New fuel pump, but still intermittent start? No prime

circuitslave · 09-14-2008, 03:35 PM

Hi, well I changed the pump yesterday---this truck's got some power now !

It's an S10 2.8L V6 TBI. (here's the original thread: http://www.s10forum.com/forum/f135/p...g-else-336484/)
Anyway, once the truck was all back together, it started right up. Then a while later it just cranked. This happened all throughout the day.

Well, I wiggled all the wiress around the fuse box and then it started right up. I also think it might be electrical because when it wasn't starting, just cranking, the SERVICE ENGINE SOON light wasn't coming on when starting ignition. Just the check guages and battery light would come on the dash.

So the question is, can someone tell me the best way to figure out how to troubleshoot? I've got a multimeter, but not sure which relay lines to test for.
I know that the relay isn't being energized when it doesn't want to start.

Remember, I now have:

New pump
new control module for ignition
new cap and rotor and wires and plugs
new relay

I don't have any manual /wiring schematics

thanks !

SY2932 · 09-14-2008, 10:58 PM

Check the ECMB fuse to see if it's blown first.

circuitslave · 09-15-2008, 07:33 PM

Quote: Originally Posted by SY2932

Check the ECMB fuse to see if it's blown first.

Fuse is good. I'm going to check the the power to relay and signal from ECM.

If someone can just tell me why or what causes the signal to the injectors? I just found it curious as to why when I applied 12V to the pump test lead and at the same time started the engine it wouldn't run? What's the sequence? of what starts what? I mean I bypassed the relay so why didn't it start if the pump was running?

circuitslave · 09-15-2008, 07:46 PM

ALSO, if the dark green white wire to relay is what causes the relay to energize and click, why is it then that when I wiggled around the fuse box area, the truck started? Because that orange circuit is always hot, but isn't the actual circuit that energizes the relay. If that was the case, then the relay would be "clicking" energizing with a no-start situation. And this IS NOT what's happening.

Every time it's not starting, I know for a fact, that the relay is not energizing and clicking.

circuitslave · 09-15-2008, 08:05 PM

Okay, so I pulled out the ECM B fuse just to see what would happen and the relay doesn't click? Why is that? I thought they were two different circuits? Wouldn't it click and not start?

DarkKnite2009 · 09-15-2008, 10:12 PM

sounds like you got a wiring nightmare on your hands from what your explaining it sounds like you got your self some gremlins. I would just re do the harness and be done with it dude I was reading your old thread when you first posted and honestly I would said screw it a while back. and if your not sure what I mean by gremlins its an intermitant problem that is being a bitch to figure out.

circuitslave · 09-15-2008, 11:39 PM

Quote: Originally Posted by DarkKnite2009

sounds like you got a wiring nightmare on your hands from what your explaining it sounds like you got your self some gremlins. I would just re do the harness and be done with it dude I was reading your old thread when you first posted and honestly I would said screw it a while back. and if your not sure what I mean by gremlins its an intermitant problem that is being a bitch to figure out.

That is some very good advice, Darkknite2009. I think I'm going to look into that. Thanks

I will say this, though--this truck runs like a V6 truck! ( what I mean is I bought it and never knew it could drive so good. It was slugish with no power at all--I thought it was like this because it was old. After I replaced the pump, Bam ! I'm acclerating down the road like I should.

Jadesmarine · 09-15-2008, 11:43 PM

have u checked the ground (gnd for the tail light + fuel pump)

circuitslave · 09-16-2008, 05:03 AM

Quote: Originally Posted by Jadesmarine

have u checked the ground (gnd for the tail light + fuel pump)

Yeah. Grounds for those are good. I think I need to check the ECM and see and make sure those wires are good.

Jsim4 · 09-16-2008, 08:58 AM

i had a very similar problem on my truck, only difference was i wiggled the wiring harness in the engine bay and could hear the pump turn on and off. It turned out to be a loose ground on the back of the drivers side cylinder head.

lt1s10onair · 09-16-2008, 09:08 AM

ignition switch?

circuitslave · 09-16-2008, 12:02 PM

Quote: Originally Posted by Jsim4

i had a very similar problem on my truck, only difference was i wiggled the wiring harness in the engine bay and could hear the pump turn on and off. It turned out to be a loose ground on the back of the drivers side cylinder head.

hmm? Well, nothing in the engine area, but twice when I wiggled the wires around the fuse box is when it started.

Also, as I mentioned, when I tried to start the engine, with a helper applying 12 v to the pump test lead, the pump ran, but the truck still wouldn't start. So , I doubt it's only the pump issue.

