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Old 05-10-2018, 05:33 PM   #1
durk80
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Default fuel pump voltage? 91 240

My fuel pump voltage on fuse #4 is around 13.5 Volts as well as fuse 6. The remainder of the fuses when probed are closer to 13.8 Volts. Is this normal, or should I be looking for where this drop is occurring? Still having slight hesitation at start up.
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Old 05-10-2018, 07:11 PM   #2
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That's a good place to start, now head to your pumps and check there for drop.
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Old 05-11-2018, 09:14 PM   #3
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The pre-pump terminals were 12.69 and 7.9 volts. Is the 7.9 (grey wire) a reference wire?

At the fusebox, the voltage measured 12.76 at idle.


The main pump had 13.7 volts at the fuse box. At the pump, it was 12.63 volts.

I exposed the wiring to both pumps by removing the plastic edging by the rocker panel, and it looked fine. No burned or chaffed insulation.

Not sure where to go next.
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Old 05-13-2018, 10:37 AM   #4
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This weekend, I replaced the wires from both fuel pumps to the fuse block--The voltages are pretty much the same, no change. Both fuel pumps are fairly new (winter '18). The original wires still looked fine--the copper was shiny and the insulation wasn't damaged.

I've been trying to find this problem for about 2 years now and after thinking it was this or that part or connector and the fault is still eluding me. About the only things I haven't changed are the MAF, both computers, and the knock sensor. Perhaps I will check the big bundle that is near the fuse box and goes under where the instrument cluster sits. Maybe a power wire is chaffed there. Oh well, at least the dash only has one crack in it!
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Old 05-14-2018, 01:20 PM   #5
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Have you looked into adding a relay right near the fuel pump? Most folks add a standard four pin relay near the pump to increase the voltage to the pump. You basically have the existing fuel pump relay turn on a standard relay which only suppies the pump.
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Old 05-14-2018, 02:09 PM   #6
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^^

http://www.240turbo.com/volvo240mods.html#fuelpumprelay
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Old 05-14-2018, 07:18 PM   #7
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Wow! Dave, I didn't know that could be done.

A couple of questions though: Would this wiring diagram work? http://www.enginebasics.com/Advanced...p%20relay.html

Do you also wire the pre-pump with a relay as well?

Thanks!

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Have you looked into adding a relay right near the fuel pump? Most folks add a standard four pin relay near the pump to increase the voltage to the pump. You basically have the existing fuel pump relay turn on a standard relay which only suppies the pump.
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Old 05-14-2018, 07:57 PM   #8
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It's been a really long day...I just saw your link, and thank you for the diagram.

Where did you add the relay in? Closer to the pumps, or directly near the white relay?

Also pin 30 on both relays gets 12 Volts of power, correct?
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Old 05-14-2018, 08:56 PM   #9
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Also, I have the 3.1 ECU, which doesn't have 2 wires for the 87/1 terminal. It only has one orange wire.


Schematic for Relay:


Not sure if this complicates it or not.
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Old 05-14-2018, 09:21 PM   #10
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To measure the pump voltages, you want to have the pumps on (idling or system relay jumpered), and measure the voltage on both pump wires to a separate good ground. The +12volt (or so) wire should be close to battery voltage when idling. The ground wire should be close to 0volts. I wouldn't worry about a few 1/10ths of a volt drop. If you're seeing 1+ volt drops, then something isn't making a good connection.

What is the problem you're chasing? Have you checked that there's proper fuel pressure in the rail at startup?

[I think your gray wire at the tank is the fuel level sender.]
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Old 05-14-2018, 09:38 PM   #11
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@durk80 I added the relay under the dash near the existing fuel pump relay.
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Old 05-14-2018, 10:31 PM   #12
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Originally Posted by oldschoolvolvo View Post
@durk80 I added the relay under the dash near the existing fuel pump relay.
Thank you for the reply. The location makes sense when using thicker gauge wire!
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Old 05-14-2018, 10:48 PM   #13
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Originally Posted by bobxyz View Post
To measure the pump voltages, you want to have the pumps on (idling or system relay jumpered), and measure the voltage on both pump wires to a separate good ground. The +12volt (or so) wire should be close to battery voltage when idling. The ground wire should be close to 0volts. I wouldn't worry about a few 1/10ths of a volt drop. If you're seeing 1+ volt drops, then something isn't making a good connection.

