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Old 09-19-2020, 11:55 PM   #1
soroushrajabnik
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Question 78 242 Fuel Pump Circuit mystery

I'm In the process of reviving a 78 242gl that has been sitting on a farm in southern California for a few years. The car only had one owner its entire life and has an amazing chunk of service records and receipts with it. The fuel tank was basically empty thankfully so I put in about 5 gallons of fresh gas, primed the sytem to get some pressure going, and turned on the ignition to see what I could observe. First thing i noticed is that i couldnt hear either fuel pump buzz both when first turning over the key, and also when cranking. Does not Smell like fuel either. I know that the fuel pumps have both been replaced at some point, so im starting to dig into the basics going down the line, Starting with the Fuel delivery bits. The car surprisingly has the original metal volvo branded fuel pump relay made in west Germany with a 1977 manufacturing date so I cracked that open to find some scorching marks and possible shady solder joints so I started with re flowing those joints, and seeing if there was any change. No dice. All fuses are copper and brand new. Upon starting to troubleshoot here is what I have determined:

-With the relay disconnected testing at the harness I have voltage at terminal 30 (red) coming from the battery.

-With the ignition on I do have voltage at terminal 15 as well.

-With the ignition OFF I am reading 385 ohms between terminal 31 (black) and ground..... bad ground here???

-When connecting a tachometer between terminal 31B and ground I am receiving a normal steady 300 rpm signal when cranking. Am also receiving spark at the plugs but thats neither here nor there right now.

-With the relay reconnected and back probing the harness, When cranking I have voltage at terminal 87 (yellow) but NO VOLTAGE at 87B (blue).....
Even while cranking It seems that I am not getting any voltage at the actual fuel pump connections... I know that the NO voltage at 87B is suspect but as far as I know tracing the diagrams this would only affect the CPR and Lambda relay...

Here is where things get a little confusing.

-When I jumper fuse 5 and 7 I get no power at the fuel pumps, and they do not run.... the lights on the dash only come on.

-Now I ran 12v direct to the main pump, and was stumped to find nothing happened until I tapped it a couple times with a rubber mallet and it took off. I tried all the same tests, but jumpering fuses still wouldnt start the pumps.

-When I plug the fuel pump relay back in the harness and actuate the relay manually with the casing off I get power at the pumps and they both run. ALSO when I jumper between terminal 30 (red) and 87 (yellow) on the fuel pump relay harness, I also get power and both pumps run...

I am not an expert when it comes to wiring but I know the basics and I have the right tools. Im also taking these tests directly from between my bentley (fuel injection-CI 240-9) and the original greenbook (CI section 2 group 24) for my diagrams.

I would love some input from some of you who know the wiring on the earlier 240s better than I if anyone has some suggestions...

I am mainly stumped wondering why these pumps dont run when I jumper at the fuse panel, but why they do when I jumper at the harness connections for fuel pump relay... If the bad ground I may have at terminal 31 of the harness is my issue, why will the pumps run when i manually actuate the relay, and also when I jumper at the harness with the relay out???

Help!
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Old 09-20-2020, 06:24 PM   #2
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Find a copy of TP12045-1_wiring_diagrams_1977_1978.pdf (try https://ozvolvo.org/archive/). Unlike some later cars, jumpering fuses 5 and 7 won't turn on either pump -- it's the same as turning on the key in your '78. The 385ohms to ground is bad. I'd chase that down first and see if fixing the bad wire/connection, fixes the pump power.
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Old 09-21-2020, 02:01 PM   #3
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Quote:
Originally Posted by bobxyz View Post
Find a copy of TP12045-1_wiring_diagrams_1977_1978.pdf (try https://ozvolvo.org/archive/). Unlike some later cars, jumpering fuses 5 and 7 won't turn on either pump -- it's the same as turning on the key in your '78. The 385ohms to ground is bad. I'd chase that down first and see if fixing the bad wire/connection, fixes the pump power.
Bob- thank you for this info, I had been reading the CI fuel injection diagram for 1978 only.
This explains why I get power and pumps run when jumpering at the harness, but not at the fuse panel. I fished around cleaning up some grounds and I now have continuity between terminal 31 (black) and ground. The only thing thats suspect now is no voltage at 87b (blue) when cranking, but this doesnt solve my fuel pump power issue. From testing these circuits its pretty clear to me that the fuel pump relay is shot and clearly not fixable from reflowing solder joints... some of the green traces on the circuit board itself look extremely fried. New relay is on the way, so we will see how things behave with a fresh relay tied in to the system. Hoping its as simple as a new relay, and hopefully making enough pressure and everything else working together for it to fire up. I dont suspect anything is wrong, but im going to do a compression test in the time being for piece of mind while im waiting on my relay.
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Old 09-21-2020, 03:37 PM   #4
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87 and 87b are 2 contacts (poles) on the relay flapper. Both should make contact at the same time when the relay coil is energized. The coil is energized when the circuit in the relay detects tach / spark from the coil - it's a safety thing to turn off the pumps when engine isn't running.

