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Electrical Guys Help - No Power to Fuel Pump, Could it be a bad coil?

vesnyder	Oct 3 2005, 10:23 AM Post #1
Senior Member Group: Members Posts: 680 Joined: 14-April 05 From: Cleveland, OH Member No.: 3,933	Trying to figure out why my fuel pump is not getting any power and determined the power for the pump comes directly off the coil. The voltage leaving the relay panel is ~12V, but coming into the coil is only about 2-3V - that is with the wire disconnected - with it connected to the coil it is only ~.3V. Is this right? How do I determine if the coil is bad? How much for a new one?

Replies(1 - 19)

lapuwali	Oct 3 2005, 11:15 AM Post #2
Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743	Your wiring has been hacked on, as the fuel pump power normally comes off a dedicated relay on the relay board. Is this a carb'd car? The coil shouldn't affect power unless the wiring was done very oddly. The fuel pump power wire should connect to the same post on the coil as the coil + power. Where are you measuring voltage? What's your ground?

SirAndy	Oct 3 2005, 12:02 PM Post #3
Resident German Group: Admin Posts: 41,669 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California	QUOTE(vesnyder @ Oct 3 2005, 09:23 AM) the power for the pump comes directly off the coil. time to rewire. someone HACKED your setup ... do not run power for the fuel-pump off the coil! now, even if your car is converted to carbs, simply use the stock FI-Pump leads to run your fuel pump. i wrote a little blob on how to do that, which you can find in the "Classic Message Threads" section. right here: http://www.914world.com/bbs2/index.php?act=...=ST&f=5&t=25954 (IMG:style_emoticons/default/wink.gif) Andy

vesnyder	Oct 3 2005, 12:03 PM Post #4
Senior Member Group: Members Posts: 680 Joined: 14-April 05 From: Cleveland, OH Member No.: 3,933	The fuel pump power does seem to come from a dedicated relay on the relay board (and I have not traced the wire?) but when checking the voltage at the coil it seems to have dropped? Is this possible? I was using the engine tin as ground. The car is stcock L-jet as far as I know. The coild does affect the voltage - does that tell you anything? The fuel pump power wire does connect to the same one as the relay. Why is the coil in that circuit? (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif) BTW - I left the ignition on and the coild was very hot - is this normal?

Kerrys914	Oct 3 2005, 12:07 PM Post #5
Dear, the parts I just sold paid for that part ;) Group: Members Posts: 1,568 Joined: 26-December 02 From: Williamsburg, VA Member No.: 16	IIRC the L-jet fuel pump only runs when the "flapper" in the intake is moved by either air or you (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif). When you turn the key ON I don't think it runs..You MUST crank it to get flow.

vesnyder

Oct 3 2005, 12:07 PM

Post #6

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QUOTE

do not run power for the fuel-pump off the coil!

SirAndy - Did I read the wiring diagram wrong in the Hayne's Manual?

Lapuwali says:

QUOTE

The fuel pump power wire should connect to the same post on the coil as the coil + power.

(IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

bondo

Oct 3 2005, 12:09 PM

Post #7

Practicing my perpendicular parking

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QUOTE (vesnyder @ Oct 3 2005, 11:03 AM)

The fuel pump power does seem to come from a dedicated relay on the relay board (and I have not traced the wire?) but when checking the voltage at the coil it seems to have dropped? Is this possible? I was using the engine tin as ground. The car is stcock L-jet as far as I know.

The coild does affect the voltage - does that tell you anything? The fuel pump power wire does connect to the same one as the relay. Why is the coil in that circuit?

(IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

BTW - I left the ignition on and the coild was very hot - is this normal?

Unless you made some major changes, it's d-jet. (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

When I first got the car, I had the same problem. I swapped relays around on the relay board and it fixed it. I never had a problem after that. I suspect it's an internal relay board problem, and swapping the relays just wiggled the bad connection enough to make it work again.