What is the problem you're chasing? Have you checked that there's proper fuel pressure in the rail at startup?

[I think your gray wire at the tank is the fuel level sender.]
The problem I am chasing has gotten worse. I drove 300 miles today, and noticed at highway speeds that when I took my foot off the gas, it would buck and not decrease in speed smoothly.This happened frequently, but not all of the time. At stop lights, the idle would vary--sometimes it would be slightly high, other times it would be lower. Sometimes, it would feel like it was taking forever for the engine to rev as well. I usually get 28 mpg, but today I got 23.


you are right, I *really* need to get a set-up to measure fuel pressure as I am lacking a fuel rail with the coveted schraeder valve. A great diagnostic tool to have for sure.
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Old 05-15-2018, 10:10 PM   #14
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Quote:
Originally Posted by oldschoolvolvo View Post
Quote:
Have you looked into adding a relay right near the fuel pump? Most folks add a standard four pin relay near the pump to increase the voltage to the pump. You basically have the existing fuel pump relay turn on a standard relay which only supplies the pump.
Thank you oldschoolvolvo and dl242gt for the schematics and the suggestions! I had a spare relay and socket laying around, and was able to wire it up tonight with your help It seemed to start much easier, and sometime when it's not raining, I'll have to check the voltage numbers to see if it improved.


Under the hood, I also performed the wiggle check, and found an injector connector not fully seated, so that probably had something to do with smelling gas from the tailpipe and poor mileage.

Thank you once again for all for your expert advice because I've needed it, and have learned a lot along the way!
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Old 05-16-2018, 08:02 AM   #15
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Old 05-16-2018, 01:57 PM   #16
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Well, I did celebrate last night, but now I'm unsure. The car barely wanted to run and start this morning. It was also raining again today and water on the floor, so I went to use the wipers and the fuse blew for that. I'll have to check the wiper wiring to the fuse box, and the connectors to the switch and motor to see what is shorting out.

I'm not sure what I did to cause this problem, but maybe it is related to the engine stumble?
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Old 05-16-2018, 05:46 PM   #17
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Sometimes these problems take a slow steady approach. The water on the floor can be a windshield leak. That can cause weird electrical problems like you are experiencing. The water can actually seep into the wiring harness and get to relays. Which makes them not function properly or blow fuses. It'll be a good idea to see if there is water in the harness for the wiper relay and check other relays under the dash for water.

Keep at it. You'll get it figured out.
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Old 05-16-2018, 09:55 PM   #18
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Quote:
Sometimes these problems take a slow steady approach. The water on the floor can be a windshield leak. That can cause weird electrical problems like you are experiencing. The water can actually seep into the wiring harness and get to relays. Which makes them not function properly or blow fuses. It'll be a good idea to see if there is water in the harness for the wiper relay and check other relays under the dash for water.
Tonight I unplugged the connectors to the wiper motor and the fuse still blew when I turned on the wiper switch. Next, I took off the switch and checked for any signs of melting/ corrosion. There was some oxidization on the terminals which I cleaned. Then, I checked the relay stuffed behind the metal plate, and noticed that I had placed the relay in the socket the wrong way!

After switching it around and putting in a new fuse, there were no problems.

As for the other problem, I will keep searching and find it eventually! Thank you for your help and reassurance, dl242gt!
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Old 05-18-2018, 10:46 PM   #19
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I replaced the spark plugs today, cleaned the cap and rotor up. The last set of plugs I replaced about 3 months ago. They were completely carbon black! I gapped the new ones for .029 as I couldn't find the specs for the correct opening ( I believe the range is .028-.030).Darn thing sounds just like before. Right off of idle it sounds like it wants to stall--but never does. The exhaust, of course stinks--reminds me when I used to ride a snowmobile. The heated film resistance is 107 ohms. The Haynes manual says it should be 108 ohms. It doesn't give any suggestion for what to do if its off though.

Yesterday I the check engine light came on and flashed 113, 212, 231, 232 codes. Looks like I'll need a new 02 sensor at the least.
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