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Old 12-23-2011, 06:45 PM   #1 (permalink)
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help with my POS

Hey guys, my 1987 gmc half ton is acting up. Its a 305 tbi. When i start it, 9 out of 10 times it will fire up fine but that one time it nearly drains the battery and i need another truck to boost it to make sure she starts. Today, it did that so i got a boost and it ran for about 2-3 miles then at a light to turn left, it stalled right out. So i rolled it into a parking lot and got it boosted again and put it in reverse and after about 10-15 feet it stalled out again so we just towed her home. Even when it was running, it had no guts at about 20-30 percent throttle. I would have to feather it to get it to go or just hold it at the same point and after a few seconds she would go. Don't know if this is linked or what...

In the past few months, I installed a new coil, plugs, distributor cap, rotor, fuel pump, fuel filter, sending unit, starter, battery and exhaust front to back. My old man who's a mechanic took a look at it and said there was spark. And when i turn it over I can see spurts of fuel at the injectors. I just really don't get what's going on and hoping someone here can help. As its sitting now, its in my driveway because I don't know if continuous boosting and stalling is good. Any ideas? This is my dd AND mild rig so without the girl, im kind of stuck/lost/bored lol.

Any help would be great. Thanks!

Last edited by JohnRichard; 12-23-2011 at 06:47 PM.
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Old 12-23-2011, 07:29 PM   #2 (permalink)
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Pick-up module in the dizzy is my bet.
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Old 12-23-2011, 11:01 PM   #3 (permalink)
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Alternator?
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Old 12-24-2011, 09:05 AM   #4 (permalink)
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start with even the simpler stuff: check the battery cables to make sure they are good. if your old man's a mechanic see if he can help you perform a cranking voltage drop test on the cables. make sure to move the cables around in case they have an intermittant open, and check from the center of the battery terminal to the connection at the block and to the starter. perform a test with the headlights on measuring from the block to the body to make sure all the ground connections between the body and engine block are good. stupid sh@@ like this can make you throw good money down the drain, and performing this simple check is free.
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Old 12-24-2011, 09:49 AM   #5 (permalink)
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start with even the simpler stuff: check the battery cables to make sure they are good. if your old man's a mechanic see if he can help you perform a cranking voltage drop test on the cables. make sure to move the cables around in case they have an intermittant open, and check from the center of the battery terminal to the connection at the block and to the starter. perform a test with the headlights on measuring from the block to the body to make sure all the ground connections between the body and engine block are good. stupid sh@@ like this can make you throw good money down the drain, and performing this simple check is free.
Damn, I agree with you again.

Unfortunately, what you are describing, falls under the category of troubleshooting, and it's so much easier to blindly throw parts at a problem, than it is to actually look at the symptoms, determine what might create the problem, and then systematically either rule them out, or verify them.




OP..... Look at your symptoms. Does the word intermittent come to mind?
Everything points to an electrical problem. Additional information would be valuable, both to those who are trying to assist you, and for you to understand what is happening. When you say it needs jumped, do you mean that it immediately needs a boost, or that you crank on it until you drain the battery? That little detail might be important.
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Old 12-24-2011, 09:53 AM   #6 (permalink)
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Damn, I agree with you again.

Unfortunately, what you are describing, falls under the category of troubleshooting, and it's so much easier to blindly throw parts at a problem, than it is to actually look at the symptoms, determine what might create the problem, and then systematically either rule them out, or verify them.
.
here's to ya dahoyle.... cheers
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Old 12-24-2011, 09:10 PM   #7 (permalink)
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your problem with it spuddering and you having to feather the throttle sounds like that might be a tp sensor. have your father see what they are ment to have for voltage and backprobe the conector to check voltage sounds like you might have a bad spot in the winding. but try with what they said first if you have ground problems it will throw your tp sensor readings off
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Old 12-24-2011, 09:51 PM   #8 (permalink)
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so.. here i was at work, looking at a tractor....

it had 12 volts to the starter, but wouldnt crank.

the amperage was good between battery terminals, so it had enough power to crank.

the cables were tight, so it SHOULD crank, right?

I took one cable loose (the + cable) to look at it, found that even though the cable end looked fine, the bolt was corroded almost in half. So... I decided to change the bolt to get a newer bolt in it and ensure that it would have the right clamping force on it.

I loosened the bolt, half the cable end came off in my hand.

it might look good, but that isnt a guarantee.
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Old 12-25-2011, 08:57 PM   #9 (permalink)
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How is your charging system? Did it die when you put your foot on the brakes? Sounds like low voltage.
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Old 12-26-2011, 01:32 AM   #10 (permalink)
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Make sure your altenator is grounded good. Is the battery charged? Check all ground wires in engine bay and check both cables on battery. Check the voltage while turning engine over to see if voltage drops off. Check at starter and battery. I have seen cable ohm out good until starter load is put on them. Feathering the throttle to keep it running could be from the fuel pump not getting enough voltage to keep motor running good, etc.
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Old 12-26-2011, 04:08 PM   #11 (permalink)
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Thanks for all the suggestions. I just got home today from out of town christmas stuff so first thing tomorrow I'll be working on it. I'll be checking all grounds for sure. When i did my headers I checked all the wires around the alternator and starter because the headers get hot and everything is ok. And i didn't blindly throw parts at it. Everything I did, I traced the problem and it got solved. My old man first suggested the tps because of the lack of throttle but he said the pick up module makes sense because apparetky the type I have commonly failed. Plus it also sounds reasonable he said because it will fire up fine but once she gets warm it acts up. Sometimes when its run for a while and i shut it down then restart, it doesn't want to. And a pickup module controls spark and fuel timing/mix, right? So that makes sense to me....I think...