The connections in the relay board are riveted together, and coated with tar-y stuff. It's a pretty common upgrade to chip all that away, clean the underside and solder all the connections.

vesnyder	Oct 3 2005, 12:27 PM Post #8
Senior Member Group: Members Posts: 680 Joined: 14-April 05 From: Cleveland, OH Member No.: 3,933	Bondo - Thanks for jumping in. D-Jet, that's right! The voltage is coming out of the relay panel?

lapuwali	Oct 3 2005, 12:38 PM Post #9
Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743	My coil + comment was directed at making it work IF you had a carb'd car and IF you really were trying to pull fuel pump power off the coil (which, SirAndy notwithstanding, is a common practice). Since you have D-Jet, you can ignore this comment. With D-Jet, the fuel pump power is switched through a dedicated relay on the relay board, which is itself switched by the ECU. Power for the coil also comes from a relay on the relay board, which is switched by the ignition switch. If your coil and fuel pump are on the same relay, something is wrong. When you turn on the key, the fuel pump should come on for a short while (1-2 seconds), then it will turn OFF until the engine is running. So, if you've switched on the key and are measuring fuel pump voltage with the engine off, then it's no surprise the fuel pump isn't running. Aside from the brief prime pulse, the ECU ensures the fuel pump is off while the engine isn't running. If you suspect the fuel pump isn't working at all, then you can try to hot-wire the fuel pump directly from the battery just to see if the pump works. If the pump works but you can't start the car, you need to start the usual no-start diagnostic, which usually should start with the ignition. You should have +12 volts between the coil + and the engine tin with the key turned on. If you don't, there's your no start problem, and it's mostly likely the main relay, or the ignition switch, or the wiring between them.

SirAndy	Oct 3 2005, 12:45 PM Post #10
Resident German Group: Admin Posts: 41,669 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California	QUOTE(lapuwali @ Oct 3 2005, 11:38 AM) (which, SirAndy notwithstanding, is a common practice) so, does that make it right then? i mean, if it's "common practice" and all. i'm not sure running the fuel pump directly off the coil is a good idea, regardless if it's "common practice" or not. you're not only eliminating the relay but also the fuse from the pump circuit and IMHO that can't be good ... but what do i know ... (IMG:style_emoticons/default/confused24.gif) Andy

bd1308	Oct 3 2005, 12:52 PM Post #11
Sir Post-a-lot Group: Members Posts: 8,020 Joined: 24-January 05 From: Louisville,KY Member No.: 3,501	it's not a good idea at all....and you also eliminate the ECU controls as well, imagine the safety issues there....especially in the event of a wreck or something.......... b

vesnyder	Oct 3 2005, 01:52 PM Post #12
Senior Member Group: Members Posts: 680 Joined: 14-April 05 From: Cleveland, OH Member No.: 3,933	Looking at the wiring diagram, the fuel pump power comes from the relay panel, and connects to the coil - and then powers the pump. This does not emilinate the relay or the fuse from the circuit? lapuwali - thanks for the details on when the fuel pump comes on! My analysis that the pump is not getting any power is not vaild?

Dave_Darling	Oct 3 2005, 02:07 PM Post #13
914 Idiot Group: Members Posts: 14,991 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California	The coil is not powered by a relay--it is powered by the ignition switch. The power going to the coil is used to trigger the relay for the power supply to the fuel injection, and that power is one of the two things that triggers the relay that sends power to the fuel pump. D-jet fuel pump troubleshooting: http://www.914fan.net/fuelpump.html Article by Bill Williams http://members.rennlist.com/pbanders/FPChecklist.htm Flowcharts by Brad Anders --DD