If 87 works, but 87b doesn't, it's very likely the relay. I think you said it worked when pushing on the flapper by hand. If so, your flapper points for the 87b side are corroded or worn down. You could try running a bit of emery paper through the relay points while pushing down gently. If it works, you have a somewhat-working relay to keep as a spare, but I wouldn't trust it enough to leave it installed.
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Old 09-21-2020, 08:01 PM   #5
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87 and 87b are 2 contacts (poles) on the relay flapper. Both should make contact at the same time when the relay coil is energized. The coil is energized when the circuit in the relay detects tach / spark from the coil - it's a safety thing to turn off the pumps when engine isn't running.

If 87 works, but 87b doesn't, it's very likely the relay. I think you said it worked when pushing on the flapper by hand. If so, your flapper points for the 87b side are corroded or worn down. You could try running a bit of emery paper through the relay points while pushing down gently. If it works, you have a somewhat-working relay to keep as a spare, but I wouldn't trust it enough to leave it installed.
Yep I have a good idea of whats going on in there from tinkering with it for awhile and looking at the diagrams. I'll try a couple things while the new relay is in the mail. just realized the "flapper" terminal going to 87b was bent ever so slightly so when the relay actuates itself while cranking, it wasnt making the connection there even though it was at 87. Bent that back the other way and now im getting power through 87 and 87b from the relay on its own while cranking. I know on the LH cars when you first click the key over you can usually hear the FP relay prime the pump and it buzzes for a second before you actually turn the key all the way over... do the K-jet cars not do this? Only supply fuel while cranking and running? seems the relay may be working as it should now, either way i'll try the new one when it comes. I know that I have spark just from quickly grounding each wire at the strut tower, but the real question is whether I have compression, and if the cold start injector, frequency valve, aux air, and all of those bits are working as they should as well. I'll start checking that out. Ive heard it sputter a couple times as if it wants to start, but I really need to crack the fuel lines at the filter and after as well as at each injector to get a general idea of what my fuel delivery looks like up at the actual engine.
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Old 09-21-2020, 09:59 PM   #6
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compression came out looking decent.

1. 141 psi
2. 143 psi
3. 141 psi
4. 142 psi

I had a 79 wagon a few years back that ended up having a bad CPR and was hard to start before i replaced it, but it would still sputter consistently with my foot on the gas trying to start. Hoping this isnt the case with this car too as they are pretty expensive remanufactured. One step at a time.
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Old 09-25-2020, 04:43 PM   #7
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After replacing questionable fuel pump relay I now have power going to all the right places at the right times, I can hear the in tank pump as well as hear and feel the main fuel pump. After initially turning the engine over with the key in the run position, the pumps continue to run, as well as frequency valve etc. I cracked the fuel line before the filter to find that I am not getting fuel at the filter yet, just a hum and a gurgling sound coming from the line. I have read that it can take up to two gallons of fuel to prime this system and build pressure? Either way i'm getting under the car in a second to try to see what sort of output i'm getting at the main pump and so on.
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Old 09-25-2020, 07:18 PM   #8
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Pulled the in tank sending unit to find that the hose connecting the top of the in tank pump to the feed line was totally done and not even connected to the pump anymore. I ordered the parts surrounding the in tank pump when I got a new relay as I was anticipating it needing the attention anyway. Luckily the pump seems to have been running fine from what i can tell and a little cleaning up and sealing up should fix this issue now.
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Old 09-25-2020, 07:35 PM   #9
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That's a common problem. IPD sells a short length of the special grade submersible hose just for this - link

You said that your pumps keep running after cranking? They should shut off when the fuel pump relay no longer get a tach signal from the coil.
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Old 09-25-2020, 08:29 PM   #10
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Quote:
Originally Posted by bobxyz View Post
That's a common problem. IPD sells a short length of the special grade submersible hose just for this - link

You said that your pumps keep running after cranking? They should shut off when the fuel pump relay no longer get a tach signal from the coil.
yup thats exactly what I ordered. Just referencing cleanflametrap's write up on in tank pump stuff to get the length right as far as how far down the pump itself should be mounted. luckily this isn't the first or even second time i've had to do this particular job, it's just been awhile. I'm gonna sort this in tank pump out, drain the tank dry from the top, and put everything back together before I sort out if I have some type of other wiring issue going on.
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Old 09-26-2020, 05:44 PM   #11
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Running so well! After I put all the fuel system bits back together and tightened all the lines down it didn't take long for it to fire up. Starts on one crank . I got a little lucky with it being an inland empire car. Super dusty and ashy but luckily everything seems to be running just as it should.
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