I'll keep you guys posted. Once again, thanks for the help
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Old 12-26-2011, 04:37 PM   #12 (permalink)
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Thanks for all the suggestions. I just got home today from out of town christmas stuff so first thing tomorrow I'll be working on it. I'll be checking all grounds for sure. When i did my headers I checked all the wires around the alternator and starter because the headers get hot and everything is ok. And i didn't blindly throw parts at it. Everything I did, I traced the problem and it got solved. My old man first suggested the tps because of the lack of throttle but he said the pick up module makes sense because apparetky the type I have commonly failed. Plus it also sounds reasonable he said because it will fire up fine but once she gets warm it acts up. Sometimes when its run for a while and i shut it down then restart, it doesn't want to. And a pickup module controls spark and fuel timing/mix, right? So that makes sense to me....I think...

I'll keep you guys posted. Once again, thanks for the help
Nope, that is blindly throwing parts at it. There is nothing about your description that would point me to any particular item, other than the electrical system. Now, there is nothing wrong with swapping parts, as long as you have determined that they are BAD.

Symptoms don't determine which parts are bad, troubleshooting determines which parts are bad. There is not a simpler item in any vehicle, to troubleshoot, than a TPS. I mean, come on. There are dozens of threads which explain it perfectly well. ITS A FUCKING VOLTAGE CHECK. You do have a voltmeter, don't you???? If not, then go buy one right now.

What part of your symptoms said to replace your fuel pump? Did you put a pressure gauge on it? Yeah, thought not. More blindly replacing parts.

I'll even confess to having a set of all the sensors and such for a TBI, for troubleshooting the system. They were damn near free, and tested good. I've never had to resort to using them, but have no doubt they could be handy, if I was sitting in the woods somewhere, without the means to do it right.

On the other hand, I really doubt that I'll ever need them to troubleshoot.
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Old 12-27-2011, 10:14 AM   #13 (permalink)
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Nope, that is blindly throwing parts at it. There is nothing about your description that would point me to any particular item, other than the electrical system. Now, there is nothing wrong with swapping parts, as long as you have determined that they are BAD.

Symptoms don't determine which parts are bad, troubleshooting determines which parts are bad. There is not a simpler item in any vehicle, to troubleshoot, than a TPS. I mean, come on. There are dozens of threads which explain it perfectly well. ITS A FUCKING VOLTAGE CHECK. You do have a voltmeter, don't you???? If not, then go buy one right now.

What part of your symptoms said to replace your fuel pump? Did you put a pressure gauge on it? Yeah, thought not. More blindly replacing parts.

I'll even confess to having a set of all the sensors and such for a TBI, for troubleshooting the system. They were damn near free, and tested good. I've never had to resort to using them, but have no doubt they could be handy, if I was sitting in the woods somewhere, without the means to do it right.

On the other hand, I really doubt that I'll ever need them to troubleshoot.

The truck sat for the longest time. Just the fact it started being in the shape it was is a miracle. When i got my trucks exhaust done at a muffler and rad shop the guy who's a good friend of mine told me I needed one. The pump would barely pump the fuel. It could hardly be heard in the tank. So while he was doing my exhaust, he did my fuel pump and sending unit. I saw the tank come off and when we dropped it, the rubber lines ripped right off the metal sending unit tubes. Web I did my cap, rotor and ignition coil, I needed it. The cap showed serious wear and came with the rotor for a few extra bucks. Using my military discount at the local parts store, I picked up the 3 parts for 30 bucks. So really, no big deal to me throwing 30$ knowing for sure these parts are perfect. When i bought the truck, the battery had no cca - needed a new one. The starter solenoid was done - needed a new one.

Every part I replaced, I could justify. Almost every replacement was okayed by my father who I know would never steer me wrong or make me pay for shit I don't need. He's been a mechanic for 30 years, raced and built cars and trucks his whole life and was a GM mechanic for almost 20 yrs. What im saying is clearly I have shit to learn.

Today I'll be going at the truck with my haines manual and engine bay schematic. Checking all grounds, wires, terminals, etc. Thanks for the tips so far

Last edited by JohnRichard; 12-27-2011 at 10:19 AM. Reason: spelling
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Old 01-01-2012, 05:34 PM   #14 (permalink)
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Changed the pickup module today and got her running. Thanks for your help guys!
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