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i am sorry if this is covered in another thread, i have read through many and cannot find my answer.. have a 99.. with fuel issues.. replaced fuel pump, and regulator, still "0" pressure under hood.. trying to check voltage at pump.. have 2 grey wires, a blue and black going into fuel pump.. voltmeter shows power (5 volts) to 1 grey and the blue.. but no power to the other grey and i assume the black is ground.. can anyone advise me where to go from here. Is it possible that the brand new fuel pump is bad?
Did you wait a bit to see if the rails build pressure? It took mine a few times and a bunch of engine cranking before the air got out of the sytrm and the pressure built up.
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Last edited by Vetteman Jack; May 2, 2019 at 06:03 PM.
Yes I did try several times, fuel pump is not engaging or coming on at all.. I am at a loss
See below schematic, the 5 volts you are measuring I suspect is the fuel level system
Check the under hood fuse/micro relay...
Check for 12 volts on the gray wire PIN "A" on the connector C408 boxed in red.
Note, when placing the key to the "engine run" position, the micro relay will briefly close (by the PCM) to pre-pressurize the fuel system for apprx 3to5 seconds then the relay will open and turn the fuel pump off as the PCM does not see the engine running..
Cheers
Goose,
Last edited by 69; May 1, 2019 at 08:13 PM.
Reason: info added
I did a YouTube video on the fuel pump relay circuit testing...you have to that FIRST !!...hope it helps...let me know if you have any questions !!...I’d have to look at a 99 and see the ground circuit on the load and control side...numbers and location might be different !!
See below schematic, the 5 volts you are measuring I suspect is the fuel level system
Check the under hood fuse/micro relay...
Check for 12 volts on the gray wire PIN "A" on the connector C408 boxed in red.
Note, when placing the key to the "engine run" position, the micro relay will briefly close (by the PCM) to pre-pressurize the fuel system for apprx 3to5 seconds then the relay will open and turn the fuel pump off as the PCM does not see the engine running..
Cheers
Goose,
Ok, here is what I have so far.. I am getting power at relay, and at dark blue, also a very small amount of power at black ground but nothing at grey wire A.. so I disconnected ground and ran a jumper direct from battery to pump, pump came on and car started.. so I know pump is good.. I also cleaned connections as suggested, I am assuming I must have a broken wire on A between the relay and pump.. does that sound correct to you guys. Also any Ideas why I would be getting power on that ground? it is a very small amount ..something like .3 volts. but it was enough to interfere with ground.
If you jumper pins 87 and 30 (circuit 1639 and 120) does the pump operate ??....on the 1999 schematic I can’t see at the bottom of the page if there is a body ground...it’s cut off...is the ground at the fuel level sensor the only one ??...I’m trying to figure out why you disconnected ground to jumper the pump on !!...did you jumper the fuel pump AT THE PUMP ??...if you did and the pump started running we know the pump itself is good...if you jump pins 87 and 30 and pump did not operate you have an open to the pump or maybe a bad connection from the relay to the pin inside the the fuse box...did the video help and did you use it to check the grounds...did you use a test light ???
Ok, here is what I have so far.. I am getting power at relay, and at dark blue, also a very small amount of power at black ground but nothing at grey wire A.. so I disconnected ground and ran a jumper direct from battery to pump, pump came on and car started.. so I know pump is good.. I also cleaned connections as suggested, I am assuming I must have a broken wire on A between the relay and pump.. does that sound correct to you guys. Also any Ideas why I would be getting power on that ground? it is a very small amount ..something like .3 volts. but it was enough to interfere with ground.
I'm a bit confused by your follow-up post as you state to the following;
OP>I am getting power at relay, and at dark blue
69 Response>The dark blue wire is for the fuel level/indication system and has no effect on the fuel pump.
OP>I disconnected ground and ran a jumper direct from battery to pump, pump came on and car started..I also cleaned connections as suggested, I am assuming I must have a broken wire on A between the relay and pump..
69 Response> If you ran a jumper from the battery ground to the pump plug ground Pin "D" and the pump came to life, this would indicate that you DO NOT have a broken wire from pin "A" gray wire of the pump plug to the fuel pump relay.
Note the gray wire from pin "A" of the pump plug to the fuel pump relay supplies the 12 volts to operate the pump.
Can you please clarify> did you run a ground jumper from the battery to the pump or did you run a positive 12volts jumper from the battery to the gray wire on pin "A" pump?
OK, regarding your fuel pump replacement, can you clarify, did you replace just the pump or did you replace the complete fuel module assembly which contains the pump and fuel level sensor? It’s important to understand for troubleshooting.
Additional tips, although this post is for a 2001, you can apply the same testing procedures using the 99 wire schematic.
I too am going by the schematic... the only ground i find is the one that runs over to the other tank.. I was getting a very small power reading on that ground.. something like .3.. ..I jumpered direct from battery to pump.. still nothing until i disconnected ground and re grounded to the frame. Then the pump worked and the car started and actually ran for the 1st time in over a year.. that is why i am thinking there must be a break between relay and pump... just not sure how to find the break
I'm a bit confused by your follow-up post as you state to the following;
OP>I am getting power at relay, and at dark blue
69 Response>The dark blue wire is for the fuel level/indication system and has no effect on the fuel pump.
OP>I disconnected ground and ran a jumper direct from battery to pump, pump came on and car started..I also cleaned connections as suggested, I am assuming I must have a broken wire on A between the relay and pump..
69 Response> If you ran a jumper from the battery ground to the pump plug ground Pin "D" and the pump came to life, this would indicate that you DO NOT have a broken wire from pin "A" gray wire of the pump plug to the fuel pump relay.