Nobody has still been able to answer my question though:

If the fuse box area has the orange 440 circuit. If the fuse was blown or I pulled it, wouldn't THIS STILL ALLOW THE RELAY TO CLICK ENERGIZE? Because from what I've read, the relay gets it's power on a different circuit.

circuitslave · 09-16-2008, 12:03 PM

Quote: Originally Posted by lt1s10onair

ignition switch?

Not sure. Maybe I'll look into that as well, thanks.

Jsim4 · 09-16-2008, 07:12 PM

Have you tested the relay?

circuitslave · 09-19-2008, 05:01 PM

Quote: Originally Posted by Jsim4

Have you tested the relay?

The relay is new---and I still have the old one which works---my guess is that it's a wiring issue--the ECM is not giving signal, IMO. Truck has been starting fine---as it always has, with this ongoing issue. The thing is, the engine harness is no longer available.

I'm going to do some checking on wiring this weekend. Thanks for the advice, though.

09-14-2008, 03:35 PM	#1
circuitslave Registered User Join Date: Dec 2007 Posts: 69 Location: User is: OffLine	New fuel pump, but still intermittent start? No prime Hi, well I changed the pump yesterday---this truck's got some power now ! It's an S10 2.8L V6 TBI. (here's the original thread: http://www.s10forum.com/forum/f135/p...g-else-336484/) Anyway, once the truck was all back together, it started right up. Then a while later it just cranked. This happened all throughout the day. Well, I wiggled all the wiress around the fuse box and then it started right up. I also think it might be electrical because when it wasn't starting, just cranking, the SERVICE ENGINE SOON light wasn't coming on when starting ignition. Just the check guages and battery light would come on the dash. So the question is, can someone tell me the best way to figure out how to troubleshoot? I've got a multimeter, but not sure which relay lines to test for. I know that the relay isn't being energized when it doesn't want to start. Remember, I now have: New pump new control module for ignition new cap and rotor and wires and plugs new relay I don't have any manual /wiring schematics thanks !
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09-14-2008, 10:58 PM	#2
SY2932 life begins @ 20 psi Age: 36 Join Date: Dec 2001 Posts: 669 Location: Groom Lake User is: OffLine	Re: New fuel pump, but still intermittent start? No prime Check the ECMB fuse to see if it's blown first.
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09-15-2008, 07:33 PM	#3
circuitslave Registered User Join Date: Dec 2007 Posts: 69 Location: User is: OffLine	Re: New fuel pump, but still intermittent start? No prime Quote: Originally Posted by SY2932 Check the ECMB fuse to see if it's blown first. Fuse is good. I'm going to check the the power to relay and signal from ECM. If someone can just tell me why or what causes the signal to the injectors? I just found it curious as to why when I applied 12V to the pump test lead and at the same time started the engine it wouldn't run? What's the sequence? of what starts what? I mean I bypassed the relay so why didn't it start if the pump was running?
	[Reply w/Quote]

09-15-2008, 07:46 PM	#4
circuitslave Registered User Join Date: Dec 2007 Posts: 69 Location: User is: OffLine	Re: New fuel pump, but still intermittent start? No prime ALSO, if the dark green white wire to relay is what causes the relay to energize and click, why is it then that when I wiggled around the fuse box area, the truck started? Because that orange circuit is always hot, but isn't the actual circuit that energizes the relay. If that was the case, then the relay would be "clicking" energizing with a no-start situation. And this IS NOT what's happening. Every time it's not starting, I know for a fact, that the relay is not energizing and clicking.
	[Reply w/Quote]

09-15-2008, 08:05 PM	#5
circuitslave Registered User Join Date: Dec 2007 Posts: 69 Location: User is: OffLine	Re: New fuel pump, but still intermittent start? No prime Okay, so I pulled out the ECM B fuse just to see what would happen and the relay doesn't click? Why is that? I thought they were two different circuits? Wouldn't it click and not start?
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09-15-2008, 10:12 PM	#6
DarkKnite2009 Registered User Age: 21 Join Date: Sep 2008 Posts: 73 Location: Clearwater, Fl User is: OffLine	Re: New fuel pump, but still intermittent start? No prime sounds like you got a wiring nightmare on your hands from what your explaining it sounds like you got your self some gremlins. I would just re do the harness and be done with it dude I was reading your old thread when you first posted and honestly I would said screw it a while back. and if your not sure what I mean by gremlins its an intermitant problem that is being a bitch to figure out.
	[Reply w/Quote]

