comparing fuel system relays

Dammit - your links work fine. Dammit - I've been looking in my Mitchells EFI book. Dammit - it has the LH for 87-88 240 (& 740, 760, 780, & 82 & 83-86 240 DL & GL). (Earliest Volvo is 1970 ES; latest are the '88s as mentioned.) I'm not adding any info - I'm just cursing and letting you know. (... that I have that info...) "Radio Suppression Relay" - probably because it was once used to power a relay and when off, it suppressed its sound (and power consumption etc). Else using the relay provided clean power to the radio, hence eliminating noise... Yeah - some names are ridiculous. I think I prefer on-off or SPST, but I work from and use "circuit" diagrams so names and labels are usually unnecessary. I'll compare those bluddy Volvo diagrams later.... UPDATED: It's later... Yep - "radio suppression" probably because it removes injector etc noise from the radio supply. And I assume the 87-88 740 LH EFI, hence the radio interference suppression relay. (It's also a fixed (locked) dizzy with electronic timing...?) That fuel relay is merely 2 SPST relays in a single package BUT one relay has a series diode in its coil, hence only actuating if the polarity is correct.   (As with spike-suppression diodes, I prefer to mount diodes externally and use ordinary relays.) The first half (SPST) is energised (grounded) by the ECU (#12, Red) which connects (Brn) fuse #1 +12V to (BluY) the Air Mass Meter (hot-wire) and ECU #9, as well as actuating the radio interference suppression relay which powers the Air Ctrl Valve and injectors (Grn). It also actuates the polarity-dioded other half (SPST) which supplies the "Lamda Sond" - I presume (heater for the) O2 sensor (green) - and the fuel pump via fuse 11 (pink) [ No color logic. I'm used to schemes where a green base color means indicators/flashers, blue is accessories, red is lights... ] Anyhow, that "fuel pump" relay looks ok in that splits the injectors from the pump - ie one contact for each. But I am surprised the first half is not the polarity protected relay... Why worry about wrong polarity to the pump if you have already supplied it to the ECU? EFIs I deal with usually have a polarity sensitive relay (from the IGN) that connects power to the ECU - typically a DPST relay which also feeds the injectors, though that could also be 2xSPST. Fuel pumps are usually a separate relay controlled by the ECU (though some include external oil-pressure bypasses etc which - as I have repeatedly stated - is silly if not moronic).    The 2 systems (yours and my "typical" EFIs) seem similar though I think mine are more straightforward - ie, relays based on IGN with only the fuel relay being ECU controlled. But have I got your system analysis right so far???

I'm following some of this Peter, I'm assuming take the 85 lines out and feed separate 40 amp Bosch/Tycho style relays with inline 1N4004 diodes. Most of the SPST (4 pins)are normally 40 amp rating, the SPDT (5 pin) versions are 30/40 rating. Those shown in the photos just have a different pin (round) style. N.B. Those colours you referred to are old UK Ripaults/Lucas. Volvo and Saab NEVER followed any logical wiring colours, UK, German DIN etc. Volvo STILL go their own way and Saab went to Opel/Vauxhall (Holden) after the GM takeover.

So the Prince of Darkness shed some light... That would explain the root of my wiring - my Jap vehicles being derived from Hillman & Rootes Group. With experience, wiring diagrams become unnecessary.

howie ll wrote: ... SPST (4 pins)are normally 40 amp rating, the SPDT (5 pin) versions are 30/40 rating.

Yeah - the NO contacts are 40A as usual - it's the spring-loaded NC contacts that are de-rated. Volvo and SAAB - what do you expect from those northern pagans (bless their souls). But give me a Viggen any day.... And yes - the split relay feed could be done various ways. A single diode (polarity sensitive) relay could feed others - ie, the IGN could go to an 86 via a diode and that relay (30, 87) power the ECU and another relay (for injectors), or the diode could simply feed both relay's 86 direct. Or 85 if it's ground switching (sticking to convention).    At the moment, handyguy's wiring seems ok - but that's based on my Mitchells info (I haven't considered his linked diagram), and ignoring the "polarity" diode - ie, should it be in a master upstream power relay? Anyhow, back to the revolution. (Demonstrations in Melbourne (Aust) against the distribution of wealth...)

Viggens? You surely meant the Grippen? Nice piece of kit, especially the 4+ Gen with Israeli avionics and missiles but unfortunately you will be getting F35s, what you the Japanese and the Israelis REALLY want are F22s pref. for the Israelis preferably devoid of US avionics and software. recently saw some spec on the Israeli MB tank, individual Recaros, individual flat screen displays, all weather 360deg. vision, active and passive defences, individual AC, on board self diagnostics and ah the irony, a German gun! Joking aside all other tanks are target practice for the Merkavas, Abraams, Challies and Leos. As for that Aussie joke the Collins (note; Swedish origin) buy US or GB nukes, cheaper and more reliable.

Nah - Viggen - the Grippen is too small. Ah yes, the might Collins. Probably a case like Jindalee (OTH Radar) - totally incompetent management (I wonder if they eventually signed off to start the Jin contract - it still wasn't signed-off 6 years into the project!). I hope our F35s don't have the US software, though maybe if they fly back at the Equator as our F18s did, we can get a refund for "lack of delivery". Our navy uses Bofors - or used too. Never a problem using a neutral countries weapons - we never fired ours either. (Well, not in "war".) But German guns should be good - plenty of practice, and they invented DU (we just use Depleted Uranium on out batteries). But we still have out rail guns...

What I came to the conclusion of was the system (fuel relay) as it exists does control one HD relay to run the injectors, IAC (idle air) motor, etc. through 87/1. However 87/2 has two wires at the terminal: approximately a 14ga and a 16ga. I used the 16ga to feed the O2 sensor (heater) - light duty load, IIRC about 1.5A. I then used the 14ga to feed Pos 86 (switch) on a second radio suppression relay, which then runs the 2 fuel pumps. Thus, the only real "load" on the fuel relay is the O2's heater wire. Its typically 87/2 that discolors and/or melts over time. IIRC, the fuel pumps alone have a constant draw of 15-20A. Volvo has been known for the skimpy wiring to begin with. I'm floored at the heavy loads (especially in the 700/900 series) where a 20-25A continuous draw will be carried on a 14ga single wire (about every other car in the yards will have either the fuel pump or AC fuse melted in the holder). I've developed a habit of splitting these loads into multiple relays and with larger wiring on about any I get ahold of. The older Volvos had chronic wiring issues, especially those in the early to mid 80's when they made the harnesses in North America. They used a wire with a plastic-like insulation that got brittle and split/corroded and prematurely failed. There was such a bitching about it that Volvo sold the "updated" harnesses to the end user at something like a 70% discount. They began making the harnesses in Belgium (special ed schools did much of it) and they were night and day using a more pliable and heat resistant wire as well as copper connections (replacing aluminum). What I like about doing this swap/upgrade is that not only does it get a far more improved and efficient ignition system, but the harnesses for it - from the 740 model - was mostly all contained inside the cabin under the dash so its very well preserved in comparison to the 240 setup that baked it under the hood. I typically use Techflex loom/sheathing when making my new harnesses which is not only slick looking but also protects against the heat. And all of the relays are relocated inside the cabin now also.