SirAndy	Oct 3 2005, 02:08 PM Post #14
Resident German Group: Admin Posts: 41,669 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California	QUOTE(vesnyder @ Oct 3 2005, 12:52 PM) This does not emilinate the relay or the fuse from the circuit? we all already passed you and left you in the dust ... (IMG:style_emoticons/default/biggrin.gif) from your original post it sounded like you had a carb-converted car and someone had run a hot wire directly from the coil to the pump. now that we know you got D-Jet, that has been eliminated, but we're still debating on how "safe" that really is, running the pump straight off the coil. in case you haven't noticed, this was/is a (IMG:style_emoticons/default/hijacked.gif) (IMG:style_emoticons/default/rolleyes.gif) Andy

lapuwali	Oct 3 2005, 02:16 PM Post #15
Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743	I didn't say, or mean to suggest, it was good practice to run the fuel pump off the coil, only that it's commonly done. Just trying to help solve this one problem, not re-engineer the wiring completely. My mistake on the coil not being powered by the relay in stock form. I assumed the 25A fuse and the associated relay on the relay board ran the coil. Back to the original topic... Is there a dedicated wire on your car from the coil + terminal directly to the fuel pump? If not, then we need to back up and find out exactly what your problem actually is. If so, then someone has hacked up your wiring, and all bets are off on what should happen v. what's actually happening on your car.

vesnyder	Oct 3 2005, 02:59 PM Post #16
Senior Member Group: Members Posts: 680 Joined: 14-April 05 From: Cleveland, OH Member No.: 3,933	I do not think I was looking at the corect wiring diagram. There is not a wire from the coil to the pump? I think the fuel pump is wired into the relay and fuse on the relay panel. I checked the pump while I had somebody turn the car over and still did not get any power - shoudl I assume that there is an issue at the relay board? Will hopefully do some more checking to ensure it is the fuse/relay at the panel? Sorry for all the confusion!

SirAndy	Oct 3 2005, 03:12 PM Post #17
Resident German Group: Admin Posts: 41,669 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California	QUOTE(vesnyder @ Oct 3 2005, 01:59 PM) Will hopefully do some more checking to ensure it is the fuse/relay at the panel? on a stock D-Jet, the pump will run for 2 or 3 seconds when you turn on the key to build up pressure, then shut off. no need to crank the motor. the FI-brain controls the power to the fuelpump, so no power to the pump can mean a lot of things. if you get power to the pump relay, check and see if the brain is grounding out the pump relay correctly. if not, check your engine harness and see if all ground wires for the brain are attached and make good contact (white wires) if all that checks out OK, try a loaner brain (they rarely fail, so suspect other problems first) ... (IMG:style_emoticons/default/cool.gif) Andy

vesnyder	Oct 3 2005, 04:16 PM Post #18
Senior Member Group: Members Posts: 680 Joined: 14-April 05 From: Cleveland, OH Member No.: 3,933	It is working, but who know for how long? I took an external 12V source and hooked it up to the fuel pump to make sure it was in facet the fuel pump. The car started right up! So at least I know it is the fuel pump. Reconnect the wires and try it again just for grins - and it runs fine?? WTH?? Any ideas? Is it a fluke, and when I get more than ten miles from my house is it going to strand me again? I can tell what kind of car this is going to be!!

SirAndy

Oct 3 2005, 04:42 PM

Post #19

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QUOTE (vesnyder @ Oct 3 2005, 03:16 PM)

I can tell what kind of car this is going to be!!

it's probably just the relay not making good contact.
if you have a new/spare relay, switch them out. make sure the contacts are clean, if corroded use a wirebrush (disconnect battery before brushing the female connectors on the relay board!) ...

if the relay fits in too easy, carefully pry thr pins apart just a bit to give it a more schnugg fit.

(IMG:http://www.914world.com/bbs2/html/emoticons/beerchug.gif) Andy

PS: also, take out the fuse and clean it's contacts as well ...

bondo	Oct 3 2005, 04:59 PM Post #20
Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California	Glad you got it running! Something worth mentioning.. as a 73 it originally had the fuel pump by the engine. Someone who owned it before me moved it up front by the master cylinder. Something in that wiring could also be causing a problem, since it's non-stock. Worth a look at least.

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