09-15-2008, 11:39 PM	#7
circuitslave Registered User Join Date: Dec 2007 Posts: 69 Location: User is: OffLine	Re: New fuel pump, but still intermittent start? No prime Quote: Originally Posted by DarkKnite2009 sounds like you got a wiring nightmare on your hands from what your explaining it sounds like you got your self some gremlins. I would just re do the harness and be done with it dude I was reading your old thread when you first posted and honestly I would said screw it a while back. and if your not sure what I mean by gremlins its an intermitant problem that is being a bitch to figure out. That is some very good advice, Darkknite2009. I think I'm going to look into that. Thanks I will say this, though--this truck runs like a V6 truck! ( what I mean is I bought it and never knew it could drive so good. It was slugish with no power at all--I thought it was like this because it was old. After I replaced the pump, Bam ! I'm acclerating down the road like I should.
	[Reply w/Quote]

09-15-2008, 11:43 PM	#8
Jadesmarine Adapt And Overcome! Age: 24 Join Date: Jul 2007 Posts: 685 Location: 29 Palms User is: OffLine	Re: New fuel pump, but still intermittent start? No prime have u checked the ground (gnd for the tail light + fuel pump)
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09-16-2008, 05:03 AM	#9
circuitslave Registered User Join Date: Dec 2007 Posts: 69 Location: User is: OffLine	Re: New fuel pump, but still intermittent start? No prime Quote: Originally Posted by Jadesmarine have u checked the ground (gnd for the tail light + fuel pump) Yeah. Grounds for those are good. I think I need to check the ECM and see and make sure those wires are good.
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09-16-2008, 08:58 AM	#10
Jsim4 Registered User Join Date: Jun 2008 Posts: 9 Location: User is: OffLine	Re: New fuel pump, but still intermittent start? No prime i had a very similar problem on my truck, only difference was i wiggled the wiring harness in the engine bay and could hear the pump turn on and off. It turned out to be a loose ground on the back of the drivers side cylinder head.
	[Reply w/Quote]

09-16-2008, 09:08 AM	#11
lt1s10onair Local Tech Age: 25 Join Date: Jan 2008 Posts: 1,274 Location: westwood, nj User is: OffLine	Re: New fuel pump, but still intermittent start? No prime ignition switch?
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09-16-2008, 12:02 PM	#12
circuitslave Registered User Join Date: Dec 2007 Posts: 69 Location: User is: OffLine	Re: New fuel pump, but still intermittent start? No prime Quote: Originally Posted by Jsim4 i had a very similar problem on my truck, only difference was i wiggled the wiring harness in the engine bay and could hear the pump turn on and off. It turned out to be a loose ground on the back of the drivers side cylinder head. hmm? Well, nothing in the engine area, but twice when I wiggled the wires around the fuse box is when it started. Also, as I mentioned, when I tried to start the engine, with a helper applying 12 v to the pump test lead, the pump ran, but the truck still wouldn't start. So , I doubt it's only the pump issue. Nobody has still been able to answer my question though: If the fuse box area has the orange 440 circuit. If the fuse was blown or I pulled it, wouldn't THIS STILL ALLOW THE RELAY TO CLICK ENERGIZE? Because from what I've read, the relay gets it's power on a different circuit. Last edited by circuitslave : 09-16-2008 at 12:09 PM.
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09-16-2008, 12:03 PM	#13
circuitslave Registered User Join Date: Dec 2007 Posts: 69 Location: User is: OffLine	Re: New fuel pump, but still intermittent start? No prime Quote: Originally Posted by lt1s10onair ignition switch? Not sure. Maybe I'll look into that as well, thanks.
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09-16-2008, 07:12 PM	#14
Jsim4 Registered User Join Date: Jun 2008 Posts: 9 Location: User is: OffLine	Re: New fuel pump, but still intermittent start? No prime Have you tested the relay?
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09-19-2008, 05:01 PM	#15
circuitslave Registered User Join Date: Dec 2007 Posts: 69 Location: User is: OffLine	Re: New fuel pump, but still intermittent start? No prime Quote: Originally Posted by Jsim4 Have you tested the relay? The relay is new---and I still have the old one which works---my guess is that it's a wiring issue--the ECM is not giving signal, IMO. Truck has been starting fine---as it always has, with this ongoing issue. The thing is, the engine harness is no longer available. I'm going to do some checking on wiring this weekend. Thanks for the advice, though.
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