, 2006, 02:48:00 PM »
Probe the grey wire at the RH fuel tank with a test light to ground. It should illuminate the test lamp for 2 seconds and then go out when the key is turned to run. It should illuminate the test lamp while cranking the engine also.

Post your results from this test.

,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

Offline jailbreak74

  • Newbie
  • Posts: 4
Re: 1987 1/2 ton pickup electrical problem
« Reply #3 on: September 12, 2006, 04:47:00 PM »
thanks for the ideas guys,nothing to the grey wire at all, and no power at all to the fuel pump relay on the firewall. i'm really racking my brain now...i'm definitly leaning towards the electrical side now, i'm getting no power to certain components in the fuse box. i have no power what so ever to ecm b, no horn , no headlights or tail lights. the ign in this panel isn't fused, it just has a single lead coming out of it, no power to that either by the way. i have power to ecm 1. i cant even try to pull a code out because there is no power to the test block. when the key is on the engine light doesn't come on at all, so there must not be any power to the ecm. it's strange as @#%$, the thing will turn over all day long, and it'll fire if you spray a little fuel into the tbi for a second or 2...there's got to be a short somewhere, that's why i've been looking for a good wiring diagram. i found 4 fusable links, and i'm getting power to both sides of all 4, 2 down near the starter, 1 behind the alternator, and 1 coming off the junction block on the drivers side firewall..am i missing any that you know of? thanks again guys....JB


Offline Z28 c10

  • Registered Users
  • *
  • Posts: 174
Re: 1987 1/2 ton pickup electrical problem
« Reply #4 on: September 12, 2006, 09:26:00 PM »
Check this out.

Photobucket - Video and Image Hosting" />


just an idea. My main power comes from the alt., and branches out from here from what I remember,

 JayTater

 Z28 C10

Edited by: Z28 c10 at: 9/12/06 8:28 pm

Offline VileZambonie

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 17383
Check
« Reply #5 on: September 13, 2006, 04:30:00 PM »
Well you found your problem already. If you say you have no B+ @ the fuel pump relay then you have either an open fusible link or blew ecm B fuse. Circuit 440 (orange) cavity A @ the fuel pump relay should be hot at all times. Check for B+ at the fuse and if no B+ and you are sure your fusible links are all good then you have an open between the back of the fuse panel and the fusible link.

,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

arlbrl

  • Guest
Same Issues
« Reply #6 on: September 14, 2006, 08:15:00 PM »
I have the same problems only difference is that I swapped an engine, tranny and complete wiring harness out of a 1990 Suburban into my 85 C-10.  Out of no where I lost power to all the same.  The truck cranks over but will not start.  Does any one have a wiring diagram for a 1990 Suburban showing the location of the fuseable links?  Any suggestions are greatful!!!!!