Stumped
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Senior User
Joined: Aug 2004
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From: Igo, Northern Calif
Stumped
Need some help myu son has a 1990 bll, with a 2.9. It was running just fine he changed the postive cable on the battery now it won't run.(it turns over)He and his buddy checked it out and found no spark to the plugs. they changed out the modual on the side of the distributer still no spark.I went out to check it out afer reading the manual. Their is no fire out of the coil, they changed out the coil with a spare. We get a weak spark as the key is turned to the start postion and when you let key go back to the run postion.
Any ideas as what is going on???
It has the TFI-IV ignition system.
Any ideas as what is going on???
It has the TFI-IV ignition system.
Postmaster
Joined: Dec 2001
Posts: 3,742
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From: UT
I don't know exactly how a '90 is wired in, but many of these have a "pigtail" off of the battery cable for the power supply to the engine management computer (PCM or ECM or ECA). Any chance the main computer power supply got left off?
Elder User
Joined: Dec 2007
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If it's the same setup as ours? You'll have a power box/main fuse block right behind the solenoid. It's attached to the always 'on' +12vdc from the battery at the solenoid. This appears to be a very weak point, as battery acid seems to attack this wire badly.
If the cable has the insulation in tact? Try and flex the small cable gently. If it flexes pretty easy, and looks good? It's probably okay. If the cable feels super "tight" and like the whole thing is a hard lump? The acid might have seeped into this small 4" or so cable, and rendered it to high a resistance to allow correct current flow.
It also controls the fuel pump(s) as well the computer. Might be wise to check for a blown fuse in this panel sense you're already there. If you turn the truck to 'on' or 'start'? Do you hear the pump(s) kick 'on' for about 5 seconds before shutting off? (if so? That's a fair sign it's getting power to the box)
S-
If the cable has the insulation in tact? Try and flex the small cable gently. If it flexes pretty easy, and looks good? It's probably okay. If the cable feels super "tight" and like the whole thing is a hard lump? The acid might have seeped into this small 4" or so cable, and rendered it to high a resistance to allow correct current flow.
It also controls the fuel pump(s) as well the computer. Might be wise to check for a blown fuse in this panel sense you're already there. If you turn the truck to 'on' or 'start'? Do you hear the pump(s) kick 'on' for about 5 seconds before shutting off? (if so? That's a fair sign it's getting power to the box)
S-
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Senior User
Joined: Aug 2004
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From: Igo, Northern Calif
Tedybear thats is why iam stumped. Their is power to everything. The power cable to the main fuse box is a little worn but ever fuse has power to it. The relays are working also.
Elder User
Joined: Dec 2007
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This is an oddball one then. Changed the coil, and now have weak spark--good lord I need my diagrams. LOL. Fuel pumps working ok? Pull a plug and see if it is 'wet' with fuel after trying to start it?
Seems a classic no-spark problem...where does the coil get it's power from..and is it getting it? If the coil appears to be 'firing' at the right times--but extremely weak? I'd guess the pickup in the disty and module should be ok.
I'll have to ponder this one for a while (and see if I can find that damn shop manual LOL) How are the grounds to the battery? Even a weak ground can bugger up the works. Heck, I'd be willing to suggest even throwing on the old battery cable and seeing if that works. (true issue with ours--new cable from Advance, installed...dead as a dodo...installed the old cable? Fired right up. Cable only had a few strands attaching it to the actual battery terminal. One good 'pull'? And it fell apart in my hands)
S-
Seems a classic no-spark problem...where does the coil get it's power from..and is it getting it? If the coil appears to be 'firing' at the right times--but extremely weak? I'd guess the pickup in the disty and module should be ok.
I'll have to ponder this one for a while (and see if I can find that damn shop manual LOL) How are the grounds to the battery? Even a weak ground can bugger up the works. Heck, I'd be willing to suggest even throwing on the old battery cable and seeing if that works. (true issue with ours--new cable from Advance, installed...dead as a dodo...installed the old cable? Fired right up. Cable only had a few strands attaching it to the actual battery terminal. One good 'pull'? And it fell apart in my hands)
S-
Thread Starter
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Senior User
Joined: Aug 2004
Posts: 297
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From: Igo, Northern Calif
This is an oddball one then. Changed the coil, and now have weak spark--good lord I need my diagrams. LOL. Fuel pumps working ok? Pull a plug and see if it is 'wet' with fuel after trying to start it?