Note the gray wire from pin "A" of the pump plug to the fuel pump relay supplies the 12 volts to operate the pump.
Can you please clarify> did you run a ground jumper from the battery to the pump or did you run a positive 12volts jumper from the battery to the gray wire on pin "A" pump?
OK, regarding your fuel pump replacement, can you clarify, did you replace just the pump or did you replace the complete fuel module assembly which contains the pump and fuel level sensor? It’s important to understand for troubleshooting.
Additional tips, although this post is for a 2001, you can apply the same testing procedures using the 99 wire schematic.
...I am getting power at relay, and at dark blue, also a very small amount of power at black ground but nothing at grey wire A... ...I am assuming I must have a broken wire on A between the relay and pump... ...Also any Ideas why I would be getting power on that ground? it is a very small amount ..something like .3 volts. but it was enough to interfere with ground.
Originally Posted by rudystrick
I have not tried jumpering 87 and 30,
I too am going by the schematic... the only ground i find is the one that runs over to the other tank.. I was getting a very small power reading on that ground.. something like .3.. ..I jumpered direct from battery to pump.. still nothing until i disconnected ground and re grounded to the frame. Then the pump worked and the car started and actually ran for the 1st time in over a year.. that is why i am thinking there must be a break between relay and pump... just not sure how to find the break
Just to make sure we are on the same page. When you say the following, you mean what I wrote in bold, right?:
Relay 35 -> CKT 1639 (Pin 30) -> 12v
Dark Blue -> CKT 1936 -> 5v
Ground -> CKT 150 -> Voltage greater than 0v
Grey -> CKT 120 (Pin 87 - Relay 35) -> 0v
All this seems to point that your Ground CKT 150 is open. A good ground has to be at 0v, not having a floating voltage like in this case.
Although it was truncated, Ground CKT 150 goes to the Splice Pack shown in the lower left corner of the schematic below. It provides ground to both, coil of Relay 35 and Pump Motor (Point D). If that ground is open Relay 35 can't close, therefore no voltage is provided to CKT 120 (Pin 87 of relay and Point A of pump motor).
Furthermore, even if you bring +12v to Point A directly from the battery as you did, the fuel pump won't operate unless you also provide an alternate ground, as you also found out.
Just to make sure we are on the same page. When you say:
Relay 35 -> CKT 1639 (Pin 30) -> 12v
Dark Blue -> CKT 1936 -> 12v
Ground -> CKT 150 -> Voltage greater than 0v
Grey -> CKT 120 (Pin 87 - Relay 35) -> 0v
All this seems to point that your Ground CKT 150 is open. A good ground has to be at 0v, not having a floating voltage like in this case.
Although it was truncated, Ground CKT 150 goes to the Splice Pack shown in the lower left corner of the schematic below. It provides ground to both, coil of Relay 35 and Pump Motor (Point D). If that ground is open Relay 35 can't close, therefore no voltage is provided to CKT 120 (Pin 87 of relay and Point A of pump motor).
Furthermore, even if you bring +12v to Point A directly from the battery as you did, the fuel pump won't operate unless you also provide an alternate ground, as you also found out.
Simple 12 volt test light or load light connected to battery positive and connected to circuit 150 (pin 85 or however the relay is numbered on a ‘99)...light comes on...bing bang boom the ground is good !!...guess OP didn’t watch my video !!...assuming it’s a splice pack to a body ground like an ‘01.
EDIT; found a wiring schematic in my Corvette fuel injection book and a ‘99 relay control side ground is the same G105 and pump grounded at G104. However there are 2 separate grounds !!
To clarify: the OPS..,AKA.,,Rudy’s statements are confusing !!
Yes, I know my statements have been a little confusing.. I am sorry... what we have here is a communications breakdown.. Rudy is the husband doing the work (who does not know how to post or do anything on computer).. I am Lynn the wife, with computer skills but little mechanical knowledge attempting to communicate what he is telling me which is not always clear.. sorry guys I will try to do better.
Last edited by rudystrick; May 6, 2019 at 09:51 AM.
Yes, I know my statements have been a little confusing.. I am sorry... what we have here is a communications breakdown.. Rudy is the husband doing the work (who does not know how to post or do anything on computer).. I am Lynn the wife, with computer skills but little mechanical knowledge attempting to communicate what he is telling me which is not always clear.. sorry guys I will try to do better.
Thats fine Mrs. Rudy !!...we call it “lost in translation”...LOL !!...so is his fuel pump operating normally now ??...BTW, you two make a great team !!
You are right, I did not watch the video, somehow missed it,(bypassed thinking it was just a picture (duh) , The fuel pump is not running. I did find out through the whole "jumpering" thing that it does run.. so I know the pump itself is not the issue. Still working on resolving the issue of power .. but after watching the video this morning it clarified a few things.. we will go step by step from the video today. Will post this evening and let you know what we get. Again thanks for your patience with our bad communication..
Last edited by rudystrick; May 6, 2019 at 10:14 AM.
Great !!...if you jumped across Pins 87 and 30 and the pump worked that half of the relay is good...the pump is functional and ground 401 is OK....you just have to work on the "control side" of the relay...pins 86 and 85 !!….best to check the ground (G105) with a test light...we have to make sure you get that test light lit with a test light...a test light is the best way to check pin 86 as I explained in the video about the "bias voltage"...I'll PM you my cell if you need some clarification....I'm messing around with stuff on my car today so I'm available !!
fuel pump wiring
(duh) , The fuel pump is not running. I did find out through the whole "jumpering" thing that it does run.. so I know the pump itself is not the issue. Still working on resolving the issue of power .. but after watching the video this morning it clarified a few things.. we will go step by step from the video today. Will post this evening and let you know what we get. Again thanks for your patience with our bad communication..