Seems a classic no-spark problem...where does the coil get it's power from..and is it getting it? If the coil appears to be 'firing' at the right times--but extremely weak? I'd guess the pickup in the disty and module should be ok.
I'll have to ponder this one for a while (and see if I can find that damn shop manual LOL) How are the grounds to the battery? Even a weak ground can bugger up the works. Heck, I'd be willing to suggest even throwing on the old battery cable and seeing if that works. (true issue with ours--new cable from Advance, installed...dead as a dodo...installed the old cable? Fired right up. Cable only had a few strands attaching it to the actual battery terminal. One good 'pull'? And it fell apart in my hands)
S-
Seems a classic no-spark problem...where does the coil get it's power from..and is it getting it? If the coil appears to be 'firing' at the right times--but extremely weak? I'd guess the pickup in the disty and module should be ok.
I'll have to ponder this one for a while (and see if I can find that damn shop manual LOL) How are the grounds to the battery? Even a weak ground can bugger up the works. Heck, I'd be willing to suggest even throwing on the old battery cable and seeing if that works. (true issue with ours--new cable from Advance, installed...dead as a dodo...installed the old cable? Fired right up. Cable only had a few strands attaching it to the actual battery terminal. One good 'pull'? And it fell apart in my hands)
S-
Keep the ideas coming,two heads are better than one.
Thanks again. Jim
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Lead Driver
Joined: Aug 2006
Posts: 5,670
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From: Sand Lake, MI
Sounds like a bad connection at the coil to me, the connector on this type coil tend to loose connection all the time.
Sounds like changing the coil got it a little better connection but still not good enough.
What I do is strip off about 2 inches of the casing off a length of 14g wire and with the connector off the coil stick the bare end of that wire all the way into the positive side on the connector. Then plug the connector back into the coil, then clip off the excess wire hanging out. Now it has a solid connection with that piece of bare wire biting into the female end of the connector and prong on the coil.
You can run the wire over to the positive post on the battery before sniping off the excess and see if it starts, if it starts disconnect the wire from the battery end and try it again. A quick test will show you exactly what's going on there.
Sounds like changing the coil got it a little better connection but still not good enough.
What I do is strip off about 2 inches of the casing off a length of 14g wire and with the connector off the coil stick the bare end of that wire all the way into the positive side on the connector. Then plug the connector back into the coil, then clip off the excess wire hanging out. Now it has a solid connection with that piece of bare wire biting into the female end of the connector and prong on the coil.
You can run the wire over to the positive post on the battery before sniping off the excess and see if it starts, if it starts disconnect the wire from the battery end and try it again. A quick test will show you exactly what's going on there.
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Post Fiend
Joined: Jun 2002
Posts: 13,873
Likes: 3
From: Atlanta GA
When they changed the cables did they happen to put the (+) battery/starter cable on the wrong terminals on the relay?
> Their is no fire out of the coil
Check the two little red wires (I/S) with the elbows, squish them up a bit and make sure they make good contact with the threaded rods. Make sure they are on the correct terminals.
Leave the key in the ON position and try using a remote to start the truck.
> Their is no fire out of the coil
Check the two little red wires (I/S) with the elbows, squish them up a bit and make sure they make good contact with the threaded rods. Make sure they are on the correct terminals.
Leave the key in the ON position and try using a remote to start the truck.
Senior User
Joined: Feb 2003
Posts: 161
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From: Pullman,WA
I had this happen on my 86 BII a while back, there is a "brain" located inside the passenger side kick panel down by your right foot( sit in the passenger seat and tap your foot to the right side), pull that panel off and have that tested, new one is about 115$...took me a week of hair pulling and new parts to figure it out..lol..
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